Reaction electrodes and electrochemical reactors using the same

Abstract

To provide a reaction catalyst which reduces the influence of oxygen (O2) and an electrochemical reactor using the same.SOLUTION: In a state where a first surface is in contact with a liquid and a second surface different from the first surface is in contact with a gas, the reaction catalyst is used for producing a reaction product by using a substance contained in the gas or the liquid as a raw material. In the reaction catalyst, a hydrophilic porous layer 40, a catalytic porous layer 30 containing a catalyst used for a reaction to produce the reaction product, and a water-repellent porous layer 34 are arranged in order from the liquid side to the gas side.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention Reaction electrodes This relates to electrochemical reactors using the same. [Background technology]

[0002] An electrochemical reduction reactor for carbon dioxide (CO2) is known (including an artificial photosynthesis cell combined with a solar cell) that comprises an anode electrode and a cathode electrode, and supplies and discharges an electrolyte between them (Patent Document 1). At the cathode electrode, carbon dioxide (CO2) is reduced to produce formic acid (HCOOH), carbon monoxide (CO), etc., and at the anode electrode, water (H2O) is oxidized to produce oxygen (O2). In the case of a method in which a gas containing carbon dioxide (CO2) is dissolved in an electrolyte and supplied to the cathode electrode (liquid phase supply method), the reaction efficiency decreases when the concentration of carbon dioxide (CO2) in the gas decreases due to constraints imposed by the solubility and diffusion coefficient of carbon dioxide (CO2).

[0003] Furthermore, a configuration can be adopted in which one side of the cathode electrode is in contact with the liquid and the other side is in contact with a gas containing carbon dioxide (CO2), thereby supplying carbon dioxide (CO2) from the gas side (gas phase supply method). In this case, as shown in Figure 11, the catalyst porous layer 50 and the water-repellent porous layer 52 are arranged sequentially as the cathode electrode from the electrolyte side to the gas side. When such a method is adopted, carbon dioxide (CO2) is supplied rapidly, and high reaction efficiency is maintained even at low carbon dioxide (CO2) concentrations. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-59760 [Overview of the project] [Problems that the invention aims to solve]

[0005] Incidentally, when oxygen (O2) is mixed with carbon dioxide (CO2) supplied from the gas side, the reaction efficiency of carbon dioxide (CO2) reduction decreases. The reason for this is thought to be that the solubility of oxygen (O2) is much lower than that of carbon dioxide (CO2) (approximately 1 / 330 in water), so as shown in Figure 11, the concentration of oxygen (O2) in the catalyst porous layer 50 filled with liquid is low, but the concentration of oxygen (O2) is high in the region near the interface between the catalyst porous layer 50 and the water-repellent porous layer 52 that is in contact with the gas, and the reduction of carbon dioxide (CO2) by the catalyst porous layer 50 in that region is hindered.

[0006] Therefore, there is a need for a reaction catalyst that reduces the influence of oxygen (O2) near the interface between the catalyst porous layer 50 and the water-repellent porous layer 52, and an electrochemical reactor using the same.

[0007] Furthermore, as shown in Figure 12, the concentration of carbon dioxide (CO2) supplied from the gas side begins to decrease from the interface between the water-repellent porous layer 52 and the catalyst porous layer 50, and is presumed to be almost zero at the interface between the catalyst porous layer 50 and the electrolyte. Therefore, the reaction efficiency is low in regions of the catalyst porous layer 50 where the concentration of carbon dioxide (CO2) is low.

[0008] Therefore, there is a need for a reaction catalyst that improves reaction efficiency by increasing the concentration of carbon dioxide (CO2) within the porous catalyst layer 50, and an electrochemical reactor using the same. [Means for solving the problem]

[0009] One aspect of the present invention is a reaction catalyst used to produce a reaction product using a substance contained in a gas or liquid as a raw material, in a state in which a first surface is in contact with a liquid and a second surface different from the first surface is in contact with a gas, characterized in that a hydrophilic porous layer containing a catalyst used in the reaction to produce the reaction product, a catalyst porous layer, and a hydrophobic porous layer are arranged in order from the liquid side toward the gas side.

[0010] In this case, the hydrophilic porous layer is preferably made of a porous hydrophilic polymer material.

[0011] Furthermore, the hydrophilic polymer material preferably contains at least one of cellulose, nylon, cellulose acetate, polyvinyl alcohol, polyacrylic acid, and polyacrylate salt.

[0012] Furthermore, the hydrophilic porous layer is preferably made of a porous polymer material whose surface has been treated to make it hydrophilic.

[0013] Furthermore, the polymer material preferably contains at least one of an olefin polymer, vinyl chloride, acrylonitrile-butadiene-styrene copolymer resin (ABS resin), and polycarbonate.

[0014] Furthermore, the hydrophilization treatment is preferably at least one of ultraviolet irradiation, plasma irradiation, ozone oxidation, corona discharge, high-voltage discharge, and graft polymerization of hydrophilic groups.

[0015] Furthermore, the thickness of the hydrophilic porous layer is preferably 600 μm or less. Also, the thickness of the hydrophilic porous layer is preferably 100 μm or more and 600 μm or less.

[0016] Furthermore, the average pore size of the hydrophilic porous layer is preferably in the range of 0.1 μm to 200 μm.

[0017] Furthermore, the porosity of the hydrophilic porous layer is preferably in the range of 10% to 90%.

[0018] Furthermore, the catalyst porous layer preferably includes at least one of the following: a porous material having electrical conductivity and catalytic activity; a material on which the catalyst is supported on an electrically conductive porous material; a material on which a porous material is coated with a substance having electrical conductivity and catalytic activity; or a material on which a catalyst is supported on a porous material that is coated with a substance having electrical conductivity.

[0019] Further, it is preferable that the catalyst porous layer is one in which multi-walled carbon nanotubes and a ruthenium complex are supported on carbon paper.

[0020] Further, it is preferable that the water-repellent porous layer is one in which carbon paper is coated with polytetrafluoroethylene (PTFE).

[0021] Further, it is preferable that the liquid contains water and oxygen is generated as the reaction product substance from the water.

[0022] Further, it is preferable that a second hydrophilic porous layer is disposed between the catalyst porous layer and the water-repellent porous layer.

[0023] Another aspect of the present invention is an electrochemical reactor provided with the above reaction catalyst.

Advantages of the Invention

[0024] According to the present invention, it is possible to provide a reaction catalyst with reduced influence of oxygen (O2) and an electrochemical reactor using the same.

Brief Description of the Drawings

[0025] [Figure 1] It is a schematic cross-sectional view showing the configuration of the electrochemical reactor in the first embodiment. [Figure 2] It is an exploded cross-sectional view showing the configuration of the cathode electrode in the first embodiment. [Figure 3] It is a diagram showing the results of electrochemical measurement in the first embodiment. [Figure 4] It is a diagram for explaining the operation of the cathode electrode in the first embodiment. % [Figure 5] It is a schematic cross-sectional view showing the configuration of the electrochemical reactor in the second embodiment. [Figure 6] It is an exploded cross-sectional view showing the configuration of the cathode electrode in the second embodiment. [Figure 7]This figure shows the results of the electrochemical measurements in the second embodiment. [Figure 8] This is a diagram illustrating the operation of the cathode electrode in the second embodiment. [Figure 9] This is a schematic cross-sectional view showing the configuration of an electrochemical reactor in the third embodiment. [Figure 10] This is an exploded cross-sectional view showing the configuration of the cathode electrode in the third embodiment. [Figure 11] This diagram illustrates the challenges of conventional electrochemical reactors. [Figure 12] This diagram illustrates the challenges of conventional electrochemical reactors. [Modes for carrying out the invention]

[0026] [First Embodiment] Figure 1 is a schematic cross-sectional view showing the configuration of a test apparatus simulating the electrochemical reactor 100 in the first embodiment.

[0027] The electrochemical reactor 100 comprises a cell 10, a cathode electrode 12, a counter electrode 14, a reference electrode 16, a separation membrane 18, a gas passage 20, and an electrolyte 22.

[0028] The cathode electrode 12 functions as a reaction catalyst. As shown in the exploded cross-sectional view in Figure 2, the cathode electrode 12 is composed of a catalyst porous layer 30, a hydrophilic porous layer 32, and a hydrophobic porous layer 34. Specifically, the cathode electrode 12 can be constructed by laminating the catalyst porous layer 30, the hydrophilic porous layer 32, and the hydrophobic porous layer 34 and sandwiching them between two support plates 36. In addition, a conductive sheet 38 is electrically connected to the hydrophobic porous layer 34 as an electrode.

[0029] The cathode electrode 12 is used to generate reaction products using substances contained in the gas as raw materials, with its first surface in contact with the liquid inside the electrochemical reactor 100 (e.g., electrolyte 22) and its second surface, which is different from the first surface, in contact with the gas outside the electrochemical reactor 100. A catalyst porous layer 30 is placed on the first surface, which is the liquid side, and a water-repellent porous layer 34 is placed on the second surface, which is the gas side. A hydrophilic porous layer 32 is placed between the catalyst porous layer 30 and the water-repellent porous layer 34. The catalyst porous layer 30 is a layer containing a catalyst used in the reaction to generate the reaction products.

[0030] The catalyst porous layer 30 preferably includes at least one of the following: a porous material having electrical conductivity and catalytic activity; a material in which a catalyst is supported on an electrically conductive porous material; a material in which a porous material is coated with a substance having electrical conductivity and catalytic activity; or a material in which a catalyst is supported on a porous material that is coated with a substance having electrical conductivity.

[0031] The catalyst is a catalyst that contributes to the chemical reaction produced in the electrochemical reactor 100. For example, in the case of a chemical reaction that reduces carbon dioxide (CO2) to produce formic acid and carbon monoxide (CO), the catalyst used in the cathode electrode 12 preferably contains a ruthenium complex. For example, the catalyst porous layer 30 can be a structure in which a ruthenium complex polymer (RuCP) is supported on multi-walled carbon nanotubes (MWCNTs) / carbon paper (CP) (CP / MWCNT / RuCP). However, the catalyst is not limited to this, and any catalyst that promotes the chemical reaction required in the electrochemical reactor 100 is acceptable.

[0032] The hydrophilic porous layer 32 is preferably composed of a porous hydrophilic polymer material or a porous polymer material whose surface has been hydrophilized. Examples of hydrophilic polymer materials include cellulose, nylon, cellulose acetate, polyvinyl alcohol, polyacrylic acid, and polyacrylate salts. The hydrophilic porous layer 32 can be composed of at least one of these. Examples of porous polymer materials used with a hydrophilized surface include olefin polymers, vinyl chloride, acrylonitrile-butadiene-styrene copolymer resin (ABS resin), and polycarbonate. The hydrophilic porous layer 32 can be composed of at least one of these surfaces with a hydrophilic treatment. The hydrophilization treatment can be at least one of ultraviolet irradiation (UV irradiation), plasma irradiation, ozone oxidation, corona discharge, high-voltage discharge, or graft polymerization of hydrophilic groups.

[0033] The thickness of the hydrophilic porous layer 32 is preferably 150 μm or less, and more preferably 50 μm or more and 150 μm or less. If the thickness of the hydrophilic porous layer 32 is less than 50 μm, the reaction-promoting effect may not be sufficient, and if it exceeds 150 μm, the reaction-promoting effect may decrease.

[0034] Furthermore, the average pore size of the hydrophilic porous layer 32 is preferably in the range of 0.1 μm to 200 μm, and more preferably in the range of 0.5 μm to 50 μm. If the average pore size exceeds 200 μm, the strength is weak and it may break during operation, and if it is less than 0.1 μm, the propagation of reaction products in the liquid may be hindered. The average pore size of the hydrophilic porous layer 32 can be measured using a mercury porosimeter.

[0035] The porosity of the hydrophilic porous layer 32 is in the range of 10% to 90%, and more preferably in the range of 20% to 80%. If the porosity exceeds 90%, the strength is weak and it may break during operation, and if it is less than 10%, the propagation of reaction products in the liquid may be hindered. The porosity of the hydrophilic porous layer 32 can be measured using a mercury porosimeter.

[0036] The water-repellent porous layer 34 is preferably composed of a porous water-repellent polymer material or a porous polymer material whose surface has been treated to be water-repellent. The water-repellent porous layer 34 can be, for example, a porous body coated with a fluororesin. The water-repellent porous layer 34 preferably has an average pore size of 400 μm or less. The water-repellent porous layer 34 can be, for example, carbon paper (CP) coated with polytetrafluoroethylene (PTFE).

[0037] The support plate 36 is a member that supports the laminate of the catalyst porous layer 30, the hydrophilic porous layer 32, and the hydrophobic porous layer 34 that constitute the cathode electrode 12. The support plate 36 is not particularly limited as long as it is a material that has mechanical strength to hold the cathode electrode 12 and resistance to chemical reactions, but can be made of resin, glass, or metal, for example. The support plate 36 can be made of polycarbonate, for example. The support plate 36 has openings for passing liquid or gas such as the electrolyte 22 through.

[0038] The electrolyte 22 should be a liquid suitable for the chemical reaction that occurs in the electrochemical reactor 100. For example, in the case of a chemical reaction that reduces carbon dioxide (CO2) to produce formic acid and carbon monoxide (CO), the electrolyte 22 is preferably a phosphate buffer aqueous solution or a borate buffer aqueous solution.

[0039] [Examples] Cell 10 of the electrochemical reactor 100 was a modified version of a glass cell (EC Frontier, plate electrode evaluation cell, VM4) used for evaluating electrochemical reactions. A counter electrode 14 was placed in the first cell of cell 10, and a reference electrode 16 was placed in the second cell. A separation membrane 18 was placed between the counter electrode 14 and the reference electrode 16. In this embodiment, a Pt counter electrode was used as the counter electrode 14, an Hg / HgSO4 reference electrode as the reference electrode 16, and a Nafion 117 membrane (registered trademark) as the separation membrane 18.

[0040] In the second cell constituting the H-shaped cell 10, an opening hole serving as a connection port was provided on the opposite side from the first cell, and the cathode electrode 12 was positioned in contact with this connection port. The catalyst porous layer 30 of the cathode electrode 12 used a configuration in which Ru complex polymer (RuCP) was supported on multi-wall carbon nanotubes (MWCNT) / carbon paper (CP) (CP / MWCNT / RuCP) (Reference N. Kato, et al., Joule 5, 687 (2021)). The water-repellent porous layer 34 used CP coated with PTFE (thickness 180 μm, Chemix, TGP-H-060H) (CP+PTFE).

[0041] The hydrophilic porous layer 32 was made of vinylon paper (Hirose Paper Co., Ltd., VN1012, 50 μm thick and VN1036, 100 μm thick). The density of these materials was 0.26 g / cm³. 3 (Measured value) Typical density of vinylon fiber: 1.26~1.30 g / cm³ 3 The porosity obtained was 79-80%. The thickness of the hydrophilic porous layer 32 was adjusted by the number of layers of vinylon paper. Specifically, a hydrophilic porous layer 32 with a thickness of 50 μm was achieved using 50 μm thick VN1012, a hydrophilic porous layer 32 with a thickness of 100 μm was achieved using 100 μm thick VN1036, and a hydrophilic porous layer 32 with a thickness of 150 μm was achieved by layering 50 μm thick VN1012 and 100 μm thick VN1036.

[0042] Furthermore, a Ti sheet (100 μm thick) was electrically connected as a conductive sheet 38 for electrical contact. These laminates were sandwiched between two perforated polycarbonate plates, which served as support plates 36, and the surrounding area was sealed with silicone resin to form the cathode electrode 12. The area of ​​the holes in the support plates 36 was 0.95 cm². 2 That's what I decided.

[0043] A gas passage 20 was attached to the second cell of the H-shaped cell 10, with the cathode electrode 12 in between, and a gas containing the reactant was supplied through the gas passage 20. In this embodiment, a gas containing carbon dioxide (CO2) or a mixture of carbon dioxide (CO2) and oxygen (O2) was supplied.

[0044] A 0.4 M potassium phosphate buffer solution was used as the electrolyte 22. The electrolyte 22 was supplied into the cell 10 so that a portion of the counter electrode 14 and the reference electrode 16 were submerged. In addition, the electrolyte 22 was stirred using a stirrer to prevent the formic acid generated at the cathode electrode 12 from accumulating near the reaction region.

[0045] Electrochemical measurements were performed on the electrochemical reactor 100 configured in this way. The electrochemical measurements showed a current density of 2 mA / cm². 2 or 4mA / cm 2 Chronopotentiometry (CP) measurements were performed for 1 to 1.5 hours under the specified conditions. A portion of electrolyte 22 was collected before and after the measurement, and the concentration of formic acid generated during the measurement was quantified using an ion chromatograph. The Faraday efficiency of formic acid generation was then determined from this value.

[0046] Figure 3 shows the change in Faraday efficiency with respect to the thickness of the hydrophilic porous layer 32, as determined by electrochemical measurements in this embodiment. In Figure 3, the square (■) indicates the result when only carbon dioxide (CO2) is supplied from the gas passage 20 to the cell 10, the cross (×) indicates the result when 10% oxygen (O2) is supplied in addition to carbon dioxide (CO2) from the gas passage 20 to the cell 10, and the circle (●) indicates the result when 1% oxygen (O2) is supplied in addition to carbon dioxide (CO2) from the gas passage 20 to the cell 10.

[0047] When only carbon dioxide (CO2) was supplied from the gas passage 20 to the cell 10, a Faraday efficiency of over 80%, comparable to that without the hydrophilic porous layer 32, was obtained when the hydrophilic porous layer 32 was 50 μm and 100 μm thick. In contrast, a slight decrease in Faraday efficiency was observed when the hydrophilic porous layer 32 was 150 μm thick. On the other hand, when 1% oxygen (O2) was supplied in addition to carbon dioxide (CO2) from the gas passage 20 to the cell 10, the Faraday efficiency dropped significantly to about 20% when the hydrophilic porous layer 32 was not provided.

[0048] In contrast, even when 10% oxygen (O2) was supplied to the cell 10 in addition to carbon dioxide (CO2) from the gas passage 20, a Faraday efficiency of 60% or more was obtained when the thickness of the hydrophilic porous layer 32 was 50 μm and 100 μm. Furthermore, even when the thickness of the hydrophilic porous layer 32 was 150 μm, a Faraday efficiency of about 50% was obtained.

[0049] In other words, by providing a hydrophilic porous layer 32 between the catalyst porous layer 30 and the hydrophobic porous layer 34 in the cathode electrode 12, a higher Faraday efficiency could be obtained compared to the case without the hydrophilic porous layer 32, even when the supplied gas contains oxygen (O2).

[0050] As shown in Figure 4, when a mixture of carbon dioxide (CO2) and oxygen (O2) is supplied from the hydrophobic porous layer 34 side, the oxygen (O2) in the cathode electrode 12 of this embodiment decreases from the interface between the hydrophobic porous layer 34 and the hydrophilic porous layer 32 toward the liquid (electrolyte 22) side. The oxygen (O2) concentration near the interface between the hydrophilic porous layer 32 and the catalyst porous layer 30 (indicated by an "x" in Figure 4) is lower than the oxygen (O2) concentration near the interface between the catalyst porous layer 50 and the hydrophobic porous layer 52 in the conventional cathode electrode shown in Figure 11. It is presumed that this reduces the influence of oxygen (O2) on the catalyst porous layer 30, resulting in a higher Faraday efficiency.

[0051] [Second Embodiment] Figure 5 is a schematic cross-sectional view showing the configuration of a test apparatus simulating the electrochemical reactor 200 in the second embodiment.

[0052] The electrochemical reactor 200 comprises a cell 10, a cathode electrode 24, a counter electrode 14, a reference electrode 16, a separation membrane 18, a gas passage 20, and an electrolyte 22.

[0053] As shown in the exploded cross-sectional view of Figure 6, the cathode electrode 24 is composed of a hydrophilic porous layer 40, a catalyst porous layer 30, and a hydrophobic porous layer 34. Specifically, the cathode electrode 24 can be constructed by laminating the hydrophilic porous layer 40, the catalyst porous layer 30, and the hydrophobic porous layer 34 and sandwiching them between two support plates 36. A conductive sheet 38 is electrically connected to the hydrophobic porous layer 34 as an electrode.

[0054] The cathode electrode 24 is used to generate reaction products using substances contained in the gas as raw materials, with its first surface in contact with the liquid inside the electrochemical reactor 200 (e.g., electrolyte 22) and its second surface, which is different from the first surface, in contact with the gas outside the electrochemical reactor 200. A hydrophilic porous layer 40 is placed on the first surface, which is the liquid side, and a hydrophobic porous layer 34 is placed on the second surface, which is the gas side. A catalyst porous layer 30 containing a catalyst used in the reaction to generate the reaction products is placed between the hydrophilic porous layer 40 and the hydrophobic porous layer 34. A conductive sheet 38 is electrically connected to the hydrophobic porous layer 34 to obtain electrical contact.

[0055] The catalyst porous layer 30, the water-repellent porous layer 34, the support plate 36, and the conductive sheet 38 are the same as in the first embodiment, so their description will be omitted.

[0056] The hydrophilic porous layer 40 is preferably composed of a porous hydrophilic polymer material or a porous polymer material whose surface has been hydrophilized. Examples of hydrophilic polymer materials include cellulose, nylon, cellulose acetate, polyvinyl alcohol, polyacrylic acid, and polyacrylate salts. The hydrophilic porous layer 40 can be composed of at least one of these. Examples of porous polymer materials used with a hydrophilized surface include olefin polymers, vinyl chloride, acrylonitrile-butadiene-styrene copolymer resin (ABS resin), and polycarbonate. The hydrophilic porous layer 40 can be composed of at least one of these surfaces with a hydrophilic treatment. The hydrophilization treatment can be at least one of ultraviolet irradiation (UV irradiation), plasma irradiation, ozone oxidation, corona discharge, high-voltage discharge, or graft polymerization of hydrophilic groups.

[0057] The thickness of the hydrophilic porous layer 40 is preferably 600 μm or less, and more preferably 100 μm or more and 600 μm or less. If the thickness of the hydrophilic porous layer 40 is less than 100 μm, the reaction-promoting effect may not be sufficient, and if it exceeds 600 μm, the reaction-promoting effect may decrease.

[0058] Furthermore, the average pore size of the hydrophilic porous layer 40 is preferably in the range of 0.1 μm to 200 μm, and more preferably in the range of 0.5 μm to 50 μm. If the average pore size exceeds 200 μm, the strength is weak and it may break during operation, and if it is less than 0.1 μm, the propagation of reaction products in the liquid may be hindered. The average pore size of the hydrophilic porous layer 40 can be measured using a mercury porosimeter.

[0059] The porosity of the hydrophilic porous layer 40 is in the range of 10% to 90%, and more preferably in the range of 20% to 80%. If the porosity exceeds 90%, the strength is weak and it may break during operation, and if it is less than 10%, the propagation of reaction products in the liquid may be hindered. The porosity of the hydrophilic porous layer 40 can be measured using a mercury porosimeter.

[0060] [Example] The cell 10 of the electrochemical reactor 200 used an H-type glass cell (Easy Frontier, Plate Electrode Evaluation Cell, VM4) for evaluating an electrochemical reaction. The counter electrode 14 was placed in the first cell of the cell 10, and the reference electrode 16 was placed in the second cell. A separation membrane 18 was placed between the counter electrode 14 and the reference electrode 16. In this example, a Pt counter electrode was applied as the counter electrode 14, a Hg / HgSO4 reference electrode was applied as the reference electrode 16, and a Nafion 117 membrane (registered trademark) was applied as the separation membrane 18, respectively.

[0061] In the second cell constituting the H-type cell 10, an opening hole serving as a connection port was provided on the side opposite to the first cell, and the cathode electrode 24 was placed in contact with the connection port. For the catalytic porous layer 30 of the cathode electrode 24, a structure in which a Ru complex polymer (RuCP) was supported on a multi-wall carbon nanotube (MWCNT) / carbon paper (CP) (CP / MWCNT / RuCP) was used (Reference: N. Kato, et al., Joule 5, 687 (2021)). For the water-repellent porous layer 34, CP (thickness 180 μm, Chemix, TGP-H-060H) (CP+PTFE) coated with PTFE was used.

[0062] Vinylon paper (Hirose Paper Manufacturing, VN1036, thickness 100 μm and VN10100, thickness 300 μm) was used for the hydrophilic porous layer 40. The density of the vinylon paper V1036 is 0.28 g / cm 3 and the porosity calculated from the general density of vinylon fibers of 1.26 to 1.30 g / cm 3 was 78%. Also, the density of the vinylon paper V10100 is 0.34 g / cm 3 and the porosity calculated from the general density of vinylon fibers of 1.26 to 1.30 g / cm 3The porosity obtained was 73-74%. The thickness of the hydrophilic porous layer 32 was adjusted by the number of layers of vinylon paper. Specifically, a hydrophilic porous layer 32 with a thickness of 100 μm was achieved using 100 μm thick VN1036, a hydrophilic porous layer 32 with a thickness of 300 μm was achieved using 300 μm thick VN10100, and a hydrophilic porous layer 32 with a thickness of 600 μm was achieved by layering two 300 μm thick VN10100 sheets.

[0063] Furthermore, a Ti sheet (100 μm thick) was electrically connected as a conductive sheet 38 for electrical contact. These laminates were sandwiched between two perforated polycarbonate plates, which served as support plates 36, and the surrounding area was sealed with silicone resin to form the cathode electrode 24. The area of ​​the holes in the support plates 36 was 0.95 cm². 2 That's what I decided.

[0064] A gas passage 20 was attached to the second cell of the H-shaped cell 10, with the cathode electrode 24 in between, and a gas containing the reactant was supplied through the gas passage 20. In this embodiment, carbon dioxide (CO2) was supplied.

[0065] A 0.4 M potassium phosphate buffer solution was used as the electrolyte 22. The electrolyte 22 was supplied into the cell 10 so that a portion of the counter electrode 14 and the reference electrode 16 were submerged. In addition, the electrolyte 22 was stirred using a stirrer to prevent the formic acid generated at the cathode electrode 24 from accumulating near the reaction region.

[0066] Electrochemical measurements were performed on the electrochemical reactor 200 configured in this way. The electrochemical measurements showed a current density of 2 mA / cm². 2 or 4mA / cm 2 Chronopotentiometry (CP) measurements were performed for 1 to 1.5 hours under the specified conditions. A portion of electrolyte 22 was collected before and after the measurement, and the concentration of formic acid generated during the measurement was quantified using an ion chromatograph. The Faraday efficiency of formic acid generation was then determined from this value.

[0067] Figure 7 shows the change in Faraday efficiency with respect to the thickness of the hydrophilic porous layer 40, as determined from electrochemical measurements in this embodiment. In Figure 3, the square (■) indicates a current density of 2 mA / cm². 2 In the results, the circle (○) indicates a current density of 4 mA / cm². 2 The results for that case are shown.

[0068] Current density 2mA / cm 2 and 4mA / cm 2 In all cases, a higher Faraday efficiency could be obtained when using the cathode electrode 24 provided with the hydrophilic porous layer 40 compared to when the hydrophilic porous layer 40 was not provided (when the thickness of the hydrophilic porous layer 40 was 0). In other words, by providing the hydrophilic porous layer 40 on the liquid (electrolyte 22) side of the catalyst porous layer 30 in the cathode electrode 24, a higher Faraday efficiency could be obtained compared to when the hydrophilic porous layer 40 was not provided. In particular, the Faraday efficiency could be improved when the thickness of the hydrophilic porous layer 40 was 600 μm or less.

[0069] As shown in Figure 8, when carbon dioxide (CO2) is supplied from the water-repellent porous layer 34 side, it is presumed that in the cathode electrode 24 of this embodiment, the concentration of carbon dioxide (CO2) supplied from the gas side begins to decrease from the interface between the water-repellent porous layer 34 and the catalyst porous layer 30, and becomes almost zero at the interface between the hydrophilic porous layer 40 and the electrolyte. Therefore, it is presumed that the concentration of carbon dioxide (CO2) is maintained relatively high in the region from the interface between the water-repellent porous layer 34 and the catalyst porous layer 30 to the interface between the catalyst porous layer 30 and the hydrophilic porous layer 40, thereby promoting the reaction with carbon dioxide (CO2) in the catalyst porous layer 30.

[0070] [Third Embodiment] A configuration combining the electrochemical reactor 100 in the first embodiment and the electrochemical reactor 200 in the second embodiment may also be used. Figure 9 is a schematic cross-sectional view showing the configuration of a test apparatus simulating the electrochemical reactor 300 in the third embodiment.

[0071] The electrochemical reactor 300 comprises a cell 10, a cathode electrode 26, a counter electrode 14, a reference electrode 16, a separation membrane 18, a gas passage 20, and an electrolyte 22.

[0072] As shown in the exploded cross-sectional view of Figure 10, the cathode electrode 26 is composed of a hydrophilic porous layer 40, a catalyst porous layer 30, a hydrophilic porous layer 32, and a hydrophobic porous layer 34. Specifically, the cathode electrode 26 can be constructed by laminating the hydrophilic porous layer 40, the catalyst porous layer 30, the hydrophilic porous layer 32, and the hydrophobic porous layer 34 and sandwiching them between two support plates 36. In addition, a conductive sheet 38 is electrically connected to the hydrophobic porous layer 34 as an electrode.

[0073] The cathode electrode 26 has a hydrophilic porous layer 40 on the first surface facing the liquid, a hydrophobic porous layer 34 on the second surface facing the gas, and a catalyst porous layer 30 and a hydrophilic porous layer 32 positioned between the hydrophilic porous layer 40 and the hydrophobic porous layer 34.

[0074] Since the hydrophilic porous layer 40, catalyst porous layer 30, hydrophilic porous layer 32, water-repellent porous layer 34, support plate 36, and conductive sheet 38 are the same as in the first or second embodiment, their descriptions will be omitted.

[0075] The electrochemical reactor 300 in this embodiment provides the technical benefits of combining the electrochemical reactor 100 in the first embodiment and the electrochemical reactor 200 in the second embodiment. Specifically, it is possible to improve the reaction efficiency in the porous catalyst layer 30.

[0076] In the above embodiment, an electrochemical reactor that generates oxygen (O2) through the reduction reaction of carbon dioxide (CO2) was described as an example, but the scope of application of the cathode electrode is not limited to this. That is, any electrochemical reactor used in a reaction that generates some kind of gas through the action of a catalyst supported on a porous catalyst layer is within the scope of application. In this case, the catalyst supported on the porous catalyst layer of the cathode electrode should be a catalyst that contributes to the reaction that is the purpose of the electrochemical reactor.

[0077] [Structure of the present invention] Configuration 1: A reaction catalyst used to produce a reaction product using a substance contained in the gas or liquid as a raw material, in a state in which the first surface is in contact with a liquid and the second surface, which is different from the first surface, is in contact with a gas, A reaction catalyst characterized in that a hydrophilic porous layer containing a catalyst used in the reaction to produce the reaction product, a catalyst porous layer, and a hydrophobic porous layer are arranged in order from the liquid side to the gas side. Configuration 2: The reaction catalyst described in configuration 1, The reaction catalyst is characterized in that the hydrophilic porous layer is made of a porous hydrophilic polymer material. Configuration 3: The reaction catalyst described in configuration 2, The hydrophilic polymer material is characterized by comprising at least one of cellulose, nylon, cellulose acetate, polyvinyl alcohol, polyacrylic acid, and polyacrylate salt, as a reaction catalyst. Configuration 4: The reaction catalyst described in configuration 1, The reaction catalyst is characterized in that the hydrophilic porous layer is made of a porous polymer material whose surface has been treated to make it hydrophilic. Configuration 5: The reaction catalyst described in configuration 4, The reaction catalyst is characterized in that the polymer material comprises at least one of an olefin polymer, vinyl chloride, acrylonitrile-butadiene-styrene copolymer resin (ABS resin), and polycarbonate. Configuration 6: A reaction catalyst according to configuration 4 or 5, The reaction catalyst is characterized in that the hydrophilization treatment is at least one of ultraviolet irradiation, plasma irradiation, ozone oxidation, corona discharge, high-voltage discharge, and graft polymerization of hydrophilic groups. Composition 7: A reaction catalyst described in any one of configurations 1 to 6, The reaction catalyst is characterized in that the thickness of the hydrophilic porous layer is 600 μm or less. Composition 8: The reaction catalyst described in configuration 7, The reaction catalyst is characterized in that the thickness of the hydrophilic porous layer is 100 μm or more and 600 μm or less. Composition 9: A reaction catalyst described in any one of configurations 1 to 8, The reaction catalyst is characterized in that the average pore size of the hydrophilic porous layer is in the range of 0.1 μm to 200 μm. Configuration 10: A reaction catalyst described in any one of configurations 1 to 9, The reaction catalyst is characterized in that the porosity of the hydrophilic porous layer is in the range of 10% to 90%. Composition 11: A reaction catalyst described in any one of configurations 1 to 10, The catalyst porous layer is characterized by comprising at least one of the following: a porous material having electrical conductivity and catalytic activity; a material on which the catalyst is supported on an electrically conductive porous material; a material on which a porous material is coated with a substance having electrical conductivity and catalytic activity; and a material on which a catalyst is supported on a porous material coated with a substance having electrical conductivity. Composition 12: The reaction catalyst described in configuration 11, The catalyst porous layer is characterized by having multi-walled carbon nanotubes and a ruthenium complex supported on carbon paper. Composition 13: A reaction catalyst according to any one of configurations 1 to 12, The reaction catalyst is characterized in that the water-repellent porous layer is made of carbon paper coated with polytetrafluoroethylene (PTFE). Composition 14: A reaction catalyst described in any one of configurations 1 to 13, The aforementioned liquid contains water, and the reaction catalyst is characterized by generating oxygen from the water as the reaction product. Composition 15: A reaction catalyst described in any one of configurations 1 to 14, A reaction catalyst characterized in that a second hydrophilic porous layer is disposed between the catalyst porous layer and the water-repellent porous layer. Composition 16: An electrochemical reactor comprising a reaction catalyst described in any one of configurations 1 to 15. [Explanation of Symbols]

[0078] 10 Cell, 12 cathode electrode, 14 counter electrode, 16 reference electrode, 18 separation membrane, 20 gas passage, 22 electrolyte, 24 cathode electrode, 26 cathode electrode, 30 catalyst porous layer, 32 hydrophilic porous layer, 34 hydrophobic porous layer, 36 support plate, 38 conductive sheet, 40 hydrophilic porous layer, 40 catalyst porous layer, 50 catalyst porous layer, 52 hydrophobic porous layer, 100, 200, 300 electrochemical reactor.

Claims

1. A reaction electrode used to produce a reaction product using a substance contained in the gas or liquid as a raw material, in a state in which the first surface is in contact with a liquid and the second surface, which is different from the first surface, is in contact with a gas, From the liquid side toward the gas side, a hydrophilic porous layer containing a catalyst used in the reaction to produce the reaction product, a catalyst porous layer, and a hydrophobic porous layer are arranged in that order. A reaction electrode characterized in that a second hydrophilic porous layer with a thickness of 50 μm or more and 150 μm or less is disposed between the catalyst porous layer and the water-repellent porous layer.

2. The reaction electrode according to claim 1, The reaction electrode is characterized in that the hydrophilic porous layer is made of a porous hydrophilic polymer material.

3. The reaction electrode according to claim 2, The hydrophilic polymer material is characterized by comprising at least one of cellulose, nylon, cellulose acetate, polyvinyl alcohol, polyacrylic acid, and polyacrylate salt, as the reaction electrode.

4. The reaction electrode according to claim 1, The reaction electrode is characterized in that the hydrophilic porous layer is made of a porous polymer material whose surface has been treated to make it hydrophilic.

5. The reaction electrode according to claim 4, The reaction electrode is characterized in that the polymer material comprises at least one of an olefin polymer, vinyl chloride, acrylonitrile-butadiene-styrene copolymer resin (ABS resin), and polycarbonate.

6. A reaction electrode according to claim 4 or 5, The reaction electrode is characterized in that the hydrophilization treatment is at least one of ultraviolet irradiation, plasma irradiation, ozone oxidation, corona discharge, high-voltage discharge, and graft polymerization of hydrophilic groups.

7. A reaction electrode according to any one of claims 1 to 5, A reaction electrode characterized in that the thickness of the hydrophilic porous layer is 600 μm or less.

8. The reaction electrode according to claim 7, The reaction electrode is characterized in that the thickness of the hydrophilic porous layer is 100 μm or more and 600 μm or less.

9. A reaction electrode according to any one of claims 1 to 5, The reaction electrode is characterized in that the average pore size of the hydrophilic porous layer is in the range of 0.1 μm to 200 μm.

10. A reaction electrode according to any one of claims 1 to 5, The reaction electrode is characterized in that the porosity of the hydrophilic porous layer is in the range of 10% to 90%.

11. A reaction electrode according to any one of claims 1 to 5, The reaction electrode is characterized in that the catalyst porous layer comprises at least one of the following: a porous material having electrical conductivity and catalytic activity; a material on which the catalyst is supported on an electrically conductive porous material; a material on which a porous material is coated with a substance having electrical conductivity and catalytic activity; and a material on which a catalyst is supported on a porous material coated with a substance having electrical conductivity.

12. The reaction electrode according to claim 11, The reaction electrode is characterized in that the catalyst porous layer is made of carbon paper on which multi-walled carbon nanotubes and a ruthenium complex are supported.

13. A reaction electrode according to any one of claims 1 to 5, The reaction electrode is characterized in that the water-repellent porous layer is made of carbon paper coated with polytetrafluoroethylene (PTFE).

14. A reaction electrode according to any one of claims 1 to 5, The reaction electrode is characterized in that the liquid contains water and generates oxygen from the water as the reaction product.

15. An electrochemical reactor comprising a reaction electrode according to any one of claims 1 to 5.

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