Photocatalytic cell and hydrogen gas generation system

Abstract

To provide a photocatalyst cell capable of suppressing oxidation of a reduction product in an electrolytic solution by oxygen gas.SOLUTION: The photocatalyst cell is provided so as to be tilted at an angle of not less than 5 ° but not more than 45 ° with respect to a horizontal plane. The photocatalytic cell includes a translucent member, an electrolytic solution, a photocatalytic sheet containing photocatalytic particles, an injection port through which the electrolytic solution is injected into the photocatalytic cell, a discharge port through which the electrolytic solution is discharged to the outside of the photocatalytic cell, and an exhaust port through which gas inside the photocatalytic cell is discharged. the exhaust port is located higher than the injection port, and a gap between surfaces of the translucent member and the photocatalytic sheet is equal to or larger than 5mm and equal to or smaller than 50mm. The inlet and the outlet are provided so that the electrolytic solution flows from the upper part to the lower part in the gap between the translucent member and the photocatalyst sheet.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a photocatalytic cell and a hydrogen gas generation system. [Background technology]

[0002] Hydrogen gas is expected to be a next-generation energy source because it does not emit CO2 when used. In particular, "green hydrogen," produced by electrolyzing water using electricity from solar or wind power, is expected to be a promising energy source because it does not emit CO2 even during the production process. However, green hydrogen has the problem of high production costs. The electrolysis voltage of industrially used water electrolyzers is 1.5 to 2.1 V, which means it consumes a lot of power. A known device that can generate hydrogen gas from water at a low electrolysis voltage is one that combines a photocatalyst that reduces iron ions in an electrolyte with an electrolytic cell that generates hydrogen gas (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-157801 Summary of the Invention [Problem to be solved by the invention]

[0004] When light is irradiated onto a photocatalyst in an electrolyte, the photocatalytic activity reduces trivalent iron ions to divalent iron ions, but oxygen gas is also generated at the same time. This oxygen gas can sometimes oxidize divalent iron ions to trivalent iron ions, making it impossible to efficiently generate divalent iron ions. The present invention has been made in view of the above circumstances, and provides a photocatalytic cell that can prevent reduction products in an electrolyte from being oxidized by oxygen gas. [Means for solving the problem]

[0005] The present invention provides a photocatalytic cell that is installed at an angle of 5° to 45° with respect to a horizontal plane. The photocatalytic cell comprises a translucent member arranged to take in light from above or diagonally above, an electrolyte solution contained in the photocatalytic cell, a photocatalytic sheet containing photocatalytic particles arranged to receive the light taken in from the translucent member, an inlet arranged to inject the electrolyte solution into the photocatalytic cell, an outlet arranged to discharge the electrolyte solution to the outside of the photocatalytic cell, and an exhaust outlet arranged to discharge gas inside the photocatalytic cell, at least a part of the photocatalytic sheet is immersed in the electrolyte solution, the position of the exhaust outlet is higher than the position of the inlet, the gap width between the translucent member and the photocatalyst sheet is 5 mm to 50 mm, and the inlet and the exhaust outlet are arranged so that the electrolyte solution flows from the top to the bottom through the gap between the translucent member and the photocatalyst sheet. [Effects of the Invention]

[0006] When oxygen gas bubbles are generated by the photocatalytic activity caused by the photocatalytic particles contained in the photocatalyst sheet receiving light, the bubbles rise to the vicinity of the translucent member due to buoyancy. The gap width between the translucent member and the photocatalyst sheet is 5 mm or more and 50 mm or less, allowing the bubbles to quickly rise to the vicinity of the translucent member. Furthermore, because the photocatalytic cell is installed at an angle, the bubbles rise obliquely upward along the translucent member, rising into the gas phase above the injection port, and the oxygen gas can be discharged to the outside of the photocatalytic cell through the exhaust port. In this way, oxygen gas can be discharged from the electrolyte, preventing the oxygen gas from oxidizing reduction products (e.g., cations) in the electrolyte. Furthermore, since the electrolyte flows from top to bottom through the gap between the translucent member and the photocatalyst sheet, reduction products (e.g., cations) generated by reduction due to the photocatalytic activity caused by the photocatalyst particles receiving light can flow downward along with the electrolyte and can be discharged to the outside of the photocatalytic cell through the outlet. Because oxygen gas bubbles rise along the translucent member 5, the probability that reduction products contained in the electrolyte flowing downward will come into contact with the oxygen gas bubbles can be reduced, and oxidation of the reduction products by oxygen gas can be suppressed. Furthermore, since the photocatalytic cell is installed at an angle, the electrolyte can flow from the top to the bottom due to gravity, making it possible to omit pumps used to flow the electrolyte or reduce the power consumption of the pumps. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic cross-sectional view of a photocatalytic cell according to one embodiment of the present invention. [Figure 2] 1 is a schematic cross-sectional view of a photocatalytic cell according to one embodiment of the present invention. [Figure 3] 1 is a schematic cross-sectional view of a hydrogen gas generation system according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] The photocatalytic cell of the present invention is installed at an angle of 5° to 45° with respect to a horizontal plane. The photocatalytic cell comprises a translucent member arranged to take in light from above or diagonally above, an electrolyte solution contained in the photocatalytic cell, a photocatalyst sheet containing photocatalyst particles arranged to receive the light taken in from the translucent member, an inlet arranged to inject the electrolyte solution into the photocatalytic cell, an outlet arranged to discharge the electrolyte solution to the outside of the photocatalytic cell, and an exhaust outlet arranged to discharge gas inside the photocatalytic cell, wherein at least a part of the photocatalyst sheet is immersed in the electrolyte solution, the position of the exhaust outlet is higher than the position of the inlet, the gap width from the surface of the translucent member to the surface of the photocatalyst sheet is 5 mm to 50 mm, and the inlet and the exhaust outlet are arranged so that the electrolyte solution flows from the top to the bottom through the gap between the translucent member and the photocatalyst sheet.

[0009] Preferably, the electrolyte solution contains first cations, and the electrolyte solution and the photocatalyst particles are provided so that the first cations are reduced to second cations by photocatalytic activity caused by the photocatalyst particles receiving light. Preferably, the first cation is a trivalent iron ion and the second cation is a divalent iron ion. The position of the exhaust port is preferably 10 mm or more higher than the position of the injection port. The photocatalytic particles preferably include tungsten oxide particles.

[0010] The present invention also provides a hydrogen gas generation system comprising the photocatalytic cell of the present invention and an electrolyzer having a cathode and an anode, wherein the electrolyzer is configured to generate hydrogen gas from water or hydrogen ions at the cathode and to oxidize second cations to first cations at the anode, the photocatalytic cell and the electrolyzer being configured to supply an electrolyte containing the second cations generated by the photocatalytic cell to the electrolyzer, and also configured to supply an electrolyte containing the first cations generated at the anode to the photocatalytic cell.

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The configurations shown in the drawings and the following description are merely examples, and the scope of the present invention is not limited to those shown in the drawings and the following description.

[0012] Photocatalytic Cell 1 and 2 are schematic cross-sectional views of the photocatalytic cell of this embodiment. The photocatalytic cell 13 of this embodiment is installed so as to be tilted at an angle of 5° to 45° relative to the horizontal plane. The photocatalytic cell 13 has a translucent member 5 arranged to take in light from above or diagonally above, an electrolyte 2a contained in the photocatalytic cell 13, a photocatalyst sheet 3 containing photocatalytic particles arranged to receive the light taken in from the translucent member 5, an inlet 10a arranged to inject the electrolyte 2a into the photocatalytic cell 13, an outlet 11a arranged to discharge the electrolyte 2a to the outside of the photocatalytic cell 13, and an exhaust outlet 12 arranged to discharge gas inside the photocatalytic cell 13, and is characterized in that at least a part of the photocatalyst sheet 3 is immersed in the electrolyte 2a, the position of the exhaust outlet 12 is higher than the position of the inlet 10a, the gap width from the surface of the translucent member 5 to the surface of the photocatalyst sheet 3 is 5 mm or more and 50 mm or less, and the inlet 10a and the outlet 11a are arranged so that the electrolyte 2a flows from the top to the bottom through the gap between the translucent member 5 and the photocatalyst sheet 3.

[0013] The photocatalytic cell 13 is a cell that contains the electrolytic solution 2a and the photocatalytic sheet 3. The photocatalytic cell 13 may be included in a cation reduction device that reduces first cations contained in the electrolytic solution 2a to second cations by photocatalytic activity. The photocatalytic cell 13 may also be included in a device that generates hydrogen gas or oxygen gas from the electrolytic solution 2a by photocatalytic activity.

[0014] The photocatalytic cells 13 are installed so as to be tilted at an angle of 5° or more and 45° or less with respect to the horizontal plane. By installing the photocatalytic cells 13 at an angle, sunlight can be more easily incident on the photocatalytic cells 13, and the amount of light received by the photocatalytic particles contained in the photocatalyst sheet 3 can be increased. This increases the photocatalytic activity of the photocatalytic particles. The photocatalytic cells 13 can also have a flat shape.

[0015] The photocatalytic cell 13 can have a light-transmitting member 5. This allows light transmitted through the light-transmitting member 5 to be irradiated onto the photocatalytic particles contained in the photocatalyst sheet 3, allowing the photocatalytic particles to have photocatalytic activity. The material of the light-transmitting member 5 may be glass such as quartz glass, or resin such as acrylic resin, polycarbonate, or polyvinyl chloride. The light-transmitting member 5 is provided so as to introduce light into the photocatalytic cell 13 from above or obliquely from above. The light-transmitting member 5 can also have a flat plate shape. 1 and 2, the photocatalytic cell 13 has a container 4 and a light-transmitting member 5 that closes the opening of the container 4. As shown in FIG. 2, the light-transmitting member 5 is fixed to the container 4 by a cover 8 and bolts 9. In addition, a buffer material 7 is provided between the light-transmitting member 5 and the cover 8, and a sealing member 6 is provided between the container 4 and the light-transmitting member 5. The photocatalytic cell 13 can have a flat shape, and the light-transmitting member 5, which serves as the light-receiving surface, can be placed on the wide surface of this flat shape. When the photocatalytic cell 13 is installed at an angle, the light-transmitting member 5 can take in light (for example, sunlight) into the photocatalytic cell 13 from diagonally above.

[0016] The photocatalyst sheet 3 is a sheet containing photocatalyst particles. The photocatalyst sheet 3 may include a carrier sheet and a plurality of photocatalyst particles. At least a portion of the photocatalyst sheet 3 is immersed in the electrolyte solution 2a. The photocatalyst sheet 3 can be placed at the bottom of the container 4. The gap width from the surface of the light-transmitting member 5 to the surface of the photocatalyst sheet 3 is 5 mm or more and 50 mm or less, preferably 5 mm or more and 40 mm or less, and more preferably 5 mm or more and 30 mm or less. This shortens the distance that light passes through the electrolyte 2a before reaching the photocatalyst particles, allowing more light to be received by the photocatalyst particles. In addition, the distance that oxygen gas bubbles generated in the photocatalyst sheet 3 travel due to buoyancy to reach the vicinity of the light-transmitting member 5 can be shortened, thereby preventing reduction products (e.g., divalent iron ions) generated by photocatalytic activity from being oxidized by oxygen gas.

[0017] It is possible to fill 90% or more of the gap between the light-transmitting member 5 and the photocatalyst sheet 3 with the electrolyte 2a. This makes it possible to narrow the contact area between the electrolyte 2a and the gas phase, and to suppress oxidation of reduction products (for example, divalent iron ions) contained in the electrolyte 2a.

[0018] Photocatalyst particles are particles that exhibit photocatalytic activity upon receiving light. The photocatalyst particles may be supported or fixed on a carrier sheet. The photocatalyst particles may include tungsten oxide particles (WO3 particles). Tungsten oxide has a wider light absorption band than titanium oxide and exhibits photocatalytic activity even when absorbing visible light that does not include ultraviolet light. Therefore, photocatalytic activity can be exhibited even when light incident on the photocatalyst cell 13 passes through the electrolyte solution 2a and then irradiates the tungsten oxide particles (photocatalyst particles). Furthermore, tungsten oxide has a larger specific gravity than titanium oxide. This allows the mass per unit area of ​​the photocatalyst sheet 3 to be increased. This prevents the photocatalyst sheet 3 from floating in the electrolyte solution 2a and prevents the position of the photocatalyst sheet 3 from changing within the photocatalyst cell 13.

[0019] The tungsten oxide particles (WO3 particles) contained in the photocatalyst particles may have a composition that deviates from the stoichiometric composition as long as they have photocatalytic activity. Furthermore, the tungsten oxide particles may contain impurity atoms or additive atoms to the extent that the photocatalytic activity is not lost. Furthermore, the photocatalyst particles may have a co-catalyst on their surface. Examples of the co-catalyst include platinum group metals such as Pt, Pd, Rh, Ru, Os, and Ir. The average particle diameter D50 of the photocatalyst particles (primary particles) contained in the photocatalyst sheet 3 is, for example, 150 nm or more, preferably 200 nm or more and 50 μm or less, and more preferably 500 nm or more and 30 μm or less.

[0020] The carrier sheet is included in the photocatalyst sheet 3 and is a sheet that supports the photocatalyst particles. The carrier sheet is paper, nonwoven fabric, woven fabric, a resin sheet, a glass sheet, a ceramic sheet, or the like. The photocatalyst particles may be attached to the surface of the carrier sheet. Furthermore, when the carrier sheet is paper or nonwoven fabric, the photocatalyst particles may be embedded in the carrier sheet.

[0021] In the photocatalytic cell 13, the photocatalytic sheet 3 and photocatalytic particles are in contact with the electrolyte solution 2a. This allows the first cations contained in the electrolyte solution 2a to be reduced to second cations through photocatalytic activity, or the photocatalytic cell 13 can generate hydrogen gas or oxygen gas from the electrolyte solution 2a through photocatalytic activity. For example, when the photocatalytic particles are exposed to light, the first cations in the electrolyte solution 2a are reduced to second cations, and oxygen gas is generated from the electrolyte solution 2a. This can be explained as follows: Light excites electrons in the valence band of the photocatalytic particles to the conduction band, forming holes in the valence band. The electrons in the conduction band move to the surface of the photocatalytic particles, adding electrons to the first cations and reducing them to second cations (first reaction). The holes in the valence band also move to the surface of the photocatalytic particles and react with HO to generate oxygen gas (second reaction). The generated oxygen gas turns into bubbles in the electrolyte 2a, rises along the light-transmitting member 5, moves into the gas phase in the photocatalytic cell 13, and is discharged to the outside of the photocatalytic cell 13 through at least one exhaust port 12. For example, if the primary cation is a trivalent iron ion (Fe 3+ ), and the second cation is divalent iron ion (Fe 2+ ), the following reaction is thought to proceed: 1st reaction: Fe 3+ + e - → Fe 2+ Second reaction: 2H2O → O2+ 4H + + 4e - The divalent iron ions (Fe 2+ ) and hydrogen ions (H + ) can be used in the electrolysis device 30 described below.

[0022] The electrolytic solution 2a may be an aqueous solution containing first cations, which are reduced to second cations by photocatalytic activity caused by the photocatalytic particles receiving light. When the electrolytic solution 2a contains iron sulfate (FeSO4, Fe2(SO4)3), the first cation is a trivalent iron ion, and the second cation is a divalent iron ion. When the electrolyte 2a contains iron perchlorate (Fe(ClO4)3, Fe(ClO4)2), the first cation is a trivalent iron ion and the second cation is a divalent iron ion. The first and second cations may be metal complex ions, and the metal contained in the metal complex ions may be, for example, iron or cobalt.

[0023] The pH of the electrolytic solution 2a may be within a pH range in which the zeta potential of the photocatalytic particles is 0 V or higher. This generates an electrostatic attraction force that increases the probability of contact between the photocatalytic particles and the first cations, thereby increasing the probability that the first cations are reduced to second cations through photocatalytic activity. This makes it possible to produce an electrolytic solution containing a larger amount of second cations. Furthermore, by using this electrolytic solution to generate hydrogen gas in a hydrogen gas generation system described below, the efficiency of hydrogen gas generation can be improved.

[0024] When the photocatalytic particles contain tungsten oxide particles, the pH of the electrolyte 2a can be made lower than 2 (to the acidic side). This allows the zeta potential of the photocatalytic particles to be 0 V or higher, and also allows divalent iron ions and trivalent iron ions to exist stably in the electrolyte 2a. This makes it possible to prevent divalent iron ions from being oxidized to trivalent iron ions by oxygen dissolved in the electrolyte 2a, oxygen gas in the gas phase, oxygen gas generated by photocatalytic activity, and the like. For example, the pH of the electrolytic solution 2a may be adjusted by adjusting the iron sulfate concentration, iron perchlorate concentration, or the like of the electrolytic solution 2a, or the pH of the electrolytic solution 2a may be adjusted by adding an acidic substance such as sulfuric acid or perchloric acid to the electrolytic solution 2a. Furthermore, when an electrolyte solution is prepared by dissolving approximately 50 g of iron perchlorate n-hydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.: n=approximately 8) in 10 L of water, the pH of the electrolyte solution will be approximately 2. The iron ion concentration of the electrolyte solution 2a is preferably, for example, 10 mmol / L to 1 mol / L. This is a concentration at which the iron ions can stably maintain their respective valence states. More preferably, the iron ion concentration of the electrolyte solution 2a is 10 mmol / L to 100 mmol / L. A lower iron ion concentration reduces the effect of iron ions on the coloring of the electrolyte solution, and can suppress a decrease in the amount of light received by the photocatalyst.

[0025] 1, the photocatalytic cell 13 can have an inlet 10a provided to supply an electrolyte solution 2a containing a first cation into the photocatalytic cell 13, and an outlet 11a provided to discharge the electrolyte solution 2a containing a second cation from the inside of the photocatalytic cell 13. The inlet 10a and the outlet 11a are provided so that the electrolyte solution 2a flows through the gap between the light-transmitting member 5 and the photocatalytic sheet 3 from the upper part (the upper part of the photocatalytic cell 13) to the lower part (the lower part of the photocatalytic cell 13). Because the electrolyte solution 2a flows from the upper part to the lower part due to its own weight, a pump or the like used to flow the electrolyte solution 2a can be omitted, or the power consumption of the pump can be reduced. Furthermore, the first cations contained in the electrolyte 2a injected into the photocatalytic cell 13 through the injection port 10a can be brought into contact with the photocatalytic particles, and the first cations can be reduced and converted into second cations by photocatalytic activity. Furthermore, the electrolyte 2a containing the second cations generated by the photocatalytic activity can be extracted from the photocatalytic cell 13, making it possible to utilize the electrolyte 2a containing the second cations.

[0026] As described above, the oxygen gas bubbles generated by photocatalytic activity rise along the light-transmitting member 5, so the flow direction of the electrolyte 2a can be made opposite to the direction in which the bubbles rise. This reduces the probability that reduction products (e.g., divalent iron ions) contained in the electrolyte 2a flowing downward will come into contact with the oxygen gas bubbles, and makes it possible to prevent the reduction products from being oxidized by the oxygen gas.

[0027] At least one exhaust port 12 is provided to discharge gas from inside the photocatalytic cell 13 and is positioned higher than the inlet 10a. The exhaust port 12 can be positioned, for example, 10 mm or higher than the inlet 10a. This allows the exhaust port 12 to be positioned higher than the liquid level of the electrolyte 2a, forming a gas phase between the inlet 10a and the exhaust port 12. This prevents the electrolyte 2a from accumulating near the connection between the inside of the cell and the exhaust port 12, which could cause resistance to gas discharge. This allows the gas in the gas phase inside the photocatalytic cell 13 to be efficiently discharged to the outside of the photocatalytic cell 13 through the exhaust port 12. When the photocatalytic cell 13 has multiple exhaust ports 12, the multiple exhaust ports 12 can be positioned at substantially the same height. Furthermore, the exhaust ports 12 can be positioned so as not to overlap with the bolts 9.

[0028] The photocatalytic cell 13 can have an emergency exhaust outlet 14 that is located at a position higher than the inlet 10a and lower than the exhaust outlet 12. The emergency exhaust outlet 14 can be located, for example, on the side of the photocatalytic cell 13. The emergency exhaust outlet 14 is provided so that when an excess of the electrolyte solution 2a is supplied from the inlet 10a into the inside of the photocatalytic cell 13 and the liquid level of the electrolyte solution 2a in the photocatalytic cell 13 becomes higher than the inlet 10a and reaches the height of the emergency exhaust outlet 14, the electrolyte solution 2a inside the photocatalytic cell 13 is discharged from the emergency exhaust outlet 14 to the outside of the photocatalytic cell 13. By providing such an emergency exhaust outlet 14, it is possible to prevent the electrolyte solution 2a from flowing into the exhaust outlet 12.

[0029] Hydrogen Gas Generation System FIG. 3 is a schematic cross-sectional view of the hydrogen gas generation system of this embodiment. The hydrogen gas generation system 40 of this embodiment includes a photocatalytic cell 13 and an electrolyzer 30 having a cathode 16 and an anode 17. The electrolyzer 30 is configured to generate hydrogen gas from water or hydrogen ions at the cathode 16 and to oxidize second cations to first cations at the anode 17. The photocatalytic cell 13 and the electrolyzer 30 are configured to supply the electrolytic solution 2a containing the second cations generated by the photocatalytic cell 13 to the electrolyzer 30, and to supply the electrolytic solution 2a containing the first cations generated at the anode 17 to the photocatalytic cell 13.

[0030] The electrolyzer 30 may have a power supply unit configured to apply a voltage between the anode 17 and the cathode 16. The electrolyzer 30 may also have an anode chamber 22 and a cathode chamber 21 separated by an ion exchange membrane 18. The electrolytic solution 2a containing the second cations generated by the photocatalytic cell 13 is supplied to the electrolyzer 30, the anode chamber 22 is filled with the electrolytic solution 2a, and the cathode chamber 21 is filled with the electrolytic solution 2b. Then, when a voltage is applied between the anode 17 and the cathode 16 using the power supply, an anodic reaction proceeds on the surface of the anode 17, and a cathodic reaction proceeds on the surface of the cathode 16. In addition, hydrogen ions (H+ ) moves through the ion exchange membrane 18 to the electrolyte 2b in the cathode chamber 21. The electrolyte 2b can be an acidic electrolyte.

[0031] At the anode 17, a reaction proceeds in which the second cations contained in the electrolyte 2a in the anode chamber 22 donate electrons to the anode 17 and are oxidized to the first cations (anode reaction). For example, if the primary cation is a trivalent iron ion (Fe 3+ ), and the second cation is divalent iron ion (Fe 2+ ), the following anodic reaction is thought to occur: Anode reaction: Fe 2+ → Fe 3+ + e -

[0032] The anode chamber 22 may have an inlet 10b provided to supply the electrolyte solution 2a containing the second cations generated in the photocatalytic cell 13 into the anode chamber 22, and an outlet 11b provided to discharge the electrolyte solution 2a containing the first cations generated from the second cations in the anode 17 from the anode chamber 22. The inlet 10b and the outlet 11b may be provided so that the electrolyte solution 2a injected from the inlet 10b passes through the anode chamber 22 and then is discharged from the outlet 11b. By circulating the electrolyte solution 2a in this manner, the anode reaction can proceed continuously and stably.

[0033] The electrolyte solution 2a containing the second cations produced in the photocatalytic cell 13 may be supplied to the anode chamber 22 of the electrolyzer 30 through a liquid supply pipe or a pump. Alternatively, the electrolyte solution 2a containing the second cations produced in the photocatalytic cell 13 may be supplied to the anode chamber 22 of the electrolyzer 30 by its own weight. Alternatively, the electrolyte solution 2a containing the second cations produced in the photocatalytic cell 13 may be stored in a storage tank. Then, the electrolyte solution 2a may be transported together with the storage tank, and the electrolyte solution 2a stored in the storage tank at the transport destination may be supplied to the anode chamber 22 of the electrolyzer 30.

[0034] The electrolyte solution 2a containing the first cations discharged from the anode chamber 22 of the electrolyzer 30 may be supplied to the photocatalytic cell 13 through a liquid transfer pipe or a pump 15. Alternatively, the electrolyte solution 2a containing the first cations discharged from the anode chamber 22 of the electrolyzer 30 may be supplied to the photocatalytic cell 13 by its own weight. Alternatively, the electrolyte solution 2a containing the first cations discharged from the anode chamber 22 of the electrolyzer 30 may be stored in a storage tank. Then, the electrolyte solution 2a may be transported together with the storage tank, and the electrolyte solution 2a stored in the storage tank at the transport destination may be supplied to the photocatalytic cell 13. Furthermore, such a circulation system for the electrolyte solution 2a may be provided so as to add water to the circulating electrolyte solution 2a, thereby making it possible to replenish the water consumed in the second reaction described above.

[0035] At the cathode 16, the following cathode reaction proceeds in which hydrogen ions contained in the electrolyte 2b in the cathode chamber 21 receive electrons to generate hydrogen gas. Cathodic reaction: 2H + + 2e - → H2 The generated hydrogen gas is discharged to the outside of the cathode chamber 21 through the hydrogen gas discharge hole 19 and stored in the hydrogen storage tank.

[0036] The above-described anode and cathode reactions proceed at a lower applied voltage (the voltage applied between the cathode 16 and the anode 17 by the power supply unit) than in conventional water electrolysis devices. This reduces the cost of hydrogen gas production. [Explanation of symbols]

[0037] 2a, 2b: Electrolyte 3: Photocatalytic sheet 4: Container 5: Light-transmitting member 6: Sealing member 7: Cushioning material 8: Cover 9: Bolt 10a, 10b: Inlet 11a, 11b: Outlet 12: Exhaust port 13: Photocatalytic cell 14: Emergency outlet 15: Pump 16: Cathode 17: Anode 18: Ion exchange membrane 19: Hydrogen gas outlet 20: Nut 21: Cathode chamber 22: Anode chamber 30: Electrolyzer 40: Hydrogen gas generation system

Claims

1. A photocatalytic cell that is installed at an angle of 5° to 45° with respect to a horizontal plane, The photocatalytic cell has a translucent member arranged to take in light from above or obliquely above, an electrolyte solution contained in the photocatalytic cell, a photocatalytic sheet containing photocatalytic particles arranged to receive the light taken in from the translucent member, an inlet arranged to inject the electrolyte solution into the photocatalytic cell, an outlet arranged to discharge the electrolyte solution to the outside of the photocatalytic cell, and an exhaust port arranged to discharge gas inside the photocatalytic cell, At least a portion of the photocatalyst sheet is immersed in the electrolyte solution, The position of the exhaust port is higher than the position of the inlet, The gap width from the surface of the translucent member to the surface of the photocatalyst sheet is 5 mm or more and 50 mm or less, A photocatalytic cell characterized in that the inlet and outlet are provided so that the electrolyte flows from the top to the bottom through the gap between the light-transmitting member and the photocatalytic sheet.

2. the electrolyte solution includes a first cation; 2. The photocatalytic cell according to claim 1, wherein the electrolytic solution and the photocatalytic particles are provided so that first cations are reduced to second cations by photocatalytic activity generated when the photocatalytic particles receive light.

3. the first cation is a trivalent iron ion; 3. The photocatalytic cell according to claim 2, wherein the second cation is a divalent iron ion.

4. 2. The photocatalytic cell according to claim 1, wherein the position of the exhaust port is 10 mm or more higher than the position of the injection port.

5. The photocatalytic cell of claim 1 , wherein the photocatalytic particles include tungsten oxide particles.

6. An electrolysis device comprising the photocatalytic cell according to claim 2 or 3 and an electrolysis device having a cathode and an anode, the electrolyzer is configured to produce hydrogen gas from water or hydrogen ions at a cathode and to oxidize second cations to first cations at an anode; The photocatalytic cell and the electrolysis device are arranged to supply an electrolyte containing second cations produced by the photocatalytic cell to the electrolysis device, and the hydrogen gas generation system is arranged to supply an electrolyte containing first cations produced at the anode to the photocatalytic cell.

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