WO2024208974A1

WO2024208974A1 - Hybrid energy storage and electrolyser device

Info

Publication number: WO2024208974A1
Application number: PCT/EP2024/059200
Authority: WO
Inventors: Bernhard Manfred Hermann WENINGER
Original assignee: Individual
Current assignee: Individual
Priority date: 2023-04-05
Filing date: 2024-04-04
Publication date: 2024-10-10
Anticipated expiration: 2025-10-05
Also published as: NL2034504B1

Abstract

A device (200; 300) for providing electrical energy and/or an energy carrier, such as hydrogen, comprises at least one cell unit (10; 110). The cell unit (10; 110) comprises an iron based electron storage electrode (12; 112) and an air electrode (20; 120). Upon charging iron compounds are reduced to iron metal in the iron based electrode. Upon overcharging hydrogen is generated that can be stored in a storage for later use. At the air electrode oxygen is generated upon charging and overcharging. The device may have a compact design and relatively high volumetric storage capacity. An energy system based on this device in combination with an external power source and/or an electricity grid is also described. Operation of the device comprises supplying electrical power from an external power source to the cell unit, thereby providing an electrically charged iron based electrode and/or hydrogen and/or oxygen stored in a storage.

Description

Title: HYBRID ENERGY STORAGE AND ELECTROLYSER DEVICE

Field of the invention

The invention relates to a device for providing electrical energy and/or an energy carrier, such as hydrogen (H2), as well as to an energy system comprising such a device. The invention also relates to a method for providing electrical energy and/or an energy carrier. Furthermore the invention relates to the use of the device and/or energy system.

Background of the invention

From WO 2016/178564A1 a hybrid battery and electrolyser is known based on modified operation of a Ni-Fe battery to take into account variation in time of the availability of renewable energy, such as wind energy and solar power. Diurnal electricity storage would be most energy efficient in batteries. Seasonal storage scales would require the conversion to artificial fuels based on abundant elements. Upon reaching full capacity of the battery an equal or larger amount of charge can be used to produce hydrogen and/or oxygen. In this known system the charged electrodes consist of NiOOH and Fe respectively and function as oxygen and hydrogen gas evolution catalysts respectively. In a functional cell of this known system a separator such as a membrane is present between a first electrolyte compartment and a second electrolyte compartment for separating the oxygen and hydrogen gases while having permeability for monovalent electrolyte ions.

Although nickel is an abundant material, it is considered a relatively expensive material for use in electrodes in hybrid battery and electrolyser systems. Nickel also limits the battery capacity. A nickel electrode has a storage capacity of up to about 0.3 Ah/cm³, whereas an iron electrode has a storage capacity of up to about 0.8 Ah/ cm³. Therefore nickel electrodes have a thickness of about two times the thickness of the iron electrode. Another drawback of this known configuration is the presence of the membrane within the functional unit of the hybrid system. The membrane allows passage of the liquid electrolyte from one compartment to the other. However, hydrogen and oxygen may dissolve in the electrolyte and pass through the membrane as well. The amount of dissolved gas is proportional to the operation pressure. Thus the amount of gas that may pass through the membrane is dependent on the amount of dissolved gas in the electrolyte and on the pressure differential between the electrolyte compartments. Any amount of gas passing through the membrane is considered a system loss. Furthermore, the membrane occupies space in the hybrid apparatus, increases the ionic resistance and complicates the design as proper pressure balancing is typically required to avoid crossover between the first and second electrolyte compartment.

Furthermore iron electrodes tend to lose capacity due to self-discharge when they are not in use.

An aspect of the invention concerns the provision of a hybrid energy storage and electrolyser device that does not suffer from one or more of the drawbacks described above, or at least to provide a suitable alternative. Another aspect of the invention concerns the provision of an energy management system comprising such a device. Yet another aspect relates to the provision of a method of providing electrical energy and/or an energy carrier. A further aspect is the use of the hybrid energy storage and electrolyser device and/or energy management system.

Summary of the invention

In an aspect the invention provides a hybrid energy storage and electrolyser device for storage of electrical energy and production of energy carriers, such as hydrogen, comprises at least one cell unit comprising an iron based electron storage electrode configured for reduction of iron compounds to metallic iron upon charging and for hydrogen evolution upon overcharging and for oxidation of metallic iron to iron compounds upon discharging, having a first electrical connection; an air electrode configured for oxygen evolution upon charging and overcharging and oxygen and/or water conversion into hydroxyl ions and/or hydrogen upon discharging, having a second electrical connection; at least one electrolyte compartment configured for containing an electrolyte and gases generated at one or more of the electron storage electrode and air electrode, and having a liquid inlet and an outlet for liquid and gases; an air compartment configured for containing a gas, in particular a gas comprising oxygen, having a gas inlet and a gas outlet; a liquid-gas separation unit, configured for separating the electrolyte and gases generated at one or more of the electron storage electrode and air electrode; a storage configured for storing separated gases external from the cell unit, and being in fluid communication with the liquid-gas separation unit; a flow control unit configured for circulating a flow of electrolyte through the electrolyte compartment and liquid-gas separation unit; a charge control unit configured for receiving electrical power from an external power source and configured for supplying electrical power received from the external power source to the cell unit during charging and overcharging and configured for receiving electrical power from the cell unit and configured for supplying electrical power received from the cell unit, during discharging to an external load; a control system configured for controlling the flow control unit, the storage and charge control unit.

In another aspect the invention provides an energy system comprising the hybrid energy storage and electrolyser device of the invention and an external power source and/or an electricity grid.

In a further aspect the invention provides a method of storing electrical energy and one or more energy carriers comprising hydrogen and/or oxygen using the hybrid energy storage and electrolyser device according to the invention, comprising the steps of supplying electrical power from the external power source to the cell unit, thereby providing an electrically charged iron based electrode and/or hydrogen and/or oxygen stored in the storage.

The hybrid device according to the invention has an electrical energy storage functionality, as well as an electrolysis functionality. In the invention the nickel based (Ni(OH)2/NiOOH) electrode known from WO 2016/178564A1 is replaced by a reversible oxygen electrode (also known as air electrode). Upon charging and overcharging oxygen is generated at the liquid side of the air electrode: 4 OH- -^ 02 + 2H2O + 4 e-. Upon discharging the reverse reaction takes place: Oxygen is absorbed at the electrode facing the air compartment and at the liquid side hydroxyl ions are formed in the (alkaline) electrolyte contained in an electrolyte compartment. If oxygen is not supplied to the air electrode during discharging of the battery functionality, the air compartment may be omitted. Then, if some electrical energy is supplied by the charge control unit, water can be dissociated at this air electrode at the electrolyte side: 2 H2O + 2 e' — > H2 + 2 OH resulting in additional hydrogen generation. However, preferably in view of ensuring different ways of operation an air compartment configured for containing a gas, preferably a gas comprising oxygen, having a gas inlet and a gas outlet is part of the hybrid device.

At the negative iron based electrode metallic iron is formed during charging Fe(OH)2 + 2 e' — > Fe + 2 OH- and Fe3O4 + 4H2O+ 8 e' — > 3Fe + 8 OH' and if the case may be, other iron compounds to metallic iron. Some hydrogen may be generated at the iron based electrode during chemical reduction thereof to Fe metal upon charging. Upon overcharging that is to say after the reduction to Fe metal is substantially completed, hydrogen is produced at the iron based electrode 2 H2O + 2 e- -^H₂ + 2 OH'. Upon discharging the reactions are reversed. Use of an air electrode allows a compact and simple design of the hybrid device without pressure balancing, especially if the separation of generated gases is performed outside the cell unit. E.g. a NiFe battery system having a cell configuration of nickel electrode of 5 mm thick, two electrolyte compartments each 1 mm thick and an iron electrode having a thickness of 3 mm would result in a system storage capacity of about 0.15 Ah/cm³. In the iron oxygen (air) configuration according to the invention the iron electrode can be thicker. An example configuration of a 4 mm thick iron electrode, 1.8 mm thick air electrode and air compartment, and two electrolyte compartments of 1 mm has a system storage capacity of 0.4 Ah/cm³. Thus the iron oxygen system has a volumetric storage capacity, based on Ah, that is about 2.5 times higher than the NiFe configuration. The replacement of the nickel electrode also offers a cost advantage.

In the art it has been said that an iron-air battery is an insufficient electrical energy system because of voltaic losses (ratio between average voltages for charging and discharging) and faradaic losses due to hydrogen evolution. In the hybrid device according to the invention that generates hydrogen on purpose, the faradaic losses are reduced. The generated hydrogen is collected and can be stored for further use.

Furthermore, the device may be operated efficiently at lower current densities, such as 10-50 mA/cm², when gas separation is allowed to occur outside the cell unit. For example, upon charging the current density may be in the range up to 50 mA/cm², and upon discharging in the range of 10-25 mA/cm².

Detailed description of the invention

Hybrid device

The hybrid device according to the invention for storage of electrical energy and production of energy carriers, especially at least hydrogen, comprises a cell unit as basic element. A cell unit comprises an iron based electrode as an electron storage electrode, which is configured for reduction of iron compounds to metallic iron upon charging and for hydrogen evolution upon overcharging and for oxidation of metallic iron to iron compounds upon discharging. The iron based electron storage electrode has a first electrical connection, which can be accessed from the outside of the cell unit. A cell unit also comprises an air electrode that is configured for oxygen evolution upon charging and overcharging and oxygen and/or water conversion into hydroxyl ions and/or hydrogen upon discharging. The air electrode has a second electrical connection. Between the two electrodes one or more electrolyte compartments are arranged. An electrolyte compartment is configured for containing an electrolyte and gases generated at one or more of the electron storage electrode and air electrode. An electrolyte compartment is provided with a liquid inlet for supplying a liquid, such as electrolyte, and an outlet for outputting liquid and generated gases. Typically the liquid electrolyte is an alkaline solution comprising hydroxides, such as KOH, LiOH and/or NaOH. Circulation of a flow of the electrolyte from the electrolyte compartment to the gas-liquid separation unit contributes to separation of generated gas from the liquid electrolyte. In an embodiment an air compartment facing another - typically opposite - side of the air electrode configured for containing a gas, typically a gas comprising oxygen, having a gas inlet and a gas outlet, is present. The gases generated during operation of the hybrid device according to the invention are separated from the electrolyte in a liquid-gas separation unit that is configured for separating the electrolyte and gases generated at one or more of the electron storage electrode and air electrode. The gas-liquid separation unit is in flow communication with the outlet of the electrolyte compartment. The electrolyte from which the gases have been separated is returned to the inlet of the electrolyte compartment. The separated gases are stored in a storage. Hydrogen and oxygen may be stored as a gas mixture and used subsequently e.g. for combustion. Preferably, hydrogen is stored separately, after separation.

In an embodiment the device comprises a gas separator for separating hydrogen from oxygen. This separation may be performed internally in the cell unit or externally from the cell unit.

Hydrogen can be separated from oxygen externally from the cell unit, e.g. using a cryogenic separation or pressure swing adsorption. Hydrogen separation by means of an external gas permeation membrane, such as a hollow fibre based membrane for selective permeation of hydrogen, available from Air Liquide, is also conceivable. Separation preferably occurs outside the cell unit, allowing a compact design, in particular a compact arrangement of the electrodes in parallel, without pressure balancing between electrolyte compartments and reduces ionic resistance.

A sensor configured for determining the composition of the gas mixture may be used for controlling the operation of the external gas separator. During charging only oxygen is generated, then no gas-separation is required. Only during overcharging gas separation is necessary, then the sensor could trigger the operation of the external gas separator.

A membraneless hybrid device based on a cell unit having an iron electrode and a nickel electrode according to WO 2016/178564A1 , provided with an external gas separator as explained above, is also contemplated.

In another embodiment the hydrogen and oxygen are allowed to be generated in different electrolyte compartments, that are separated from one another by a membrane, as a gas separator. In an embodiment thereof a first electrolyte compartment configured for containing a first electrolyte and generated hydrogen and a second electrolyte compartment configured for containing a second electrolyte and generated oxygen gas are separated by the gas separator, wherein the gas separator comprises a membrane configured for transmitting ions and blocking gases. Examples of membranes include alkaline resistant membranes manufactured from polymer or a polymer composite, such as a Zirfon membrane, available from Agfa. Typically the first and second electrolyte will be the same, e.g. an alkaline electrolyte, in particular a KOH solution.

The hybrid device also comprises a storage that is configured for storing separated gases external from the cell unit. The storage is in fluid communication with the liquid-gas separation unit, and if present the gas separator. In an embodiment the storage comprises at least a container configured for containing hydrogen. The storage may also be configured to store one or more gases under pressure. Hydrogen can be used directly as a fuel, such as direct engine propulsion. Hydrogen can also be used indirectly, such as a starting material in a fuel cell for generating electricity.

A flow control unit configured for circulating a flow of electrolyte through the electrolyte compartment and liquid-gas separation unit is also provided, as well as a charge control unit configured for receiving electrical power from an external power source and configured for supplying electrical power received from the external power source to the cell unit during charging and overcharging and configured for receiving electrical power from the cell unit and configured for supplying electrical power received from the cell unit, during discharging to an external load. The flow control unit controls the flow of electrolyte.

The charge control unit controls the electrical power input to the cell unit resulting in a potential difference between the iron based electrode and air electrode during charging and overcharging. Optionally the hybrid device may be discharged without oxygen supply to the air electrode. Then hydrogen and hydroxyl ions are generated at the air electrode from water. For this embodiment of discharging the charge control unit is configured to supply some energy to the unit cell to drive the discharge process which provides hydrogen as output.

A control system configured for controlling the flow control unit, the storage and charge control unit, is also present. The control system may also be configured for controlling discharging of the cell unit, optionally in combination with the charge control unit. Discharging to a load may comprise discharging electrical energy to a defined object, such as a vehicle, or more generally to an electrical grid.

Optionally the hybrid device may be provided with a temperature control system configured for controlling the temperature of the cell unit, typically within a certain range. As heat is developed during charging and overcharging, based on signals from the temperature control system the control system may control the charging control system.

Optionally the hybrid device may be provided with a pressure control system configured for controlling the pressure of the electrolyte in the cell unit and thus the pressure of the gas generated. Such a pressure control system may also be configured for controlling a compressor for storing the generated hydrogen at elevated pressure.

Electrodes The unit cell of the hybrid device comprises an iron based electron storage electrode and an air electrode.

Sintered iron electrodes require sufficient initial porosity for proper operation and material utilization.

A base material for a manufacturing process of iron electrodes, known from LIS4109060, is reduced iron particles with a high internal porosity. Other iron powders can be used similarly. The base materials may be mixed with pore forming compounds such as ammonium carbonate for the subsequent manufacturing process. The base materials may also be mixed with conductive additives such as carbon. Usually, the base materials are poured into a press mould and then pressed to an electrode body having the desired porosity and/or thickness. Finally, the pressed electrode body is sintered in a furnace in an inert or reducing atmosphere. The iron electrode may also be manufactured as outlined in WO2016178564A1. Larger sintered iron electrodes require an internal high density conductive network to allow for efficient distribution of the current inside the electrode. Optimized electric conductivity reduces the voltage drop from the current collector connection (aka tab) to the electrode surface and facilitates a more uniform voltage distribution. An improved voltage distribution enhances the material utilization during discharging and allows for more efficient charge utilization upon charging. In other words, the supplied charge contributes longer to the process of reduction of iron (Fe(OH)2 + 2e- -> Fe + 2OH-) during charging and hydrogen evolution can be delayed.

The formation of higher density areas as such is already known for iron-electrode manufacturing, e.g. from WO2022103893A1. This known production process is based on a continuous material distribution throughout the electrode with additional compaction at certain areas to achieve high density zones.

This approach of “edge coining” was also used in the 1980s by SNDC. Edge coining meant that the edges of the electrode were pressed to about halve of the thickness of the electrode. This measure increased the lifetime of the electrode and improved the electric conductivity across the electrode. In this way a uniform material distribution throughout the electrode was achieved.

In a further aspect the invention relates to a modified process of manufacturing an electrode, in particular the iron electrode, wherein a configuration is applied that allows for more electrode material to be positioned in areas where a higher density is required. According to this aspect of the invention a method of manufacturing an electrode having an integrated high density conductive network comprises the steps of supplying a particulate conductive material, in particular iron containing particles, in a press and supplying pressure and/or heat to the particulate conductive material in the press, wherein the step of supplying conductive material comprises providing the particulate conductive material in a press mould, such that the amount of particulate conductive material at predetermined positions is larger than at surrounding areas.

In this aspect of the invention a high density network is manufactured at predetermined positions by adding more material to these areas than to surrounding areas and then compressing it to a uniform thickness. Thereby more electrically conductive material is present in the high density zones, which results in increased conductivity, which reduces the voltage drop inside the electrode, as well as mechanical stability. The surrounding areas are porous and provide access for the electrolyte.

In an embodiment thereof, a press mould is used, which has recesses in areas where a higher density is desired. The recesses may be applied in a mould having a flat bottom (except for the recesses) for a discontinuous production process.

In an embodiment thereof a filling system, such as a moveable hopper, is used, which allows to pour more material on those areas where a higher density is desired. In both embodiments locally higher initial levels of active material are attained. By pressing these base materials with differing heights in a press with a flat surface to a uniform thickness, the areas which initially contain more material will be compressed more and will provide zones with a higher density, while the areas with a normal filling level will provide porosity for proper operation and material utilization.

In yet another embodiment thereof the recesses are applied in a roll mould for a continuous manufacturing process. In both processes manufacturing takes place in two stages. In a first stage the material is filled and pre-compacted in the shaped mould to a pre-compacted body. In a second stage the pre-compacted body is further compacted using a mould having a different surface shape, thereby forming an electrode with a desired overall low density with an integrated high density network at the predetermined positions in the electrode.

In the embodiment of a moveable filling system which can pour more material on predetermined areas, compacting can be done in a single step and the areas which have been provided with more material will form the high density zones.

The iron based electrode is subject to self-discharging upon stand-still, resulting in loss of capacity. In order to prevent this kind of self-discharge in an embodiment the iron based electrode is releasably mounted. When not in use, a charged iron based electrode may be removed and stored for longer times in an inert (in this case oxygen free) gas. For example, after removal the iron based electrodes may be rinsed with demi-water, allowed to dry in an inert atmosphere, and then packaged in an inert environment, e.g. in nitrogen or argon. A charged iron based electrode can also be stored in vacuum. The stored charged electrodes can be reloaded in the device upon demand.

In an embodiment of releasing the energy stored in the iron electrodes these electrodes are used as a separate energy source for the production of hydrogen. Releasing hydrogen is possible by using a cell comprising the charged iron electrodes. These electrodes are grouped, for example in groups 1,2,3.... N, each group comprising a number of charged iron electrodes. Then hydrogen can be generated by discharging the group 1 electrodes by using group 2 electrodes as counter electrode. The (discharging) reaction for the group 1 iron electrodes is: Fe + 2OH- -> Fe(OH)2 + 2e-. The (overcharging) reaction for the group 2 iron electrodes is: 2H2O + 2e- -> H2 + 2OH-, Thus upon discharging the group 1 iron electrodes the group 2 iron electrodes are overcharged and hydrogen is generated. Some voltage is necessary to drive the process, about 0.2V. When the group 1 electrodes are discharged, they are removed from the cell and stored for recharging. In the next sequence the group 2 electrodes are discharged using the group 3 electrodes as counter electrode (or vice versa). This procedure can go on until group n-1 is discharged using the last group n electrodes as counter electrode. The cell, wherein this sequence of discharging steps can take place, has a simple configuration. The iron electrodes can be arranged in parallel and/or serial configuration. Both groups involved in a discharging and overcharging step, share one electrolyte compartment. Gas separation is not required, because only hydrogen is produced. In another embodiment a charged iron based electrode is retained in the cell unit and stored therein under an inert gas. For example, when not in use, the electrolyte is removed from the electrolyte compartment, and the electrode is treated with a flow (flush/jet) of an inert gas to remove electrolyte droplets adhering to the electrode surface, then the electrode is rinsed with demi-water and allowed to dry and maintained under an inert gas atmosphere. In view thereof in an embodiment the electrolyte compartment is provided with a drain configured for discharging liquids (electrolyte and demi-water), as well as a gas inlet for introducing an inert gas.

The air electrode or reversible oxygen electrode can be arranged in a way that the reduction of oxygen occurs at the (dry) side of the air compartment in contact with a gas that comprises oxygen such as air and production of oxygen at the (wet) side of the electrolyte compartment in contact with the electrolyte, comparable to a gas diffusion electrode. Typically, the gas in the air compartment side will be maintained at a slight overpressure to avoid cross-over. The air electrode typically comprises an electrocatalyst, such as Ag or NiFeP on a porous support, for example a carbon based electrode. Advantageously at the electrolyte side the air electrode is hydrophilic and at the gas side the air electrode is hydrophobic.

Further details

As an oxygen source for the air electrode a gas mixture comprising oxygen can be used. If air is used, carbon dioxide needs to be removed from the air prior to introduction in the air compartment. An alkaline electrolyte, such as a strong KOH solution, absorbs carbon dioxide and together they may react to form carbonate ions, such as potassium carbonate. The carbonate accumulates in the system resulting in a reduced electrolyte conductivity and blocking of pores in the porous structured electrodes.

In an embodiment the hybrid device according to the invention comprises a carbon capturing unit configured for removal of carbon dioxide from a gas comprising oxygen and carbon dioxide, in communication with the gas inlet of the air compartment. A carbon capturing unit may be a scrubbing unit comprising an CO2 adsorbent like strong alkaline solution or an amine like monoethylamine.

Use of pure oxygen requires safety precautions, but allows to achieve a higher cell efficiency (about +60 mV).

Typically the hybrid device according to the invention comprises a plurality of cell units, wherein at least two of the cell units are arranged in series and/or wherein at least two of the cell units are arranged in parallel. A parallel configuration with external separation of hydrogen from oxygen allows a compact design. The electrodes can be accessed from both sides, which improves the material utilizations and reduces losses.

In yet another aspect the invention relates to a method of storing electrical energy and/or one or more energy carriers comprising hydrogen and/or oxygen using the hybrid energy storage and electrolyser device according to invention as described above. The method comprises the steps of supplying electrical power from an external power source to the cell unit, thereby providing an electrically charged iron based electrode and/or hydrogen and/or oxygen stored in the storage.

The external power source may be a renewable electricity source, such a solar energy, wind power, water power and combinations thereof. The stored energy whether electricity or hydrogen can be supplied subsequently on demand to an external load.

As explained above, in an embodiment the method further comprises exchanging an electrically charged iron based electrode for a fresh electrode, i.e. an uncharged iron based electrode, and storing the electrically charged iron based electrode in an inert atmosphere. In another embodiment the method further comprises replacing the electrolyte in the electrolyte compartment by an inert gas.

In an embodiment the method comprises also controlling the potential difference and/or current flow between the iron based electrode and the air electrode for simultaneous production of hydrogen and oxygen, in particular during overcharging.

In another embodiment the method comprises controlling the potential difference and/or current flow between the electrode for time shifted hydrogen and oxygen production. During charging the device is controlled such that the iron based electrode is reduced to iron metal avoiding overcharging (and thus generation of hydrogen) and generation of oxygen at the air electrode occurs, while during discharging iron is oxidized at the iron based electrode and oxygen, if supplied, is consumed at the air electrode. If the oxygen reactant is not supplied to the air electrode, the voltage between the iron electrode and the air electrode will start generating hydrogen from the available water in the aqueous electrolyte. Eventually a small amount of electrical energy needs to be supplied to the air electrode to release the hydrogen, e.g. about at most 0.5V at operation around 0.2V per cell unit. Thus in such an embodiment the method comprises controlling the potential difference and/or the current flow between the iron based electrode and air electrode for time shifted hydrogen production..

The invention is further illustrated in the attached drawings, wherein:

Fig. 1A is a diagrammatic view of an embodiment of a unit cell of a hybrid device according to the invention;

Fig. 1 B is a diagrammatic view of another embodiment of a unit cell of a hybrid device according to the invention;

Fig. 2A is a diagrammatic view of an embodiment of a hybrid device comprising a unit cell according to Fig. 1A;

Fig. 2B is a diagrammatic view of an embodiment of a hybrid device comprising a unit cell according to Fig. 1B;

Fig. 3 is a diagrammatic view of an embodiment of a parallel configuration of unit cells; Fig. 4 is a diagrammatic view of an embodiment of a serial configuration of unit cells;. Figs. 5A and 5B show schematically top views of embodiments of an iron based electrode having an integrated high density conductive network for improved electrical conduction; Fig. 6 shows possible shapes of recesses on the surface of an otherwise flat mould; and Fig. 7 shows an embodiment of a continuous production process.

Fig. 1 shows a diagrammatic view of an embodiment of a unit cell of a hybrid device for storage of electrical energy and/or producing hydrogen according to the invention. The unit cell, in its entirety indicated by reference number 10, comprises an iron based electrode 12. The connection thereof to a terminal is not shown in Fig. 1. In the unit cell 10 the iron based electrode12 faces an electrolyte compartment 14 configured for containing an aqueous alkaline electrolyte and hydrogen generated at the first iron based electrode 12. Opposite the iron electrode 12 a separator 16, like a membrane is arranged which separates the first electrolyte compartment 14 from a second electrolyte compartment 18. At the opposite side of the second electrolyte compartment an air electrode 20, such as gas diffusion electrode, is arranged. The air electrode 20 is also in contact with a gas compartment (air compartment) 22. The second electrolyte compartment 18 is configured to contain the aqueous alkaline electrolyte and oxygen generated at the air electrode 20. The air compartment 22 is configured for containing a gas, typically a gas mixture comprising oxygen such as air. The compartments 14, 18 and 22 each have an inlet and outlet (see Fig. 2A). The separator 16 is configured to block transport of gases (H2 and/or 02) and to allow transport of ion species (ion permeability) like hydroxyl and monovalent cations such as Na+, Li+ and K+. Spacers (not shown) may be present for spacing the separator and the electrodes. The main iron reduction reaction upon charging and the hydrogen evolution reaction during overcharging are shown for the iron based electrode 12, as well as the reversible reaction of oxygen at the air electrode. Multiple unit cells 10 may be arranged in a housing either in series or parallel. Fig. 1B shows a different embodiment of a unit cell having a single electrolyte compartment. In particular, a unit cell 110 comprises a first iron based electrode 112, a single electrolyte compartment 114, an air electrode 120, and an air compartment 122. Spacers (not shown) may be present in the compartments. Gases (H2 and 02) are generated in the same compartment, although on different electrodes 112, 120 respectively. Fig. 2A depicts an embodiment of a hybrid device having an electrical energy storing functionality and a gaseous energy carrier production functionality comprising a unit cell according to Fig. 1A, as explained above. The hybrid device 200 comprises the unit cell 10 having the iron based electrode 12 and air electrode 20. The electrolyte compartment 14 thereof comprises an inlet 24 for electrolyte and an outlet 26 for electrolyte and hydrogen gas. The outlet 26 is functionally connected via conduit 28 to gas liquid separator 30, where hydrogen gas is separated from the electrolyte. The separated hydrogen gas is stored in storage 32. A compressor (not shown) may be incorporated in order to allow storage of the hydrogen at high pressure. The separated electrolyte is recycled to the inlet 24 of the electrolyte compartment 24 via conduit 34. The iron based electrode 12 has a connector 36 for providing electrical connection to the external of the cell unit 10. The air electrode has a connector 37 for providing electrical connection to the external of the cell unit. The second electrolyte compartment 18 has an inlet 38 for electrolyte and an outlet 40 for electrolyte and oxygen gas. The outlet 40 is via liquid gas separator 42 connected to storage 44 for oxygen. This storage 44 may be omitted. The air compartment 22 has a separate inlet 46 for a gas that comprises oxygen, derived from a carbon dioxide scrubber 48, and an outlet 49. The hydrogen gas liquid separator 30 may comprise a H2 valve and/or H2O dryer and an 02 deoxidiser. The oxygen gas liquid separator 42 may comprise an 02 valve and/or a H2O/H2 condenser. A flow control system generally depicted with reference numeral 50 is configured to control the circulation of the electrolyte flows through the respective electrolyte compartments and associated circulation loop comprising the respective gas liquid separator, as well as for controlling the gas flow through the air compartment. A charge control unit 60 is configured for receiving electrical power from an external source 62 and for supplying the received electrical power to the cell unit 10 during charging and overcharging. The device may be controlled by a control system 70, that is configured for controlling at least the flow control unit 50, the charge control unit 60 and the storages 32, 44. Upon discharging electrical energy may be generated and supplied to an external load 80.

Fig. 2B depicts a diagrammatic view of an embodiment of a hybrid device having an electrical energy storing functionality and a gaseous energy carrier production functionality comprising a unit cell according to Fig. 1 B. The hybrid device 300 comprises the unit cell 110 having the iron based electrode 112 with electrical connector 136 and the air electrode 120 with electrical connector 137. The electrolyte compartment 114 has an inlet 124 for electrolyte and an outlet 126 for electrolyte and generated gases. The outlet 126 is functionally connected to a liquid gas separator 130. The separated gases comprising hydrogen and oxygen are separated from one another in gas separator 190 and hydrogen is stored in storage 132, while oxygen is stored in storage 144. The electrolyte is returned to the inlet 124 under control of a flow control unit 150. The air compartment 122 is provided with a separate inlet 146 for a gas that comprises oxygen, such as carbon dioxide depleted air, derived from a carbon dioxide scrubber 148, and an outlet 149. The flow control system 150 is configured to control the circulation of the electrolyte flow through the electrolyte compartment 114 and associated circulation loop comprising the gas liquid separator 130 . A charge control unit 160 is configured for receiving electrical power from an external source 162 and for supplying the received electrical power to the cell unit 110 during charging and overcharging. The device may be controlled by a control system 170, that is configured for controlling at least the flow control unit 150, the charge control unit 160 and the storages 132, 144. Upon discharging electrical energy may be generated and supplied to an external load 180.

A control system 70, 170 may also be configured to additionally control the compartment pressures, storage pressures, charge/overcharge/discharge management and so on. A plurality of unit cells 10 or 110 is typically arranged in a housing.

The various functions may be part of subsystems, e.g. for each cell compartment and storage, such that conditions can be adjusted at wish, allowing optimization.

The iron based electrode may be releasably mounted in the unit cell, such that instead of producing hydrogen upon overcharging, the metallic iron electrode is exchanged for a fresh uncharged iron based electrode, wherein the charged metallic iron electrode is stored in a protected inert environment for later use as a battery.

Fig. 3 shows a parallel configuration of multiple, mirrored unit cells according to embodiment of Fig. 1 B, and Fig. 4 shows a serial configuration of unit cells according to embodiment of Fig. 1B having bipolar plates 195 between the unit cells.

Fig. 5 shows an iron based electrode 212 with a current collector tab 224 having high density areas 226, in this embodiment relatively thin strips or lines, and lower density zones 228 for optimized material utilization. These zones 226 extend from the current collector tab 224 to the edge surfaces 230 of the electrode 212. The edges of the electrode and the area below the current collector tab maybe high density zones. Fig. 5A schematically illustrates an optimized iron bases electrode having the current collector tab at the side. In the embodiment of Fig. 5B the current collector tab 224 is arranged in the middle. Fig. 6 shows possible shapes of recesses 250 on the surface of a flat mould 252. These recesses represent a negative of the high- density conductive network integrated in the electrode.

Fig. 7 shows an embodiment of a continuous manufacturing process of iron electrode. Base material is fed from a hopper 700 between a first set of roll moulds 702. Optionally a current collector 706is centrally fed between the nip of the roll moulds 702. The roll moulds 702 are provided with recesses (not shown; compare Fig. 6; negative of high density network). The circumference of a roll mould 702 matches a multitude of the electrode size. The first set of roll moulds 702 ensures pre-compaction. From the first set of roll moulds 702 the thus precompacted body is fed between a second set of moulds 704 without recesses, wherein the pre-compacted body is further compacted to an uniform thickness, thereby achieving an iron based electrode having porous areas and areas of high density.

Claims

1. Hybrid energy storage and electrolyser device for storage of electrical energy and production of energy carriers, such as hydrogen, comprising at least one cell unit comprising an iron based electron storage electrode configured for reduction of iron compounds to metallic iron upon charging and for hydrogen evolution upon overcharging and for oxidation of metallic iron to iron compounds upon discharging, having a first electrical connection; an air electrode configured for oxygen evolution upon charging and overcharging and oxygen and/or water conversion into hydroxyl ions and/or hydrogen upon discharging, having a second electrical connection; at least one electrolyte compartment configured for containing an electrolyte and gases generated at one or more of the electron storage electrode and air electrode, and having a liquid inlet and an outlet for liquid and gases; an air compartment configured for containing a gas, in particular a gas comprising oxygen, having a gas inlet and a gas outlet; a liquid-gas separation unit, configured for separating the electrolyte and gases generated at one or more of the electron storage electrode and air electrode; a storage configured for storing separated gases external from the cell unit, and being in fluid communication with the liquid-gas separation unit; a flow control unit configured for circulating a flow of electrolyte through the electrolyte compartment and liquid-gas separation unit; a charge control unit configured for receiving electrical power from an external power source and configured for supplying electrical power received from the external power source to the cell unit during charging and overcharging and configured for receiving electrical power from the cell unit and configured for supplying electrical power received from the cell unit, during discharging to an external load; a control system configured for controlling the flow control unit, the storage and charge control unit.

2. Hybrid energy storage and electrolyser device according to claim 1, further comprising a gas separator for separating hydrogen gas from oxygen gas.

3. Hybrid energy storage and electrolyser device according to claim 2, comprising a first electrolyte compartment configured for containing a first electrolyte and generated hydrogen and a second electrolyte compartment configured for containing a second electrolyte and generated oxygen gas, wherein the first electrolyte compartment and the second electrolyte compartment are separated by the gas separator, wherein the gas separator comprises a membrane configured for conducting ions and blocking gases.

4. Hybrid energy storage and electrolyser device according to claim 2, comprising an external gas separator in communication with the separation unit.

5. Hybrid energy storage and electrolyser device according to any one of the preceding claims, wherein the air electrode is a gas diffusion electrode, a side contacting the electrolyte compartment and another side contacting the air compartment.

6. Hybrid energy storage and electrolyser device according to any one of the preceding claims, wherein the iron based electrode is releasably mounted.

7. Hybrid energy storage and electrolyser device according to any one of the preceding claims, wherein the electrolyte compartment is provided with a drain configured for discharging liquid from the electrolyte compartment, and a gas inlet for supplying inert gas.

8. Hybrid energy storage and electrolyser device according to any one of the preceding claims, further comprising a carbon dioxide capturing unit configured for removal of carbon dioxide from a gas comprising oxygen and carbon dioxide, in communication with the gas inlet of the air compartment

9. Hybrid energy and electrolyser according to any one of the preceding claims, comprising a plurality of cell units, wherein at least two of the cell units are arranged in series and/or wherein at least two of the cell units are arranged in parallel.

10. Energy system comprising the hybrid energy storage and electrolyser device according to any one of the preceding claims and an external power source and/or an electricity grid.

11. A method of storing electrical energy and one or more energy carriers comprising hydrogen and/or oxygen using the hybrid energy storage and electrolyser device according to any one of the preceding claims, comprising the steps of supplying electrical power from the external power source to the cell unit, thereby providing an electrically charged iron based electrode and/or hydrogen and/or oxygen stored in the storage.

12. Method according to claim 11, further comprising exchanging an electrically charged iron based electrode for an uncharged t iron based electrode, and storing of the electrically charged iron based electrode in an inert atmosphere.

13. Method according to claim 11, further comprising replacing the electrolyte in the electrolyte compartment by inert gas.

14. Method according to claim 11, comprising controlling the potential difference and/or the current flow between the iron based electrode and air electrode for simultaneous hydrogen and oxygen production.

15. Method according to claim 11, comprising controlling the potential difference and/or the current flow between the iron based electrode and air electrode for time shifted hydrogen production.

16. Method of manufacturing an electrode having an integrated high density conductive network, comprising the steps of supplying a particulate conductive material in a press and supplying pressure and/or heat to the particulate conductive material in the press, wherein the step of supplying conductive material comprises providing the particulate conductive material in a mould, such that the amount of particulate conductive material at predetermined positions is larger than at surrounding areas.

17. Method according to claim 16, wherein the particulate conductive material comprises iron containing particles.