HK1260067A1 - Photoelectrochemical cell, photoelectrode and method of manufacturing a photoelectrode - Google Patents

Description

Photoelectrode of Substrate Electrode (SE) interface irradiation type and photoelectrochemical cell

The present application claims the benefit of european patent application EP15382658.1 filed on 12/23/2015.

Technical Field

The present disclosure relates to photoelectrodes for photoelectrochemical cells, in particular for filter press photoelectrochemical cells. The disclosure further relates to a method of manufacturing such a photoelectrode and a photoelectrochemical cell comprising the photoelectrode.

Background

Photoelectrochemical cells for oxidation and reduction (redox) reactions are well known. In photoelectrochemical cells, e.g. CO₂Can be reduced at the cathode while oxygen evolution occurs at the anode. Electrochemical reactions of carbon dioxide are known to produce organic compounds. Alternatively, water can be reduced to hydrogen, in which case hydrogen is obtained at the cathode and oxygen is evolved at the anode. Hydrolysis under the action of radiation is a known way of producing hydrogen as a clean chemical fuel.

Photoelectrodes based on absorbers made of semiconductors with a band gap in the central range of the solar spectrum are known to optimize photon absorption efficiency. Such photoelectrodes have been used to increase the productivity of photoelectrochemical reaction processes in order to achieve better yields than using metal oxide absorbers (e.g., such as TiO)₂Such as broadband semiconductors) that have higher current densities and lower diffusion lengths for minority carriers, such metal oxide absorbers typically have higher bandgaps and greater losses due to higher recombination of photogenerated carriers.

In this sense, photoelectrodes based on semiconductor materials, such as silicon, III-V compounds (GaAs or Gap, etc.), have been used in photoelectrochemical processes to increase current density. Their bandgap dependence on the solar spectrum, passivation options to obtain small surface recombination velocities and the resulting increased lifetime of minority carriers and at the same time controllable doping levels allow higher current densities to be achieved than those obtained with metal oxide absorbers having larger bandgaps, and increase the open circuit voltage (close to their theoretical maximum). An example of obtaining a current density using different absorbers may be, for example, TiO₂Photoelectrode: 1.2mA/cm²(ii) a And silicon-based photoelectrodes: 18mA/cm²。

Generally, such photoelectrode is used in a case where light is incident on an electrolyte electrode interface (EE irradiation), that is, a photoelectrocatalytic reaction occurs on an irradiated side of the photoelectrode, and thus a photoelectrocatalytic system cannot be efficiently formed as a photoelectrode on, for example, a photoelectrochemical cell (PEC) having a filter press configuration. In such systems, the photons need to cross the electrolyte solution with the result that some of the photons are lost by being absorbed in the electrolyte solution. Thus, there is a need for highly transparent electrolytes in the energy range of the solar spectrum. Furthermore, the use of an electrolytic catalyst layer to activate the electrocatalytic process constitutes another limiting factor for photon absorption, as it is a limiting factor for the effective transparency of the system. In addition, the deposition of the electrocatalyst layer at the illuminated interface constitutes a limiting factor in optimizing the passivation process to increase the minority carrier lifetime and optimizing the system design (from an optical perspective), for example by providing an anti-reflection layer.

Other known systems use silicon as the wafer/substrate, with light incident at the substrate electrode interface (SE illumination type). However, in SE illumination, the electrode-electrolyte interface is on the opposite side with respect to the incident light, and due to the thickness of the absorber (which is typically greater than the carrier diffusion length), most of the electrons are lost due to recombination near the substrate surface. The photocurrent generated by, for example, a SE-irradiated silicon (Si) substrate is thus limited.

It is an object of the present disclosure to provide a photoelectrode for a photoelectrochemical cell, for example having a filter press configuration, which is capable of operating under SE illumination and which at least partially overcomes the drawbacks of the prior art, thereby increasing the current density produced.

Disclosure of Invention

In a first aspect, a photoelectrode for a photoelectrochemical cell is provided. The photoelectrode extends from a front end surface to an opposite back end surface, wherein the front end surface is illuminated, in use, by incident light and the back end surface contacts, in use, an electrolyte of the photoelectrochemical cell. The photoelectrode includes: a back contact solar cell extending from a solar cell front surface to an opposite solar cell back surface facing the back end surface, the solar cell front surface constituting, in use, a photoelectrode front end surface to be illuminated by incident light, wherein the solar cell back surface comprises an emitter contact and a collector contact. The emitter contact and the collector contact are spaced apart by a first opening in the back surface of the solar cell, the emitter contact and the collector contact being collected in an emitter busbar and a collector busbar, respectively. The photoelectrode further comprises a contact passivation layer covering the back surface of the solar cell to separate the emitter contact and the collector contact from the electrolyte when in use. The contact passivation layer further includes a second opening corresponding to the first opening of the back surface of the solar cell. The photoelectrode further comprises a resin layer covering the opening and a portion of the contact passivation layer such that, in use, only charge carriers from the emitter contact pass through the contact passivation layer in their path to the electrolyte, while charge carriers from the collector contact are collected in the collector busbar. The photoelectrode further comprises an electrocatalyst layer covering the resin layer, the contact passivation layer, or both, respectively, wherein the electrocatalyst layer constitutes the back end surface that contacts the electrolyte in use.

According to this aspect, there is thus provided a SE irradiation type photoelectrode suitable for a photoelectrochemical cell. To this end, the present disclosure starts from a known back contact solar cell which is insulated (waterproof) in a special way so as to be able to operate in contact with an electrolyte. This particular way starts with a coating with a passivation layer to prevent the contacts of the solar cell from corroding in contact with the electrolyte, and a resin layer is provided corresponding to the collector contacts. In this way, the flow of charge carriers from the collector contacts, i.e. the contacts not covered by resin, cannot pass through the passivation layer to contact the electrolyte of the photoelectrochemical cell, but they are collected in the collector busbars. In other words, the region covered with the resin corresponds to the collector region, and the region not covered with the resin corresponds to the emitter region.

As used herein, the term "busbar" should be understood to mean a region, such as a metal strip or rod, in which electrical contacts can be collected or concentrated for further transfer to, for example, a counter electrode.

In some examples, the contact passivation layer may include titanium (Ti). In other examples, the contact passivation layer may include a metal selected from chromium (Cr), aluminum (Al), zinc (Zn), alloys thereof, and combinations thereof.

This special insulation also comprises the provision of an electrocatalyst layer to facilitate/accelerate the interaction of charge carriers from the emitter region (contacts not covered by the resin layer) of the photoelectrode with the reactants in the electrolyte when incident light impinges on the opposite surface (front end surface) of the photoelectrode. By doing so, a back contact solar cell or a substrate electrode interface (SE) irradiation type cell can be used in a photoelectrochemical cell in which an electrochemical redox reaction is performed with an electrolyte.

Throughout this disclosure, a back contact solar cell should be understood as a solar cell in which both the emitter contact and the collector contact are disposed on the same side (rear side) opposite to the side (front side) from which light is radiated. This means that inside the photoelectrochemical cell the electrode-electrolyte interface is on the opposite side with respect to the incident light. Examples of known back contact solar cells may include, for example, interdigitated back contact cells (IBC).

The fact that the contacts are located on the back surface (opposite to the surface irradiated by the light) ensures that the entire front surface of the photoelectrode is an effective photon absorption surface. In this way, photons from the incident light no longer need to pass through the electrolyte solution, thus avoiding a loss of part of the photons due to absorption in the electrolyte solution. This also affects the elimination of the need for the type of electrolyte that can be used as a high transparency electrolyte in the solar spectral energy range. Thus saving costs.

Another aspect of using SE illumination is that it provides a greater degree of freedom, at least in terms of the structure and material of the front end surface, at least when compared to the structure and material of the photoelectrode used for EE illumination. This is because when SE or back illumination is used, the front end surface does not need to contact the electrolyte, thereby reducing corrosion of the front end surface and thus extending the life of the photoelectrode.

The use of SE illumination further promotes an increase in the effective area of the electrode, since the rear end surface of the photoelectrode can all contact the electrolyte. In addition, all contacts (emitter and collector) are provided at the back surface, thus simplifying their collection and preventing shadow loss.

In some embodiments, the back contact solar cell can include a semiconductor substrate having a substrate front surface defining the solar cell front surface and an opposing substrate back surface facing the solar cell back surface.

In these embodiments, the semiconductor substrate may be selected from n-type and p-type. The back contact solar cell may further include one or more n⁺Type doped region and p⁺And a type doped region. N is⁺Type doped region and p⁺The n-type doped regions may be alternately disposed on the back surface of the substrate⁺Type doped region and p⁺The distribution of the type-doped regions depends on the type of the semiconductor substrate. The back contact solar cell may further include a metal collector covering the n⁺Type doped region and p⁺A type doping region to define the emitter contact and the collector contact such that, in use, the metal collector collects the emitter region in the emitter busbar and the collector region in the collector busbar. In this case, the solar cell backThe first opening of the surface may be aligned with said n⁺Type doped region and p⁺The junction between the type-doped regions is disposed in the metal collector in a corresponding manner, thereby separating the emitter contact from the collector contact. In these cases, the metal collector constitutes the back surface of the solar cell.

As used herein, a p-type semiconductor should be understood to contain primarily free holes, while an n-type semiconductor should be understood to contain primarily free electrons. Further, n is⁺Denotes an n-type semiconductor with a high doping concentration, and p⁺Representing a p-type semiconductor with a high doping concentration.

One or more n are provided on the back surface of the substrate⁺Type doped region and p⁺The type-doped regions allow, for example, alternating distribution of holes and electrons, thus optimizing current density and open circuit voltage. And providing a metal collector overlying the doped region allows emitter and collector contacts to be collected independently at each busbar, thus ensuring that the back end surfaces are not in electrical contact. This enhances the passivation of the back end surface, i.e. optimizes the surface recombination velocity and thus extends the lifetime of the charge carriers travelling to the doped region.

In some embodiments, the solar cell may further include a first passivation layer disposed between the metal collector and the doped region. The first passivation layer may be provided with a further opening corresponding to each doped region, such that in use the further opening allows charge carriers to migrate from the doped region to the metal collector. The provision of the first passivation layer avoids or at least reduces recombination at the surface of the doped region. This enhances the efficiency of photon exit from the incident light. In some examples, the first passivation layer may include silicon dioxide (SiO)₂) Aluminum oxide (Al)₂O₃) Or a combination thereof. Alternatively, oxynitrides or nitrides such as Si are foreseen₃N₄。

In some embodiments, the photoelectrode may further comprise an anti-reflection layer covering a portion or portions of the front surface of the solar cell which, in use, are illuminated by incident light. The provision of the anti-reflection layer increases the photon absorption efficiency. In some of these cases, the entire front surface of the solar cell may be covered with the antireflection layer.

In some of these embodiments, the anti-reflection layer may include aluminum oxide (Al)₂O₃). In further embodiments, the anti-reflective layer may include hafnium oxide (HfO)₂) Silicon monoxide (SiO), zirconium dioxide (ZrO)₂) Tantalum oxide (Ta)₂O₅) Cerium fluoride (CeF)₂) Magnesium oxide (MgO), magnesium fluoride (MgF)₂) Or titanium dioxide (TiO)₂). In some of these embodiments, the anti-reflective layer may comprise a roughened surface, which may be made, for example, by a nano-structuring technique.

In some embodiments, the photoelectrode may further include a second passivation layer disposed between the photocatalyst layer and the resin layer or the photocatalyst layer and the contact passivation layer. In some examples, the second passivation layer may include titanium dioxide (TiO 2). In further examples, other metal oxides are contemplated, such as aluminum oxide (Al)₂O₃) And silicon dioxide (SiO)₂). The second passivation layer reinforces an already existing contact passivation layer that is configured to improve stability against photoelectrode corrosion. In a further alternative form, electronically (or hole) conducting resins or polymers are foreseen.

In some embodiments, based on metal oxides such as TiO₂、SiO₂、Al₂O₃The second passivation layer may have a thickness from 1nm to 250 nm. When Al is used₂O₃Or SiO₂In some cases, a thickness of about 1nm to 5nm may be previously obtained due to the tunnel effect.

The second passivation layer may be deposited using any deposition technique known in the art, such as Atomic Layer Deposition (ALD), Chemical Vapor Deposition (CVD), Pulsed Laser Deposition (PLD), sputtering, sol-gel process, doctor blading, screen printing, or spray painting. In some embodiments, the second passivation layer may further include a doping element, such as aluminum (Al), niobium (Nb), or vanadium (V).

In some embodiments, the resin layer may be made of a polymer having high chemical resistance and heat resistance. In some cases, a polyamic acid formulation may be envisioned. For example, commercially available from Fujifilm electronics materialsIn some of these examples, the resin layer may have a heat resistance equal to or higher than 200 ℃ and higher than 10 ℃¹⁶Volume resistivity of Ohm cm.

In some embodiments, the electrocatalyst may be selected from a metal, a metal oxide or hydroxide, a metal nitride, a metal phosphide, or a conductive polymer. The electrocatalyst may be selected as a function of the reactions to be carried out in the photoelectrochemical cell, as will be apparent to the skilled person.

In some embodiments, the resin layer may cover a portion of the contact passivation layer corresponding to the collector contact, such that in use only charge carriers from the emitter contact pass through the contact passivation layer in their path to contact the electrolyte of the photoelectrochemical cell, while positive charge carriers (holes) from the collector contact are collected in the collector busbar. In these cases, the photo-electrode is a cathode. The holes of the collector contacts collected in the collector busbars can thus be conveyed to the counter electrode (anode) forming part of the photoelectrochemical cell.

In some embodiments, the resin layer may cover a portion of the contact passivation layer corresponding to the collector contact, such that in use only positive charge carriers (holes) from the emitter contact pass through the contact passivation layer in their path to contact the electrolyte of the photoelectrochemical cell, while electrons from the collector contact are collected in the collector busbar. In these cases, the photoelectrode is the anode. Electrons collected in the collector contacts in the collector busbars in use can thus be transferred to the counter electrode (cathode) forming part of the photoelectrochemical cell.

In a further aspect, a photoelectrochemical cell may be provided. The photoelectrochemical cell comprises a first photoelectrode substantially as described above. The first photoelectrode is arranged such that, in use, incident light irradiates a front end surface thereof, while a rear end surface thereof contacts the electrolyte.

Within the photoelectrochemical cell, the overall process is thus composed of two main parts: light absorption by the solar cell, resulting in the generation of charge carriers (emitter and collector contacts); and driving a catalytic reaction when in contact with the electrolyte with the excited photo-carriers. The inventors have found that the use of a photoelectrode substantially as described above results in an improved efficiency of the example of a photoelectrochemical cell.

In yet another aspect, a method of manufacturing a photoelectrode substantially as described above is provided. The method comprises the following steps: providing a back contact solar cell; and arranging a contact passivation layer covering the back surface of the solar cell, wherein the contact passivation layer is provided with a second opening corresponding to the first opening. The method further comprises the following steps: providing a resin layer to seal the openings, wherein the resin layer further covers a portion of the contact passivation layer corresponding to the collector contact; and providing an electrocatalyst layer covering the resin layer and the contact passivation layer, respectively.

Drawings

Non-limiting examples of the present disclosure will now be described with reference to the accompanying drawings, in which:

FIG. 1a shows a cross-sectional view of a photoelectrode according to one embodiment;

FIG. 1b shows an exploded view of FIG. 1 a;

FIGS. 2a and 2b show cross-sectional views of a photocathode and a photoanode, respectively, according to one embodiment;

FIG. 2c shows a top view of an interdigitated version of emitter and collector contacts;

FIG. 3 shows a top view of the photoelectrode of FIG. 2a disposed in a photoelectrochemical cell;

FIG. 4 shows the photocathode current density (i) in the photoelectrode according to example 1_{Cathode electrode}) Varies as a function of the potential of the respective photoelectrode;

FIG. 5a shows the photoanode current density (i) in a photoelectrode according to example 2_Anode) Varies as a function of the potential of the respective photoelectrode;

FIG. 5b shows the anodic current density (i) as a function of time when an absolute value voltage is applied according to example 2_Anode)；

FIG. 6 shows photoelectrode current density (i) in a photoelectrode according to example 3_{Cathode electrode}) Varies as a function of the potential of the respective photoelectrode;

FIG. 7a shows photoelectrode cathode current densities (i) according to examples 4a and 4b_{Cathode electrode}) As a function of the potential of the respective photoelectrode (the solid black line indicates photoelectrode with Pt-example 4 a; gray dashed line indicates photoelectrode with Ni — Mo — example 4 b);

FIG. 7b shows the photocathode current density as a function of time (i) when applying an absolute value voltage to a photoelectrode with Pt according to example 4a_{Cathode electrode}) (ii) a And

FIG. 7c showsPhotoelectrode current density (i) as a function of time when applying an absolute value voltage to a photoelectrode having Ni-MO according to example 4b_{Cathode electrode})。

Detailed Description

In all the following figures, the same reference numerals will be used for matching parts.

Fig. 1a and 1b show cross-sectional views of a photoelectrode according to one embodiment.

The photoelectrode may extend from a front end surface 10 to an opposite back end surface 20. The front end surface 10 is in use illuminated by incident light L, while the back end surface 20 is in use in contact with the electrolyte of the photo electrochemical cell.

As shown in fig. 1a and 1b, the photoelectrode may comprise a back contact solar cell 100 that may extend from a solar cell front surface 110 to an opposing solar cell back surface 120. The solar cell front surface 110 may define a photoelectrode front end surface 10 that is illuminated, in use, by incident light L.

In this embodiment, the solar cell back surface 120 may include emitter contacts E and collector contacts C. The contacts E and C may be spaced apart by the first opening 101 of the solar cell back surface 120. The emitter contacts E and the collector contacts C may cross each other, i.e. be arranged in alternating rows. See fig. 2 c. Emitter contact E and collector contact C may be arranged in an interdigitated manner, defining a "finger", and may be collected at opposite ends, i.e. emitter contact E may be collected in emitter buss bar 111 or pad region, and collector contact C may be collected in collector buss bar 121 or pad region. In alternative embodiments, other ways of alternately arranging the emitter contact and the collector contact are foreseen, as long as the region of the emitter contact can be identified/distinguished from the region of the collector contact and the collector contact can be collected and/or gathered for further transmission (in use) to e.g. the counter electrode.

The photoelectrode may further include a contact passivation layer 130 covering the back surface 120 of the solar cell. When the photoelectrode is used in a photoelectrochemical cell, the contact passivation layer separates the emitter contact E and the collector contact C of the solar cell back surface 120 from the electrolyte. This reduces corrosion of contacts disposed at the back surface of the solar cell. In these cases, the contact passivation layer 130 may include titanium (Ti). Alternatively, the contact passivation layer may include chromium (Cr), aluminum (Al), zinc (Zn), or an alloy thereof.

The contact passivation layer 130 may further include a second opening 131 corresponding to the first opening 101 of the solar cell back surface 120.

A resin layer 140 may be further provided to seal the openings 101 and 131. In the embodiment of fig. 1a and 1b, the resin layer may comprise a portion 141 covering the interior of the first and second openings 101, 131 and another portion 142 covering an adjacent area at or near the mouthpiece of the second opening 131. In these cases, the resin layer may further include a portion 143 covering a portion of the contact passivation layer corresponding to the collector contact C. Thus, in use, only charge carriers from the emitter contact E traverse the contact passivation layer 130 in their course of reaching the electrolyte, while charge carriers from the collector contact C are collected in the collector busbar (see fig. 2C). In the alternative, the portion of the resin layer that seals the openings may have other distributions, such as plugs or straight layers, as long as it can seal the openings.

In all cases, the resin layer may include a polyamic acid formulation that is commercially available asObtained from Fujifilm Electronic Materials.

In addition, in this embodiment, the electrocatalyst layer 150 may cover the resin layer 140, the contact passivation layer 130, or both, respectively. The electrocatalyst layer 150 thus constitutes the back end surface 20 of the photoelectrode which, in use, contacts the electrolyte.

Fig. 2a and 2b show cross-sectional views of a photocathode and a photoanode, respectively, according to another embodiment. The embodiment of fig. 2a and 2b differs from the embodiment of fig. 1a and 1b in that a passivation layer 160 may be disposed between the electrocatalyst layer 150 and the resin layer 140 or between the electrocatalyst layer 150 and the contact passivation layer 130. In these embodiments, the passivation layer 160 may include titanium dioxide (TiO)₂). In alternative embodiments, the passivation layer may include other metal oxides, such as, for example, aluminum oxide (Al)₂O₃) Silicon dioxide (SiO)₂) Or molybdenum disulfide (MoS)₂). In yet another embodiment, resins or polymers that conduct electrons (or holes) are contemplated.

The embodiment of fig. 2a and 2b further differs from the embodiment of fig. 1a and 1b in that a back contact solar cell comprising a semiconductor substrate or wafer is shown. The semiconductor substrate may be a monocrystalline silicon or polycrystalline silicon (c-Si) semiconductor substrate. In fig. 2a, a p-type c-Si semiconductor substrate 102 is shown, while in fig. 2b an n-type c-Si semiconductor substrate 103 is shown. In alternative embodiments, other semiconductor substrates capable of absorbing incident light and generating free charge carriers are contemplated. For example amorphous silicon, cadmium telluride (CdTe), III-V compounds such as gallium arsenide (GaAs) or gallium phosphide (GaP), or chalcogenides such as CIS or cuprum indium gallium arsenide (CIGS), among others.

In both cases, the semiconductor substrate or wafer may extend from a substrate front surface 1022, 1032 (see fig. 1a and 1b) facing the solar cell front surface to an opposite substrate back surface 1021, 1031 facing the solar cell back surface. The substrate back surfaces 1021, 1031 may be provided with n arranged alternately (e.g., crossing each other)⁺Type doped regions 1 and p⁺And doping regions 2, thereby forming a plurality of rows of contacts (corresponding to the doped regions). In these cases, n⁺Type doped regions 1 and p⁺Type dopingRegion 2 may be covered by a metal collector 170, which metal collector 170 may be provided with n⁺Type doped regions 1 and p⁺The junction between the type doping regions 2 corresponds to an opening. The metal collector may thus have a geometry matching the doped region. In this embodiment, the metal collector may be made of, for example, aluminum. Alternatively, other metals, conductive polymers or conductive metal oxides such as AZO or ITO are contemplated.

In addition, in this embodiment, as shown in fig. 2a and 2b, a passivation layer 180 may be disposed between the doped regions 1, 2 and the metal collector 170. The passivation layer 180 may be provided with openings 181 corresponding to the doped regions 1, 2, such that in use these openings 181 allow charge carriers to be transported from the doped regions 1, 2 to the metal collector 170. In this case, the passivation layer may be made of, for example, silicon dioxide (SiO)₂) Or aluminum oxide (Al)₂O₃) And (4) preparing.

In the embodiment of fig. 2a, the resin layer 140 may cover p and p of the contact passivation layer 130⁺The type doping region 2. In these cases, only from n⁺Charge carriers of type-doped region 1 may contact the electrolyte in the photoelectrochemical cell in their path through metal collector 170 and contact passivation layer 130. In addition, in these cases, p is derived from⁺Charge carriers of the type-doped region 2 may be captured by the metal collector 170 and collected in a collector busbar (see fig. 2c) and thereby configured to be transported to a counter electrode, which may be provided in a photo electrochemical cell. This means that p/p⁺The junction (semiconductor type/doped region type) can be isolated from the electrolyte, and p/n⁺The junction may be in electrical contact with the electrolyte to transfer corresponding charge from the emitter contacts to the electrocatalyst. The photoelectrode is thus the cathode.

In this embodiment, the electrocatalyst layer 150 may be formed from a material selected from a Hydrogen Evolution Reaction (HER) catalyst capable of reducing water to hydrogen or capable of reducing CO₂Reduction to e.g. CO, CH₄HCOOH and C₂H₄CO of products such as₂Reduction ofCatalyst preparation of the catalyst. In alternative cases, other catalysts may be envisaged, such as for example nitrate and nitrite reduction catalysts in aqueous solution.

In the embodiment of fig. 2b, the resin layer 140 may cover n of the contact passivation layer 130⁺The type doping region 1. In these cases, only p is from⁺Charge carriers of type-doped region 2 may contact the electrolyte in the photoelectrochemical cell in their path through metal collector 170 and contact passivation layer 130. In addition, in these cases, n is the number of atoms from⁺Charge carriers of the type-doped region 1 may be captured by the metal collector 170 and collected in the collector busbar, thereby being configured to be transported to a counter electrode, which may also be provided in the photoelectrochemical cell. This means that n/n⁺The junction (semiconductor type/doped region type) can be isolated from the electrolyte, and n/p⁺The junction may be in electrical contact with the electrolyte to transfer corresponding charge from the emitter contacts to the electrocatalyst. The photoelectrode is thus the anode.

In this embodiment, the electrocatalyst layer 150 may be made from a catalyst selected from Oxygen Evolution Reaction (OER) catalysts. The OER catalyst is capable of oxidizing water to oxygen. Examples of these catalysts may include nickel (Ni), iron-nickel alloys (Ni-Fe), molybdenum (Mo), iron (Fe), iridium (Ir), tantalum (Ta), rubidium (Ru), and alloys, hydroxides, oxides thereof. In the alternative, other catalysts, such as catalysts for the electro-oxidation of contaminants in aqueous solution, may be foreseen.

In all cases, the electrocatalyst may depend on the photoelectrode, if it is the photoanode or the photocathode, and the target molecules to be reduced or oxidized in the reactions to be performed in the electrochemical cell. From a general point of view, if the photoelectrode is a photoanode, a good oxygen precipitating agent is desired, such as an OER catalyst capable of oxidizing, for example, water to oxygen. If the photoelectrode is a photocathode, an electrocatalyst (HER catalyst) capable of reducing water to hydrogen is desired. Alternatively, it is also desirable to be able to be at CO₂Is reduced intoCO is generated during formic acid₂An electrocatalyst that reduces to products such as Sn.

In other cases, the electrocatalyst may be selected from a metal, a metal oxide or hydroxide, a metal nitride, a metal phosphide, or a conductive polymer. Generally, it is an object to provide an electrocatalyst suitable for the desired oxidation or reduction reactions. The electrocatalyst may be deposited directly on the surface of the electrode, on a protective coating (such as TiO2), or on a more porous conductive substrate by several methods as a wire mesh or foam to increase the active surface area and thus enhance electron transfer with the electrolyte at the contact surface.

The embodiment of fig. 2a and 2b further differs from the embodiment of fig. 1a and 1b in that the substrate front surfaces 1022, 1032 can be textured. In these cases, the texture may take the shape of an inverted pyramid. Other alternative shapes are contemplated. One aspect of providing a textured shape is that it reduces reflections by increasing the chance that reflected light bounces back into the surface rather than out into the surrounding air. This means that the effective photon absorption is thus increased. In these cases, the incident path created by the inverted pyramid increases the effective light absorption.

The embodiment of fig. 2a and 2b also differs from the embodiment of fig. 1a and 1b in that an anti-reflection layer 190 may be provided covering the substrate front surfaces 1022, 1032. In these embodiments, the anti-reflection layer may include aluminum oxide (Al)₂O₃). Alternatively, other antireflective materials may be used, such as hafnium oxide (HfO)₂) Silicon monoxide (SiO), zirconium dioxide (ZrO)₂) Tantalum oxide (Ta)₂O₅) Cerium fluoride (CeF)₂) Magnesium oxide (MgO), magnesium fluoride (MgF)₂) Or titanium dioxide (TiO)₂). The provision of an anti-reflection layer enhances photon absorption at least by reducing the reflectivity of incident light.

In addition, in these embodiments, the antireflection layer may be provided so as to cover the entire front surface of the substrate. In more cases, the substrate front surface may be only partially covered by an anti-reflection layer.

An anti-reflection layer substantially as described above may further be provided in the substrate having a flat front surface.

Substrates all photoelectrodes such as those described above can be used in photoelectrochemical cells.

Fig. 2c shows a plan view of the interdigitated emitter and collector contacts of either of fig. 2a and 2 b. In this figure, the interdigitated arrangement of doped regions can be clearly identified as an alternating arrangement and extends up to the rows or fingers 11, 12 (corresponding to the emitter and collector contacts) of the busbar or pad regions 111, 121, respectively, where the active current can be collected for transfer to the counter electrode. In this embodiment, the "bus bar" or pad regions 111, 121 are disposed at opposite ends along the longitudinal length of the doped regions of the solar cell.

Fig. 3 shows one embodiment of a photoelectrochemical cell that may include a compartment (e.g., a tank) 3 filled with an electrolyte. In the wall of the compartment 3, a first photoelectrode 5 (i.e. photocathode) may be provided, substantially as shown in fig. 2 a. In an alternative case, the first photoelectrode may be substantially as shown in any one of fig. 1a, 1b or 2 b.

Additionally, in the embodiment of fig. 3, the second electrode 4 may be arranged within the compartment 3 and spaced apart from the first photoelectrode 5. In this case, the second electrode 4 may be an anode. The first photoelectrode and the second electrode may be electrically connected to each other, thus producing a desired chemical reaction as a function of the type of electrode and electrolyte of the cell. An ion exchange separator 6 may further be disposed within the electrolyte and spaced apart from the first photoelectrode 5 and the second electrode 4. The arrangement of the ion exchange separator may thus divide the compartment into two sub-compartments. At each sub-compartment, different or the same electrolyte may be used, depending on the situation. For example, a catholyte and an anolyte are contemplated.

In general, the ion exchange separator may be a separator that is chemically resistant to the anolyte and catholyte, and thus depends on the reaction to be carried out in the photoelectrochemical cell. In some cases, an anion exchange membrane may be used. In other cases, cation exchange membranes may be used.

An example of an anion exchange membrane may include a Polytetrafluoroethylene (PTFE) backbone having perfluorinated side chains of varying lengths connected to the backbone by ether linkages and terminating in sulfonic acid (-SO3H), represented by the following structure:

wherein M is an integer of 0 to 3 (preferably M ═ 1, 2 or 3), n is an integer greater than 2 (preferably 2 or 3), x and y are each an integer of 1 to 100 (preferably an integer of 3 to 80), and M is each H or an alkali metal or alkaline earth metal such as Na, K, Li, Ca, Mg.

Examples of cation exchange membranes that may be constructed from a polymer backbone with quaternized amine functional groups for free OH "ion mobility may be used in the present disclosure including: trimethylamine (TMA), methylimidazole, pentamethylguanidine salt and diazabicyclo [2,2,2] octane and derivatives.

Other separators are envisioned, such as nanofiltration membranes or metal oxide based ceramic based ion conducting membranes.

The enlarged detail of figure 3 shows a cross-sectional view of the first photoelectrode. The cross-sectional view differs from fig. 2a in that the passivation layer (reference numeral 160 of fig. 2 a) may be removed.

As further shown in the enlarged detail of fig. 3, the photocathode may be arranged with its anti-reflection layer 190 facing the outside of the casing 3. And the photocathode may be further arranged with its electrocatalyst layer 150 facing the interior of the compartment 3 to contact the electrolyte solution that may be disposed within the compartment 3.

The enlarged detail of fig. 3 also shows the ion exchange separator 6 and the contact 41 of the second electrode 4. The connection cable 7 can connect the contact 41 of the second electrode 4 with the corresponding busbar (collector) of the first photoelectrode (photocathode).

In all cases, in order to introduce a photoelectrode substantially as described above into a photoelectrochemical cell comprising an electrolyte and to make electrical contact in the corresponding busbar, the photoelectrode may be disposed within a holder that allows electrical contact to be made with the collector busbar, and a gasket may be housed to prevent short circuiting due to contact with the electrolyte.

In a further alternative, the second electrode may also be a photoelectrode substantially as described above, for example the second electrode may be selected from the examples of fig. 2a or fig. 2 b. In these cases, the semiconductor substrate type of the first photoelectrode may be different from the semiconductor type of the second photoelectrode. This means that if the first photoelectrode comprises an n-type semiconductor substrate (photoanode), the second photoelectrode comprises a p-type semiconductor substrate (photocathode), and vice versa.

In some embodiments, the electrolyte may include a compound of formula M, depending on the desired reaction to be performed in the photoelectrochemical cell_mX_nA salt, wherein: m may be selected from magnesium, calcium, lithium, potassium and sodium; x may be selected from the anions of weak or strong acids selected from carbonates, bicarbonates, sulfates, hydroxides, and halides. In some of these cases, the electrolyte may be selected from NaHCO₃、NaCO₂CH₃、KHCO₃、K₂CO₃、Na₂SO₄、K₂SO₄KCl and KClO₄。

In further embodiments, the supporting electrolyte may include a compound of the formula M_mX_nSalts, wherein M may be selected from lithium, potassium, sodium, magnesium, calcium and strontium; y may be derived from halides, sulfates, nitrates, chloric acidSalts and phosphates are selected from the hydroxide or counter ions of mineral acids. In some of these cases, the electrolyte may be selected from NaOH, KOH, H₂SO₄、KCl、HCl、H₃PO₄、NaHCO₃、K₂HPO₄、K₂SO₄And Na₂SO₄。

In further embodiments, different passivation layers or different electrocatalyst layers may be used to optimize the application of photoelectrodes substantially as described above for different reactions, in order to obtain different products with increased productivity and efficiency (whether used as photoanodes or photocathodes) in photoreduction, e.g., of water or CO2, depending on the contact configuration.

In some embodiments, the incident light may be natural sunlight or any type of radiation source that includes an absorption range of, for example, silicon. This means that essentially any radiation source having a wavelength in the central range of the solar spectrum can be used. In general, incident light comprising wavelengths in the interval 350nm to 1100nm may be used.

Procedure of experiment

To fabricate a photoelectrode substantially as described above, the starting point is the back contact solar cell of IBC technology. IBC solar cells are manufactured by Polytechnical University of Catalonia (UPC).

The IBC solar cell used has a width of 9cm²(3X 3cm) of the area of action. Thus, four IBC solar cells were fabricated from each silicon wafer of standard 4 inch size.

The IBC solar cell is manufactured with a cross-section substantially as described with reference to fig. 2a and 2 b. This means that they comprise n-type and p-type doped regions (reference numerals 1 and 2 of fig. 2a and 2 b) that cross each other, that is, arranged in rows or fingers (reference numerals 11 and 12 of fig. 2c) along the length of the solar cell. The doped region is covered by an aluminum layer (metal collector 170 of fig. 2a and 2 b) with a thickness of 3 to 5 microns.

The following example is made on these IBC solar cells.

EXAMPLE 1 photocathode for Hydrogen evolution

The IBC solar cell includes a p-type wafer made of silicon and having a thickness of 280 μm.

A 25nm titanium (Ti) layer is applied on top of the metal collector of the IBC solar cell. The titanium layer is applied by an electron beam process.

Deposited to a thickness of 2 micronsLayer (e.g. a resin commercially available from Fujifilm) to connect the openings and p as described with reference to, for example, fig. 2a⁺The type-doped region is sealed.

The layer is applied by a spin-coating process followed by a photolithography process using a negative exposure mask to expose the n-layer⁺Regions corresponding to the type-doped regions and the emitter bus bar, such that, in use, n is derived from⁺The charge carriers of the doped region reach the electrolyte and allow electrical contact from the emitter bus. A small overlap of about 50 microns is created in the collector bar region to ensure insulation between the emitter and collector contacts. Deposition of TiO by Atomic Layer Deposition (ALD) to a thickness of approximately 100nm at 200 ℃ and 3700 cycles₂And (3) a layer.

By thermal evaporation on TiO₂A platinum (Pt) layer was deposited on the layer to a thickness of about 2nm and further annealed at 200 c under vacuum for 1 hour.

Solar simulator Solar Light 16S (Solar lamp 16S) radiation photoelectrode equipped with 300W Xe lamp and AM 1.5G filter to produce 100mWcm^-2The radiant flux of (a).

And irradiated with a photo-electrode containing 0.5M H₂SO₄Is contacted with the electrolyte.

FIG. 4 shows cyclic voltammetry measurements of photocathodes with photoelectrode current density (i) shown as a function of individual photoelectrode potential_{Cathode electrode}) A change in (c). The scan rate was 20 mV/s. A hydrogen induced current efficiency of 95% was estimated from voltammetry measurements.

₂EXAMPLE 2-photoanode for oxygen-hydrogen evolution or CO reduction catalyst in counter electrode

The IBC solar cell includes an n-type wafer made of silicon and having a thickness of 280 μm.

A 30nm titanium (Ti) layer is applied on top of the metal collector of the IBC solar cell. The titanium layer is applied by an evaporation process.

Deposited to a thickness of 5 micronsLayer (e.g. resin commercially available from Fujifilm) to open and n as described with reference to, for example, fig. 2b⁺The type-doped region is sealed.

The layer is applied by a spin-coating process followed by a photolithography process using a negative exposure mask to expose the p-layer⁺Regions corresponding to the type-doped regions and the emitter bus bar such that, in use, p is derived from⁺The charge carriers of the type-doped region reach the electrolyte and allow electrical contact from the emitter bus. A small overlap of about 50 microns is created in the collector bar region to ensure insulation between the emitter and collector contacts.

Deposition of TiO by Atomic Layer Deposition (ALD) to a thickness of approximately 100nm at 150 ℃ and 3700 cycles₂And (3) a layer.

By thermal evaporation on TiO₂A nickel (Ni) layer is deposited on the layer to a thickness of about 25 nm.

Solar simulator Solar Light 16S (Solar lamp 16S) radiation photoelectrode equipped with 300W Xe lamp and AM 1.5G filter to produce 100mWcm^-2The radiant flux of (a).

And the irradiated photo-electrode was in contact with an electrolyte containing 1M KOH.

FIG. 5a shows cyclic voltammetry measurements of a photoanode, where photoelectrode current density (i) is shown as a function of individual photoelectrode potential_Anode) A change in (c). The scan rate was 20 mV/s.

The 1 hour stability is shown in figure 5 b. FIG. 5b shows the anode current density (i) as a function of time_Anode). The applied voltage was 1.23V (relative to the Reversible Hydrogen Electrode (RHE)). There was an initial loss of about 15% to 20% during the first 5 minutes, after which the photocurrent stabilized for 1 hour.

EXAMPLE 3 photocathode for Hydrogen evolution

The IBC solar cell includes a p-type wafer made of silicon and having a thickness of 280 μm.

A 30nm titanium (Ti) layer is applied on top of the metal collector of the IBC solar cell. The titanium layer is applied by an evaporation process.

Deposited to a thickness of 5 micronsLayer (e.g. a resin commercially available from Fujifilm) to connect the openings and p as described with reference to, for example, fig. 2a⁺The type-doped region is sealed.

The layer is applied by a spin-coating process followed by a photolithography process using a negative exposure mask to expose the n-layer⁺Type doped regionA region corresponding to the emitter bus bar such that, in use, n is derived from⁺The charge carriers of the type-doped region reach the electrolyte and allow electrical contact from the emitter bus. A small overlap of about 50 microns is created in the collector bar region to ensure insulation between the emitter and collector contacts. A platinum (Pt) layer having a thickness of about 5nm was deposited on the resin layer by thermal evaporation and further subjected to drop-casting.

Solar simulator Solar Light 16S (Solar lamp 16S) radiation photoelectrode equipped with 300W Xe lamp and AM 1.5G filter to produce 100mWcm^-2The radiant flux of (a).

And irradiated with a photo-electrode containing 0.5M H₂SO₄Is contacted with the electrolyte.

FIG. 6 shows cyclic voltammetry measurements of photocathodes, where photoelectrode current density (i) is shown as a function of individual photoelectrode potential_{Cathode electrode}) A change in (c). The scan rate was 20 mV/s.

₂EXAMPLE 4 a-photocathode for H precipitation

The IBC solar cell includes a p-type wafer made of silicon and having a thickness of 280 μm.

A 25nm titanium (Ti) layer is applied on top of the metal collector of the IBC solar cell. The titanium layer is applied by an electron beam process.

Deposited to a thickness of 5 micronsLayer (e.g. a resin commercially available from Fujifilm) to connect the openings and p as described with reference to, for example, fig. 2a⁺The type-doped region is sealed.

The layer is applied by a spin coating process, after which a negative through is usedExposing the mask to perform a photolithography process to expose and n⁺Regions corresponding to the type-doped regions and the emitter bus bar, such that, in use, n is derived from⁺The charge carriers of the type-doped region reach the electrolyte and allow electrical contact from the emitter bus. A small overlap of about 50 microns is created in the collector bar region to ensure insulation between the emitter and collector contacts.

A protective conductive layer of nickel epoxy (thickness about 500 microns) was deposited at room temperature and a nickel foam of thickness about 1.6mm coated with platinum (Pt) by electrodeposition was positioned over the resin. The conductive polymer was then cured at 150 ℃ for 1 hour to ensure good adhesion of the metal foam (i.e., platinum coated nickel foam).

Solar simulator Solar Light 16S (Solar lamp 16S) radiation photoelectrode equipped with 300W Xe lamp and AM 1.5G filter to produce 100mWcm^-2The radiant flux of (a).

Irradiated light electrode and the film containing 0.5M H₂SO₄Is contacted with the electrolyte.

₂FIG. 4 b-photocathode for H precipitation

Fig. 4b differs from fig. 4a in that the nickel foam is coated with nickel molybdenum (NI-Mo), which is also coated by electrodeposition, instead of platinum.

Solar simulator Solar Light 16S (Solar lamp 16S) radiation photoelectrode equipped with 300W Xe lamp and AM 1.5G filter to produce 100mWcm^-2The radiant flux of (a).

The illuminated photoelectrode with Ni — Mo was contacted with an electrolyte containing 1M KOH.

FIG. 7a shows cyclic voltammetry measurements of photocathodes according to examples 4a and 4b (solid black lines indicate the photoelectrode of example 4 a; dashed gray lines indicate the photoelectrode of example 4b), in which the photocathode current density (i)_{Cathode electrode}) Shown as varying as a function of the potential of the respective photoelectrode.The scan rate was 20 mV/s.

Fig. 7b and 7c show the one hour stability test. FIGS. 7b and 7c show the cathode current density (i) as a function of time for photoelectrodes with Pt (i.e., the photoelectrode of example 4 a) and Ni-Mo (i.e., the photoelectrode of FIG. 4b), respectively_{Cathode electrode}). For photoelectrodes with Pt, the applied voltage was 0.3V with respect to the Reversible Hydrogen Electrode (RHE), while for photoelectrodes with Ni — Mo, the applied voltage was 0V with respect to the Reversible Hydrogen Electrode (RHE).

Although only a few examples are disclosed herein, other alternatives, modifications, uses, and/or equivalents of the disclosure are possible. Moreover, all possible combinations of the described examples are also covered. Accordingly, the scope of the present disclosure should not be limited by particular examples, but should be determined only by a fair reading of the claims that follow.

Claims (17)

1. A photoelectrode for a photoelectrochemical cell extending from a front end surface (10) to an opposite back end surface (20), wherein the front end surface (10) is illuminated, in use, by incident light (L) and the back end surface (20) contacts, in use, an electrolyte of the photoelectrochemical cell, wherein the photoelectrode comprises:

-a back contact solar cell (100), the back contact solar cell (100) extending from a solar cell front surface (110) to an opposite solar cell back surface (120) facing the back end surface (20), the solar cell front surface (110) constituting, in use, the front end surface (10) of the photoelectrode to be illuminated by incident light (L);

wherein the solar cell back surface (120) comprises an emitter contact (E) and a collector contact (C) which are spaced apart by a first opening (101, 171) of the solar cell back surface (120), the emitter contact (E) and the collector contact (C) being collected in an emitter busbar (111) and a collector busbar (121), respectively; and is

Wherein the photoelectrode further comprises:

-a contact passivation layer (130), the contact passivation layer (130) covering the solar cell back surface (120) to separate the emitter contact (E) and the collector contact (C) from the electrolyte when in use, wherein the contact passivation layer (130) further comprises a second opening (131) corresponding to the first opening (101, 171) of the solar cell back surface (120);

-a resin layer (140), which resin layer (140) covers the first opening (101, 171), the second opening (131) and a portion of the contact passivation layer (130), such that in use only charge carriers from the emitter contact (E) pass through the contact passivation layer in their path to the electrolyte, while charge carriers from the collector contact (C) are collected in the collector busbar (111); and

-an electrocatalyst layer (150), the electrocatalyst layer (150) covering the resin layer (140), the contact passivation layer (130), or both, respectively, wherein the electrocatalyst layer (150) constitutes the back end surface (20) that in use contacts the electrolyte.

2. The photoelectrode of claim 1 wherein said back contact solar cell (100) comprises:

a) a semiconductor substrate (102, 103), the semiconductor substrate (102, 103) having:

i) a substrate front surface (1022, 1032) defining the solar cell front surface (110); and

ii) an opposite substrate back surface (1021, 1031) facing the solar cell back surface (120), wherein the semiconductor substrate (102, 103) is selected from n-type (103) and p-type (102);

b) one or more of p⁺A type-doped region (2) and n⁺A type-doped region (1), wherein said p⁺A type-doped region (2) and n⁺Type-doped regions (1) are alternately arranged on the back surface (1021, 1031) of the substrate, wherein the p-type doping regions⁺A type-doped region (2) and n⁺The distribution of the type-doped regions (1) depends on the type of the semiconductor substrate (102, 103); and

c) a metal collector (170), the metal collector (170) covering the p⁺A type-doped region (2) and n⁺-doping regions (1) of type to define, respectively, the emitter contacts (E) and the collector contacts (C), so that, in use, the metal collectors (170) collect the emitter contacts (E) in the emitter busbars (121) and the collector contacts (C) in the collector busbars (111), wherein the first openings (171) of the solar cell back surfaces (120) are in correspondence with the n⁺Type doped region (1) and p⁺The junction between the type-doped regions (2) is arranged in a corresponding manner in the metal collector (170) so as to separate the emitter contact (E) from the collector contact (C), wherein the metal collector (170) constitutes the solar cell back surface (120).

3. Photoelectrode according to claim 2, wherein the semiconductor type is p-type (102), said emitter contact (E) being formed by said n⁺A type-doped region (1) and the collector contact (C) is defined by the p⁺The type-doped region (2) is defined.

4. Photoelectrode according to claim 2, wherein the semiconductor type is n-type (102), the emitter contact (E) being formed by said p⁺A type-doped region (2) and the collector contact (C) is defined by the n⁺The type-doped region (1) is defined.

5. The photoelectrode of any of claims 1 to 4, wherein said resin layer (140) is chemically stable, heat resistant equal to or higher than 200 ℃ and volume resistivity higher than 10¹⁶ohm cm polymer.

6. The photoelectrode of any of claims 1 to 5 further comprising a second passivation layer (160) disposed between the electrocatalyst layer (150) and the resin layer (140) or between the electrocatalyst layer (150) and the contact passivation layer (130).

7. A photoelectrochemical cell comprising a first photoelectrode (5), the first photoelectrode (5) being a photoelectrode (5) according to any one of claims 1 to 6, said first photoelectrode (5) being arranged such that, in use, incident light (L) impinges on a front end surface (10) of the first photoelectrode, while a back end surface (20) of the first photoelectrode contacts an electrolyte.

8. The photoelectrochemical cell of claim 7, further comprising:

a second electrode (4) arranged spaced apart from the first photoelectrode (5); and

an ion exchange separator (6) located between the first photoelectrode (5) and the second electrode (4),

wherein the first photoelectrode (5) and the second electrode (4) are electrically connected to each other.

9. Photoelectrochemical cell according to claim 8, wherein one of said first photoelectrode (5) and said second electrode (4) is a photoelectrode according to claim 3 and the other of said first photoelectrode (5) and said second electrode (4) is a photoelectrode according to claim 4.

10. The photoelectrochemical cell of claim 7, further comprising:

a) a cathode compartment comprising: a cathode support frame comprising a cathode material for use as a cathode; fluid and gaseous CO₂First distribution frame and fluid and gaseous CO₂A second distribution frame; one or more cathode gaskets placed between the cathode support frame and the distribution frame and serving as the lateral two ends of the cathode compartment; wherein the cathode support frame is disposed between the first and second distribution frames;

b) an anode compartment comprising: an anode support frame comprising an anode material for use as an anode; a fluid distribution frame arranged such that the fluid distribution frame is located on a portion of the anode compartment that is closer to the membrane than the anode support frame; and one or more anode gaskets placed between the anode support frame and the fluid distribution frame and serving as the lateral two ends of the anode compartment; and

c) an ion exchange membrane disposed between the cathode compartment and the anode compartment;

wherein:

i) the cathode material is a material having fixed CO₂An electrically conductive porous electrode of electrocatalyst material;

ii) the fluid and gaseous CO₂First distribution frame, fluid and gaseous CO₂The second distribution frame and the cathode gasket are arranged such that, in use, they allow catholyte and gaseous CO to be passed through different inlet apertures₂Separately introduced into the cathode compartment and which allow the catholyte, liquid and gaseous products and/or unreacted CO to be introduced through outlet openings₂Discharging together;

iii) the fluid distribution frame, the anode support frame and anode gasket are arranged such that, in use, they allow introduction of anolyte into the anode compartment through an inlet aperture and they allow joint discharge of the anolyte and oxidation products through an outlet aperture;

iv) the anode material is a photo-catalytic anode material and is located on the side of the optical window of the anode support frame facing the membrane; and the anode material is arranged such that it is contactable, in use, with the anode electrolyte introduced into the anode compartment via the inlet aperture and is activatable when radiation used to illuminate the anode compartment reaches the optical window from an opposite side of the optical window not facing the diaphragm; and is

v) the photocatalytic anode material and the gas diffusion cathode material have a surface area ratio comprised within 1:1 to 1:0.02, wherein the anode material is the photoelectrode according to claim 4.

11. The photoelectrochemical cell of claim 7, further comprising:

a) a cathode compartment comprising: a cathode support frame comprising a cathode material for use as a cathode; a fluid distribution frame; one or more cathode gaskets placed between the cathode support frame and the fluid distribution frame and serving as the lateral two ends of the cathode compartment;

b) an anode compartment comprising: an anode support frame comprising an anode material for use as an anode; a fluid distribution frame arranged such that the fluid distribution frame is located on a portion of the anode compartment that is closer to the membrane than the anode support frame; and one or more anode gaskets placed between the anode support frame and the fluid distribution frame and serving as the lateral two ends of the anode compartment; and

c) an ion exchange separator disposed between the cathode compartment and the anode compartment;

wherein:

i) the cathode material is an electrode having a fixed Hydrogen Evolution Reaction (HER) electrocatalyst material;

ii) the fluid distribution frame and cathode gasket are arranged such that, in use, they allow catholyte to be introduced into the cathode compartment through the inlet aperture, and they allow the catholyte and reaction products to be expelled together through the outlet aperture;

iii) the fluid distribution frame, the anode support frame and anode gasket are arranged such that, in use, they allow introduction of anolyte into the anode compartment through an inlet aperture and they allow joint discharge of the anolyte and oxidation products through an outlet aperture;

iv) the anode material is an electrode comprising an Oxygen Evolution Reaction (OER) electrocatalyst material; and is

v) the anode material and the cathode material have a surface area ratio comprised between 1:1 and 1:0.02,

wherein the cathode material is a photoelectrode according to claim 3 or the anode material is a photoelectrode according to claim 4, the photoelectrode being located on the side of the optical window facing the membrane and being activatable when the radiation used to illuminate reaches the optical window from the opposite side of the optical window not facing the membrane.

12. A method of manufacturing the photoelectrode of any one of claims 1 to 6, the method comprising:

-providing a back contact solar cell (100);

-providing a contact passivation layer (130) covering a back surface (120) of the solar cell, the contact passivation layer (130) being provided with a second opening (131) corresponding to the first opening (101, 171);

-providing a resin layer (140) to seal the first opening (101, 171) and the second opening (131), wherein the resin layer further covers a portion of the contact passivation layer (130) corresponding to the collector contact; and

-providing an electrocatalyst layer (150) covering the resin layer (140) and the contact passivation layer (130), respectively.

13. The method of claim 12, further comprising: providing a passivation layer (160) between the electrocatalyst layer (150) and the contact passivation layer (130) or between the electrocatalyst layer (150) and the resin layer (140), or providing a passivation layer (160) both between the electrocatalyst layer (150) and the contact passivation layer (130) and between the electrocatalyst layer (150) and the resin layer (140); wherein the passivation layer (160) is provided by ionic layer deposition (ALD), Pulsed Laser Deposition (PLD), by a sol-gel process, by a doctor blade method or by a screen printing method.

14. The method according to claim 12 or 13, wherein the resin layer (140) is provided by spin coating and photolithography is used to open areas not covered by the resin layer.

15. The method according to any of claims 12 to 14, wherein the contact passivation layer (130) is provided by an evaporation process.

16. The method according to any of claims 12 to 15, wherein the electrocatalyst layer (150) is provided by an evaporation process or by thin film deposition.

17. The method of claim 16, wherein thin film deposition comprises: the deposition is performed on a substrate selected from the group consisting of foam and screen.