Gas diffusion electrode and electrochemical reaction apparatus

Abstract

To provide a gas diffusion electrode enabling a C2 compound to be efficiently generated under a high current density condition, and an electrochemical reaction apparatus equipped with this gas diffusion electrode.SOLUTION: A gas diffusion electrode for electrochemically reducing either or both of carbon dioxide and carbon monoxide is provided. The gas diffusion electrode comprises a gas diffusion layer and a catalyst layer provided on the surface of the gas diffusion layer, The catalyst layer includes catalyst particles and hydrophobic particles, the catalyst particles includes copper (Cu) components, and the hydrophobic particles include fluororesin, the mass per unit area (M1) of the catalyst particles in the catalyst layer is 0.70 mg / cm2, and the ratio (M2 / M1) of the mass per unit area (M2) of the hydrophobic particles to the mass per unit area (M1) of the catalytic particles is 0.10 or more and 1.70 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas diffusion electrode and an electrochemical reactor. [Background technology]

[0002] In recent years, there has been a growing global movement to reduce emissions of greenhouse gases such as carbon dioxide (CO2) and carbon monoxide (CO). As one solution to greenhouse gas reduction, attention has been focused on the reaction of electrochemically reducing CO2 and / or CO (hereinafter sometimes referred to as "CO2 / CO") to convert them into C2 compounds (compounds with two carbon atoms), and gas diffusion electrodes equipped with catalysts that promote the reaction of electrochemically reducing CO2 / CO (hereinafter sometimes referred to as the "CO2 / CO reduction reaction") have been developed.

[0003] Copper (Cu) is known to be a suitable catalyst material contained in a gas diffusion electrode that promotes the CO2 / CO reduction reaction. For example, Patent Document 1 discloses an electrode catalyst in which copper-containing particles are supported on a substrate. Patent Document 2 also discloses an electrode catalyst in which an alloy catalyst containing a Cu component and a Ni component is supported on a conductive substrate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-147990 [Patent Document 2] Japanese Patent Application Publication No. 2020-89878 Summary of the Invention [Problem to be solved by the invention]

[0005] Among the products produced by the CO2 / CO reduction reaction, C2 compounds such as ethylene (C2H4) are useful in the chemical industry and are in high demand. However, conventional gas diffusion electrodes have room for improvement in efficiently obtaining C2 compounds such as ethylene. Specifically, conventional technologies have had problems with efficiently producing the target C2 compounds under high current density conditions, and the faradaic efficiency of C2 compounds is low. In other words, it has been difficult to increase the production amount of C2 compounds on an industrial scale.

[0006] The present inventors have conducted extensive research in light of these conventional problems, and have found that a gas diffusion electrode having a gas diffusion layer and a catalyst layer can efficiently produce C2 compounds while increasing the current density by using a catalyst layer containing catalyst particles and hydrophobic particles of a predetermined material and further controlling the amounts of the catalyst particles and the hydrophobic particles.

[0007] The present invention was completed based on these findings, and an objective of the present invention is to provide a gas diffusion electrode that can efficiently produce C2 compounds at an increased current density, and an electrochemical reaction device equipped with this gas diffusion electrode. [Means for solving the problem]

[0008] The present invention encompasses the following aspects (1) to (9). In this specification, the expression "to" includes the numerical values ​​on both ends. In other words, "X to Y" is synonymous with "at least X and at most Y."

[0009] (1) A gas diffusion electrode for electrochemically reducing either or both of carbon dioxide and carbon monoxide, the gas diffusion electrode comprises a gas diffusion layer and a catalyst layer provided on a surface of the gas diffusion layer; the catalyst layer includes catalyst particles and hydrophobic particles; The catalyst particles contain a copper (Cu) component, the hydrophobic particles contain a fluororesin; The mass (M1) per unit area of ​​the catalyst particles in the catalyst layer is 0.70 mg / cm 2or above, and the ratio (M2 / M1) of the mass per unit area of ​​the hydrophobic particles (M2) to the mass per unit area of ​​the catalyst particles (M1) is 0.10 or more and 1.70 or less.

[0010] (2) In the catalyst layer, the mass per unit area of ​​the hydrophobic particles (M2) is 0.10 mg / cm 2 The gas diffusion electrode of (1) above is as described above.

[0011] (3) The gas diffusion electrode according to (1) or (2), wherein the catalyst layer contains the catalyst particles and hydrophobic particles in a mixed state.

[0012] (4) The gas diffusion electrode according to any one of (1) to (3) above, wherein the thickness of the catalyst layer is 200 μm or less.

[0013] (5) The gas diffusion electrode according to any one of the above (1) to (4), wherein the copper (Cu) component is metallic copper.

[0014] (6) The gas diffusion electrode according to any one of (1) to (5) above, wherein the fluororesin contains polytetrafluoroethylene.

[0015] (7) The gas diffusion electrode according to any one of the above (1) to (6), wherein the gas diffusion electrode is a cathode electrode.

[0016] (8) An electrochemical reaction device for electrochemically reducing either or both of carbon dioxide and carbon monoxide, comprising: a cathode; an anode; an anion exchange membrane provided between the cathode and the anode; a cathode-side liquid flow path provided between the cathode and the anion exchange membrane; and an anode-side liquid flow path provided between the anode and the anion exchange membrane, The cathode is an electrochemical reaction device comprising the gas diffusion electrode according to any one of (1) to (7) above. [Effects of the Invention]

[0017] According to the present invention, there are provided a gas diffusion electrode capable of efficiently producing C2 compounds under conditions of increased current density, and an electrochemical reaction device equipped with this gas diffusion electrode. [Brief explanation of the drawings]

[0018] [Figure 1] 1 shows a schematic cross-section of one embodiment of a gas diffusion electrode. [Figure 2] 1 shows a schematic cross-section of an embodiment of an electrolysis cell of an electrochemical reactor. [Figure 3] FIG. 1 is a schematic diagram showing the flow of materials in an electrolysis cell of an electrochemical reactor. DETAILED DESCRIPTION OF THE INVENTION

[0019] <<1. Gas diffusion electrode>> The gas diffusion electrode of this embodiment is used for electrochemically reducing either or both of carbon dioxide (CO) and carbon monoxide (CO) (CO / CO). Specifically, it is used as a cathode in an electrochemical reaction device for electrochemically reducing CO / CO. The gas diffusion electrode is preferably used as a cathode in an electrochemical reaction for electrochemically reducing carbon dioxide (CO). In other words, the gas diffusion electrode is preferably a cathode electrode.

[0020] When electrochemically reducing CO2 / CO, a feed gas containing CO2 / CO is used. The feed gas may contain either CO2 or CO, or both. "Electrochemically reducing CO2 / CO" includes electrochemically reducing either CO2 or CO, and electrochemically reducing both CO2 and CO.

[0021] In the CO2 / CO reduction reaction, carbon compounds are produced by the reduction of CO2 / CO, and hydrogen is produced by the reduction of water. The carbon compounds produced are in liquid or gaseous form, and the hydrogen produced is in gaseous form.

[0022] Examples of carbon compounds include C1 compounds (compounds with one carbon atom) and C2 compounds (compounds with two carbon atoms).

[0023] Examples of C2 compounds produced by the reduction of CO2 / CO include acetic acid (CH3COOH), acetates (e.g., alkali metal acetates such as sodium acetate and potassium acetate), acetaldehyde (CH3CHO), ethanol (C2H5OH), and ethylene (C2H4). Among these compounds, ethylene is preferred because of its usefulness in the chemical industry. That is, the C2 compounds produced by the reduction of CO2 / CO preferably contain ethylene. The C2 compounds produced by the reduction of CO2 / CO may contain one or more other compounds in addition to ethylene. Of the C2 compounds produced, ethylene is gaseous, while ethanol and acetic acid are both liquid. The type of acetate produced depends on the type of electrolyte used. For example, sodium acetate is produced when the electrolyte contains sodium ions, and potassium acetate is produced when the electrolyte contains potassium ions.

[0024] Examples of C1 compounds produced by the reduction of carbon dioxide (CO2) include carbon monoxide (CO), formic acid (HCOOH), formate salts (e.g., alkali metal formates such as sodium formate and potassium formate), formaldehyde (HCHO), methanol (CH3OH), and methane (CH4). The C1 compounds produced by the reduction of CO2 may include one or more compounds. Among the C1 compounds produced, for example, CO and methane are gaseous, while formic acid, methanol, and formaldehyde are liquid. The type of formate salt produced depends on the type of electrolyte used. For example, sodium formate is produced when the electrolyte contains sodium ions, and potassium formate is produced when the electrolyte contains potassium ions.

[0025] Examples of C1 compounds produced by the reduction of carbon monoxide (CO) include methanol (CH3OH), formaldehyde (HCHO), and methane (CH4). The C1 compounds produced by the reduction of CO may include one or more compounds. Among the C1 compounds produced, for example, methane is gaseous, while methanol and formaldehyde are both liquid.

[0026] The reaction of electrochemically reducing carbon dioxide (CO2) to produce carbon monoxide (CO), the reaction of electrochemically reducing carbon monoxide (CO) to produce ethylene (C2H4), and the reaction of electrochemically reducing water (H2O) to produce hydrogen (H2) are shown in the following formulas (A) to (C), respectively.

[0027] CO2+2H + +2e - →CO+H2O (A) 2CO+8H + +8e - →C2H4+2H2O (B) 2H2O+2e - →H2+2OH - (C)

[0028] The CO2 / CO reduction reaction can be carried out under known conditions, except that the gas diffusion electrode of this embodiment is used as the cathode.

[0029] The gas diffusion electrode of this embodiment will be described below with reference to the drawings. As shown in Fig. 1, the gas diffusion electrode 10 includes a gas diffusion layer 11 and a catalyst layer 12 provided on the surface of the gas diffusion layer 11. The catalyst layer 12 includes catalyst particles 12a and hydrophobic particles 12b.

[0030] <Gas diffusion layer> As shown in Fig. 1, the gas diffusion layer 11 includes a substrate 11a. The substrate 11a is, for example, in the form of a sheet. When the substrate 11a is in the form of a sheet, the thickness of the substrate 11a is, for example, 10 µm or more and 1000 µm or less, preferably 100 µm or more and 500 µm or less, and more preferably 150 µm or more and 350 µm or less. It is preferable that both the minimum thickness and the maximum thickness of the substrate 11a are within the above-mentioned ranges.

[0031] The substrate 11a has gas permeability, which allows the raw material gas containing CO2 / CO to be efficiently supplied to the catalyst layer 12. In addition, the gaseous product produced by the reduction reaction of CO2 / CO and the hydrogen produced by the reduction of water can be efficiently collected.

[0032] In order to effectively realize gas permeability, the substrate 11a is preferably a porous body. Examples of porous bodies include nonwoven fabrics (including paper) and woven fabrics. The porous body has a mode pore size of, for example, 1 μm to 500 μm, preferably 10 μm to 300 μm, more preferably 20 μm to 250 μm, and even more preferably 25 μm to 200 μm. The mode pore size can be determined, for example, by mercury intrusion porosimetry.

[0033] The substrate 11a is electrically conductive, which allows the CO2 / CO reduction reaction to occur efficiently.

[0034] From the viewpoint of effectively realizing conductivity, the substrate 11a preferably contains a conductive material. The substrate 11a may contain one type of conductive material or may contain two or more types of conductive materials. Examples of conductive materials include carbon materials. Examples of carbon materials include carbon fiber, carbon black, graphite, activated carbon, carbon nanotubes, carbon nanofibers, fullerene, and amorphous carbon. The carbon material is a material that is composed of, for example, 50% by mass or more of carbon. The carbon fiber is a fiber that is composed mostly of carbon (for example, 90% by mass or more).

[0035] The substrate 11a may be, for example, a conductive porous body. As the conductive porous body, for example, a porous body containing a carbon material may be used. As the porous body containing a carbon material, it is preferable to use a porous body made of carbon fiber. As the porous body made of carbon fiber, for example, nonwoven fabric (including paper) made of carbon fiber and woven fabric made of carbon fiber can be mentioned. Nonwoven fabric (including paper) made of carbon fiber is also called carbon paper. Woven fabric made of carbon fiber is also called carbon cloth.

[0036] The substrate 11a may be a porous material such as a mesh material made of a metal or alloy, a punched material made of a metal or alloy, or a sintered metal fiber material. Examples of metals include titanium, nickel, and iron. Examples of alloys include stainless steel (SUS).

[0037] As shown in Fig. 1, the gas diffusion layer 11 preferably has a permeation layer 11b formed on the surface of the substrate 11a. The permeation layer 11b may be formed on at least a portion of the surface of the substrate 11a. The permeation layer 11b has excellent permeability. The permeation layer 11b has pores with a smaller average pore diameter than the substrate 11a and a larger surface area than the substrate 11a. This allows a larger amount of the catalyst layer 12 to be supported on the permeation layer 11b.

[0038] The "surface of the substrate 11a" includes the inner and outer surfaces of the substrate 11a. The inner surface of the substrate 11a includes the inner surfaces of pores present inside the substrate 11a (i.e., not exposed on the outer surface of the substrate 11a). The outer surface of the substrate 11a includes the inner surfaces of pores exposed on the outer surface of the substrate 11a.

[0039] The transmission layer 11b preferably has a portion formed on at least a part of the outer surface of the base material 11a. In addition to the portion formed on at least a part of the outer surface of the base material 11a, the transmission layer 11b may also have a portion formed on at least a part of the inner surface of the base material 11a.

[0040] When the substrate 11a is in a sheet form, the transmission layer 11b is preferably formed on one surface of the substrate 11a, and more preferably on at least a part of the outer surface of one surface of the substrate 11a. The transmission layer 11b may be formed on at least a part of one surface of the substrate 11a.

[0041] The thickness of the portion of the transmission layer 11b that is present on the outer surface of the substrate 11a is, for example, 1 μm to 500 μm, preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm, and even more preferably 70 μm to 150 μm. It is preferable that both the minimum and maximum thicknesses of the portion of the transmission layer 11b that is present on the outer surface of the substrate 11a are within the above-mentioned ranges.

[0042] The permeation layer 11b has gas permeability, which allows the raw material gas containing CO2 / CO to be efficiently supplied to the catalyst layer 12. In addition, the gaseous product produced by the reduction reaction of CO2 / CO and the hydrogen produced by the reduction of water can be efficiently collected.

[0043] To effectively achieve gas permeability, the permeation layer 11b is preferably porous, and is preferably a microporous layer (MPL). The microporous layer has a modal pore size of, for example, 5 nm to 500 nm, preferably 10 nm to 300 nm, more preferably 15 nm to 100 nm, and even more preferably 15 nm to 70 nm. The modal pore size can be determined by mercury intrusion porosimetry. The microporous layer typically has a smaller average pore size and a higher density than the substrate 11a.

[0044] The permeation layer 11b is formed, for example, for the purpose of improving the water repellency of the gas diffusion layer 11. By improving the water repellency of the gas diffusion layer 11, the hydrogen generation reaction due to the reduction of water can be suppressed, and the generation of carbon compounds due to the reduction of CO / CO can be made more dominant.

[0045] When the permeation layer 11b is formed for the purpose of improving the water repellency of the gas diffusion layer 11, the permeation layer 11b preferably contains a fluororesin.

[0046] Examples of fluororesins include polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, etc. Among these, polytetrafluoroethylene is preferred.

[0047] To effectively improve water repellency, the mass percentage of elemental fluorine in the permeation layer 11b, based on the mass of the gas diffusion electrode 10, is preferably 5% by mass to 30% by mass, more preferably 8% by mass to 25% by mass, and even more preferably 10% by mass to 20% by mass. The mass of elemental fluorine in the permeation layer 11b can be determined, for example, by alkali fusion-ion electrode method. The alkali fusion-ion electrode method can be performed according to the conditions described in the Examples.

[0048] The permeable layer 11b has electrical conductivity. This allows the CO2 / CO reduction reaction to be carried out efficiently. From the viewpoint of effectively realizing electrical conductivity, the permeable layer 11b preferably contains an electrically conductive material. The permeable layer 11b may contain one type of electrically conductive material, or may contain two or more types of electrically conductive materials. Examples of electrically conductive materials include carbon materials. The description of the carbon material is the same as above.

[0049] To effectively achieve conductivity, the mass percentage of the carbon material in the permeable layer 11b based on the mass of the permeable layer 11b is preferably 70% by mass to 95% by mass, more preferably 75% by mass to 92% by mass, and even more preferably 80% by mass to 90% by mass. The mass of the carbon material in the permeable layer 11b can be determined, for example, by a combustion method.

[0050] The transmission layer 11b can be formed by coating a solution or dispersion (preferably an emulsion) containing a fluororesin on the surface of the substrate 11a (or on one surface of the substrate 11a when the substrate 11a is in a sheet form). A known coating method can be used for this. Examples of the coating method include bar coating, blade coating, screen printing, spray coating, curtain coating, and roll coating. The amount of the fluororesin coating may be adjusted by coating multiple layers of the solution or dispersion containing the fluororesin. The solution or dispersion containing the fluororesin can be prepared according to a conventional method using a fluororesin, a solvent or dispersion medium (e.g., water), a surfactant (e.g., a nonionic surfactant), and the like. Alternatively, a commercially available solution or dispersion containing a fluororesin may be used. The types of the fluororesin, solvent, dispersion medium, surfactant, and the like can be appropriately selected. The concentration of the fluororesin is, for example, 1% by mass to 70% by mass, preferably 3% by mass to 60% by mass, based on the mass of the solution or dispersion containing the fluororesin. The layer formed by coating with the fluororesin-containing solution or dispersion may be dried, if necessary, at a drying temperature of, for example, 10° C. to 120° C., and preferably 20° C. to 100° C., for a drying time of, for example, 0.5 hours to 48 hours, and preferably 1 hour to 24 hours.

[0051] <Catalyst layer> 1, the catalyst layer 12 is present on the surface of the gas diffusion layer 11. Here, the "surface of the gas diffusion layer 11" means the surface of the permeation layer 11b when the permeation layer 11b is formed, or means the surface of the substrate 11a when the permeation layer 11b is not formed.

[0052] The "surface of the permeable layer 11b" includes the inner and outer surfaces of the permeable layer 11b. The meaning of "the surface of the permeable layer 11b" is the same as that of the above-mentioned "surface of the substrate 11a" in which "substrate 11a" is replaced with "permeable layer 11b."

[0053] When the permeation layer 11b is formed, the catalyst layer 12 preferably has a portion supported on at least a part of the outer surface of the permeation layer 11b. In addition to the portion supported on at least a part of the outer surface of the permeation layer 11b, the catalyst layer 12 may also have a portion supported on at least a part of the inner surface of the permeation layer 11b.

[0054] When the permeation layer 11b is not formed, the catalyst layer 12 preferably has a portion supported on at least a portion of the outer surface of the substrate 11a. In addition to the portion supported on at least a portion of the outer surface of the substrate 11a, the catalyst layer 12 may also have a portion supported on at least a portion of the inner surface of the substrate 11a.

[0055] The catalyst layer 12 includes catalyst particles 12a and hydrophobic particles 12b. The catalyst particles function to promote the electrochemical reduction of CO2 / CO. The catalyst particles include a copper (Cu) component. The copper component is contained in the catalyst particles in a form that can function as a catalytically active component, such as metallic copper, an alloy containing copper, a complex containing copper, or a compound containing copper (e.g., Cu(OH)2, Cu2O, CuO, etc.).

[0056] In order to efficiently carry out the CO / CO reduction reaction, it is preferable that at least a portion of the copper component contained in the catalyst particles is metallic copper, more preferably 50 mass% or more of the copper component is metallic copper, and it is particularly preferable that all of the copper component is metallic copper, i.e., the copper component is metallic copper.

[0057] The catalyst particles may contain one or more metal elements other than copper. Examples of metal elements other than copper include gold (Au), platinum (Pt), palladium (Pd), silver (Ag), zinc (Zn), nickel (Ni), cobalt (Co), iron (Fe), aluminum (Al), tin (Sn), manganese (Mn), chromium (Cr), titanium (Ti), cadmium (Cd), indium (In), gallium (Ga), lead (Pb), ruthenium (Ru), and rhenium (Re). The metal elements other than copper are contained in the catalyst particles 12a in a form capable of functioning as a catalytically active component, such as a metal, alloy, complex, or compound (e.g., hydroxide, oxide, etc.).

[0058] The mass per unit area of ​​the catalyst particles in the catalyst layer (M1) is 0.70 mg / cm 2 That's all. M1 is 0.70 mg / cm 2 By increasing M1 to 0.70 mg / cm or more, the CO2 / CO reduction reaction based on the catalyst particles is promoted, and as a result, the production efficiency of C2 compounds is improved. 2 If the concentration is less than 1.00 mg / cm, the CO2 / CO reduction reaction does not proceed sufficiently. 2 More than 1.50 mg / cm is preferred. 2 More preferably, the upper limit of M1 is not particularly limited. For example, 7.00 mg / cm 2 6.00 mg / cm or less 2 The following is the result.

[0059] The mass per unit area of ​​the catalyst particles (M1) is the amount (mass) of catalyst particles contained in a unit area of ​​the catalyst layer, and is also called the basis weight of the catalyst particles. Similarly, the mass per unit area of ​​the hydrophobic particles (M2) is the amount (mass) of hydrophobic particles contained in a unit area of ​​the catalyst layer, and is also called the basis weight of the hydrophobic particles. The method for measuring the masses per unit area (M1, M2) will be explained in the Examples below.

[0060] Hydrophobic particles have the effect of preventing the catalyst layer from being submerged in water and increasing the amount of three-phase interface. Because catalyst particles are hydrophilic, if the catalyst layer is composed solely of catalyst particles, the electrolyte will penetrate the catalyst layer, causing the catalyst layer to become submerged. This reduces the amount of feed gas CO2 / CO reaching the catalyst particle surface. In particular, CO gas is insoluble in the strong alkaline electrolyte, so CO cannot reach the submerged catalyst layer. Therefore, while the two-phase (solid-liquid) interfacial reaction (reaction (C) above) using water (H2O) as the feedstock proceeds and hydrogen (H2) production occurs preferentially, the three-phase (solid-liquid-gas) interfacial reaction (reactions (A) and (B) above) using CO2 / CO as the feedstock is inhibited. Therefore, the production of C2 compounds such as ethylene is suppressed when catalyst particles are used alone.

[0061] In contrast, incorporating hydrophobic particles into the catalyst layer increases the water repellency of the catalyst layer. Reducing the submersion of the catalyst layer increases the amount of three-phase interfaces. As a result, the efficiency of C2 compound production at high current densities can be improved. Specifically, the presence of hydrophobic particles allows CO2 / CO to exist in the form of bubbles in the catalyst layer. The presence of CO2 / CO gas near the catalyst particles increases the CO2 / CO gas concentration near the catalyst particles. As a result, the rate of the CO2 / CO reduction reaction improves, and the concentration of CO adsorbed on the catalyst particles increases. Promoting CO-CO coupling improves the efficiency of producing C2 compounds such as ethylene.

[0062] The hydrophobic particles contain a fluororesin. The fluororesin has excellent water repellency. By using a fluororesin with excellent water repellency for the hydrophobic particles, it is possible to more reliably achieve the effect of forming a three-phase interface and thereby promoting the production of C2 compounds. Examples of fluororesins include polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, etc. It is particularly preferable that the fluororesin contains polytetrafluoroethylene.

[0063] The ratio (M2 / M1) of the mass per unit area of ​​the hydrophobic particles (M2) to the mass per unit area of ​​the catalyst particles (M1) in the catalyst layer is 0.10 or more and 1.70 or less. By controlling the ratio (M2 / M1) within a specific range, a desirable three-phase interface is realized, resulting in improved C2 compound production efficiency. On the other hand, if the ratio (M2 / M1) is less than 0.10, the proportion of hydrophobic particles is too small, causing the electrolyte to penetrate into the catalyst layer. As a result, the two-phase (solid-liquid) interface reaction (reaction of the above formula (C)) occurs preferentially, resulting in hydrogen (H2) production, but reduced C2 compound production efficiency. On the other hand, if the ratio (M2 / M1) is more than 1.70, the proportion of catalyst particles is too small. As a result of insufficient contact between the catalyst particles and the electrolyte, H2 is not released from the electrolyte. + The supply amount decreases, making it difficult for the CO2 / CO reduction reaction (the reactions of the above formulas (A) and (B)) to occur. As a result, the production efficiency of C2 compounds also decreases. From the viewpoint of increasing the production efficiency of C2 compounds, the ratio (M2 / M1) is preferably 0.20 or more and 1.40 or less, and more preferably 0.40 or more and 1.35 or less.

[0064] Preferably, in the catalyst layer, the mass per unit area of ​​the hydrophobic particles (M2) is 0.10 mg / cm 2 That's all. By increasing M2 while satisfying the above-mentioned ranges of M1 and M2 / M1, the water repellency of the catalyst layer can be increased while maintaining the reduction reaction based on the catalyst particles. Therefore, it is possible to further increase the production efficiency of C2 compounds. From the viewpoint of increasing the production efficiency of C2 compounds, M2 is set to 0.50 mg / cm 2 More than 0.70 mg / cm is preferred. 2 More preferably, the upper limit of M2 is not particularly limited. For example, 7.00 mg / cm 2 Less than 6.00 mg / cm 2 The following is also acceptable.

[0065] Preferably, the catalyst layer contains a mixture of catalyst particles and hydrophobic particles. This allows a relatively uniform three-phase interface to be formed within the catalyst layer. That is, in the mixed state, hydrophobic particles are present near each catalyst particle. Because a three-phase interface is formed near many catalyst particles, it is possible to further improve the efficiency of C2 compound production. Another advantage is that the catalyst layer can be easily produced by a simple method of coating and drying an ink containing a mixture of catalyst particles and hydrophobic particles on a gas diffusion layer.

[0066] At least some of the gaps between the catalyst particles and the hydrophobic particles have voids that communicate with the outside. In other words, the catalyst layer is porous and has external communication pores, and can be said to be gas permeable. CO2 / CO and the electrolyte can enter and exit the catalyst layer through the voids that communicate with the outside.

[0067] The catalyst layer may be composed of only catalyst particles and hydrophobic particles, or may contain other additive components. Examples of additive components include binders, dispersants, and surfactants. However, to ensure the interaction between the catalyst particles and hydrophobic particles, it is desirable that the proportion of the additive components is not excessively high. The proportion of the additive components in the catalyst layer is preferably 20% by mass or less.

[0068] From the viewpoint of improving the CO2 / CO2 permeability in the thickness direction of the catalyst layer and improving the contact efficiency between CO2 / CO2 and the electrolyte, the thickness of the catalyst layer is preferably 200 μm or less, more preferably 60 μm or less. The lower limit of the thickness of the catalyst layer is not particularly limited. For example, it may be 1 μm or more, or may be 2 μm or more. Here, the thickness of the catalyst layer means the thickness of the portion of the catalyst layer that exists on the outer surface of the permeation layer or the outer surface of the substrate.

[0069] The diffusion electrode of this embodiment comprises a catalyst layer made of catalyst particles and hydrophobic particles of a predetermined material, and the amounts of the catalyst particles and hydrophobic particles are controlled within specific ranges. This has the effect of enabling efficient production of C2 compounds at high current densities. That is, the faradaic efficiency of C2 compounds is high under conditions of high current densities, i.e., high conversion rates. For example, at a current density of 0.4 A / cm 2 At this time, the faradaic efficiency of ethylene (C2H4) is preferably 50% or more, and more preferably 55% or more.

[0070] <<2. Gas Diffusion Electrode Manufacturing Method>> The gas diffusion electrode of this embodiment may be manufactured by any method as long as it satisfies the above-mentioned requirements. However, a suitable manufacturing method includes the following steps: preparing an ink containing catalyst particles, hydrophobic particles, and a dispersion medium (ink preparation step), coating the ink onto the surface of a gas diffusion layer to form a coating layer (coating step), and drying the coating layer to form a catalyst layer on the surface of the gas diffusion layer (drying step). Each step is described in detail below.

[0071] <Ink preparation process> In the ink preparation process, ink containing catalyst particles, hydrophobic particles, and a dispersion medium is prepared. The details of the catalyst particles and hydrophobic particles are as described above. Specifically, the catalyst particles contain a copper (Cu) component. The hydrophobic particles contain a fluororesin. Water or an organic solvent can be used as the dispersion medium. However, when applying ink to the surface of a gas diffusion layer on which a water-repellent permeable layer has been formed, it is preferable to use an organic solvent, such as an alcohol-based solvent, as the dispersion medium. Examples of alcohol-based solvents include methanol, ethanol, propanol, and butanol. A single solvent may be used as the dispersion medium, or a mixed solvent containing multiple solvents may be used as the dispersion medium.

[0072] The ink may be prepared by a known method. For example, catalyst particles and hydrophobic particles may be added to a dispersion medium and subjected to a dispersion treatment. In this case, additives such as a binder, a dispersant, and a surfactant may be added as needed. The dispersion treatment may be performed using a known device, such as a homogenizer or an ultrasonic dispersion device.

[0073] <Coating process> In the coating step, ink is coated on the surface of the gas diffusion layer to form a coating layer. The ink coating may be performed by a known method, such as bar coating, blade coating, screen printing, spray coating, curtain coating, or roll coating. Coating may be performed only once, or multiple times to obtain a coating layer of the required thickness.

[0074] <Drying process> In the drying step, the coating layer is dried. The dispersion medium contained in the coating layer is evaporated and removed by drying, and a catalyst layer containing catalyst particles and hydrophobic particles is formed on the surface of the gas diffusion layer. The drying temperature may be determined depending on the type of dispersion medium, and is, for example, 20°C or higher and 120°C or lower. The drying time is, for example, 0.5 hours or higher and 24 hours or lower.

[0075] In this way, the gas diffusion electrode of this embodiment, which includes a catalyst layer provided on the surface of the gas diffusion layer, can be produced. The coating step and the drying step may each be performed once, or the series of steps consisting of the coating step and the drying step may be repeated to increase the thickness of the catalyst layer.

[0076] <<3. Electrochemical Reaction Device>> The electrochemical reaction device of this embodiment is used for electrochemically reducing either or both of carbon dioxide (CO) and carbon monoxide (CO). This electrochemical reaction device includes a cathode, an anode, an anion exchange membrane provided between the cathode and the anode, a cathode-side liquid flow path provided between the cathode and the anion exchange membrane, and an anode-side liquid flow path provided between the anode and the anion exchange membrane. The cathode includes the gas diffusion electrode described above.

[0077] A cross-sectional view of one embodiment of an electrochemical reaction device is shown schematically in Fig. 2. As shown in Fig. 2, an electrochemical reaction device 20 includes a cathode 21, an anode 22, an anion exchange membrane 23 provided between the cathode 21 and the anode 22, a liquid flow path 28a provided between the cathode 21 and the anion exchange membrane 23 and through which a cathode-side electrolyte flows, and a liquid flow path 29a provided between the anode 22 and the anion exchange membrane 23 and through which an anode-side electrolyte flows.

[0078] The electrochemical reaction device 20 may include a liquid flow path structure 28 for forming a liquid flow path 28a, and a liquid flow path structure 29 for forming a liquid flow path 29a. The electrochemical reaction device 20 may include a gas flow path structure 24 in which a gas flow path 24a is formed, and a gas flow path structure 25 in which a gas flow path 25a is formed. The electrochemical reaction device 20 may include a power supply 26 and a power supply 27.

[0079] A slit is formed in liquid flow path structure 28, and the region in the slit surrounded by cathode 21, anion exchange membrane 23, and liquid flow path structure 28 forms liquid flow path 28a. A slit is formed in liquid flow path structure 29, and the region in the slit surrounded by anode 22, anion exchange membrane 23, and liquid flow path structure 29 forms liquid flow path 29a.

[0080] A groove is formed on the cathode 21 side of the gas flow channel structure 24, and the portion of the groove surrounded by the gas flow channel structure 24 and the cathode 21 forms a gas flow channel 24a. A groove is formed on the anode 22 side of the gas flow channel structure 25, and the portion of the groove surrounded by the gas flow channel structure 25 and the anode 22 forms a gas flow channel 25a.

[0081] In the electrochemical reaction device 20, a liquid flow path 28a is formed between the cathode 21 and the anion exchange membrane 23, a liquid flow path 29a is formed between the anode 22 and the anion exchange membrane 23, a gas flow path 24a is formed between the cathode 21 and the power supply 26, and a gas flow path 25a is formed between the anode 22 and the power supply 27.

[0082] Each of the power supply members 26 and 27 is electrically connected to a power supply (not shown) that supplies power to the electrochemical reaction device 20. The gas flow path structure 24 and the gas flow path structure 25 are each an electrical conductor, and are configured so that a voltage can be applied between the cathode 21 and the anode 22 by power supplied from the power supply.

[0083] The cathode 21 is an electrode that reduces CO2 / CO to produce carbon compounds and reduces water to produce hydrogen. The produced carbon compounds are in liquid or gaseous form, and the produced hydrogen is in gaseous form.

[0084] The cathode 21 electrochemically reduces CO2 / CO and allows the generated gaseous carbon compounds and hydrogen to permeate to the gas flow path 24a. The generated liquid carbon compounds flow through the liquid flow path 28a together with the cathode-side electrolyte A and then flow out from the outlet of the liquid flow path 28a through the liquid flow path 63.

[0085] The cathode 21 includes a gas diffusion electrode 10. The cathode 21 may be configured with the gas diffusion electrode 10. The gas diffusion electrode 10 has been described above. The gas diffusion electrode 10 is disposed such that the substrate 11a is located on the gas flow path 24a side and the catalyst 12 is located on the liquid flow path 28a side.

[0086] The anode 22 is an electrode for oxidizing hydroxide ions to generate oxygen. The generated oxygen is in gaseous form. The anode 22 electrochemically oxidizes the hydroxide ions and allows the generated oxygen to permeate to the gas flow path 25a.

[0087] The anode 22 may be, for example, an electrode including a gas diffusion layer and a catalyst (hereinafter sometimes referred to as "anode catalyst") formed on the liquid flow path 29a side of the gas diffusion layer. The anode catalyst may be in the form of catalyst particles, a catalyst layer, or the like. The anode catalyst is preferably in the form of a catalyst layer. The gas diffusion layer may be the gas diffusion layer 11, or a known gas diffusion layer other than the gas diffusion layer 11 may be used.

[0088] As the anode catalyst, a known anode catalyst can be used. Examples of the anode catalyst include metals such as platinum, palladium, and nickel, alloys or intermetallic compounds thereof, metal oxides such as manganese oxide, iridium oxide, nickel oxide, cobalt oxide, iron oxide, tin oxide, indium oxide, ruthenium oxide, lithium oxide, and lanthanum oxide, and metal complexes such as ruthenium complexes and rhenium complexes. One type of anode catalyst may be used alone, or two or more types of anode catalysts may be used in combination.

[0089] For example, carbon paper, carbon cloth, etc. can be used as the gas diffusion layer of the anode 22. A porous body such as a mesh material, a punched material, or a sintered metal fiber body may also be used as the gas diffusion layer of the anode 22. Examples of materials for the porous body include metals such as titanium, nickel, and iron, and alloys such as stainless steel (SUS).

[0090] Examples of materials for the liquid flow path structures 28, 29 include fluororesins such as polytetrafluoroethylene. Examples of materials for the gas flow path structures 24, 25 include metals such as titanium and SUS, and carbon. Examples of materials for the power feeders 26, 27 include metals such as copper, gold, titanium, and SUS, and carbon. The power feeders 26, 27 may be made of a copper base material whose surface has been plated with gold or other plating. The anion exchange membrane 23 may be a known anion exchange membrane.

[0091] The electrochemical reaction device 20 includes a flow cell in which the cathode-side electrolytic solution A supplied through the liquid flow path 64 flows through the liquid flow path 28a, the anode-side electrolytic solution B supplied through the liquid flow path 65 flows through the liquid flow path 29a, and the raw material gas G supplied through the gas flow path 76 flows through the gas flow path 24a.

[0092] One end of the liquid flow path 64 is connected to the electrochemical reaction device 20, and the other end of the liquid flow path 64 is connected to a supply device (not shown) for supplying a cathode-side electrolyte A to the electrochemical reaction device 20. One end of the liquid flow path 65 is connected to the electrochemical reaction device 20, and the other end of the liquid flow path 65 is connected to a supply device (not shown) for supplying an anode-side electrolyte B to the electrochemical reaction device 20. One end of the gas flow path 76 is connected to the electrochemical reaction device 20, and the other end of the gas flow path 76 is connected to a supply device (not shown) for supplying a raw material gas G to the electrochemical reaction device 20.

[0093] An alkaline aqueous solution can be used as each of the cathode-side electrolyte A and the anode-side electrolyte B. Examples of the alkaline aqueous solution include an aqueous potassium hydroxide solution, an aqueous sodium hydroxide solution, an aqueous potassium carbonate solution, and an aqueous sodium carbonate solution. An aqueous potassium hydroxide solution is preferred from the viewpoints of excellent solubility of carbon dioxide and suppression of hydrogen generation due to a reduction reaction of water.

[0094] The pH of the cathode-side electrolyte solution A and the anode-side electrolyte solution B can be adjusted as appropriate, but the pH of the anode-side electrolyte solution B is preferably lower than the pH of the cathode-side electrolyte solution A. The pH of the cathode-side electrolyte solution A is, for example, greater than 14, and the pH of the anode-side electrolyte solution B is, for example, 14 or lower (specifically, 8 or higher and 14 or lower). Examples of methods for adjusting the pH of the electrolyte include a method of adding an alkali or an aqueous alkali solution to the electrolyte to increase the pH, and a method of dissolving carbon dioxide in the electrolyte to decrease the pH.

[0095] The cathode-side electrolyte A supplied through the liquid flow path 64 can be an alkaline aqueous solution (e.g., a potassium hydroxide aqueous solution) having an alkali concentration of, for example, 0.1 mol / L to 5 mol / L, preferably 1 mol / L to 3 mol / L. The temperature of the cathode-side electrolyte A supplied through the liquid flow path 64 can be adjusted as appropriate, but is, for example, 10°C to 60°C. The flow rate of the cathode-side electrolyte A supplied through the liquid flow path 64 can be adjusted as appropriate, but is, for example, 10 mL / min to 100 mL / min.

[0096] The anode-side electrolyte B supplied through the liquid flow path 65 may be an alkaline aqueous solution (e.g., a potassium hydroxide aqueous solution) having an alkali concentration of, for example, 0.1 mol / L to 5 mol / L, preferably 1 mol / L to 3 mol / L. The temperature of the anode-side electrolyte B supplied through the liquid flow path 65 can be adjusted as appropriate, but is, for example, 10°C to 60°C. The flow rate of the anode-side electrolyte B supplied through the liquid flow path 65 can be adjusted as appropriate, but is, for example, 10 mL / min to 100 mL / min.

[0097] The raw material gas G supplied through the gas flow path 76 contains CO2 / CO. The raw material gas G supplied through the gas flow path 76 may contain either CO2 or CO, or may contain both CO2 and CO. When the raw material gas G supplied through the gas flow path 76 contains CO2, the concentration of CO2 in the raw material gas G can be adjusted as appropriate, but is, for example, 1% by volume or more and 100% by volume or less. When the raw material gas G supplied through the gas flow path 76 contains CO, the concentration of CO in the raw material gas G can be adjusted as appropriate, but is, for example, 1% by volume or more and 100% by volume or less. The temperature of the raw material gas G supplied through the gas flow path 76 can be adjusted as appropriate, but is, for example, 10°C or more and 60°C or less. The flow rate of the raw material gas G supplied through the gas flow path 76 can be adjusted as appropriate, but is, for example, 50 mL / min or more and 500 mL / min or less.

[0098] The cathode-side electrolyte A supplied through the liquid flow path 64 flows through the liquid flow path 28a and flows out from the outlet of the liquid flow path 28a through the liquid flow path 63. The anode-side electrolyte B supplied through the liquid flow path 65 flows through the liquid flow path 29a and flows out from the outlet of the liquid flow path 29a through the liquid flow path 66.

[0099] By flowing the cathode-side electrolyte A through the liquid flow path 28a, the anode-side electrolyte B through the liquid flow path 29a, and the feed gas G through the gas flow path 24a, and applying a voltage between the cathode 21 and the anode 22, carbon compounds are produced at the cathode 21 by reduction of CO / CO in the feed gas G, and hydrogen is produced by reduction of water. The produced carbon compounds are liquid or gaseous, and the produced hydrogen is gaseous. At the anode 22, hydroxide ions in the anode-side electrolyte B are oxidized to generate oxygen. A gaseous product E containing the gaseous carbon compounds and hydrogen permeates the gas diffusion layer (gas diffusion layer 11 of the gas diffusion electrode 10) of the cathode 21, reaches the gas flow path 24a, and flows out through the outlet of the gas flow path 24a via the gas flow path 67. The product E flowing out of the electrochemical reaction device 20 may be sent to a reactor (not shown) and brought into gas-phase contact with an olefin polymerization catalyst in the reactor to polymerize ethylene. The liquid carbon compound produced at the cathode 21 flows through the liquid flow path 28a together with the cathode-side electrolyte A, and flows out through the liquid flow path 63 from the outlet of the liquid flow path 28a.

[0100] Examples of carbon compounds produced by the reduction of CO2 / CO at the cathode 21 include C1 compounds (compounds with one carbon atom) and C2 compounds (compounds with two carbon atoms).

[0101] Examples of C2 compounds produced by the reduction of CO2 / CO at the cathode 21 include acetic acid (CH3COOH), acetates (e.g., acetates of alkali metals such as sodium acetate and potassium acetate), acetaldehyde (CH3CHO), ethanol (C2H5OH), and ethylene (C2H4). Among these compounds, ethylene is preferred because of its usefulness in the chemical industry. That is, the C2 compounds produced by the reduction of CO2 / CO preferably contain ethylene. The C2 compounds produced by the reduction of CO2 / CO may contain one or more other compounds in addition to ethylene. Of the C2 compounds produced, ethylene is gaseous, while ethanol and acetic acid are each liquid. The type of acetate produced depends on the type of electrolyte used. For example, sodium acetate is produced when the electrolyte contains sodium ions, and potassium acetate is produced when the electrolyte contains potassium ions.

[0102] Examples of C1 compounds produced by the reduction of carbon dioxide (CO2) at the cathode 21 include carbon monoxide (CO), formic acid (HCOOH), formate salts (e.g., alkali metal formates such as sodium formate and potassium formate), formaldehyde (HCHO), methanol (CH3OH), and methane (CH4). The C1 compounds produced by the reduction of CO2 may include one or more compounds. Among the C1 compounds produced, for example, CO and methane are gaseous, while formic acid, methanol, and formaldehyde are liquid. The type of formate salt produced depends on the type of electrolyte used. For example, sodium formate is produced when the electrolyte contains sodium ions, and potassium formate is produced when the electrolyte contains potassium ions.

[0103] Examples of C1 compounds produced by the reduction of carbon monoxide (CO) at the cathode 21 include formaldehyde (HCHO), methanol (CHOH), and methane (CH). The C1 compounds produced by the reduction of CO may include one or more compounds. Among the C1 compounds produced, for example, methane is gaseous, and methanol and formaldehyde are each liquid.

[0104] An example of the flow of materials in the electrolysis cell of the electrochemical reaction device 20 is shown in Fig. 3. As shown in Fig. 3, at the cathode 21, gaseous carbon compounds and liquid carbon compounds are produced by reduction of CO2 / CO in the feed gas G, and hydrogen is also produced. The product E, which contains the gaseous carbon compounds and hydrogen produced at the cathode 21, permeates the gas diffusion layer (gas diffusion layer 11 of the gas diffusion electrode 10) of the cathode 21, reaches the gas flow path 24a, and flows out from the outlet of the gas flow path 24a through the gas flow path 67. The liquid carbon compounds produced at the cathode 21, together with the cathode-side electrolyte A, flow through the liquid flow path 28a and then flow out from the outlet of the liquid flow path 28a through the liquid flow path 63.

[0105] The hydroxide ions (OH - ) moves through the anode-side electrolyte B to the anode 22, where it is oxidized by the reaction of formula (D) below to produce oxygen (O2). The produced oxygen permeates the gas diffusion layer of the anode 22, reaches the gas flow channel 25a, and flows out from the outlet of the gas flow channel 25a.

[0106] 4OH - →O2+2H2O (D) [Example]

[0107] The present invention will be described in more detail using the following examples, but the present invention is not limited to the following examples.

[0108] (1) Preparation of gas diffusion electrode [Example 1] A commercially available gas diffusion layer (Sigracet 39 BB, SGL Carbon) was obtained. The gas diffusion layer (Sigracet 39 BB) was composed of carbon paper and a microporous layer (MPL) containing fluorine formed on one side of the carbon paper. The layer thickness was 315 μm and the fluorine content was 14 mass%. Next, the obtained gas diffusion layer (Sigracet 39 BB) was cut into a square with each side measuring 37 mm to prepare a gas diffusion layer for the gas diffusion electrode.

[0109] Separately, copper metal particles (Cu particles) with an average particle size (average particle size of primary particles) of 25 nm and polytetrafluoroethylene particles (PTFE particles) with an average particle size (average particle size of primary particles) of 1,000 nm were prepared. 2-Propanol was used as a dispersion medium, and a 5% by mass Nafion® solution was used as a binder. The prepared Cu particles (37.6 mg) and PTFE particles (33.6 mg) were added to 2-propanol (5 mL), and the resulting mixture was subjected to ultrasonic dispersion treatment for 10 minutes. Next, 5 μL of Nafion® solution (Sigma-Aldrich, 274704-100ML) was added to the dispersed mixture, and the mixture was subjected to ultrasonic dispersion treatment for 30 minutes to prepare an ink.

[0110] Next, the prepared gas diffusion layer (Sigracet 39 BB) was placed on a hot plate heated to 80°C with the MPL-coated surface facing upward, and the entire amount of ink was spray-coated onto the top surface. The ink-coated gas diffusion layer was then placed in a dryer set to 80°C and dried for 1 hour. This resulted in the production of a gas diffusion electrode. The catalyst layer had a thickness of 15 μm.

[0111] [Example 2] When preparing the ink, the amount of PTFE particles was changed to 16.7 mg. Otherwise, a gas diffusion electrode was produced in the same manner as in Example 1. The thickness of the catalyst layer was 11 μm.

[0112] [Example 3] When preparing the ink, the amount of PTFE particles was changed to 50.2 mg, and the volume of 2-propanol was changed to 4 mL. Otherwise, a gas diffusion electrode was fabricated using the same procedure as in Example 1. The thickness of the catalyst layer was 18 μm.

[0113] [Example 4] When preparing the ink, the amount of Cu particles was changed to 75.2 mg, the amount of PTFE particles to 66.8 mg, and the amount of Nafion (registered trademark) solution (Sigma-Aldrich, 274704-100ML) to 10 μL. A gas diffusion electrode was fabricated using the same procedure as in Example 1. The thickness of the catalyst layer was 25 μm.

[0114] [Example 5] When preparing the ink, the amount of Cu particles was changed to 85.1 mg, the amount of PTFE particles to 75.0 mg, and the volume of 2-propanol to 7 mL. Otherwise, a gas diffusion electrode was fabricated using the same procedure as in Example 1. The thickness of the catalyst layer was 38 μm.

[0115] [Example 6] When preparing the ink, the amount of Cu particles was changed to 102.0 mg, the amount of PTFE particles to 90.1 mg, and the volume of 2-propanol to 7 mL. Otherwise, a gas diffusion electrode was fabricated using the same procedure as in Example 1. The thickness of the catalyst layer was 46 μm.

[0116] [Example 7] When preparing the ink, the amount of Cu particles was changed to 32.3 mg, and the amount of PTFE particles was changed to 3.8 mg. Otherwise, a gas diffusion electrode was fabricated using the same procedure as in Example 1. The thickness of the catalyst layer was 10 μm or less.

[0117] [Example 8] When preparing the ink, the amount of Cu particles was changed to 32.3 mg, and the amount of PTFE particles was changed to 7.3 mg. Otherwise, a gas diffusion electrode was fabricated using the same procedure as in Example 1. The thickness of the catalyst layer was 10 μm or less.

[0118] [Comparative Example 1] A gas diffusion electrode was fabricated by sputtering Cu onto the MPL side of the gas diffusion layer (Sigracet 39 BB). The sputtering conditions were as follows: The thickness of the catalyst layer was 10 μm or less.

[0119] -Sputtering method: DC magnetron sputtering -Exhaust system: rotary pump + cryopump - Target material: Cu - Target size: φ8 inches - Sputtering rate: 0.8 nm / sec -Pre-sputtering: 5 minutes -Sputtering time: 33 seconds - Gas diffusion layer temperature: 25°C - Target thickness of Cu sputtered film: 25nm

[0120] Comparative Example 2 The ink preparation procedure was modified as follows. Metallic copper particles (Cu particles) with an average particle size (average particle size of primary particles) of 25 nm, polytetrafluoroethylene particles (PTFE particles) with a particle size distribution (particle size distribution of primary particles) of 25 to 50 nm, and carbon black (Vulcan XC-72, manufactured by CABOT) were prepared. 2-Propanol was used as a dispersion medium, and a 5% by mass Nafion® solution was used as a binder. 2-Propanol (3 mL) was then added to the prepared Cu particles (6.0 mg), PTFE particles (5.1 mg), and carbon black (6.2 mg), respectively, followed by ultrasonic dispersion treatment for 10 minutes. The resulting dispersions were mixed, and 120 μL of Nafion® solution (Sigma-Aldrich, 274704-100ML) (120 μL) was added. The mixture was then subjected to ultrasonic dispersion treatment for 30 minutes to prepare the ink. Other than that, a gas diffusion electrode was produced in the same manner as in Example 1. The thickness of the catalyst layer was 10 μm or less.

[0121] Comparative Example 3 When preparing the ink, the amount of Cu particles was changed to 37.6 mg, the amount of PTFE particles to 66.9 mg, and the volume of 2-propanol to 4 mL. Otherwise, a gas diffusion electrode was fabricated using the same procedure as in Example 1. The thickness of the catalyst layer was 20 μm.

[0122] Comparative Example 4 When preparing the ink, the amount of Cu particles was changed to 6.2 mg, the amount of PTFE particles to 5.1 mg, the amount of Nafion (registered trademark) solution (Sigma-Aldrich, 274704-100ML) to 1 μL, and the volume of 2-propanol to 3 mL. A gas diffusion electrode was fabricated using the same procedure as in Example 1. The thickness of the catalyst layer was 19 μm.

[0123] (2) Evaluation The gas diffusion electrodes obtained in Examples 1 to 8 and Comparative Examples 1 to 4 were evaluated for various properties as follows.

[0124] <Basis weight> The mass per unit area of ​​the catalyst particles in the catalyst layer (basis weight; M1) and the mass per unit area of ​​the hydrophobic particles (basis weight; M2) were measured using the following equations (1) to (5). The measurement results are shown in Table 1.

[0125] Charge amount ratio X M1 = (mass of catalyst particles contained in the mixture) / (total mass of catalyst particles, hydrophobic particles, and binder contained in the mixture) (1) Charge amount ratio X M2 = (mass of hydrophobic particles contained in the mixed solution) / (total mass of catalyst particles, hydrophobic particles, and binder contained in the mixed solution) (2) Mass of catalyst layer Y = (mass of gas diffusion electrode) - (mass of gas diffusion layer) (3) M1=Y×X M1 / (gas diffusion electrode area) (4) M2=Y×X M2 / (gas diffusion electrode area) (5)

[0126] <Thickness of catalyst layer> The thickness of the catalyst layer was calculated by subtracting the thickness of the gas diffusion layer from the thickness of the entire gas diffusion electrode. The thickness of each layer was measured using a micrometer (MDC-25PX, manufactured by Mitutoyo Corporation). The measurement results in each example and comparative example are as described above. Note that since it is below the detection limit of 10 μm, it is expressed as 10 μm or less.

[0127] <CO2 electrolysis test> Using the electrochemical reaction device 20 shown in Fig. 2, which includes the gas diffusion electrodes of Examples 1 to 8 and Comparative Examples 1 to 4 as the cathode, a CO electrolysis test was conducted. As the anode-side electrolyte B supplied through the liquid flow path 65, a 1 mol / L potassium hydroxide (KOH) aqueous solution (flow rate: 50 mL / min) was used. As the cathode 21, any of the gas diffusion electrodes of Examples 1 to 8 and Comparative Examples 1 to 4 was used. As the anode 22, a commercially available porous metal body Ni foam (EQ-bcnf-03, manufactured by MTI corporation) was used. As the anion exchange membrane 23, Sustainion X37-50 Grade RT (manufactured by Dioxide Materials) was used. As the raw material gas G supplied through the gas flow path 76, carbon monoxide gas (flow rate: 300 mL / min) was used. The CO electrolysis test was conducted under the following conditions.

[0128] -Electrolysis conditions: constant current electrolysis [[ID=!2]]-Current value: 0.4 A / cm 2 -Electrolysis time: 30 minutes

[0129] In the CO electrolysis test, the gaseous product concentrations were measured inline from gas flow path 67 using a gas column chromatograph (990 Micro GC, manufactured by Agilent) 20 minutes after the start of the test. Hydrogen (H), carbon monoxide (CO), and methane (CH) were quantified using a Molsieve 5A column (manufactured by GL Sciences) with argon as the carrier gas. Ethylene (CH) was quantified using a PoraPLOT Q column (manufactured by GL Sciences) with helium as the carrier gas. The measured concentrations were converted to determine the amount (mol) of each product generated 20 minutes after the start of the test.

[0130] The Faraday efficiency (%) of each product was calculated based on the following formula (6): In the formula, the "predetermined time" is 20 minutes.

[0131] Faraday efficiency of each product (%) = amount of substance of each product produced at a given time (mol) × n / number of electrons consumed at a given time (mol) × 100 (6)

[0132] In the above formula (6), "n" is the number of electrons required to produce each product. Specifically, "n" is the number of electrons required to produce each product in the reaction formula. - The reaction equation for the production of ethylene and other products is as follows:

[0133] 2H + +2e - →H2 CO2+2H + +2e - →CO+H2O CO2+8H + +8e - →CH4+2H2O 2CO2+12H + +12e - →C2H4+4H2O 2CO2+14H + +14e - →C2H6+4H2O CO+6H + +6e - →CH4+H2O 2CO+8H + +8e - →C2H4+2H2O 2CO+10H + +10e - →C2H6+2H2O

[0134] (3) Evaluation results The evaluation results obtained for Examples 1 to 8 and Comparative Examples 1 to 4 are summarized in Table 1 below. Table 1 below shows the basis weights and basis weight ratios of catalyst particles (Cu particles) and hydrophobic particles (PTFE particles). In addition, when the current density was 0.4 A / cm 2 The figure shows the faradaic efficiency of ethylene (C2H4) production when

[0135] The basis weight of the catalyst particles (mass per unit area) and the ratio of the basis weight of the hydrophobic particles to the basis weight of the catalyst particles (basis weight ratio) are within the range specified in this embodiment (0.70 mg / cm 2 In Examples 1 to 8, which satisfied the above condition (0.10 or more and 1.70 or less), the faraday efficiency was relatively high at 45% or more.

[0136] In contrast to this, in Comparative Examples 1 to 4 in which the basis weight and basis weight ratio of the catalyst particles did not satisfy the ranges specified in this embodiment, the Faraday efficiency was relatively low at 38% or less.

[0137] [Table 1]

[0138] From the above results, it can be seen that the gas diffusion electrode and electrochemical reaction device of this embodiment can efficiently produce C2 compounds at an increased current density. [Explanation of symbols]

[0139] 10 Gas diffusion electrode 11 Gas diffusion layer 11a Base material 11b Transparent layer 12 Catalyst layer 12a Catalyst particles 12b Hydrophobic particles 20 Electrochemical Reactor 21 Cathode 22 Anode 23 Anion exchange membrane 24 Gas flow path structure 24a Gas flow path 25 Gas flow path structure 25a Gas flow path 26 Power feeder 27 Power feeder 28 Liquid flow path structure 28a Liquid flow path 29 Liquid flow path structure 29a Liquid flow path A Cathode side electrolyte B Anode side electrolyte G CO2 / CO-containing raw material gas

Claims

1. A gas diffusion electrode for electrochemically reducing either or both of carbon dioxide and carbon monoxide, comprising: the gas diffusion electrode comprises a gas diffusion layer and a catalyst layer provided on a surface of the gas diffusion layer; the catalyst layer includes catalyst particles and hydrophobic particles; the catalyst particles contain a copper (Cu) component; the hydrophobic particles contain a fluororesin; The mass per unit area of ​​the catalyst particles in the catalyst layer (M １ ) is 0.70 mg / cm ２ or more, and the mass per unit area of ​​the catalyst particles (M １ ) to the mass per unit area of ​​the hydrophobic particles (M ２ ) ratio (M ２ / M １ ) is 0.10 or more and 1.70 or less.

2. In the catalyst layer, the mass per unit area of ​​the hydrophobic particles (M ２ ) is 0.10 mg / cm ２ The gas diffusion electrode according to claim 1 .

3. 3. The gas diffusion electrode according to claim 1, wherein the catalyst layer contains a mixture of the catalyst particles and hydrophobic particles.

4. 3. The gas diffusion electrode according to claim 1, wherein the catalyst layer has a thickness of 200 μm or less.

5. 3. The gas diffusion electrode according to claim 1, wherein the copper (Cu) component is metallic copper.

6. 3. The gas diffusion electrode according to claim 1, wherein the fluororesin comprises polytetrafluoroethylene.

7. 3. The gas diffusion electrode according to claim 1, wherein the gas diffusion electrode is a cathode electrode.

8. An electrochemical reaction device for electrochemically reducing either or both of carbon dioxide and carbon monoxide, comprising: a cathode; an anode; an anion exchange membrane provided between the cathode and the anode; a cathode-side liquid flow path provided between the cathode and the anion exchange membrane; and an anode-side liquid flow path provided between the anode and the anion exchange membrane, An electrochemical reaction device, wherein the cathode comprises the gas diffusion electrode according to claim 1 or 2.

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