WO2011028264A2

WO2011028264A2 - Methods and systems involving materials and electrodes for water electrolysis and other electrochemical techniques

Info

Publication number: WO2011028264A2
Application number: PCT/US2010/002368
Authority: WO
Inventors: Arthur J. Esswein; Steven Y. Reece; Daniel G. Nocera; Kimberly Sung; Zachary I. Green
Original assignee: Sun Catalytix Corp
Current assignee: Sun Catalytix Corp
Priority date: 2009-08-27
Filing date: 2010-08-27
Publication date: 2011-03-10
Anticipated expiration: 2012-02-27
Also published as: WO2011028264A3

Abstract

Methods and systems for electrolysis and/or other electrochemical techniques are provided. In some cases, the methods and systems can be used for energy storage, particularly in the area of energy conversion, and/or production of oxygen, hydrogen, and/or oxygen and/or hydrogen containing species.

Description

METHODS AND SYSTEMS INVOLVING MATERIALS AND ELECTRODES FOR WATER ELECTROLYSIS AND OTHER ELECTROCHEMICAL

TECHNIQUES Related Applications

This application claims the benefit of U.S. Provisional Patent Application Serial No. 61/237,507, filed August 27, 2009, entitled "Improved Methods and Compositions Involving Catalytic Materials, Electrodes, and Systems for Water Electrolysis and Other Electrochemical Techniques," by Esswein, et al., and U.S. Provisional Patent

Application Serial No. 61/285,844, filed December 1 1, 2009, entitled "Improved

Methods and Compositions Involving Catalytic Materials, Electrodes, and Systems for Water Electrolysis and Other Electrochemical Techniques," by Esswein, et al., each incorporated herein by reference. Field of the Invention

The present invention generally relates to methods and systems involving materials and electrode for electrolysis of water and other electrochemical techniques.

Background of the Invention

Electrolysis of water, that is, splitting water into its constituent elements, oxygen and hydrogen gases, is a very important process not only for the production of oxygen and/or hydrogen gases, but for energy storage. Energy is consumed in splitting water into hydrogen and oxygen gases and, when hydrogen and oxygen gases are re-combined to form water, energy is released.

In order to store energy via electrolysis, catalysts are required which efficiently mediate the bond rearranging "water splitting" reaction to 0₂ and H₂. The standard reduction potentials for the 0₂/H₂0 and H₂0/H₂ half-reactions are given by Equation 1 and Equation 2.

0₂ +4H⁺ +4e^' - H₂0 E° =+1.23-0.05¾?#) V (1) 2H₂ 4H⁺ +4e^~ £° = 0.00-0.059Q9//) V (2)

2H₂+ 0₂ > 2H₂0 (3) For a catalyst to be efficient for this conversion, the catalyst should operate close to the thermodynamically-limiting value of each half-reaction, which are defined by half-cell potentials, E°. Voltage in addition to E° that is required to attain a given catalytic activity, referred to as overpotential, limits the conversion efficiency and considerable effort has been expended by many researchers in efforts to reduce overpotential in this reaction. Of the two reactions, anodic water oxidation may be considered to be more complicated and challenging. It may be considered that oxygen gas production from water at low overpotential and under benign conditions presents the greatest challenge to water electrolysis. The oxidation of water to form oxygen gas requires removing four electrons coupled to the removal of four protons in order to avoid prohibitively high- energy intermediates. In addition to controlling multi-proton-coupled electron transfer reactions, a catalyst, in some cases, should also be able to tolerate prolonged exposure to oxidizing conditions.

While there have been significant studies involving materials and electrodes for electrolysis and other electrochemical reactions, there remains significant room for improvement.

Summary of the Invention

In some embodiments, the present invention provides methods. In some cases, a method of producing oxygen and/or hydrogen gas from water comprises providing an electrode comprising a catalytic material comprising a metal ionic species and a first anionic species, wherein the electrode is operated in a liquid medium comprising a second anionic species in a concentration of greater than about 0.3 M, or in a non-liquid medium comprising a second anionic species having an equivalent weight of less than about 1500 g/mol, and wherein the first anionic species and the second anionic species are not an oxide and/or hydroxide.

In some embodiments, the present invention provides systems. In some cases, a system for catalytically producing oxygen and/or hydrogen gas from water, comprises an electrode comprising a catalytic material comprising metal ionic species and a first anionic species, and a second anionic species in a liquid medium at a concentration greater than about 0.3 M, or in a non-liquid medium having an equivalent weight of less than about 1500 g/mol, wherein the first anionic species and the second anionic species are not an oxide and/or hydroxide.

Brief Description of the Drawings

FIGS. 1 A- IB illustrate the formation of an electrode, according to one

embodiment.

FIGS. 2A-2E illustrate the formation of a catalytic material on a current collector, according to one embodiment.

FIGS. 3A-3C illustrate a non-limiting example of a dynamic equilibrium of a catalytic material, according to one embodiment.

FIGS. 4A-4C represent an illustrative example of changes in oxidation state that may occur for a single metal ionic species during a dynamic equilibrium of an electrode, according to one embodiment, during use.

FIG. 5 shows a non-limiting example of an electrolytic device.

FIG. 6 shows a non-limiting example of an electrochemical device.

FIG. 7 illustrates a non-limiting example of an electrolytic device employing water in a gaseous state.

FIG. 8 shows temperature dependent electro-catalytic activity of a catalytic material, according to a non-limiting embodiment.

FIG. 9 shows the bulk electrolysis of a catalytic material comprising a first anionic species and operated in an electrolyte comprising a second anionic species, according to a non-limiting embodiment.

FIG. 1 OA shows an SEM micrograph of a high surface area nickel foam current collector associated with a catalytic material.

FIG. 10B shows the current response of the electrode from FIG. 10A.

FIG. 1 1 shows the bulk electrolysis of a catalytic material comprising a first anionic species and operated in sodium carbonate and potassium carbonate, according to a non-limiting embodiment.

Other aspects, embodiments, and features of the invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings. The accompanying figures are schematic and are not intended to be drawn to scale. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. All patent applications and patents incorporated herein by reference are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control.

Detailed Description

The present invention generally relates to methods and systems involving materials and electrodes for electrolysis of water and other electrochemical techniques. In some aspects of the present invention, methods and system are provided that produce or facilitate the production of oxygen and/or hydrogen gas from water (Equations 1 , 2 above) at low energy input (low "overpotential"). The methods and systems of the invention may allow for the facile, low-energy conversion of water to hydrogen gas and/or oxygen gas, where this process can be easily driven by a standard solar panel (e.g., a photovoltaic cell), wind-driven generator, or any other power source that provides an electrical output. In some cases, the hydrogen and oxygen gases may be recombined at any time, for example, using a fuel cell, whereby they form water and release significant energy that can be captured in the form of mechanical energy, electricity, or the like. In other cases, the hydrogen and/or oxygen gases may be used together, or separately, in another process.

The invention, in one aspect, involves the discovery that it can be desirable to expose, to a catalytic material associated with an electrode for electrolysis, an anionic species that is the same as or different from at least one anionic species of contained in the catalytic material, optionally at a higher concentration. Unexpected and surprising performance of an electrochemical cell is observed at a threshold concentration of the anionic species in a medium to which the catalytic material is exposed, or with a second anionic species, or both. In some cases, at least one performance parameter of an electrochemical reaction and/or system can be improved by altering the ions and/or compounds (e.g., composition, concentration, etc.) to which a catalytic material is exposed (e.g., which are in or surround a catalytic material), wherein the catalytic material is being employed in the electrochemical reaction and/or system. For example, in some embodiments of the present invention, the activity (e.g., current density of an electrode (e.g., comprised in an electrochemical system and/or employed in an

electrochemical reaction) comprising a catalytic material may increase upon exposure to selected ions or species, overpotential may be changed, and/or robustness or stability of the catalyst may be improved under set conditions.

In some embodiments, the present invention involves a system or a method comprising an electrode comprising a catalytic material. Many catalytic materials as described herein are made of readily-available, low-cost material, and are easy to make. Generally, the catalytic material comprises metal ionic species and a first anionic species. For example, the catalytic material may comprise metal ionic species such as cobalt and a first anionic species containing phosphorus (e.g., forms of phosphate). During the electrochemical reaction, the electrode may be exposed to a second anionic species. At least one performance parameter (e.g., current density, overpotential, catalytic turnover, rate of oxygen production, etc.) of the system/electrode may improve over a period of operation time following exposure to the second anionic species. In some cases, the second anionic species may be selected so as to interact with the catalytic material, during operation of the electrode, to increase the electrode activity under set conditions. For example, the electrode current density at a particular voltage, the voltage at a particular current density, the rate of oxygen production at a specific power input, etc. may improve over a period of operation of the electrode . In addition, in some cases, the second anionic species can be selected to significantly improve the stability of the catalytic material over time. During operation of the catalytic material in the presence of a second anionic species, the second anionic species may or may not be incorporated into the catalytic material. Without wishing to be bound by theory, in some embodiments, the improvement in at least one parameter may be due to the incorporation of at least one second anionic species into the catalytic material (e.g., by replacing a first anionic species, by filling an empty interstices of a lattice, etc.).

Although the compositions, electrodes, catalytic materials, systems and methods described herein are primarily related to water electrolysis (i.e., forming oxygen gas, hydrogen gas, and/or other products from water), the invention is not limited in this way. Where the invention is described as involving a first electrode and/or a second electrode (one or both of which can be catalytic), with production of oxygen gas via water electrolysis at the first electrode and/or production of hydrogen gas at the second electrode, it is to be understood that the first electrode can facilitate oxidation of any species, water or otherwise, to produce oxygen gas or another oxidized product.

Examples of reactants that can be oxidized in this context can include methanol, formic acid, ammonia, etc. Examples of oxidized products can include C0₂, N₂, etc. At the second electrode, a reaction can be facilitated in which water (or hydrogen ions) is reduced to make hydrogen gas, but it is to be understood that a variety of reactants not limited to water (e.g., acetic acid, phosphoric acid, etc.) can be reduced to form hydrogen gas and any number of other products of the reduction reaction (e.g., acetate, phosphate, etc.). This reaction at the second electrode can be run in reverse, in "fuel cell" operation, such that hydrogen gas (and/or other exemplary products noted above) is oxidized to form water (and/or other exemplary reactants noted above). In some cases, the compositions, electrodes, methods, and/or systems may be used for reducing hydrogen gas. In some cases, the compositions, electrodes, methods, and/or systems may be used in connection with a photoelectrochemical cell.

It is also to be understood that where a catalyst and/or electrode is used to

"produce" hydrogen gas, oxygen gas, or another species from a source such as water, the reaction catalyzed can be the direct reaction from the source to the product, or the catalyst can facilitate such a reaction by catalyzing a reaction of a reactant to a product where the reactant originates from the source, but is not the source. For example, "producing" hydrogen gas from water includes, as one example in water under basic conditions, the reaction of water to form hydrogen gas, and as another example in water under acidic conditions, the reaction of hydrogen ion (ultimately from the source, water) to form hydrogen gas.

In some embodiments, a method of catalytically producing oxygen and/or hydrogen gas from water comprises providing an electrochemical system, wherein the electrochemical system comprises a first electrode, a second electrode biased negatively with respect to the first electrode, and an electrolyte. The first electrode may comprise a current collector (as described herein) and a catalytic material, the catalytic material comprising a metal ionic species and a first anionic species. The electrode may be exposed to a second anionic species (e.g., using the methods described herein) in a liquid and/or non-liquid (e.g., solid, gel). In some cases, the electrolyte (e.g., a liquid and/or non-liquid electrolyte) may comprise the second anionic species. The second ionic species may be selected so as to interact with the catalytic material during operation of the system, thereby improving at least one performance parameter of the first electrode (e.g., increasing the current density able to be produced by the first electrode). The electrochemical system may be used (e.g., by application of a voltage to the first and the second electrode) to catalyze the production of oxygen and/or hydrogen gas from water.

As described herein, the first anionic species and the second anionic species may be oxide and/or hydroxide but, in some embodiments, they are not. Generally, the first anionic species and the second anionic species are different. However, as described herein, in some embodiments, the first anionic species and the second anionic species may be the same.

One of ordinary skill in the art will be aware of simple methods to determine whether an anionic species is suitable for use in the invention as the second anionic species describe herein. I.e., to determine whether performance of an electrode and/or system is suitable (e.g., it may have improved - e.g., increased) following and/or during exposure to a second anionic species. For example, simple screening test that can easily be run on a standard lab bench, without the effort of constructing a complete, commercial scale electrolysis system, can be carried out as follows. A first determination of selected performance parameter of the first electrode (e.g., comprising the catalytic material comprising the metal ionic species and the first anionic species) and/or system may be determined essentially immediately (e.g., about 1 second, about 5 seconds, about 10 seconds, about 20 seconds, about 30 seconds, about 1 minute, etc.) after applying potential to the first electrode and/or system. After application of a potential to the first electrode for a selected period of time (e.g., about 2 minutes, about 3 minutes, about 4 minutes, about 5 minutes, about 10 minutes, about 20 minutes, about 30 minutes, about 40 minutes, about 50 minutes, about 60 minutes, about 90 minutes, about 2 hours, about 4 hours, about 8 hours, about 12 hours, or about 24 hours), a second determination of the performance parameter may be determined. A comparison (which may indicate improved performance, e.g. lower overpotential, better current density, better

robustness/stability, or the like) of performance parameter may be determined by comparing the first determination of the performance parameter and the second determination of a performance parameter. In some cases, the time at which the second determination is determined is at the or after the time in which the electrode and/or system has reached equilibrium (e.g., when the performance parameter has reached a steady state).

In some cases, the potential applied to the first electrode is the minimum potential necessary to cause the electrochemical reaction to occur for the system (e.g., the minimum potential required by the first electrode to form oxygen gas from water). In some cases, the potential applied is about 0.05 V, about 0.1 V, about 0.2 V, about 0.3 V, about 0.4 V, about 0.5 V, about 1.0 V, or more, greater than the minimum potential necessary to cause the electrochemical reaction to occur for the system. As will be understood by those of ordinary skill in the art, the minimum potential necessary may depend on the components and arrangement of the electrochemical system.

In some cases, exposure of the electrode to a second anionic species may increase the current density able to be produced by the first electrode. For example, the current density able to be produced by the first electrode may increase by about 5%, about 10%, about 15%, about 20%, about 25%, about 40%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, or about 100%.

Those of ordinary skill in the art will be aware of other performance parameter which may be suitable to determine in connection with the invention. For example, in some embodiments, the rate of oxygen production may be determined, wherein the rate of oxygen production increases by about 1 %, about 2%, by about 5%, about 10%, about 15%, about 20%, about 25%, about 40%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, or about 100%. As another example, the minimum overpotential necessary to carry out the electrochemical reaction may decrease by about 1 %, about 2%, about 3%, about 5%, about 10%, about 1 %, about 20%, about 25%, about 40%, about 40%, or about 50%.

Alternatively, or in addition to realization of an improved performance parameter, through selection of the second anionic species to which a catalytic material is exposed may also result in improved robustness of the catalytic material. That is, a catalytic material may be stable for a longer period of time when it is operated in the presence of a second anionic species as compared to operation in the absence of a second anionic species. Changes in the stability of an electrode operated in the presence of a second anionic species may be determined by operating the electrode, under essentially identical condition, either in the absence or presence of the second anionic species, and determining any differences in the stability. In some cases, the robustness of the catalytic material is increased such that the rate of oxygen production does not decrease by more than about 1%, about 2%, about 3%, about 4%, about 5%, about 10%, about 15%, about 20%, over about 1 hour, about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 8 hours, about 10 hours, about 15 hours, about 20 hours, about 30 hours, about 40 hours, about 50 hours, about 75 hours, about 100 hours, or more. In some cases, the stability and/or robustness of a system may be determined beginning at a point in time where the electrochemical system has reached equilibrium. For example, in some cases, as described herein, the performance of the system increases over a period of time when a catalytic material is exposed to a second anionic species. Accordingly, the operating parameters of the system may be changing for a period of time, and thus, the stability may be determined after an initial period of time has elapsed such that the performance has reached equilibrium.

An electrode may be exposed to a second anionic species using techniques that will be known to those of ordinary skill in the art. For example, the second anionic species may be provided in a liquid and/or non-liquid medium (e.g., solid, gel). In some cases, the electrode is exposed to a liquid medium comprising the second anionic species (e.g., a solution comprising the second anionic species). For example, an electrode may be substantially immersed in a solution comprising water and the second anionic species in a selected concentration. In some cases, the solution comprising the second anionic species may also function as the electrolyte. It should be understood, that in some cases, additional additives (e.g., the first anionic species) and/or impurities (e.g., NaCl) may be present in the solution (which may or might not be functioning as an electrolyte) containing the second anionic species, as described herein. In some cases, an electrolyte (e.g., a solid and/or gel electrolyte) may be present in addition to the solution comprising the second anionic species. In some embodiments, the second electrolyte may be provided in a non-liquid medium (e.g., solid, gel). In some cases, the second anionic species may be provided in a solid and/or gel electrolyte.

It should be understood that while much of the application herein focuses on embodiments where the second anionic species is provided in a liquid medium, this is by no means limiting, and in any of such embodiments, the second anionic species may be alternatively provided in a non-liquid medium (e.g., in some cases, a solid and/or gel electrolyte), as described herein. That is, it should be understood, that for any embodiment where a second anionic species is described as being provided in a liquid medium at a particular concentration or according to certain parameters, a non-liquid medium may be substituted for the liquid medium, wherein the second anionic species is present at corresponding concentration levels and/or parameters.

In some embodiments, a method for producing oxygen gas from water comprises providing a system comprising a first electrode and a second electrode, the first electrode comprising a current collector and a catalytic material comprising a metal ionic species and a first anionic species. The first electrode may be exposed to the second anionic species. As noted, in one aspect, the first electrode is exposed to a liquid medium comprising the second anionic species at a concentration from about 0.3 M to about 3.0 M, where unexpectedly good performance is observed. In some cases, the second anionic species is provided in an amount between about 0.3 M and about 2.0 M, or between about 0.5 M and about 2.0 M, between about 0.5 M and about 1.5 M. In some cases, the second anionic species is provided in an amount of at least about 0.01 M, at least about 0.05 M, at least about 0.1 M, at least about 0.2 M, at least about 0.3 M, at least about 0.5 M, at least about 0.6 M, at least about 0.7 M, at least about 0.8 M, at least about 0.9 M, at least about 1.0 M, at least about 1.2 M, at least about 1.5 M, at least about 2.0 M, at least about 3.0 M, at least about 4.0 M, or greater.

In embodiments where the second anionic species is provided in a non-liquid medium, the second anionic species may be present at an equivalent weight of least about 300 g/mol, at least about 400 g/mol, least about 500 g/mol, least about 600 g/mol, least about 700 g/mol, least about 800 g/mol, least about 900 g/mol, least about 1000 g/mol, least about 1 100 g/mol, least about 1200 g/mol, or least about 1300 g/mol, least about 1400 g/mol, least about 1500 g/mol, least about 1600 g/mol, or least about 1700 g/mol. In some cases, the second anionic species may be present at an equivalent weight of less than about 300 g/mol, less than about 400 g/mol, less than about 500 g/mol, less than about 600 g/mol, less than about 700 g/mol, less than about 800 g/mol, less than about 900 g/mol, less than about 1000 g/mol, less than about 1 100 g/mol, less than about 1200 g/mol, less than about 1300 g/mol, less than about 1400 g/mol, less than about 1500 g/mol, less than about 1600 g/mol, or less than about 1700 g/mol. In some cases, the second anionic species is present in an amount between about 300 g/mol and about 1600 g/mol, between about 400 g/mol and about 1500 g/mol, between about 500 g/mol and about 1500 g/mol, between about 600 g/mol and about 1500 g/mol, or between about 700 g/mol and about 1500 g/mol. The term "equivalent weight," as used herein, is given its ordinary meaning in the art and refers to the mass of medium per mole, or equivalent, of the second anionic species. For example, in embodiments where the medium is a polymer, the term equivalent weight refers to the mass of polymer divided by the moles of second anionic species present in the polymer. Suitable non-liquid mediums and/or electrolytes are described herein.

In some embodiments, oxygen gas is produced at the first electrode at an overpotential of less than about 0.4 volts at an electrode current density of at least about 1 mA/cm², at least about 5 mA/cm², at least about 10 mA/cm², at least about 15 mA/cm², 20 mA/cm², at least about 25 mA/cm², at least about 30 mA/cm², at least about 40 mA/cm², at least about 50 mA/cm², at least about 60 mA/cm², at least about 70 mA/cm², at least about 80 mA cm², at least about 90 mA/cm², at least about 100 mA/cm², or greater. In some embodiments, oxygen gas is produced at the first electrode at an overpotential of less than about 0.45 volts, or about 0.50 volts, or about 0.55 volts at an electrode current density of at least about 50 mA/cm², at least about 60 mA/cm², at least about 70 mA/cm², at least about 80 mA/cm², at least about 90 mA/cm², at least about 100

2 2 2

mA/cm , at least about 1 10 mA/cm , at least about 120 mA/cm , at least about 130 mA/cm², at least about 140 mA/cm², at least about 150 mA/cm², at least about 200 mA/cm , or greater

In some aspects of the present invention, systems are provided, wherein the system comprises an electrode comprising a current collector and a catalytic material comprising metal ionic species and a first anionic species, wherein the catalytic material is associated with the current collector and an electrolyte comprising a second anionic species in any range described herein. The first anionic species and the second anionic species may be as described herein. In some cases, the first type or anionic species and the second anionic species may be selected to function as described herein (e.g., increased performance and/or stability). In a particular embodiment, the catalytic material comprises cobalt ions and a first anionic species, wherein the first anionic species is a form of phosphate. In some cases, the second anionic species may be selected according the parameters described herein for selecting a first anionic species to be comprised in the catalytic material. In some cases, the second anionic species may be a good proton- accepting species, as described herein. In some embodiments, the first anionic species may comprises phosphorus (e.g., in the form of a phosphate, as described herein), and the second anionic species may comprise boron (e.g., in the form of borate, as described herein) or at least one form of carbonate (e.g., H₂C0₃, (HC0₃)^" _, (C0₃)^"2).

In some cases, the anionic species may be a polyanion. The term polyanion is given its ordinary meaning in the art and refers to an anion a molecule or chemical complex having more than one negative charges at more than one site.

Some aspects of the present invention relate to the discovery that increasing the concentration of one or more anionic species to which the catalytic material is exposed during formation on the electrode and/or use, may improve the performance of at least one parameter for an electrochemical reaction and/or system. That is, in some cases, the first anionic species and the second anionic species may be the same, but the second anionic species is present in a concentration in which unexpected enhancement is at least one performance parameter is observed (e.g., current density,

overpotentialjStability/robustness. etc.). The concentration of the second anionic species may be as compared to the concentration of the first anionic species present during the formation of the catalytic material. A non-limiting example of a system includes a catalytic material comprising metal ionic species and a form of phosphate, wherein the phosphate was present at a concentration of about 0.1 M during the formation of the catalytic material. Upon increasing the concentration of the phosphate in the electrolyte during operation (e.g., to about 0.5 M, about 1.0 M, or as described above; the second anionic species), an unexpected increase in the current density may be observed due the presence of a higher amount of phosphate in solution. In some embodiments, the improved performance (wherein the first type and the second anionic species are the same) may be illustrated by measuring a performance parameter of the system/electrode using the first anionic species (e.g., an anionic species present in a first concentration) and measuring a performance parameter of the system/electrode using the second anionic species (e.g., the same anionic species present in a second, higher, concentration). The above and other characteristics of the second anionic species and its ability to enhance the performance of an electrode and/or a system, may serve as selective screening tests for identification of second anionic species which are suitable for use with the particular system/electrode/catalytic material. Those of ordinary skill in the art can, through simple bench-top testing, reference to scientific literature, simple electrochemical testing, and the like, select a second anionic species based upon the present disclosure, without undue experimentation.

Described above are various aspects of the invention generally, and other aspects of the systems and methods will now be described in more detail, including information regarding the formation of the electrodes, characteristics, and other properties and components of the compositions, methods, and systems.

As noted, in some embodiments of the invention, catalytic materials and electrodes are provided which may produce oxygen gas and/or hydrogen gas from water. As shown in Equation 1 , water may be split to form oxygen gas, electrons, and hydrogen ions. Although it need not be, an electrode and/or device may be operated in benign conditions (e.g., neutral or near-neutral pH, ambient temperature, ambient pressure, etc.). In some cases, the electrodes described herein operate catalytically. That is, an electrode may be able to catalytically produce oxygen gas from water, but the electrode might not necessarily participate in the related chemical reactions such that it is consumed to any appreciable degree. Those of ordinary skill in the art will understand the meaning of

"catalytically" in this context. An electrode may also be used for the catalytic production of other gases and/or materials.

In some embodiments, an electrode comprises a current collector and a catalytic material associated with the current collector. A "catalytic material" as used herein, means a material that is involved in and increases the rate of a chemical electrolysis reaction (or other electrochemical reaction) and which, itself, undergoes reaction as part of the electrolysis, but is largely unconsumed by the reaction itself, and may participate in multiple chemical transformations. A catalytic material may also be referred to as a catalyst and/or a catalyst composition. A catalytic material is not simply a bulk current collector material which provides and/or receives electrons from an electrolysis reaction, but a material which undergoes a change in chemical state of at least one ion during the catalytic process. For example, a catalytic material might involve a metal center which undergoes a change from one oxidation state to another during the catalytic process. Thus, catalytic material is given its ordinary meaning in the field in connection with this invention. As will be understood from other descriptions herein, a catalytic material of the invention that may be consumed in slight quantities during some uses and may be, in many embodiments, regenerated to its original chemical state.

In some embodiments, an electrode comprises a current collector and a catalytic material associated with the current collector. A "current collector," as used herein, is given two alternative definitions. In a typical arrangement, a catalytic material is associated with a current collector which is connected to an external circuit for application of voltage and/or current to the current collector, for receipt of power in the form of electrons produced by a power source, or the like. Those of ordinary skill in the art will understand the meaning of current collector in this context. More specifically, the current collector refers to the material between the catalytic material and the external circuit, through which electric current flows during a reaction of the invention or during formation of the electrode. Where a stack of materials are provided together including both an anode and a cathode, and one or more catalytic materials associated with the cathode and/or anode, where current collectors may be separated by membranes or other materials, the current collector of each electrode (e.g., anode and/or cathode) is that material through which current flows to or from the catalytic material and external circuitry connected to the current collector. Generally, the current collector will typically be an object, separate from the external circuit, easily identifiable as such by those of ordinary skill in the art. The current collector may comprise more than one material, as described herein. In another arrangement, a wire connected to an external circuit may, itself, define the current collector. For example, a wire connected to external circuitry may have an end portion on which is absorbed a catalytic material for contact with a solution or other material for electrolysis. In such a case, the current collector is defined as that portion of the wire on which catalytic material is absorbed.

As used herein, a "catalytic electrode" is a current collector, in addition to any catalytic material adsorbed thereto or otherwise provided in electrical communication with (as defined herein) the current collector. The catalytic material may comprise metal ionic species and a first anionic species (and/or other species), wherein the metal ionic species and the first anionic species are associated with the current collector. Where "electrode" is used herein to describe what those of ordinary skill in the art would understand to be the "catalytic electrode," it is to be understood that a catalytic electrode as defined above is intended.

"Electrolysis," as used herein, refers to the use of an electric current to drive an otherwise non-spontaneous chemical reaction. For example, in some cases, electrolysis may involve a change in redox state of at least one species and/or formation and/or breaking of at least one chemical bond, by the application of an electric current.

Electrolysis of water, as provided by the invention, can involve splitting water into oxygen gas and hydrogen gas, or oxygen gas and another hydrogen-containing species, or hydrogen gas and another oxygen-containing species, or a combination. In some embodiments, devices of the present invention are capable of catalyzing the reverse reaction. That is, a device may be used to produce energy from combining hydrogen and oxygen gases (or other fuels) to produce water.

In all descriptions of the use of water for catalysis herein, it is to be understood that the water may be provided in a liquid and/or gaseous state. The water used may be relatively pure, but need not be, and it is one advantage of the invention that relatively impure water can be used. The water provided can contain, for example, at least one impurity (e.g., halide ions such as chloride ions). In some cases, the device may be used for desalination of water.

FIG. 1 depicts a non-limiting example of an electrode, and also depicts a non- limiting example of a formation of an electrode, according to some embodiments. FIG. 1A shows container 10 comprising current collector 12 and water source (e.g., an aqueous solution) 14 in which are suspended, but more typically dissolved, metal ionic species 16 and first anionic species 18. Current collector 12 is in electrical

communication 20 with a circuit including a power source (not shown) such as a photovoltaic cell, wind power generator, electrical grid, or the like. It should be understood, however, that the catalytic material associated with the current collector may comprise additional components (e.g., cationic species), as described herein. FIG. IB shows the arrangement of FIG. 1 A upon application of a sufficient voltage to the current collector under conditions causing association of catalytic material to the current collector. As shown, metal ionic species 22 and first anionic species 24 associate with the current collector 26 to form a deposited catalytic material 28 under these conditions. In some cases, when associating with the current collector, the metal ionic species may be oxidized or reduced as compared to the metal ionic species in solution, as described herein. In some cases, association of the metal ionic species with the current collector may comprise a change in oxidation state of the metal ionic species from (n) to (n+x), wherein x may be 1 , 2, 3, and the like.

Where a catalytic material is associated with a current collector in this manner, it typically accumulates in the form of a solid or near-solid at the current collector surface, upon exposure to an appropriate precursor solution and application of a voltage under appropriate conditions as described herein. Some of those conditions involve exposing the current collector to the forming conditions for a period of time, and at a voltage, such that a threshold amount of catalytic material associates with the current collector.

Various embodiments involve various amounts of such material, as described elsewhere herein.

Electrodes as described herein are generally formed prior to incorporation of a system (e.g., comprising a second anionic species). In some cases, a composition comprises a metal ionic species and a first anionic species may be associated with a current collector (e.g., via use of a binder). The composition comprising a metal ionic species and a first anionic species may be formed by mixing salts of the metal ionic species and anionic species in the presence of a reducing agent (e.g., sodium

borohydride, lithium aluminum hydride, hydrazine, sodium and potassium

hypophosphite) or oxidizing agent (e.g., hydrogen peroxide, sodium hypochlorite), optionally in the presence of a substrate material. The composition (e.g., solid, gel) may form associated with the substrate and/or as a suspension (e.g., particulate matter).

In some cases, an electrode may be formed using methods described herein (e.g., exposing a current collector to a solution comprising metal ionic species and a first anionic species, followed by application of a voltage to the current collector and association of a catalytic material comprising the metal ionic species and the first anionic species with the current collector). The electrode may then be incorporated into a system comprising a second anionic species. In some cases, following formation of the electrode using a system, the second anionic species may be provided to the system, without the need to remove or alter the system (e.g., by adding the second anionic species to an electrolyte present in the original system). Without wishing to be bound by theory, the formation of a catalytic material on a current collector may proceed according to the following example. A current collector may be immersed in a solution comprising metal ionic species (M) with an oxidation state of (n) (e.g., Mⁿ) and the first anionic species (e.g., A^"y). As voltage is applied to the current collector, metal ionic species near to the current collector may be oxidized to an oxidation state of (n+x) (e.g., M^(n+x)). The oxidized metal ionic species may interact with the first anionic species near the electrode to form a substantially insoluble complex, thereby forming a catalytic material. In some cases, the catalytic material may be in electrical communication with the current collector. A non-limiting example of this process is depicted in FIG. 2. FIG. 2 A shows a single metal ionic species 40 with an oxidation state of (n) in solution 42. Metal ionic species 44 may be near current collector 46, as depicted in FIG. 2B. As shown in FIG. 2C, metal ionic species may be oxidized to an oxidized metal ionic species 48 with an oxidation state of (n+x) and (x) electrons 50 may be transferred to current collector 52 or to another species near or associated with the metal ionic species and/or the current collector. FIG. 2D depicts a single first anionic species 54 nearing oxidized metal ionic species 56. In some instances, as depicted in FIG. 2E, first anionic species 58 and oxidized metal ionic species 60 may associate with current collector 62 to form a catalytic material. In some instances, the oxidized metal ionic species and the first anionic species may interact and form a complex (e.g., a salt) before associating with the electrode. In other instances, the metal ionic species and first anionic species may associate with each other prior to oxidation of the metal ionic species. In other instances, the oxidized metal ionic species and/or the first anionic species may associate directly with the current collector and/or with another species already associated with the current collector. In these instances, the metal ionic species and/or the first anionic species may associate with the current collector (either directly, or via formation of a complex) to form the catalytic material (e.g., a composition associated with the current collector).

In some cases, an electrode may be formed by immersing a current collector comprising the metal ionic species in a solution comprising the first anionic species (e.g., phosphate). The metal ionic species (e.g., in an oxidation state of Mⁿ) may be oxidized and/or may dissociate from the current collector into solution. The metal ionic species that are oxidized and/or dissociated from the current collector may interact with the first anionic species, and may re-associate with the current collector, thereby forming a catalytic material.

As noted above, the catalytic material used for electrolysis of water (and/or other electrochemical reactions) is primarily current collector-associated, rather than functioning largely as a homogeneous solution-based catalytic materials. Such a catalytic material "associated with" a current collector will now be described with reference to a metal ionic species and/or the first anionic species which can define a catalytic material. In some cases, the first anionic species and the metal ionic species may interact with each other prior to, simultaneously to, and/or after the association of the species with the current collector, and result in a catalytic material with a high degree of solid content resident on, or otherwise immobilized with respect to, the current collector. In this arrangement, the catalytic material can be solid including various degrees of electrolyte or solution (e.g., the material can be hydrated with various amounts of water), and/or other species, fillers, or the like, but a unifying feature among such catalytic material associated with current collectors is that they can be observed, visually or through other techniques described more fully below, as largely resident on or immobilized with respect to the current collector, either in electrolyte solution or after removal of the current collector from solution.

In some cases, the catalytic material may associate with the current collector via formation of a bond, such as an ionic bond, a covalent bond (e.g., carbon-carbon, carbon- oxygen, oxygen-silicon, sulfur-sulfur, phosphorus-nitrogen, carbon-nitrogen, metal- oxygen, or other covalent bonds), a hydrogen bond (e.g., between hydroxyl, amine, carboxyl, thiol, and/or similar functional groups), a dative bond (e.g., complexation or chelation between metal ions and monodentate or multidentate ligands), Van der Waals interactions, and the like. "Association" of the composition (e.g., catalytic material) with the current collector would be understood by those of ordinary skill in the art based on this description. In some embodiments, the interaction between a metal ionic species and a single first anionic species may comprise an ionic interaction, wherein the metal ionic species is directly bound to other species and the first anionic species is a counterion not directly bound to the metal ionic species. In a specific embodiment, a single first anionic species and a metal ionic species form an ionic bond and the complex formed is a salt. A catalytic material associated with a current collector is generally arranged with respect to the current collector so that it is in sufficient electrical communication with the current collector to carry out purposes of the invention as described herein. "Electrical communication," as used herein, is given its ordinary meaning as would be understood by those of ordinary skill in the art whereby electrons can flow between the current collector and the catalytic material in a facile enough manner for the electrode to operate as described herein. That is, charge may be transferred between the current collector and the catalytic material (e.g., the metal ionic species and/or the first anionic species present in the catalytic material).

In some embodiments, the catalytic material and the current collector may be integrally connected. The term "integrally connected," when referring to two or more objects or materials, means objects and/or materials that do not become separated from each other during the course of normal use, e.g., separation requires at least the intentional separation of the objects and/or material, for example, including the use of tools. A catalytic material may be considered to be associated with, or otherwise in direct electrical communication with a current collector during operation of an electrode comprising the catalytic material and current collector even in instances where a portion of the catalytic material may be dissociated from the current collector (e.g., when taking part in a catalytic process involving a dynamic equilibrium in which catalytic material is repeatedly removed from and re-associated with a current collector).

In some embodiments, the electrode comprising the catalytic material is a regenerative catalytic electrode. As used herein, a "regenerative electrode" refers to an electrode which is capable of being compositionally regenerated as it is used in a catalytic process, and/or over the course of a change between catalytic use settings. Thus, a regenerative catalytic electrode is one that includes one more species associated with the electrode (e.g., adsorbed on the electrode) which, under certain conditions, dissociate from the electrode, and then a significant portion or substantially all of those species re-associate with the electrode at a later point in the electrode's life or use cycle. For example, at least a portion of the catalytic material may dissociate from the electrode and become solvated or suspended in a fluid to which the electrode is exposed, and then become re-associated (e.g., adsorbed) at the electrode. The disassociation/re-association may take place as a part of the catalytic process itself, as catalytic species cycle between various states (e.g., oxidation states), in which they are more or less soluble in the fluid. This phenomenon during use, for example nearly or essentially steady-state use of the electrode, can be defined as a dynamic equilibrium. "Dynamic equilibrium," as used herein, refers to an equilibrium comprising metal ionic species and the first anionic species, wherein at least a portion of the metal ionic species are cyclically oxidized and reduced (as discussed elsewhere herein). Regeneration over the course of a change between catalytic use settings can be defined by a dynamic equilibrium which experiences a significant delay in its cyclical nature.

In some embodiments, at least a portion of the catalytic material may dissociate from the electrode and become solvated or suspended in the fluid (or solution and/or other medium) as a result of a significant reaction setting change, and then become re- associated at a later stage (e.g., during operation while exposed to a second anionic species). A significant reaction setting change, in this context, can be a significant change in potential applied to the electrode, significantly different current density at the electrode, significantly different properties of a fluid to which the electrode is exposed (or removal and/or changing of the fluid), or the like. In one embodiment, the electrode is exposed to catalytic conditions under which the catalytic material catalyzes a reaction, then the circuit of which the electrode is a part is changed so that the catalytic reaction is significantly slowed or even essentially stopped (e.g., the process is turned off), and then the system can be returned to the original catalytic conditions (or similar conditions that promote the catalysis), and at least a portion or essentially all of the catalytic material can re-associate with the electrode. Re-association of some or essentially all of the catalytic material with the electrode can occur during use and/or upon change in conditions as noted above, and/or can occur upon exposure of the catalytic material, the electrode, or both to a regenerative stimulus such as a regenerative electrical potential, current, temperature, electromagnetic radiation, or the like. In some cases, the regeneration may comprise a dynamic equilibrium mechanism involving oxidation and/or reduction processes, as described elsewhere herein.

Regenerative electrodes can exhibit disassociation and re-association of catalytic species at various levels. In one set of embodiments, at least 0.1 % by weight of catalytic material associated with the electrode disassociates as described herein, and in other embodiments as much as about 0.25%, about 0.5%, about 0.6%, about 0.8%, about 1.0 %, about 1.25%, about 1.5 %, about 1.75%, about 2.0%, about 2.5%, about 3%, about 4%, about 5%, or more of the catalytic material disassociates, and some or all re- associates as discussed. In various embodiments, of the amount of material that disassociates, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 85%, at least about 90%, at least about 95%, at least about 97%, at least about 98%, at least about 99%, or essentially all material re-associates. Those of ordinary skill in the art will understand the meaning of disassociation and re-association of material in this regard, and will know of techniques for measuring these factors (for example, scanning electron microscopy and/or elemental analyses of the electrode, chemical analysis of the fluid, electrode performance, or any combination). Further, those of ordinary skill in the art will quickly be able to select catalytic materials which meet these parameters with knowledge of solubilities and/or catalytic reaction screening, or combinations. As a specific example, in some cases, during use of a catalytic material comprising cobalt ions and the first anionic species comprising phosphorus, at least a portion of the cobalt ions and the first anionic species comprising phosphorus

periodically associate and dissociate from the electrode.

It should be understood, however, in some embodiments, that not every metal ionic species and/or the first anionic species which exhibits a change in oxidation state will dissociate and re-associate with a current collector. In some cases, only a small portion (e.g., less than about 20%, less than about 15%, less than about 10%, less than about 5%, less than about 2%, less than about 1%, or less) of the oxidized/reduced metal ionic species may dissociate/associate with the current collector during operation or between uses.

In some embodiments, a dynamic equilibrium may comprise at least a portion of the metal ionic species being cyclically oxidized and reduced, wherein the metal ionic species are thereby associated and disassociated, respectively, from the current collector. An example of a dynamic equilibrium (or regenerative mechanism) which can, but need not necessarily, take place in accordance with the invention is depicted in FIG. 3. FIG. 3A depicts an electrode comprising current collector 80 and catalytic material 82 comprising metal ionic species 84 and the first anionic species 86. The dynamic equilibrium is depicted in FIGS. 3B-3C. FIG. 3B shows the same electrode, wherein a portion of metal ionic species 88 and the first anionic species 90 have disassociated from current collector 92. FIG. 3C shows the same electrode at some point later in time where a portion of the metal ionic species and the first anionic species (e.g., 94) which disassociated from the current collector have re-associated with current collector 96. Additionally, different metal ionic species and the first anionic species (e.g., 98) may have disassociated from the current collector. Metal ionic species and the first anionic species can repeatedly disassociate and associate with the current collector. For example, the same metal ionic species and the first anionic species may disassociate and associate with the current collector. In other instances, the metal ionic species and/or the first anionic species may only disassociate and/or associate with the current collector once. A single metal ionic species may associate with the current collector

simultaneously as a second single metal ionic species disassociates from the electrode. The number of single metal ionic species and/or single first anionic species that may disassociate and/or associate simultaneously and/or within the lifetime of the electrode has no numerical limit.

It should be understood that a solution in which metal ionic species and/or the first anionic species may be solubilized may be transiently present (e.g., the solution might not necessarily be in contact with the current collector during the entire operation and/or formation of the electrode). For example, in instances where water is provided to the electrode in a gaseous state, in some embodiments, the solution may be comprised of transiently formed aqueous molecules and/or droplets on the surface of the electrode and/or electrolyte. In other instances, where the electrolyte is a solid, the solution may be present in addition to the electrolyte (e.g., as water droplets on the surface of the electrode and/or solid electrolyte) or in combination with the fuel (e.g., water). The electrode may be operated with a combination of solid electrolyte/gaseous fuel, fluid electrolyte/gaseous fuel, solid electrolyte/fluid fuel, fluid electrolyte/fluid fuel, or any combination thereof.

In some embodiments, the metal ionic species in solution may have an oxidation state of (n), while the metal ionic species associated with the current collector may have an oxidation state of (n+x), wherein x is any whole number. The change in oxidation state may facilitate the association of the metal ionic species on the current collector. It may also facilitate the oxidation of water to form oxygen gas or other electrochemical reactions. The cyclically oxidized and reduced oxidation states for a single metal ionic species in dynamic equilibrium may be expressed according to Equation 3:

M" Ό· M^{n+X) + x{eT ) (3)

where M is a metal ionic species, n is the oxidation state of the metal ionic species, x is the change in the oxidation state, and x(e^") is the number of electrons, where x may be any whole number. In some cases, the metal ionic species may be further oxidized and/or reduced, (e.g., the metal ionic species may access oxidation states of M⁽ⁿ⁺¹⁾, M⁽ⁿ⁺²⁾, etc.)

An illustrative example of changes in oxidation state that may occur for a single metal ionic species during a dynamic equilibrium is shown in FIG. 4. FIG. 4A depicts current collector 100 and a single metal ionic species 102 in oxidation state of (n), (e.g., M"). The metal ionic species 102 may be oxidized to a metal ionic species 104 with an oxidation state of (n+1) (e.g., M⁽ⁿ⁺¹⁾) and associate with current collector 106, as shown in FIG. 4B. At this point, the metal ionic species (e.g., M⁽ⁿ⁺¹⁾) may disassociate from current collector 106 and/or may undergo a further change in oxidation state. In some cases, as shown in FIG. 4C, the metal ionic species may be further oxidized to a single metal ionic species 108 with an oxidation state of (n+2) (e.g., M⁽ⁿ⁺²⁾) and may remain associated with the current collector (or may disassociate from the current collector). At this point, metal ionic species 108 (e.g., M⁽ⁿ⁺²⁾) may accept electrons (e.g., from water or another reaction component) and may be reduced to form metal ionic species with a reduced oxidation state of (n) or (n+1) (e.g., M⁽ⁿ⁺¹⁾, 106 or M", 102). In other cases, the metal ionic species 106 (e.g., M^ⁿ⁺¹^) may be reduced and reform metal ionic species in oxidation state (n) (e.g., M", 102). The metal ionic species in oxidation state (n) may remain associated with the current collector or may disassociate from the current collector (e.g., dissociate into solution).

Those of ordinary skill in the art will be able to use suitable screening tests to determine whether a metal ionic species and/or the first anionic species are in dynamic equilibrium and/or whether an electrode is regenerative. For example, in some cases, the dynamic equilibrium may be determined using radioisotopes of the metal ionic species and/or the first anionic species. In such cases, an electrode comprising a current collector and a catalytic material comprising radioisotopes may be prepared. The electrode may be placed in an electrolyte which comprises non-radioactive ionic species. The catalytic material may dissociate from the current collector and therefore, the solution may comprise radioactive isotopes of the first anionic species and/or metal ionic species. This may be determined by analyzing an aliquot of the electrolyte for the radioisotopes. Upon application of the voltage to the current collector, in instances where the metal ionic species and the first anionic species are in dynamic equilibrium, the radioisotopes of the metal ionic species may re-associate with the current collector. Aliquots of the electrolyte may be analyzed to determine the amount of radioisotope present in the electrolyte at various time points after application of the voltage. If the metal ionic species and the first anionic species are in dynamic equilibrium, the percentage of radioisotopes in solution may decrease with time as the radioisotopes re- associate with the current collector. For a non-limiting working example, see Example 18. This screening technique may be used both to determine how a catalytic material may be functioning, and to select materials which can be suitable for forming a catalytic material.

Further techniques useful for selecting suitable catalytic material follow. Without wishing to be bound by theory, the solubility of a material comprising the first anionic species and oxidized metal ionic species may influence the association of the metal ionic species and/or the first anionic species with the current collector. For example, if a material formed by (c) number of the first anionic species and (b) number of oxidized metal ionic species is substantially insoluble in the solution, the material may be influenced to associate with the current collector. This non-limiting example may be expressed according to Equation 4:

b(M^(n+x)) + c(A-^y) ^ { [M]_b[A]_c }^{(b(ri+x) y))}(s) (4)

where M^^n+X^ is the oxidized metal ionic species, A^"y is the first anionic species, and

{[M]b[A]c}^(b(n+x)"c(yW is at least a portion of catalytic material formed, where b and c are the number of metal ionic species and the first anionic species, respectively. Therefore, the equilibrium may be driven towards the formation of the catalytic material by the presence of an increased amount of the first anionic species. In some cases, the solution surrounding the current collector may comprise an excess of the first anionic species, as described herein, to drive the equilibrium towards the formation of the catalytic material associated with the current collector. It should be understood, however, that the catalytic material does not necessarily consist essentially of a material defined by the formula {[M]_b[A]_c}^(n+x"y), as, in most cases, additional components can be present in the catalytic material (e.g., a second anionic species). However, the guidelines described herein (e.g., regarding K_sp) provide information to select complimentary first anionic species and metal ionic species that may aid in the formation and/or stabilization of the catalytic material. In some cases, the catalytic material may comprise at least one bond between a metal ionic species and a single first anionic species (e.g., a bond between a cobalt ion and an anionic species comprising phosphorus).

Selection of metal ionic species and the first anionic species for use in a catalytic material will now be described in greater detail. It is to be understood that any of a wide variety of such species meeting the criteria described herein can be used and, so long as they participate in catalytic reactions described herein, they need not necessarily behave, in terms of their oxidation/reduction reactions, cyclical association/disassociation from the current collector etc., in the manner described in the application. But in many cases, metal ionic and the first anionic species selected as described herein, do behave according to one or more of the oxidations/reduction and solubility theories described herein. In some embodiments, the metal ionic species (Mⁿ) and the first anionic species (A^"y) may be selected such that they exhibit the following properties. In most cases, the metal ionic species and the first anionic species will be soluble in an aqueous solution. In addition, the metal ionic species may be provided in an oxidized form, for example with an oxidation state of (n), where (n) is one, two, three, or greater, i.e., in some cases, the metal ionic species have access to at least one oxidation state greater than (n), for example, (n+1) and/or (n+2).

The solubility product constant, K_sp, as will be known to those of ordinary skill in the art, is a simplified equilibrium constant defined for the equilibria between a composition comprising the species and their respective ions in solution and may be defined according to Equation 6, based on the equilibrium shown in Equation 5.

{M_yA„ }_w y{M)"w + n{A)-\_aq) (S)

Κ_Ψ = [Μ]"[ΑΥ (6)

In Equations 5 and 6, M is the metal ionic species with a charge of (n), A is the first anionic species with a charge of (-y). The solid complex M_yA_n may disassociate into solubilized metal ionic species and the first anionic species. Equation 6 shows the solubility product constant expression. As will be known to those of ordinary skill in the art, the solubility product constant value may change depending on the temperature of the aqueous solution. Therefore, when choosing metal ionic species and the first anionic species for the formation of an electrode the solubility product constant should be determined at the temperature at which the electrode is to be formed and/or operated in. In addition, the solubility of a solid complex may change depending on the pH. This effect should be taken into account when applying the solubility product constant to the selection of a metal ionic species and the first anionic species.

In many cases, the metal ionic species and the first anionic species are selected together, for example, such that a composition comprising the metal ionic species with an oxidation state of (n) and the first anionic species is soluble in an aqueous solution, the composition having a solubility product constant which is greater than the solubility product constant of a composition comprising the metal ionic species with an oxidation state of (n+x) and the first anionic species. That is, the composition comprising the metal ionic species with an oxidation state of (n) and the first anionic species may have a K_sp value substantially greater than the K_sp for the composition comprising the metal ionic species with an oxidation state of (n+x) and the first anionic species. For example, the metal ionic species and the first anionic species may be selected such that the K_sp value of composition comprising the first anionic species and the metal ionic species with an oxidation state of (n) (e.g., Mⁿ) is greater than the K_sp value of the composition comprising the first anionic species and the metal ionic species with an oxidation state of (n+x) (e.g., M^(n+X)) by a factor of at least about 10, at least about 10², at least about 10³, at least about 10⁴, at least about 10⁵, at least about 10⁶, at least about 10⁸, at least about 10¹⁰, at least about 10¹⁵, at least about 10²⁰, at least about 10³⁰, at least about 10⁴⁰, at least about 10⁵⁰, and the like. Where these K_sp values are realized, a catalytic material may be more likely to serve as an electrode or current collector-associated material.

In some instances, a catalytic material, such as a composition comprising a metal ionic species with an oxidation state of (n+x) and the first anionic species may have a K_sp between about 10^'3 and about 10^"50. In some cases, the solubility constant of this composition may be between about 10^"4 and about 10^"50, between about 10^"5 and about 10^"40, between about 10^"6 and about 10 ³⁰, between about 10^"3 and about 10^"30, between about 10^"3 and about 10^"20, and the like. In some cases, the solubility constant may be less than about 10^"3, less than about 10^"4, less than about 10^"6, less than about 10^"8, less than about 10^"10, less than about 10^"15, less than about 10^"20, less than about 10^"25, less than about 10^"30, less than about 10^"40, less than about 10^"50, and the like. In some cases, the composition comprising metal ionic species with an oxidation state of (n) and the first anionic species may have a solubility product constant greater than about 10^"3, greater than about 10^"4, greater than about 10^"5, greater than about 10^"6, greater than about

8 12 1 5 18

10^" , greater than about 10^" , greater than about 10^" , greater than about 10^" , greater than about 10^" , and the like. In a particular embodiment, the composition comprising metal ionic species and the first anionic species may be selected such that the

composition comprising the metal ionic species with an oxidation state of (n) and the

I ft

first anionic species have a K_sp value between about 10^" and about 10^" and the composition comprising the metal ionic species with an oxidation state of (n+x) and the first anionic species have a K_sp value less than about 10^"10. Non-limiting examples of metal ionic species and the first anionic species that can be soluble in an aqueous solution and have a K_sp value in a suitable range includes Co(II)/HP0₄ ^"2, Co(II)/H₂B0₃\ Co(II)/HAs0₄ ^"2, Fe(II)/C0₃ ^"2, Mn(II)/C0₃ ^"2, and Ni(II)/H₂B0₃ ^". In some cases, these combinations may additionally comprise at least a second the first anionic species, for example, oxide and/or hydroxide ions. The composition that forms on the current collector may comprise the metal ionic species and the first anionic species selected, as well as additional components (e.g., oxygen, water, hydroxide, counter cations, counter anions, etc.).

As noted, an electrode can be formed by deposition of a catalytic material from solution. Whether the electrode has been properly formed, with proper association of the catalytic material with the current collector, may be important to monitor, both for selecting proper metal ionic species and/or the first anionic species and, of course, determining whether an appropriate electrode has been formed. The electrode may be determined to have been formed using various procedures. In some instances, the formation of a catalytic material on the current collector may be observed. The formation of the material may be observed by a human eye, or with use of magnifying devices such as a microscope or via other instrumentation. In one case, application of a voltage to the electrode, in conjunction with an appropriate counter electrode and other components (e.g., circuitry, power source, electrolyte) may be carried out to determine whether the system produces oxygen gas at the electrode when the electrode is exposed to water. In some cases, the minimum voltage applied to the electrode which causes oxygen gas to form at the electrode may be different than the voltage required to form gas from the current collector alone. In some cases, the minimum voltage required for the electrode will be less than the voltage required for the current collector alone (i.e., the overpotential will be less for the electrode that includes both the current collector and catalytic material, than for the current collector alone).

The catalytic material (and/or the electrode comprising the catalytic material) may also be characterized in terms of performance. One way of doing this, among many, is to compare the current density of the electrode versus the current collector alone.

Typical current collectors are described more fully below and can include indium tin oxide (ITO), and the like. The current collector may be able to function, itself, as a catalytic electrode in water electrolysis, and may have been used in the past to do so. So, the current density during catalytic water electrolysis (where the electrode catalytically produces oxygen gas from water), using the current collector, as compared to essentially identical conditions (with the same counter electrode, same electrolyte, same external circuit, same water source, etc.), using the electrode including both current collector and catalytic material, can be compared. In most cases, the current density of the electrode will be greater than the current density of the current collector alone, where each is tested independently under essentially identical conditions. For example, the current density of the electrode may exceed the current density of the current collector by a factor of at least about 10, about 100, about 1000, about 10⁴, about 10⁵, about 10⁶, about 10⁸, about 10¹⁰, and the like. In a particular case, the difference in the current density is at least about 10⁵. In some embodiments, the current density of the electrode may exceed the current density of the current collector by a factor between about 10⁴ and about 10¹⁰, between about 10⁵ and about 10⁹, or between about 10⁴ and about 10⁸. The current density may either be the geometric current density or the total current density, as described herein.

This characteristic, namely, significantly increased catalytic activity of the electrode (comprising a current collector and catalytic material associated with the current collector) as compared to the current collector alone, may be used to monitor formation of a catalytic electrode. That is, the formation of the catalytic material on the current collector may also be observed by monitoring the current density over a period of time. The current density, in most cases, will increase during application of a voltage to the current collector. In some instances, the current density may reach a plateau after a period of time (e.g., about 2 hours, about 4 hours, about 6 hours, about 8 hours, about 10 hours, about 12 hours, about 24 hours, and the like).

Metal ionic species useful as one portion of a catalytic material may be any metal ion selected according to the guidelines described herein. In most embodiments, the metal ionic species have access to oxidation states of at least (n) and (n+x). In some cases, the metal ionic species have access to oxidation states of (n), (n+1) and (n+2). (n) may be any whole number, and includes, but is not limited to, 0, 1, 2, 3, 4, 5, 6, 7, 8, and the like. In some cases, (n) is not zero. In particular embodiments, (n) is 1 , 2, 3 or 4. (x) may be any whole number and includes, but is not limited to 0, 1 , 2, 3, 4, and the like. In particular embodiments, (x) is 1, 2, or 3. Non-limiting examples of metal ionic species include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Rh, Ru, Ag, Cd, Pt, Pd, Ir, Hf, Ta, W, Re, Os, Hg, and the like. In some cases, the metal ionic species may be a lanthanide or actinide (e.g., Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, Pa, U, etc.). In a particular embodiment, the metal ionic species comprises cobalt ions, which may be provided as a catalytic material in the form of Co(II), Co(III) or the like. In some embodiments, the metal ionic species is not Mn. The metal ionic species may be provided (e.g., to the solution) as a metal compound, wherein the metal compound comprises metal ionic species and counter anions. For example, the metal compound may be an oxide, a nitrate, a hydroxide, a carbonate, a phosphite, a phosphate, a sulphite, a sulphate, a triflate, and the like.

An anionic species (e.g., a first anionic species) selected for use as a catalytic material may be any anionic species that is able to interact with the metal ionic species as described herein and to meet threshold catalytic requirements as described. In some cases, the anionic compound may be able to accept and/or donate hydrogen ions, for example, H₂P0₄ ^" or HP0₄ ^"2. Non-limiting examples of the first anionic species include forms of phosphate (H₃P0₄ or HP0₄ ^~2, H₂P0₄ ^"2 or P0₄ ^"3), forms of sulphate (H₂S0₄ or HS0₄\ S0₄ ^"2), forms of carbonate (H₂C0₃ or HC0₃ ^~, C0₃ ^"2), forms of arsenate (H₃As0₄ or HAs0₄ ^"2, H₂As0₄ ^"2 or As0₄ ^"3), forms of phosphite (H₃P0₃ or HP0₃ ^"2, H₂P0₃ ^"2 or P0₃ ^" ³), forms of sulphite (H2SO3 or HSO₃ ^~, SO₃ ^~2), forms of silicate, forms of borate (e.g., H₃B0₃, Η₂ΒΟ₃ ^~, HB0₃ ^" , etc.), forms of nitrates, forms of nitrites, and the like.

In some cases, the first anionic species comprised in the catalytic material may be a form of phosphonate. A phosphonate is a compound comprising the structure

PCKOR'XOR^CR³) wherein R¹, R², and R³ can be the same or different and are H, an alkyl, an alkenyl, an alkynyl, a heteroalkyl, a heteroalkenyl, a heteroalkynyl, an aryl, or a heteroaryl, all optionally substituted, or are optionally absent (e.g., such that the compound is an anion, dianion, etc.). In a particular embodiment, R , R , and R can be the same or different and are H, alkyl, or aryl, all optionally substituted. A non-limiting example of a phosphonate is a form of PO(OH)₂R' (e.g., P0₂(OH)(R')^", P0₃(R')^"2), wherein R¹ is as defined above (e.g., alkyl such as methyl, ethyl, propyl, etc.; aryl such as phenol, etc.). In a particular embodiment, the phosphonate may be a form of methyl phosphonate (PO(OH)₂Me), or phenyl phosphonate (PO(OH)₂Ph). Other non-limiting examples of phosphorus-containing anionic species include forms of phosphinites (e.g., P(OR')R²R³) and phosphonites (e.g., P(OR')(OR )R³) wherein R¹, R², and R³ are as described above. In other cases, the first anionic species may comprise one any form of the following compounds: R¹SO₂(OR²)), SO(OR^!)(OR²), CO(OR')(OR²),

PO(OR')(OR²), AsO(OR')(OR²)(R³), wherein R¹, R², and R³ are as described above. With respect to the first anionic species discussed above, those of ordinary skill in the art will be able to determine appropriate substituents for the anionic species. The substituents may be chosen to tune the properties of the catalytic material and reactions associated with the catalytic material. For example, the substituent may be selected to alter the solubility constant of a composition comprising the first anionic species and the metal ionic species.

In some embodiments, the first anionic species may be good proton-accepting species. As used herein, a "good proton-accepting species" is a species which acts as a good base at a specified pH level. For example, a species may be a good proton- accepting species at a first pH and a poor proton-accepting species at a second pH.

Those of ordinary skill in the art can identify a good base in this context. In some cases, a good base may be a compound in which the pK_a of the conjugate acid is greater than the pK_a of the proton donor in solution. As a specific example, SO₄ ^"2 may be a good proton-accepting species at about pH 2.0 and a poor proton-accepting species at about pH 7.0. A species may act as a good base around the pK_a value of the conjugate acid. For example, the conjugate acid of HP0₄ ^"2 is H₂PCV, which has a pK_a value of about 7.2. Therefore, HPO₄ ^"2 may act as a good base around pH 7.2. In some cases, a species may act as a good base in solutions with a pH level at least about 4 pH units, about 3 pH units, about 2 pH units, or about 1 pH unit, above and/or below the pK_a value of the conjugate acid. Those of ordinary skill in the art will be able to determine at which pH levels an anionic species is a good proton-accepting species.

An anionic species (e.g., a first type, second type, third type, etc.) may be provided as an neutral compound comprising the anionic species and a counter cation, for example, a metal ion (e.g., K⁺, Na⁺, Li⁺ _, Mg⁺², Ca⁺², Sr⁺²), NP ⁺ (e.g., NH₄ ⁺)_, H⁺, and the like. In a specific embodiment, the compound employed may be K₂HP0_4.

The catalytic material may comprise the metal ionic species and the first anionic species in a variety of ratios (amounts relative to each other). In some cases, the catalytic material comprises the metal ionic species and the anionic species in a ratio of less than about 20: 1 , less than about 15: 1 , less than about 10: 1 , less than about 7: 1, less than about 6: 1, less than about 5: 1 , less than about 4: 1 , less than about 3: 1 , less than about 2: 1 , greater than about 1 : 1 , greater than about 1 :2, greater than about 1 :3, greater than about 1 :4, greater than about 1 :5, greater than about 1 : 10, and the like. In some cases, the catalytic material may comprise additional components, such as counter cations and/or counter anions from the metallic compound and/or anionic compound provided to the solution. For example, in some instances, the catalytic material may comprise the metal ionic species, the anionic species, and a counter cation and/or anion in a ratio of about 2: 1 : 1 , about 3: 1 : 1, about 3:2: 1 , about 2:2: 1 , about 2: 1 :2, about 1 :1 : 1, and the like. The ratio of the species in the catalytic material will depend on the species selected. In some instances, a counter cation may be present in a very small amount and serve as a dopant to, for example, to improve the conductivity or other properties of the material. In these instances, the ratio may be about X: 1 :0.1 , about X: 1 :0.005, about X: 1 :0.001 , about X: 1 :0.0005, etc., where X is 1 , 1.5, 2, 2.5, 3, and the like. In some instances, the catalytic material may additionally comprise at least one of water, oxygen gas, hydrogen gas, oxygen ions (e.g., O^"2), peroxide, hydrogen ion (e.g., H⁺), and/or the like.

In some embodiments, a catalytic material may comprise more than one metal ionic species and/or anionic species (e.g., at least about 2, at least about 3, at least about 4, at least about 5, or more, of metal ionic species and/or anionic species). For example, more than one metal ionic species and/or anionic species may be provided to the solution in which the current collector is immersed. In such instances, the catalytic material may comprise more than one metal ionic species and/or anionic species. Without wishing to be bound by theory, the presence of more than one metal ionic species and/or anionic species may allow for the properties of the electrode to be tuned, such that the

performance of the electrode may be altered by using combinations of species in different ratios. In a particular embodiment, a first metal ionic species (e.g., Co(II)) and second metal ionic species (e.g., Ni(II)) may be provided in the solution in which the current collector is immersed, such that the catalytic material comprises the first metal ionic species and the second metal ionic species (e.g., Co(II) and Ni(II)). Where a first and second metal ionic species are used together, each can be selected from among metal ionic species described as suitable for use herein.

Where both first type and a second metal ionic and/or anionic species are used, both the first and second species need not both be catalytically active, or if both are catalytically active they need not be active to the same level or degree. The ratio of the first metal ionic and/or anionic species to the second metal ionic and/or anionic species may be varied and may be about 1 : 1 , about 1 :2, about 1 :3, about 1 :4, about 1 :5, about 1 :6, about 1 :7, about 1 :8, about 1 :9, about 1 : 10, about 1 :20, or greater. In some instances, the second species may be present in a very small amount and serve as a dopant to, for example, to improve the conductivity or other properties of the material.

In some cases, a first and a second anionic species (e.g., a form of borate and a form of phosphate) may be provided to the solution and/or otherwise used in

combination in a catalytic material. Wherein first and a second anionic species are catalytically active anionic species, they can be selected from among anionic species described as suitable for use herein.

In some cases, the catalytic material may comprise a metal ionic species, a first anionic species, and a third anionic species. In some instances, the first anionic species is hydroxide and/or oxide ions, and the third anionic species is not hydroxide and/or oxide ions. Therefore, at least the first anionic species or the third anionic species is not hydroxide or oxide ions. It should be understood, however, that when at least one anionic species is an oxide or hydroxide, the species might not be provided to the solution but instead, may be present in the water or solution the species is provided in and/or may be formed during a reaction (e.g., between the first anionic species and the metal ionic species).

In some embodiments, the catalytic metal ionic species/anionic species (e.g., the catalytic material) do not consist essentially of metal ionic species/O^"2 and/or metal ionic species/OH^". A material "consists essentially of a species if it is made of that species and no other species that significantly alters the characteristics of the material, for purposes of the invention, as compared to the original species in pure form.

Accordingly, where a catalytic material does not consist essentially of metal ionic species/O^" and/or metal ionic species/OH^", the catalytic material has characteristics significantly different than a pure metal ionic species/O^"2 and/or metal ionic species/OH^", or a mixture. In some cases, a composition that does not consist essentially of metal ionic species/O^" and or metal ionic species/OH^" comprises less than about 90%, less than about 80%, less than about 70%, less than about 60%, less than about 50%, less than about 40%, less than about 30%, less than about 20%, less than about 10%, less than about 5%, less than about 1 %, and the like, weight percent of O^"2 and/or OH^" ions/molecules. In some instances, the composition that does not consist essentially of metal ionic species/O^"2 and/or metal ionic species/OH^" comprises between about 1% and about 99%, between about 1% and about 90%, between about 1% and about 80%, between about 1% and about 70%, between about 1% and about 60%, between about 1% and about 50%, between about 1% and about 25%, etc., weight percent O^"2 and/or OH^" ions/molecules. The weight percent of O^"2 and/or OH^" ions/molecules may be

determined using methods known to those of ordinary skill in the art. For example, the weight percent may be determined by determining the approximate structure of the material comprise in the composition. The weight percentage of the O^"2 and/or OH^" ions/molecules may be determined by dividing the weight of O^"2 and/or OH^"

ions/molecules over the total weight of the composition multiplied by 100%. As another example, in some cases, the weight percentage may be approximately determined based upon the ratio of metal ionic species to anionic species in a composition and knowledge regarding the general coordination chemistry of the metal ionic species.

In a specific embodiment, the composition (e.g., catalytic material) associated with the current collector may comprise cobalt ions and anionic species comprising phosphorus (e.g., HP0₄ ^" ). In some cases, the composition may additionally comprise cationic species (e.g., K⁺). In some cases, the current collector the composition is associated with does not consist essentially of platinum. An anionic species comprising phosphorus may be any molecule that comprises phosphorus and is associated with a negative charge. The ratio of cobalt ions/anionic species comprising phosphorus/cationic species may be about 2: 1 : 1 , about 3:1 : 1 , about 4: 1 : 1 , about 2:2: 1, about 2: 1 :2, about 2:3: 1 , about 2: 1 :3, and the like. Non-limiting examples of anionic species comprising phosphorus include H₃P0₄, H₂P0₄\ HP0₄ ^"2, P0₄ ^"3, H₃P0₃, H₂P0₃ ^", HP0₃ ^"2, P0₃ ^"3, R'PO(OH)₂, R'P0₂(OH)^", R'P0₃ ^"2, or the like, wherein R¹ is H, an alkyl, an alkenyl, an alkynyl, a heteroalkyl, a heteroalkenyl, a heteroalkynyl, an aryl, or a heteroaryl, all optionally substituted.

The above and other characteristics of the metal ionic species and anionic species may serve as selective screening tests for identification of particular metal ionic and anionic species useful for particular applications. Those of ordinary skill in the art can, through simple bench-top testing, reference to scientific literature, simple diffractive instrumentation, simple electrochemical testing, and the like, select metal ionic species and anionic species based upon the present disclosure, without undue experimentation.

The catalytic material may be porous, substantially porous, non-porous, and/or substantially non-porous. The pores may comprise a range of sizes and/or be

substantially uniform in size. In some cases, the pores may or might not be visible using imaging techniques (e.g., scanning electron microscope). The pores may be open and/or closed pores. In some cases, the pores may provide pathways between the bulk electrolyte surface and the surface of the current collector.

In some instances, the catalytic material may be hydrated. That is, the catalytic material may comprise water and/or other liquid and/or gas components. Upon removal of the current collector comprising the catalytic material from solution, the catalytic material may be dehydrated (e.g., the water and/or other liquid and/or gas components may be removed from the catalytic material). In some cases, the catalytic material may be dehydrated by removing the material from solution and leaving the material to sit under ambient conditions (e.g., room temperature, air, etc.) for at least about 1 hour, at least about 2 hours, at least about 4 hours, at least about 8 hours, at least about 12 hours, at least about 24 hours, at least about 2 days, at least about 1 week, or more. In some cases, the catalytic material may be dehydrated under non-ambient conditions. For example, the catalytic material be dehydrated at elevated temperature and/or under vacuum. In some instances, the catalytic material may change composition and/or morphology upon dehydration. For example, in instances where the catalytic material forms a film, the film may comprise cracks upon dehydration.

Without wishing to be bound by theory, in some cases, the catalytic material may reach a maximum performance (e.g., rate of 0₂ production, overpotential at a specific current density, Faradaic efficiency, etc.) based upon the thickness of the catalytic material. For example, Where a porous current collector is used, the thickness of the deposited catalytic material and the pore size of current collector may advantageously be selected in combination so that pores are not substantially filled with the catalytic material.

The physical structure of the catalytic material may vary. For example, the catalytic material may be a film and/or particles associated with at least a portion of the current collector (e.g., surface and/or pores) that is immersed in the solution. In some embodiments, the catalytic material might not form a film associated with the current collector. Alternatively or in addition, the catalytic material may be deposited on a current collector as patches, islands, or some other pattern (e.g., lines, spots, rectangles), or may take the form of dendrimers, nanospheres, nanorods, or the like. A pattern in some cases can form spontaneously upon deposition of catalytic material onto the current collector and/or can be patterned onto a current collector by a variety of techniques known to those of ordinary skill in the art (lithographically, via microcontact printing, etc.). Further, a current collector may be patterned itself such that certain areas facilitate association of the catalytic material while other areas do not, or do so to a lesser degree, thereby creating a patterned arrangement of catalytic material on the current collector as the electrode is formed. Where a catalytic material is patterned onto an electrode, the pattern might define areas of catalytic material and areas completely free of catalytic material, or areas with a particular amount of catalytic material and other areas with a different amount of catalytic material. The catalytic material may have an appearance of being smooth and/or bumpy. In some cases, the catalytic material may comprise cracks, as can be the case when the material dehydrated. In some cases, the thickness of catalytic material may be of substantially the same throughout the material or may vary. Those of ordinary skill in the art will easily be able to establish a thickness-determining protocol that accounts for any non- uniformity or patterning of catalytic material on a surface. The average thickness of the catalytic material may be at least about 10 nm, at least about 100 nm, at least about 300 nm, at least about 500 nm, at least about 700 nm, at least about 1 um (micrometer), at least about 2 um, at least about 5 um, at least about 1 mm, at least about 1 cm, or greater.

In some embodiments, the catalytic material may be described as a function of mass of catalytic material per unit area of the current collector. In some cases, the mass of catalytic material per area of the current collector may be about 0.01 mg/cm , about 0.05 mg/cm², about 0.1 mg/cm², about 0.5 mg/cm², about 1.0 mg/cm², about 1.5 mg/cm²,

2 2 2 2 about 2.5 mg/cm , about 3.0 mg/cm , about 4.0 mg/cm , about 5.0 mg/cm , or the like. In some cases, the mass of catalytic material per unit area of the current collector may be

2

between about 0.1 mg/cm and about 5.0 mg/cm , between about 0.5 mg/cm and about 3.0 mg/cm², between about 1.0 mg/cm² and about 2.0 mg/cm², and the like. Where the amount of catalytic material associated with a current collector is defined or investigated in terms of mass per unit area, and the material is present non-uniformly relative to the current collector surface (whether through patterning or natural variations in amount over the surface), the mass per unit area may be averaged across the entire surface area within which catalytic material is found (e.g., the geometric surface area). In some cases, the mass of the catalytic material per unit area may be a function of the thickness of the catalytic material.

The formation of the catalytic material may proceed until the potential (e.g., voltage) applied to the current collector is turned off, until there is a limiting quantity of materials (e.g., metal ionic species and/or anionic species) and/or the catalytic material has reached a critical thickness beyond which additional film formation does not occur or is very slow. Voltage may be applied to the current collector for minimums of about 1 minute, about 5 minutes, about 10 minutes, about 20 minutes, about 30 minutes, about 60 minutes, about 2 hours, about 4 hours, about 8 hours, about 12 hours, about 24 hours, and the like. In some cases, a potential may be applied to the current collector between 24 hours and about 30 seconds, between about 12 hours and about 1 minute, between about 8 hours and about 5 minutes, between about 4 hours and about 10 minutes, and the like. The voltages provided herein, in some cases, are supplied with reference to a normal hydrogen electrode (NHE). Those of ordinary skill in the art will be able to determine the corresponding voltages with respect to an alternative reference electrode by knowing the voltage difference between the specified reference electrode and NHE or by referring to an appropriate textbook or reference. The formation of the catalytic material may proceed until about 0.1%, about 1%, about 5%, about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about 99%, or about 100% of the metal ionic species and/or anionic species initially added to the solution have associated with the current collector to form the catalytic material.

The voltage applied to the current collector may be held steady, may be linearly increased or decreased, and/or may be linearly increased and decreased (e.g., cyclic). In some cases, the voltage applied to the current collector may be substantially similar throughout the application of the voltage. That is, the voltage applied to the current collector might not be varied significantly during the time that the voltage in applied to the current collector. In such instances, the voltage applied to the current collect may be at least about 0.1 V, at least about 0.2 V, at least about 0.4 V, at least about 0.5 V, at least about 0.7 V, at least about 0.8 V, at least about 0.9 V, at least about 1.0 V, at least about 1.2 V, at least about 1.4 V, at least about 1.6 V, at least about 1.8 V, at least about 2.0 V, at least about 3 V, at least about 4 V, at least about 5 V, at least about 10 V, and the like. In some cases, the voltage applied is between about 1.0 V and about 1.5 V, about 1.1 V and about 1.4 V, or is about 1.1 V. In some instances, the voltage applied to the current collector may be a linear range of voltages, and/or cyclic range of voltages. Application of a linear voltage refers to instances where the voltage applied to the electrode (and/or current collector) is swept linearly in time between a first voltage and a second voltage. Application of a cyclic voltage refers to application of linear voltage, followed by a second application of linear voltage wherein the sweep direction has been reversed. For example, application of a cyclic voltage is commonly used in cyclic voltammetry studies. In some cases, the first voltage and the second voltage may differ by about 0.1 V, about 0.2 V, about 0.3 V, about 0.5 V, about 0.8 V, about 1.0 V, about 1.5 V, about 2.0 V, or the like. In some cases, the voltage may be swept between the first voltage and the second voltage at a rate of about 0.1 mV/sec, about 0.2 mV/sec, about 0.3 mV/sec, about 0.4 mV/sec, about 0.5 mV/sec, about 1.0 mV/sec, about 10 mV/sec, about 100 mV/sec, about 1 V/sec, or the like. The potential applied may or might not be such that oxygen gas is being formed during the formation of the electrode. In some cases, the

morphology of the catalytic material may differ depending on the potential applied to the current collector during formation of the electrode.

In another embodiment, an electrode of system comprising a catalytic material may be prepared as follows. A catalytic material may be associated with a current collector as described above in any manner described herein. The catalytic material can be removed from the current collector (and, optionally, the process can be cyclically repeated with additional catalytic material associated with the electrode, removed, etc.) and the catalytic material can be optionally dried, stored, and/or mixed with an additive (e.g., a binder) or the like. The catalytic material may be packaged for distribution and used as a catalytic material. In some cases, the catalytic material can later be applied to a current collector, can simply be added to a solution of water and associated with a different current collector as described above, e.g., in an end-use setting, or used otherwise as would be recognized by those of ordinary skill in the art. Those of ordinary skill in the art can readily select binders that would be useful for addition to such catalytic material, for example, poly tetrafluoroethylene (Teflon™), Nafion™, or the like. For eventual use in an electrolyzer or other electrolysis system, non-conductive binders may be most suitable. Conductive binders may be used where they are stable to electrolyzer conditions.

In some embodiments, after formation of the catalytic material, the electrode may be essentially immediately exposed to a second anionic species. In other embodiments, after application of and formation of an electrode comprising a current collector, metal ionic species, and anionic species, the electrode may be removed from the solution and stored, prior to exposure to a second anionic species. In some cases, the catalytic material associated with the current collector may dehydrate during storage. The electrode may be stored for at least about 1 day, at least about 2 days, at least about 5 days, at least about 10 days, at least about 1 month, at least about 3 months, at least about 6 months or at least about 1 year, with no more than 10% loss in electrode performance per month of storage, or no more than 5%, or even 2%, loss in performance per month of storage. Electrodes as described herein may be stored under varying conditions. In some cases, the catalytic material associated with the current collector after storage may be substantially similar to the catalytic material immediately after formation. In other cases, the catalytic material associated with the current collector after storage may be substantially different than the catalytic material immediately after formation.

The current collector may comprise a single material or may comprise a plurality of materials, provided that at least one of the materials is substantially electrically conductive. In some cases, the current collector may comprise a single material, for example, ITO, platinum, FTO, nickel, carbon mesh, or the like. In other cases, the current collector may comprise at least two materials. In some instances, the current collector may comprise a core material and at least one material substantially covering the core material. In other instances, the current collector may comprise two materials, wherein the second material may be associated with a portion of the first material (e.g., may be located between the first material and the catalytic materials). The materials may be substantially non-conductive (e.g., insulating) and/or substantially conductive. As a non-limiting example, the current collector may comprise a substantially non-conductive core material and an outer layer of substantially conductive material (e.g., a core material may comprise vicor glass and the vicor glass may be substantially covered (e.g., coated with a layer) of a substantially conductive material (e.g., ITO, FTO, etc.)). Non-limiting examples of non-conductive core materials include inorganic substrates, (e.g., quartz, glass, etc.) and polymeric substrates (e.g., polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polystyrene, polypropylene, etc.). As another example, the current collector may comprise a substantially conductive core material and a

substantially conductive or substantially non-conductive material. In some cases, at least one of the materials is a membrane material, as will be known to those of ordinary skill in the art. For example, a membrane material may allow for the conductivity of protons, in some cases.

Non-limiting examples of substantially conductive materials, of which the current collector may comprise, include indium tin oxide (ITO), fluorine tin oxide (FTO), antimony-doped tin oxide (ATO), aluminum-doped zinc oxide (AZO), glassy carbon, carbon mesh, metals, metal alloys, lithium-containing compounds, metal oxides (e.g., platinum oxide, nickel oxide, zinc oxide, tin oxide, vanadium oxide, zinc-tin oxide, indium oxide, indium-zinc oxide), graphite, zeolites, and the like. Non-limiting examples of suitable metals, of which the current collector may comprise, (including metals comprised in metal alloys and metal oxides) include gold, copper, silver, platinum, ruthenium, rhodium, osmium, iridium, nickel, cadmium, tin, lithium, chromium, calcium, titanium, aluminum, cobalt, zinc, vanadium, nickel, palladium, or the like, and combinations thereof (e.g., alloys such as palladium silver).

The current collector may also comprise other metals and/or non-metals known to those of ordinary skill in the art as conductive (e.g., ceramics, conductive polymers). In some cases, the current collector may comprise an inorganic conductive material (e.g., copper iodide, copper sulfide, titanium nitride, etc.), an organic conductive material (e.g., conductive polymer such as polyaniline, polythiophene, polypyrrole, etc.), and laminates and/or combinations thereof. In some cases, the current collector may comprise a semiconductor material. In another embodiment, the current collector comprises Raney nickel on cold rolled steel.

In some instances, the current collector may comprise nickel (e.g., nickel foam or nickel mesh). Nickel foam and nickel mesh materials will be known to those of ordinary skill in the art and may be purchase from commercial sources. Nickel mesh usually refers to woven nickel fibers. Nickel foam generally refers to a material of non-trivial thickness (e.g., about 2 mm) comprising a plurality of holes and/or pores. In some cases, nickel foam may be an open-cell, metallic structure based on the structure of an open-cell polymer foam, wherein nickel metal is coated onto the polymer foam.

Other types of foam materials will be known to those to ordinary skill in the art and may be used an a current collector. Non-limiting examples of materials a foam current collector may comprise include titanium, cupper, niobium, zirconium, titanium, tantalum, and stainless steel

The current collector may be transparent, semi-transparent, semi-opaque, and/or opaque. The current collector may be solid, semi-porous, and/or porous. The current collector may be substantially crystalline or substantially non-crystalline, and/or homogenous or heterogeneous.

In some embodiments, the current collector and/or electrode does not consist essentially of platinum. That is, the current collector and/or the electrode, in this embodiment, has an electrochemical characteristic significantly different from that of pure platinum. This by no means limits the current collector and/or electrode formed from containing some amount of platinum. The current collector and/or electrode (i.e., current collector and catalytic material) can have characteristics that differ as compared to a current collector and/or electrode that consists essentially of platinum. In some embodiments, the current collector and/or electrode comprises less than about 5 weight percent, less than about 10 weight percent, less than about 20 weight percent, less than about 25 weight percent platinum, less than about 50 weight percent, less than about 60 weight percent, less than about 70 weight percent, less than about 75 weight percent, less than about 80 weight percent, less than about 85 weight percent, less than about 90 weight percent, less than about 95 weight percent, less than about 96 weight percent, less than about 97 weight percent, less than about 98 weight percent, less than about 99 weight percent, less than about 99.5 weight percent, or less than about 99.9 weight percent platinum. In some cases, the current collector and/or electrode does not consist of platinum, another precious metal (e.g., rhodium, iridium, ruthenium, etc.), precious metal oxide (e.g., rhodium oxide, iridium oxide, etc.) and/or combination thereof.

In some embodiments, the current collector (prior to addition of any catalytic material) may have a high surface area. In some cases, the surface area of the current collector may be greater than about 0.01 m²/g, greater than about 0.05 m²/g, greater than

2 2 2

about 0.1 m /g, greater than about 0.5 m /g, greater than about 1 m /g, greater than about 5 m²/g, greater than about 10 m²/g, greater than about 20 m²/g, greater than about 30 m²/g, greater than about 50 m²/g, greater than about 100 m²/g, greater than about 150

2 2 2

m /g, greater than about 200 m /g, greater than about 250 m /g, greater than about 300 m /g, or the like. In other cases, the surface area of the current collector may be between about 0.01 m²/g and about 300 m²/g, between about 0.1 m²/g and about 300 m²/g, between about 1 m²/g and about 300 m²/g, between about 10 m²/g and about 300 m²/g between about 0.1 m²/g and about 250 m²/g, between about 50 m²/g and about 250 m²/g, or the like. In some cases, the surface area of the current collector may be due to the current collector comprising a highly porous material. The surface area of a current collector may be measured using various techniques, for example, optical techniques (e.g., optical profiling, light scattering, etc.), electron beam techniques, mechanical techniques (e.g., atomic force microscopy, surface profiling, etc.), electrochemical techniques (e.g., cyclic voltammetry, etc.), etc., as will be known to those of ordinary skill in the art. The porosity of a current collector (or other component, for example, an electrode) may be measured as a percentage or fraction of the void spaces in the current collector. The percent porosity of a current collector may be measure using techniques known to those of ordinary skill in the art, for example, using volume/density methods, water saturation methods, water evaporation methods, mercury intrusion porosimetry methods, and nitrogen gas adsorption methods. In some embodiments, the current collector may be at least about 10% porous, at least about 20% porous, at least about 30% porous, at least about 40% porous, at least about 50% porous, at least about 60% porous, or greater. The pores may be open pores (e.g., have at least one part of the pore open to an outer surface of the electrode and/or another pore) and/or closed pores (e.g., the pore does not comprise an opening to an outer surface of the electrode or another pore). In some cases, the pores of a current collector may consist essentially of open pores (e.g., the pores of the current collector are greater than at least 70%, greater than at least 80%, greater than at least 90%, greater than at least 95%, or greater, of the pores are open pores). In some cases, only a portion of the current collector may be substantially porous. For example, in some cases, only a single surface of the current collector may be substantially porous. As another example, in some cases, the outer surface of the current collector may be substantially porous and the inner core of the current collector may be substantially non-porous. In a particular embodiment, the entire current collector is substantially porous.

The current collector may be made highly porous and/or comprise a high surface area using techniques known to those of ordinary skill in the art. For example, an ITO current collector may be made highly porous using etching techniques. As another example, the vicor glass may be made highly porous using etching technique followed by substantially all the surfaces of the vicor glass being substantially coated with a substantially conductive material (e.g., ITO, FTO, etc.). In some cases, the material that substantially coats a non-conductive core may comprise a film or a plurality of particles (e.g., such that they form a layer substantially covering the core material).

In some cases, the current collector may comprise a core material, wherein at least a portion of the core material is associated with at least one different material. The core material may be substantially or partially coated with at least one different material. As a non-limiting example, in some cases, an outer material may substantially cover a core material, and a catalytic material may be associated with the outer material. The outer material may allow for electrons to flow between the core material and the catalytic material, the electrons being used by the catalytic material, for example, for the production of oxygen gas from water. Without wishing to be bound by theory, the outer material may act as a membrane and allow electrons generated at the core material to be transmitted to the catalytic material. The membrane may also function by reducing and/or preventing oxygen gas formed at the catalytic material from being transversed through the material. This arrangement may be advantageous in devices where the separation of oxygen gas and hydrogen gas formed from the oxidation of water is important. In some cases, the membrane may be selected such that the production of oxygen gas in/at the membrane is limited.

The current collector may be of any size or shape. Non-limiting examples of shapes include sheets, cubes, cylinders, hollow tubes, spheres, and the like. The current collector may be of any size, provided that at least a portion of the current collector may be immersed in the solution comprising the metal ionic species and the anionic species. The methods described herein are particularly amenable to forming the catalytic material on any shape and/or size of current collector. In some cases, the maximum dimension of the current collector in one dimension may be at least about 1 mm, at least about 1 cm, at least about 5 cm, at least abut 10 cm, at least about 1 m, at least about 2 m, or greater. In some cases, the minimum dimension of the current collector in one dimension may be less than about 50 cm, less than about 10 cm, less than about 5 cm, less than about 1 cm, less than about 10 mm, less than about 1 mm, less than about 1 um, less than about 100 nm, less than about 10 nm, less than about 1 nm, or less. Additionally, the current collector may comprise a means to connect the current collector to power source and/or other electrical devices. In some cases, the current collector may be at least about 10%, at least about 30%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, at least about 100% immersed in the solution.

The current collector may or may not be substantially planar. For example, the current collector may comprise ripples, waves, dendrimers, spheres (e.g., nanospheres), rods (e.g., nanorods), a powder, a precipitate, a plurality of particles, and the like. In some embodiments, the surface of the current collector may be undulating, wherein the distance between the undulations and/or the height of the undulations are on a scale of nanometers, micrometers, millimeters, centimeters, or the like. In some instances, the planarity of the current collector may be determined by determining the roughness of the current collector. As used herein, the term "roughness" refers to a measure of the texture of a surface (e.g., current collector), as will be known to those of ordinary skill in the art. The roughness of the current collector may be quantified, for example, by determining the vertical deviations of the surface of the current collector from planar. Roughness may be measured using contact (e.g., dragging a measurement stylus across the surface such as a profilometers) or non-contact methods (e.g., interferometry, confocal microscopy, electrical capacitance, electron microscopy, etc.). In some cases, the surface roughness, R_a, may be determined, wherein R_a is the arithmetic average deviations of the surface valleys and peaks, expressed in micrometers. The R_a of a non-planar surface may be greater than about 0.1 um, greater than about 1 um, greater than about 5 um, greater than about 10 um, greater than about 50 um, greater than about 100 um, greater than about 500 um, greater than about 1000 um, or the like.

The solution (e.g., used for the forming an electrode) may be formed from any suitable material. In most cases, the solution may be a liquid and may comprise water. In some embodiments the solution consists of or consists essentially of water, i.e. be essentially pure water or an aqueous solution that behaves essentially identically to pure water, in each case, with the minimum electrical conductivity necessary for an electrochemical device to function. In some embodiments, the solution is selected such that the metal ionic species and the anionic species are substantially soluble. In some cases, when the electrode is to be used in a device immediately after formation, the solution may be selected such that it comprises water (or other fuel) to be oxidized by a device and/or method as described herein and/or such that the second anionic species is substantially soluble. For example, in instances where oxygen gas is to be catalytically produced from water, the solution may comprise water (e.g., provided from a water source).

The metal ionic species and the first anionic species may be provided to the solution by substantially dissolving compounds comprising the metal ionic species and the anionic species. In some instances, this may comprise substantially dissolving a metal compound comprising the metal ionic species and anionic compound comprising the first anionic species. In other instance, a single compound may be dissolved that comprises both the metal ionic species and the first anionic species. The metal compound and/or the anionic compound may be of any composition, such as a solid, a liquid, a gas, a gel, a crystalline material, and the like. The dissolution of the metal compound and anionic compound may be facilitated by agitation of the solution (e.g., stirring) and/or heating of the solution. In some cases, the solution may be sonicated. The metal species and/or first anionic species may be provided in an amount such that the concentration of the metal ionic species and/or anionic species is at least about 0.1 mM, at least about 0.5 mM, at least about 1 mM, at least about 10 mM, at least about 0.1 M, at least about 0.5 M, at least about 1 M, at least about 2 M, at least about 5M, and the like. In some cases, the concentration of the first anionic species may be greater than the concentration of the metal ionic species, so as to facilitate the formation of the catalytic material, as described herein. As non-limiting examples, the concentration of the first anionic species may be about 2 times greater, about 5 times greater, about 10 times greater, about 25 times greater, about 50 times greater, about 100 times greater, about 500 times greater, about 1000 times greater, and the like, of the concentration of the metal ionic species. In some instances, the concentration of the metal ionic species is greater than the concentration of the first anionic species.

In some cases, the pH of the solution may be about neutral. That is, the pH of the solution may be between about 6.0 and about 8.0, between about 6.5 and about 7.5, and/or the pH is about 7.0. In other cases, the pH of the solution is about neutral or acidic. In these cases, the pH may be between about 0 and about 8, between about 1 and about 8, between about 2 and about 8, between about 3 and about 8, between about 4 and about 8, between about 5 and about 8, between about 0 and about 7.5, between about 1 and about 7.5, between about 2 and about 7.5, between about 3 and about 7.5, between about 4 and about 7.5, or between about 5 and about 7.5. In yet other cases, the pH may be between about 6 and about 10, between about 6 and about 1 1 , between about 7 and about 14, between about 2 and about 12, and the like. In some embodiments, the pH of the solution may be about neutral and/or basic, for example, between about 7 and about 14, between about 8 and about 14, between about 8 and about 13, between about 10 and about 14, greater than 14, or the like. The pH of the solution may be selected such that the first anionic species and the metal ionic species are in the desired state. For example, some first anionic species may be affected by a change in pH level, for example, phosphate. If the solution is basic (greater than about pH 12), the majority of the phosphate is in the form P0₄ ^" . If the solution is approximately neutral, the phosphate is in approximately equal amounts of the form HP0₄ ^"2 and the form H₂P0₄ ^"'. If the solution is slightly acidic (less than about pH 6), the phosphate is mostly in the form H₂P0₄ ^". The pH level may also affect the solubility constant for the anionic species and the metal ionic species.

In one embodiment, an electrode as described herein may comprise a current collector and a composition comprising metal ionic species and anionic species in electrical communication with the current collector. The composition, in some cases, may be formed by self-assembly of the metal ionic species and anionic species on the current collector and may be sufficient non-crystalline such that the composition allows for the conduction of protons. In some embodiments, an electrode may allow for a conductivity of protons of at least 10^"1 S cm^"1, at least about 20^"' S cm^"1, at least about 30 ¹ S cm^"1, at least about 40^"1 S cm^"1, at least about 50^"' S^"1 cm^"1, at least about 60^"1 S cm^'1, at least about 80^"' S cm^"1, at least about 100^"1 S cm^"1, and the like.

In some embodiments, an electrode as described herein may be capable of producing oxygen gas from water at a low overpotential. Voltage in addition to a thermodynamically determined reduction or oxidation potential that is required to attain a given catalytic activity is herein referred to as "overpotential," and may limit the efficiency of the electrolytic device. Overpotential is therefore given its ordinary meaning in the art, that is, it is the potential that must be applied to a system, or a component of a system such as an electrode to bring about an electrochemical reaction (e.g., formation of oxygen gas from water) minus the thermodynamic potential required for the reaction. Those of ordinary skill in the art understand that the total potential that must be applied to a particular system in order to drive a reaction can typically be the total of the potentials that must be applied to the various components of the system. For example, the potential for an entire system can typically be higher than the potential as measured at, e.g., an electrode at which oxygen gas is produced from the electrolysis of water. Those of ordinary skill in the art will recognize that where overpotential for oxygen production from water electrolysis is discussed herein, this applies to the voltage required for the conversion of water to oxygen itself, and does not include voltage drop at the counter electrode.

The thermodynamic potential for the production of oxygen gas from water varies depending on the conditions of the reaction (e.g., pH, temperature, pressure, etc.). Those of ordinary skill in the art will be able to determine the required thermodynamic potential for the production of oxygen gas from water depending on the experimental conditions. For example, the pH dependence of water oxidation may be determined from a simplified form of the Nernst equation to give Equation 7:

E_pH = E° - 0.059F x (pH) (7) where E_pH is the potential at a given pH, E° is the potential under standard conditions

(e.g., 1 atm, about 25 °C) and pH is the pH of the solution. For example, at pH 0, E =

1.229 V, at pH 7, E = 0.816 V, and at pH 14, E = 0.403 V.

The thermodynamic potential for the production of oxygen gas from water at a specific temperature (Εχ) may be determined using Equation 8:

E_j = [1 .5184 - (1 .5421 x 1 (Γ³ )(Γ)] + [(9.523 x 1 (Γ⁵ )(Γχΐη(Γ))] + [(9.84 x 1 CT⁸ )T ² ] (8) where T is given in Kelvin. For example, at 25 °C, E_T = 1.229 V, and at 80 °C, E_T = 1.18

V .

The thermodynamic potential for the production of oxygen gas from water at a given pressure (E_p) may be determined using Equation 9: Ε_ρ = Ε_τ + & ^]η{[{Ρ - Ρ ^Λ ] Η -)} (9)

2F P wo

where T is in Kelvin, F is Faraday's constant, R is the universal gas constant, P is the operating pressure of the electrolyzer, P_w is the partial pressure of water vapor over the chosen electrolyte, and P_w0 is the partial pressure of water vapor over pure water. By this equation, at a 25 °C, the Ep increases by 43 mV for a tenfold increase in pressure.

In some instances, an electrode as described herein may be capable of

catalytically producing oxygen gas from water (e.g., gaseous and/or liquid water) with an overpotential of less than about 1 volt, less than about 0.75 volts, less than about 0.5 volts, less than about 0.4 volts, less than about 0.35 volts, less than about 0.325 volts, less than about 0.3 volts, less than about 0.25 volts, less than about 0.2 volts, less than about 0.1 volts, or the like, wherein the electrode is exposed to a second anionic species. In some embodiments, the overpotential is between about 0.1 volts and about 0.4 volts, between about 0.2 volts and about 0.4 volts, between about 0.25 volts and about 0.4 volts, between about 0.3 volts and about 0.4 volts, between about 0.25 volts and about 0.35 volts, or the like. In another embodiment, the overpotential is about 0.325 volts. In some cases, the overpotential of an electrode is determined under standardized conditions of an electrolyte with a neutral pH (e.g., about pH 7.0), ambient temperature (e.g., about 25 °C), ambient pressure (e.g., about 1 atm), a current collector that is non-porous and planar (e.g., an ITO plate), and at a geometric current density (as described herein) of about 1 mA/cm . As described above, selection of an appropriate second anionic species may cause the current density to increase over time of the operation of the electrode. It is to be understood that systems of the invention can be used under conditions other than those described immediately above and in fact those of ordinary skill in the art will recognize that a very wide variety of conditions can exist in use of the invention. But the conditions noted above are provided only for the purpose of specifying how features such as overpotential, amount of oxygen and/or hydrogen produced, and other performance characteristics defined herein are measured for purposes of clarity of the present invention.

In some embodiments, an electrode (e.g., during exposure to a second anionic species) may be capable of catalytically producing oxygen gas from water (e.g., gaseous and/or liquid water) with a Faradaic efficiency of about 100%, greater than about 99.8%, greater than about 99.5%, greater than about 99%, greater than about 98%, greater than about 97%, greater than about 96%, greater than about 95%, greater than about 90%, greater than about 85%, greater than about 80%, greater than about 70%, greater than about 60%, greater than about 50%, etc. The term, "Faradaic efficiency," as used herein, is given its ordinary meaning in the art and refers to the efficacy with which charge (e.g., electrons) are transferred in a system facilitating an electrochemical reaction. Those of ordinary skill in the art will be aware of methods and systems for determining Faradaic efficiency.

As will be known to those of ordinary skill in the art, an example of a side reaction that may occur during the catalytic formation of oxygen gas from water is the production of hydrogen peroxide. In some cases, an electrode, in use, may produce oxygen that is in the form of hydrogen peroxide of less than about 0.01%, less than about 0.05%), less than about 0.1%, less than about 0.2%, less than about 0.3%, less than about 0.4%, less than about 0.5%, less than about 0.6%, less than about 0.7%, less than about 0.8%, less than about 0.9%, less than about 1%, less than about 1.5%, less than about 2%, less than about 3%, less than about 4%, less than about 5%, less than about 10%, etc. That is, less than this percentage of the molecules of oxygen produced is in the form of hydrogen peroxide.

In some cases, the performance of an electrode may also be expressed, in some embodiments, as a turnover frequency. The turnover frequency refers to the number of oxygen molecules produced per second per catalytic site. In some cases, a catalytic site may be a metal ionic species (e.g., a cobalt ion). The turnover frequency of an electrode (e.g., comprising a current collector and a catalytic material) may be less than about 0.01 , less than about 0.005, less than about 0.001 , less than about 0.0007, less than about 0.0005, less than about 0.00001 , less than about 0.000005, or less, moles of oxygen gas per second per catalytic site. In some cases, the turnover frequency may be determined under standardized conditions (e.g., ambient temperature and pressure, 1 mA/cm², planar current collector, etc.). Those of ordinary skill in the art will be aware of methods to determine the turnover frequency.

In some embodiments, systems and/or devices may be provided that comprise an electrode described above and/or an electrode prepared using the above described methods, and further comprising a second anionic species. In particular, a device may be an electrochemical device (e.g., an energy conversion device). Non-limiting examples of electrochemical devices includes electrolytic devices, fuel cells, and regenerative fuel cells, as described herein. In some embodiments, the device is an electrolytic device. An electrolytic device may function as an oxygen gas and/or hydrogen gas generator by electrolytically decomposing water (e.g., liquid and/or gaseous water) to produce oxygen and/or hydrogen gases. An energy conversion device, in some embodiments, may be used to provide at least a portion of the energy required to operate an automobile, a house, a village, a cooling device (e.g., a refrigerator), etc. In some embodiments, a device may be used to produce 0₂ and/or H₂. The 0₂ and/or H₂ may be converted back into electricity and water, for example, using a device such as a fuel cell. In some cases, however, the 0₂ and/or H₂ may be used for other purposes (e.g., medical, industrial, and/or scientific purposes). In some embodiments, an electrolytic device for electrochemically producing oxygen and hydrogen gas from water and systems and methods associated with the same, may be provided. In one configuration, the device comprises a chamber, a first electrode, a second electrode, wherein the first electrode (e.g., comprising a catalytic material comprising a first anionic species and a metal anionic species) is biased positively with respect to the second electrode, an electrolyte, wherein each electrode is in fluid contact with the electrolyte, and a power source in electrical communication with the first and the second electrode. In some embodiments, the electrolytic device further comprises a source of a second anionic species. For example, the electrolyte may comprise the second anionic species. A first electrode may be considered biased negatively or positively towards a second electrode means that the first voltage potential of the first electrode is negative or positive, respectfully, with respect to the second voltage potential of the second electrode. The second electrode may be biased negatively or positively with respect to the second electrode by less than about less than about 1.23 V (e.g., the minimum defined by the thermodynamics of transforming water into oxygen and hydrogen gas), less than about 1.3 V, less than about 1.4 V, less than about 1.5 V, less than about 1.6 V, less than about 1.7 V, less than about 1.8 V, less than about 2 V, less than about 2.5 V, and the like. In some cases, the bias may be between about 1.5 V and about 2.0 V, between about 1.6 V and about 1.9 V, or is about 1.6 V.

Protons may be provided to the devices described herein using any suitable proton source, as will be known to those of ordinary skill in the art. The proton source may be any molecule or chemical which is capable of supplying a proton, for example, H⁺, H₃0⁺, NH₄ ⁺, etc. A hydrogen source (e.g., for use as a fuel in a fuel cell) may be any substance, compound, or solution including hydrogen such as, for example, hydrogen gas, a hydrogen rich gas, natural gas, etc. The oxygen gas provided to a device may or may not be substantially pure. For example, in some cases, any substance, compound or solution including oxygen may be provided, such as, an oxygen rich gas, air, etc.

An example of an electrolytic device is depicted in FIG. 5. Power source 120 is electrically connected to first electrode 122 and second electrode 124, wherein the first and/or second electrodes are electrodes as described herein. First electrode 122 and second electrode 124 are in contact with an electrolyte 162. In this example, electrolyte 126 comprises water, and optionally second anionic species (not shown). However, in some cases, a physical barrier (e.g., porous diaphragm comprised of asbestos, microporous separator of polytetrafluoroethylene (PTFE)), and the like may separate the electrolyte solution in contact with the first electrode from the electrolyte solution in contact with the second electrode, while still allowing ions to flow from one side to another. In other embodiments, the electrolyte might not be a solution and may be a solid polymer that conducts ions. In such cases, water may be provided to the device using any suitable water source.

In this non-limiting embodiment, the electrolytic device may be operated as follows. The power source may be turned on and electron-holes pairs may be generated. Holes 128 are injected into first electrode 122 and electrons 130 are injected into second electrode 124. At the first electrode, water is oxidized to form oxygen gas, four protons, and four electrons, as shown in the half reaction 132. At the second electrode, the electrons are combined with protons (e.g., from a proton source) to produce hydrogen, as shown in the half reaction 134. There is a net flow of electrons from the first electrode to the second electrode. The oxygen and hydrogen gases produced may be stored and/or used in other devices, including fuel cells, or used in commercial or other applications.

In some embodiments, an electrolytic device may comprise a first

electrochemical cell in electrical communication with a second electrochemical cell. The first electrochemical cell may comprise an electrode as described herein and may produce oxygen gas from water. The electrons formed at the electrode during the formation of oxygen gas may be transferred (e.g., through circuitry) to the second electrochemical cell. The electrons may be used in the second electrochemical cell in a second reaction (e.g., for the production of hydrogen gas from hydrogen ions). In some embodiments, materials may be provided which allow for the transport of hydrogen ions produced in the first electrochemical cell to the second electrochemical cell. Those of ordinary skill in the art will be aware of configurations and materials suitable for such a device.

In some case, a device may comprise an electrode comprising a catalytic material associated with a current collector comprising a first material and a second material. For example, as shown in FIG. 6, a device may comprise housing 298, first outlet 320 and second outlet 322 for the collection of 0₂ and H₂ gases produced during water oxidation, first electrode 302 and second electrode 307 (comprising first material 306, second material 316, and catalytic material 308). In some cases, material 304 may be present between first electrode 302 and second electrode 306 (e.g., a non-doped semiconductor). The device comprises an electrolyte (e.g., 300, 318), optionally comprising a second anionic species. Second material 316 may be a porous electrically conductive material (e.g., valve metal, metallic compound) wherein the electrolyte (e.g., 318) fills the pores of the material. Without wishing to be bound by theory, material 316 may act as a membrane and allow for the transmission of electrons generated at first material 306 to outer surface 324 of second material 316. Second material 316 may also be selected such that no oxygen gas is produced in the pores of second material 316, for example, if the overpotential for production of oxygen gas is high. Oxygen gas may form on or near surface 324 of second material 316 (e.g., or via the catalytic material associated with outer surface 324 of second material 316). Non-limiting examples of materials which may be suitable for use as second material 316 includes titanium zirconium, vanadium, hafnium, niobium, tantalum, tungsten, or alloys thereof. In some cases, the material may be a valve metal nitride, carbide, borides, etc., for example, titanium nitride, titanium carbide, or titanium boride. In some cases, the material may be titanium oxide, or doped titanium oxide (e.g., with niobium tantalum, tungsten, fluorine, etc.).

Electrolytic devices may operate at a low overpotential when catalytically forming oxygen gas from water (e.g., gaseous and/or liquid water). In some cases, an electrolytic device may catalytically produce oxygen gas from water at an overpotential as described herein. The overpotential may be determined under standardized conditions (e.g., neutral pH (e.g., about pH 7.0), ambient temperature (e.g., about 25 °C), ambient pressure (e.g., about 1 atm), a current collector that is non-porous and planar (e.g., an ITO plate), and at a geometric current density of about 1 mA/cm²). In some

embodiments, however, the pH of the solution under standard operating conditions may be selected to be the pH of a buffer solution (e.g., due to the presence of a first type and/or a second anionic species, which may be buffers). For example, if the solution comprises borate ions, the pH of the solution may be about 9.2.

In some cases, a fuel cell (or fuel-to-energy conversion device) and systems and methods associated with the same may be provided. A typical, conventional fuel cell comprises two electrodes, a first electrode and a second electrode, an electrolyte in contact with both the first and the second electrodes, and an electrical circuit connecting the first and the second electrodes from which power created by the device is drawn.

The construction and operation of a fuel cell will be known to those of ordinary skill in the art. Non-limiting examples of fuel cell devices which may comprise an electrode and/or catalytic material and include proton exchange membrane (PEM) fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, alkaline fuel cells, direct methanol fuel cells, zinc air fuel cells, protonic ceramic fuel cells, and microbial fuel cells. In some embodiments, a device may be a regenerative fuel cell, using catalytic materials, electrodes, or devices as described herein. A regenerative fuel cell is a device that comprises a fuel cell and an electrolytic device.

The performance of an electrode of a device may be measured by current density (e.g., geometric and/or total current density), wherein the current density is a measure of the density of flow of a conserved charge. For example, the current density is the electric current per unit area of cross section. In some cases, the current density (e.g., geometric current density and/or total current density, as described herein) of an electrode as described herein is greater than about 0.1 mA/cm , greater than about 1 mA/cm , greater

2 2 2 than about 5 mA/cm , greater than about 10 mA/cm , greater than about 20 mA/cm , greater than about 25 mA/cm , greater than about 30 mA/cm , greater than about 50 mA/cm , greater than about 100 mA/cm , greater than about 200 mA/cm , and the like.

In some embodiments, the current density can be described as the geometric current density. The geometric current density, as used herein, is current divided by the geometric surface area of the electrode. The geometric surface area of an electrode will be understood by those of ordinary skill in the art and refers to the surface defining the outer boundaries of the electrode (or current collector), for example, the area that may be measured by a macroscopic measuring tool (e.g., a ruler) and does not include the internal surface area (e.g., area within pores of a porous material such as a foam, or surface area of those fibers of a mesh that are contained within the mesh and do not define the outer boundary, etc.).

In some cases, the current density can be described as the total current density, which is also known as specific current density (e.g., the current density per active surface). Total current density, as used herein, is the current density divided by essentially the total surface area (e.g., the total surface area including all pores, fibers, etc.) of the electrode. In some cases, the total current density may be approximately equal to the geometric current density (e.g., in cases where the electrode is not porous and the total surface area is approximately equal to the geometric surface area).

In some embodiments, a device and/or electrode as described herein is capable of producing at least about 1 umol (micromole), at least about 5 umol, at least about 10 umol, at least about 20 umol, at least about 50 umol, at least about 100 umol, at least about 200 umol, at least about 500 umol, at least about 1000 umol oxygen and/or hydrogen, or more, per cm at the electrode at which oxygen production or hydrogen production occurs, respectively, per hour. The area of the electrode may be the geometric surface area or the total surface area, as described herein.

In some cases, an electrolytic device may be constructed and arranged to be electrically connectable to and able to be driven by the photovoltaic cell (e.g., the photovoltaic cell may be the power source for the device for the electrolysis of water).

The devices and methods as described herein, in some cases, may proceed at about ambient conditions. Ambient conditions define the temperature and pressure relating to the device and/or method. For example, ambient conditions may be defined by a temperature of about 25 °C and a pressure of about 1.0 atmosphere (e.g., 1 atm, 14 psi). In some cases, the conditions may be essentially ambient. Non-limiting examples of essentially ambient temperature ranges include between about 0 °C and about 40 °C, between about 5 °C and about 35 °C, between about 10 °C and about 30 °C, between about 15 °C and about 25 °C, at about 20 °C, at about 25 °C, and the like. Non-limiting examples of essentially ambient pressure ranges include between about 0.5 atm and about 1.5 atm, between about 0.7 atm and about 1.3 atm, between about 0.8 and about 1.2 atm, between about 0.9 atm and about 1.1 atm, and the like. In a particular case, the pressure may be about 1.0 atm. Ambient or essentially ambient conditions can be used in conjunction with any of the devices, compositions, catalytic materials, and/or methods described herein, in conjunction with any conditions (for example, conditions of pH, etc.).

In some cases, the devices and/or methods as described herein may proceed at temperatures above, below, or at ambient temperature. For example, a device and/or method may be operated at temperatures greater than about 30 °C, greater than about 40 °C, greater than about 50 °C, greater than about 60 °C, greater than about 70 °C, greater than about 80 °C, greater than about 90 °C, greater than about 100 °C, greater than about 120 °C, greater than about 150 °C, greater than about 200 °C, or greater, orless than about 20 °C, less than about 10 °C, less than about 0 °C, less than about -10 °C, less than about -20 °C, less than about -30 °C, less than about -40 °C, less than about -50 °C, less than about -60 °C, less than about -70 °C, or the like.

In some embodiments, the water provided and/or formed during use of a method and/or device as described herein may be in a gaseous state. Those of ordinary skill in the art can apply known electrochemical techniques carried out with steam, in some cases, without undue experimentation. As an exemplary embodiment, water may be provided in a gaseous state to an electrolytic device (e.g., high-temperature electrolysis or steam electrolysis) comprising an electrode in some cases. In some cases, the gaseous water to be provided to a device may be produced by a device or system which inherently produces steam (e.g., a nuclear power plant). The electrolytic device, in some cases, may comprise a first and a second porous electrodes (e.g., electrode as described herein, nickel-cermet steam/hydrogen electrode, mixed oxide electrode (e.g., comprising lanthanum, strontium, etc.), cobalt oxygen electrodes, etc.) and an electrolyte. The electrolyte may be non-permeable to selected gases (e.g., oxygen, oxides, molecular gases (e.g., hydrogen, nitrogen, etc.)). Non-limiting examples of electrolytes include yttria-stabilized zirconia, barium-stabilized zirconia, etc. A non-limiting example of one electrolytic device that may use water in a gaseous state is shown in FIG. 7. An electrolytic device is provided which comprises first electrode 200, second electrode 202, non-permeable electrolyte 204, power source 208, and circuit 206 connecting first electrode and second electrode, wherein second electrode 202 is biased positively with respect to first electrode 200. Gaseous water 210 is provided to first electrode 200.

Oxygen gas 212 is produced at the first electrode 200, and may sometimes comprise gaseous water 214. Hydrogen gas 216 is produced at second electrode 202. In some embodiments, steam electrolysis may be conducted at temperatures between about 100 °C and about 1000 °C, between about 100 °C and about 500 °C, between about 100 °C and about 300 °C, between about 100 °C and about 200 °C, or the like. Without wishing to be bound by theory, in some cases, providing water in a gaseous state may allow for the electrolysis to proceed more efficiently as compared to a similar device when provided water in a liquid state. This may be due to the higher input energy of the water vapor. In some instances, the gaseous water provided may comprise other gases (e.g., hydrogen gas, nitrogen gas, etc.).

Individual aspects of the overall electrochemistry and/or chemistry involved in electrochemical devices such as those described herein are generally known, and not all will be described in detail herein. It is to be understood that the specific electrochemical devices described herein are exemplary only, and the components, connections, and techniques as described herein can be applied to virtually any suitable electrochemical device including those with a variety of solid, liquid, and/or gaseous fuels, and a variety of electrodes, and electrolytes, which may be liquid or solid under operating conditions (where feasible; generally, for adjacent components one will be solid and one will be liquid if any are liquids). It is also to be understood that the electrochemical device unit arrangements discussed are merely examples of electrochemical devices that can make use of electrodes as recited herein. Many structural arrangements other than those disclosed herein, which make use of and are enabled as described herein, will be apparent to those of ordinary skill in the art.

An electrochemical device accordingly may be combined with additional electrochemical devices to form a larger device or system. In some embodiments, this may take the form of a stack of units or devices (e.g., fuel cell and/or electrolytic device). Where more than one electrochemical device is combined, the devices may all be devices as described herein, or one or more devices as described herein may be combined with other electrochemical devices, such as conventional solid oxide fuel cells. It is to be understood that where this terminology is used, any suitable electrochemical device, which those of ordinary skill in the art would recognize could function in accordance with the systems and techniques of the present invention, can be substituted.

Water may be provided to the systems, devices, electrodes, and/or for the methods described herein using any suitable source. In some cases, the water provided is from a substantially pure water source (e.g., distilled water, deionized water, chemical grade water, etc.). In some cases, the water may be bottled water. In some cases, the water provided is from a by a natural and/or impure water source (e.g., tap water, lake water, ocean water, rain water, lake water, pond water, sea water, potable water, brackish water, industrial process water, etc.). In some cases, although it need not be, the water is not purified prior to use (e.g., before being provided to the system/electrode for electrolysis). In some instances, the water may be filtered to remove particulates and/or other impurities prior to use. In some embodiments, the water that is electrolyzed to produce oxygen gas (e.g., using an electrode and/or device as described here) may be substantially pure. The purity of the water may be determined using one or more methods known to those of ordinary skill in the art, for example, resistivity, carbon content (e.g., through use of a total organic carbon analyzer) , UV absorbance, oxygen- absorbance test, limulus ameobocyte lysate test, etc. In some embodiments, the at least one impurity may be substantially non-participative in the catalytic reaction. That is, the at least one impurity does not participate in aspects of the catalytic cycle and/or regeneration mechanism.

In some embodiments, the water may contain at least one impurity. The at least one impurity may be solid (e.g., particulate matter), a liquid, and/or a gas. In some cases, the impurity may be solubilized and/or dissolved. For example, an impurity may comprise ionic species. In some cases, an impurity may be an impurity which may generally be present in a water source (e.g., tap water, non-potable water, potable water, sea water, etc.). In a particular embodiment, the water source may be sea water and one of the impurities may be chloride ions, as discussed more herein. In some cases, an impurity may comprise a metal such as a metal element (including heavy metals), a metal ion, a compound comprising at least one metal, an ionic species comprising a metal, etc. For example, an impurity comprising metal may comprise an alkaline earth metal, an alkali metal, a transition metal, or the like. Specific non-limiting examples of metals include lithium, sodium, magnesium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, potassium, mercury, lead, barium, etc. In some instances, an impurity comprising a metal may be the same or different than the metal comprised in the metal ionic species of an electrode and/or catalytic material as described herein. In some cases, the impurity may comprise organic materials, for example, small organic molecules (e.g., bisphenol A, trimethylbenzene, dioxane, nitrophenol, etc.), microorganisms (such as bacteria (e.g., e. coli, coliform, etc.), microbes, fungi, algae, etc.), other biological materials, pharmaceutical compounds (e.g., drugs, decomposition products from drugs), herbicides, pyrogens, pesticides, proteins, radioactive compounds, inorganic compounds (e.g., compounds comprising boron, silicon, sulfur, nitrogen, cyanide, phosphorus, arsenic, sodium, etc.; carbon dioxide, silicates (e.g., H₄Si0₄), ferrous and ferric iron compounds,*chlorides, aluminum, phosphates, nitrates, etc.), dissolved gases, suspended particles (e.g., colloids), or the like. In some cases, an impurity may be a gas, for example, carbon monoxide, ammonia, carbon dioxide, oxygen gas, and/or hydrogen gas. In some cases, the gas impurity may be dissolved in the water. In some cases, an electrode may be capable of operating at approximately the same, at greater than about 95%, at greater than about 90%, at greater than about 80%, at greater than about 70%, at greater than about 60%, at greater than about 50%, or the like, of the activity level using water containing at least one impurity versus the activity using water that does not substantially contain the impurity under essentially identical conditions. In some cases, an electrode may catalytically produce oxygen from water containing at least one impurity such that less than about 5 mol %, less than about 3 mol %, less than about 2 mol %, less than about 1 mol %, less than about 0.5 mol %, less than about 0.1 mol %, less than about 0.01 mol % of the products produced comprise any portion of the at least one impurity.

In some cases, an impurity may be present in the water in an amount greater than about 1 ppt, greater than about 10 ppt, greater than about 100 ppt, greater than about 1 ppb, greater than about 10 ppb, greater than about 100 ppb, greater than about 1 ppm, greater than about 10 ppm, greater than about 100 ppm, greater than about 1000 ppm, or greater. In other cases, an impurity may be present in the water in an amount less than about 1000 ppm, less than about 100 ppm, less than about 10 ppm, less than about 1 ppm, less than about 100 ppb, less than about 10 ppb, less than about 1 ppb, less than about 100 ppt, less than about 10 ppt, less than about 1 ppt, or the like. In some cases, the water may contain at least one impurity, at least two impurities, at least three impurities, at least five impurities, at least ten impurities, at least fifteen impurities, at least twenty impurities, or greater. In some cases, the amount of impurity may increase or decrease during operation of the electrode and/or device. That is, an impurity may be formed during use of the electrode and/or device. For example, in some cases, the impurity may be a gas (e.g., oxygen gas and/or hydrogen gas) formed during the electrolysis of water. Thus, in some cases, the water may contain less than about 1000 ppm, less than about 100 ppm, less than about 10 ppm, less than about 1 ppm, less than about 100 ppb, less than about 10 ppb, less than about 1 ppb, less than about 100 ppt, less than about 10 ppt, less than about 1 ppt, or the like, prior to operation of the electrode and/or device. In some cases, the at least one impurity (and/or additive) may be preasent in an amount of about or at least about 0.001 uM, about 0.005 uM, about 0.01 uM, about 0.05 uM, about 0.1 uM, about 0.5 uM, about 0.001 mM, about 0.005 mM, about 0.01 mM, about 0.05 mM, about 0.1 mM, about 0.5 mM, about 1 mM, about 5 mM, about 0.01 M, about 0.05 M, or more.

In some embodiments, the at least one impurity may be an ionic species. In some cases, when the water contains at least one ionic species, the water purity may be determined, at least in part, by measuring the resistivity of the water. The theoretical resistivity of water at 25 °C is about 18.2 MH'cm. The resistivity of water that is not substantially pure may be less than about 18 MH'cm, less than about 17 MQ»cm, less than about 16 MQ'cm, less than about 15 MQ'cm, less than about 12 MQ^»cm, less than about 10 MQ'cm, less than about 5 MQ^»cm, less than about 3 MQ»cm, less than about 2 MQ'cm, less than about 1 MQ'cm, less than about 0.5 MQ^»cm, less than about 0.1 MH'cm, less than about 0.01 MH'cm, less than about 1000 Q^»cm, less than about 500 Ω·αη, less than about 100 Q^»cm, less than about 10 Q^»cm, or less. In some cases, the resistivity of the water may be between about 10 MQ^»cm and about 1 Ω·αη, between about 1 MQ'cm and about 10 Q*cm, between about 0.1 MQ^»cm and about 100 Q»cm, between about 0.01 ΜΩ· cm and about 1000 0*cm, between about 10,000 2*cm and about 1 ,000 Q^»cm, between about 10,000 Q^»cm and about 100 Ω·αη, between about 1,000 and about 1 Q^»cm, between about 1 ,000 and about 10 Q*cm, and the like. In some cases, when the water source is tap water, the resistivity of the water may be between about 10,000 Ω·αη and about 1,000 Ω·αη. In some cases, when the water source is sea water, the resistivity of the water may be between about 1 ,000 Q»cm and about 10 Ω·αη. In some instances, where the water may be taken from an impure source and purified prior to use, the water may be purified in a manner which does not resistivity of the water by a factor of more than about 5%, about 10%, about 20%, about 25%, about 30%, about 50% , or the like. Those of ordinary skill in the art will be aware of methods to determine the resistivity of water. For example, the electrical resistance between parallel electrodes immersed in the water may be measured.

In some cases, where the water is obtained from an impure water source and/or has a resistivity of less than about 16 MQ^»cm the water may be purified (e.g., filtered) in a manner that changes its resistivity by a factor of less than about 50%, less than about 30%, less than about 25%, less than about 20%, less than about 15%, less than about 10%, less than about 5%, or less, after being drawn from the source prior to use in the electrolysis.

In some embodiments, the water may contain halide ions (e.g., fluoride, chloride, bromide, iodide), for example, such that an electrode may be used for the desalination of sea water. In some cases, the halide ions might not be oxidized (e.g., to form halogen gas such as Cl₂) during the catalytic production of oxygen from water. In some cases, an electrode may catalytically produce oxygen from water comprising halide ions such that less than about 5 mol %, less than about 3 mol %, less than about 2 mol %, less than about 1 mol %, less than about 0.5 mol %, less than about 0.1 mol %, less than about 0.01 mol % of the gases evolved comprise oxidized halide species.

Various components of a device, such as the electrode, power source, electrolyte, separator, container, circuitry, insulating material, gate electrode, etc. can be fabricated by those of ordinary skill in the art from any of a variety of components, as well as those described in any of those patent applications described herein. Components may be molded, machined, extruded, pressed, isopressed, infiltrated, coated, in green or fired states, or formed by any other suitable technique. Those of ordinary skill in the art are readily aware of techniques for forming components of devices herein.

In some cases, a device may be portable. That is, the device may be of such size that it is small enough that it is movable. In some embodiments, a device of the present invention is portable and can be employed at or near a desired location (e.g., water supply location, field location, etc.). For example, the device may be transported and/or stored at a specific location. In some case, the device may be equipped with straps or other components (e.g., wheels) such that the device may be carried or transported from a first location to a second location. Those of ordinary skill in the art will be able to identify a portable device. For instance, the portable device may have a weight less than about 25 kg, less than about 20 kg, less than about 15 kg, less than about 1 kg, less than about 8 kg, less than about 7 kg, less than about 6 kg, less than about 5 kg, less than about 4 kg, less than about 3 kg, less than about 2 kg, less than about 1 kg, and the like, and/or have a largest dimension that is no more than 50 cm, less than about 40 cm, less than about 30 cm, less than about 20 cm, less than about 10 cm, and the like. The weight and/or dimensions of the device typically may or might not include components associated with the device (e.g., water source, water source reservoir, oxygen and/or hydrogen storage containers, etc.).

In some embodiments, the system may comprise an ion exchange membrane For example, anion exchange membranes and/or cation exchange membranes (i.e. ones with anion and/or cation exchangeable ions) may be used and are readily available from commercial sources (e.g., Tokuyama (Japan) or Fuma-Tech (Germany) - quaternary ammonium groups associated with a polymer). Non-limiting examples of anionic exchange membranes include poly(ethylene-co-tetrafluoroethylene),

poly(hexafluoropropylene-co- tetrafluoroethylene), poly(epichlorhydrin-ally glycidyl ether), poly(ether imide), poly(ethersulfone) cardo, poly(2,6-dimethyl-l ,4-phenylene oxide), polysulfone, or polyethersulfone, associates with a plurality of cationic species (e.g., quaternary ammonium groups, phosphonium groups, etc.).

An electrolyte, as known to those of ordinary skill in the art is any substance containing free ions that is capable of functioning as an ionically conductive medium. In some cases, an electrolyte may comprise water, which may act as the water source. The electrolyte may be a liquid, a gel, and/or a solid. In some cases, the second anionic species may be contained in the electrolyte. The electrolyte may be a liquid and/or non- liquid (e.g., solid, gel). The electrolyte may also comprise methanol, ethanol, sulfuric acid, methanesulfonic acid, nitric acid, mixtures of HC1, organic acids like acetic acid, etc. In some cases, the electrolyte may comprise mixtures of solvents, such as water, organic solvents, amines and the like. In some cases, the pH of the electrolyte may be about neutral. That is, the pH of the electrolyte may be between about 5.5 and about 8.5, between about 6.0 and about 8.0, about 6.5 about 7.5, and/or the pH is about 7.0. In a particular case, the pH is about 7.0. In other cases, the pH of the electrolyte is about neutral or acidic. In these cases, the pH may range from about 0 to about 8, about 1 to about 8, about 2 to about 8, about 3 to about 8, about 4 to about 8, about 5 to about 8, about 0 to about 7.5, about 1 to about 7.5, about 2 to about 7.5, about 3 to about 7.5, about 4 to about 7.5, about 5 to about 7.5. In yet other cases, the pH may be between about 6 and about 10, about 6 and about 1 1 , about 7 and about 14, about 2 and about 12, and the like. In a specific embodiment, the pH is between about 6 and about 8, between about 5.5 and about 8.5, between about 5.5 and about 9.5, between about 5 and about 9, between about 3 and about 1 1 , between about 4 and about 10, or any other combination thereof.

In some cases, the electrolyte is not a liquid. That is, in some cases, the electrolyte is a solid and/or gel. In some cases, the electrolyte may comprise a solid polymer electrolyte. The solid polymer electrolyte may serve as a solid electrolyte that conducts protons and separate the gases produces and or utilized in the electrochemical cell. Non-limiting examples of a solid polymer electrolyte are polyethylene oxide, polyacrylonitrile, cured or crosslinked polyacrylates and/or polyurethanes, and commercially available NAFION. Non-limiting embodiments of non-liquid electrolytes include electrolytes formed by using a lithium salt and an ion-conductive polymer such as polyethylene oxide or polypropylene oxide; gel polymer electrolytes formed by using a non-ionic conductive polymer such as poly(vinyl chloride), polyacrylonitrile, polymethyl methacrylate, poly(vinylidene fluoride), poly(vinyl) sulfone, or combinations thereof.

In some cases, the electrolyte may be used to selectively transport one or more ionic species. In some embodiments, the electrolyte(s) are at least one of oxygen ion conducting membranes, proton conductors, carbonate (CO3^"2) conductors, OH^" conductors, and/or mixtures thereof. In some cases, the electrolyte(s) are at least one of cubic fluorite structures, doped cubic fluorites, proton-exchange polymers, proton- exchange ceramics, and mixtures thereof. Further, oxygen-ion conducting oxides that may be used as the electrolyte(s) include doped ceria compounds such as gadolinium- doped ceria (Gdi_-xCe_x02-d) or samarium-doped ceria (Smi_-xCe_x0_2-d), doped zirconia compounds such as yttrium-doped zirconia (Yi_-xZr_x02-d) or scandium-doped zirconia (Sci_-xZr_x0_2-d), perovskite materials such as Lai_-xSr_xGai_-yMg_y0_3-d, yttria-stabilized bismuth oxide, and/or mixtures thereof. Examples of proton conducting oxides that may be used as electrolyte(s) include, but are not limited to, undoped and yttrium-doped BaZr0_3-d, BaCe0_3-d, and SrCe0_3-d as well as Lai_-xSr_xNb0_3-d.

In some embodiments, the electrolyte may comprise an ionically conductive material. In some embodiments, the ionically conductive material may comprise the anionic species comprised in the catalytic material on at least one electrode. The presence of the anionic species in the electrolyte, during use of the electrode comprising a catalytic material, may shift the dynamic equilibrium towards the association of the anionic species and/or metal ionic species with the current collector, as described herein. Non-limiting examples of other ionically conductive materials include metal oxy- compounds, soluble inorganic and/or organic salts (e.g., sodium or potassium chloride, sodium sulfate, quaternary ammonium hydroxides, etc.).

In some cases, the electrolyte comprises the second anionic species, as described herein. In some cases, the electrolyte may optionally comprise at least one additive. For example, the additive may be an anionic species (e.g., as comprised in the catalytic material associated with a current collector). For example, an electrode used in a device may comprise a current collector and a catalytic material comprising at least one anionic species and at least one metal ionic species.

In some cases, the electrolyte may be recirculated in the electrochemical device. That is, a device may be provided which is able to move the electrolyte in the

electrochemical device. Movement of the electrolyte in the electrochemical device may help decrease the boundary layer of the electrolyte. The boundary layer is the layer of fluid in the immediate vicinity of an electrode. In general, the extent to which a boundary layer exists is a function of the flow velocity of the liquid in a solution.

Therefore, if the fluid is stagnant, the boundary layer may be much larger than if the fluid was flowing. Therefore, movement of the electrolyte in the electrochemical device may decrease the boundary layer and improve the efficiency of the device.

In most embodiments, a device may comprise at least one electrode as described herein. In some instances, the device can comprise electrodes besides those as described herein. For example, an electrode may comprise any material that is substantially electrically conductive. The electrode may be transparent, semi-transparent, semi- opaque, and/or opaque. The electrode may be a solid, semi-porous or porous. Non- limiting examples of electrodes include indium tin oxide (ITO), fluorine tin oxide (FTO), glassy carbon, metals, lithium-containing compounds, metal oxides (e.g., platinum oxide, nickel oxide), graphite, nickel mesh, carbon mesh, and the like. Non-limiting examples of suitable metals include gold, copper, silver, platinum, nickel, cadmium, tin, and the like. In some instances, the electrode may comprise nickel (e.g., nickel foam or nickel mesh). The electrodes may also be any other metals and/or non-metals known to those of ordinary skill in the art as conductive (e.g., ceramics). The electrodes may also be photoactive electrodes used in photoelectrochemical cells. The electrode may be of any size or shape. Non-limiting examples of shapes include sheets, cubes, cylinders, hollow tubes, spheres, and the like. The electrode may be of any size. Additionally, the electrode may comprise a means to connect the electrode and to another electrode, a power source and/or another electrical device.

Various electrical components of device may be in electrical communication with at least one other electrical component by a means for connecting. A means for connecting may be any material that allows the flow of electricity to occur between a first component and a second component. A non-limiting example of a means for connecting two electrical components is a wire comprising a conductive material (e.g., copper, silver, etc.). In some cases, the device may also comprise electrical connectors between two or more components (e.g., a wire and an electrode). In some cases, a wire, electrical connector, or other means for connecting may be selected such that the resistance of the material is low. In some cases, the resistances may be substantially less than the resistance of the electrodes, electrolyte, and/or other components of the device.

In some embodiments, a power source may supply DC or AC voltage to an electrochemical device. Non-limiting examples include batteries, power grids, regenerative power supplies (e.g., wind power generators, photovoltaic cells, tidal energy generators), generators, and the like. The power source may comprise one or more such power supplies (e.g., batteries and a photovoltaic cell). In a particular embodiment, the power supply is a photovoltaic cell.

In some embodiments, a device may comprise a power management system, which may be any suitable controller device, such as a computer or microprocessor, and may contain logic circuitry which decides how to route the power streams. The power management system may be able to direct the energy provided from a power source or the energy produced by the electrochemical device to the end point, for example, to an electrolytic device. It is also possible to feed electrical energy to a power source and/or to consumer devices (e.g., cellular phone, television).

In some cases, electrochemical devices may comprise a separating membrane. The separating membranes or separators for the electrochemical device may be made of suitable material, for example, a plastic film. Non-limiting examples of plastic films included include polyamide, polyolefin resins, polyester resins, polyurethane resin, or acrylic resin and containing lithium carbonate, or potassium hydroxide, or sodium- potassium peroxide dispersed therein.

A container may be any receptacle, such as a carton, can, or jar, in which components of an electrochemical device may be held or carried. A container may be fabricated using any known techniques or materials, as will be known to those of ordinary skill in the art. For example, in some instances, the container may be fabricated from gas, polymer, metal, and the like. The container may have any shape or size, providing it can contain the components of the electrochemical device. Components of the electrochemical device may be mounted in the container. That is, a component (e.g., an electrode) may be associated with the container such that it is immobilized with respect to the container, and in some cases, is supported by the container. A component may be mounted to the container using any common method and/or material known to those skilled in the art (e.g., screws, wires, adhesive, etc). The component may or might not physically contact the container. In some cases, an electrode may be mounted in the container such that the electrode is not in contact with the container, but is mounted in the container such that it is suspended in the container.

Where the catalytic material and/or electrode is used in connection with an electrochemical device such as a fuel cell, any suitable fuels, oxidizers, and/or reactants may be provided to the electrochemical devices. In a particular embodiment, the fuel is hydrogen gas which is reacted with oxygen gas to produce water as a product. However, other fuels and oxidants can be used. For example, a hydrocarbon gas, such as methane, may be used as a fuel to produce water and carbon dioxide as a product. Other hydrocarbon gases, such as natural gas, propane, hexane, etc., may also be used as fuel. Furthermore, these hydrocarbon materials may be reformed into a carbon containing fuel, such as carbon monoxide, or previously supplied carbon monoxide may also be used as fuel.

The fuel may be supplied to and/or removed from a device and/or system using a fuel transport device. The nature of the fuel delivery may vary with the type of fuel and/or the type of device. For example, solid, liquid, and gaseous fuels may all be introduced in different manners. The fuel transport device may be a gas or liquid conduit such as a pipe or hose which delivers or removes fuel, such as hydrogen gas or methane, from the electrochemical device and/or from the fuel storage device. Alternatively, the device may comprise a movable gas or liquid storage container, such as a gas or liquid tank, which may be physically removed from the device after the container is filled with fuel. If the device comprises a container, then the device may be used as both the fuel storage device while it remains attached to the electrochemical device, and as a container to remove fuel from the electrochemical device. Those of ordinary skill in the art will be aware of systems, methods, and/or techniques for supplying and/or removing fuel from a device or system.

A variety of definitions are now provided which may aid in understanding various aspects of the invention.

In general, the term "aliphatic," as used herein, includes both saturated and unsaturated, straight chain (i.e., unbranched) or branched aliphatic hydrocarbons, which are optionally substituted with one or more functional groups, as defined below. As will be appreciated by one of ordinary skill in the art, "aliphatic" is intended herein to include, but is not limited to, alkyl, alkenyl, alkynyl moieties. Illustrative aliphatic groups thus include, but are not limited to, for example, methyl, ethyl, n-propyl, isopropyl, allyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, sec-pentyl, isopentyl, tert-pentyl, n-hexyl, sec-hexyl, moieties and the like, which again, may bear one or more substituents, as previously defined.

As used herein, the term "alkyl" is given its ordinary meaning in the art and may include saturated aliphatic groups, including straight-chain alkyl groups, branched-chain alkyl groups, cycloalkyl (alicyclic) groups, alkyl substituted cycloalkyl groups, and cycloalkyl substituted alkyl groups. An analogous convention applies to other generic terms such as "alkenyl," "alkynyl," and the like. Furthermore, as used herein, the terms "alkyl," "alkenyl," "alkynyl," and the like encompass both substituted and unsubstituted groups.

In some embodiments, a straight chain or branched chain alkyl may have 30 or fewer carbon atoms in its backbone, and, in some cases, 20 or fewer. In some embodiments, a straight chain or branched chain alkyl has 12 or fewer carbon atoms in its backbone (e.g., Ci-Ci₂ for straight chain, C3-C12 for branched chain), has 6 or fewer, or has 4 or fewer. Likewise, cycloalkyls have from 3-10 carbon atoms in their ring structure or from 5, 6 or 7 carbons in the ring structure. Examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl, tert-butyl, cyclobutyl, hexyl, cyclochexyl, and the like. In some cases, the alkyl group might not be cyclic. Examples of non-cyclic alkyl include, but are not limited to, methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, n- pentyl, neopentyl, n-hexyl, n- heptyl, n-octyl, n-decyl, n-undecyl, and dodecyl.

The terms "alkenyl" and "alkynyl" refer to unsaturated aliphatic groups analogous in length and possible substitution to the alkyls described above, but that contain at least one double or triple bond respectively. Alkenyl groups include, but are not limited to, for example, ethenyl, propenyl, butenyl, l-methyl-2-buten-l-yl, and the like. Non-limiting examples of alkynyl groups include ethynyl, 2- propynyl (propargyl), 1 -propynyl, and the like.

The terms "heteroalkenyl" and "heteroalkynyl" refer to unsaturated aliphatic groups analogous in length and possible substitution to the heteroalkyls described above, but that contain at least one double or triple bond respectively.

As used herein, the term "halogen" or "halide" designates -F, -CI, -Br, or -I. The term "aryl" refers to aromatic carbocyclic groups, optionally substituted, having a single ring (e.g., phenyl), multiple rings (e.g., biphenyl), or multiple fused rings in which at least one is aromatic (e.g., 1 ,2,3,4-tetrahydronaphthyl, naphthyl, anthryl, or phenanthryl). That is, at least one ring may have a conjugated Pi electron system, while other, adjoining rings can be cycloalkyls, cycloalkenyls, cycloalkynyls, aryls, and/or heterocycyls. The aryl group may be optionally substituted, as described herein.

"Carbocyclic aryl groups" refer to aryl groups wherein the ring atoms on the aromatic ring are carbon atoms. Carbocyclic aryl groups include monocyclic carbocyclic aryl groups and polycyclic or fused compounds (e.g., two or more adjacent ring atoms are common to two adjoining rings) such as naphthyl group. Non-limiting examples of aryl groups include phenyl, naphthyl, tetrahydronaphthyl, indanyl, indenyl and the like.

The terms "heteroaryl" refers to aryl groups comprising at least one heteroatom as a ring atom, such as a heterocycle. Non-limiting examples of heteroaryl groups include pyridyl, pyrazinyl, pyrimidinyl, pyrrolyl, pyrazolyl, imidazolyl, thiazolyl, oxazolyl, isooxazolyl, thiadiazolyl, oxadiazolyl, thiophenyl, furanyl, quinolinyl, isoquinolinyl, and the like.

It will also be appreciated that aryl and heteroaryl moieties, as defined herein, may be attached via an aliphatic, alicyclic, heteroaliphatic, heteroalicyclic, alkyl or heteroalkyl moiety and thus also include -(aliphatic)aryl, -(heteroaliphatic)aryl, - (aliphatic)heteroaryl, -(heteroaliphatic)heteroaryl, -(alkyl)aryl, -(heteroalkyl)aryl, - (heteroalkyl)aryl, and -(heteroalkyl)-heteroaryl moieties. Thus, as used herein, the phrases "aryl or heteroaryl" and "aryl, heteroaryl, (aliphatic)aryl, -(heteroaliphatic)aryl, - (aliphatic)heteroaryl, -(heteroaliphatic)heteroaryl, -(alkyl)aryl, -(heteroalkyl)aryl, - (heteroalkyl)aryl, and -(heteroalkyl)heteroary" are interchangeable.

Any of the above groups may be optionally substituted. As used herein, the term "substituted" is contemplated to include all permissible substituents of organic compounds, "permissible" being in the context of the chemical rules of valence known to those of ordinary skill in the art. It will be understood that "substituted" also includes that the substitution results in a stable compound, e.g., which does not spontaneously undergo transformation such as by rearrangement, cyclization, elimination, etc. In some cases, "substituted" may generally refer to replacement of a hydrogen with a substituent as described herein. However, "substituted," as used herein, does not encompass replacement and/or alteration of a key functional group by which a molecule is identified, e.g., such that the "substituted" functional group becomes, through

substitution, a different functional group. For example, a "substituted phenyl group" must still comprise the phenyl moiety and can not be modified by substitution, in this definition, to become, e.g., a pyridine ring. In a broad aspect, the permissible

substituents include acyclic and cyclic, branched and unbranched, carbocyclic and heterocyclic, aromatic and nonaromatic substituents of organic compounds. Illustrative substituents include, for example, those described herein. The permissible substituents can be one or more and the same or different for appropriate organic compounds. For purposes of this invention, the heteroatoms such as nitrogen may have hydrogen substituents and/or any permissible substituents of organic compounds described herein which satisfy the valencies of the heteroatoms.

Examples of substituents include, but are not limited to, aliphatic, alicyclic, heteroaliphatic, heteroalicyclic, halogen, azide, alkyl, aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxyl, alkoxyl, amino, nitro, sulfhydryl, imino, amido, phosphonate, phosphinate, carbonyl, carboxyl, silyl, ether, alkylthio, heteroalkylthio, heteroarylthio, sulfonyl, sulfonamido, ketone, aldehyde, ester, heterocyclyl, aromatic or heteroaromatic moieties, -CF₃, -CN, aryl, aryloxy, perhaloalkoxy, aralkoxy, heteroaryl, heteroaryloxy, heteroarylalkyl, heteroaralkoxy, azido, amino, halide, alkylthio, oxo, acylalkyl, carboxy esters, -carboxamido, acyloxy, aminoalkyl, alkylaminoaryl, alkylaryl, alkylaminoalkyl, alkoxyaryl, arylamino, aralkylamino, alkylsulfonyl, -carboxamidoalkylaryl,

-carboxamidoaryl, hydroxyalkyl, haloalkyl, alkylaminoalkylcarboxy-,

aminocarboxamidoalkyl-, cyano, alkoxyalkyl, perhaloalkyl, arylalkyloxyalkyl, (e.g., S0₄(R')₂), a phosphate (e.g., P0₄(R')₃), a silane (e.g., Si(R')₄), a urethane (e.g.,

R'O(CO)NHR'), and the like. Additionally, the substituents may be selected from F, CI, Br, I, -OH, -N0 , -CN, -NCO, -CF₃, -CH₂CF₃, -CHC1₂, -CH₂OR_x, -CH₂CH₂OR_x, - CH₂N(R_X)₂, -CH₂S0₂CH₃, -C(0)R_x, -C0₂(R_x), -CON(R_x)₂, -OC(0)R_x, -C(0)OC(0)R_x, - OC0₂R_x, -OCON(R_x)₂, -N(R_X)₂, -S(0)₂R_x, -OC0₂R_x, -NR_x(CO)R_x, -NR_x(CO)N(R_x)₂, wherein each occurrence of R_x independently includes, but is not limited to, H, aliphatic, alicyclic, heteroaliphatic, heteroalicyclic, aryl, heteroaryl, alkylaryl, or alkylheteroaryl, wherein any of the aliphatic, alicyclic, heteroaliphatic, heteroalicyclic, alkylaryl, or alkylheteroaryl substituents described above and herein may be substituted or

unsubstituted, branched or unbranched, cyclic or acyclic, and wherein any of the aryl or heteroaryl substituents described above and herein may be substituted or unsubstituted.

The following references are herein incorporated by reference: U.S. Provisional Patent Application Serial No. 61/073,701, filed June 18, 2008, entitled "Catalyst

Compositions and Electrodes for Photosynthesis Replication and Other Electrochemical Techniques," by Nocera, et al., U.S. Provisional Patent Application Serial No.

61/084,948, filed July 30, 2008, entitled "Catalyst Compositions and Electrodes for Photosynthesis Replication and Other Electrochemical Techniques," by Nocera, et al., U.S. Provisional Patent Application Serial No. 61/103,879, filed October 8, 2008, entitled "Catalyst Compositions and Electrodes for Photosynthesis Replication and Other Electrochemical Techniques," by Nocera, et al., U.S. Provisional Patent Application Serial No. 61/146,484, filed January 22, 2009, entitled "Catalyst Compositions and Electrodes for Photosynthesis Replication and Other Electrochemical Techniques," by Nocera, et al., U.S. Provisional Patent Application Serial No. 61/179,581 , filed May 19, 2009, entitled "Catalyst Compositions and Electrodes for Photosynthesis Replication and Other Electrochemical Techniques," by Nocera, et al., U.S. Provisional Patent

Application Serial No. 61/237,507, filed August 27, 2009, entitled "Improved Methods and Compositions Involving Catalytic Materials, Electrodes, and Systems for Water Electrolysis and Other Electrochemical Techniques," by Esswein, et al., and U.S.

Provisional Patent Application Serial No. 61/285,844, filed December 1 1, 2009, entitled "Improved Methods and Compositions Involving Catalytic Materials, Electrodes, and Systems for Water Electrolysis and Other Electrochemical Techniques," by Esswein, et al.

The following examples are intended to illustrate certain embodiments of the present invention, but do not exemplify the full scope of the invention.

Example 1

In the following examples, the abbreviation Co-OEC refers to a cobalt-oxygen evolving compound which is a catalytic material formed on the surface of an electrode. The Co-OEC is generally prepared according to the methods described herein. In most embodiments, the Co-OEC containing electrode is prepared by controlled potential electrolysis of Co²⁺ salts in pH 7 phosphate (Pi) electrolyte. For example, in Example 3, the Co-OEC catalyst materials were prepared by electrodeposition onto FTO-coated glass supports (TEC7, Hartford Glass). Prior to deposition, FTO electrodes (1 < 3 cm) were cleaned by sonication according to the following: detergent solution (Triton X-100, diluted to 0.1% by volume, 2 min), 18 ΜΩ/cm² water (2 min), and isopropanol (1 min). The electrodes were then biased at 0.9 V vs. Ag/AgCl in a solution containing 0.5 mM Co²⁺ + 0.1 M KPi at pH 7 until the total charge passed equaled 0.05 C / cm². The resulting Co-OEC functionalized electrodes were stored in 0.1 M KPi solution until use.

Example 2

The following example describes a non-limiting example wherein the temperature of the system during electrolysis is controlled.

The electrical energy input required to drive the water splitting reaction decreases as the solution temperature increases: ΔΕ = 1.482 V (thermoneutral, OK), 1.229 V (25 °C), 1.200 V (60 °C), and 1.183 V (80 °C). However, a number of other kinetic parameters such as diffusion, solution conductivity, electron transfer rates, and 0₂ bond formation may be affected by temperature. Data on a thin film of Co-OEC deposited on ITO and operated in 0.1 M pH 7 KPi buffer revealed that at a current density of 1 mA/cm , the catalytic material required approximately 240 mV less potential at 63 °C as compared to 10 °C. FIG. 8 shows the temperature dependent electro-catalytic activity of Co-OEC films deposited on ITO measured in 0.1 M pH 7 KPi. Example 3

The following example describes the operation of a electrode comprising a current collector and a catalytic material comprising a first anionic species and a metallic species in an electrolyte comprising a second anionic species, and demonstrates surprising results.

The electrolyte composition and pK_a may affect the proton transfer kinetics and the chemical makeup/morphology of a catalytic material. Experimental results of Co- OEC functionalized FTO anodes in 1.0 M borate buffer (pH 9.2) revealed an unexpected increase in catalytic activity with time of operation (FIG. 9). Control experiments show the activity increase is not solely a function of solution pH, suggesting that the chemical characteristics of the buffering medium may have a large effect on catalyst activity. In addition, with regard to electrode stability, as FIG. 9 shows, stable catalytic

material/electrode operation for 30 hours was been obtained using FTO-coated glass substrates and 1.0 M KBi electrolyte in a standard 2-compartment H-cell configuration. FIG. 9 shows the bulk electrolysis of Co-OEC prepared in 0.1 M KPi buffer (pH 7) and run in 1.0 M KBi buffer (pH 9.2). The absolute value of the current is plotted vs.

electrolysis time.

A catalytic material comprising cobalt ions and anionic species comprising phosphorus (e.g., phosphate) was deposited in thick layers on a macroporous Ni foam substrate (FIG. 10A). A dark black catalytic material functionalized Ni foam anodes gave large current responses when operated in 1.0 M KPi (pH 7) solutions at 25 °C (FIG. 10B) Current densities of 100 mA/cm were achieved in this configuration with the anode biased at approximately 550 mV overpotential. Control experiments using bare Ni foam gave very little current and unequivocally establish that the current was derived from the Co-OEC catalyst layer. These results demonstrate that increasing the electrode surface area has a significant effect on the observed current density with relatively minor investments in optimization. FIG. 10A shows an SEM micrograph of a high surface area Ni foam electrode support deposited with the Co-OEC catalyst. FIG. 10B shows the current response of 1 cm² Ni foam anode with and without Co-OEC in 1.0 M KPi (pH 7) buffer at 25 °C.

Similar unexpected results were observed as above when operating an electrode comprising a Co-OEC in a carbonate buffer. As described below, a Co-OEC material was evaluated for its catalytic ability to evolve oxygen (0₂) in buffered solutions containing sodium carbonate (Na₂C0₃) and potassium carbonate (K₂C0₃).

Sodium carbonate anhydrous (Mallinckrodt), sodium bicarbonate (BDH), sodium hydroxide (BDH), potassium carbonate (Sigma-Aldrich), potassium bicarbonate (J.T. Baker), and potassium hydroxide (BDH) were used as received. Sodium carbonate buffer solutions were prepared to 1.0 M concentration by dissolving sodium carbonate and sodium bicarbonate in 18 ΜΩ/cm water and adjusting the pH with sodium hydroxide. Potassium carbonate buffer solutions were prepared to 1.0 M concentration by dissolving potassium carbonate and potassium bicarbonate in 18 ΜΩ/cm water and adjusting the pH with potassium hydroxide. All buffer solutions were filtered through a 0.2 μιη Nylaflo membrane (VWR) prior to use.

Electrochemical experiments were performed in a three electrode cell

configuration using a potentiostat (CH Instruments model 600D Electrochemical Analyzer) with a Ag/AgCl reference electrode (BASi) and a Pt wire counter electrode (Alfa Aesar).

The Co-OEC catalyst films were prepared by electrodeposition onto FTO-coated glass supports (TEC7, Hartford Glass). Prior to deposition, FTO electrodes (1 x 3 cm) were cleaned by sonication according to the following: detergent solution (Triton X-100, diluted to 0.1% by volume, 2 min), 18 ΜΩ/cm² water (2 min), and isopropanol (1 min). The electrodes were then biased at 0.9 V vs. Ag/AgCl in a solution containing 0.5 mM Co²⁺ + 0.1 M KPi at pH 7 until the total charge passed equaled 0.05 C / cm². The resulting Co-OEC functionalized electrodes were stored in 0.1 M KPi solution until use.

Bulk electrolysis of Co-OEC was performed by biasing the working electrode at 480 mV overpotential for 0₂ evolution (0.905 V vs. Ag/AgCl) in sodium and potassium carbonate solutions at pH 10.3. Experiments were performed in custom-built

polycarbonate flow cells, with buffered electrolyte flowing across the working electrode at 1 10 mL/min using a peristaltic pump (Cole-Parmer Masterflex).

FIG. 1 1 shows the bulk electrolysis of Co-OEC catalyst operated in sodium and potassium carbonate solutions at pH 10.3. In the case of potassium carbonate, an initial current density of 1.5 mA/cm² was observed that rapidly decays to ~0.35 mA/cm² on the seconds to minutes timescale. This initial current decay corresponds to capacitive charging of the catalyst film and solution double layer. Following this initial decay, the current was observed to steadily increase to a maximum of ~3.7 mA/cm² over 20 hours and remains stable for an additional ~55 hours of operation. Similar results were observed using sodium carbonate as the electrolyte, with a maximum current density of -2.5 mA/cm² achieved after 75 hours of operation.

Example 4

The following describes a screening test for determining enhancement of Co- OEC activity by operation in a solution containing a second anionic species, and demonstrates surprising results.

Co-OEC films are grown at 0.9 V vs. Ag/AgCl on clean FTO-coated glass slides of 1 cm active area in a solution of 0.5 mM Co in 0.1 M potassium phosphate buffer at pH 7. All Co-OEC films in this example were grown to a charge limit of 0.05 C/cm . Three-electrode electrolysis was performed at a constant overpotential of 480 mV using an Ag/AgCl reference electrode and a platinum counter electrode. The resulting current density was measured as a function of electrolysis time. Enhancement of Co-OEC activity may be characterized by a rise in the current density during the electrolysis experiment.

The use of a second anionic species ion to increase the activity of Co-OEC catalysts for oxygen evolution was investigated. In this non-limiting example, potassium borate (KBi) and potassium carbonate were the electrolytes employed (e.g., wherein the second anionic species is borate or carbonate, respectively). The performance results are shown in Table 1. For maximum buffering capacity, electrolytes were prepared at or near the pKa. Under the conditions listed in the table, an initial current rise was observed in potassium borate and potassium carbonate. Co-OEC performance was also evaluated in electrolytes containing mixtures of potassium borate and potassium phosphate, as shown in Table 2.

Table 1. Efi ect of electrolyte composition on Co-OEC current density

Conceittratio Conductivity I itial Peak

Electrolyte

n (mol L) (mS/cm) activity⁴ activity* Stability

1.25

P otassium 0.4 1 mA/cm² at 150

1 9.2 25 mA/cm at borate mA/cm days

12 hours

2.25

P otassium 0.75 2.25 mA/cm² at

1 10.3 105.3 mA/cm at c rbonate mA/cm² 110 hours

30 hours In Table 1 : (a) Activities determined at 480 mV overpotential for oxygen evolution.

While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the functions and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used.

Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present invention.

The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one."

The phrase "and/or," as used herein in the specification and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to "A and/or B," when used in conjunction with open-ended language such as "comprising" can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

As used herein in the specification and in the claims, "or" should be understood to have the same meaning as "and/or" as defined above. For example, when separating items in a list, "or" or "and/or" shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as "only one of or "exactly one of," or, when used in the claims, "consisting of," will refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or" as used herein shall only be interpreted as indicating exclusive alternatives (i.e. "one or the other but not both") when preceded by terms of exclusivity, such as "either," "one of," "only one of," or "exactly one of." "Consisting essentially of," when used in the claims, shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase "at least one," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and/or B") can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

In the claims, as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of and "consisting essentially of shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 21 11.03.

What is claimed:

Claims

1. A method of producing oxygen and/or hydrogen gas from water comprising; providing an electrode comprising a catalytic material comprising a metal ionic species and a first anionic species;

wherein the electrode is operated in a liquid medium comprising a second anionic species in a concentration of greater than about 0.3 M, or in a non-liquid medium comprising a second anionic species having an equivalent weight of less than about 1500 g/mol, and

wherein the first anionic species and the second anionic species are not an oxide and/or hydroxide.

2. A system for catalytically producing oxygen and/or hydrogen gas from water, comprising:

an electrode comprising a catalytic material comprising metal ionic species and a first anionic species; and

a second anionic species in a liquid medium at a concentration greater than about 0.3 M, or in a non-liquid medium having an equivalent weight of less than about 1500 g/mol,

3. The method or system of any preceding claim, wherein the second ionic species is selected so as to interact with the catalytic material to be able to improve at least one performance parameter of the first electrode under set conditions.

4. The method or system of any preceding claim, wherein the second ionic species is selected so as to interact with the catalytic material to be able to increase the current density able to be produced by the first electrode under set conditions.

5. The method or system of any preceding claim, wherein the first anionic species comprises phosphorus.

6. The method or system of any preceding claim, wherein the second anionic species comprises boron.

7. The method or system of any preceding claim, wherein the metal ionic species comprises cobalt ions.

8. The method of system of any preceding claim, wherein the liquid medium

comprises water, and optionally, is functioning as an electrolyte.

9. The method of any preceding claim, wherein the first electrode comprises a

current collector, and the catalytic material is associate with the current collector.

10. The method or system of any preceding claim, further comprising a second

electrode biased negatively with respect to the first electrode.

1 1. The method of any preceding claim, further comprising causing the

electrochemical system to catalyze the production of oxygen and/or hydrogen gas from water.

12. The method or system of any preceding claim, wherein the first anionic species and the second anionic species are not oxide and/or hydroxide.

13. The method or system of any preceding claim, wherein the first anionic species and the second anionic species are different.

14. The method of any preceding claim, wherein oxygen gas is produced at the first electrode at an overpotential of less than about 0.4 volts at an electrode current density of at least about 20 mA/cm , or at an overpotential of less than about 0.55 volts at an electrode current density of at least about 100 mA/cm , or at an overpotential of less than about 0.35 V at an electrode current density of at least 1 mA/cm², or at an overpotential of less than about 0.325 V at an electrode current density of at least 1 mA/cm .

15. The method or system of any preceding claim, wherein the metal ionic species comprises cobalt ions and the first anionic species is a form of phosphate.

16. The method or system of any preceding claim, wherein the concentration of the second anionic species is between about 0.3 and 3.0 M, or greater than about 0.5 M, or greater than about 1.0M, or greater than about 1.5 M, or greater than about 2.0 M.

17. The method or system of any preceding claim, wherein the non-liquid medium comprises second anionic species having an equivalent weight between about 400 g/mol and about 1500 g/mol.

18. The method or system of any preceding claim, wherein the current density able to be produced by the first electrode increase by about 5%, about 10%, about 15%, about 20%, about 25%, about 40%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, or about 100%, at about 1 minute, about 2 minutes, about 3 minutes, about 4 minutes, about 5 minutes, about 10 minutes, about 20 minutes, about 30 minutes, about 40 minutes, about 50 minutes, about 60 minutes, about 90 minutes, about 2 hours, about 4 hours, about 8 hours, about 12 hours, or about 24 hours after application of a voltage to the first electrode as compared to the current density produced immediately upon application of a voltage.

19. The method or system of any preceding claim, wherein the catalytic material comprises metal ionic species with an oxidation state of (n+x) and anionic species, having a K_sp that is less, by a factor of at least 10³, than the K_sp value of a composition comprising the metal ionic species with an oxidation state of (n) and the anionic species.

20. The method or system of any preceding claim, wherein the catalytic material additionally comprises a third anionic species.

21. The method or system of claim 20, wherein the third anionic species comprises oxides and/or hydroxides.

22. The method or system of any preceding claim, wherein the anionic species

comprising phosphorus is selected from the group consisting of HPO₄ ^"2, H₂P0₄ ^"2 _; P0₄ ^"3, H3PO3, HPO3^"2, H₂P0₃ ^"2 or P0₃ ^"3

23. The method or system of any preceding claim, wherein the first type or the

second anionic species is selected from the group comprising forms of phosphate, forms of sulphate, forms of carbonate, forms of arsenate, forms of phosphite, forms of silicate, or forms of borate.

24. The method or system of any preceding claim, wherein the current collector has a surface area between about 0.01 m²/g and about 300 m²/g, or is greater than about 10 m /g, or greater than about 50 m /g, or greater than about 100 m /g, or greater

2 2

than about 150 m /g, or greater than about 200 m Ig.

25. The method or system of any preceding claim, wherein current collector

comprises at least one of a metal, a metal oxide, a metal alloy, a ceramic, an inorganic conductive material, or an organic conductive material.

26. The method or system of any preceding claim, wherein gaseous hydrogen is

evolved at the second electrode.

27. The method or system of any preceding claim, further comprising an electrolyte, and optionally, wherein the second anionic species is contained in the electrolyte.

28. The method or system of any preceding claim, wherein the electrolyte is a solid polymer electrolyte.

29. The method or system of any preceding claim, wherein the electrolyte has a pH between about 9.5 and about 5.5, or between about 8 and about 6, or between about 7 and about 4, or between about 3 and about 1 1 , or between about 6 and about 12.

30. The method or system of any preceding claim, wherein the system further comprises an anion exchange membrane.

31. The method or system of any preceding claim, wherein the first anionic species and the second anionic species are the same.

32. The method or system of any preceding claim, wherein the first anionic species and the second anionic species are different.