Catalyst layer for carbon dioxide reduction electrode, cathode, ion exchange membrane-electrode assembly, and solid electrolyte electrolysis device

Abstract

Provided are a catalyst layer for a carbon dioxide reduction electrode, a cathode, an ion exchange membrane-electrode assembly, and a solid electrolyte electrolysis device, which have high electrolysis efficiency in a carbon dioxide electrolytic reduction reaction. The catalyst layer for carbon dioxide reduction electrodes contains a catalyst, alkali metal ions, and a polymer material capable of releasing the alkali metal ions.

Description

Technical Field

[0001] The technology of the present application relates to a catalyst layer for a carbon dioxide reduction electrode, a cathode, an ion exchange membrane-electrode assembly, and a solid electrolyte type electrolysis device. Background Art

[0002] Carbon dioxide is emitted when extracting energy from fossil fuels and the like. It is said that the increase in the concentration of carbon dioxide in the atmosphere is one of the causes of global warming. Since carbon dioxide is an extremely stable substance, there have been almost no utilization routes in the past. However, due to the increasing severity of global warming in this era, there is a demand for new technologies for converting carbon dioxide into other substances and recycling it again. For example, carbon dioxide reduction type devices that can directly reduce gaseous carbon dioxide are being developed.

[0003] Generally, in a carbon dioxide reduction type device, as the cathode, there is a gas diffusion layer that absorbs carbon dioxide gas and a catalyst layer that promotes the carbon dioxide reduction reaction, and it is in contact with an electrolyte solution through an ion exchange membrane. Due to its structure, the ion exchange membrane has the property of allowing not only ions but also electrolytes to pass through. As a result, the following phenomena are often observed: the phenomenon that the electrolyte supplied to the anode penetrates the ion exchange membrane and the moisture inside the catalyst layer becomes excessive; the phenomenon that it precipitates in the form of a salt near the cathode and blocks the flow path. Sometimes, due to this phenomenon, there are adverse effects such as preventing the supply of carbon dioxide to the cathode catalyst, resulting in a decrease in electrolysis performance such as current density and selectivity. In particular, the higher the reaction temperature, the more likely this effect is to occur significantly.

[0004] In contrast, for example, in Non-Patent Documents 1 and 2, research has been conducted on using pure water instead of an electrolyte. In addition, Non-Patent Document 3 proposed a system for alternately supplying pure water and a concentrated electrolyte solution to the cathode.

[0005] Prior Art Documents

[0006] Non-Patent Documents

[0007] Non-Patent Document 1: M.C.O. Monteiro, F. Dattila, B. Hagedoorn, R. Garcia-Muelas, N. Lopez, M.T.M. Koper, Nature catalysis, 2021, 4, 654 - 662.

[0008] Non-Patent Document 2: J.A. Rebstock, Q. Zhu, L.R. Baker, Chemical Science, 2022, 13, 7634 - 7643.

[0009] Non-Patent Document 3: B. Endrodi, A. Samu, E. Kecsenovity, T. Halmagyi, D. Sebok, C. Janaky, Nature Energy, 2021, 6, 439-448. Summary of the Invention

[0010] Problems to be Solved by the Invention

[0011] However, Non-Patent Documents 1 and 2 reported that: when using pure water without using an electrolyte, the rate and selectivity of the carbon dioxide reduction reaction are significantly reduced.

[0012] It is known that: although the intermediates of the carbon dioxide reduction reaction are less stable, they are sufficiently stabilized by temporarily forming bonds with alkali metal ions. The method disclosed in Non-Patent Document 3 seemingly solves the opposite requirements of suppressing salt precipitation by not using alkali metal ions and achieving intermediate stability by using alkali metal ions, but this method has the following problems: the operating rate of the battery unit is reduced, and in addition, there is no mechanism to keep metal ions near the catalyst, and the stability is insufficient.

[0013] The technology of the present application is carried out in view of the above situation. The technical problem of the present application is to provide a catalyst layer for a carbon dioxide reduction electrode, a cathode, an ion exchange membrane-electrode assembly, and a solid electrolyte type electrolysis device with high electrolysis efficiency for the carbon dioxide electrolytic reduction reaction.

[0014] Means for Solving the Problems

[0015] <1> A catalyst layer for a carbon dioxide reduction electrode, which contains: a catalyst, an alkali metal ion, and a polymer material capable of releasing the aforementioned alkali metal ion.

[0016] <2> The catalyst layer for a carbon dioxide reduction electrode according to <1>, wherein the aforementioned catalyst and the aforementioned alkali metal ion are dispersed in a polymer material capable of releasing the aforementioned alkali metal ion and integrated into one body.

[0017] <3> The catalyst layer for a carbon dioxide reduction electrode according to <1>, wherein the aforementioned catalyst layer for a carbon dioxide reduction electrode has a reaction layer containing the aforementioned catalyst and a layer containing the aforementioned alkali metal ion and a polymer material capable of releasing the aforementioned alkali metal ion.

[0018] <4> The catalyst layer for a carbon dioxide reduction electrode according to <3>, wherein the reaction layer containing the aforementioned catalyst and the layer containing the aforementioned alkali metal ion and a polymer material capable of releasing the aforementioned alkali metal ion are integrally provided.

[0019] <5>The catalyst layer for a carbon dioxide reduction electrode according to <1> or <2>, wherein the polymer material capable of releasing the aforementioned alkali metal ions contains a cation exchange resin.

[0020] <6>The catalyst layer for a carbon dioxide reduction electrode according to <1>, <3> or <4>, wherein the polymer material capable of releasing the aforementioned alkali metal ions contains a polymer gel.

[0021] <7>The catalyst layer for a carbon dioxide reduction electrode according to any one of <1> to <6>, wherein the aforementioned catalyst contains one or more selected from Catalyst A and Catalyst B. Catalyst A has a metal ion selected from copper ions, nickel ions, iron ions, cobalt ions, zinc ions, manganese ions, molybdenum ions and aluminum ions, a nitrogen-containing compound and a carbon-containing carrier. Catalyst B has inorganic fine particles or a metal complex and has a carbon-containing carrier. The inorganic fine particles are selected from gold, silver, copper, nickel, iron, cobalt, zinc, chromium, palladium, tin, manganese, aluminum, indium, bismuth, molybdenum and carbon nitride. The metal complex is obtained by coordinating a ligand on a metal selected from copper, nickel, iron, cobalt, zinc, manganese, molybdenum and aluminum or an ion of the metal.

[0022] <8>A cathode having the catalyst layer for a carbon dioxide reduction electrode according to any one of <1> to <7> and a gas diffusion layer.

[0023] <9>An ion exchange membrane-electrode assembly having the cathode according to <8>, a solid electrolyte and an anode.

[0024] <10>The ion exchange membrane-electrode assembly according to <9>, wherein the aforementioned solid electrolyte is an anion exchange membrane.

[0025] <11>A solid electrolyte type electrolysis device having:

[0026] The cathode according to <8>;

[0027] An anode forming a pair of electrodes with the aforementioned cathode;

[0028] A solid electrolyte interposed in a contact state between the aforementioned cathode and the aforementioned anode; and

[0029] A voltage application unit for applying a voltage between the aforementioned cathode and the aforementioned anode.

[0030] <12>The solid electrolyte type electrolysis device according to <11>, further having an electrolytic solution in contact with the aforementioned anode, and the electrolytic solution is pure water.

[0031] <13>The solid electrolyte type electrolysis device according to <11> or <12>, wherein the aforementioned solid electrolyte is an anion exchange membrane.

[0032] Effect of the Invention

[0033] According to the technology of the present application, a catalyst layer for a carbon dioxide reduction electrode, a cathode, an ion exchange membrane-electrode assembly, and a solid electrolyte type electrolysis device with high electrolysis efficiency for the carbon dioxide electrolytic reduction reaction can be provided. Description of the Drawings

[0034] Figure 1 It is a schematic cross-sectional view of an ion exchange membrane-electrode assembly suitably used in the present embodiment.

[0035] Figure 2 It is a schematic cross-sectional view of a catalyst layer for a carbon dioxide reduction electrode suitably used in the present embodiment.

[0036] Figure 3 It is a schematic cross-sectional view of a catalyst layer for a carbon dioxide reduction electrode suitably used in the present embodiment.

[0037] Figure 4 It is a schematic diagram of a solid electrolyte type electrolysis device suitably used in the present embodiment. Detailed Description of the Embodiment

[0038] The upper limit value and the lower limit value of the numerical range described in this specification can be arbitrarily combined. For example, when "A to B" and "C to D" are described as numerical ranges, the numerical ranges of "A to D" and "C to B" are also included in the scope of the present application.

[0039] In addition, the numerical range "lower limit value to upper limit value" described in this specification means equal to or higher than the lower limit value and equal to or lower than the upper limit value unless otherwise specified.

[0040] <Catalyst Layer for Carbon Dioxide Reduction Electrode>

[0041] The catalyst layer for a carbon dioxide reduction electrode according to the embodiment of the present application contains a catalyst, alkali metal ions, and a polymer material capable of releasing alkali metal ions.

[0042] Hereinafter, the "catalyst layer for a carbon dioxide reduction electrode" may sometimes be simply referred to as the "catalyst layer". In addition, the "polymer material capable of releasing alkali metal ions" may sometimes be simply referred to as the "polymer material according to the embodiment of the present application".

[0043] The presence of an electrolyte, particularly an alkali metal ion as a cationic species, is necessary to drive the carbon dioxide reduction reaction with a high selectivity. However, as described above, since the ion exchange membrane allows the electrolyte to permeate, there may occur a phenomenon in which the moisture inside the catalyst layer becomes excessive, and a problem in which it precipitates in the form of a salt near the cathode and clogs the flow path. Such a phenomenon causes adverse effects such as hindering the supply of carbon dioxide to the cathode catalyst, and easily reduces the electrolysis efficiency. In addition, when the electrolyte is pure water, it is likely to reduce the stability of the intermediate of the carbon dioxide reduction reaction, and easily reduces the electrolysis efficiency.

[0044] In contrast, the electrolysis efficiency of the carbon dioxide electrolytic reduction reaction of the catalyst layer for a carbon dioxide reduction electrode according to an embodiment of the present application is high.

[0045] The reason is not yet certain, but it is considered that: by allowing a catalyst, an alkali metal ion, and a polymer material capable of releasing an alkali metal ion to coexist in the catalyst layer, an alkali metal ion can be stably supplied to the intermediate generated by the carbon dioxide reduction reaction, and the electrolysis efficiency can be improved. In addition, it is considered that: through the chemical interaction between the polymer material and the alkali metal ion according to the embodiment of the present application, the detachment of the alkali metal ion from the catalyst layer is suppressed, and thus, precipitation in the form of a salt near the cathode can be suppressed, and the electrolysis efficiency can be improved.

[0046] As described above, it is considered that: the catalyst layer for a carbon dioxide reduction electrode according to the embodiment of the present application can control the concentration of the alkali metal ion near the cathode to such an extent that the reduction reaction is promoted and precipitation does not occur in the form of a salt, and thus, the electrolysis efficiency can be improved.

[0047] Hereinafter, the catalyst layer for a carbon dioxide reduction electrode, the cathode, the ion exchange membrane-electrode assembly, and the solid electrolyte type electrolytic device according to the embodiment of the present application will be described in detail.

[0048] 〔Structure of catalyst layer〕

[0049] Figure 1 It is a schematic cross-sectional view of an ion exchange membrane-electrode assembly suitably used in the present embodiment.

[0050] Figure 1 An ion exchange membrane-electrode assembly 50 is shown in which includes a gas diffusion layer 10, a catalyst layer 20 for a carbon dioxide reduction electrode, a solid electrolyte 30, and an anode 40.

[0051] The catalyst layer 20 includes the catalyst 23 according to the present embodiment, the alkali metal ion according to the present embodiment, and the polymer material 24 according to the present embodiment. By combining the gas diffusion layer 10 and the catalyst layer 20, the cathode (negative electrode) according to the present embodiment is constituted.

[0052] As Figure 1 shown, carbon dioxide (CO2) is supplied to the catalyst layer 20 through the gas diffusion layer 10 and carbon monoxide (CO) is generated through a reduction reaction.

[0053] The catalyst layer 20 according to the embodiment of the present application may be Figure 2 a single-layer structure as shown, or may be Figure 3 a laminated structure of two or more layers as shown.

[0054] Figure 2 The catalyst layer 20a with a single-layer structure shown contains the catalyst 23a according to the present embodiment, the alkali metal ions according to the present embodiment, and the polymer material 24a according to the present embodiment.

[0055] Figure 3 The catalyst layer 20b with a laminated structure shown has a reaction layer 21 containing the catalyst 23b according to the present embodiment and a layer 22 (also referred to as a cation supply layer 22) containing the alkali metal ions according to the present embodiment and the polymer material 24b according to the present embodiment.

[0056] 1. Single-layer structure

[0057] When the catalyst layer 20 according to the embodiment of the present application is a single-layer structure, the catalyst layer 20 (catalyst layer 20a) contains the catalyst 23a, and alkali metal ions and a polymer material 24 capable of releasing alkali metal ions in the same layer.

[0058] From the viewpoint of stably supplying alkali metal ions to the intermediate generated through the redox reaction in the catalyst layer 20a, in the catalyst layer 20a, the catalyst 23a and the alkali metal ions are preferably dispersed in the polymer material capable of releasing alkali metal ions and integrated.

[0059] The alkali metal ions are not easily detached from the catalyst layer due to the chemical interaction between the polymer material according to the present embodiment and the alkali metal ions. However, from the viewpoint of further suppressing the detachment of the alkali metal ions from the catalyst layer, it is preferable that a part of the polymer material according to the present embodiment is substituted with alkali metal ions. By substituting a part of the polymer material according to the present embodiment with alkali metal ions, alkali metal ions can be stably supplied to the intermediate generated through the redox reaction, and the detachment of the alkali metal ions from the catalyst layer can be further suppressed. Therefore, precipitation in the form of a salt near the cathode can be suppressed, and the electrolysis efficiency can be improved.

[0060] Therefore, the alkali metal ions contained in the catalyst layer 20a and the polymer material 24a capable of releasing alkali metal ions are preferably polymer materials substituted with alkali metal ions and capable of releasing alkali metal ions.

[0061] Details of the alkali metal ions contained in the catalyst layer 20a and the polymer material 24a capable of releasing alkali metal ions are described later.

[0062] From the viewpoint of further improving the electrolysis activity and the reduction reaction rate of CO2, the content of the catalyst 23a in the catalyst layer 20a is preferably 50 to 99% by mass, more preferably 75 to 97% by mass, and still more preferably 90 to 95% by mass.

[0063] From the viewpoint of further improving the electrolysis activity and the reduction reaction rate of CO2, the content of the polymer material capable of releasing alkali metal ions in the catalyst layer 20a (the amount of the polymer material itself, excluding the amount of alkali metal ions) is preferably 1 to 50% by mass, more preferably 1 to 30% by mass, and still more preferably 2 to 20% by mass.

[0064] From the viewpoint of further improving the electrolysis activity and the reduction reaction rate of CO2, the content of alkali metal ions in the catalyst layer 20a is preferably 0.01 to 20% by mass, more preferably 0.01 to 10% by mass, and still more preferably 0.1 to 5% by mass.

[0065] It should be noted that the content of alkali metal ions in the catalyst layer 20a can be measured by X-ray photoelectron spectroscopy.

[0066] 2. Laminated structure

[0067] When the catalyst layer 20 described in the embodiment of the present application is a laminated structure, for example, the catalyst layer 20 may have a two-layer structure such as a layer containing a catalyst and a layer containing an alkali metal ion and a polymer material capable of releasing an alkali metal ion, or a three-layer structure such as a layer containing a catalyst, a layer containing an alkali metal ion, and a layer containing a polymer material capable of releasing an alkali metal ion. The components contained in each layer may vary. In addition, like a four-layer structure obtained by alternately laminating a layer containing a catalyst / a layer containing an alkali metal ion and a polymer material capable of releasing an alkali metal ion, the same layer can be laminated two or more times.

[0068] Figure 3 Among them, as an example of the laminated structure, a catalyst layer 20b having a two-layer structure of a reaction layer 21 containing a catalyst 23b and a cation supply layer 22 containing an alkali metal ion and a polymer material 24b capable of releasing an alkali metal ion is shown.

[0069] The reaction layer 21 functions as a layer for performing a carbon dioxide reduction reaction in the presence of the catalyst 23b, and the cation supply layer 22 functions as a layer for supplying alkali metal ions to the reaction layer 21.

[0070] Among the above, as Figure 3 shown, the catalyst layer of the laminated structure preferably has a reaction layer 21 containing the catalyst 23b and a layer 22 (cation supply layer 22) containing an alkali metal ion and a polymer material 24b capable of releasing an alkali metal ion.

[0071] By supplying alkali metal ions from the cation supply layer 22 to the reaction layer 21, the intermediate generated in the dioxide reduction reaction can be stabilized, and the electrolysis efficiency can be improved.

[0072] From the viewpoint of more effectively supplying alkali metal ions from the cation supply layer 22 to the reaction layer 21, the reaction layer 21 and the cation supply layer 22 are preferably provided integrally. In other words, the reaction layer 21 and the cation supply layer 22 are preferably adjacent.

[0073] In addition, the catalyst layer 20b is preferably such that the reaction layer 21 is adjacent to the gas diffusion layer 10 and the cation supply layer 22 is adjacent to the solid electrolyte 30.

[0074] The reaction layer 21 contains the catalyst 23b. The catalyst 23b can use the same catalyst as the catalyst 23a, as described in detail later.

[0075] In the reaction layer 21, the catalyst 23b is dispersed in the dispersion medium 25. The dispersion medium 25 is not particularly limited as long as it can disperse the catalyst 23b, and for example, an ionomer can be used. The details of the ionomer are described later.

[0076] It should be noted that the reaction layer 21 may or may not contain alkali metal ions. Since the catalyst layer 20b has a cation supply layer 22, the content of alkali metal ions in the reaction layer 21 can be set to 0% by mass.

[0077] The details of the alkali metal ion and the polymer material 24b capable of releasing an alkali metal ion contained in the cation supply layer 22 are described later.

[0078] From the viewpoint of further improving the electrolysis activity and the reduction reaction rate of CO2, the content of the catalyst 23b in the reaction layer 21 is preferably 50 to 99% by mass, more preferably 75 to 97% by mass, and further preferably 90 to 95% by mass.

[0079] From the viewpoint of further improving the electrolytic activity and the rate of the CO2 reduction reaction, the content of the polymer material capable of releasing alkali metal ions in the cation supply layer 22 is preferably 5 to 99% by mass, more preferably 10 to 95% by mass, and still more preferably 20 to 95% by mass.

[0080] From the viewpoint of suppressing the precipitation of the alkali metal salt in the form of a salt near the cathode, the layer thickness of the cation supply layer 22 is preferably 0.005 to 0.5 mm.

[0081] Hereinafter, each component contained in the catalyst layer will be described. In addition, the following symbols are omitted Figures 1 - 3 for the description.

[0082] [Alkali metal ions]

[0083] Examples of the alkali metal ions include lithium ions (Li + ), sodium ions (Na + ), potassium ions (K + ), rubidium ions (Rb + ), cesium ions (Cs + ), etc.

[0084] The amount of ions supplied to the intermediate generated by the carbon dioxide reduction reactivity varies depending on the adsorption force between the polymer material capable of releasing alkali metal ions and the alkali metal ions. Specifically, when a cation exchange resin is used as the polymer material described in this embodiment and the ion exchange group is a sulfonic group, the adsorption force for the alkali metal ions is in the order of Li + <Na + <K + <Rb + ... and increases. In order to make the amount of alkali metal ions supplied to the intermediate sufficient and prevent the precipitation of salts due to excessive supply, it is preferable to control the adsorption force.

[0085] The adsorption force varies depending on the combination of the alkali metal ions and the polymer material described in this embodiment. The alkali metal ions are preferably at least one selected from potassium ions, sodium ions, rubidium ions, and cesium ions, and more preferably at least one selected from potassium ions, rubidium ions, and cesium ions.

[0086] The alkali metal ions can be used alone or in combination of two or more.

[0087] [Polymer material capable of releasing alkali metal ions]

[0088] As the polymer material capable of releasing alkali metal ions, ionomers, polymer gels, etc. can be used.

[0089] The polymer material described in this embodiment may be used alone or in combination of two or more kinds.

[0090] In addition, an ionomer can be used as the dispersion medium in the reaction layer of the catalyst layer of the laminated structure.

[0091] (Ionomer)

[0092] The ionomer functions as a binder resin in the catalyst layer of the single-layer structure or in the reaction layer of the catalyst layer of the laminated structure. It is a matrix resin (continuous phase) capable of dispersing and immobilizing the catalyst described in this embodiment, and also has the function of conducting ions generated by electrolysis and improving the CO2 electrolysis efficiency. In addition, from the viewpoint of improving the conduction efficiency of ions generated by electrolysis, the ionomer is preferably conductive, more preferably a polyelectrolyte. The polyelectrolyte is further preferably an ion exchange resin. The ion exchange resin can be a cation exchange resin or an anion exchange resin.

[0093] Examples of the cation exchange resin include fluororesin having a sulfo group and styrene-divinylbenzene copolymer having a sulfo group. In addition, commercially available products can also be used, such as Nafion (manufactured by Chemours), Aquivion (manufactured by Solvay Specialty Polymers), DIAION (manufactured by Mitsubishi Chemical), Fumasep (manufactured by FUMATECH), etc.

[0094] Examples of the anion exchange resin include resins having one or more ion exchange groups selected from quaternary amino groups, primary amino groups, secondary amino groups, and tertiary amino groups. Commercially available products can also be used, such as Sustainion (manufactured by Dioxide Materials), Fumasep (manufactured by FUMATECH), PENTION (manufactured by Xergy), DURION (manufactured by Xergy), NEOSEPTA (manufactured by ASTOM), TOYOPEARL (manufactured by Tosoh), etc.

[0095] From the viewpoint of improving conductivity, the base point density of the anion exchange resin is preferably 2.0 - 5.0 mmol / 3 , more preferably 2.5 mmol / 3 or more and less than 4.5 mmol / 3 , further preferably 2.9 mmol / 3 or more and less than 4.5 mmol / 3 .

[0096] The base point density of the anion exchange resin can be determined by performing1 It is obtained from the integral value of the signal during HNMR measurement.

[0097] In addition, regarding the anion exchange resin, the dry state means a state in which the anion exchange resin does not contain free water. For example, the anion exchange resin can be made into a dry state by heating in a vacuum.

[0098] (Polymer gel)

[0099] From the viewpoints of containing and releasing alkali metal ions and ensuring ionic conductivity, the polymer gel preferably uses a polymer gel having water content and hydrophilicity. As the polymer gel having water content and hydrophilicity, polyacrylamide, agarose, starch, gelatin, etc. can be used. Among them, the polymer gel is preferably polyacrylamide, gelatin, and agarose, and more preferably polyacrylamide and agarose.

[0100] Among the above, when using the catalyst layer in a single-layer structure as Figure 2 shown, from the viewpoints of easily supplying alkali metal ions to the intermediate generated by the carbon dioxide reduction reaction and suppressing detachment from the catalyst layer, the polymer material capable of releasing alkali metal ions preferably contains an ionomer, and more preferably contains a cation exchange resin.

[0101] Furthermore, from the viewpoints of more easily supplying alkali metal ions to the intermediate and further suppressing detachment from the catalyst layer, in the catalyst layer of the single-layer structure as Figure 2 shown, the "alkali metal ions and the polymer material capable of releasing alkali metal ions" preferably contains a cation exchange resin substituted with alkali metal ions. Specifically, the sulfonic group of the cation exchange resin can be exemplified by a form having an alkali metal ion as a counter ion.

[0102] By using a cation exchange resin substituted with alkali metal ions, cations can be supplied from the same resin to the catalytic active site during the electrolysis reaction, and the carbon dioxide reduction reaction is easily promoted.

[0103] The method of substituting the cation exchange resin with alkali metal ions is not particularly limited.

[0104] For example, after coating a solution obtained by dissolving a cation exchange resin in a solvent such as ethanol on a substrate and drying it, the substrate is immersed in an aqueous inorganic salt solution such as a carbonate or bicarbonate containing 0.01 to 5 mol / L of an alkali metal species. The aqueous inorganic salt solution impregnated with the substrate is placed in a reduced-pressure environment, the residual bubbles are removed, and then left standing for 1 hour or more, whereby the cation exchange resin can be subjected to metal ion substitution.

[0105] In addition, the catalyst layer is made into Figure 3When the laminated structure is as shown, the polymer material capable of releasing alkali metal ions contained in the cation supply layer preferably contains a polymer gel, and the "alkali metal ions and the polymer material capable of releasing alkali metal ions" preferably contain a polymer gel, and the polymer gel contains an aqueous solution containing an alkali metal salt. As the aqueous solution containing an alkali metal salt, an aqueous solution having the same composition as the electrolyte can be cited. Specifically, aqueous solutions of KHCO3, NaHCO3, Cs2CO3, etc. can be cited.

[0106] As the polymer material according to this embodiment in the cation supply layer, by using a polymer gel, the supply of alkali metal ions from the cation supply layer to the reaction layer can be smoothly performed, and the electrolysis efficiency can be improved.

[0107] In the catalyst layer of the laminated structure, the dispersion medium contained in the reaction layer is preferably an ionomer, and the catalyst is preferably covered with the ionomer. By covering the catalyst with the ionomer, it is easy to form an ion conduction channel between the covered catalyst and the solid electrolyte, and it is easy for the ions generated by the reaction to move, and the electrolysis efficiency can be improved.

[0108] The dispersion medium contained in the reaction layer is more preferably a cation exchange resin.

[0109] [Catalyst]

[0110] The catalyst according to the embodiment of the present application is not particularly limited as long as it is a catalyst that promotes the carbon dioxide reduction reaction. From the viewpoint of improving the electrolysis efficiency, it preferably contains one or more selected from the following catalyst A and the following catalyst B.

[0111] Here, catalyst A has a metal ion selected from copper ions, nickel ions, iron ions, cobalt ions, zinc ions, manganese ions, molybdenum ions, and aluminum ions, a nitrogen-containing compound, and a carbon-containing carrier.

[0112] Catalyst B has inorganic fine particles or a metal complex and has a carbon-containing carrier. The inorganic fine particles are selected from gold, silver, copper, nickel, iron, cobalt, zinc, chromium, palladium, tin, manganese, aluminum, indium, bismuth, molybdenum, and carbon nitride, and the metal complex is obtained by coordinating a ligand to a metal selected from copper, nickel, iron, cobalt, zinc, manganese, molybdenum, and aluminum or an ion of the metal.

[0113] In the catalyst A according to the embodiment of the present application, the component showing the catalytic action of the carbon dioxide reduction reaction is the above metal ion. However, in the technology of the present application, the constitution of a metal ion coordinated to a nitrogen atom of a nitrogen-containing compound and a carbon-containing carrier is called a "catalyst".

[0114] In the catalyst B described in the embodiments of the present application, the component that exhibits the catalytic action of the carbon dioxide reduction reaction is the above-mentioned inorganic fine particles or the above-mentioned metal complex. However, in the technology of the present application, the above-mentioned inorganic fine particles or the above-mentioned metal complex are referred to as "catalyst source", and the constitution having the catalyst source and the above-mentioned carbon-containing carrier is referred to as "catalyst".

[0115] [Catalyst source (metal ion) of catalyst A]

[0116] In the catalyst A described in this embodiment, as the catalyst source, it has metal ions selected from copper ions, nickel ions, iron ions, cobalt ions, zinc ions, manganese ions, molybdenum ions, and aluminum ions.

[0117] The metal ions in this embodiment have the function of generating at least carbon monoxide through the reduction reaction.

[0118] The metal ions exist in a single-atom state and are preferably supported on the carbon-containing carrier described in this embodiment. By making the catalyst source exist in a single-atom state, the activity can be improved.

[0119] In the case of carrying out the CO2 reduction reaction, gold and silver are widely used as the catalyst source. They are rare and expensive. Therefore, as an alternative to gold and silver catalysts, it is preferable that metal ions other than gold and silver are coordinated to nitrogen atoms and thus supported in the form of a carbon-containing monomer.

[0120] The metal of the metal ions in this embodiment is selected from copper, nickel, iron, cobalt, zinc, manganese, molybdenum, and aluminum.

[0121] Among the above, from the viewpoint of the reaction efficiency of the carbon dioxide reduction reaction, the metal of the metal ions is preferably nickel, cobalt, iron, copper, zinc, and manganese, more preferably nickel, cobalt, iron, and copper, and further preferably nickel, cobalt, and iron. The catalyst A described in this embodiment may contain only one kind of metal ion or may contain two or more kinds.

[0122] The upper limit of the content of the metal ions in catalyst A is not particularly limited. From the viewpoint of further increasing the active site density, it is preferably less than 50% by mass. From the same viewpoint, the content of the metal ions coordinated to the nitrogen atoms in catalyst A is more preferably 0.8 to 15% by mass, and further preferably 0.9 to 10% by mass.

[0123] It should be noted that in the present application, the active site density refers to the content (mass%) of the metal ions coordinated to the nitrogen atoms of the nitrogen-containing compound in catalyst A.

[0124] The content of the metal ions coordinated to the nitrogen atoms can be obtained by the following operation.

[0125] By X-ray absorption fine structure analysis (XAFS), it is possible to determine the content ratio of metal ions and metal fine particles bonded (coordinated) to nitrogen atoms in catalyst A.

[0126] In addition, the total metal content in the catalyst in which metal ions coordinated to nitrogen atoms and metal fine particles are included is measured by fluorescence X-ray analysis (XRF).

[0127] Based on the measurement results of XAFS and the measurement results of XRF, the content of metal ions coordinated to nitrogen atoms can be calculated.

[0128] For example, in the case of using Ni ions as a catalyst source, the content of Ni ions coordinated to nitrogen atoms can be calculated by multiplying the total Ni content including Ni metal and Ni ions measured by XRF by the ratio of Ni ions in all Ni obtained by XAFS.

[0129] It should be noted that metal fine particles do not form active sites and metal aggregation exists.

[0130] [Nitrogen-containing compound]

[0131] The nitrogen-containing compound contained in catalyst A is not particularly limited, and examples thereof include pentaethylenehexamine, tetraethylenepentamine, triethylenetetramine, diethylenetriamine, ethylenediamine, diethylamine, etc. From the viewpoint of improving the electrolytic activity, pentaethylenehexamine, tetraethylenepentamine, and triethylenetetramine are preferred, and pentaethylenehexamine and tetraethylenepentamine are more preferred.

[0132] From the viewpoint of increasing the density of active sites, the content of the nitrogen-containing compound in catalyst A according to the present embodiment is preferably 5 to 75% by mass, more preferably 10 to 60% by mass, and further preferably 20 to 50% by mass.

[0133] [Catalyst source of catalyst B (inorganic fine particles, metal complex)]

[0134] In catalyst B according to the present embodiment, as a catalyst source, it has inorganic fine particles or a metal complex.

[0135] The inorganic fine particles and metal complex in the present embodiment have the function of generating at least carbon monoxide through a reduction reaction.

[0136] (Inorganic fine particles)

[0137] The inorganic fine particles in the present embodiment are inorganic fine particles selected from gold, silver, copper, nickel, iron, cobalt, zinc, chromium, palladium, tin, manganese, aluminum, indium, bismuth, molybdenum, and carbon nitride, and one kind can be used alone, or two or more kinds can be used in combination.

[0138] Among these, from the viewpoint of the reaction efficiency of the carbon dioxide reduction reaction, the material of the inorganic fine particles is preferably silver, gold, zinc, tin, copper, and bismuth, more preferably silver, gold, copper, and tin, and still more preferably silver, gold, and copper.

[0139] From the viewpoint of the reaction rate of the carbon dioxide reduction reaction, the average particle diameter of the inorganic fine particles as the catalyst source is preferably 65 nm or less, preferably 60 nm or less, preferably 50 nm or less, preferably 40 nm or less, preferably 30 nm or less. In addition, the lower limit value of the average particle diameter is not limited, and from the aspect of ease of manufacture, it is preferably 1 nm or more, and more preferably 5 nm or more.

[0140] The aforementioned average particle diameter can be measured by photograph observation using a scanning electron microscope or the like.

[0141] (Metal complex)

[0142] The metal complex in the present embodiment is a metal complex obtained by coordinating a ligand to a metal or an ion of the metal. The metal here is selected from copper, nickel, iron, cobalt, zinc, manganese, molybdenum, and aluminum.

[0143] Among these, from the viewpoint of the reaction efficiency of the carbon dioxide reduction reaction, the metal is preferably nickel, cobalt, iron, copper, zinc, and manganese, more preferably nickel, cobalt, iron, and copper, and still more preferably nickel, cobalt, and iron. The metal complex may contain only one kind of metal or an ion of the metal, or may contain two or more kinds.

[0144] The type of the ligand is not particularly limited, and examples thereof include a phthalocyanine complex, a porphyrin complex, a pyridine complex, a covalently bonded triazine structure carrying a metal, a metal-organic structure, and the like. Among them, a phthalocyanine complex, a porphyrin complex, a pyridine complex, and a covalently bonded triazine structure carrying a metal are preferred, a phthalocyanine complex, a porphyrin complex, and a covalently bonded triazine structure carrying a metal are more preferred, and a porphyrin complex and a covalently bonded triazine structure carrying a metal are still more preferred. The metal complex may contain only one kind of ligand, or may contain two or more kinds.

[0145] [Carbon-containing carrier]

[0146] Catalyst A and catalyst B each independently contain a carbon-containing carrier.

[0147] Since carbon usually has conductivity, the carbon-containing carrier described in the present embodiment is a conductive carrier.

[0148] The carbon-containing carrier described in this embodiment is not limited as long as it is a conductive material that can be used as a gas diffusion layer in an electrode included in a device for reducing carbon dioxide, and examples thereof include carbon such as carbon black (furnace black, acetylene black, Ketjen black, medium thermal carbon black, etc.), activated carbon, graphite, carbon nanotubes, carbon nanofibers, carbon nanohorns, graphene nanoplatelets, and nanoporous carbon. Among them, from the viewpoint of increasing the density of active sites, carbon black is preferred.

[0149] From the viewpoints of increasing the density of active sites and increasing the current density, the primary particle size of the carbon black is preferably 10 to 100 nm, more preferably 10 to 50 nm. The primary particle size of the carbon black can be measured using a transmission electron microscope.

[0150] From the same viewpoints, the secondary particle size (aggregate particle size) of the carbon black is preferably small, and carbon black with a large amount of functional groups is preferred.

[0151] The carbon black can be a commercially available product, and examples thereof include Vulcan (registered trademark) XC-72 (manufactured by Cabot) and BLACKPEARL2000 (manufactured by Cabot Corporation).

[0152] The particle size of the catalyst (catalyst A, catalyst B) described in this embodiment is preferably 10 nm to 50 μm.

[0153] By making the particle size of the catalyst 50 μm or less, the density of active sites becomes high, and the reduction reaction rate of CO2 can be increased. In addition, by making the particle size of the catalyst 10 nm or more, precipitation of salts of the electrolyte from the solid electrolyte can be suppressed, and the workability is excellent.

[0154] From the viewpoint of further increasing the density of active sites and the viewpoint that the catalyst is easily uniformly dispersed in the ionomer in the reaction layer of the single-layer catalyst layer or the laminated catalyst layer, the particle size of the catalyst is preferably 20 nm to 40 μm, more preferably 30 nm to 20 μm.

[0155] The particle size of the catalyst can be confirmed using a laser diffraction / scattering particle size distribution measuring device.

[0156] [Manufacturing method of catalyst]

[0157] The manufacturing method of the catalyst described in this embodiment is not particularly limited.

[0158] Examples of the method for manufacturing catalyst A include the method for manufacturing the following catalyst, which has: a mixing step of mixing metal ions, a nitrogen-containing compound, and a carbon-containing carrier to obtain a mixture; and a calcination step of calcining the obtained mixture to obtain a calcined product. The method for manufacturing catalyst A may further have a cleaning step of cleaning the calcined product, a pulverization step of pulverizing the calcined product, and the like.

[0159] In addition, catalyst B can be manufactured by supporting inorganic fine particles and metal complexes as catalyst sources on a carbon-containing carrier by known methods such as vapor deposition, precipitation, adsorption, stacking, bonding, welding, physical mixing, and spraying.

[0160] <Cathode>

[0161] The cathode (negative electrode) described in this embodiment has the catalyst layer for carbon dioxide reduction electrode and the gas diffusion layer described in this embodiment.

[0162] The cathode (negative electrode) described in this embodiment has high electrolysis efficiency by having the catalyst layer described in this embodiment.

[0163] 〔Gas diffusion layer〕

[0164] The gas diffusion layer contains, for example, carbon paper, non-woven fabric, or metal mesh. Examples include graphite carbon, vitreous carbon, titanium, SUS steel, and the like.

[0165] <Ion exchange membrane-electrode assembly>

[0166] The ion exchange membrane-electrode assembly described in this embodiment has the cathode, solid electrolyte, and anode described in this embodiment.

[0167] The ion exchange membrane-electrode assembly described in this embodiment includes a cathode containing the catalyst layer described in this embodiment, and thus has high electrolysis efficiency.

[0168] 〔Solid electrolyte〕

[0169] The ion exchange membrane-electrode assembly described in this embodiment has a solid electrolyte.

[0170] A polymer membrane can be used as the solid electrolyte. Various ionomers can be used as the polymer, which can be a cation exchange resin or an anion exchange resin, and preferably an anion exchange resin. That is, the solid electrolyte is preferably an anion exchange membrane.

[0171] Commercially available products can be used as the solid electrolyte as a cation exchange membrane or an anion exchange membrane.

[0172] In addition, when an anion exchange membrane is used as the solid electrolyte, the base point density is preferably 0.5 to 5.0 mmol / 3 and more preferably 2.5 mmol / 3 or more and less than 4.5 mmol / 3 and further preferably 2.9 mmol / 3 or more and less than 4.5 mmol / 3 .

[0173] As the cation exchange membrane, for example, a strongly acidic cation exchange membrane obtained by introducing a sulfo group into a fluororesin matrix, Nafion 117, Nafion 115, Nafion 212, Nafion 350 (manufactured by Chemrous); a strongly acidic cation exchange membrane obtained by introducing a sulfo group into a styrene-divinylbenzene copolymer matrix, NEOCEPTA CSE (manufactured by ASTOM), etc. can be used.

[0174] As the anion exchange membrane, for example, an anion exchange membrane having one or more ion exchange groups selected from a quaternary ammonium group, a primary amino group, a secondary amino group, and a tertiary amino group can be mentioned. Specifically, for example, NEOCEPTA (registered trademark) ASE, AHA, ACS, AFX (manufactured by ASTOM), SELEMION (registered trademark) AMVN, DSVN, AAV, ASVN, AHO (manufactured by Asahi Glass), etc. can be mentioned.

[0175] Regarding the reduction reaction of carbon dioxide, the reduction reaction in the cathode (cathode) according to the present embodiment varies depending on the type of solid electrolyte. When using a cation exchange membrane as the solid electrolyte, the reduction reactions represented by the following reaction formulas (1) and (2) occur. When using an anion exchange membrane as the solid electrolyte, the reduction reactions represented by the following reaction formulas (3) and (4) occur.

[0176] CO2 + 2H - + 2e - → CO + H2O (1)

[0177] 2H + + 2e - → H2 (2)

[0178] H2O + CO2 + 2e - → CO + 2OH - (3)

[0179] 2H2O + 2e - → H2 + 2OH - (4)

[0180] [Anode]

[0181] The oxidation reaction in the anode varies depending on the type of solid electrolyte. In the case of using a cation exchange membrane as the solid electrolyte, the oxidation reaction represented by the following reaction formula (5) occurs. In the case of using an anion exchange membrane as the solid electrolyte, the oxidation reaction represented by the following reaction formula (6) occurs.

[0182] 2H2O → O2 + 4H + + 4e - (5)

[0183] 4OH - → O2 + 2H2O + 4e - (6)

[0184] The anode is a gas diffusion electrode including a gas diffusion layer.

[0185] The gas diffusion layer includes, for example, a metal mesh. Examples of the electrode material of the anode include Ir, IrO2, Ru, RuO2, Co, CoOx, Cu, CuOx, Fe, FeOx, FeOOH, FeMn, Ni, NiOx, NiOOH, NiCo, NiCe, NiC, NiFe, NiCeCoCe, NiLa, NiMoFe, NiSn, NiZn, SUS, Au, Pt.

[0186] <Solid electrolyte type electrolysis device>

[0187] The solid electrolyte type electrolysis device described in this embodiment has: the cathode described in this embodiment, an anode that forms a pair of electrodes with the cathode, a solid electrolyte interposed in a contact state between the cathode and the anode, and a voltage application unit that applies a voltage between the cathode and the anode.

[0188] The solid electrolyte type electrolysis device described in this embodiment includes a cathode (cathode) including the catalyst layer described in this embodiment, and thus has high electrolysis efficiency.

[0189] Figure 4 It is a schematic diagram of a solid electrolyte type electrolysis device suitable for use in this embodiment.

[0190] Figure 4 The following solid electrolyte type electrolysis device 800 is shown in, which has: the cathode (cathode) 200 described in this embodiment, an anode (anode) 400 that forms a pair of electrodes with the cathode 200, a solid electrolyte 300 interposed in a contact state between the cathode 200 and the anode 400, and a voltage application unit 700 that applies a voltage between the cathode 200 and the anode 400.

[0191] Figure 4 The solid electrolyte type electrolysis device 800 shown also has a cathode current collector plate 100, an anode current collector plate 500, and an electrolytic solution 600.

[0192] The cathode described in the above-described embodiment is used as cathode 200. In addition, solid electrolyte 300 is the same as the solid electrolyte 30 in Figure 1 , and solid electrolyte 300 is preferably an anion exchange membrane. Anode 400 is the same as the anode 40 in Figure 1 .

[0193] Details of cathode 200, solid electrolyte 300, and anode 400 are as described above.

[0194] Hereinafter, for each element other than cathode 200, solid electrolyte 300, and anode 400, description will be made without symbols.

[0195] 〔Cathode current collector〕

[0196] As the cathode current collector (cathode current collector), for example, metal materials such as copper (Cu), nickel (Ni), stainless steel (SUS), nickel-plated steel, and brass can be cited. Among them, from the viewpoints of ease of processing and cost, copper is preferred. Regarding the shape of the cathode current collector, in the case where the material is a metal material, for example, metal foil, metal plate, metal thin film, expanded metal, perforated metal, and foamed metal can be cited.

[0197] The cathode current collector may be provided with a gas supply hole for supplying a raw material gas containing carbon dioxide to the cathode and a gas recovery hole for recovering the generated gas containing carbon monoxide. By having the gas supply hole and the gas recovery hole, the raw material gas can be uniformly and efficiently fed to the cathode, and the generated gas (including unreacted raw material gas) can be discharged. The gas supply hole and the gas recovery hole may each independently have only one or two or more. In addition, the shape, position, size, etc. of the gas supply hole and the gas recovery hole are not limited and can be appropriately set. And, when the cathode current collector has air permeability, the gas supply hole and the gas recovery hole are not necessarily required.

[0198] It should be noted that when the cathode has the function of conducting electrons, the cathode current collector is not necessarily required.

[0199] 〔Anode current collector〕

[0200] In order to receive electrons from the anode, the anode current collector (anode current collector) is preferably made of a metal material such as titanium (Ti), copper (Cu), nickel (Ni), stainless steel (SUS), nickel-plated steel, or brass, which has conductivity and also has the rigidity to support the anode. From this viewpoint, the anode current collector can be suitably made of such metal materials.

[0201] The anode current collector plate may be provided with a gas flow path for feeding a raw material gas (such as H2O) to the anode. By providing the anode current collector plate with a gas flow path, it is possible to uniformly and efficiently feed the raw material gas to the anode. It should be noted that the number, shape, position, size, etc. of the gas flow paths are not limited and can be set appropriately.

[0202] [[Voltage application unit]]

[0203] The voltage application unit functions to apply a voltage between the cathode and the anode by applying a voltage to the cathode current collector plate and the anode current collector plate. Here, since the two current collector plates are conductors, electrons are supplied to the cathode, and on the other hand, electrons are received from the anode. In addition, in order to apply an appropriate voltage, the voltage application unit may be electrically connected to a control unit (not shown).

[0204] [[Electrolyte]]

[0205] Examples of the electrolyte include pure water, an aqueous solution of an electrolyte, etc. Examples of the aqueous solution of an electrolyte include an aqueous carbonate solution, an aqueous bicarbonate solution (such as an aqueous KHCO3 solution), an aqueous sulfate solution, an aqueous borate solution, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous sodium chloride solution, etc.

[0206] The liquidity of the aqueous solution is preferably pH 5 or more.

[0207] Generally, if pure water is used as the electrolyte, it is impossible to stably supply alkali metal ions to the intermediate generated by the carbon dioxide reduction reaction, so the electrolysis efficiency is reduced. However, the solid electrolyte type electrolysis device according to the present embodiment is provided with the catalyst layer according to the present embodiment. Therefore, even if pure water is used as the electrolyte, it is possible to stably supply alkali metal ions to the intermediate generated by the carbon dioxide reduction reaction, and the electrolysis efficiency can be improved.

[0208] From the viewpoint of suppressing salt precipitation, the concentration of the above-mentioned electrolytes such as carbonates and bicarbonates in the electrolyte is preferably less than 0.1 mol / L.

[0209] In addition, from the viewpoint of further suppressing the precipitation of alkali metal salts in the form of salts near the cathode, the solid electrolyte type electrolysis device preferably has an electrolyte in contact with the anode, and the electrolyte is pure water.

[0210] (Reaction gas supply unit)

[0211] In the solid electrolyte type electrolysis device according to the present embodiment, a reaction gas supply unit (not shown) may be provided outside the solid electrolyte type electrolysis device. That is, as long as CO2 as a reaction gas is supplied to the catalyst layer provided on the cathode, the reaction gas can be supplied from the reaction gas supply unit to the gas supply hole through pipes (not shown), or it can be arranged to blow the reaction gas to the surface of the cathode current collector plate on the side opposite to the surface in contact with the cathode. In addition, from an environmental perspective, the reaction gas is preferably the factory exhaust gas discharged from factories.

[0212] [CO Generation Method]

[0213] Next, a CO generation method using the solid electrolyte type electrolysis device according to the present embodiment will be described.

[0214] First, a reaction gas as a raw material, that is, CO2, is supplied to the solid electrolyte type electrolysis device in a gas phase state by a reaction gas supply unit (not shown). At this time, CO2 is supplied to the cathode through, for example, the gas supply holes provided in the cathode current collector plate.

[0215] Next, the CO2 supplied to the cathode passes through the catalyst layer of the cathode. Thus, in the case where a cation exchange membrane is used as the solid electrolyte, the reduction reactions of the above reaction formulas (1) and (2) occur, and in the case where an anion exchange membrane is used as the solid electrolyte, the reduction reactions of the above reaction formulas (3) and (4) occur, thereby generating a synthesis gas containing at least CO and H2.

[0216] Next, the generated synthesis gas containing CO and H2 is sent to a gas recovery device (not shown) through, for example, the gas recovery holes provided in the cathode current collector plate, and recovered according to the specified gases respectively.

[0217] Examples

[0218] Next, the technology of the present application will be specifically described using examples, but the technology of the present application is not limited to these examples at all.

[0219] <1. Evaluation of a Solid Electrolyte Type Electrolysis Device with a Single - Layer Catalyst Layer>

[0220] [Example 1]

[0221] [Manufacture of Catalyst]

[0222] In a beaker, 0.4 g of carbon black (carbon-containing support described in this embodiment) with a primary particle size of 30 nm, 1.1 mmol of pentaethylenehexamine, and 0.7 mmol of nickel(II) chloride hexahydrate were mixed into 15 mL of ethanol to obtain an ethanol dispersion. After irradiating the obtained ethanol dispersion with ultrasonic waves for 10 minutes, the ethanol dispersion was heated and dried to evaporate ethanol, obtaining a mixture. Using a calcination furnace, the obtained mixture was heated in an inert gas at 900 °C for 10 seconds or more for calcination. Thereafter, the product was washed with an aqueous sulfuric acid solution, and the solid was recovered using a suction filter. Further, the solid was vacuum-dried at 60 °C overnight to obtain a catalyst powder (intermediate) supporting a Ni complex.

[0223] It should be noted that the primary particle size of carbon black was determined by laser diffraction particle size distribution measurement.

[0224] Furthermore, 0.3 g of the obtained catalyst powder, 10 g of zirconia balls with a diameter of 0.5 mm, and 10 mL of water were put into a pot together, and using a planetary ball mill device, they were pulverized at a rotation speed of 800 rpm for 20 minutes, and the catalyst slurry was recovered. The slurry was washed again with an aqueous sulfuric acid solution, the solid was recovered using a suction filter, and the solid was vacuum-dried at 60 °C overnight to obtain the final catalyst powder (catalyst A described in this embodiment).

[0225] [Manufacture of cathode]

[0226] 22 mg of the obtained catalyst powder was dispersed in ethanol, and 3 mg of "Nafion (registered trademark)" (cation exchange resin) manufactured by Chemours Company, which is used as a binder, was mixed into the dispersion. After mixing, the dispersion was irradiated with ultrasonic waves for 10 minutes, and the dispersion was left standing in a vacuum chamber under a reduced pressure environment of 10 kPa (absolute pressure) for 10 minutes. Using a spray coater, the dispersion was coated on a carbon paper (gas diffusion layer) in such a manner that the loading amount at the time of drying became 2 - 3 mg / cm 2 to form a cathode precursor.

[0227] [Substitution of alkali metal ions]

[0228] The cathode precursor was immersed in a 2 mol / L aqueous potassium bicarbonate solution. In the state where the cathode precursor was immersed, the aqueous solution was left standing in a vacuum chamber under a reduced pressure environment of 10 kPa (absolute pressure) for 10 minutes to remove residual bubbles inside the cathode precursor. Thereafter, it was left standing for 12 hours or more to perform metal ion substitution on the cation exchange resin, obtaining a cathode (cathode) having a catalyst layer with a single-layer structure containing a cation exchange resin substituted with an alkali metal ion. In the cathode, a coating film of the dispersion serves as the catalyst layer, and the carbon paper serves as the gas diffusion layer.

[0229] [Manufacture of Solid Electrolyte-Type Electrolytic Device]

[0230] An ion-exchange membrane using a fluororesin having an aromatic ring in the main chain and a quaternary ammonium group bonded to the main chain as a side chain (the base point density is 2.8 mmol / 3 ) as a base material, and a carbon anode supporting iridium oxide (manufactured by Dioxide Materials Co., Ltd.) are pasted on the above-mentioned cathode to form an ion-exchange membrane-electrode assembly.

[0231] A structure is formed in which the anode (positive electrode) is in contact with the electrolyte solution tank, and the electrolyte solution is set to pure water.

[0232] 〔Example 2〕

[0233] In the manufacture of the solid electrolyte-type electrolytic device of Example 1, the electrolyte solution was set to a 0.01 mol / L aqueous solution of KHCO3, and except for this, the same operations as in Example 1 were performed to manufacture the solid electrolyte-type electrolytic device of Example 2.

[0234] 〔Example 3〕

[0235] In the manufacture of the solid electrolyte-type electrolytic device of Example 1, instead of the aqueous potassium bicarbonate solution, the cathode precursor was immersed in a 2 mol / L aqueous solution of rubidium carbonate, and except for this, the same operations as in Example 1 were performed to manufacture the solid electrolyte-type electrolytic device of Example 3.

[0236] 〔Example 4〕

[0237] In the manufacture of the solid electrolyte-type electrolytic device of Example 1, the electrolyte solution was set to a 0.1 mol / L aqueous solution of KHCO3, and except for this, the same operations as in Example 1 were performed to manufacture the solid electrolyte-type electrolytic device of Example 4.

[0238] 〔Comparative Example 1〕

[0239] In the manufacture of the solid electrolyte-type electrolytic device of Example 1, for the cathode precursor, no substitution of alkali metal ions was performed, and the cathode precursor was used as the cathode. Except for this, the same operations as in Example 1 were performed to manufacture the solid electrolyte-type electrolytic device of Comparative Example 1.

[0240] 〔Comparative Example 2〕

[0241] In the manufacture of the solid electrolyte-type electrolytic device of Comparative Example 1, the electrolyte solution was set to a 0.01 mol / L aqueous solution of KHCO3, and except for this, the same operations as in Comparative Example 1 were performed to manufacture the solid electrolyte-type electrolytic device of Comparative Example 2.

[0242] 〔Example 5〕

[0243] [Manufacture of Catalyst]

[0244] In a beaker, 0.1 g of carbon black (carbon-containing carrier described in this embodiment) with a primary particle size of 30 nm was mixed into 100 mL of ethanol, and the resulting ethanol dispersion was irradiated with ultrasonic waves for 10 minutes. Subsequently, the dispersion was left standing in a vacuum chamber under a reduced pressure environment of 10 kPa (absolute pressure) for 10 minutes. Then, 11.7 mL of a 0.1 mol / L AgNO3 solution and 1 mL of a 2.3 mol / L sodium hypophosphite solution were mixed and stirred at 15 °C for 16 hours to reduce silver nitrate. After the reaction ended, the resulting slurry was washed with distilled water, and the solid was recovered using a centrifuge. The solid was vacuum-dried at 60 °C overnight to obtain a catalyst powder (catalyst B described in this embodiment) supporting Ag particles.

[0245] The resulting catalyst is carbon black supporting Ag particles as a catalyst source. With respect to 100 parts by mass of carbon black not supporting Ag particles, the mass of the supported Ag particles is 40 parts by mass.

[0246] It should be noted that the primary particle size of carbon black is determined by laser diffraction particle size distribution measurement.

[0247] [Manufacture of cathode]

[0248] 43 mg of the resulting catalyst powder was dispersed in ethanol, and 6 mg of "Nafion (registered trademark)" (cation exchange resin) manufactured by Chemours Company was mixed into the dispersion as a binder. After mixing, the dispersion was irradiated with ultrasonic waves for 10 minutes and exposed in a vacuum chamber under a reduced pressure environment of 10 kPa (absolute pressure) for 10 minutes. Using a spray coater, the dispersion was coated on a carbon paper (gas diffusion layer) such that the loading amount upon drying became 2 - 3 mg / cm 2 to form a cathode precursor.

[0249] [Substitution of alkali metal ions]

[0250] The cathode precursor was immersed in a 2 mol / L aqueous potassium bicarbonate solution. In the state where the cathode precursor was immersed, the aqueous solution was left standing in a vacuum chamber under a reduced pressure environment of 10 kPa (absolute pressure) for 10 minutes to remove residual bubbles inside the cathode precursor. Subsequently, it was left standing for 12 hours or more to perform metal ion substitution on the cation exchange resin, obtaining a cathode (cathode) having a single-layer structure catalyst layer containing a cation exchange resin substituted with alkali metal ions. In the cathode, a coated film of the dispersion serves as the catalyst layer, and the carbon paper serves as the gas diffusion layer.

[0251] [Manufacture of solid electrolyte type electrolytic device]

[0252] On the above-mentioned cathode, a fluororesin having an aromatic ring in the main chain and a quaternary ammonium group bonded to the main chain as a side chain (the base point density is 2.8 mmol / 3 ) is pasted as a substrate for the ion exchange membrane, and a carbon anode supporting iridium oxide (manufactured by Dioxide Materials) is used to fabricate an ion exchange membrane-electrode assembly.

[0253] A structure is formed in which the anode (positive electrode) is in contact with the electrolyte tank, and pure water is used as the electrolyte.

[0254] [Comparative Example 3]

[0255] In the manufacture of the solid electrolyte type electrolytic device of Example 5, for the cathode precursor, alkali metal ion substitution was not performed, and the cathode precursor was used as the cathode. Except for this, the same operations as in Example 5 were carried out to manufacture the solid electrolyte type electrolytic device of Comparative Example 3.

[0256] [Evaluation Method of Solid Electrolyte Type Electrolytic Device]

[0257] Using the solid electrolyte type electrolytic devices of Examples 1 to 5 and Comparative Examples 1 to 3, pure CO2 was supplied to the cathode. Under the condition that the battery cell was heated to 90 °C, the applied potential of the cathode was set to -2.6 V with respect to the anode, and CO2 was electrolyzed to measure the CO generation current density [mA / cm 2 and the CO selectivity [%] when CO was generated. In addition, the precipitation of salt near the cathode was visually confirmed.

[0258] The results are shown in Tables 1 to 3.

[0259] It should be noted that the results of the systems with the catalyst type of Ni and pure water as the electrolyte (Examples 1, 3, and Comparative Example 1) are shown in Table 1, the results of the systems with the catalyst type of Ni and potassium bicarbonate aqueous solution as the electrolyte (Examples 2, 4, and Comparative Example 2) are shown in Table 2, and the results of the systems with the catalyst type of Ag and pure water as the electrolyte (Example 5 and Comparative Example 3) are shown in Table 3.

[0260] [Table 1]

[0261] Table 1

[0262]

[0263] According to Table 1, it can be seen that when alkali metal ion substitution is not performed on the cation exchange resin and the catalyst layer does not contain alkali metal ions (Comparative Example 1), the CO selectivity is 0%, and the CO generation current density is 1 mA / cm 2 or less.

[0264] On the other hand, it can be seen that when K + or Rb+ When a substituted cation exchange resin is used as the "alkali metal ion and polymer material capable of releasing alkali metal ions" in the catalyst layer (Examples 1 and 3), a significant CO selectivity is confirmed even under pure water conditions, and the electrolysis efficiency is high.

[0265] [Table 2]

[0266] Table 2

[0267]

[0268] As can be seen from Table 2, when the electrolyte is an aqueous potassium bicarbonate solution, the CO selectivity increases in both the system where the catalyst layer does not contain alkali metal ions (Comparative Example 2) and the system containing alkali metal ions (Examples 2 and 4). However, in the system where the catalyst layer does not contain alkali metal ions (Comparative Example 2), the CO production current density becomes low and the electrolysis efficiency is poor.

[0269] [Table 3]

[0270] Table 3

[0271]

[0272] The results shown in Table 3 are the same as the tendency in Table 1. Even when the catalyst type is Ag, without subjecting the cation exchange resin to alkali metal ion substitution and in the case where the catalyst layer does not contain alkali metal ions (Comparative Example 3), the CO selectivity is 10% and the CO production current density is as low as 1 mA / cm 2 .

[0273] On the other hand, it can be seen that when the cation exchange resin substituted with K + is used as the "alkali metal ion and polymer material capable of releasing alkali metal ions" in the catalyst layer (Example 5), compared with Comparative Example 3, the CO selectivity is high, the CO production current density also increases, and the electrolysis efficiency is high.

[0274] <2. Evaluation of a solid electrolyte type electrolysis device having a catalyst layer with a laminated structure>

[0275] [Example 6]

[0276] [Manufacture of the cathode]

[0277] To an aqueous agarose solution heated to 90 °C at a concentration of 0.2 g / L, potassium bicarbonate was mixed so that the concentration became 0.5 mol / L, and then it was cooled to obtain a gel-like solid. The obtained solid was pulverized with an agate mortar and coated on the side surface of the dispersion-coated film of the cathode precursor manufactured in Example 1 at a loading amount of 50 mg / cm 2 to form a gel-coated film, thereby fabricating a cathode (cathode).

[0278] In the cathode, a dispersion-coated film of a cathode precursor serves as a reaction layer in the catalyst layer, a gel-coated film serves as a cation supply layer in the catalyst layer, and carbon paper serves as a gas diffusion layer.

[0279] [Manufacture of Solid Polymer Electrolyte Electrolytic Device]

[0280] On the above cathode, a fluororesin having an aromatic ring in the main chain and a quaternary ammonium group bonded to the main chain as a side chain (the base point density is 2.8 mmol / 3 ) is pasted as a substrate ion exchange membrane, and a carbon anode supporting iridium oxide (manufactured by Dioxide Materials Co., Ltd.) is used to form an ion exchange membrane-electrode assembly.

[0281] A structure is formed in which the anode is in contact with the electrolyte tank, and pure water is used as the electrolyte.

[0282] [Example 7]

[0283] In the manufacturing process of the solid polymer electrolyte electrolytic device of Example 6, in the formation of the gel-coated film, potassium hydrogencarbonate is changed to sodium hydrogencarbonate, and otherwise, the same operations as in Example 6 are performed to manufacture the solid polymer electrolyte electrolytic device of Example 7.

[0284] [Example 8]

[0285] In the manufacturing process of the solid polymer electrolyte electrolytic device of Example 6, in the formation of the gel-coated film, potassium hydrogencarbonate is changed to cesium carbonate, and otherwise, the same operations as in Example 6 are performed to manufacture the solid polymer electrolyte electrolytic device of Example 8.

[0286] [Comparative Example 4]

[0287] In the manufacture of the solid polymer electrolyte electrolytic device of Example 6, potassium hydrogencarbonate used for forming the gel-coated film is not mixed, and otherwise, the same operations as in Example 6 are performed to manufacture the solid polymer electrolyte electrolytic device of Comparative Example 4.

[0288] [Example 9]

[0289] [Manufacture of Cathode]

[0290] In a beaker, 0.1 g of carbon black (carbon-containing carrier described in this embodiment) with a primary particle size of 30 nm was mixed into 100 mL of ethanol, and the resulting ethanol dispersion was irradiated with ultrasonic waves for 10 minutes. Thereafter, the dispersion was allowed to stand in a vacuum chamber under a reduced pressure environment of 10 kPa (absolute pressure) for 10 minutes. Thereafter, 11.7 mL of a 0.1 mol / L AgNO3 solution and 1 mL of a 2.3 mol / L sodium hypophosphite solution were mixed and stirred at 15 °C for 16 hours to reduce silver nitrate. After the reaction was completed, the resulting slurry was washed with distilled water, and the solid was recovered using a centrifuge. The solid was vacuum-dried at 60 °C overnight to obtain a catalyst powder (catalyst B described in this embodiment) supporting Ag particles.

[0291] The resulting catalyst is carbon black supporting Ag particles as a catalyst source. With respect to 100 parts by mass of carbon black not supporting Ag particles, the mass of the supported Ag particles is 40 parts by mass.

[0292] It should be noted that the primary particle size of carbon black is determined by laser diffraction particle size distribution measurement.

[0293] 43 mg of the resulting catalyst powder was dispersed in ethanol, and 12 mg of an anion exchange resin [XC-1 (manufactured by Dioxide Materials)] as a binder was mixed into the dispersion. After mixing, the dispersion was irradiated with ultrasonic waves for 10 minutes and exposed in a vacuum chamber under a reduced pressure environment of 10 kPa (absolute pressure) for 10 minutes. Using a spray coater, the dispersion was coated on a carbon paper (gas diffusion layer) such that the loading amount in the dried state became 2 - 3 mg / cm 2 to form a cathode precursor.

[0294] Cesium carbonate salt was mixed into an aqueous agarose solution heated to 90 °C to a concentration of 0.5 mol / L, and then cooled to obtain a gel-like solid. The resulting solid was pulverized using an agate mortar and coated on the side surface of the dispersion-coated film of the manufactured cathode precursor at a loading amount of 50 mg / cm 2 to form a gel-coated film, thereby fabricating a cathode (the cathode).

[0295] In the cathode (the cathode), the dispersion-coated film of the cathode precursor serves as the reaction layer in the catalyst layer, the gel-coated film serves as the cation supply layer in the catalyst layer, and the carbon paper serves as the gas diffusion layer.

[0296] [Manufacture of Solid Oxide Electrolysis Device]

[0297] On the above cathode, an ion exchange membrane (manufactured by DioxideMaterials, trade name "X37-50grade60", which is a polystyrene-based main chain with imidazolium-based ion exchange groups in the side chain) and a carbon anode supporting iridium oxide (manufactured by DioxideMaterials) were pasted to form an ion exchange membrane-electrode assembly.

[0298] A structure was made in which the anode (positive electrode) was in contact with the electrolyte tank, and pure water was used as the electrolyte.

[0299] [Comparative Example 5]

[0300] In the manufacturing process of the solid electrolyte type electrolytic device of Example 9, cesium carbonate salt was not mixed in the formation of the gel coating film. Otherwise, the same operations as in Example 9 were carried out to manufacture the solid electrolyte type electrolytic device of Comparative Example 5.

[0301] [Evaluation Method of Solid Electrolyte Type Electrolytic Device]

[0302] Using the solid electrolyte type electrolytic devices of Examples 6 to 9 and Comparative Examples 4 to 5, pure CO2 was supplied to the cathode. Under the condition that the battery unit was heated to 90 °C, the applied potential of the cathode was set to -2.6 V relative to the anode, and CO2 was electrolyzed to measure the CO generation current density [mA / cm 2 and the CO selectivity [%] when CO was generated. In addition, the precipitation of salt near the cathode was visually confirmed.

[0303] The results are shown in Tables 4 to 5.

[0304] It should be noted that the results of the systems with the catalyst type of Ni (Examples 6 to 8 and Comparative Example 4) are shown in Table 4, and the results of the systems with the catalyst type of Ag (Example 9 and Comparative Example 5) are shown in Table 5.

[0305] [Table 4]

[0306] Table 4

[0307]

[0308] From Table 4, it can be confirmed that even if the reaction layer in the catalyst layer does not contain alkali metal ions, by laminating a cation supply layer containing alkali metal ions on the reaction layer, a high CO selectivity of 70% or more can be obtained when pure water is used as the electrolyte. In addition, it can be seen that regarding the CO generation current density, Examples 6 to 8 are also higher than Comparative Example 4, and the electrolysis efficiency is excellent.

[0309] [Table 5]

[0310] Table 5

[0311]

[0312] As can be seen from Table 5, even when using an Ag catalyst, a high CO selectivity was also confirmed. In addition, in this experiment where an anion exchange resin was used as the dispersion medium of the reaction layer in the catalyst layer, that is, the ionomer, an effect was also confirmed. Therefore, it can be confirmed that the cation supply is directly from the cation supply layer, rather than from the cation exchange resin.

[0313] Industrial applicability

[0314] According to this embodiment, for a solid electrolyte type electrolysis device, by using, for example, CO2 gas emitted from a factory as a raw material and utilizing renewable energy such as a solar cell facing the voltage application unit, a synthesis gas containing at least CO and H2 based on a desired production ratio can be generated. The synthesis gas generated by such operation can generate fuel base materials, chemical raw materials, etc. through methods such as Fischer-Tropsch synthesis and methanation.

[0315] Explanation of reference numerals

[0316] 10 Gas diffusion layer

[0317] 20 Catalyst layer for carbon dioxide reduction electrode

[0318] 21 Reaction layer

[0319] 22 Layer containing alkali metal ions and polymer material (cation supply layer)

[0320] 23 Catalyst

[0321] 24 Alkali metal ions and polymer material

[0322] 30 Solid electrolyte (ion exchange membrane)

[0323] 40 Anode

[0324] 50 Ion exchange membrane-electrode assembly

[0325] 100 Cathode current collector

[0326] 200 Cathode

[0327] 300 Solid electrolyte (ion exchange membrane)

[0328] 400 Anode

[0329] 500 Anode current collector

[0330] 600 Electrolyte solution

[0331] 700 Voltage application unit

[0332] 800 Solid electrolyte type electrolytic device

Claims

1. A catalyst layer for a carbon dioxide reduction electrode, comprising: a catalyst, an alkali metal ion, and a polymer material capable of releasing the alkali metal ion.

2. The catalyst layer for a carbon dioxide reduction electrode according to claim 1, wherein, The catalyst and the alkali metal ions are dispersed in a polymer material capable of releasing the alkali metal ions to form a single entity.

3. The catalyst layer for a carbon dioxide reduction electrode according to claim 1, wherein, The catalyst layer for the carbon dioxide reduction electrode has a reaction layer containing the catalyst and a layer containing the alkali metal ions and a polymer material capable of releasing the alkali metal ions.

4. The catalyst layer for a carbon dioxide reduction electrode according to claim 3, wherein, The reaction layer containing the catalyst and the layer containing the alkali metal ions and the polymer material capable of releasing the alkali metal ions are provided integrally.

5. The catalyst layer for a carbon dioxide reduction electrode according to claim 1 or 2, wherein, The polymer material capable of releasing the alkali metal ions contains a cation exchange resin.

6. The catalyst layer for a carbon dioxide reduction electrode according to any one of claims 1, 3 or 4, wherein, The polymer material capable of releasing the alkali metal ions contains a polymer gel.

7. The catalyst layer for a carbon dioxide reduction electrode according to any one of claims 1 to 6, wherein, The catalyst contains one or more selected from catalyst A and catalyst B. Catalyst A has metal ions selected from copper ions, nickel ions, iron ions, cobalt ions, zinc ions, manganese ions, molybdenum ions, and aluminum ions, a nitrogen-containing compound, and a carbon-containing carrier. Catalyst B has inorganic fine particles or a metal complex and has a carbon-containing carrier. The inorganic fine particles are selected from gold, silver, copper, nickel, iron, cobalt, zinc, chromium, palladium, tin, manganese, aluminum, indium, bismuth, molybdenum, and carbon nitride. The metal complex is obtained by coordinating a ligand to a metal selected from copper, nickel, iron, cobalt, zinc, manganese, molybdenum, and aluminum or an ion of the metal.

8. A cathode having the catalyst layer for a carbon dioxide reduction electrode according to any one of claims 1 to 7 and a gas diffusion layer.

9. An ion exchange membrane-electrode assembly having the cathode according to claim 8, a solid electrolyte, and an anode.

10. The ion exchange membrane-electrode assembly according to claim 9, wherein, The solid electrolyte is an anion exchange membrane.

11. A solid electrolyte type electrolysis device having: The cathode according to claim 8; An anode forming a pair of electrodes with the cathode; A solid electrolyte interposed in a contact state between the cathode and the anode; and A voltage application unit for applying a voltage between the cathode and the anode.

12. The solid electrolyte type electrolysis device according to claim 11, further having an electrolytic solution in contact with the anode, and the electrolytic solution is pure water.

13. The solid electrolyte type electrolysis device according to claim 11 or 12, wherein, The solid electrolyte is an anion exchange membrane.

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