Cathode electrode, composite of cathode electrode and substrate, electrolytic reduction device provided with cathode electrode, and method for producing composite of cathode electrode and substrate

Abstract

Provided is a cathode electrode in which the selectivity of hydrogen can be suppressed from being increased even when a catalyst layer is immersed in an electrolyte solution, and in which a catalytic reaction for producing an olefin such as ethylene and an alcohol such as ethanol by a reduction reaction of carbon dioxide can be stably and efficiently maintained over a long period of time. The present invention provides a cathode electrode for electrically reducing carbon dioxide, the cathode electrode having a first layer that is positioned on the surface layer of the cathode electrode and has a first thickness, and a second layer that is adjacent to the first layer in the thickness direction of the first layer and has a second thickness, the first layer containing copper, and the second layer containing copper. The first layer is subjected to surface modification by a cation exchange material substituted by metal ions, and the second layer is a cathode electrode of a mixed layer of copper and carbon.

Description

TECHNICAL FIELD The present application relates to a cathode electrode for electroreduction of carbon dioxide, a cathode electrode composite, an electrolytic reduction device provided with the cathode electrode, and a method for manufacturing the cathode electrode composite. BACKGROUND In recent years, the negative effects of global warming are causing changes in the environment of the earth, and many problems are occurring. It is widely believed that one of the causes of the changes in the environment of the earth is the increase in the concentration of greenhouse gases in the atmosphere, and in particular, the increase in the concentration of carbon dioxide, which accounts for the majority of the greenhouse gases. In order to reduce the concentration of carbon dioxide in the atmosphere, in addition to increasing afforestation on land and photosynthesis by marine algae, active research is being conducted on the absorption and recovery of carbon dioxide in the atmosphere. Furthermore, in addition to the absorption and recovery of carbon dioxide, research is being conducted on the use of carbon derived from carbon dioxide as a raw material for organic compounds.

[0003] Specifically, research is being conducted on the conversion of carbon dioxide into, for example, C2 compounds such as ethylene and ethanol, C1 compounds such as carbon monoxide, methane, methanol, and formic acid, by reduction of carbon dioxide, and the use thereof for the synthesis of organic compounds. Among these compounds, ethylene and ethanol, which are C2 compounds, are particularly important, and have great utility as derivatives in the synthesis of various organic compounds, and have higher use value than C1 compounds such as carbon monoxide and methane.

[0004] In recent years, in the reduction reaction of carbon dioxide as described above, catalysts such as photocatalysts and electrode catalysts have been widely used, and the development of catalysts having more excellent performance is also being sought. Catalysts for the reduction reaction of carbon dioxide are required not only to have high reaction efficiency, but also to have selectivity for specific reactions, and from this viewpoint, the selection of the catalytic material is important. For example, gold, silver, and zinc are used as catalytic materials in order to efficiently generate carbon monoxide and increase the proportion of carbon monoxide in the reduced substance. In addition, copper is used as a catalytic material in order to efficiently generate hydrocarbons such as methane, ethane, and ethylene. In particular, copper is attracting attention as a cathode reduction electrode catalyst for carbon dioxide because it can generate C2 compounds such as ethylene.

[0005] As a catalytic layer for the above-mentioned reduction reaction of carbon dioxide and containing a metal catalyst such as copper, there has been proposed a catalytic layer containing a metal catalyst supported on a carbon material, an ion-conducting substance, and a hydrophilic polymer, characterized in that the ratio of the BET specific surface area measured by water vapor adsorption through the catalytic layer to the BET specific surface area measured by nitrogen adsorption through the catalytic layer is 0.08 or less (Patent Document 1). In Patent Document 1, by controlling the ratio of the above-mentioned BET specific surface areas, the wettability of the catalytic layer is reduced, thereby increasing the hydrophobicity of the catalytic layer and preventing water from remaining in the catalytic layer, and further promoting the diffusion of carbon dioxide gas. By promoting the diffusion of carbon dioxide gas in the catalytic layer, the conversion efficiency of carbon dioxide is improved.

[0006] On the other hand, in order to achieve the generation of organic compounds such as ethylene from the reduction reaction of carbon dioxide in industry, it is required that the catalytic reaction for generating organic compounds such as ethylene be able to maintain a high selectivity for organic compounds such as ethylene stably for a long period of several hundred hours. In Patent Document 1, although the method prevents water from remaining in the catalytic layer by increasing the hydrophobicity of the catalytic layer, thereby promoting the diffusion of carbon dioxide gas, when the catalytic layer is immersed in an electrolyte, the hydrophobicity of the catalytic layer alone cannot prevent the retention of water in the catalytic layer, and thus there is room for improvement in terms of maintaining a high efficiency of the catalytic reaction for generating organic compounds such as ethylene stably for a long period of time.

[0007] In addition, for a cathode electrode for the reduction of carbon dioxide, in order to obtain an excellent synthesis efficiency of organic compounds such as ethylene, it is necessary to make the reaction of the reduction of carbon dioxide dominant over the reaction of hydrogen produced by a side reaction (water decomposition reaction) when the reduction of carbon dioxide is performed, thereby reducing the selectivity of hydrogen and increasing the selectivity of the reduction product of carbon dioxide. However, in Patent Document 1, when the catalytic layer is immersed in an electrolyte, not only the diffusion of carbon dioxide gas is hindered, but also the water molecules contained in the electrolyte cause the generation of hydrogen to be dominant, and thus the selectivity of hydrogen increases in the reduction of carbon dioxide, and thus there is room for improvement in terms of obtaining a high selectivity of the reduction product of carbon dioxide.

[0008]

Prior Art Documents

Patent Documents

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0009] [Technical means for solving the problem] The structure of the present application is outlined as follows.

[0010] [1] A cathode electrode that electro-reduces carbon dioxide, The cathode electrode has a first layer having a first thickness at a surface layer of the cathode electrode, and a second layer having a second thickness that is contiguous to the first layer in a thickness direction of the first layer, The first layer contains copper, and the first layer is surface-modified by a cation exchange material that is substituted with metal ions, and the second layer is a mixed layer of copper and carbon.

[0011] [2] The cathode electrode according to [1], wherein a ratio of the second thickness of the second layer to the first thickness of the first layer is greater than 0 and less than or equal to 100.

[0012] [3] The cathode electrode according to [1] or [2], wherein the second layer has a first region on the first layer side and a second region contiguous to the first region, with a central portion in the thickness direction of the second layer as a boundary, and a content (vol%) of the copper in the first region is higher than a content (vol%) of the copper in the second region.

[0013] [4] The cathode electrode according to [1] or [2], wherein the copper of the first layer includes divalent copper, and zero-valent copper and / or monovalent copper, and the copper of the second layer includes divalent copper, and zero-valent copper and / or monovalent copper.

[0014] [5] The cathode electrode according to [1] or [2], wherein the copper of the first layer includes reduced monovalent copper and / or reduced divalent copper that is reduced to zero-valent copper by a reduction treatment, and monovalent copper and / or divalent copper that is not reduced to zero-valent copper, and the copper of the second layer includes reduced monovalent copper and / or reduced divalent copper that is reduced to zero-valent copper by a reduction treatment, and monovalent copper and / or divalent copper that is not reduced to zero-valent copper.

[0015] [6] The cathode electrode according to [1] or [2], wherein the first layer further contains at least one additive element selected from the group consisting of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon, and the second layer further contains at least one additive element selected from the group consisting of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon.

[0016] [7] The cathode electrode according to [6], wherein the content of the additive element in the first layer is 0.10 atom% or more and 1.0 atom% or less with respect to 100 atom% of the copper contained in the first layer, and the content of the additive element in the second layer is 0.10 atom% or more and 1.0 atom% or less with respect to 100 atom% of the copper contained in the second layer.

[0017] [8] The cathode electrode according to [6], wherein the content of the additive element in the first layer is 0.25 atom% or more and 0.70 atom% or less with respect to 100 atom% of the copper contained in the first layer, and the content of the additive element in the second layer is 0.25 atom% or more and 0.70 atom% or less with respect to 100 atom% of the copper contained in the second layer.

[0018] [9] The cathode electrode according to [6], wherein the additive element in the first layer contains aluminum, and the additive element in the second layer contains aluminum.

[0019]

[10] The cathode electrode according to [1] or [2], wherein the cation exchange substance contains a sulfonated tetrafluoroethylene-based polymer.

[0020]

[11] The cathode electrode according to [1] or [2], wherein the metal ion contains an alkali metal ion and / or an alkaline earth metal ion.

[0021]

[12] The cathode electrode according to [1] or [2], wherein the metal ion-substituted cation exchange substance is formed in a layer shape on the surface of the first layer.

[0022]

[13] The cathode electrode according to [1] or [2], wherein the metal ion-substituted cation exchange substance is mixed with the copper of the first layer.

[0023]

[14] The cathode electrode according to [1] or [2], wherein the cathode has a porous structure.

[0024]

[15] A composite which is a composite of a cathode electrode and a substrate, comprising a substrate, and a cathode electrode according to [1] or [2], wherein the second layer of the cathode electrode is disposed on the substrate.

[0025]

[16] The composite according to

[15] , wherein the substrate has a porous structure.

[0026]

[17] The composite according to

[16] , wherein the material of the substrate having a porous structure is carbon, fluorine-containing resin, or metal.

[0027]

[18] The composite according to

[16] , wherein the material of the substrate having a porous structure is carbon, and the carbon layer of the carbon is contiguous to the second layer.

[0028]

[19] An electrolytic reduction device that electroreduces carbon dioxide into carbon monoxide, olefin, and / or alcohol, comprising the cathode electrode according to [1] or [2].

[0029]

[20] An electrolytic reduction device that electroreduces carbon dioxide into carbon monoxide, olefin, and / or alcohol, comprising the composite according to

[15] .

[0030]

[21] A method for manufacturing a composite of a cathode electrode that electroreduces carbon dioxide and a substrate, the method comprising: a preparation step of a substrate having a carbon layer and having a porous structure; a sputtering layer formation step of forming a sputtering layer having copper on the carbon layer of the substrate by sputtering; and a metal ion-substituted cation exchanger application step of applying a metal ion-substituted cation exchanger to the sputtering layer to perform surface modification of the sputtering layer.

[0031]

[22] The method for manufacturing a composite according to

[21] , wherein the copper includes divalent copper, and zero-valent copper and / or monovalent copper.

[0032]

[23] The method for manufacturing a composite according to

[21] , wherein the copper includes reduced 1-valent copper and / or reduced 2-valent copper that is reduced to zero-valent copper by reduction treatment, and 1-valent copper and / or 2-valent copper that is not reduced to zero-valent copper.

[0033]

[24] The method for manufacturing a composite according to any one of

[21] to

[23] , wherein the sputtering layer further contains at least one additive element selected from the group consisting of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon.

[0034]

[25] The method for manufacturing a composite according to

[22] or

[23] , further comprising a copper oxidation treatment step of oxidizing at least a part of the copper in the sputtering layer to the 1-valent copper and / or the 2-valent copper after the sputtering layer formation step and before the metal ion-substituted cation exchanger application step.

[0035]

[26] The production method of the composite body as described in

[25] , further comprising a partial reduction step of partially reducing the 1-valent copper and / or the 2-valent copper oxidized in the copper oxidation treatment step into 0-valent copper and / or 1-valent copper, before the metal ion-substituted cation exchange substance application step.

[0036]

[27] The production method of the composite body as described in

[25] , wherein the copper oxidation treatment step is electroless plating.

[0037]

[28] The production method of the composite body as described in

[24] , wherein the sputtering layer formation step includes a copper sputtering layer formation step of forming a copper sputtering layer as the copper sputtering layer having the copper sputtering layer by sputtering, and an additive element sputtering layer formation step of forming an additive element sputtering layer as the sputtering layer containing the additive element on the copper sputtering layer by sputtering.

[0038]

[29] The production method of the composite body as described in

[28] , wherein the sputtering layer formation step further includes a copper sputtering layer formation step of forming a copper sputtering layer having the copper sputtering layer on the additive element sputtering layer by sputtering.

[0039]

[30] A production method of a composite body which is a composite body of a cathode electrode for electro-reducing carbon dioxide and a base material, the production method comprising: a step of preparing a base material having a porous structure; a second layer formation step of applying a second suspension liquid which is a mixture of copper and carbon on the base material to form a second layer which is a mixed layer of copper and carbon; a first layer formation step of applying a first suspension liquid containing copper on the second layer to form a first layer containing copper; a metal ion-substituted cation exchange substance application step of applying a metal ion-substituted cation exchange substance to the first layer to perform surface modification of the first layer with the metal ion-substituted cation exchange substance.

[0040]

[31] The production method of the composite body as described in

[30] , wherein the copper of the first layer contains 2-valent copper, and 0-valent copper and / or 1-valent copper, and the copper of the second layer contains 2-valent copper, and 0-valent copper and / or 1-valent copper.

[0041]

[32] The production method of the composite body as described in

[30] , wherein the copper of the first layer contains reduction-use 1-valent copper and / or reduction-use 2-valent copper which are reduced to 0-valent copper by a reduction treatment, and 1-valent copper and / or 2-valent copper which are not reduced to 0-valent copper, and the copper of the second layer contains reduction-use 1-valent copper and / or reduction-use 2-valent copper which are reduced to 0-valent copper by a reduction treatment, and 1-valent copper and / or 2-valent copper which are not reduced to 0-valent copper.

[0042]

[33] The method for producing the composite body according to any one of

[30] to

[32] , wherein the first suspension further contains at least one additive element selected from the group consisting of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon, and the second suspension further contains at least one additive element selected from the group consisting of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon.

[0043] [Effects of Invention] In one embodiment of the cathode electrode of the present application, the cathode electrode contains a first layer having a first thickness at a surface layer of the cathode electrode, and a second layer having a second thickness adjacent to the first layer in a thickness direction of the first layer, and since the first layer contains copper and the second layer is a mixed layer of copper and carbon, even if the amount of carbon dioxide gas supplied to the first layer is reduced due to the first layer at the surface layer of the cathode electrode being immersed in the electrolyte, an interface as a reduction reaction site, that is, an interface (three-phase interface) of carbon dioxide (CO2) gas, water (H2O) molecules contained in the electrolyte, and copper (Cu) as a catalyst can be formed in the second layer which is a mixed layer of copper and carbon. Therefore, according to one embodiment of the cathode electrode of the present application, even if the first layer containing copper as a catalyst is immersed in the electrolyte, the selectivity of hydrogen as a byproduct is reduced, and the catalytic reaction of olefins such as ethylene and alcohols such as ethanol generated by the reduction reaction of carbon dioxide can be efficiently and stably continued for a long period of time.

[0044] Further, according to one embodiment of the cathode electrode of the present application, the first layer at the surface layer of the cathode electrode is modified by a metal ion-substituted cation exchange substance, and the amount of water molecules supplied to copper constituting the cathode electrode is controlled by the metal ion-substituted cation exchange substance, and thus the selectivity of hydrogen is reduced, and the catalytic reaction of olefins such as ethylene and alcohols such as ethanol generated by the reduction reaction of carbon dioxide can be efficiently and stably continued for a long period of time. The metal ion-substituted cation exchange substance refers to a structure in which hydrogen ions (H+) of the cation exchange substance are substituted with metal ions, and thus the content of hydrogen ions (H+) in the structure is also reduced. + +

[0045] Further, according to one embodiment of the cathode electrode of the present application, by controlling the ratio of the second thickness of the second layer to the first thickness of the first layer to be greater than 0 and less than or equal to 100, the interface (three-phase interface) of carbon dioxide gas, water molecules contained in the electrolyte, and copper as a catalyst can be more reliably ensured in the second layer, and thus even if the first layer is immersed in the electrolyte, the catalytic reaction of olefins such as ethylene and alcohols such as ethanol generated by the reduction reaction of carbon dioxide can be more efficiently and stably continued for a long period of time.

[0046] ​​In addition, according to the embodiment of the cathode electrode of the present application, the second layer is divided into a first region on the side close to the first layer and a second region adjacent to the first region with the center of the thickness direction of the second layer as a boundary, and the content of copper (vol%) of the first region is higher than the content of copper (vol%) of the second region, so that the interface (triple phase interface) of carbon dioxide gas, water molecules contained in the electrolyte, and copper as a catalyst in the second layer can be more reliably ensured, and thus the catalytic reaction of olefins such as ethylene and alcohols such as ethanol generated by the reduction reaction of carbon dioxide can be more long-term stably and efficiently continued even when the first layer is immersed in the electrolyte.

[0047] It is considered that the interface (for example, the interface of 0-valent copper and 1-valent copper) of copper in different valence states existing in the cathode electrode in which the reduction reaction of carbon dioxide occurs using copper as a catalytic material mainly causes carbon derived from carbon dioxide to form a C-C bond, and functions as a site for stabilizing the C-C bond. In other words, it is considered that the interface (for example, the interface of 0-valent copper and 1-valent copper) of copper in different valence states is a main active site of the reduction reaction of carbon dioxide. From the above, according to the embodiment of the cathode electrode of the present application, by the copper of the first layer including 2-valent copper, and 0-valent copper and / or 1-valent copper, and the copper of the second layer including 2-valent copper, and 0-valent copper and / or 1-valent copper, or by the copper of the first layer being reduced to reduction-use 1-valent copper and / or reduction-use 2-valent copper for reduction to 0-valent copper, and 1-valent copper and / or 2-valent copper not reduced to 0-valent copper, and the copper of the second layer being reduced to reduction-use 1-valent copper and / or reduction-use 2-valent copper for reduction to 0-valent copper, and 1-valent copper and / or 2-valent copper not reduced to 0-valent copper, the catalytic reaction of olefins such as ethylene and alcohols such as ethanol generated by the reduction reaction of carbon dioxide can be further ensured to be long-term stably and efficiently continued.

[0048] In the cathode electrode in which copper is used as a catalytic material, when the reduction reaction of carbon dioxide is performed, 1-valence copper is reduced to 0-valence copper, and 2-valence copper is reduced to 0-valence copper or 1-valence copper. It is considered that, when the reduction reaction of carbon dioxide is continued for a long time, as the 2-valence copper is reduced to 0-valence copper or 1-valence copper, the 1-valence copper is reduced to 0-valence copper, and the interface of the copper in different valences (for example, the interface of 0-valence copper and 1-valence copper) has a tendency to decrease. As described above, according to the embodiment of the cathode electrode of the present application, by further containing at least one additive element selected from the group of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon in the first layer, and by further containing at least one additive element selected from the group of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon in the second layer, the additive element is allowed to maintain the function of oxygen in the cathode electrode, and thus the reduction of 1-valence copper to 0-valence copper can be moderately inhibited. As described above, even if the reduction reaction of carbon dioxide is continued for a long time, as long as the presence ratio of 0-valence copper and 1-valence copper is actually optimized, the generation and stability of C-C bond can be maintained, and thus the catalytic reaction for generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be further ensured to be continued stably for a long time.

[0049] Further, both ethylene and ethanol are C2 compounds, and the generation of C-C bond on the catalytic material is an intermediate link in the reaction path. Therefore, the active site on the catalytic material for the generation of ethylene and the generation of ethanol is the same site or very close, and thus the stability of the generation of ethylene and the stability of the generation of ethanol show similar trends, which indicates that the reduction reaction of carbon dioxide is performed in the same way whether ethylene is generated or ethanol is generated.

[0050] In addition, according to the embodiment of the cathode electrode of the present application, by containing the additive element in the first layer at 0.10 atom% or more and 1.0 atom% or less with respect to 100 atom% of copper contained in the first layer, and by containing the additive element in the second layer at 0.10 atom% or more and 1.0 atom% or less with respect to 100 atom% of copper contained in the second layer, even if the reduction reaction of carbon dioxide is continued for a long time, the presence ratio of 0-valence copper and 1-valence copper can be actually optimized. Therefore, the catalytic reaction for generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be more stably continued for a long time.

[0051] Further, according to the one embodiment of the cathode electrode of the present application, by making the additive element of the first layer contain 0.25 atom% or more and 0.70 atom% or less with respect to 100 atom% of copper contained in the first layer, and by making the additive element of the second layer contain 0.25 atom% or more and 0.70 atom% or less with respect to 100 atom% of copper contained in the second layer, even if the reduction reaction of carbon dioxide is continued for a long period of time, the existence ratio of zero-valent copper to one-valent copper can be reliably maintained within the optimum range. Therefore, the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be further continued more stably for a long period of time.

[0052] Further, according to the one embodiment of the cathode electrode of the present application, since the additive element of the first layer contains aluminum and the additive element of the second layer contains aluminum, the function of moderately retaining oxygen within the cathode electrode can be reliably achieved, and as a result, even if the reduction reaction of carbon dioxide is continued for a long period of time, the existence ratio of zero-valent copper to one-valent copper can be reliably maintained within the optimum range. Therefore, the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be continued more stably for a long period of time.

[0053] Further, according to the one embodiment of the cathode electrode of the present application, since the cation exchange substance contains a sulfonated tetrafluoroethylene-based polymer and the metal ion is an alkali metal ion and / or an alkaline earth metal ion, the amount of water molecules supplied to copper constituting the cathode electrode can be reliably controlled. Therefore, the selectivity of hydrogen as a byproduct is more reliably suppressed, and thus it is more stably ensured that the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be continued efficiently and stably for a long period of time.

[0054] Further, according to the one embodiment of the cathode electrode of the present application, whether the metal ion-substituted cation exchange substance forms a layered structure on the surface of the first layer or is mixed together with copper in the first layer, the amount of water molecules supplied to copper can be more accurately controlled by the presence of the metal ion-substituted cation exchange substance.

[0055] Further, according to the one embodiment of the cathode electrode of the present application, since the cathode electrode has a porous structure, in the case of the reduction reaction of carbon dioxide in the cathode electrode, the contact of water and carbon dioxide becomes smooth, and the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol can be continued more stably for a long period of time.

[0056] In one embodiment of the cathode electrode and substrate composite of the present application, because the cathode electrode of the present application is equipped with a substrate and a second layer on the substrate, even if the first layer on the surface of the cathode electrode is immersed in an electrolyte, carbon dioxide gas can smoothly contact the second layer of the cathode electrode. Therefore, according to one embodiment of the cathode electrode and substrate composite of the present application, even if the first layer on the surface of the cathode electrode is immersed in an electrolyte, the selectivity of hydrogen, a byproduct of a reaction, is reduced, and the catalytic reaction of the reduction reaction of carbon dioxide to generate olefins such as ethylene and alcohols such as ethanol can continue at high efficiency for a long period of time.

[0057] The manufacturing method of the cathode electrode and substrate composite of the present application includes the following steps: a step of preparing a substrate having a carbon layer and a porous structure; a sputtering layer forming step of forming a sputtering layer having copper on the carbon layer of the substrate by sputtering; and a metal ion-substituted cation exchange substance application step of applying a metal ion-substituted cation exchange substance to the surface of the sputtering layer by substituting metal ions for the cation exchange substance on the sputtering layer, thereby reducing the selectivity of hydrogen, a byproduct of a reaction, even if the surface of the cathode electrode is immersed in an electrolyte. Therefore, a composite can be manufactured in which the catalytic reaction of the reduction reaction of carbon dioxide to generate olefins such as ethylene and alcohols such as ethanol can continue at high efficiency for a long period of time. In addition, according to the manufacturing method of the cathode electrode and substrate composite of the present application, because of the metal ion-substituted cation exchange substance application step, the metal ion-substituted cation exchange substance can control the amount of water molecules supplied to the copper that constitutes the cathode electrode, and therefore, a composite can be manufactured in which the selectivity of hydrogen is reduced and the catalytic reaction of the reduction reaction of carbon dioxide to generate olefins such as ethylene and alcohols such as ethanol can continue at high efficiency for a long period of time.

[0058] The manufacturing method of the cathode electrode and substrate composite according to the present application includes the following steps: a step of preparing a substrate having a porous structure; a step of forming a second layer on the substrate by applying a second suspension containing a mixture of copper and carbon to form a second layer which is a mixed layer of copper and carbon; a step of forming a first layer on the second layer by applying a first suspension containing copper to form a first layer containing copper; and a step of applying a metal ion-substituted cation exchange substance to the first layer to modify the surface of the first layer. Through the above steps, even if the first layer located at the surface layer of the cathode electrode is immersed in an electrolyte, the selectivity of hydrogen, a by-product of a side reaction, is reduced, so that a composite in which a catalytic reaction for generating olefins such as ethylene and alcohols such as ethanol by a reduction reaction of carbon dioxide can be continuously and efficiently performed for a long period of time with stability can be manufactured. In addition, according to the manufacturing method of the cathode electrode and substrate composite according to the present application, by the step of applying the metal ion-substituted cation exchange substance, the water molecule amount supplied to the copper constituting the cathode electrode can be controlled by the metal ion-substituted cation exchange substance, so that the reduction in the selectivity of hydrogen can be suppressed, and thus a composite in which a catalytic reaction for generating olefins such as ethylene and alcohols such as ethanol by a reduction reaction of carbon dioxide can be continuously and efficiently performed for a long period of time with stability can be manufactured. BRIEF DESCRIPTION OF DRAWINGS Figure 1 is a schematic view showing a cross section of the cathode electrode and substrate composite according to the present application.

[0060] Figure 2 is a cross-sectional view for explaining a reduction reaction of carbon dioxide in the cathode electrode and substrate composite according to the present application.

[0061] Figure 3 is an explanatory view for explaining an electrolytic polishing treatment step in the manufacturing method of the cathode electrode and substrate composite.

[0062] Figure 4 is an explanatory view for explaining a sputtering layer forming step and a copper oxidation treatment step in the manufacturing method of the cathode electrode and substrate composite.

[0063] Figure 5 is an explanatory view for explaining a partial reduction step in the manufacturing method of the cathode electrode and substrate composite.

[0064] Figure 6 is an explanatory view showing a state after the metal ion-substituted cation exchange substance is applied in the manufacturing method of the cathode electrode and substrate composite.

[0065] Figure 7 is a schematic view showing an electrolytic reduction device provided with the cathode electrode according to the present application.

[0066] Figure 8 is a schematic explanatory view showing another electrolytic reduction device provided with the cathode electrode of the present application.

DETAILED DESCRIPTION

[0068] As shown in Figure 1 , 2 , the cathode electrode 100 of the present application is a cathode electrode for electro-reducing carbon dioxide. The cathode electrode 100 has a first layer 111 having a first thickness, which is located at a surface layer of the cathode electrode 100, and a second layer 112 having a second thickness, which is located adjacent to the first layer 111 in a thickness direction of the first layer 111. The outer surface of the first layer 111 of the cathode electrode 100 is exposed to an external environment of the cathode electrode 100 and the composite 120 described later. On the other hand, the second layer 112 of the cathode electrode 100 is not exposed to the external environment of the composite 120.

[0069] The cathode electrode 100 includes a first site 101 and a second site 102 opposite to the first site 101. The second site 102 of the cathode electrode 100 is exposed to the external environment of the cathode electrode 100 and the composite 120. The second site 102 of the cathode electrode 100 is in contact with an electrolyte 130, which is an aqueous solution in which an electrolyte is dissolved. The outer surface of the first layer 111 of the cathode electrode 100 corresponds to the outer surface of the second site 102 of the cathode electrode 100. As described above, the first layer 111 of the cathode electrode 100 is in contact with the electrolyte 130.

[0070] On the other hand, on the side of the first site 101 of the cathode electrode 100, the first site 101 of the cathode electrode 100 is not exposed to the external environment of the composite 120 because of the base material 1 of the composite 120 described later. The surface of the second layer 112 of the cathode electrode 100 corresponds to the surface of the first site 101 of the cathode electrode 100.

[0071] The first layer 111 of the cathode electrode 100 contains copper (Cu), and the first layer 111 is modified by a metal ion-substituted cation exchange substance. As described above, the first layer 111 of the cathode electrode 100 contains copper as a catalytic material as a necessary component, and the metal ion-substituted cation exchange substance for modifying the surface of the first layer 111. The metal ion-substituted cation exchange substance is a hydrogen ion (H+ ) is substituted with metal ions, and the content of hydrogen ions (H + ) is reduced. On the other hand, the first layer 111 does not contain carbon.

[0072] The second layer 112 of the cathode electrode 100 is a mixed layer of copper (Cu) and carbon (C). As described above, the second layer 112 of the cathode electrode 100 contains copper as a catalytic material and carbon as a material that uniformly distributes the diffusion of carbon dioxide gas as necessary components. As the carbon that constitutes the second layer 112, for example, particulate carbon such as carbon black can be cited.

[0073] Therefore, the cathode electrode 100 is provided with a double-layer structure including the first layer 111 that contains copper but does not contain carbon and the second layer 112 that contains copper and carbon.

[0074] The cathode electrode 100 contains the first layer 111 that is located on the surface of the cathode electrode 100 and has a first thickness and the second layer 112 that has a second thickness and is adjacent to the first layer 111 in the thickness direction of the first layer 111. Since the first layer 111 contains copper and the second layer 112 is a mixed layer of copper and carbon, even if the first layer 111 located on the surface of the cathode electrode 100 decreases the amount of supply of carbon dioxide gas to the first layer 111 due to immersion in the electrolyte 130, the amount of supply of carbon dioxide gas to the second layer 112 can be maintained due to the carbon contained in the second layer 112 that is a mixed layer of copper and carbon. Therefore, even if the first layer 111 is immersed in the electrolyte 130, an interface (three-phase interface) composed of carbon dioxide (CO2) gas, water (H2O) molecules contained in the electrolyte 130, and copper as a catalyst (Cu) as a place of reduction reaction is formed in the second layer 112.

[0075] As described above, in the cathode electrode 100, even if the first layer 111 containing copper as a catalyst is immersed in the electrolyte 130, the selectivity of hydrogen as a byproduct of the reduction reaction of carbon dioxide is reduced, so that the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be continued efficiently and stably for a long period of time.

[0076] In addition, in the cathode electrode 100, the first layer 111 located on the surface of the cathode electrode 100 is surface-modified by a cation exchange material (a cation exchange material in which hydrogen ions (H + ) are substituted with metal ions), so the amount of supply of water molecules, that is, hydrogen ions (H +) The supply amount is controlled by the metal ion-substituted cation exchange material. In addition, since the surface of the metal ion-substituted cation exchange material of the first layer 111 is modified, copper in the first layer 111 more easily invades into carbon located in the lower layer due to the effect of the metal ion, and it is believed that this greatly promotes the formation of the second layer 112 as a mixed layer of copper and carbon. As described above, for the cathode electrode 100 equipped with a double layer structure of the first layer 111 containing copper and not containing carbon, and the second layer 112 containing copper and carbon, the metal ion-substituted cation exchange material performs surface modification of the first layer 111, and plays an important promoting role. Furthermore, since the cation exchange material has been substituted with metal ions, the content of hydrogen ions is reduced, and thus hydrogen ions are also prevented from being supplied from the cation exchange material to copper. Therefore, the configuration of the cathode electrode 100 is able to prevent a configuration in which hydrogen ions are excessively supplied to copper as a catalytic material. Furthermore, the cation exchange material is stable in the state in which hydrogen ions possessed by the cation exchange material are substituted with metal ions, compared to the state in which hydrogen ions are not substituted with metal ions, and thus the state in which the cation exchange material is substituted with metal ions is also able to be maintained in the cathode electrode 100.

[0077] Therefore, in the cathode electrode 100, the selectivity of hydrogen as a byproduct of the reduction reaction of carbon dioxide is reduced, and the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide is able to be continuously and efficiently performed stably for a long period of time.

[0078] The ratio of the second thickness of the second layer 112 to the first thickness of the first layer 111 is not particularly limited, and the lower limit thereof is 0.01, more preferably 0.05, further preferably 0.1, and particularly preferably 0.5, from the viewpoint that the interface (three-phase interface) formed by the carbon dioxide gas and the water molecules contained in the electrolyte 130 and the copper as a catalyst is more reliably ensured in the second layer 112, and as a result, even if the first layer 111 is immersed in the electrolyte 130, the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be stably continued for a longer period of time with high efficiency. On the other hand, the upper limit of the ratio of the second thickness of the second layer 112 to the first thickness of the first layer 111 is 100, more preferably 50, further preferably 10, and particularly preferably 5.0, from the viewpoint that the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be stably continued with high efficiency.

[0079] The distribution of the content of copper in the second layer 112 is not particularly limited, but from the viewpoint that the interface (three-phase interface) formed by the carbon dioxide gas and the water molecules contained in the electrolyte 130 and the copper as a catalyst is more reliably ensured in the second layer 112, and as a result, even if the first layer 111 is immersed in the electrolyte 130, the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be stably continued for a longer period of time with high efficiency, the second layer 112 includes, with the central portion of the second layer 112 in the thickness direction as a boundary, a first region on the first layer 111 side and a second region adjacent to the first region, and the content of copper (vol%) in the first region is preferably higher than the content of copper (vol%) in the second region.

[0080] The cation exchange material constituting the metal ion-substituted cation exchange material, i.e., the cation exchange material before being substituted with metal ions, can include, for example, a cation exchange resin, and as the cation exchange resin, for example, a sulfonated tetrafluoroethylene-based polymer (trade name: "Nafion"), a perfluoroalkyl compound (PFAS)-based polymer, a polyethylenedioxythiophene (PEDOT)-based polymer, and the like can be included. Among these, the sulfonated tetrafluoroethylene-based polymer is preferable from the viewpoint that the surface modification of the first layer 111 containing copper is easy.

[0081] The metal ions that constitute the cation exchange material are not particularly limited as long as the hydrogen ions of the cation exchange material can be replaced with the metal ions. However, from the viewpoint of being able to reliably control the amount of water molecules supplied to the copper that constitutes the cathode electrode 100, and more reliably reduce the selectivity of the byproduct hydrogen, thereby being able to more reliably generate olefins such as ethylene and alcohols such as ethanol through the catalytic reaction of the reduction reaction of carbon dioxide, the metal ions that constitute the cation exchange material are preferably alkali metal ions and alkaline earth metal ions. As the alkali metal ions, lithium ions (Li + ), sodium ions (Na + ), potassium ions (K + ), rubidium ions (Rb + ), cesium ions (Cs + ), and francium ions (Fr r + ) can be listed. As the alkaline earth metal ions, beryllium ions (Be 2+ ), magnesium ions (Mg 2+ ), calcium ions (Ca 2+ ), strontium ions (Sr 2+ ), barium ions (Ba 2+ ), and radium ions (Ra 2+ ) can be listed. These metal ions can be used alone or in combination of two or more.

[0082] Among these metal ions, from the viewpoint of more reliably controlling the amount of water molecules supplied to the copper that constitutes the cathode electrode 100, and more reliably reducing the selectivity of the byproduct hydrogen, alkali metal ions are more preferable, and lithium ions (Li + ), sodium ions (Na + ), potassium ions (K + ), and rubidium ions (Rb + ) are further preferable. From the viewpoint of being able to further control the amount of water molecules supplied to the copper, and further reduce the selectivity of the byproduct hydrogen, potassium ions (K + ) are particularly preferable.

[0083] The modification method of the first layer 111 as the metal ion-substituted cation exchange substance surface is not particularly limited, but from the viewpoint of being able to more appropriately control the amount of water molecules supplied to the copper by the presence of the metal ion-substituted cation exchange substance, the method in which the metal ion-substituted cation exchange substance forms a layer on the surface of the first layer 111, the method in which the metal ion-substituted cation exchange substance is mixed with the copper of the first layer 111, and particularly preferably the method in which the metal ion-substituted cation exchange substance forms a layer on the surface of the first layer 111. As the method in which the metal ion-substituted cation exchange substance forms a layer on the surface of the first layer 111, for example, the method in which the metal ion-substituted cation exchange substance forms a layer on the surface of the copper of the first layer 111 can be exemplified.

[0084] The content of the metal ion-substituted cation exchange substance is not particularly limited, but the lower limit value thereof is, from the viewpoint of being able to reliably control the amount of water molecules supplied to the copper to be able to ensure that the excess supply of hydrogen ions to the copper is prevented, preferably 125 g or more and 24333 g or less of the accumulation amount of the cation exchange substance with respect to 100 g of the total of the copper element of the first layer 111 and the copper element of the second layer 112.

[0085] The method for producing the metal ion-substituted cation exchange substance can be, for example, a method in which a solution (for example, an aqueous solution) of a cation exchange substance and a solution (for example, an aqueous solution) containing a metal ion are mixed, and the hydrogen ions of the cation exchange substance are substituted with the metal ions, whereby the metal ion-substituted cation exchange substance can be obtained.

[0086] In the cathode electrode 100 of the present application, as one embodiment of the first cathode electrode, the copper as the catalytic material of the first layer 111 includes divalent copper, and zero-valent copper and / or monovalent copper, and the copper as the catalytic material of the second layer 112 includes divalent copper, and zero-valent copper and / or monovalent copper. In one embodiment of the first cathode electrode, the essential components of the first layer 111 and the second layer 112 include divalent copper and zero-valent copper and / or monovalent copper. As the monovalent copper, cuprous oxide (Cu2O) can be exemplified, and as the divalent copper, cupric oxide (CuO) can be exemplified. In addition, as the zero-valent copper, copper (Cu) monomer can be exemplified.

[0087] In the reduction reaction of carbon dioxide on the cathode electrode 100 using copper as a catalytic material, it is considered that the interface of copper in different valence states existing in the cathode electrode 100 (for example, the interface of 0-valence copper and 1-valence copper) mainly functions as a site for forming a C-C bond from carbon derived from carbon dioxide and stabilizing the C-C bond. That is, it is considered that the interface of copper in different valence states (for example, the interface of 0-valence copper and 1-valence copper) is a main active site for the reduction reaction of carbon dioxide. From the above, by including 2-valence copper, and 0-valence copper and / or 1-valence copper in the copper of the first layer 111, and including 2-valence copper, and 0-valence copper and / or 1-valence copper in the copper of the second layer 112, it is further ensured that the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be continued at a high efficiency stably for a long period.

[0088] In the cathode electrode 100 of the present application, as one embodiment of the second cathode electrode, the copper of the first layer 111 includes reduction-use 1-valence copper and / or reduction-use 2-valence copper which can be reduced to 0-valence copper by reduction treatment, and 1-valence copper and / or 2-valence copper which is not reduced to 0-valence copper, and the copper of the second layer 112 includes reduction-use 1-valence copper and / or reduction-use 2-valence copper which is reduced to 0-valence copper by reduction treatment, and 1-valence copper and / or 2-valence copper which is not reduced to 0-valence copper. In one embodiment of the second cathode electrode, a part of the 1-valence copper and / or 2-valence copper of the first layer 111 is reduced to 0-valence copper, and a part of the 1-valence copper and / or 2-valence copper of the second layer 112 is reduced to 0-valence copper. From the above, in one embodiment of the second cathode electrode, as copper (Cu), there are present: reduction-use 1-valence copper and / or reduction-use 2-valence copper, and 1-valence copper and / or 2-valence copper which is not reduced to 0-valence copper. The above-described one embodiment of the second cathode electrode includes 1-valence copper and / or 2-valence copper as a necessary component of the first layer 111 and the second layer 112. In one embodiment of the second cathode electrode, by performing reduction treatment, the reduction-use 2-valence copper is reduced to 0-valence copper or 1-valence copper, and the reduction-use 1-valence copper is reduced to 0-valence copper. Therefore, in one embodiment of the second cathode electrode, by performing reduction treatment, a cathode electrode including 0-valence copper, 1-valence copper and / or 2-valence copper is obtained.

[0089] As the 1-valence copper, cuprous oxide (Cu2O) can be exemplified, and as the 2-valence copper, cupric oxide (CuO) can be exemplified. In addition, as the 0-valence copper, copper (Cu) monomer can be exemplified.

[0090] The copper of the first layer 111 contains reduced copper for reduction of 1-valent copper and / or reduced copper for reduction of 2-valent copper which are reduced to 0-valent copper by reduction treatment, and 1-valent copper and / or 2-valent copper which are not reduced to 0-valent copper, and the copper of the second layer 112 contains reduced copper for reduction of 1-valent copper and / or reduced copper for reduction of 2-valent copper which are reduced to 0-valent copper by reduction treatment, and 1-valent copper and / or 2-valent copper which are not reduced to 0-valent copper, thereby further ensuring that the catalytic reaction of reduction reaction of carbon dioxide to generate olefins such as ethylene and alcohols such as ethanol can be continued at high efficiency stably for a long period.

[0091] In the cathode electrode 100 (including one embodiment of the first cathode electrode, one embodiment of the second cathode electrode) of the present application, in addition to copper (Cu) as a catalytic material, at least one additive element (M) selected from the group of silver (Ag), gold (Au), cadmium (Cd), tin (Sn), aluminum (Al), boron (B), gallium (Ga), zinc (Zn), titanium (Ti), and silicon (Si) can be included as an arbitrary component.

[0092] In the cathode electrode 100 using copper as a catalytic material, in the reduction reaction of carbon dioxide, 1-valent copper is reduced to 0-valent copper, and 2-valent copper is reduced to 0-valent copper or 1-valent copper. Therefore, as the reduction reaction of carbon dioxide is continued for a long period, 2-valent copper is reduced to 0-valent copper or 1-valent copper, and 1-valent copper is reduced to 0-valent copper, and the interface of copper of different valences (for example, the interface of 0-valent copper and 1-valent copper) has a tendency to decrease. Here, the first layer 111 further includes at least one additive element (M1) selected from the group of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon in addition to copper, and the second layer 112 further includes at least one additive element (M2) selected from the group of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon in addition to copper, and therefore, since the additive element (M1) and the additive element (M2) have a function of holding oxygen in the cathode electrode 100, the reduction of 1-valent copper to 0-valent copper can be moderately suppressed. As described above, even if the reduction reaction of carbon dioxide is continued for a long period, by actually optimizing the presence ratio of 0-valent copper and 1-valent copper, the generation and stability of C-C bonds can be maintained, and therefore, the catalytic reaction of the reduction reaction of carbon dioxide to generate olefins such as ethylene and alcohols such as ethanol can be continued stably for a long period.

[0093] The form of the at least one additive element (M) selected from the group of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon is not particularly limited, and examples of the form of the additive element (M) include the form of the additive element (M) itself (additive element (M) monomer). In addition to the form of the additive element (M) itself, the form of a hydroxide and the form of an oxide are also possible. In addition, the additive element (M) can exist in a mixture of the form of the additive element (M) itself and the form of a hydroxide and the form of an oxide. The additive element (M) can be used alone or two or more kinds can be used in combination.

[0094] The content of the additive element (M1) of the first layer 111 is not particularly limited, but the lower limit value thereof, relative to the total 100 atomic % of the copper element including all of the 0-valent copper, 1-valent copper, and 2-valent copper, etc. contained in the first layer 111, is preferably 0.10 atomic %, more preferably 0.20 atomic %, and particularly preferably 0.25 atomic %, from the viewpoint that even if the reduction reaction of carbon dioxide is continued for a long period of time, the existence ratio of the 0-valent copper and the 1-valent copper is actually optimized, and the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be continued for a long period of time more stably. On the other hand, the upper limit value of the content of the additive element (M1) of the first layer 111, relative to the total 100 atomic % of the copper element including all of the 0-valent copper, 1-valent copper, and 2-valent copper, etc. contained in the first layer 111, is preferably 1.0 atomic %, more preferably 0.85 atomic %, and particularly preferably 0.70 atomic %, from the viewpoint that even if the reduction reaction of carbon dioxide is continued for a long period of time, the existence ratio of the 0-valent copper and the 1-valent copper is actually optimized, and the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be continued for a long period of time more stably.

[0095] The content of the additive element (M2) of the second layer 112 is not particularly limited, but the lower limit value thereof, relative to 100 atomic % of copper elements including all of the copper of 0-valence copper, 1-valence copper, and 2-valence copper, and the like, in the second layer 112, is preferably 0.10 atomic %, more preferably 0.20 atomic %, and particularly preferably 0.25 atomic %, from the viewpoint that even if the reduction reaction of carbon dioxide is continued for a long period of time, the existence ratio of 0-valence copper and 1-valence copper is reliably optimized, and the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be continued more stably for a longer period of time. On the other hand, the upper limit value of the content of the additive element (M2) of the second layer 112, relative to 100 atomic % of copper elements including all of the copper of 0-valence copper, 1-valence copper, and 2-valence copper, and the like, in the second layer 112, is preferably 1.0 atomic %, more preferably 0.85 atomic %, and particularly preferably 0.70 atomic %, from the viewpoint that even if the reduction reaction of carbon dioxide is continued for a long period of time, the existence ratio of 0-valence copper and 1-valence copper is reliably optimized, and the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be continued more stably for a longer period of time.

[0096] As the additive element (M1) of the first layer 111 and the additive element (M2) of the second layer 112, silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, or silicon can be used, because they are more easily oxidized than copper, and have a tendency to have a higher affinity with oxygen than copper. On the other hand, among the additive element (M1) of the first layer 111 and the additive element (M2) of the second layer 112, aluminum is preferable because it can ensure the function of moderately retaining oxygen within the cathode electrode 100, and thus, even if the reduction reaction of carbon dioxide is continued for a long period of time, the existence ratio of 0-valence copper and 1-valence copper can be reliably optimized, and the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be continued more stably for a longer period of time.

[0097] The structure of the cathode electrode 100 is not particularly limited; it can be solid or porous. However, from the viewpoint that the catalytic reaction for the formation of olefins such as ethylene and alcohols such as ethanol can be more stable and sustained over a longer period due to the smoother contact between water and carbon dioxide in the carbon dioxide reduction reaction of the cathode electrode 100, a porous structure is preferred. While the proportion of pores (porosity) in the porous structure is not particularly limited, its lower limit is preferably 1% by volume, and particularly preferably 10% by volume, from the viewpoint that it allows carbon dioxide to permeate more smoothly into the cathode electrode 100, thereby further improving the formation efficiency of olefins such as ethylene and alcohols such as ethanol. On the other hand, the upper limit of the porosity of the porous structure is preferably 99% by volume, and particularly preferably 90% by volume, from the viewpoint that maintaining a surface area conducive to the catalytic reaction of the cathode electrode 100 can further improve the formation efficiency of olefins such as ethylene and alcohols such as ethanol. For example, a porous structure of the cathode electrode 100 can be formed by performing the partial reduction treatment described later.

[0098] The cathode electrode 100 of the present invention, for example, supplies gaseous carbon dioxide to one side of the first part 101 and liquid water to one side of the second part 102. Under the catalytic action of the cathode electrode 100, carbon dioxide can react with water and electroreduced to generate olefins such as ethylene and alcohols such as ethanol.

[0099] [Cathode electrode and substrate composite] The cathode electrode 100 of the present invention can be used as a single cathode electrode 100, and as will be described below, it can also be used as a substrate 1 and a composite 120.

[0100] like Figure 1 , 2 As shown, the composite 120 of the cathode electrode 100 and the substrate 1 includes the substrate 1 and the cathode electrode 100 of the present invention with a second layer 112 disposed on the substrate 1. The substrate 1 may also have a carbon layer 113 in its surface portion. Examples of the carbon layer 113 include, for example, a carbon layer 113 formed of particulate carbon, and more specifically, a carbon layer 113 formed of carbon black.

[0101] The substrate 1 is provided on the side of the first portion 101 of the cathode electrode 100. That is, on the substrate 1, the side of the first portion 101 of the cathode electrode 100 is disposed. In addition, in the composite 120, the carbon layer 113 of the substrate 1 is adjacent to the second layer 112 of the cathode electrode 100. As described above, in the composite 120, the first layer 111 of the cathode electrode 100, the second layer 112 of the cathode electrode 100, and the carbon layer 113 of the substrate 1 are stacked to form a three-layer structure. By supplying the carbon dioxide gas from the side of the substrate 1 of the composite 120 (i.e., the side of the first portion 101 of the cathode electrode 100), the carbon dioxide gas can be uniformly diffused in the second layer 112 of the cathode electrode 100, and thus the supply of carbon dioxide to the cathode electrode 100 will be smoother.

[0102] The substrate is not provided on the side of the second portion 102 of the cathode electrode 100, which is exposed to the outside environment of the cathode electrode 100 and the composite 120. The cathode electrode 100 is a cover film that covers the surface of the substrate 1. In the composite 120 of the cathode electrode 100 and the substrate 1, even if the first layer 111 located on the surface layer of the cathode electrode 100 is immersed in the electrolyte 130, the gaseous carbon dioxide can smoothly contact the second layer 112 of the cathode electrode 100. Therefore, in the composite 120 of the present application, even if the first layer 111 located on the surface layer of the cathode electrode 100 is immersed in the electrolyte 130, the selectivity of the byproduct hydrogen will be reduced, and the catalytic reaction for generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be continuously and efficiently performed for a long period of time.

[0103] The substrate 1 can be solid or porous, but from the viewpoint that the carbon dioxide gas can smoothly contact the cathode electrode 100 and the catalytic reaction for generating olefins such as ethylene and alcohols such as ethanol can be continuously and more stably performed for a long period of time, a porous structure having gas permeability is preferable.

[0104] The material of the substrate 1 having a porous structure is not particularly limited, but from the viewpoint that the catalytic reaction for generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be continuously and more stably performed for a long period of time and that the composite 120 of the cathode electrode 100 and the substrate 1 can be obtained, for example, carbon, fluorine-containing resin, and metal are preferable.

[0105] As the carbon, for example, a composite of carbon black and carbon fiber, and the like can be exemplified. As shown in FIG. 1, in the composite 120, the substrate 1 is a carbon material of a composite of a carbon layer 113 formed of carbon black and a carbon fiber 114, and the structure is such that the carbon layer 113 is stacked on the carbon fiber 114. In the composite 120, the carbon layer 113 provided on the carbon fiber 114 is adjacent to the second layer 112. Figure 1 、 2 As shown in FIG. 1, in the composite 120, the substrate 1 is a carbon material of a composite of a carbon layer 113 formed of carbon black and a carbon fiber 114, and the structure is such that the carbon layer 113 is stacked on the carbon fiber 114. In the composite 120, the carbon layer 113 provided on the carbon fiber 114 is adjacent to the second layer 112.

[0106] As the fluorine-containing resin, for example, polytetrafluoroethylene, polyvinylidene fluoride, perfluoroalkoxy alkane, perfluoroethylene propylene copolymer, ethylene-tetrafluoroethylene copolymer, polytrifluorochloroethylene, ethylene-trifluorochloroethylene copolymer, and the like can be exemplified. As the metal, for example, copper (Cu), niobium (Nb), aluminum (Al), titanium (Ti), porous metal composed of an alloy containing one or more of the above metals, stainless steel, and the like can be exemplified. When the material of the porous structure of the substrate 1 is metal, and the metal is copper (Cu), as the porous metal, for example, a sintered body of copper particles can be exemplified.

[0107] The average thickness of the substrate 1 is not particularly limited, and for example, a plate-shaped member of 0.2 mm or more and 1.5 mm or less can be exemplified.

[0108] The cathode electrode 100 in the composite 120 of the cathode electrode 100 and the substrate 1 is, for example, a sputtered layer formed on the substrate 1 by sputtering, and contains copper and an additive element (M) added as necessary.

[0109] [Method for manufacturing composite of cathode electrode and substrate] The method for manufacturing the composite of the cathode electrode and the substrate for electro-reducing carbon dioxide (first manufacturing method) can be known as described below. Figure 3 is an explanatory diagram for explaining the electrolytic polishing process in the method for manufacturing the composite of the cathode electrode and the substrate. Figure 4 is an explanatory diagram for explaining the sputtered layer forming process and the copper oxidation process in the method for manufacturing the composite of the cathode electrode and the substrate. Figure 5 is an explanatory diagram for explaining the partial reduction process in the method for manufacturing the composite of the cathode electrode and the substrate. Figure 6 is an explanatory diagram for explaining the state of the cation exchanger to which metal ion substitution is applied in the method for manufacturing the composite of the cathode electrode and the substrate.

[0110] As the first production method of the cathode electrode and the substrate composite, the following steps are included: (1) a step of including a carbon layer and being provided with a porous structure substrate; (2) an electrolytic polishing treatment step of performing electrolytic polishing treatment on the provided substrate as needed; (3) a sputtering layer forming step of forming a sputtering layer containing copper on the carbon layer of the substrate on which electrolytic polishing treatment is performed as needed; (4) a copper oxidation treatment step of oxidizing at least a part of the copper of the sputtering layer to 1-valence copper and / or 2-valence copper after the sputtering layer forming step as needed; (5) a partial reduction step of partially reducing the 1-valence copper and / or 2-valence copper oxidized by the copper oxidation treatment step to 0-valence copper and / or 1-valence copper as needed; and (6) a sputtering layer surface modification and metal ion substitution cation exchange substance application step of modifying the sputtering layer surface with a metal ion substitution cation exchange substance and applying the metal ion substitution cation exchange substance as needed on the sputtering layer on which the copper oxidation treatment step and the partial reduction step are performed. In the above steps, the (1) step, the (3) step, and the (6) step are mandatory, and the (2) step, the (4) step, and the (5) step are optional.

[0111] By the above-mentioned production method of the cathode electrode and the substrate composite, a cathode electrode in which the surface of the first layer is modified with a metal ion substitution cation exchange substance can be formed on the substrate. It is believed that modifying the surface of the first layer of the cathode electrode with the metal ion substitution cation exchange substance promotes the invasion of copper in the first layer into the carbon layer of the substrate in the lower layer by the action of the metal ion, which greatly promotes the formation of the second layer as a mixed layer of copper and carbon. As a result, in the step of modifying the surface of the first layer with the metal ion substitution cation exchange substance (i.e., the metal ion substitution cation exchange substance application step), a cathode electrode provided with a double-layer structure of the first layer containing copper and not containing carbon and the second layer containing copper and carbon can be produced.

[0112] By the above-mentioned production method of the cathode electrode and the substrate composite, a composite can be produced, which is characterized in that even if the surface layer of the cathode electrode is immersed in an electrolyte, the selectivity of hydrogen, a byproduct of a side reaction, can be reduced, and thus the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be continued at a high efficiency for a long time stably. In addition, in the above-mentioned production method of the cathode electrode and the substrate composite, due to the metal ion substitution cation exchange substance application step, the metal ion substitution cation exchange substance can control the amount of water supplied to the copper constituting the cathode electrode, and thus the selectivity of hydrogen can be reduced, and the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide can be continued at a high efficiency for a long time stably, and thus a composite having this characteristic can be produced.

[0113] As the cathode electrode formed by the above-mentioned manufacturing method of a cathode electrode and a base material composite, there can be mentioned a cathode electrode in which copper includes 2-valent copper, and 0-valent copper and / or 1-valent copper; or a cathode electrode in which copper is reduced to 0-valent copper by reduction treatment, and 1-valent copper and / or 2-valent copper which is not reduced to 0-valent copper.

[0114] (1) Step of preparing a base material having a carbon layer and a porous structure The step of preparing a base material having a carbon layer and having a porous structure is a step of preparing the above-mentioned base material. The material of the base material having a carbon layer and the porosity of the porous structure can be appropriately selected in accordance with the characteristics required for the cathode electrode and the base material composite.

[0115] (2) Step of electrolytic polishing treatment The step of electrolytic polishing treatment is a step which is carried out as necessary, for example, when a metal is used as the material of the base material. The step of electrolytic polishing treatment is as follows: first, the surface of the base material is degreased with an organic solvent such as hexane, and is washed and dried, and then, as shown in FIG. 2, a mixed acid solution 11 is charged into a container 10, the base material 1 as an anode is immersed in the mixed acid solution 11, the cathode 2 is immersed at a position apart from the base material 1, and then an electrolytic potential is applied to the base material 1 as an anode and the cathode 2. The surface of the base material 1 is electrolytically polished by applying the electrolytic potential to the base material 1 as an anode and the cathode 2. By electrolytically polishing the surface of the base material 1, a working deterioration layer on the surface of the base material 1 can be reduced or removed. As the mixed acid solution 11, there can be mentioned, for example, a mixed acid aqueous solution of phosphoric acid and sulfuric acid. As the cathode 2, there can be mentioned, for example, titanium or the like. Further, as shown in FIG. 3, in the case where the base material 1 of the composite 120 is a carbon material, the step of electrolytic polishing treatment can not be carried out. Figure 3 Figure 1 2

[0116] (3) Step of forming a sputtering layer As shown in FIG. 4, the step of forming a sputtering layer is a step of forming a sputtering layer 20 containing copper on the base material 1 by sputtering. When the sputtering layer 20 contains, as an arbitrary component, at least one additive element (M) selected from the group consisting of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon in addition to copper (Cu), as shown in FIG. 5, the sputtering layer 20 can be formed by sputtering using a target 30 containing copper and the additive element (M). Figure 4 Figure 4 ​​​​As shown, the sputtering layer formation process includes a copper (Cu) sputtering layer formation process that forms a copper (Cu) sputtering layer on a substrate 1 by sputtering, and an additive element (M) sputtering layer formation process that forms an additive element (M) sputtering layer on the copper (Cu) sputtering layer by sputtering. Furthermore, a copper (Cu) sputtering layer formation process that further forms a copper (Cu) sputtering layer on the formed additive element (M) sputtering layer by sputtering. By adjusting the amount of electricity from the power source and the sputtering time, the content of the additive element (M) relative to 100 atomic percent of copper (Cu) can be controlled. Additionally, as needed, to ensure uniform distribution of copper (Cu) and the additive element (M) throughout the overall sputtering layer 20, the copper (Cu) sputtering layer formation process and the additive element (M) sputtering layer formation process can be performed alternately multiple times. A cathode electrode comprising divalent copper, 0-valent copper, and / or 1-valent copper, and optionally containing additive elements, can be formed on a substrate 1 through a sputtering layer formation process. Alternatively, it may comprise 1-valent copper for reduction and / or 2-valent copper for reduction that has been reduced to 0-valent copper through a reduction treatment, as well as 1-valent copper and / or 2-valent copper that is not reduced to 0-valent copper, and optionally containing additive elements.

[0117] (4) Copper oxidation treatment process The copper oxidation process is a process performed as needed when it is necessary to adjust the ratio of monovalent copper (Cu2O) and / or divalent copper (CuO) to a predetermined amount. Figure 4 As shown, the copper oxidation process involves oxidizing the formed sputtered layer 20 by electroless plating, thereby oxidizing at least a portion of the 0-valent copper (Cu) contained in the sputtered layer 20 into 1-valent copper (Cu2O) and / or 2-valent copper (CuO), thus forming the oxidation treatment section 22. As an example of electroless plating oxidation treatment, an oxidation treatment method in which the sputtered layer 20 is immersed in an aqueous copper sulfate solution can be cited.

[0118] (5) Partial reduction process The partial reduction process is a step performed to further optimize the ratio of valent copper to divalent copper (Cu₂O) oxidized in the copper oxidation process, reducing the oxidized monovalent copper (Cu) and / or divalent copper (CuO) to valent copper (Cu₂O) as needed. The partial reduction process is as follows: Figure 5As shown, the composite 1' obtained by forming a sputtered layer 20 on the substrate 1 and the anode 33 are immersed in a partial reduction aqueous solution 32 housed in a two-chamber electrolytic cell 30 with a diaphragm 31, and an electrolytic potential is applied to the two-chamber electrolytic cell 30 by a power source 34 to perform a partial reduction treatment. Furthermore, by performing the partial reduction treatment, the sputtered layer 20 can be made porous. Examples of anodes 33 include platinum. Examples of partial reduction aqueous solutions 32 include potassium bicarbonate aqueous solutions that can be used on both the composite 1' side and the anode side.

[0119] (6) Application process of cation exchange material with metal ion substitution The application process of cation exchange substances substituted with metal ions, such as... Figure 6 As shown, a process is described in which a metal ion-substituted cation exchanger 21 is applied to the sputtered layer 20, which undergoes copper oxidation and partial reduction processes, to modify the surface of the sputtered layer 20. When an oxidation treatment section 22 is formed through the copper oxidation process, the metal ion-substituted cation exchanger 21 is also applied to the oxidation treatment section 22. As a method for applying the metal ion-substituted cation exchanger 21 to the sputtered layer 20, a spraying method, for example, is the spraying of a solution of the metal ion-substituted cation exchanger 21. By applying the metal ion-substituted cation exchanger 21 to the sputtered layer 20, at least a portion of monovalent copper (Cu₂O) is oxidized to divalent copper (CuO).

[0120] By applying a metal ion-substituted cation exchanger 21 to the sputtered layer 20, a structure can be obtained in which the surface of the first layer on the surface of the cathode electrode is modified with a metal ion-substituted cation exchanger. Furthermore, by applying the metal ion-substituted cation exchanger 21 to the sputtered layer 20, the metal ions promote the penetration of copper from the first layer on the surface of the cathode electrode into the carbon layer of the substrate, thereby forming a second layer that is a mixed layer of copper and carbon. As can be seen from the above, the metal ion-substituted cation exchanger application process can form a bilayer structure in the sputtered layer 20, comprising a first layer containing copper but not carbon, and a second layer containing both copper and carbon.

[0121] Next, another manufacturing method (second manufacturing method) for the composite of the cathode electrode and the substrate for electroreduction of carbon dioxide will be described.

[0122] As the second manufacturing method of the composite of the cathode electrode and the base material, the following steps are included: (1) a step of preparing a base material having a porous structure; (2) a second layer forming step of applying a second suspension liquid, which is a mixture of copper and carbon, on the base material to form a second layer, which is a mixed layer of copper and carbon; (3) a first layer forming step of applying a first suspension liquid containing copper on the second layer to form a first layer containing copper; and (4) a metal ion-substituted cation exchanger application step of applying a metal ion-substituted cation exchanger to the surface of the first layer to modify the surface of the first layer. In the second manufacturing method, the copper oxidation treatment step and / or the partial reduction step described above can be performed as needed after the first layer forming step and before the metal ion-substituted cation exchanger application step.

[0123] The manufacturing method of the composite of the cathode electrode and the base material described above can form a cathode electrode having a two-layer structure of a second layer containing copper and carbon on the base material and a first layer modified by a metal ion-substituted cation exchanger. It is believed that the modification of the surface of the first layer of the cathode electrode by the metal ion-substituted cation exchanger promotes the penetration of copper in the first layer into the second layer located below, thereby contributing to the thickness of the second layer, which is a mixed layer of copper and carbon, due to the effect of the metal ions.

[0124] The manufacturing method of the composite of the cathode electrode and the base material described above can reduce the selectivity of hydrogen, a byproduct of a side reaction, even when the first layer located on the surface of the cathode electrode is immersed in an electrolyte. Therefore, the catalytic reaction of olefins such as ethylene and alcohols such as ethanol generated by the reduction reaction of carbon dioxide can continue at a high efficiency for a long period of time, and a composite having such a performance can be manufactured. In the manufacturing method of the composite of the cathode electrode and the base material described above, the metal ion-substituted cation exchanger application step allows the metal ion-substituted cation exchanger to control the amount of copper, which constitutes the cathode electrode, supplied to water molecules. Therefore, the selectivity of hydrogen can be reduced, the catalytic reaction of olefins such as ethylene and alcohols such as ethanol generated by the reduction reaction of carbon dioxide can continue at a high efficiency for a long period of time, and a composite having such a performance can be manufactured.

[0125] As the cathode electrode formed by the manufacturing method of the cathode electrode and the substrate composite described above, two types can be listed: one is a cathode electrode in which the copper of the first layer contains divalent copper, and zero-valent copper and / or monovalent copper, and the copper of the second layer contains divalent copper, and zero-valent copper and / or monovalent copper. Alternatively, the other is a cathode electrode in which the copper of the first layer contains, by reduction treatment, reduced-to-zero-valent copper reduction-use monovalent copper and / or reduction-use divalent copper, and monovalent copper and / or divalent copper not reduced to zero-valent copper, and the copper of the second layer contains, by reduction treatment, reduced-to-zero-valent copper reduction-use monovalent copper and / or reduction-use divalent copper, and monovalent copper and / or divalent copper not reduced to zero-valent copper.

[0126] (1) Step of preparing a substrate having a porous structure The step of preparing a substrate having a porous structure is a step of preparing the substrate described above. The material of the substrate and the porosity of the porous structure can be appropriately selected in accordance with the characteristics required for the cathode electrode and the substrate composite.

[0127] (2) Step of forming a second layer The step of forming a second layer is a step of applying a second suspension liquid, which is a mixture of copper and carbon, to the prepared substrate, and forming a second layer, which is a mixed layer of copper and carbon. For example, in a dispersion medium such as a solvent, copper, carbon such as carbon black, and, if necessary, at least one additive element (M2) selected from silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon are added, and a second suspension liquid can be prepared by stirring them. As a method of applying the second suspension liquid to the substrate, there is no particular limitation, and, for example, spraying, a bar coater, and the like can be listed. The second suspension liquid applied to the substrate can form a second layer by drying treatment.

[0128] (3) Step of forming a first layer The step of forming a first layer is a step of further applying a first suspension liquid containing copper to the second layer, thereby forming a first layer containing copper on the second layer. For example, in copper in a dispersion medium such as a solvent, at least one additive element (M1) selected from silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon is added, if necessary, and a first suspension liquid can be prepared by stirring them. Carbon such as carbon black is not contained in the first suspension liquid. As a method of applying the first suspension liquid to the second layer, there is no particular limitation, and, for example, spraying, a bar coater, and the like can be listed. The first suspension liquid to be applied to the second layer can form a first layer by drying treatment.

[0129] (4) Step of applying a metal ion-substituted cation exchange substance A metal ion-substituted cation exchange substance application process, a metal ion-substituted cation exchange substance is applied to the first layer, and a process in which the metal ion-substituted cation exchange substance modifies the surface of the first layer. As the method of applying the metal ion-substituted cation exchange substance to the first layer, a spraying method in which a solution of the metal ion-substituted cation exchange substance is sprayed, for example, can be cited. By applying the metal ion-substituted cation exchange substance to the first layer, at least a part of the monovalent copper (Cu2O) is oxidized to divalent copper (CuO).

[0130] In the above-mentioned first production method and the second production method, by increasing the density of the first layer containing copper and the second layer which is a mixed layer of copper and carbon, and by the reduction reaction of carbon dioxide, the decrease in the volume of the first layer and the second layer which are catalytic layers can be surely suppressed, and therefore, from the viewpoint of being able to prevent moisture contained in an electrolyte from invading the catalytic layers, thereby avoiding the increase in the selectivity of the by-product hydrogen, the first production method in which the metal ion-substituted cation exchange substance 21 is applied to the sputtered layer 20 to form the first layer and the second layer is preferred.

[0131] [Electrolytic reduction device] Next, two kinds of electrolytic reduction devices will be described: one equipped with the cathode electrode of the present invention and used for the electrolytic reduction of carbon dioxide to carbon monoxide, olefin and / or alcohol; and the other equipped with the composite of the cathode electrode of the present invention and a substrate and used for the electrolytic reduction of carbon dioxide to carbon monoxide, olefin and / or alcohol. Figure 7 is an explanatory diagram showing an outline of an electrolytic reduction device equipped with the cathode electrode of the present invention. Figure 8 is an explanatory diagram showing an outline of another electrolytic reduction device equipped with the cathode electrode of the present invention.

[0132] As shown in Figure 7 , as the electrolytic reduction device 210, a 3-chamber type electrolytic reduction device, for example, can be cited. Specifically, the electrolytic reduction device 210 can cite, for example, an electrolytic cell 214 including a cathode gas chamber 211, a cathode liquid chamber 212 and an anode liquid chamber 213 which are distinguished from each other. The cathode gas chamber 211 and the cathode liquid chamber 212 are separated by a cathode 216 which is a gas diffusion electrode. The cathode liquid chamber 212 and the anode liquid chamber 213 are distinguished by a separator 217 having ion conductivity. An anode electrode 218 is disposed on the anode liquid chamber 213. Carbon dioxide gas is supplied to the cathode gas chamber 211. Cathode liquid is supplied to the cathode liquid chamber 212. Anode liquid is supplied to the anode liquid chamber 213. The anode electrode 218 and the cathode 216 are connected to a direct current power source 219.

[0133] The anolyte and the catholyte are aqueous solutions using an electrolyte dissolved in water. The electrolyte includes, for example, at least one of potassium, sodium, lithium, or these compounds. The electrolyte is selected from at least one compound of the group of, for example, LiOH, NaOH, KOH, Li2CO3, Na2CO3, K2CO3, LiHCO3, NaHCO3, and KHCO3.

[0134] The cathode 216 is a gas diffusion electrode having a gas diffusion layer 221 and a microporous layer 222. In the electrolytic reduction device 210, as the cathode 216, the cathode electrode of the present application having the first layer of the cation exchange material surface-modified by the metal ion of the composite of the first layer and the second layer is used, and the microporous layer 222 corresponds to the substrate of the composite. The gas diffusion layer 221 can inhibit the permeation of the aqueous solution containing the catholyte, although it can allow the gas containing carbon dioxide to pass through. The microporous layer 222 can allow the gas containing carbon dioxide and the aqueous solution containing the catholyte to pass through. The gas diffusion layer 221 and the microporous layer 222 are each formed in a planar shape. The gas diffusion layer 221 is provided on the cathode gas chamber 211 side, and the microporous layer 222 is provided on the catholyte chamber 212 side.

[0135] As the gas diffusion layer 221, for example, a material after a hydrophobic coating layer such as polytetrafluoroethylene on the surface of a porous conductive substrate such as carbon paper, carbon felt, carbon cloth, or the like can be listed. The conductive substrate is connected to the negative electrode of the direct current power source 219 and receives the supply of electrons. The microporous layer 222 is formed on the surface of the gas diffusion layer 221 using carbon, fluorine-containing resin, metal, or the like and is used to load a catalyst. In the electrolytic reduction device 210, as the catalyst loaded on the microporous layer 222, the cathode electrode of the present application including the first layer of the cation exchange material surface-modified by the metal ion of the first layer and the second layer is used. In addition, by using a renewable energy source as the direct current power source 219 of the electrolytic reduction device 210, while reducing the environmental load, it is also possible to generate olefins such as ethylene and alcohols such as ethanol through the reduction reaction of carbon dioxide. Furthermore, instead of using a gas diffusion electrode having a gas diffusion layer 221 and a microporous layer 222, a gas diffusion electrode in which a part of the microporous layer 222 functions as the gas diffusion layer 221 can be provided.

[0136] In addition, as Figure 8 indicated, as another electrolytic reduction device 210, for example, an electrolytic reduction device 210 of an MEA type electrolytic cell configuration can be listed. Furthermore, in the other electrolytic reduction device 210 as Figure 8 indicated, the same configuration as the electrolytic reduction device 210 as Figure 7 indicated, the same configuration as the electrolytic reduction device 210 as Figure 7The electrolytic reduction device 210 of the MEA type electrolytic cell configuration is the same as the electrolytic reduction device 210 shown in FIG. 1. The electrolytic reduction device 210 of the MEA type electrolytic cell configuration does not have the catholyte chamber 212 because the catholyte is not used. Therefore, the electrolytic reduction device 210 of the MEA type electrolytic cell configuration is the electrolytic reduction device 210 having the electrolytic cell 214 provided with the cathode gas chamber 211 and the anolyte chamber 213 which are separated from each other, instead of the electrolytic cell 214 provided with the cathode gas chamber 211, the catholyte chamber 212, and the anolyte chamber 213. The cathode gas chamber 211 and the anolyte chamber 213 are separated by the separator 217 which is sandwiched by the cathode electrode and the anode electrode 218. The anode electrode 218 is disposed in the anolyte chamber 213. The carbon dioxide gas is supplied to the cathode gas chamber 211. The anolyte is supplied to the anolyte chamber 213. The anode electrode 218 and the cathode electrode are connected to the direct current power source 219. In the electrolytic reduction device 210 of the MEA type electrolytic cell configuration, since the separator 217 itself is used as the electrolyte and the catholyte is not used, the electrolytic reduction device 210 of the MEA type electrolytic cell configuration is suitable for integration.

[0137] Even in the electrolytic reduction device 210 of the MEA type electrolytic cell configuration, the cathode electrode is the gas diffusion electrode having the gas diffusion layer 221 and the microporous layer 222. Also in the electrolytic reduction device 210 of the MEA type electrolytic cell configuration, the composite of the present application is used as the cathode electrode, the composite being the cathode electrode having the first layer and the second layer, the first layer being modified with the surface of the cation exchanger substituted with metal ions, and the substrate, and the microporous layer 222 corresponds to the substrate of the composite.

[0138] [EXAMPLE] Next, the examples of the present application will be described. It should be noted that the present application is not limited to the following examples.

[0139] [Example 1] Preparation of the Cathode Electrode Sputtering Layer Formation Step On the substrate (porous carbon of a composite of a carbon layer formed of carbon black and carbon fibers), a copper layer was formed by sputtering under conditions of DC 100 W, argon 6.0 seem, 5 minutes to form a first copper sputtered layer. Thereafter, on the formed first copper sputtered layer, an aluminum layer was formed by sputtering under conditions of DC 50 W, argon 6.0 seem, 30 seconds to form a first aluminum sputtered layer. Thereafter, on the formed first aluminum sputtered layer, a copper layer was formed by sputtering under conditions of DC 100 W, argon 6.0 seem, 5 minutes to form a second copper sputtered layer. Thereafter, on the formed second copper sputtered layer, an aluminum layer was formed by sputtering under conditions of DC 50 W, argon 6.0 seem, 30 seconds to form a second aluminum sputtered layer. Thereafter, on the formed second aluminum sputtered layer, a copper layer was formed by sputtering under conditions of DC 100 W, argon 6.0 seem, 5 minutes to form a third copper sputtered layer, thereby obtaining a sputtered layer as a laminate composed of 5 layers.

[0140] Copper oxidation treatment step The obtained sputtered layer of the laminate was immersed in an aqueous solution of copper sulfate and potassium sulfate (9.7 mM of copper ions, 0.5 M of sulfate ions) 100 mL, and chemical plating was performed at 20°C for 20 minutes, whereby a part of the 0-valent copper contained in the copper sputtered layer was oxidized to 1-valent copper and / or 2-valent copper.

[0141] Metal ion-substituted cation exchange substance application step An aqueous solution of a cation exchange resin (sulfonated tetrafluoroethylene-based polymer, "Nafion" (registered trademark), DuPont) (concentration 5 mass%) was mixed with an aqueous potassium hydroxide solution (concentration 8 M) to prepare an aqueous solution of a cation exchange resin substituted with potassium ions (aqueous solution of a cation exchange resin in which hydrogen ions of the cation exchange resin are substituted with potassium ions). The obtained aqueous solution of the cation exchange resin substituted with potassium ions was sprayed on the surface of the sputtered layer of the laminate composed of 5 layers on which the chemical plating copper oxidation treatment step was performed (coating amount of the aqueous solution of the cation exchange resin substituted with potassium ions 650 μL) and was heated and dried, and the cation exchange resin substituted with potassium ions was modified on the surface of the sputtered layer in such a manner that the amount of the cation exchange resin (Nafion) accumulated with respect to 100 g of copper elements becomes 125 g to 24333 g before and after coating. The surface of the sputtered layer was modified by the modification with the cation exchange resin substituted with potassium ions, thereby forming a first layer modified by the surface of a cation exchange substance substituted with metal ions, and a second layer as a mixed layer in which copper in the first layer is mixed with carbon and in which the copper in the first layer is facilitated to intrude into the carbon layer in the lower layer by the action of the metal ions.

[0142] As described above, the cathode electrode was prepared as a sputtering layer on the substrate, and a composite of the cathode electrode and the substrate was produced.

[0143] [Comparative Example 1] A composite of the cathode electrode and the substrate was produced in the same manner as in Example 1 except that the step of applying the cation exchange material substituted with metal ions was not performed. As described above, in Comparative Example 1, a composite of the cathode electrode and the substrate was prepared, which had not yet formed the second layer as a mixed layer in which copper and carbon were mixed.

[0144] Evaluation Items [Stability Test] The ethylene gas selectivity (E24, unit: %) after 24 hours from the start of the reduction reaction of carbon dioxide was measured. When E24 reached 50% or more, it was evaluated that the catalytic reaction of generating ethylene from the reduction reaction of carbon dioxide could be continued stably for a long period of time, and the stability of the catalytic reaction was excellent. The ethylene gas selectivity was evaluated as follows.

[0145] [Ethylene Gas Selectivity (%)] From the concentration of ethylene contained in the outlet gas of the electrolytic cell (electrolyte: 1M aqueous KHCO3 solution, electrolyte flow rate: 50 mL / min) and the gas flow rate, the number of moles of electrons passing through the electrolytic cell per unit time was calculated (carbon dioxide gas flow rate: 40 mL / min). On the other hand, from the set current value (-530 mA) of the potentiostat, the number of moles of electrons passing through the electrolytic cell per unit time was calculated. The ratio of the former to the latter was evaluated as the ethylene selectivity (%). The concentration of ethylene contained in the outlet gas was measured using a gas chromatograph (model: Agilent 990 Micro Gas Chromatograph). The gas flow rate was measured using a mass flow meter.

[0146] The measurement results of Examples and Comparative Examples are shown in Table 1 below.

[0147] [Table 1]

[0148] As shown in Table 1 above, in Example 1 in which the first layer was modified by the surface of the cation exchange material substituted with potassium ions and the second layer was formed by mixing copper and carbon, the ethylene gas selectivity (E24) after 24 hours from the start of the reduction reaction of carbon dioxide was 50% or more, even if the catalytic layer was immersed in the electrolyte, the increase in the selectivity of hydrogen could be prevented, and the catalytic reaction of generating ethylene from the reduction reaction of carbon dioxide could be continued stably for a long period of time, and the stability of the catalytic reaction was excellent.

[0149] On the other hand, in Comparative Example 1 in which the second layer as a mixed layer in which copper and carbon are mixed was not formed, the ethylene gas selectivity (E24) after 24 hours from the start of the carbon dioxide reduction reaction was 45%, and even if the catalytic layer was immersed in the electrolyte, it was not possible to evaluate that the catalytic reaction of generating ethylene and the like by the reduction reaction of carbon dioxide could be continued stably for a long period of time.

[0150]

Industrial applicability

[0151]

Explanation of symbols

Claims

1. A cathode electrode which electro-reduces carbon dioxide, the cathode electrode having a first layer having a first thickness at a surface layer of the cathode electrode, and a second layer having a second thickness which is contiguous to the first layer in a thickness direction of the first layer, the first layer containing copper, and the first layer being surface-modified by a metal ion-substituted cation exchange material, and the second layer being a mixed layer of copper and carbon.

2. The cathode electrode according to claim 1, a ratio of the second thickness of the second layer to the first thickness of the first layer being greater than 0 and less than or equal to 100.

3. The cathode electrode according to claim 1 or 2, the second layer having a first region on the first layer side and a second region contiguous to the first region, with a central portion in a thickness direction of the second layer as a boundary, a content of the copper (vol%) of the first region being higher than a content of the copper (vol%) of the second region.

4. The cathode electrode according to claim 1 or 2, the copper of the first layer including divalent copper, and zero-valent copper and / or monovalent copper, and the copper of the second layer including divalent copper, and zero-valent copper and / or monovalent copper.

5. The cathode electrode according to claim 1 or 2, the copper of the first layer including reduced 1-valent copper and / or reduced 2-valent copper which is reduced to zero-valent copper by a reduction treatment, and 1-valent copper and / or 2-valent copper which is not reduced to zero-valent copper, and the copper of the second layer including reduced 1-valent copper and / or reduced 2-valent copper which is reduced to zero-valent copper by a reduction treatment, and 1-valent copper and / or 2-valent copper which is not reduced to zero-valent copper.

6. The cathode electrode according to claim 1 or 2, the first layer further containing at least one additive element selected from the group consisting of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon, and the second layer further containing at least one additive element selected from the group consisting of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon.

7. The cathode electrode according to claim 6, a content of the additive element of the first layer being 0.10 atom% or more and 1.0 atom% or less with respect to 100 atom% of the copper contained in the first layer, and a content of the additive element of the second layer being 0.10 atom% or more and 1.0 atom% or less with respect to 100 atom% of the copper contained in the second layer.

8. The cathode electrode according to claim 1 or 2, the cation exchange material including a sulfonated tetrafluoroethylene-based polymer.

9. The cathode electrode according to claim 1 or 2, the metal ion including an alkali metal ion and / or an alkaline earth metal ion.

10. The cathode electrode according to claim 1 or 2, the metal ion-substituted cation exchange material being formed as a layer on a surface of the first layer.

11. The cathode electrode according to claim 1 or 2, the metal ion-substituted cation exchange material being mixed with the copper of the first layer.

12. The cathode electrode according to claim 1 or 2, having a porous structure.

13. A composite which is a composite of the cathode electrode according to claim 1 or 2 and a substrate, having the substrate, and the cathode electrode according to claim 1 or 2 disposed on the substrate.

14. An electrolytic reduction device which electroreduces carbon dioxide to carbon monoxide, olefin and / or alcohol, and which is provided with the cathode electrode according to claim 1 or 2.

15. An electrolytic reduction device which electroreduces carbon dioxide to carbon monoxide, olefin and / or alcohol, and which is provided with the composite according to claim 13.

16. A method of manufacturing a composite which is a composite of a cathode electrode for electroreducing carbon dioxide and a substrate, the method of manufacturing comprising: a step of preparing a substrate having a porous structure; on the substrate, a second layer is formed by applying a second suspension to form a second layer, wherein the second suspension is a mixture of copper and carbon, and the second layer is a mixed layer of copper and carbon; a first layer forming step of applying a first suspension containing copper on the second layer to form a first layer containing copper; a metal ion-substituted cation exchanger application step of applying a metal ion-substituted cation exchanger to the first layer to perform surface modification of the first layer.

17. The method of manufacturing a composite according to claim 16, wherein the copper of the first layer comprises divalent copper, and zero-valent copper and / or monovalent copper, and the copper of the second layer comprises divalent copper, and zero-valent copper and / or monovalent copper.

18. The method of manufacturing a composite according to claim 16, wherein the copper of the first layer comprises reduced monovalent copper and / or reduced divalent copper which is reduced to zero-valent copper by reduction treatment, and monovalent copper and / or divalent copper which is not reduced to zero-valent copper, and the copper of the second layer comprises reduced monovalent copper and / or reduced divalent copper which is reduced to zero-valent copper by reduction treatment, and monovalent copper and / or divalent copper which is not reduced to zero-valent copper.

19. The method of manufacturing a composite according to any one of claims 16 to 18, wherein the first suspension further contains at least one additive element selected from the group consisting of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium and silicon, and the second suspension further contains at least one additive element selected from the group consisting of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium and silicon.

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