Photoelectrode

Abstract

The invention relates to the field of photocatalytic hydrogen generation using sunlight and water. It addresses the technical problem of efficiently splitting water into hydrogen and oxygen using a specially designed photoelectrode. The photoelectrode comprises a semiconductive photo-harvester containing e. g. metal silicide, an oxidation cocatalyst with magnesium tin oxide, and a reduction cocatalyst of cobalt, nickel, and manganese alloys. The manufacturing method includes preparing a silicon-based photosensitive material, applying protective and anti- reflective coatings, and bonding the cocatalysts using techniques like sputtering. The photoelectrode is used in a transparent container filled with water and exposed to sunlight to generate hydrogen and oxygen, which can be collected and stored for energy applications, such as fuel cells. This invention aims to provide a renewable and environmentally friendly method for hydrogen production, overcoming challenges related to material stability and water impurities.

Description

DescriptionTitle of Invention : PhotoelectrodeTechnical Field

[0001] The invention relates to the product and processes as per the prior art portion of the independent claims.Background Art

[0002] Hydrogen production through photocatalytic water splitting has attracted significant attention as a potential solution for sustainable and clean energy. The fundamental principle involves the absorption of solar energy by a photocatalyst, which generates electron-hole pairs. These charge carriers facilitate the reduction of protons to hydrogen and the oxidation of water to oxygen at the surface of the catalyst. Despite extensive research since the 1970s, the practical implementation of this technology remains challenged by low conversion efficiencies, material degradation, and economic viability.

[0003] Photocatalysts typically comprise a semiconductor that absorbs photons and generates electron-hole pairs. These pairs then migrate to the surface where they participate in redox reactions. Semiconductors such as titanium dioxide (TiO2) and bismuth vanadate (BiV04) have been extensively studied due to their suitable band gaps and stability. However, the efficiency of these materials is often limited by rapid recombination of electron-hole pairs and insufficient absorption of visible light.

[0004] To address these issues, cocatalysts are employed to enhance charge separation and provide active sites for redox reactions. Common oxidation cocatalysts include metal oxides like ruthenium oxide (RuO2) and iridium oxide ( lrO2), which facilitate the oxygen evolution reaction (OER). For the hydrogen evolution reaction (HER), reduction cocatalysts such as platinum (Pt) and molybdenum sulfide (MoS2) are often used. The integration of dual cocatalysts has shown promise in reducing activation energy barriers and improving overall photocatalytic performance.

[0005] Various fabrication techniques are used to construct photoelectrodes, including physical vapor deposition (PVD) and chemical vapor deposition (CVD).Sputtering, a form of PVD, is particularly advantageous for creating thin films and coatings with precise control over composition and thickness. The magnetron sputtering process, which enhances ionization efficiency and deposition rates using a magnetic field, is widely used for depositing semiconductor and cocatalyst layers.

[0006] Water splitting systems are typically configured as photoelectrochemical (PEC) cells where photoanodes and photocathodes are immersed in an electrolyte solution. PEC cells can operate in tandem or parallel illumination modes. Tandem cells, where photoelectrodes are stacked, can harness a broader spectrum of sunlight but are complex and challenging to fabricate. Parallel illumination cells, where photoelectrodes are placed side by side, offer simpler construction and effective solar energy harvesting.Summary of Invention

[0007] The invention is set out in the appended set of claims.Technical Problem

[0008] The present invention addresses a multifaceted technical problem inherent in the field of photocatalytic hydrogen generation through water splitting. This problem can be delineated into several key challenges, each of which significantly hampers the efficiency, stability, and economic viability of current technologies.

[0009] One of the primary technical challenges in photocatalytic water splitting is the inefficient separation of photogenerated electron-hole pairs and their rapid recombination. In conventional photocatalysts, such as semiconductor materials, photons with energy equal to or greater than the band gap excite electrons from the valence band to the conduction band, creating electron-hole pairs. However, these charge carriers often recombine before they can participate in the redox reactions required for hydrogen and oxygen production. This recombination process results in substantial energy losses and significantly reduces the overall efficiency of photocatalytic water splitting.

[0010] The efficiency of photocatalytic water splitting is also constrained by the limited ability of many semiconductor materials to absorb light, particularly in the visible spectrum. While materials like titanium dioxide (TiO2) are stable andeffective under ultraviolet (UV) light, their performance under visible light — the most abundant portion of the solar spectrum — is suboptimal. This limitation necessitates the development of photo-harvesters that can efficiently utilize a broader range of the solar spectrum to maximize hydrogen production.

[0011] The stability of photocatalysts in aqueous environments, especially in the presence of pollutants and high salinity, poses a significant technical problem. Water sources used in photocatalytic systems often contain various dissolved chemicals and impurities that can react with the photoelectrode materials, leading to corrosion and degradation. This not only decreases the lifespan of the photoelectrodes but also diminishes their catalytic activity over time, further reducing hydrogen production efficiency.

[0012] The economic feasibility of photocatalytic water splitting is currently limited by the reliance on expensive and rare materials, such as platinum, which is commonly used as a reduction cocatalyst. The high cost and limited availability of such materials impede the scalability and widespread adoption of this technology. Thus, there is a critical need for alternative materials that are both abundant and cost-effective, without compromising on performance.

[0013] The fabrication of efficient photoelectrodes involves complex and precise methods to ensure the proper deposition of catalytic layers and the creation of stable, high-performance interfaces. Techniques such as sputtering and chemical dipping require meticulous control over process parameters to achieve the desired material properties and layer uniformity. Simplifying these fabrication processes while maintaining or enhancing the performance of the photoelectrodes is a significant technical challenge.

[0014] Finally, integrating advanced photoelectrodes into practical, scalable systems for hydrogen production involves addressing design and operational challenges. This includes the development of containers that can effectively separate and collect the generated hydrogen and oxygen gases, ensuring that these gases do not mix and contaminate each other. The design must also facilitate efficient light exposure and optimal interaction between the photoelectrodes and the aqueous medium.Solution to Problem

[0015] As shall be further elucidated in the following description, this problem is solved as per the features of the independent claims.Advantageous Effects of Invention

[0016] The present invention confers several significant advantages over existing technologies in the realm of photocatalytic hydrogen generation. These advantageous effects span improvements in efficiency, stability, economic feasibility, and practical application, thereby addressing the critical technical challenges identified in the prior art.

[0017] A primary advantage of the invention is the improved separation of photogenerated electron-hole pairs, coupled with the suppression of recombination. By integrating dual cocatalysts — magnesium tin oxide (MgSnO3) for the oxidation reaction and a composite comprising, in particular being composed of, cobalt, nickel, and manganese alloys for the reduction reaction — the photoelectrode effectively promotes charge carrier separation. This configuration ensures that electrons and holes are rapidly transferred to the respective catalytic sites, thereby minimizing energy losses due to recombination. The enhanced charge separation directly translates to increased hydrogen production efficiency.

[0018] The semiconductive photo-harvester may be made from a wide range of materials. For example, silicon-based wafers may be processed efficiently and cost effective. Wafers like amorphous, Perovskite CdTe, nanoparticle PEC and I or hetero-junction-technology Si (HJT Si) may also be considered.

[0019] The invention may utilize a semiconductive photo-harvester containing a metal silicide, which is adept at absorbing a wider range of the solar spectrum, including visible light. This broad-spectrum absorption capability significantly boosts the efficiency of solar energy conversion, as it allows the photoelectrode to harness more of the available sunlight. Consequently, the overall hydrogen generation rate is markedly improved compared to conventional photocatalysts that are primarily responsive to ultraviolet light.

[0020] The semiconductive photo-harvester may may comprise an n-type silicon wafer and I or may be manufactured from an n-type silicon wafer for good availability and reduced costs.

[0021] Whereas, in principle, antimony and I or arsenic dopants for the photoharvester may improve electron-hole-separation, their use is strictly restricted or even prohibited due to current environmental regulations like the Ell REACH regulation.

[0022] Therefore, after intensive search, it has been found that a semiconductive photo-harvester comprising red phosphorous doped silicon, in particular doped monocrystalline silicon, may provide similar or even better electric properties and, hence, particularly high energy efficiencies. Phosphorous dopants may also enable sustainable, eco-friendly solutions with good up-scalability. The photoharvester may be pre-doped. In the alternative, or additionally, the photoharvester may be doped during manufacturing the photoelectrode.

[0023] The photoelectrode of the present invention may exhibit superior stability in various aqueous environments, including those with high salinity and chemical pollutants, if both sides of the semiconductive photo-harvester are provided with at least a first layer of protective coating, for example a coating layer comprising epoxy and I or silicon nitride. Epoxy may be handled in production in a very simple and cost-efficient manner, whereas silicon nitride may be favorable, for example, for use in high corrosion atmospheres like in extremely saline water.

[0024] The protective coating may comprise at least one electrically conductive coating layer, improving transfer of electric charges to and I or from the photoharvester. For example, by doping epoxy, it can be made conductive while preserving its anti-corrosive function. In general, the protective coating may comprise at least an electrically conductive and anti-corrosive layer. Preferably, the layer or the whole protective coating is also highly transparent. In the alternative, or additionally, to epoxy, the protective coating may comprise at least one layer comprising a conductive polymer, a transparent conductive adhesive (TCAs), a carbon-based material, and I or doped materials like doped silicon nitride. Boron, arsenic and I or germanium may be used for such doping.

[0025] The coating of the first layer of protective coating may have a thickness of up to 5 pm, in particular between 0.01 pm and 3 pm, for example 2 pm. Such thickness may provide sufficient protection while still having sufficient transparency.

[0026] A low thickness of the protective coating in the sub-pm range, e. g. 0.01 pm to 0.5 pm, may accelerate the coating procedure, and, hence, reduce production costs.

[0027] Thicker coatings may, on the other hand, provide an optimized protection against corrosion.

[0028] Protection may be further improved if one side of the semiconductive photoharvester comprises multiple coating layers including nickel, molybdenum, and zinc layers.

[0029] One side, in particular the other side, of the semiconductive photo-harvester may comprise multiple coating layers comprising indium tin oxide (ITO) and I or cobalt for further advanced protection.

[0030] The protective coatings applied during the fabrication process, combined with the inherent corrosion resistance of the selected materials, ensure that the photoelectrode maintains its structural integrity and catalytic performance over prolonged periods. This durability reduces the frequency of maintenance and replacement, thereby enhancing the long-term viability of the hydrogen production system.

[0031] An important advantage of the invention is its reliance on earth-abundant and cost-effective materials. The use of metal silicide for the semiconductive base, along with magnesium tin oxide and cobalt, nickel, and manganese alloys as cocatalysts, eliminates the need for expensive and rare elements such as platinum. This reduction in material costs renders the technology economically feasible and scalable for widespread adoption, facilitating the transition to sustainable hydrogen production on a global scale.

[0032] By avoiding environmentally critical materials like arsenic conformance to current regulations like Ell REACH or RoHS may be established.

[0033] The photo-harvester and I or the protective coating may have a light trapping shape. In particular, a surface, e. g. the surface of the photo-harvester, may be formed so that it traps light and, hence, increases the optical path length of entering light within the photoelectrode, thus increasing absorption rates and the total efficiency of the photoelectrode.This may be particularly important for indirect bandgap semiconductors like silicon, which may be not very efficient atabsorbing photons near their bandgap of energy. The light trapping shape may comprise patterns like pyramidal textures, random textures, grooves, gratings and / or nanostructures.

[0034] A further aspect of the invention is a method of manufacturing a photoelectrode as described previously from a photosensitive base exhibiting two sides wherein the two sides are coated with protective coating. The protective coating may comprise epoxy and I or silicon nitride. The method may provide a photoelectrode with strong resistance against oxidation and degradation.

[0035] It has been found that even small cracks or impurities can lead to extensive degradation of the photoelectrode. Therefore, it is conceivable that the photosensitive base and I or the protective coating are intensively inspected for cracks, preferably using X-rays. X-rays may be used to detect cracks and other defects in silicon wafers before they are processed further, ensuring the reliability and functionality of the final semiconductor products. X-ray diffraction imaging (XRDI) may be particular suitable for this purpose. Crack propagation in the photo-harvester or its base, e. g. a silicon wafer, under thermal stress may be depicted by combining diffraction and transmission X-ray imaging. The use of synchrotron radiation allows for high imaging frame rates which may be required to follow crack dynamics in real time.

[0036] Moreover, the semiconductive photo-harvester may be subjected to surface imaging and I or high magnification microscopy to assess surface nature and detect imperfections. For example, in-Situ imaging techniques like megahertz X- ray diffraction imaging can even visualize cracks in silicon wafers as they propagate at high speed, providing valuable insights into fracture dynamics.

[0037] During manufacturing, inspections can be carried out repeatedly, in particular before, during and I or after coating with layers of the protective coating.

[0038] The fabrication method described in the invention may involve sputtering and chemical dipping techniques forboth precise and efficient coating. The use of atomizing nozzles for protective coating application and magnetron sputtering for cocatalyst deposition may ensure uniform and high-quality layers. This streamlined process may not only enhance the performance of the photoelectrode but also reduce manufacturing complexity and costs. The abilityto use standard industrial techniques further supports the scalability of the invention.

[0039] In general, different coating methods may be used, wherein physical vapor deposition (PVD), e. g. sputtering, has shown to provide particularly uniform and resistance coatings on the photo-harvester. Moreover, PVD may be easily upscaled to large-scale applications. In the alternative, or additionally, chemical vapor deposition (CVD), electrochemical deposition, sol-gel coating, atomic deposition coating and I or molecular beam epitaxy may also be used for coating, for example for coating the cocatalyst.

[0040] For particular uniform and durable coatings, the photoelectrode may be subjected to a cooling interval. The cooling interval may be more than 1 minute and I or less than 1 hour. The cooling interval may be applied after each additional coated layer.

[0041] The photoelectrode may be dried after coating with protective coating comprising epoxy at a temperature between 50 and 60 °C, for example for 20 to 40 minutes, e. g. 0,5 hours, to balance between speed of coating and quality of the epoxy layer.

[0042] Before coating, for preparing the surface for the coating, the sides of the photoelectrode or its base, e. g. the silicon wafer surfaces, may undergo fine grounding.

[0043] An optimal adhesion and performance of the subsequent coatings may be obtained if the surface roughness is 30 nm in Ra (arithmetic mean roughness) or less. Careful control of grinding parameters, including force, wheel speed, and coolant, may be essential to minimize damage to the machined surfaces, to avoid any damage or performance degradation of the coatings.

[0044] Deionized water may be used as a coolant to prevent excessive heating and damage to the wafer. Grinding marks are undesirable for coating adhesion and can be minimized through proper grinding parameters and wheel selection.

[0045] Such fine grinding may also contribute to the surfaces’ overall flatness, which may further optimize the performance of subsequent fabrication steps. A smooth, clean surface may provide good adhesion of the coating layers. The quality of the ground surface may directly impact the performance of the coatings, such aselectrical conductivity, mechanical strength, and thermal stability. Minimizing subsurface damage may ensure the integrity of the photo-harvester substrate, preventing defects and improving the reliability of the device.

[0046] The invention includes an innovative design for the integration of the photoelectrode into a transparent, preferably polycarbonate container. This container is specially designed to ensure airtight insertion of the photoelectrode, effective separation of generated gases, and optimal exposure to sunlight. The dual-chamber configuration prevents the mixing of hydrogen and oxygen, enhancing safety and purity of the collected gases. Additionally, the container's design facilitates easy collection and storage of the gases, which can be directly fed into fuel cells for electricity generation.

[0047] Another aspect of the invention relates to a container for generating hydrogen, the container comprising a photoelectrode as previously described and I or as manufactured according to the method previously described. Due to the high conversion efficiency of the photoelectrode, the container may provide a compact, highly efficient, and even portable, solution for the production of solar hydrogen from water.

[0048] Its efficiency may be further increased if the container comprises at least one mirror, so that light entering the container, but not being absorbed by the photoelectrode, may be reflected back to the photoelectrode, thus increasing the effective absorption rate of the photoelectrode.

[0049] A further improvement may be achieved if the container comprises an ion- impermeable, electrically conductive connection between an anode and a cathode of the container, in particular of the photoelectrode. During the production of H2 and 02, also H+- and OH- - ions are produced. These ions may generate an electric potentials which may complicate the separation and production of H2 and 02. Such electric potentials may be neutralized by electrons passing through the electrically conductive connection.

[0050] By utilizing abundant and renewable solar energy to produce hydrogen from water, the invention offers substantial environmental benefits. Hydrogen, when used as a fuel, produces only water as a byproduct, thereby reducing greenhouse gas emissions and dependence on fossil fuels. The invention thuscontributes to the development of a clean and sustainable energy economy, addressing both energy security and environmental sustainability.Brief Description of Drawings

[0051] Fig. 1 shows the basic parts of a photocatalyzer with a photoelectrode.

[0052] Fig. 2 shows the reactor lid.

[0053] Fig. 3 shows the photoelectrode and separator.

[0054] Fig. 4 shows the photoelectrode fitted in the reactor vessel.

[0055] Fig. 5 shows the base part.

[0056] Fig. 6 shows the platform connecting the reactor vessel and base.

[0057] Fig. 7 is a flowchart.

[0058] Fig. 8 is a container for generating hydrogen.

[0059] Fig. 9 is a flowchart for coating a right side of the photoelectrode.

[0060] Fig. 10 is a flowchart for coating a left side of the photoelectrode.Description of Embodiments

[0061] A photosensitive base is prepared by heating crystalline silicon of grade 441 , 553, 3303 or 2202, preferably grade 2202, to a temperature of 200 °C in an inert gas oven. The heating reinforces the silicon and maintains its hardness. The heated silicon compound is allowed to cool to room temperature. Subsequently, a protective coating is applied to the silicon metal compound by means of atomized spraying systems to protect the material from corrosion and other chemical agents. The spraying is effected using atomizing nozzles to ensure an even application of the coating. The coated silicon compound is subjected to a mild temperature hot air treatment for correct drying of the coating. After the hot air treatment, the silicon compound is fitted with an anti-reflective coating to maximize sunlight capture and boost the efficiency and energy output. The coated silicon compound is again allowed to cool and checked for any cracks.

[0062] The photosensitive silicon material base obtained above is provided with an oxidation cocatalyst on one side and a reduction cocatalyst on the opposite side. To prepare the oxidation cocatalyst, a magnesium tin oxide alloy is used. The alloy is dissolved in a hydrochloric acid solution mixed with a magnesium chloridesolution. The resulting solution is applied onto the left side of the photosensitive silicon material base by means of chemical dipping. After drying, a secondary coating of the oxidation cocatalyst is applied by means of sputtering. The coating is left to cool and inspected for cracks.

[0063] To prepare the reduction cocatalyst, specially designed cobalt, nickel and manganese composites are used. First, a cobalt alloy is impregnated with cadmium particles. The impregnated alloy is coated onto the right side of the photosensitive silicon material base by means of sputtering. After the coating is cooled and inspected for cracks, a nickel and manganese alloy fused with gallium nitride is coated on top of the impregnated cobalt alloy, again by means of sputtering. The coating is then allowed to cool and inspected for cracks.

[0064] The photoelectrode thus obtained is used to generate hydrogen as follows: The photoelectrode is placed in a specially designed polycarbonate transparent container having an airtight plug-in mechanism on the inside wall. The photoelectrode is plugged into the inside wall of the container such that the container is divided into two mutually sealed chambers. The container is filled with water such that the photoelectrode is immersed in it and sealed with an airtight lid having holes designed to collect the produced gases. When the container is exposed to sunlight, the sunlight falls on the surface of the photoelectrode. On the right side of the photoelectrode, the reduction cocatalyst produces hydrogen gas. On the left side of the photoelectrode, the oxidation cocatalyst produces oxygen gas. The oxygen and hydrogen escape through the holes in the lid in a controlled manner and are collected separately. The collected gases are stored and eventually fed to a fuel cell to generate electricity.Examples

[0065] A photosensitive base was prepared by heating a 441 grade crystalline silicon block to 200 °C in an argon gas oven for two hours. The heated silicon block was allowed to cool to room temperature over a period of eight hours. To enhance the stability and durability of the photoelectrode, protective coatings are applied using atomizing nozzles. A silicon dioxide (SiO2) layer, with a thickness of 100 nm, was deposited using tetraethyl orthosilicate (TEOS) as the precursor. This was followed by a titanium dioxide (TiO2) layer, with a thickness of 50 nm, usingtitanium isopropoxide (TTIP) as the precursor. The spraying was effected at a pressure of 50 psi and a rate of 10 ml / min. The coated silicon block was heated to 80 °C in a hot air chamber for one hour. After cooling to room temperature, an anti-reflective coating comprising a silicon nitride layer was applied onto the coated silicon block by means of plasma-enhanced chemical vapor deposition. The thickness of the anti-reflective coating was 50 nm.

[0066] An oxidation cocatalyst comprising a magnesium tin oxide alloy was prepared by dissolving 5 g of the alloy in a solution prepared by mixing 20 ml of concentrated hydrochloric acid and 10 ml of 1 M magnesium chloride solution. The resulting solution was applied onto the left side of the silicon base by dipping the base into the solution for five minutes. After drying the coating at room temperature, a secondary coating comprising 100 nm of magnesium tin oxide was applied by means of magnetron sputtering with a sputtering power of 150 W, an argon flow rate of 30 seem, and a chamber pressure of 3 mTorr. The thickness of the tin oxide layer is maintained at around 50 nm.The photoelectrode was then annealed in air at 600 °C for two hours to promote the solid-state reaction between MgO and SnO2, resulting in the formation of the MgSnO3oxidation cocatalyst.

[0067] A reduction cocatalyst was prepared by impregnating a cobalt alloy with 5 % by weight of cadmium particles. The impregnated alloy was coated onto the right side of the silicon base by means of magnetron sputtering to a thickness of 200 nm with a sputtering power of 100 W, an argon flow rate of 40 seem, and a chamber pressure of 4 mTorr. A secondary coating comprising a nickel and manganese alloy fused with 10 % (by weight) of gallium nitride was applied on top of the impregnated cobalt alloy to a thickness of 100 nm, again by means of magnetron sputtering. The photoelectrode was then annealed in a hydrogen atmosphere at 400 °C for 1 hour to facilitate the formation of the cobalt-nickel- manganese alloy reduction cocatalyst.

[0068] The photoelectrode was placed in a rectangular polycarbonate container measuring 10 cm x 10 cm x 20 cm and having a wall thickness of 5 mm. The photoelectrode was plugged into the inner wall of the container by means of an airtight rubber plug such that the container was divided into two chambers of equal volume. The container was filled with distilled water and sealed with anairtight lid having two outlet holes of 5 mm diameter. The container was exposed to simulated solar irradiation (AM 1.5G, 100 mW / cm2) for eight hours. Upon exposure, the metal silicide photo-harvester absorbed photons, generating electron-hole pairs. The photogenerated were efficiently transferred to the cobalt- nickel-manganese alloy reduction cocatalyst, where they participated in the hydrogen evolution reaction (HER). Simultaneously, the photogenerated holes migrated to the MgSnO3oxidation cocatalyst, facilitating the oxygen evolution reaction (OER). Herein, the dual cocatalyst configuration enhanced charge separation and suppressed recombination, leading to improved hydrogen production efficiency. As a result, hydrogen gas was collected through one of the outlet holes at a rate of 500 ml / h, while oxygen gas was collected through the other outlet hole at a rate of 125 ml / h. The collected gases were stored in separate gas cylinders and subsequently fed to a polymer electrolyte membrane fuel cell to generate electricity.

[0069] The exemplary photoelectrode demonstrated a hydrogen evolution rate of 10.2 mmol / h / cm2and an oxygen evolution rate of 5.1 mmol / h / cm2, with a Faradaic efficiency of 95 % for hydrogen production. In subsequent tests, the photoelectrode maintained stable performance over 100 hours of continuous operation, indicating its durability and corrosion resistance.

[0070] This example demonstrates the successful fabrication and application of the claimed photoelectrode for efficient and stable photocatalytic hydrogen generation from water splitting.

[0071] Fig. 8 shows an example of a container 39 for producing hydrogen from water. If not otherwise described, the container 39 and its elements may have similar structures and functionalities as corresponding elements previously described.

[0072] Sunlight penetrates the container 39 through a transparent side and hits the photoelectrode 9. The container 39 is filled with water.

[0073] In this embodiment, the photoelectrode 9 comprises a plurality of coated and doped n-type silicon wafers, which are attached to the photoelectrode 9. A back side of the photoreactor or container 39, and preferably also other sides of the photoreactor or container 39, is equipped with a mirror 44 so that light not yetabsorbed is reflected and passed back to the photoelectrode 9 to maximize light yield.

[0074] The container 39 is divided into several chambers 42, 43, which may be filled with water:

[0075] In a first chamber 42 oxygen is produced. Water is oxidized, producing oxygen O2 and protons H+ions.

[0076] In a second chamber 43 hydrogen is produced. Water is reduced, producing hydrogen H2 and hydroxide ions OH’.

[0077] An ion-impermeable separator 45 is located between the two chambers 42, 43, ensuring the separation of the gases but allowing electron transport via the wafers of the photoelectrode 9.

[0078] An electrically conductive connection 46 for migration of electrons may connect the cathode 41 and the anode 40. When the cathode 41 and the anode 40 are electrically connected, a potential gradient is created between the H+ions in chamber 42 and the OH’ ions in chamber 43.

[0079] At the cathode 41 the H+ions recombine to form molecular hydrogen H2. At the anode 40 four OH’ ions form two H2O and 1 O2

[0080] The generated gases can then be collected and used separately.

[0081] Fig. 9 and Fig. 10 detail coating procedures 1000, 1100 for coating the photoelectrode with protective coating on its right (cathode) and on its left side (anode). As an example, the procedure is explained for a silicon wafer, in particular a red phosphorous doped monocrystalline silicon wafer, as semiconductive photo-harvester. It is to be understood that the numbers, orders and I or composition of layers may. For example, the order of the steps of the procedures 1000, 1100 described in the following may reordered. Thicknesses of some or all of the layers may be adapted to meet specific needs, environments or other performance criteria.

[0082] Fig. 9 refers to coating the right side, and Fig. 10 refers to coating the left side of the photo-harvester.

[0083] Before coating a base layer, the surface is inspected for damages or any type of imperfections present by imaging of the photo-harvester. Additionally, it is inspected for cracks or any other type of structural imperfections using X-ray.

[0084] After checking the photo-harvester or the base for cracks or any other imperfections it is coated with epoxy. In the alternative, for specifically intended uses in high corrosion atmospheres like in extremely saline water this basic coating may be based on silicon nitride. Coating thickness of this epoxy or silicon nitride layer is 2 pm. After coating the sample is put down for cooling during a cooling interval for better finish for coating. For further inspection, optical microscopy imaging data, for example maximum and medium images, may be recorded.

[0085] This general coating with epoxy or silicon nitride may be applied to both sides of the photo-harvester.

[0086] For the right-side part or cathode of the photoelectrode, the procedure 1000 can comprise a first coating step 1010 comprising a first additional coating layer with nickel as coating material. Its thickness may be between 1 and 10 pm, e. g.5 pm. Afterwards the sample is left to cool down for a cooling interval. The layer can then be checked for imperfections, e.g. using microstructure images.

[0087] In a second coating step 1020, another epoxy or silicon nitride coating layer is applied. Its thickness may be 2 pm. Afterwards the sample is left to cool down for a cooling interval. The layer can then be checked for imperfections using microstructure images.

[0088] In a third coating step 1030 a 5 pm thick Molybdenum layer is applied. Again, the sample is left to cool down for a cooling interval. The new layer can then be checked for imperfections using microstructure images.

[0089] In a fourth coating step 1040 an additional epoxy or silicon nitride layer having a thickness of 2 microns is applied. As before, the sample is left to cool down for a cooling interval. The new layer can then be checked for imperfections using microstructure images.

[0090] In a fifth coating step 1050 a zinc layer having a thickness of 5 pm is applied. Again, the sample is left to cool down for a cooling interval. The new layer can then be checked for imperfections using microstructure images.

[0091] In a sixth coating step 1060 for the right side of the silicon wafer an epoxy or silicon nitride layer of 2 pm thickness is applied. Again, the sample is left to cool down for a cooling interval. The new layer can then be checked for imperfections using microstructure images.

[0092] The left, anode, side may be coated according to procedure 1100 as shown in fig. 10.

[0093] After the general coating comprising epoxy and I or silicon nitride of 2 pm, in a first coating step 1110 a coating of 1 to 10 pm, e. g. 5 pm, comprising ITO is applied. Similar to the coating steps concerning the right side, the sample is left to cool down for a cooling interval. The new layer can then be checked for imperfections using microstructure images.

[0094] In a second coating step 1120 a layer of 1 to 5 pm, e. g. 2 pm, Cobalt may be applied. Again, the sample is left to cool down for a cooling interval. The new layer can then be checked for imperfections using microstructure images.

[0095] In a third coating step 1130 a final, third additional coating layer is applied on the left side comprising epoxy or silicon nitride again. This final layer for the left side may have a thickness between 1 and 10 pm, e. g. 2 pm.Industrial Applicability

[0096] The present invention, which pertains to the domain of photocatalytic hydrogen generation, exhibits profound industrial applicability due to its innovative design, advanced material composition, and sophisticated fabrication methodologies. This invention significantly addresses and mitigates the critical challenges that hinder current technologies, thereby offering a robust and scalable solution for sustainable hydrogen production across various industrial sectors.

[0097] The invention's primary industrial application is within the renewable energy sector, where it facilitates the efficient production of hydrogen — a clean, versatile, and high-energy-density fuel. The hydrogen generated through the described photoelectrode can be effectively utilized in numerous applications, including fuel cells, where it can produce electricity with water as the sole byproduct. This clean energy conversion process is particularly suitable for powering electric vehicles, portable electronic devices, and stationary power systems, thereby contributing tothe significant reduction of greenhouse gas emissions. Additionally, the invention offers a viable solution for energy storage by converting surplus electricity from renewable sources, such as solar and wind, into hydrogen. This stored hydrogen can later be reconverted into electricity during periods of high demand, thus balancing the supply and demand of renewable energy.

[0098] Moreover, the invention's applicability extends to industries that heavily rely on hydrogen as a critical raw material. In the chemical industry, hydrogen is essential in the production of ammonia, methanol, and various other chemicals. This invention provides a sustainable and cost-effective method for generating hydrogen, potentially reducing the chemical industry's dependence on fossil fuels and lowering its carbon footprint. Similarly, in the petrochemical industry, hydrogen is indispensable for refining processes such as hydrocracking and desulfurization. The adoption of this invention can lead to more environmentally sustainable and economically viable hydrogen production, thereby enhancing the overall efficiency of petrochemical operations.

[0099] The invention promotes environmental sustainability by offering a green alternative to traditional hydrogen production methods, which are often associated with substantial carbon emissions. By utilizing solar energy to split water into hydrogen and oxygen, the invention eliminates the need for fossil fuels, significantly reducing greenhouse gas emissions and aiding in climate change mitigation. Additionally, the photoelectrode's efficiency in varied aqueous environments, including those with high salinity and pollutants, makes it suitable for integration into water treatment facilities. This dual functionality — water purification and hydrogen production — provides substantial environmental benefits.

[0100] The design and fabrication process of the invention are inherently scalable, making it suitable for deployment across a range of industrial settings. The use of earth-abundant materials and cost-effective fabrication techniques, such as sputtering and chemical dipping, ensure that the technology can be scaled up for mass production. Furthermore, the transparent polycarbonate container design facilitates easy integration into existing industrial systems and infrastructures, thereby enhancing the practicality and scalability of the technology.

[0101] The economic viability of the invention further underscores its industrial applicability. The use of inexpensive, readily available materials significantly reduces production costs, rendering the technology economically attractive for widespread adoption. The high efficiency and durability of the photoelectrode, coupled with reduced material costs, ensure a favorable return on investment for industries implementing this technology.Reference Signs ListReference sign Description1 Oxygen output2 Pressure and temperature sensor3 Hydrogen output4 Reactor lid5 Bolt6 Bracket7 Reactor vessel8 Electrode separator9 Photoelectrode10 Water inlet11 Protective partition12 Fixing base13 Roller-fitted base part14 Locking pin15 Photoelectrode separator16 Locking pin female17 Bracket male pin18 Nuts and bolts19 Polymer separator20 Upper slit21 Locking slit22 Vertical roller wheel23 Wheel platform24 Horizontal roller wheel25 Screws26 Frame27 Roller28 Frame for weight distribution29 Rotating platform fixing point30 Clamp31 Clamping knob32 Water source33 Storage reservoir34 Photoreactor35 Separator and drying unit36 Hydrogen37 Oxygen38 Dispensing unit39 Container40 Anode41 Cathode42 chamber43 chamber44 mirror45 separator46 connection1000 Coating procedure1010 Coating step1020 Coating step1030 Coating step1040 Coating step1050 Coating step1060 Coating step1100 Coating procedure1110 Coating step1120 Coating step1130 Coating step

[0102]

Claims

Claims

1. [Photoelectrode having i. a semiconductive photo-harvester, ii. an oxidation cocatalyst containing magnesium tin oxide, and iii. a reduction cocatalyst comprising, in particular composed of, cobalt, nickel, and manganese alloys.

2. Photoelectrode as per claim 1 , wherein the semiconductive photoharvester contains a metal silicide.

3. Photoelectrode as per any of the preceding claims, wherein the semiconductive photo-harvester may comprise an n-type silicon wafer and I or may be manufactured from an n-type silicon wafer.

4. Photoelectrode as per any of the preceding claims wherein the semiconductive photo-harvester comprises red phosphorous doped silicon, in particular red phosphorous doped monocrystalline silicon.

5. Photoelectrode as per any of the preceding claims wherein both sides of the semiconductive photo-harvester are provided with a protective coating, for example a coating layer comprising epoxy and I or silicon nitride.

6. Photoelectrode as per any of the preceding claims wherein the protective coating comprises at least one electrically conductive coating layer.

7. Photoelectrode as per any of the preceding claims wherein the protective coating has a thickness of up to 5 pm, in particular between 0.01 and 3 pm, for example 2 pm.

8. Photoelectrode as per any of the preceding claims wherein one side of the semiconductive photo-harvester comprises multiple coating layers including nickel, molybdenum, and zinc layers.

9. Photoelectrode as per any of the preceding claims wherein one side of the semiconductive photo-harvester comprises multiple coating layers comprising indium tin oxide (ITO) and I or cobalt.

10. Photoelectrode as per any of the preceding claims wherein the photo-harvester and / or the protective coating has a light trapping shape.

11. Method of manufacturing a photoelectrode as per any of the preceding claims from a photosensitive base exhibiting two sides wherein the two sides are coated with protective coating, for example comprising epoxy and I or silicon nitride.

12. Method as per the preceding method claims wherein the photosensitive base and I or the protective coating are inspected for cracks using X-rays.

13. Method as per any of the preceding method claims wherein the semiconductive photo-harvester is subjected to surface imaging and high magnification microscopy to assess surface nature and imperfections.

14. Method as per any of the previous method claims wherein i. the base is prepared by heating, such as in an inert gas oven, crystalline silicon to a temperature of preferably 200 °C, ii. the base is allowed to cool, coated, for example sprayed, with protective coating, and subjected to heat treatment, such as in a hot air chamber, iii. after the treatment, the base is fitted with anti-reflective coating, allowed to cool, and checked for cracks, and iv. the sides are bonded with the oxidation cocatalyst and reduction cocatalyst, respectively, allowed to cool, and inspected for the cracks.

15. Method as per any of the preceding method claims wherein at least parts of the coating are effected by means of physical vapor deposition (PVD).

16. Method as per any of the preceding method claims wherein the oxidation cocatalyst is prepared by mixing hydrochloric acid solution with magnesium chloride solution.

17. Method as per any of the preceding method claims wherein the oxidation cocatalyst is applied by means of chemical dipping followed by sputtering with a secondary coating.

18. Method as per any of the preceding method claims wherein after each coating application, the photoelectrode is subjected to a cooling interval.

19. Method as per any of the preceding method claims wherein the photoelectrode is dried after coating with protective coating comprising epoxy at a temperature between 50 and 60 °C.

20. Method as per any of the preceding method claims wherein the reduction cocatalyst is prepared by impregnating the cobalt alloy with cadmium and fusing the Nickel and manganese alloy with gallium nitride.

21. Method as per any of the preceding method claims wherein the reduction cocatalyst is added by sputtering, first applying the impregnated cobalt alloy and then, upon cooling, applying the fused Nickel and manganese alloy.

22. Method of generating hydrogen using a photoelectrode as per any of claims 1 to 10 or using a photoelectrode manufactured according to any of the preceding method claims, wherein a. the photoelectrode is placed in a transparent, preferably polycarbonate container, b. the container is filled with water such that the photoelectrode is immersed, and c. the container is exposed to light, preferably sunlight, such that the oxidation catalyst produces oxygen while the reduction catalyst produces the hydrogen.

23. Container for generating hydrogen, the container comprising a photoelectrode as per any of claims 1 to 10 and / or a photoelectrode manufactured according to any of the preceding method claims.

24. Container as per the preceding claim, wherein the container comprises at least one mirror.

25. Container as per any of the claims 22 or 23, wherein the container comprises an ion-impermeable, electrically conductive connection between an anode and a cathode of the container. ]

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