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

The present invention provides a cathode electrode which can reduce hydrogen selectivity and can stably and efficiently continue for a long period of time in a catalytic reaction for generating an olefin such as ethylene and an alcohol such as ethanol through a reduction reaction of carbon dioxide. The invention provides a cathode electrode for electroreduction of carbon dioxide. The cathode electrode contains copper, and the copper is subjected to surface modification by cation exchange materials substituted by metal ions.

Description

Technical Field

[0001] The present invention relates to a cathode electrode for electrolytically reducing carbon dioxide to convert carbon monoxide, olefins such as ethylene, and / or alcohols, a composite of the cathode electrode and a substrate, an electrolytic reduction device having the cathode electrode, and a method for manufacturing the composite of the cathode electrode and the substrate. Background Art

[0002] In recent years, the negative impacts of global warming have been causing changes in the global environment and generating numerous problematic phenomena. It is widely believed that one of the causes of these changes is the increase in atmospheric concentrations of greenhouse gases, particularly carbon dioxide, which accounts for the majority of these gases. To reduce atmospheric carbon dioxide concentrations, research is underway to absorb and recover atmospheric carbon dioxide, in addition to increasing photosynthesis through new terrestrial forestation and marine algae. Furthermore, research is underway to utilize carbon derived from carbon dioxide as a raw material for organic compounds.

[0003] Specifically, research is underway to reduce carbon dioxide to convert it into C2 compounds such as ethylene and ethanol, and C1 compounds such as carbon monoxide, methane, ethanol, and formic acid, and to use these compounds in the synthesis of organic compounds. Among these compounds, ethylene and ethanol are particularly important, being highly useful as derivatives in the synthesis of various organic compounds. They possess greater utility than C1 compounds such as carbon monoxide and methane.

[0004] In recent years, in the reduction reaction of carbon dioxide as described above, the catalysts such as photocatalyst and electrode catalyst have been widely used, and the industry also seeks to develop a more excellent catalyst for performance simultaneously. The catalyst for the reduction reaction of carbon dioxide not only requires it to have high reaction efficiency, but also requires to have selectivity to specific reflection, and from such a viewpoint, the selection of catalytic material is most important (non-patent literature 1). For example, in efficiently reducing and generating carbon monoxide, improving the carbon monoxide ratio in the reducing material, gold, silver and zinc are used as catalytic materials. In addition, in efficiently reducing and generating hydrocarbons such as methane, ethane and ethylene, copper is used as catalytic material. Especially, because copper can generate C2 compounds such as ethylene, it has attracted much attention as the cathode reduction electrode catalyst of carbon dioxide.

[0005] As a copper-based cathode for reducing carbon dioxide, Patent Document 1, for example, proposes a cathode structure comprising a copper-containing cathode material coated with a coating comprising one or more of the group consisting of alkali metals, alkaline earth metals, lanthanides, actinides, transition metals, post-transition metals, non-metallic oxides and / or alloys thereof, mixed metal oxides, and ion-conductive polymers. However, Patent Document 1 only discloses the reduction of carbon dioxide and its conversion to organic compounds such as formic acid, followed by extraction. It does not verify whether the catalytic reaction for synthesizing organic compounds such as ethylene can maintain a high and stable selectivity for ethylene and other compounds over a long period of time.

[0006] In order to industrially realize the production of organic compounds such as ethylene through the reduction reaction of carbon dioxide, the catalytic reaction for producing organic compounds such as ethylene must be able to stably maintain a high selectivity for ethylene and other organic compounds for hundreds of hours. The cathode structure disclosed in Patent Document 1 leaves room for improvement in terms of maintaining a high efficiency and long-term stability in the catalytic reaction for producing organic compounds such as ethylene.

[0007] In addition, for carbon dioxide reduction cathode electrode, in order to obtain the excellent synthesis efficiency of organic compounds such as ethylene, when carrying out carbon dioxide reduction, it is necessary to make the carbon dioxide reduction reaction prevail relative to the reaction of the hydrogen produced by the side reaction (decomposition reaction of water), thereby reducing the selectivity of hydrogen, and improving the selectivity of carbon dioxide reduction product. However, in patent documentation 1, it is not verified that when carbon dioxide reduction is carried out, whether the selectivity of hydrogen is reduced, and whether the selectivity of carbon dioxide reduction product is improved. Therefore, the structure of the cathode of patent documentation 1, in reducing the selectivity of hydrogen, improving this aspect of the selectivity of carbon dioxide reduction product, also has room for improvement.

[0008]

Prior art literature

Non-patent literature

[0009] [Problems to be solved by the invention] In view of the above situation, the object of the present invention is to provide a cathode electrode, a composite of a cathode electrode and a substrate, an electrolytic reduction device of a cathode electrode, and a method for manufacturing the composite of a cathode electrode and a substrate, which can reduce the selectivity of hydrogen and can stably and continuously produce olefins such as ethylene and alcohols such as ethanol through the reduction reaction of carbon dioxide at high efficiency for a long time.

[0010] [Technical solutions to solve problems] The structural outline of the present invention is as follows.

[0011] [1] A cathode electrode that electrically reduces carbon dioxide, The cathode electrode comprises copper surface-modified with a cation exchange material substituted with metal ions.

[0012] [2] The cathode electrode as described in [1], wherein the copper contains divalent copper, and zero-valent copper and / or monovalent copper.

[0013] [3] The cathode electrode according to [1], wherein the copper includes monovalent copper for reduction and / or divalent copper for reduction that is reduced to zero-valent copper by reduction treatment, and monovalent copper and / or divalent copper that is not reduced to zero-valent copper.

[0014] [4] The cathode electrode according to any one of [1] to [3], further comprising at least one additional element selected from the group consisting of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon.

[0015] [5] The cathode electrode as described in [4], wherein the content of the additional element is not less than 0.10 atomic % and not more than 1.0 atomic % relative to 100 atomic % of the copper.

[0016] [6] The cathode electrode as described in [4], wherein the content of the additional element is not less than 0.25 atomic % and not more than 0.70 atomic % relative to 100 atomic % of the copper.

[0017] [7] The cathode electrode as described in [4], wherein the additional element includes the aluminum described in [4].

[0018] [8] The cathode electrode according to any one of [1] to [3], wherein the cation exchange material comprises a sulfonated tetrafluoroethylene polymer.

[0019] [9] The cathode electrode according to any one of [1] to [3], wherein the metal ions include alkali metal ions and / or alkaline earth metal ions.

[0020]

[10] The cathode electrode according to any one of [1] to [3], wherein the cation exchange material substituted with the metal ions is formed in a layer on the copper.

[0021]

[11] The cathode electrode according to any one of [1] to [3], wherein the cation exchange material substituted with the metal ions is mixed with the copper.

[0022]

[12] The cathode electrode according to any one of [1] to [3], which has a porous structure.

[0023]

[13] A composite of a cathode electrode and a substrate, comprising a substrate and the cathode electrode according to any one of [1] to [3] disposed on the substrate.

[0024]

[14] The composite body described in

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

[0025]

[15] The composite body described in

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

[0026]

[16] The composite body as described in

[14] , wherein the material of the substrate having a porous structure is metal, and the metal is the copper described in

[14] .

[0027]

[17] The composite body described in

[14] , wherein the material of the substrate having a porous structure is metal, and the metal is a sintered body of copper particles.

[0028]

[18] An electrolytic reduction device comprising the cathode electrode described in any one of [1] to [3], wherein the electrolytic reduction device is an electrolytic reduction device for electrolyzing carbon dioxide into carbon monoxide, olefins and / or alcohols.

[0029]

[19] An electrolytic reduction device comprising the composite body described in

[13] , wherein the electrolytic reduction device is an electrolytic reduction device for electrolyzing carbon dioxide into carbon monoxide, olefins and / or alcohols.

[0030]

[20] A method for manufacturing a composite of a cathode electrode for electroreduction of carbon dioxide and a substrate, The manufacturing method comprises: A step of preparing a substrate having a porous structure; a sputtering layer forming step of forming a sputtering layer having copper on the substrate by sputtering; and A metal ion-substituted cation exchange material application step is performed by applying a metal ion-substituted cation exchange material to the sputtered layer to modify the copper surface.

[0031]

[21] The method for producing a composite as described in

[20] , wherein the copper contains divalent copper, and zero-valent copper and / or monovalent copper.

[0032]

[22] The method for producing a composite as described in

[20] , wherein the copper includes monovalent copper for reduction and / or divalent copper for reduction that is reduced to zero-valent copper by reduction treatment, and monovalent copper and / or divalent copper that is not reduced to zero-valent copper.

[0033]

[23] The method for manufacturing a composite body as described in any one of

[20] to

[22] , wherein the sputtered layer further contains at least one additional element selected from silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium and silicon.

[0034]

[24] The method for manufacturing a composite as described in

[21] or

[22] comprises a copper oxidation treatment step after the sputtering layer forming step and before the cation exchange material applying step substituted by the metal ions, wherein the copper oxidation treatment step oxidizes at least a portion of the copper in the sputtering layer to form the monovalent copper and / or the divalent copper.

[0035]

[25] The method for producing a complex as described in

[24] further comprises a partial reduction step, wherein the partial reduction step is performed before the step of applying the cation exchange material substituted by the metal ions, and the monovalent copper and / or the divalent copper formed by oxidation in the copper oxidation treatment step are partially reduced to zero-valent copper and / or monovalent copper.

[0036]

[26] The method for manufacturing a composite body as described in

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

[0037]

[27] In the method for manufacturing a composite body as described in

[23] , the sputtering layer forming step comprises: a copper sputtering layer forming step of forming a copper sputtering layer as a sputtering layer containing the copper by sputtering; and an additive element sputtering layer forming step of forming an additive element sputtering layer as a sputtering layer containing the additive element on the copper sputtering layer by sputtering.

[0038]

[28] A method for manufacturing a composite body as described in

[27] , wherein the sputtering layer forming step includes a copper sputtering layer forming step of further forming a copper sputtering layer as a sputtering layer having copper on the additive element sputtering layer by sputtering. Effects of the Invention

[0039] According to one embodiment of the cathode electrode of the present invention, the cathode electrode contains copper, and the copper is surface-modified with a cation exchange material substituted with metal ions. The cation exchange material substituted with metal ions controls the amount of water molecules (H2O) supplied to the copper constituting the cathode electrode, thereby reducing the selectivity of the side reaction product hydrogen, thereby enabling the catalytic reaction of carbon dioxide reduction reaction to produce olefins such as ethylene and alcohols such as ethanol to maintain high efficiency stably for a long time. The cation exchange material substituted with metal ions is the hydrogen ion (H + ) is replaced by metal ions, so the hydrogen ions (H + ) content was reduced.

[0040] In the carbon dioxide reduction reaction occurring on the cathode electrode using copper as the catalytic material, it is believed that the interface of copper of different valence states (e.g., the interface of zero-valent copper and monovalent copper) present on the cathode electrode mainly functions as a site for forming a C-C bond with carbon derived from carbon dioxide and stabilizing the C-C bond. In other words, it is believed that the interface of copper of different valence states (e.g., the interface of zero-valent copper and monovalent copper) is the main active site of the carbon dioxide reduction reaction. As described above, according to one embodiment of the cathode electrode of the present invention, the copper includes divalent copper, zero-valent copper and / or monovalent copper, or the copper is reduced to zero-valent copper by reduction treatment, monovalent copper and / or divalent copper for reduction, which is not reduced to zero-valent copper, thereby further ensuring 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 and continuously high-efficiency for a long time.

[0041] In the cathode electrode using copper as a catalytic material, when the carbon dioxide reduction reaction is carried out, monovalent copper is reduced to zero-valent copper, and divalent copper is reduced to zero-valent copper or monovalent copper. It is believed that after the carbon dioxide reduction reaction is continued for a long time, as divalent copper is reduced to zero-valent copper or monovalent copper, monovalent copper is reduced to zero-valent copper, and the interface of copper of different valence states (for example, the interface of zero-valent copper and monovalent copper) has a decreasing trend. As described above, according to one embodiment of the cathode electrode of the present invention, by also including at least one added element selected from the group of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium and silicon in addition to copper, it is possible to have the function of keeping oxygen in the cathode electrode, thereby being able to appropriately suppress being reduced to zero-valent copper from monovalent copper. From the above, it can be known that even if the carbon dioxide reduction reaction is continued for a long time, as long as the presence ratio of zero-valent copper and monovalent copper is effectively optimized, the generation and stability of the C-C bond can be maintained, thereby being able to further ensure that the catalytic reaction of the reduction reaction of carbon dioxide to generate olefins such as ethylene and alcohols such as ethanol is continued stably for a long time.

[0042] Furthermore, ethylene and ethanol are both C2 compounds, and the formation of C-C bonds on the catalytic material is an intermediate step in their reaction pathways. Therefore, since the active sites for ethylene and ethanol production are the same or very close, the stability of ethylene and ethanol production shows similar trends, indicating that the carbon dioxide reduction reaction proceeds in the same manner regardless of whether ethylene or ethanol is produced.

[0043] According to one embodiment of the cathode electrode of the present invention, by containing the additional element in an amount of not less than 0.10 atomic % and not more than 1.0 atomic % relative to 100 atomic % of the copper, the existence ratio of zero-valent copper to monovalent copper can be effectively optimized even if the reduction reaction of carbon dioxide is continued for a long time, thereby enabling the catalytic reaction of the carbon dioxide reduction reaction to produce olefins such as ethylene and alcohols such as ethanol to be continued for a long time and more stably.

[0044] According to one embodiment of the cathode electrode of the present invention, by containing the additional element in an amount of not less than 0.25 atomic % and not more than 0.70 atomic % relative to 100 atomic % of the copper, even if the reduction reaction of carbon dioxide is continued for a long time, the existence ratio of zero-valent copper to monovalent copper can be maintained within a more suitable range, thereby enabling the catalytic reaction of the carbon dioxide reduction reaction to produce olefins such as ethylene and alcohols such as ethanol to be continued for a longer period of time and in a more stable manner.

[0045] According to one embodiment of the cathode electrode of the present invention, by making the added element contain aluminum, the function of appropriately retaining oxygen in the cathode electrode can be reliably obtained. Even if the reduction reaction of carbon dioxide is continued for a long time, the existence ratio of zero-valent copper and monovalent copper can be optimized, thereby enabling the catalytic reaction of carbon dioxide reduction reaction to produce olefins such as ethylene and alcohols such as ethanol to continue more stably for a long time.

[0046] According to one embodiment of the cathode electrode of the present invention, when the cation exchange material contains a polymer of sulfonated tetrafluoroethylene and the metal ions contain alkali metal ions and / or alkaline earth metal ions, the amount of water molecules (H2O) supplied to the copper constituting the cathode electrode can be reliably controlled, thereby more reliably reducing the selectivity of the side reaction product hydrogen, thereby more reliably enabling the catalytic reaction of carbon dioxide reduction to produce olefins such as ethylene and alcohols such as ethanol to be sustained at high efficiency for a long time.

[0047] According to one embodiment of the cathode electrode of the present invention, when the cation exchange material substituted with metal ions is formed in a layer on the copper, or when the cation exchange material substituted with metal ions is mixed with the copper, the amount of water molecules (H2O) supplied to the copper can be more appropriately controlled by the presence of the cation exchange material substituted with metal ions.

[0048] According to one embodiment of the cathode electrode of the present invention, since the cathode electrode has a porous structure, when the carbon dioxide at the cathode electrode undergoes a reduction reaction, the contact between water and carbon dioxide becomes smoother, thereby enabling the catalytic reaction of producing olefins such as ethylene and alcohols such as ethanol to continue more stably for a long time.

[0049] According to one embodiment of the composite of a cathode electrode and a substrate of the present invention, a composite of a cathode electrode and a substrate can be obtained, which comprises a substrate and the cathode electrode of the present invention, and can reduce the selectivity of the side reaction product hydrogen, thereby enabling the catalytic reaction of carbon dioxide reduction reaction to produce olefins such as ethylene and alcohols such as ethanol to be able to maintain high efficiency stably for a long time.

[0050] According to one embodiment of the composite of the cathode electrode and the substrate of the present invention, since the substrate has a porous structure and since the gaseous carbon dioxide can smoothly contact the cathode electrode, the catalytic reaction of producing olefins such as ethylene and alcohols such as ethanol can continue for a long time and more stably even if it is gaseous carbon dioxide.

[0051] According to the method for manufacturing a composite of a cathode electrode and a substrate of the present invention, a composite can be manufactured, which comprises a sputtering layer forming step of forming a sputtering layer having copper on a substrate by sputtering, and a cation exchange material applying step of applying a metal ion-substituted cation exchange material on the sputtering layer to modify the surface of the copper, thereby reducing the selectivity of hydrogen as a side reaction product, thereby enabling the catalytic reaction of the reduction reaction of carbon dioxide to produce olefins such as ethylene and alcohols such as ethanol to be stable and continuous with high efficiency for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a schematic explanatory diagram showing a cross section of a composite body of a cathode electrode and a substrate according to the present invention.

[0053] Figure 2 This is an explanatory diagram for explaining the electrolytic polishing process in the method for producing a composite of a cathode electrode and a substrate.

[0054] Figure 3 These are explanatory diagrams for explaining the sputtering layer forming step and the copper oxidation treatment step in the method for producing a composite of a cathode electrode and a substrate.

[0055] Figure 4 This is an explanatory diagram for explaining the partial reduction step in the method for producing a composite of a cathode electrode and a substrate.

[0056] Figure 5 This is an explanatory diagram showing the structure of the composite body of the cathode electrode and the substrate of the present invention.

[0057] Figure 6 This is a schematic explanatory diagram showing an electrolytic reduction device including the cathode electrode of the present invention.

[0058] Figure 7 A schematic explanatory diagram of another electrolytic reduction device including the cathode electrode of the present invention is shown. DETAILED DESCRIPTION

[0059] [Cathode electrode] The cathode electrode of the present invention is described below. The cathode electrode of the present invention is a cathode electrode for electrochemical reduction of carbon dioxide, which contains copper (Cu), wherein the copper (Cu) is surface-modified with a cation exchange material substituted with a metal ion. The cathode electrode of the present invention contains copper as an essential component of a catalytic material and a cation exchange material substituted with a metal ion that modifies the surface of the copper. The cation exchange material substituted with a metal ion is a hydrogen ion (H + ) is replaced by a metal ion, which is a hydrogen ion (H + ) content is reduced.

[0060] On the surface of copper, which is the catalyst material constituting the cathode electrode, there is a cation exchange material (the hydrogen ions (H + ) metal ion substituted cation exchange material), so the amount of water molecules (H2O) supplied to copper, that is, hydrogen ions (H + ) supply can be controlled. In addition, the metal ions of the cation exchange material are replaced by hydrogen ions (H + ) content is reduced, thus preventing the hydrogen ion (H + ) from the cation exchange material to the copper. Therefore, the cathode electrode of the present invention can be a device capable of preventing hydrogen ions (H + ) is excessively supplied to the copper serving as the catalyst. Furthermore, since the state in which the hydrogen ions of the cation exchange material are replaced by metal ions is more stable than the state in which the hydrogen ions are not replaced by metal ions, the state in which the cation exchange material replaces the metal ions can also be maintained in the cathode electrode.

[0061] As can be seen from the above, since the selectivity of hydrogen, a by-product of the carbon dioxide reduction reaction, is reduced, the catalytic reaction of producing olefins such as ethylene and alcohols such as ethanol through the carbon dioxide reduction reaction can be maintained at a high efficiency for a long time.

[0062] The cation exchange material constituting the metal ion-substituted cation exchange material, that is, the cation exchange material before metal ion substitution, includes, for example, cation exchange resins. Examples of the cation exchange resins include sulfonated tetrafluoroethylene-based polymers (trade name: ), perfluoroalkyl and polyfluoroalkyl compounds (PFAS)-based polymers, polyethylenedioxythiophene (PEDOT)-based polymers, etc. Among them, sulfonated tetrafluoroethylene-based polymers are preferred from the perspective of ease of copper surface modification.

[0063] As long as the hydrogen ions of the cation exchange material can be replaced by metal ions, there is no particular limitation on the metal ions that constitute the metal ion-substituted cation exchange material. However, from the perspective of being able to reliably control the amount of water molecules (H2O) supplied to the copper constituting the cathode electrode, and more reliably reducing the selectivity of the side reaction product hydrogen, thereby being able to more reliably and stably continue the catalytic reaction of producing olefins such as ethylene and alcohols such as ethanol through the carbon dioxide reduction reaction with high efficiency for a long time, alkali metal ions and alkaline earth metal ions are preferred. Examples of alkali metals include lithium ions (Li + ), sodium ion (Na + ), potassium ion (K + ), rubidium ions (Rb + ), cesium ions (Cs + ), and francium ions (Fr + Examples of alkaline earth metal ions include 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+ These metal ions may be used alone or in combination of two or more.

[0064] Among these metal ions, alkali metal ions are more preferred, and lithium ions (Li ions) are further preferred from the viewpoint of more reliably controlling the amount of water molecules (H 2 O) supplied to copper constituting the cathode electrode and more reliably reducing the selectivity of hydrogen produced as a side reaction. + ), sodium ion (Na + ), potassium ion (K + ), rubidium ions (Rb + ), from the viewpoint that the amount of water molecules (H2O) supplied to copper can be further controlled, thereby further reducing the selectivity of the side reaction product hydrogen, potassium ions (K + ).

[0065] There are no particular limitations on the method for surface modification of copper using a metal ion-substituted cation exchange material. However, from the perspective of being able to more appropriately control the amount of water molecules supplied to copper due to the presence of the metal ion-substituted cation exchange material, a method in which the metal ion-substituted cation exchange material forms a layer on the copper, and a method in which the metal ion-substituted cation exchange material is mixed with copper are preferred. Among these, a method in which the metal ion-substituted cation exchange material forms a layer on the copper is particularly preferred.

[0066] The content of the metal ion-substituted cation exchange material is not particularly limited, but its lower limit is such that the amount of water molecules supplied to copper can be reliably controlled to prevent excessive supply of hydrogen ions (H2O) to copper. + ) in excess, the accumulated amount of the cation exchange material relative to 100 g of the copper element is preferably 125 g or more and 24333 g or less.

[0067] As a method for preparing a metal ion-substituted cation exchange material, for example, a solution of the cation exchange material (e.g., an aqueous solution) and a solution containing metal ions (e.g., an aqueous solution) can be prepared, and then the solution of the cation exchange material and the solution containing metal ions can be mixed to replace the hydrogen ions of the cation exchange material with the metal ions, thereby obtaining a metal ion-substituted cation exchange material.

[0068] In the cathode electrode of the present invention, as one embodiment of the first cathode electrode, the copper used as the catalytic material includes divalent copper, zero-valent copper, and / or monovalent copper. In one embodiment of the first cathode electrode, divalent copper and zero-valent copper and / or monovalent copper are essential components. Examples of monovalent copper include cuprous oxide (Cu2O), and examples of divalent copper include copper oxide (CuO). In addition, examples of zero-valent copper include copper (Cu) alone.

[0069] In the carbon dioxide reduction reaction at a cathode electrode using copper as a catalytic material, the interface between copper of different valence states (e.g., the interface between zero-valent copper and monovalent copper) primarily serves as a site where carbon derived from carbon dioxide forms and stabilizes C-C bonds. In other words, the interface between copper of different valence states (e.g., the interface between zero-valent copper and monovalent copper) can be considered the primary active site for the carbon dioxide reduction reaction. As can be seen from the above, by including divalent copper, zero-valent copper, and / or monovalent copper as the catalytic material, the catalytic reaction to produce olefins such as ethylene and alcohols such as ethanol through the carbon dioxide reduction reaction can be further ensured to be stable and highly efficient over a long period of time.

[0070] In the cathode electrode of the present invention, as one embodiment of the second cathode electrode, it contains monovalent copper for reduction and / or divalent copper for reduction, which are copper reduced to zero-valent copper by reduction treatment, and monovalent copper and / or divalent copper that are not reduced to zero-valent copper. In one embodiment of the second cathode electrode, a portion of the monovalent copper and / or divalent copper is reduced to zero-valent copper. As can be seen from the above, in one embodiment of the second cathode electrode, as copper (Cu), there are monovalent copper for reduction and / or divalent copper for reduction, and monovalent copper and / or divalent copper that are not reduced to zero-valent copper. In one embodiment of the second cathode electrode, monovalent copper and / or divalent copper are essential components. In one embodiment of the second cathode electrode, the divalent copper for reduction is reduced to zero-valent copper or monovalent copper, and the monovalent copper for reduction is reduced to zero-valent copper. Therefore, in one embodiment of the second cathode electrode, after the reduction treatment, it becomes a cathode electrode containing zero-valent copper and monovalent copper and / or divalent copper.

[0071] Examples of monovalent copper include cuprous oxide (Cu2O), and examples of divalent copper include copper oxide (CuO). In addition, examples of zero-valent copper include copper (Cu) alone.

[0072] Since the copper used as the catalytic material includes reducing monovalent copper and / or reducing divalent copper that is reduced to zero-valent copper by the reduction treatment, and monovalent copper and / or divalent copper that is not reduced to zero-valent copper, it is possible to further ensure that the catalytic reaction of producing olefins such as ethylene and alcohols such as ethanol through the reduction reaction of carbon dioxide can be maintained at high efficiency stably for a long period of time.

[0073] In the cathode electrode of the present invention (including the form of the first cathode electrode and the form of the second cathode electrode), in addition to copper (Cu) added as a catalytic material, it can also contain at least one additional 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) as an arbitrary component.

[0074] In the cathode electrode of the present invention, copper as a catalytic material is used. During the reduction reaction of carbon dioxide, monovalent copper is reduced to zero-valent copper, and divalent copper is reduced to zero-valent copper or monovalent copper. Therefore, if the reduction reaction of carbon dioxide is continued for a long time, divalent copper is reduced to zero-valent copper or monovalent copper, and monovalent copper is reduced to zero-valent copper, the copper interface of different valence states (for example, the interface between zero-valent copper and monovalent copper) tends to decrease. Here, by adding copper, further comprising at least one additional element (M) selected from the group of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium and silicon, because the additional element (M) has the function of keeping oxygen in the electrode, the reduction of monovalent copper to zero-valent copper can be appropriately suppressed. As shown above, even if the reduction reaction of carbon dioxide is continued for a long time, by effectively optimizing the presence ratio of zero-valent copper and monovalent copper, the generation and stability of C-C bonds can be maintained, thereby further ensuring 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 for a long time.

[0075] The form of at least one additional element (M) selected from the group consisting of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon is not particularly limited, and examples thereof include the form of the additional element (M) itself (the additional element (M) monomer). In addition, in addition to the form of the additional element (M) itself, the form of a hydroxide and the form of an oxide can be listed. In addition, the additional element (M) can also be present in a mixed form with the form of the additional element (M) itself, the form of a hydroxide, and the form of an oxide. These additional elements (M) can be used alone or in combination of two or more.

[0076] The content of the additional element (M) is not particularly limited, but its lower limit is preferably 0.10 atomic % relative to 100 atomic % of the copper element, including all copper elements, such as zero-valent copper, monovalent copper, and divalent copper. From the viewpoint of reliably optimizing the abundance ratio of zero-valent copper to monovalent copper even when the reduction reaction of carbon dioxide is continued for a long period of time, and enabling the catalytic reaction of producing olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide to continue more stably for a long period of time, and more preferably 0.20 atomic %. Even from the viewpoint of maintaining the abundance ratio of zero-valent copper to monovalent copper within a more suitable range even when the reduction reaction of carbon dioxide is continued for a long period of time, and enabling the catalytic reaction of producing olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide to continue more stably for a relatively long period of time, the lower limit is 0.25 atomic % particularly preferably. On the other hand, the upper limit of the content of the additional element (M) is preferably 1.0 atomic % relative to 100 atomic % of copper elements (including all copper such as zero-valent copper, monovalent copper, and divalent copper), from the viewpoint of reliably optimizing the abundance ratio of zero-valent copper to monovalent copper even when the reduction reaction of carbon dioxide is continued for a long period of time, and enabling the catalytic reaction of producing olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide to continue more stably for a long period of time. The upper limit of the content of the additional element (M) is preferably 0.85 atomic %, and more preferably 0.70 atomic % from the viewpoint of maintaining the abundance ratio of zero-valent copper to monovalent copper within a more suitable range even when the reduction reaction of carbon dioxide is continued for a long period of time, and enabling the catalytic reaction of producing olefins such as ethylene and alcohols such as ethanol by the reduction reaction of carbon dioxide to continue more stably for a long period of time.

[0077] As the additive element (M), any of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon can be used as long as they are more easily oxidized than copper and tend to have a higher affinity for oxygen than copper. Among these additive elements (M), aluminum is preferred because it can reliably achieve the function of retaining oxygen in the cathode electrode at a humidified state, and even if the carbon dioxide reduction reaction continues for a long time, it can reliably optimize the abundance ratio of zero-valent copper to monovalent copper, and the catalytic reaction of producing olefins such as ethylene and alcohols such as ethanol from the carbon dioxide reduction reaction can be continued more stably over a long period of time.

[0078] The structure of cathode electrode, though there is no particular restriction, can be solid or porous, in the reduction reaction of carbon dioxide at cathode electrode, from the contact of water and carbon dioxide can be smoother, so that from the viewpoint that the catalytic reaction of the alcohols such as olefins such as ethylene and ethanol can be more stably continued for a long time, preferably porous structure.Porous structure has pore ratio (porosity), though there is no particular restriction, with regard to its lower limit, from promoting carbon dioxide to penetrate smoothly to cathode electrode, and then can further improve the viewpoint of the generation efficiency of the alcohols such as olefins such as ethylene, ethanol, etc., preferably 1 volume %, particularly preferably 10 volume %.On the other hand, with regard to the upper limit of the porosity of porous structure, from the surface area by maintaining the catalytic reaction of cathode electrode, can further improve the viewpoint of the generation efficiency of the alcohols such as olefins such as ethylene, ethanol, etc., preferably 99 volume %, particularly preferably 90% volume.

[0079] The cathode electrode of the present invention, for example, supplies gaseous (gas phase) carbon dioxide from one side of the cathode electrode and liquid water from the other side of the cathode electrode. Under the catalytic action of the cathode electrode, the gaseous (gas phase) carbon dioxide and water can react and the carbon dioxide can be electro-reduced to produce olefins such as ethylene and alcohols such as ethanol.

[0080] [Complex of cathode electrode and substrate] The cathode electrode of the present invention can be used in the state of a cathode electrode alone, and as will be described below, can also be used in the state of forming a substrate and a composite. Figure 1 This is a schematic explanatory diagram showing a cross section of a composite body of a cathode electrode and a substrate according to the present invention.

[0081] like Figure 1 As shown, the composite 120 of the cathode electrode 100 and the substrate 1 includes a substrate 1 and the cathode electrode 100 of the present invention disposed on the substrate 1. The cathode electrode 100 includes a first portion 101 and a second portion 102 opposite the first portion 101. The substrate 1 is disposed on the first portion 101 side of the cathode electrode 100. That is, the first portion 101 side of the cathode electrode 100 is disposed on the substrate 1. No substrate is disposed on the second portion 102 side of the cathode electrode 100, and the second portion 102 is exposed to the external environment of the cathode electrode 100 and the composite 120. The cathode electrode 100 is a coating covering the surface of the substrate 1. In the composite 120 of the cathode electrode 100 and the substrate 1, the cathode electrode 100, which has been surface-modified with copper having a metal ion-substituted cation exchange material according to the present invention, can reduce the selectivity of hydrogen, a side reaction product, and can stably maintain high efficiency for a long period of time in the catalytic reaction of producing olefins such as ethylene and alcohols such as ethanol through the reduction reaction of carbon dioxide.

[0082] The structure of the cathode electrode 100 formed on the substrate 1 can be solid or porous, but as mentioned above, in the case of the reduction reaction of carbon dioxide at the cathode electrode 100, a porous structure is preferred from the viewpoint that water and carbon dioxide can be in smooth contact, and the catalytic reaction of producing olefins such as ethylene and alcohols such as ethanol can be continued more stably for a long time. For example, the porous structure of the cathode electrode 100 can be formed by performing a subsequent reduction treatment. In addition, Figure 1 In FIG. 1 , for the sake of convenience, the cathode electrode 100 does not show a porous structure.

[0083] The substrate 1 can be solid or porous, but since gaseous carbon dioxide can smoothly contact the cathode electrode, and from the perspective that the catalytic reaction of producing olefins such as ethylene and alcohols such as ethanol can be continued more stably for a long time even with gaseous carbon dioxide, a porous structure with gas permeability is preferred.

[0084] As the material of porous structure substrate 1, although there is no particular restriction, the catalytic reaction of 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, and from the viewpoint of obtaining the composite of cathode electrode and substrate, it can be preferably carbon, fluororesin, metal. As carbon, for example, a composite of carbon black and carbon fiber can be listed. As fluororesin, for example, polytetrafluoroethylene, polyvinylidene fluoride, perfluoroalkoxyalkane, perfluoroethylene propylene copolymer, ethylene-tetrafluoroethylene copolymer, polytrifluorochloroethylene, ethylene-trifluorochloroethylene copolymer, etc. can be listed. As metal, for example, copper (Cu), niobium (Nb), aluminum (Al), titanium (Ti), a porous metal composed of metals such as alloys containing more than one of the above metals, stainless steel, etc. can be listed. When the material of porous structure substrate 1 is metal, and the metal is copper (Cu), as porous metal, for example, a sintered body of copper particles can be listed.

[0085] The average thickness of the substrate 1 is not particularly limited, and examples thereof include a plate material having a thickness of 0.2 mm to 1.5 mm.

[0086] The cathode electrode 100 in the composite body 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 needed. Alternatively, the cathode electrode 100 in the composite body 120 of the cathode electrode 100 and the substrate 1 may be, for example, a co-electrodeposition layer formed by co-electrodepositing the copper component and the additive element (M) added as needed on the substrate 1 by immersing the substrate 1 in a co-electrodeposition solution containing copper ions and ions of the additive element (M) added as needed.

[0087] [Method for producing a composite of a cathode electrode and a substrate] An example of a method for producing a composite of a cathode electrode and a substrate is described below. Figure 2 This is an explanatory diagram of the electrolytic polishing process in the method for producing a composite body of a cathode electrode and a substrate. Figure 3 It is an explanatory diagram showing a sputtering layer forming step and a copper oxidation treatment step in a method for producing a composite of a cathode electrode and a substrate. Figure 4 This is an explanatory diagram showing a partial reduction step in a method for producing a composite of a cathode electrode and a substrate. Figure 5 This is an explanatory diagram showing the structure of the composite of the cathode electrode and the substrate of the present invention.

[0088] A method for producing a composite of a cathode electrode and a substrate for electroreduction of carbon dioxide, comprising: (1) preparing a substrate (e.g., a substrate having a porous structure); (2) electropolishing the prepared substrate as needed; (3) forming a sputtering layer by sputtering a sputtering layer having copper on the substrate subjected to electropolishing as needed; (4) further oxidizing at least a portion of the copper in the sputtering layer to monovalent copper and / or divalent copper as needed after the sputtering layer forming step; (5) partially reducing the oxidized monovalent copper and / or divalent copper to zero-valent copper and / or monovalent copper in the copper oxidation step as needed; and (6) applying a metal ion-substituted cation exchange material to the sputtering layer subjected to the copper oxidation and partial reduction steps to modify the surface of the copper in the sputtering layer as needed. Among the above steps, step (1), step (3) and step (6) are essential steps, and step (2), step (4) and step (5) are optional steps.

[0089] By using the above-mentioned method for manufacturing a composite of a cathode electrode and a substrate, a cathode electrode can be formed on a substrate, wherein the cathode electrode is a cathode electrode in which copper as a catalytic material is surface-modified with a cation exchange material substituted with a metal ion. By using the above-mentioned method for manufacturing a composite of a cathode electrode and a substrate, the selectivity of the side reaction product hydrogen is reduced, and a composite can be manufactured that allows the catalytic reaction of generating olefins such as ethylene and alcohols such as ethanol through the reduction reaction of carbon dioxide to be maintained stably and efficiently for a long period of time. As cathode electrodes formed by the above-mentioned method for manufacturing a composite of a cathode electrode and a substrate, cathode electrodes containing copper in the form of divalent copper, zero-valent copper and / or monovalent copper, or cathode electrodes containing monovalent copper for reduction and / or divalent copper for reduction in which copper is reduced to zero-valent copper by reduction treatment and monovalent copper and / or divalent copper that is not reduced to zero-valent copper can be cited.

[0090] (1) Step of preparing a substrate (e.g., a substrate having a porous structure) The step of preparing a substrate (e.g., a substrate having a porous structure) is a step of preparing the substrate. The material of the substrate and the porosity of the porous structure can be appropriately selected according to the properties required for the composite of the cathode electrode and the substrate.

[0091] (2) Electrolytic polishing process The electrolytic polishing process is a process that is performed as needed when a metal is used as the base material. The electrolytic polishing process is as follows: First, the base surface is degreased using an organic solvent such as hexane, and then cleaned and dried. Figure 2 As shown, a mixed acid solution 11 is placed in a container 10, a substrate 1 serving as an anode is immersed in the mixed acid solution 11, a cathode 2 is immersed across the substrate 1, and an electrolytic potential is applied between the substrate 1 serving as the anode and the cathode 2. The application of the electrolytic potential to the substrate 1 serving as the anode and the cathode 2 causes the surface of the substrate 1 to be electropolished. By electropolishing the surface of the substrate 1, a surface deterioration layer on the substrate 1 can be reduced or removed. Examples of the mixed acid solution 11 include a mixed acid aqueous solution of phosphoric acid and sulfuric acid. Examples of the cathode 2 include titanium.

[0092] (3) Sputtering layer formation process like Figure 3 As shown in FIG. 1 , the sputtering layer forming step is to form a sputtering layer 20 having copper on a substrate 1 by sputtering. When the sputtering layer 20 contains at least one additional element (M) selected from the group consisting of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon as an optional component in addition to copper (Cu), as shown in FIG. Figure 3As shown, the sputtering layer forming process includes: forming a copper (Cu) sputtering layer on substrate 1 by sputtering, wherein the copper (Cu) sputtering layer forming process refers to a copper (Cu) sputtering layer having a copper (Cu) sputtering layer; and forming an additive element (M) sputtering layer on the copper (Cu) sputtering layer by sputtering, wherein the additive element (M) sputtering layer refers to an additive element (M) sputtering layer having an additive element (M) sputtering layer. Furthermore, the process also includes forming a copper (Cu) sputtering layer on the formed additive element (M) sputtering layer by sputtering, wherein the copper (Cu) sputtering layer refers to a copper (Cu) sputtering layer having a copper (Cu) sputtering layer. By adjusting the power supply and sputtering time, the content of the additive element (M) relative to 100 atomic % of the copper (Cu) can be adjusted. Furthermore, if necessary, the copper (Cu) sputtering layer forming step and the additive element (M) sputtering layer forming step may be performed alternately multiple times in order to uniformly distribute copper (Cu) and the additive element (M) throughout the sputtering layer 20. Through the sputtering layer forming step, a cathode electrode containing divalent copper and zero-valent copper and / or monovalent copper, and containing an additive element as needed, or a cathode electrode containing monovalent copper for reduction and / or divalent copper for reduction 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 containing an additive element as needed, can be formed on the substrate 1.

[0093] (4) Copper oxidation treatment process The copper oxidation treatment step is a step performed as needed when it is necessary to adjust the presence ratio of monovalent copper and / or divalent copper to a predetermined amount. Figure 3 As shown, the copper oxidation treatment step is to perform an oxidation treatment on the formed sputtered layer 20 by electroless plating, thereby oxidizing at least a portion of the zero-valent copper (Cu) contained in the sputtered layer 20 into monovalent copper (Cu2O) and / or divalent copper (CuO), thereby forming an oxidized portion 22. As an example of the oxidation treatment by electroless plating, an oxidation treatment method of immersing the sputtered layer 20 in a copper sulfate aqueous solution can be mentioned.

[0094] (5) Partial reduction process The partial reduction step is a step performed to reduce the monovalent copper and / or divalent copper oxidized in the copper oxidation treatment step to zero-valent copper and / or monovalent copper as needed, thereby further optimizing the abundance ratio of zero-valent copper to monovalent copper. Figure 4As shown, a composite 1' obtained by forming a sputtered layer 20 on a substrate 1 and an anode 33 are immersed in a partial reduction aqueous solution 32 housed in a two-chamber electrolytic cell 30 with a diaphragm 31. An electrolytic potential is applied to the two-chamber electrolytic cell 30 via a power supply 34, thereby performing a partial reduction treatment. Furthermore, the partial reduction treatment can make the sputtered layer 20 porous. Examples of the anode 33 include platinum. Examples of the partial reduction aqueous solution 32 include an aqueous potassium bicarbonate solution, which can be used on both the composite 1' side and the anode side.

[0095] (6) Metal ion-substituted cation exchange material application step like Figure 5 As shown, the metal ion-substituted cation exchange material application step is a step of applying a metal ion-substituted cation exchange material 21 to the sputtered layer 20, which has undergone the copper oxidation treatment step and the partial reduction step, as needed, to modify the copper surface of the sputtered layer 20 with the metal ion-substituted cation exchange material 21. When an oxidized portion 22 is formed by the copper oxidation treatment step, the metal ion-substituted cation exchange material 21 is also applied to the oxidized portion 22. Examples of methods for applying (imparting) the metal ion-substituted cation exchange material 21 to the sputtered layer 20 include spraying a solution of the metal ion-substituted cation exchange material 21. Application of the metal ion-substituted cation exchange material 21 to the sputtered layer 20 oxidizes at least a portion of the monovalent copper (Cu2O) to divalent copper (CuO).

[0096] [Electrolysis device] Next, an electrolytic reduction device for electrolytically reducing carbon dioxide to carbon monoxide, olefins and / or alcohols having a cathode electrode of the present invention and an electrolytic reduction device for electrolytically reducing carbon dioxide to carbon monoxide, olefins and / or alcohols having a composite of the cathode electrode of the present invention and a substrate are described. Figure 6 This is an explanatory diagram schematically showing an electrolytic reduction device including the cathode electrode of the present invention. Figure 7 This is an explanatory diagram schematically showing another electrolytic reduction device including the cathode electrode of the present invention.

[0097] like Figure 6As shown, as the electrolytic reduction device 210, a three-chamber type electrolytic reduction device can be listed, for example. Specifically, the electrolytic reduction device 210 has, for example, an electrolytic cell 214 having a cathode gas chamber 211, a cathode liquid chamber 212, and an anode liquid chamber 213 that are separated from each other. The cathode gas chamber 211 and the cathode liquid chamber 212 are separated by a cathode 216 serving as a gas diffusion electrode. The cathode liquid chamber 212 and the anode liquid chamber 213 are separated by a diaphragm 217 having ion conductivity. An anode electrode 218 is arranged in the anode liquid chamber 213. Gaseous carbon dioxide is supplied to the cathode gas chamber 211. Catholyte 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 DC power supply 219.

[0098] The anolyte and catholyte are aqueous solutions dissolved with an electrolyte. The electrolyte includes, for example, potassium, sodium, lithium, or at least one of these compounds. The electrolyte is selected from, for example, at least one compound selected from the group consisting of LiOH, NaOH, KOH, Li2CO3, Na2CO3, K2CO3, LiHCO3, NaHCO3, and KHCO3.

[0099] Cathode 216 is a gas diffusion electrode having a gas diffusion layer 221 and a microporous layer 222. In electrolytic reduction device 210, cathode 216 is a composite of a cathode electrode modified with a cation exchange material, the copper surface of which is substituted with metal ions, and a substrate. Microporous layer 222 serves as the substrate of the composite. Gas diffusion layer 221 is permeable to gases containing carbon dioxide but inhibits the permeation of aqueous solutions containing catholyte. Microporous layer 222 is permeable to both gases containing carbon dioxide and aqueous solutions containing catholyte. Gas diffusion layer 221 and microporous layer 222 are each formed into a planar shape. Gas diffusion layer 221 is positioned on the cathode gas chamber 211 side, while microporous layer 222 is positioned on the cathode liquid chamber 212 side.

[0100] As the gas diffusion layer 221, for example, materials formed on the surface of porous conductive substrates such as carbon paper, carbon felt, and carbon cloth with a waterproof film such as polytetrafluoroethylene can be listed. The conductive substrate is connected to the negative electrode of the DC power supply 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, etc., and is used to load a catalyst. In the electrolytic reduction device 210, as the catalyst loaded by the microporous layer 222, a cathode electrode modified by a cation exchange material in which the copper surface of the present invention is replaced by metal ions is used. In addition, by using renewable energy as the DC power supply 219 of the electrolytic reduction device 210, while reducing the environmental load, olefins such as ethylene and alcohols such as ethanol can also be generated by the reduction reaction of carbon dioxide. In addition, instead of using a gas diffusion electrode with a gas diffusion layer 221 and a microporous layer 222, a gas diffusion electrode can be provided that functions as the gas diffusion layer 221 by a part of the microporous layer 222.

[0101] In addition, if Figure 7 As shown in FIG. 1 , as another electrolytic reduction device 210, for example, an electrolytic reduction device 210 having a MEA type electrolytic cell structure can be cited. Figure 7 As shown, in other electrolytic reduction devices 210, Figure 6 The same structure as the electrolytic reduction device 210 is given as shown Figure 6 The electrolytic reduction device 210 shown in FIG. The electrolytic reduction device 210 with an MEA-type electrolytic cell structure does not use a catholyte and therefore does not have a catholyte chamber 212. Therefore, instead of the electrolytic cell 214 having the cathode gas chamber 211, the catholyte chamber 212, and the anolyte chamber 213, the electrolytic reduction device 210 with an MEA-type electrolytic cell structure includes an electrolytic cell 214 having a cathode gas chamber 211 and an anolyte chamber 213 that are separated from each other. The cathode gas chamber 211 and the anolyte chamber 213 are separated by a diaphragm 217 sandwiched between a cathode electrode and an anode electrode 218. The anode electrode 218 is disposed in the anolyte chamber 213. Gaseous carbon dioxide is supplied to the cathode gas chamber 211. Anolyte is supplied to the anolyte chamber 213. The anode electrode 218 and the cathode electrode are connected to a DC power supply 219. In the electrolytic reduction device 210 having the MEA type electrolytic cell structure, since the diaphragm 217 itself is used as the electrolyte and no catholyte is used, it is suitable for integration.

[0102] Even in the electrolytic reduction device 210 having an MEA-type electrolytic cell structure, the cathode electrode is a gas diffusion electrode having a gas diffusion layer 221 and a microporous layer 222. Furthermore, even in the electrolytic reduction device 210 having an MEA-type electrolytic cell structure, the composite of the present invention is used as the cathode electrode. This composite is composed of a cathode electrode whose copper surface is modified with a cation exchange material substituted with metal ions and a substrate, and the microporous layer 222 serves as the substrate of the composite.

[0103] [Example] Next, examples of the present invention will be described. However, the present invention is not limited to the following examples.

[0104] [Example 1] Preparation of cathode electrode Sputtering layer formation process On the substrate (porous carbon), a copper layer was formed by sputtering under the conditions of DC 100W, argon 6.0 sccm, and 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 the conditions of DC 50W, argon 6.0 sccm, and 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 the conditions of DC 100W, argon 6.0 sccm, and 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 the conditions of DC 50W, argon 6.0 sccm, and 30 seconds to form a second aluminum sputtered layer. Thereafter, a copper layer was formed on the formed second aluminum sputtered layer by sputtering under the conditions of DC100W, argon 6.0 sccm, and 5 minutes to form a third copper sputtered layer, thereby obtaining a sputtered layer as a laminate consisting of five layers.

[0105] Copper oxidation treatment process The sputtered layer of the laminate obtained as described above was immersed in 100 mL of an aqueous solution containing copper sulfate and potassium sulfate (9.7 mM copper ions, 0.5 M sulfate ions), and electroless plating was performed at 20° C. for 20 minutes. A portion of the zero-valent copper contained in the copper sputtered layer was oxidized to monovalent copper and / or divalent copper.

[0106] Metal ion-substituted cation exchange material application process The cation exchange resin (sulfonated tetrafluoroethylene polymer, (registered trademark), DuPont) was mixed with an aqueous solution (concentration of 5% by mass) of Nafion (DuPont) and an aqueous solution of potassium hydroxide (concentration of 8M) to prepare an aqueous solution of a cation exchange resin substituted with potassium ions (an aqueous solution of a cation exchange resin in which the hydrogen ions of the cation exchange resin were substituted with potassium ions). The obtained aqueous solution of the cation exchange resin substituted with potassium ions was sprayed onto the surface of the sputtered layer of a five-layer laminate that had undergone a copper oxidation treatment (the application amount of the aqueous solution of the cation exchange resin substituted with potassium ions was 650 μL) and heat-dried. The copper surface of the sputtered layer was modified with the cation exchange resin substituted with potassium ions so that the accumulation amount of the cation exchange resin (Nafion) per 100 g of copper element reached 125 g to 24,333 g, depending on the weight difference before and after coating.

[0107] As described above, a cathode electrode is formed as a sputtered layer on a substrate, thereby manufacturing a composite of the cathode electrode and the substrate.

[0108] [Comparative Example 1] A cathode electrode and substrate composite was produced in the same manner as in Example 1, except that the potassium hydroxide application step, described later, was used instead of the metal ion-substituted cation exchange material application step. As can be seen from the above, in Comparative Example 1, the copper of the sputtered layer of the five-layer laminate was not surface-modified with a potassium ion-substituted cation exchange resin. Instead, a cathode electrode and substrate composite was surface-modified with potassium ions and hydroxide ions.

[0109] Potassium hydroxide application process A potassium hydroxide aqueous solution was prepared by adding 500 μL of water to an 8 M potassium hydroxide aqueous solution, and the prepared potassium hydroxide aqueous solution was sprayed (the coating amount of the potassium hydroxide aqueous solution was 600 μL) on the surface of the sputtered layer of a laminate consisting of 5 layers that had undergone a copper oxidation treatment process, and then heated and dried, thereby modifying the copper surface of the sputtered layer with potassium ions and hydroxide ions.

[0110] Evaluation Project [Stability test] The ethylene selectivity (E24, unit: %) was measured 24 hours after the start of the carbon dioxide reduction reaction. When E24 reached 50% or greater, it was considered that the catalytic reaction to produce ethylene through the carbon dioxide reduction reaction was able to continue stably over a long period of time, and that the catalytic reaction stability was excellent. Ethylene selectivity was evaluated as follows.

[0111] [Ethylene gas selectivity (%)] According to the concentration and gas flow of the ethylene contained in the outlet gas of the electrolytic cell (electrolyte: 1MKHCO3 aqueous solution, electrolyte flow: 50mL / min), the number of ethylene moles per unit time and the number of moles of required electrons (carbon dioxide gas flow: 40mL / min) were calculated. On the other hand, the number of moles of electrons passing through the electrolytic cell per unit time was calculated by the set current value (-530mA) of the potentiostat. The former was evaluated as ethylene selectivity (%) relative to the latter ratio. The ethylene concentration contained in the outlet gas was measured using a gas chromatograph (model: Agilent 990 micro gas chromatograph). The gas flow was measured using a mass flow meter.

[0112] The measurement results of Examples and Comparative Examples are shown in Table 1 below.

[0113]

Table 1

[0114] As shown in Table 1 above, in Example 1, in which the copper surface of the sputtered layer was modified using a cation exchange resin substituted with potassium ions, the ethylene gas selectivity (E24) was 50% or more 24 hours after the start of the carbon dioxide reduction reaction. The catalytic reaction of generating ethylene through the reduction reaction of carbon dioxide was able to continue stably for a long time, and the stability of the catalytic reaction was excellent.

[0115] On the other hand, in Comparative Example 1, in which the surface of the sputtered copper layer was modified with potassium ions and hydroxide ions, the ethylene gas selectivity (E24) was 27% 24 hours after the start of the carbon dioxide reduction reaction, and it was not evaluated as "the catalytic reaction of generating ethylene by the carbon dioxide reduction reaction can be continued stably for a long time."

[0116] In addition, the cathode electrode of Example 1 and the cathode electrode of Comparative Example 1 before and after the stability test were analyzed by X-ray diffraction (XRD). The results showed that no significant difference was observed in the X-ray diffraction peaks of zero-valent copper (Cu), monovalent copper (Cu2O), and divalent copper (CuO) between Example 1 and Comparative Example 1, either before or after the stability test.

[0117] Industrial Application Possibilities The cathode electrode of the present invention can stably and continuously catalyze the reaction of reducing carbon dioxide to produce olefins such as ethylene and alcohols such as ethanol for a long time, thereby absorbing and recovering carbon dioxide in the atmosphere, and has high application value in the field of utilizing carbon dioxide to produce industrially useful organic compounds.

[0118]

Explanation of symbols

Claims

1. A cathode electrode that electrically reduces carbon dioxide, The cathode electrode comprises copper surface-modified with a cation exchange material substituted with metal ions. 2 . The cathode electrode according to claim 1 , wherein the copper comprises divalent copper, zero-valent copper and / or monovalent copper. 3 . The cathode electrode according to claim 1 , wherein the copper comprises monovalent copper for reduction and / or divalent copper for reduction which are reduced to zero-valent copper by reduction treatment, and monovalent copper and / or divalent copper which are not reduced to zero-valent copper. 4 . The cathode electrode according to claim 1 , further comprising at least one additional element selected from the group consisting of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium, and silicon. 5 . The cathode electrode according to claim 4 , wherein the content of the additional element is not less than 0.10 atomic % and not more than 1.0 atomic % relative to 100 atomic % of the copper. 6 . The cathode electrode according to claim 1 , wherein the cation exchange material comprises a sulfonated tetrafluoroethylene polymer. 7 . The cathode electrode according to claim 1 , wherein the metal ions comprise alkali metal ions and / or alkaline earth metal ions. 8 . The cathode electrode according to claim 1 , wherein the cation exchange material substituted with the metal ions is formed in a layer on the copper. 9 . The cathode electrode according to claim 1 , wherein the cation exchange material substituted with the metal ions is mixed with the copper.

10. The cathode electrode according to any one of claims 1 to 3, having a porous structure.

11. A composite body comprising a cathode electrode and a substrate, comprising a substrate, and the cathode electrode according to any one of claims 1 to 3 disposed on the substrate.

12. An electrolytic reduction device comprising the cathode electrode according to any one of claims 1 to 3, which electrolytically reduces carbon dioxide to carbon monoxide, olefins and / or alcohols. 13 . An electrolytic reduction device comprising the composite according to claim 11 for electrolytically reducing carbon dioxide to carbon monoxide, olefins and / or alcohols.

14. A method for producing a composite body comprising a cathode electrode for electroreduction of carbon dioxide and a substrate. The manufacturing method comprises: A step of preparing a substrate having a porous structure; a sputtering layer forming step of forming a sputtering layer having copper on the substrate by sputtering; and A metal ion-substituted cation exchange material application step is performed by applying a metal ion-substituted cation exchange material to the sputtered layer to modify the copper surface. 15 . The method for producing a composite according to claim 14 , wherein the copper comprises divalent copper, zero-valent copper and / or monovalent copper.

16. The method for producing a composite according to claim 14, wherein the copper comprises monovalent copper for reduction and / or divalent copper for reduction which are reduced to zero-valent copper by reduction treatment, and monovalent copper and / or divalent copper which are not reduced to zero-valent copper.

17. The method for producing a composite according to any one of claims 14 to 16, wherein the sputtered layer further contains at least one additional element selected from the group consisting of silver, gold, cadmium, tin, aluminum, boron, gallium, zinc, titanium and silicon.

18. The method for producing a composite according to claim 15 or 16, further comprising a copper oxidation treatment step after the sputtering layer forming step and before the step of applying the cation exchange material substituted with the metal ions, wherein the copper oxidation treatment step oxidizes at least a portion of the copper in the sputtering layer to form the monovalent copper and / or the divalent copper.

19. The method for producing a composite according to claim 18, further comprising a partial reduction step, wherein the partial reduction step is performed before the step of applying the cation exchange material substituted with the metal ions, and the monovalent copper and / or divalent copper formed by oxidation in the copper oxidation step is partially reduced to zero-valent copper and / or monovalent copper.

20. The method for manufacturing a composite body according to claim 17, wherein the sputtering layer forming process comprises: a copper sputtering layer forming process of forming a copper sputtering layer as a sputtering layer containing the copper by sputtering; and an additive element sputtering layer forming process of forming an additive element sputtering layer as a sputtering layer containing the additive element on the copper sputtering layer by sputtering.

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