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 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

Photoelectrode

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

[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 (BiVO₄) 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 (IrO₂), 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.

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

[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 and effective 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.

[0015] As shall be further elucidated in the following description, this problem is solved as per the characterizing portion of the independent claims.

[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 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 invention utilizes 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.

[0019] The photoelectrode of the present invention exhibits superior stability in various aqueous environments, including those with high salinity and chemical pollutants. 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.

[0020] 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.

[0021] The fabrication method described in the invention, involving sputtering and chemical dipping techniques, is both precise and efficient. The use of atomizing nozzles for protective coating application and magnetron sputtering for cocatalyst deposition ensures uniform and high-quality layers. This streamlined process not only enhances the performance of the photoelectrode but also reduces manufacturing complexity and costs. The ability to use standard industrial techniques further supports the scalability of the invention.

[0022] 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.

[0023] 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 thus contributes to the development of a clean and sustainable energy economy, addressing both energy security and environmental sustainability.

[0024] shows the basic parts of a photocatalyzer.

[0025] shows the reactor lid.

[0026] shows the photoelectrode and separator.

[0027] shows the photoelectrode fitted in the reactor vessel.

[0028] shows the base part.

[0029] shows the platform connecting the reactor vessel and base.

[0030] is a flowchart.

[0031] 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.

[0032] 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 chloride solution. 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.

[0033] 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.

[0034] 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.

[0035] 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, using titanium 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.

[0036] 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 sccm, 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 MgSnO₃ oxidation cocatalyst.

[0037] 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 sccm, 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.

[0038] 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 an airtight 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 MgSnO₃ oxidation 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.

[0039] The exemplary photoelectrode demonstrated a hydrogen evolution rate of 10.2 mmol / h / cm² and 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.

[0040] This example demonstrates the successful fabrication and application of the claimed photoelectrode for efficient and stable photocatalytic hydrogen generation from water splitting.

[0041] 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.

[0042] 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 to the 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047]

[0048] Reference signDescription1Oxygen output2Pressure and temperature sensor3Hydrogen output4Reactor lid5Bolt6Bracket7Reactor vessel8Electrode separator9Photo electrode10Water inlet11Protective partition12Fixing base13Roller-fitted base part14Locking pin15Photo electrode separator16Locking pin female17Bracket male pin18Nuts and bolts19Polymer separator20Upper slit21Locking slit22Vertical roller wheel23Wheel platform24Horizontal roller wheel25Screws26Frame27Roller28Frame for weight distribution29Rotating platform fixing point30Clamp31Clamping knob32Water source33Storage reservoir34Photoreactor35Separator and drying unit36Hydrogen37Oxygen38Dispensing unit

Claims

Photoelectrode havinga semiconductive photo-harvester containing a metal silicide,an oxidation cocatalyst containing magnesium tin oxide, anda reduction cocatalyst composed of cobalt, nickel, and manganese alloys.Method of manufacturing a photoelectrode as per claim 1 from a photosensitive base exhibiting two sides whereinthe base is prepared by heating, such as in an inert gas oven, crystalline silicon to a temperature of preferably 200 °C,the base is allowed to cool, sprayed with protective coating, and subjected to heat treatment, such as in a hot air chamber,after the treatment, the base is fitted with anti-reflective coating, allowed to cool, and checked for cracks, andthe sides are bonded with the oxidation cocatalyst and reduction cocatalyst, respectively, allowed to cool, and inspected for the cracks.Method as per claim 2 whereinthe spraying is effected by means of atomizing nozzles.Method as per either of the preceding method claims whereinthe oxidation cocatalyst is prepared by mixing hydrochloric acid solution with magnesium chloride solution.Method as per any of the preceding method claims whereinthe oxidation cocatalyst is applied by means of chemical dipping followed by sputtering with a secondary coating.Method as per any of the preceding method claims whereinthe reduction cocatalyst is prepared by impregnating the cobalt alloy with cadmium and fusing the Nickel and manganese alloy with gallium nitride.Method as per the previous claim whereinthe reduction cocatalyst is added by sputtering, first applying the impregnated cobalt alloy and then, upon cooling, applying the fused Nickel and manganese alloy.Method of generating hydrogen using a photoelectrode as per claim 1 whereinthe photoelectrode is placed in a transparent, preferably polycarbonate container,the container is filled with water such that the photoelectrode is immersed, andthe container is exposed to light, preferably sunlight, such that the oxidation catalyst produces oxygen while the reduction catalyst produces the hydrogen.Method as per the previous claim whereinthe photoelectrode is placed such that the container is divided into mutually sealed chambers.Method as per the previous claim whereinthe photoelectrode is plugged into the inner walls of the container.Method as per any of claims 8 to 10 whereinupon filling, the container is sealed with a lid having gas outlets such that the oxygen and hydrogen escape controllably through the respective outlets.Method as per any of claims 8 to 11 whereinthe escaping oxygen and hydrogen are collected, stored, and eventually fed to a fuel cell to generate electricity.

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