Cation reduction device and hydrogen gas generation system

Abstract

The present invention provides a cation reduction device capable of increasing cation reduction efficiency.SOLUTION: According to an aspect of the present invention, there is provided a cation reducing device including a photocatalytic cell that accommodates an electrolytic solution containing first cations and photocatalytic particles, in which the electrolytic solution and the photocatalytic particles are provided such that the first cations are reduced to second cations by photocatalytic activity generated by the photocatalytic particles receiving light, and a pH of the electrolytic solution is within a pH range in which a zeta potential of the photocatalytic particles is 0mV or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cation reduction device 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 cations 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] However, the efficiency of cation reduction in conventional devices is low. The present invention has been made in view of the above circumstances, and provides a cation reduction device that can increase the efficiency of cation reduction. [Means for solving the problem]

[0005] The present invention provides a cation reduction device comprising a photocatalytic cell containing an electrolyte solution containing first cations and photocatalytic particles, wherein the electrolyte solution and the photocatalytic particles are arranged so that the first cations are reduced to second cations by photocatalytic activity generated when the photocatalytic particles receive light, and the pH of the electrolyte solution is within a pH range in which the zeta potential of the photocatalytic particles is 0 mV or higher. [Effects of the Invention]

[0006] The pH of the electrolyte contained in the cation reduction device of the present invention is within a pH range in which the zeta potential of the photocatalyst particles is 0 mV or higher, which increases the probability of cations coming into contact with the photocatalyst particles due to electrostatic attraction, thereby increasing the efficiency of reducing the first cations to the second cations. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic cross-sectional view of a cation reduction device according to one embodiment of the present invention. [Figure 2] 1 is a schematic cross-sectional view of a hydrogen gas generation system according to one embodiment of the present invention. [Figure 3] 1 is a graph showing the results of zeta potential measurement. DETAILED DESCRIPTION OF THE INVENTION

[0008] The cation reduction device of the present invention comprises a photocatalytic cell containing an electrolyte solution containing first cations and photocatalytic particles, wherein the electrolyte solution and the photocatalytic particles are arranged so that the first cations are reduced to second cations by photocatalytic activity generated when the photocatalytic particles receive light, and the pH of the electrolyte solution is within a pH range in which the zeta potential of the photocatalytic particles is 0 mV or higher.

[0009] The pH of the electrolyte is preferably less than 2. Preferably, the first cation is a trivalent iron ion and the second cation is a divalent iron ion. The electrolyte preferably contains iron ions in an amount of 10 mmol / L or more and 1 mol / L or less. The photocatalytic cell preferably has an inlet for supplying an electrolyte solution containing a first cation into the photocatalytic cell, and an outlet for discharging an electrolyte solution containing a second cation from the photocatalytic cell. The photocatalytic particles preferably include tungsten oxide particles. The photocatalyst particles are preferably supported on a carrier or fixed to a carrier.

[0010] The present invention also provides a hydrogen gas generation system comprising the cation reduction device 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, and the cation reduction device and the electrolyzer are configured to supply an electrolyte containing the second cations generated by the cation reduction device to the electrolyzer, and are configured to supply an electrolyte containing the first cations generated at the anode to the cation reduction device.

[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] Cation reduction device FIG. 1 is a schematic cross-sectional view of a cation reduction device according to this embodiment. The cation reduction device 20 of this embodiment includes a photocatalytic cell 13 containing an electrolyte 2a containing first cations and photocatalytic particles, and the electrolyte and photocatalytic particles are arranged so that the first cations are reduced to second cations by photocatalytic activity generated when the photocatalytic particles receive light, and the pH of the electrolyte is within a pH range in which the zeta potential of the photocatalytic particles is 0 mV or higher.

[0013] The cation reduction device is a device that reduces the first cations contained in the electrolytic solution 2a to the second cations by photocatalytic activity, and this device can produce an electrolytic solution containing the second cations. The photocatalytic cell 13 is a cell that contains the electrolyte solution 2a and photocatalytic particles. The photocatalytic cell 13 can have a light-transmitting member 5. This allows light that has passed through the light-transmitting member 5 to be irradiated onto the photocatalytic particles, allowing the photocatalytic particles to have photocatalytic activity. 1, the photocatalytic cell 13 has a container 4 and a light-transmitting member 5 that closes the opening of the container 4. The light-transmitting member 5 is fixed to the container 4 by a cover 8 and a bolt 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 that serves as the light-receiving surface can be disposed on the wide surface of this flat shape.

[0014] The photocatalyst particles are not particularly limited as long as they are particles that exhibit photocatalytic activity when exposed to light, but may include, for example, tungsten oxide particles, titanium oxide particles, etc., and preferably tungsten oxide particles (WO3 particles). Tungsten oxide has a wider light absorption band than titanium oxide and reacts to visible light that does not contain ultraviolet light, so photocatalytic activity can be generated even when light incident on the photocatalytic cell 13 passes through the electrolyte solution 2a and then irradiates tungsten oxide particles (photocatalytic particles).

[0015] 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.

[0016] The photocatalyst particles may be contained in the photocatalyst cell 13 in the form of a powder, or may be contained in the photocatalyst cell 13 as a compact of photocatalyst powder, or may be contained in the photocatalyst cell 13 as a photocatalyst carrier 3 in which the photocatalyst particles are supported or fixed on a carrier. In FIG. 1, the photocatalyst carrier 3 containing the photocatalyst particles is contained in the photocatalyst cell 13. In the photocatalyst carrier 3, the photocatalyst particles may be supported or fixed on paper, may be supported or fixed on a filter, may be supported or fixed on a porous body, or may be supported or fixed on a light-transmitting member such as a glass substrate.

[0017] In the photocatalytic cell 13, the surface of the photocatalytic particles is in contact with the electrolyte solution 2a. 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, creating 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, reacting with HO to generate oxygen gas (second reaction). The generated oxygen gas moves into the gas phase in the photocatalytic cell 13 and is discharged to the outside of the photocatalytic cell 13 through the oxygen gas discharge hole 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 generated hydrogen ions (H + ) can be used in the electrolysis device 30 described below.

[0018] In the photocatalyst cell 13, the photocatalyst particles or the photocatalyst carrier 3 may be immersed in the electrolytic solution 2a. In addition, in the photocatalyst cell 13, the powdered photocatalyst particles, the molded photocatalyst particles, or the photocatalyst carrier 3 may be permeated with the electrolytic solution 2a. Furthermore, powdered photocatalyst particles, molded photocatalyst particles or the photocatalyst carrier 3 can be placed at the bottom of the container 4 .

[0019] The electrolytic solution 2a is 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.

[0020] The pH of the electrolyte solution 2a is within a pH range in which the zeta potential of the photocatalyst particles is 0 mV or higher. The resulting electrostatic attraction increases the probability of contact between the photocatalyst particles and the first cations, increasing the probability that the first cations are reduced to second cations through photocatalytic activity. This allows the production of an electrolyte solution containing a larger amount of second cations. Furthermore, by using this electrolyte solution to generate hydrogen gas in a hydrogen gas generation system (described later), the efficiency of hydrogen gas generation can be improved.

[0021] 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 mV 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.

[0022] The photocatalytic cell 13 may have an inlet 10a provided to supply the electrolytic solution 2a containing the first cations into the photocatalytic cell 13, and an outlet 11a provided to discharge the electrolytic solution 2a containing the second cations from the photocatalytic cell 13. The inlet 10a and the outlet 11a may be provided so that the electrolytic solution 2a flows through the photocatalytic cell 13. This allows the first cations contained in the electrolytic solution 2a injected into the photocatalytic cell 13 from the inlet 10a to come into contact with the photocatalytic particles, and the first cations can be reduced and converted to second cations by photocatalytic activity. Furthermore, the electrolytic solution 2a containing the second cations generated by photocatalytic activity can be extracted from the photocatalytic cell 13, making it possible to utilize the electrolytic solution 2a containing the second cations.

[0023] Hydrogen Gas Generation System FIG. 2 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 cation reduction device 20 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 cation reduction device 20 and the electrolyzer 30 are configured to supply the electrolyzer 30 with an electrolyte 2a containing the second cations generated by the cation reduction device 20, and to supply the electrolyzer 30 with an electrolyte 2a containing the first cations generated at the anode 17.

[0024] 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 cation reduction device 20 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.

[0025] 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: Fe2+ → Fe 3+ + e -

[0026] The anode chamber 22 may have an inlet 10b provided to supply the electrolyte solution 2a containing the second cations generated in the cation reduction device 20 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.

[0027] The electrolyte solution 2a containing the second cations produced in the cation reduction device 20 may be supplied to the anode chamber 22 of the electrolyzer 30 through a liquid transfer pipe or a pump. Alternatively, the electrolyte solution 2a containing the second cations produced in the cation reduction device 20 may be stored in a storage tank. The electrolyte solution 2a may then 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.

[0028] The electrolyte solution 2a containing the first cations discharged from the anode chamber 22 of the electrolyzer 30 may be supplied to the cation reduction device 20 through a liquid transfer pipe or a pump. 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. The electrolyte solution 2a may then 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 cation reduction device 20. 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.

[0029] 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.

[0030] 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.

[0031] Zeta potential measurement experiment A dispersion (pH: 3.7) was prepared by dispersing 1 wt% tungsten oxide particles in pure water. The pH of the dispersion was varied by adding 10 μL of 0.1 N HCl or 10 μL of 0.1 N NaOH to the dispersion at 20-second intervals, while the zeta potential of the tungsten oxide particles contained in the dispersion was measured using nanoparticle tracking analysis (NTA). Figure 3 is a graph showing the relationship between the pH of the dispersion and the measured zeta potential. The experimental results showed that the zeta potential of the tungsten oxide particles gradually increased as the pH of the dispersion decreased below 4, and that when the pH of the dispersion reached approximately 2, the zeta potential of the tungsten oxide particles was approximately 0 mV. [Explanation of symbols]

[0032] 2a, 2b: Electrolyte 3: Photocatalyst carrier 4: Container 5: Light-transmitting member 6: Sealing member 7: Cushioning material 8: Cover 9: Bolt 10a, 10b: Inlet 11a, 11b: Outlet 12: Oxygen gas outlet 13: Photocatalytic cell 16: Cathode 17: Anode 18: Ion exchange membrane 19: Hydrogen gas outlet 20: Cation reduction device 21: Cathode chamber 22: Anode chamber 30: Electrolyzer 40: Hydrogen gas generation system

Claims

1. A photocatalytic cell containing an electrolytic solution containing a first cation and photocatalytic particles is provided, the electrolytic solution and the photocatalyst particles are provided so that first cations are reduced to second cations by photocatalytic activity generated when the photocatalyst particles receive light; A cation reduction device, characterized in that the pH of the electrolyte is within a pH range in which the zeta potential of the photocatalyst particles is 0 mV or higher.

2. 2. The cation reduction device according to claim 1, wherein the pH of the electrolyte is less than 2.

3. the first cation is a trivalent iron ion; 2. The cation reduction device according to claim 1, wherein the second cation is a divalent iron ion.

4. 4. The cation reduction device according to claim 3, wherein the electrolyte contains iron ions in an amount of 10 mmol / L or more and 1 mol / L or less.

5. 2. The cation reduction device according to claim 1, wherein the photocatalytic cell has an inlet for supplying an electrolyte solution containing a first cation into the photocatalytic cell, and an outlet for discharging an electrolyte solution containing a second cation from the photocatalytic cell.

6. The cation reduction device according to claim 1 , wherein the photocatalytic particles include tungsten oxide particles.

7. 2. The cation reduction device according to claim 1, wherein the photocatalyst particles are supported on a carrier or fixed to a carrier.

8. A cation reduction device according to any one of claims 1 to 7, 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 cation reduction device and the electrolysis device are configured to supply an electrolyte containing second cations generated by the cation reduction device to the electrolysis device, and to supply an electrolyte containing first cations generated at the anode to the cation reduction device.

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