Gas diffusion electrode

Abstract

To improve the reaction rate by controlling an ammonium ion produced by an objective ammonia and a proton supplied to a cathode in the ammonia electrolysis synthesis at the cathode and a cathode catalyst layer.SOLUTION: There is provided a gas diffusion electrode that is integrated with a catalyst layer using a material selected from the group of materials for the cathode catalyst layer. Examples of the material for the cathode catalyst layer include a sintered body.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a gas diffusion electrode for electrolytic synthesis in which a gas diffusion layer and a catalyst layer are integrated, as well as a membrane electrode assembly including the gas diffusion electrode and a production apparatus for electrochemically synthesizing ammonia. [Background technology]

[0002] It is expected that the supply of renewable energy will expand worldwide in the future, and green ammonia derived from renewable energy will become mainstream, so it is expected that the supply price of green ammonia will decrease due to the supply price of renewable energy and the efficiency of production methods. Until now, ammonia has been produced by electrolyzing water using water electrolysis technology to produce hydrogen, and then using the Haber-Bosch process (abbreviated as HB process), but in the future, electrolytic synthesis technology that produces ammonia directly from water will be required as a discontinuous technology that simplifies the conventional production method.

[0003] A method and apparatus for producing ammonia have been reported in which ammonia is electrochemically synthesized from nitrogen gas and water as raw materials, and Nafion (registered trademark) is used as a cation exchange membrane in the diaphragm of the production apparatus (Patent Document 1).

[0004] In fuel cell research, it has been reported that ammonia, when present in low concentrations in hydrogen, can have an effect of reducing power generation performance. For example, Uribe et al. have reported that ammonium ions are substituted for protons in the sulfonic acid groups of Nafion (registered trademark) in the anode catalyst layer, resulting in reduced proton conductivity, which is the main cause of reduced power generation performance (Non-Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5966762 [Non-patent literature]

[0006] [Non-Patent Document 1] J.Electrochemical Soc., 2002, Vol. 149, No. 3, A293-A296 Summary of the Invention [Problem to be solved by the invention]

[0007] In the ammonia production method where ammonia is electrochemically synthesized, when nitrogen gas and water are used as raw materials, it is ideal to supply electrons, which act as reducing agents, from the power source of the ammonia production equipment, and protons from the water to drive the reaction. The ammonia electrolysis reaction is shown below. At the anode, water is electrolyzed, and protons (H + ) and electrons (e - ) is produced (Reaction formula 1). At that time, the protons are conducted to the cathode side through the electrolyte membrane, which acts as a separator, and the electrons are conducted to the external circuit. Meanwhile, at the cathode, a nitrogen reduction reaction involving nitrogen, protons, and electrons proceeds, producing ammonia (Reaction formula 2). Anode: H2O → 1 / 2O2+2H + +2e - (Reaction Scheme 1) Cathode: N2+6H + +6e - → 2NH3(Reaction 2)

[0008] When electrolytic synthesis of ammonia is performed at a constant potential in a production apparatus, the reaction rate of ammonia often decreases.

[0009] The present invention relates to a method for producing ammonia by electrolytic synthesis using a production apparatus that performs constant potential electrolysis. The objective of the present invention is to control the ammonium ions generated by protons supplied to the cathode and the cathode catalyst layer at the cathode and the cathode catalyst layer, thereby improving the reaction rate and preventing the reaction from stopping. [Means for solving the problem]

[0010] As a result of extensive investigations, the inventors have found that the reaction rate of ammonia production can be improved by using a material selected from a group of cathode catalyst layer materials in the cathode or cathode catalyst layer where ammonia is produced, and by using a new gas diffusion electrode integrated with the catalyst layer for electrolytic synthesis.

[0011] The present invention based on these findings includes, for example, the following items [1] to [9]. [1] A gas diffusion electrode comprising a catalyst layer including a material for a cathode catalyst layer and a cathode electrode catalyst. [2] The gas diffusion electrode according to [1], wherein the material for the cathode catalyst layer is at least one selected from the group consisting of polymer electrolytes and sintered bodies of mixtures containing a nitrogen-containing compound component and a conductive carbon material. [3] 3. The gas diffusion electrode according to claim 1, further comprising a catalyst layer comprising a material for a cathode catalyst layer, the material being made from an ink for a catalyst layer containing a cathode electrode catalyst. [4] The gas diffusion electrode according to any one of [1] to [3], wherein an additive component to an ink for a catalyst layer containing a material for a cathode catalyst layer and a cathode electrode catalyst is at least one selected from the group consisting of a binder, a conductive carbon material, and an ionic liquid. [5] The gas diffusion electrode according to [1] or [2], comprising a catalyst layer containing a material for a cathode catalyst layer, the catalyst layer being formed using an ink for a catalyst layer containing the material for a cathode catalyst layer. [6] The gas diffusion electrode according to any one of [1], [2] and [5], wherein an additive component to an ink for a catalyst layer containing a material for a cathode catalyst layer is at least one selected from the group consisting of a binder, a conductive carbon material, and an ionic liquid. [7] The method for producing a gas diffusion electrode according to any one of [1] to [6], further comprising the step of producing a catalyst layer containing a material for a cathode catalyst layer in the process for producing the gas diffusion electrode. [8] A membrane electrode assembly comprising the gas diffusion electrode according to any one of [1] to [6]. [9] 9. An ammonia production apparatus for electrochemically synthesizing ammonia, comprising the membrane electrode assembly according to claim 8. Effect of the Invention

[0012] The gas diffusion electrode of the present invention utilizes a material selected from the group of materials for a cathode catalyst layer used in the cathode and the cathode catalyst layer, and is capable of adjusting the ion conduction, electron conduction, and substance transport involved in the electrolytic reaction in the catalyst layer. Therefore, in the electrolytic synthesis of ammonia, the ammonium ions generated from the target ammonia and the protons supplied to the cathode form ammonium salts with sulfonic acid groups derived from the electrolyte present in the electrolyte membrane, the cathode, and the cathode catalyst layer, thereby suppressing the decrease in proton conductivity and the decrease in reaction rate, and thus reducing the amount of ammonia produced. In addition, since the catalyst layer and the gas diffusion layer are integrated, the current collection is excellent, and the electronic conductivity of the entire device is excellent, and an ammonia production device equipped with a membrane electrode assembly using the gas diffusion electrode can improve the amount of ammonia produced. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of an ammonia production apparatus 100 that electrochemically synthesizes ammonia using nitrogen gas and water as raw materials. [Diagram 2] FIG. 1 is a cross-sectional view showing a schematic configuration of an ammonia production apparatus 200 that electrochemically synthesizes ammonia using nitrogen gas and water as raw materials. [Diagram 3] Schematic diagram 1 showing the configuration of the gas diffusion electrode and membrane electrode assembly [Figure 4] Schematic diagram 2 showing the structure of the gas diffusion electrode and membrane electrode assembly after thermocompression bonding [Diagram 5] Schematic diagram 3 showing the configuration of the gas diffusion electrode and membrane electrode assembly [Figure 6] Schematic diagram 4 showing the configuration of the gas diffusion electrode and membrane electrode assembly [Figure 7] Schematic diagram 5 showing the configuration of the gas diffusion electrode and membrane electrode assembly [Figure 8] Ammonia production equipment 300 that electrochemically synthesizes ammonia using nitrogen gas and water as raw materials DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] In this specification, "n-" means normal, "s-" means secondary, "t-" means tertiary, "o-" means ortho, "m-" means meta, and "p-" means para. In this specification, "polymer" means both homopolymer and copolymer.

[0015] An ammonia production apparatus that electrochemically synthesizes ammonia will be described. <<Ammonia production equipment that electrochemically synthesizes ammonia>> FIG. 1 is a cross-sectional view showing a schematic configuration of an ammonia production apparatus that electrochemically synthesizes ammonia using nitrogen gas and water as raw materials. The ammonia production apparatus 100, which describes the configuration when the electrolyte membrane 102 is a cation exchange membrane (described later), has a power supply device 101, a cathode catalyst layer 103, an anode catalyst layer 203, and an electrolyte membrane 102 sandwiched between both catalyst layers, and each catalyst layer has a cathode gas diffusion layer 104 and an anode gas diffusion layer 204, which are gas diffusion layers (hereinafter sometimes abbreviated as "GDL") on the outside, and this configuration is called a membrane electrode assembly (hereinafter sometimes abbreviated as "MEA"). In the ammonia production apparatus, this MEA is sandwiched between a cathode separator 105 and an anode separator 205, which are separators. It has been described that protons are conducted in the electrolyte membrane 102 in the direction from the anode catalyst layer 203 to the cathode catalyst layer 103 . The raw materials nitrogen gas, electrolytic solution, and reaction mixture can be passed through the cathode side flow channel 106 and the cathode side flow channel 107, and ammonia produced in the form of ammonia or ammonium ions can be collected by setting a collection tank at the end of the cathode side flow channel 107. Water or an aqueous sulfuric acid solution is stored in the collection tank, and ammonia and ammonium ions can be captured here. The anode side flow channel 206 and the anode side flow channel 207 can be passed through the electrolytic solution, reaction mixture, and produced oxygen gas, and a collection tank is set at the end of the anode side flow channel 207, and the electrolytic solution, reaction mixture, and produced oxygen can be collected. The supplied nitrogen gas can also be humidified nitrogen gas.

[0016] Examples of the electrolyte on the cathode side include water, water vapor, a dilute aqueous sulfuric acid solution, an ionic liquid, etc., and examples of the reaction mixture on the cathode side include water, sulfuric acid, ammonia, ammonium ions, nitrogen gas, water vapor, by-produced hydrogen gas, etc. Examples of the electrolyte on the anode side include water, a dilute aqueous sulfuric acid solution, an ionic liquid, etc., and examples of the reaction mixture on the anode side include water, sulfuric acid, water vapor, produced oxygen gas, etc.

[0017] Figure 2 shows an ammonia production system that electrochemically synthesizes ammonia using nitrogen gas and water as raw materials. 1 is a cross-sectional view showing a schematic configuration of an ammonia producing apparatus 200 in which the electrolyte membrane 302 is an anion exchange membrane (described later), the configuration is the same as that of the above-mentioned production apparatus 100, but it has been described that hydroxide ions are conducted in the electrolyte membrane 302 in the direction from the cathode catalyst layer 103 to the anode catalyst layer 203, and that nitrogen and water need to be supplied to the cathode.

[0018] The cathode side flow path 106 and the cathode side flow path 107 can be used to pass the raw materials nitrogen gas, water, the electrolyte, and the reaction mixture, and by providing a collection tank at the end of the cathode side flow path 107, the generated ammonia can be collected in the form of ammonia and ammonium ions. The collection tank stores water and an aqueous sulfuric acid solution, where the ammonia and ammonium ions can be captured. The anode side flow path 206 and the anode side flow path 207 can be used to pass the electrolyte, the reaction mixture, and the generated oxygen gas, and by providing a collection tank at the end of the anode side flow path 207, the electrolyte, the reaction mixture, and the generated oxygen can be collected. The supplied nitrogen gas can also be humidified nitrogen gas.

[0019] Examples of the electrolyte on the cathode side include water, water vapor, a dilute sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, an ionic liquid, etc., and examples of the reaction mixture on the cathode side include water, ammonia, ammonia water, nitrogen gas, water vapor, by-produced hydrogen gas, etc. Examples of the electrolyte on the anode side include water, a dilute sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, an ionic liquid, etc., and examples of the reaction mixture on the anode side include water, a dilute sodium hydroxide aqueous solution, water vapor, generated oxygen gas, etc.

[0020] Examples of the ionic liquid include the ionic liquids described in the above-mentioned catalyst carrier, such as imidazolium salts, pyridinium salts, ammonium salts, phosphonium salts, pyrrolidinium salts, piperidinium salts, and sulfonium salts. It is also possible to add an acid such as sulfuric acid or trifluoromethanesulfonic acid to the ionic liquid, and preferred ionic liquids to which an acid is added are 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-1-methylpiperidinium bis(trifluoromethanesulfonyl)imide, and 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorotrifluorophosphate.

[0021] The cation, which is an electrolyte contained in the electrolytic solution, is preferably a proton, an imidazolium ion, or a pyrrolidinium ion, and the anion, which is an electrolyte, is preferably a perchlorate ion or a sulfate ion.

[0022] The electrolytic reaction in the catalyst layer that electrochemically synthesizes ammonia will be described. A reaction occurs in the catalyst of the cathode catalyst layer to generate ammonia from three elements: electrons supplied from the power supply device 101, nitrogen gas supplied from the cathode side flow path 106 connected to a device capable of supplying nitrogen gas, and protons supplied to the cathode catalyst layer 103 through the electrolyte membrane 102. The reaction formula is as follows: When the environment in which the catalyst of the cathode catalyst layer is placed is acidic, "N2 + 6e - +6H + →2NH3" or "N2+6e - +6H3O + →2NH3+6H2O", and when the environment in which the cathode catalyst layer is placed is alkaline, "N2+6e - +6H2O→2NH3+6OH - The environment in which the catalyst in the cathode catalyst layer is placed can be set by selecting the electrolyte membrane. In the cathode catalyst layer, the - +2H + Hydrogen is also produced as a by-product through the reaction "N2 + 3H2 → 2NH3", and the reaction involving hydrogen is also assumed to be "N2 + 3H2 → 2NH3".

[0023] Next, the electrolytic reaction in the anode catalyst layer 203 will be described. A reaction occurs with hydroxide ions from water or a dilute aqueous sodium hydroxide solution supplied from the anode side flow channel 206. When the environment in which the catalyst of the anode catalyst layer is placed is acidic, the reaction formula is "2H2O→ O2+4e - +4H + ", and when the environment in which the catalyst of the anode catalyst layer is placed is alkaline, "4OH - →O2+4e - +2H2O". The environment in which the catalyst in the anode catalyst layer is placed can be set by selecting the electrolyte membrane.

[0024] <<Gas diffusion electrode>> The present invention relates to a gas diffusion electrode, and more particularly to a gas diffusion electrode having a sheet-like gas diffusion layer made of a carbon material and an integrated catalyst layer.

[0025] The gas diffusion electrode of the present invention is suitable as an electrode component of an ammonia production apparatus that electrochemically synthesizes ammonia using nitrogen gas and water as raw materials. By producing a gas diffusion electrode using a material selected from the group of cathode catalyst layer materials described below depending on the type of electrolyte membrane and the characteristics of the target substance produced in the catalyst layer, the gas diffusion electrode can be used for the electrochemical reaction of ammonia electrolytic synthesis and can also be used for other reactions.

[0026] Next, the configuration of the gas diffusion electrode of the present invention will be described with reference to the drawings. FIG. 3 shows a schematic diagram illustrating the configuration of the gas diffusion electrode and the membrane electrode assembly of the present invention. The gas diffusion electrode of the present invention is composed of a sheet-like gas diffusion layer 104 (same as the cathode gas diffusion layer 104) made of a carbon material, a catalyst layer 11 containing a material for a cathode catalyst layer, and a cathode electrode catalyst 12. In this specification, the cathode electrode catalyst 12 may represent a catalyst supported on a catalyst carrier, or a catalyst not supported on a catalyst carrier to indicate the configuration of the gas diffusion electrode. When a catalyst not supported on a catalyst carrier is represented, it is described as "cathode catalyst 12". The cathode gas diffusion layer 104 may have a microporous layer (hereinafter sometimes abbreviated as "MPL"), and may be used in an arrangement in which the catalyst layer 11 containing a material for a cathode catalyst layer and the cathode electrode catalyst 12 are sandwiched between the microporous layer side and the electrolyte membrane 102.

[0027] The microporous layer is provided on one side of the gas diffusion layer and is a layer made of an aggregate of carbon fine particles having an average particle size of about 10 to 100 nm and a water repellent. The carbon fine particles may be treated to be water repellent. The microporous layer has a smaller average pore size than the gas diffusion layer (carbon-based sheet-like member), and has high density and excellent surface flatness. The microporous layer preferably has a pore size distribution of 1 nm to 900 nm.

[0028] <<Gas diffusion layer and gas diffusion layer with MPL layer>> The gas diffusion layer and the gas diffusion layer with MPL layer have gas diffusivity and gas permeability to supply the raw material nitrogen gas to the catalyst, and they transport ammonia, ammonium ions, electrolyte, and reaction mixture produced by the electrolytic reaction, while conducting electrons from the power supply and separator to the cathode catalyst layer.

[0029] The gas diffusion layer and the gas diffusion layer with MPL layer are conductive carbon-based sheet-like members having a pore size distribution of about 100 nm to 90 μm, and may be, for example, a known carbon-based sheet-like member used as a gas diffusion layer of a polymer electrolyte fuel cell in the field of fuel cells. Examples of the carbon-based sheet-like member include TGP-H-060, TGP-H-090, TGP-H-120, TGP-H-060H, TGP-H-090H, and TGP-H-120H from Toray Industries, EC-TP1-030T, EC-TP1-060T, EC-TP1-090T, and EC-TP1-120T from Electrochem, and 22BB, 28BC, 36BB, and 39BB from SIGRACET. Among these, TGP-H-060, TGP-H-090, TGP-H-060H, TGP-H-090H, EC-TP1-060T, and SIGRACET's 22BB, 28BC, 36BB, and 39BB are preferred.

[0030] <<Cathode electrode catalyst>> The cathode electrode catalyst 12, which is a component of the gas diffusion electrode of the present invention, represents a catalyst supported on a catalyst carrier, and examples of the catalyst include metal catalysts, oxide catalysts, metal complexes, etc., and it is also possible to use a combination of a plurality of these catalysts. Depending on the conditions of the electrolytic reaction and the electrolyte membrane, etc., the catalyst carrier and catalyst described below can be set and used as the cathode electrode catalyst.

[0031] <Catalyst carrier> The catalyst carrier may be any carrier capable of supporting a catalyst that is responsible for the electrolytic reaction in the catalyst layer that electrochemically synthesizes ammonia, and may be capable of ion conduction or electron conduction depending on the type of carrier. As long as it supports the catalyst of the present embodiment, it is not particularly limited. Examples of the catalyst carrier include carbon black, carbon materials, metal mesh, metal foam, metal oxide, composite oxide, polymer electrolyte, ionic liquid, and the like. In addition, when the catalyst carrier is used in an electrode, it is possible for it to not only support the catalyst, but also to participate as a catalyst or co-catalyst in the reaction occurring at the electrode. Examples of ions include protons, hydroxonium ions, ammonium ions, hydroxide ions, and the like. When the environment in which the catalyst layer is placed is acidic, it is preferable to use a carrier capable of supplying at least one of protons and hydroxonium ions, and when the environment in which the catalyst layer is placed is alkaline, it is preferable to use a carrier capable of supplying hydroxide ions.

[0032] Examples of carbon black include channel black, furnace black, thermal black, acetylene black, Ketjen black, and Ketjen black EC.

[0033] Examples of carbon materials include activated carbon obtained by carbonizing and activating various materials containing carbon atoms, coke, natural graphite, artificial graphite, graphitized carbon, and the like. The metal mesh may be made of a metal such as nickel, tungsten, titanium, zirconium, or hafnium. Examples of the metal foam include metal foams of aluminum, magnesium, tungsten, titanium, zirconium, hafnium, zinc, iron, tin, lead, or alloys containing these. Examples of metal oxides include aluminum oxide, zirconium oxide, titanium oxide, vanadium oxide, chromium oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide, copper oxide, zinc oxide, niobium pentoxide, molybdenum oxide, ruthenium oxide, rhodium oxide, silver oxide, tantalum oxide, tungsten oxide, osmium oxide, iridium oxide, indium oxide, platinum oxide, gold oxide, magnesium oxide, and silica. Examples of composite oxides include silica-alumina and silica-magnesia.

[0034] Examples of the polymer electrolyte include a fluorine-based polymer electrolyte, a hydrocarbon-based polymer electrolyte, a carboxyl group-containing acrylic copolymer, a carboxyl group-containing methacrylic copolymer, and an anion-conducting electrolyte.

[0035] Examples of fluorine-based polymer electrolytes include fluorine-based sulfonic acid polymers, hydrocarbon-based sulfonic acid polymers, partially fluorinated hydrocarbon-based sulfonic acid polymers, anion-conducting electrolytes, etc., such as Nafion (registered trademark) from DuPont, Aquivion (registered trademark) from Solvay, Flemion (registered trademark) from AGC, and Aciplex (registered trademark) from Asahi Kasei. Types of fluorine-based polymer electrolytes include perfluorosulfonic acid types and perfluorocarboxylic acid types, which can be selected and used. From the viewpoint of acid-base affinity with ammonium ions, preferred are fluorine-based polymer electrolytes that are weak acids, and specific examples thereof include Nafion (registered trademark) from DuPont, Flemion (registered trademark) from AGC, and Aciplex (registered trademark) from Asahi Kasei. The lineup of fluoropolymer electrolytes containing perfluorocarboxylic acids includes:

[0036] Examples of the hydrocarbon polymer electrolyte include sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, and sulfonated polyphenylene. Specific examples of carboxyl group-containing acrylic copolymers include acrylic acid, propiolic acid, crotonic acid, isocrotonic acid, myristoleic acid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, eicosenoic acid, erucic acid, nervonic acid, ω-carboxy-polycaprolactone monoacrylate, phthalic acid monohydroxyethyl acrylate, acrylic acid dimer, 2-acryloyl acrylate, ... Ioxypropylhexahydrophthalic acid, 2-acryloyloxyethyl succinic acid, maleic acid, fumaric acid, citraconic acid, mesaconic acid, atropic acid, cinnamic acid, linoleic acid, eicosadienoic acid, docosadienoic acid, linoleic acid, pinoleic acid, eleostearic acid, mead acid, dihomo-Y-linolenic acid, eicosatrienoic acid, stearidonic acid, arachidonic acid, eicosatetraenoic acid, adrenic acid, bosseopentaenoic acid, eicosapentaenoic acid, osbondo acid, Homopolymers or copolymers of sardine acid, tetracosapentaenoic acid, docosahexaenoic acid, herring acid, 2,2,2-trisacryloyloxymethyl succinic acid, 2-trisacryloyloxymethylethyl phthalic acid, etc., further, acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, tertiary butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, nonyl acrylate, decyl acrylate, dodecyl acrylate, and stearyl acrylate, diacetone acrylamide, acrylamide, 2-hydroxyethyl acrylamide, N-methylacrylamide, Nt-butylacrylamide, N-isopropylacrylamide, N-phenylacrylamide, N-methylolacrylamide, dimethylaminopropylacrylamide, dimethylaminopropylacrylamide, diacetone acrylamide, N,Examples of the copolymer include acrylamides such as N-dimethylacrylamide, N-vinylformamide, acryloylmorpholine, and acryloylpiperidine, phosphonic acids such as [3-(acryloyloxy)propyl]phosphonic acid and [3-(methacryloyloxy)propyl]phosphonic acid, esters of vinyl alcohol such as acrylonitrile and vinyl-n-butyl ether, and copolymers containing a compound having a copolymerizable double bond such as tetrahydrofurfuryl acrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, glycidyl acrylate, 2,2,2-trifluoroethyl acrylate, 2,2,3,3-tetrafluoropropyl acrylate, styrene, and vinyl toluene. The homopolymerization or copolymerization can be carried out by, for example, generating radicals using a radical polymerization initiator. Examples of the radical polymerization initiator include azo compounds such as azobisisobutyronitrile, azobis(2-methylbutyronitrile), 2,2'-azobis-2,4-dimethylvaleronitrile, and 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidinemethyl]tetrahydrate, organic peroxides such as t-butyl hydroperoxide, cumene hydroperoxide, benzoyl peroxide, dicumyl peroxide, and di-t-butyl peroxide, persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate, and hydrogen peroxide, which can be used alone or in combination of two or more kinds. Specific examples of carboxyl group-containing methacrylic copolymers include homopolymers or copolymers of methacrylic acid, ω-carboxy-polycaprolactone monomethacrylate, monohydroxyethyl phthalate methacrylate, methacrylic acid dimer, 2-methacryloyloxypropylhexahydrophthalic acid, 2-methacryloyloxyethyl succinic acid, and the like, each of which has a carboxyl group and a copolymerizable double bond, and further, methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, tertiary methacrylate, and the like. Examples of the copolymer include methacrylic acid alkyl esters such as butyl, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, nonyl methacrylate, decyl methacrylate, dodecyl methacrylate, and stearyl methacrylate, methacrylamides such as methacrylamide and dimethylaminopropyl methacrylamide, phosphonic acids such as α-phosphono-ω-(methacryloyloxy)poly(n=1-15)(oxypropylene), tetrahydrofurfuryl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, glycidyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, styrene, and vinyl toluene. The homopolymerization or copolymerization can be carried out by generating radicals using a radical polymerization initiator, for example. Examples of the radical polymerization initiator include azo compounds such as azobisisobutyronitrile, azobis(2-methylbutyronitrile), 2,2'-azobis-2,4-dimethylvaleronitrile, and 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidinemethyl]tetrahydrate; organic peroxides such as t-butyl hydroperoxide, cumene hydroperoxide, benzoyl peroxide, dicumyl peroxide, and di-t-butyl peroxide; persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; and hydrogen peroxide. These may be used alone or in combination of two or more.

[0037] Examples of the anion conductive electrolyte include Fumion (registered trademark) FAA-3-SOLUT-10 manufactured by FUMATECH BWT GmbH, A3ver.2 and AS-4 manufactured by Tokuyama Corporation (A3ver.2 and AS-4 are described, for example, in the magazine "Hydrogen Energy System", Vol. 1.35, No. 2, 2010, p. 9), anion conductive electrolytes in which quaternary ammonium groups have been introduced into olefin-based polymers such as styrene-divinylbenzene copolymers, and anion conductive electrolytes in which quaternary alkylammonium groups have been introduced into polysulfone-based polymers (non-patent literature: Angew. Chem. Int. Ed. 2007, Vol. 46, pp. 8024-8027, non-patent literature: Fuel Cell 2005, Vol. 5 (No. 2), pp. 187-200. When a cation exchange membrane (hereinafter also referred to as a cation exchange membrane) is used as the electrolyte membrane described below, Nafion (registered trademark) and Aquivion (registered trademark) are preferred, and when an anion exchange membrane (hereinafter also referred to as an anion exchange membrane) is used, FAA-3-SOLUT-10 and AS-4 are preferred.

[0038] As the polymer electrolyte, it is possible to use a combination of two or more of these polymer electrolytes. Examples of the polymer alloy in which two or more types of polymers are mixed include a polymer blend in which two or more types of polymers are physically mixed, and an interpenetrated polymer network (IPN) in which a network structure is entangled.

[0039] As a preferred polymer electrolyte, from the viewpoint of acid-base affinity with ammonium ions, a polymer electrolyte having a functional group of a weak acid is preferred, and specifically, a fluorine-based polymer electrolyte having a perfluorocarboxylic acid, a fluorine-based polymer electrolyte having a perfluorocarboxylic acid, and a methacrylic copolymer containing a carboxyl group can be mentioned. As a functional group of a weak acid, a carboxyl group, a hydroxyl group, and a phenolic hydroxyl group can be mentioned. The pKa value of the fluorine-based polymer electrolyte having a perfluorosulfonic acid group of DuPont's Nafion (registered trademark) is -6 (Non-patent document: Membrane 2002, Vol. 27, No. 3, pp. 131-138), the pKa value of the carboxyl group is 4 to 5, the pKa value of the hydroxyl group is 16 to 17, and the pKa value of the phenolic hydroxyl group is 8 to 11 (Non-patent document: March Organic Chemistry (Vol. 1), 2003, pp. 234-235), where pKa is the acid dissociation constant, and is an index that quantitatively represents the strength of an acid and the ease of dissociation of hydrogen ions.

[0040] Ionic liquids are described below. Examples of ionic liquids include imidazolium salts, pyridinium salts, ammonium salts, phosphonium salts, pyrrolidinium salts, piperidinium salts, and sulfonium salts.

[0041] Specific examples of imidazolium salts include those represented by the formula (1): [ka] Examples of the above-mentioned are represented by the following formula:

[0042] In formula (1), R 1a ~R 5a may be the same or different, and each represents a hydrogen atom, C1 to C 10 Examples of the alkyl group include an alkyl group, an allyl group, and a vinyl group. -Examples of such ions include chloride ion, bromide ion, iodide ion, tetrafluoroborate, trifluoro(trifluoromethyl)borate, dimethylphosphate ion, diethylphosphate ion, hexafluorophosphate, tris(pentafluoroethyl)trifluorophosphate, trifluoroacetate, methyl sulfate, trifluoromethanesulfonate, and bis(trifluoromethanesulfonyl)imide.

[0043] Specific examples of the formula (1) include 1-allyl-3-methylimidazolium ion, 3-ethyl-1-vinylimidazolium ion, 1-methylimidazolium ion, 1-ethylimidazolium ion, 1-n-propylimidazolium ion, 1,3-dimethylimidazolium ion, 1,2,3-trimethylimidazolium ion, 1-ethyl-3-methylimidazolium ion, 1-ethyl-2,3-dimethylimidazolium ion, 1,2,3,4-tetramethylimidazolium ion, 1,3-diethylimidazolium ion, 1-methyl-3-n-propylimidazolium ion, 1-ethyl-3-methyl imidazolium ions such as imidazolium ion, 2-ethyl-1,3-dimethylimidazolium ion, 1-ethyl-2,3-dimethylimidazolium ion, 1,3-dimethyl-n-propylimidazolium ion, 1,3,4-trimethylimidazolium ion, 2-ethyl-1,3,4-trimethylimidazolium ion, 1,2-dimethyl-3-propylimidazolium ion, 1-butyl-2,3-dimethylimidazolium ion, 1-butyl-3-methylimidazolium ion, 1-hexyl-3-methylimidazolium ion, and 1-methyl-3-n-octylimidazolium ion, and X in the formula (1) - Examples of salts include:

[0044] Specific examples of pyridinium salts include those represented by formula (2): [ka] Examples of the above-mentioned are represented by the following formula:

[0045] In formula (2), R 1b ~R 6b may be the same or different, and each may be a hydrogen atom, a hydroxymethyl group, or a C1 to C6 alkyl group. - Examples of the compound include the same compounds as those represented by formula (1) above.

[0046] Specific examples of the formula (2) include pyridinium ions such as 1-butyl-3-methylpyridinium ion, 1-butyl-4-methylpyridinium ion, 1-butyl-pyridinium ion, 1-ethyl-3-methylpyridinium ion, 1-ethylpyridinium ion, and 1-ethyl-3-(hydroxymethyl)pyridinium ion, and the like, and X in the formula (1) - Examples of salts include:

[0047] Specific examples of ammonium salts include those represented by formula (3): [ka] Examples of the above-mentioned are represented by the following formula:

[0048] In formula (3), R 1c ~R 4c may be the same or different, and each represents a hydrogen atom, a methoxyethyl group, a phenylethyl group, a methoxypropyl group, a cyclohexyl group, or a C1 to C8 alkyl group. - Examples of the compound include the same compounds as those represented by formula (1) above.

[0049] Specific examples of the compound represented by formula (3) include ammonium ions such as triethylpentylammonium ion, diethyl(methyl)propylammonium ion, methyltri-n-octylammonium ion, trimethylpropylammonium ion, cyclohexyltrimethylammonium ion, diethyl(2-methoxyethyl)-methylammonium ion, ethyl(2-methoxyethyl)-dimethylammonium ion, ethyl(3-methoxypropyl)dimethyl-ammonium ion, and ethyl(dimethyl)(2-phenylethyl)-ammonium ion, and the like, and X in formula (1) - Examples of salts include:

[0050] Specific examples of phosphonium salts include those represented by formula (4): [ka] Examples of the above-mentioned are represented by the following formula:

[0051] In formula (4), R 1d ~R 4d may be the same or different, and each represents a hydrogen atom, a methoxyethyl group, or a C1-C 10 In addition, X in formula (3) is an alkyl group. - Examples of the compound include the same compounds as those represented by formula (1) above.

[0052] Specific examples of the formula (4) include phosphonium ions such as tributylmethylphosphonium ion, tetrabutylphosphonium ion, trihexyl(tetradecyl)phosphonium ion, trihexyl(ethyl)phosphonium ion, and tributyl(2-methoxyethyl)-phosphonium ion, and the like, and X in the formula (1) - Examples of salts include:

[0053] Specific examples of pyrrolidinium salts include those represented by formula (5): [ka] Examples of the above-mentioned are represented by the following formula:

[0054] In formula (5), R 1e ~R 2e may be the same or different, and each represents a hydrogen atom, an allyl group, a methoxyethyl group, or a C1 to C8 alkyl group. - Examples of the compound include the same compounds as those represented by formula (1) above.

[0055] Specific examples of the formula (5) include pyrrolidinium ions such as 1-allyl-1-methylpyrrolidinium ion, 1-(2-methoxyethyl)-1-methylpyrrolidinium ion, 1-butyl-1-methylpyrrolidinium ion, 1-methyl-1-propylpyrrolidinium ion, 1-octyl-1-methylpyrrolidinium ion, and 1-hexyl-1-methylpyrrolidinium ion, and the like, and X in the formula (1) - Examples of salts include:

[0056] Specific examples of piperidinium salts include those of formula (6): [ka] Examples of the above-mentioned are represented by the following formula:

[0057] In formula (6), R 1f ~R 2f may be the same or different, and each represents a hydrogen atom or a C1 to C6 alkyl group. - Examples of the compound include the same compounds as those represented by formula (1) above.

[0058] Specific examples of the formula (6) include piperidinium ions such as 1-butyl-1-methylpiperidinium ion and 1-methyl-1-propylpiperidinium ion, and the like, and X in the formula (1) - Examples of salts include:

[0059] Specific examples of sulfonium salts include those represented by formula (7): [ka] Examples of the above-mentioned are represented by the following formula:

[0060] In formula (7), R 1g ~R 3g may be the same or different, and each represents a hydrogen atom or a C1 to C4 alkyl group. - Examples of the compound include the same compounds as those represented by formula (1) above.

[0061] Specific examples of the formula (7) include sulfonium ions such as triethylsulfonium ion and trisulfonium ion, and the X in the formula (1) - Examples of salts include:

[0062] More specifically, the ionic liquid may be 1-allyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium iodide, 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluoromethanesulfonate ... 1-Butyl-3-methylimidazolium trifluoro(trifluoromethyl)borate, 1-Butyl-2,3-dimethylimidazolium trifluoromethanesulfonate, 1-Butyl-3-methylimidazolium trifluoroacetate, 1-Butyl-2,3-dimethylimidazolium trifluoromethanesulfonate, 1-Butyl-3-methylimidazolium methylsulfate, 1,3-Dimethylimidazolium dimethylphosphate, 2,3-Dimethyl-1-propylimidazolium bis(trifluoromethanesulfonyl)imide, 1-Decitronellol 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1,3-dimethylimidazolium methylsulfate, 1-decyl-3-methylimidazolium bromide, 1-decyl-3-methylimidazolium chloride, 1-decyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-ethyl-2, 3-Dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium methanesulfonate, 1-ethyl-3-methylimidazolium trifluoro(trifluoromethyl)borate, 3-ethyl-1-vinylimidazolium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium trifluoroacetate, 1-ethyl-3-methylimidazolium methylsulfate, 1-ethyl-3-methylimidazolium diethylphosphate, 1-hexyl-3-methylimidazolium chloride chloride, 1-hexyl-3-methylimidazolium hexafluorophosphate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium trifluoromethanesulfonate, 1-hexyl-3-methylimidazolium bromide, 1-(2-hydroxyethyl)-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium 1-methyl-3-n-octylimidazolium iodide, 1-methyl-3-n-propylimidazolium iodide, 1-methyl-3-n-octylimidazolium bromide, 1-methyl-3-n-octylimidazolium chloride, 1-methyl-3-n-octylimidazolium hexafluorophosphate, 1-methyl-3-n-octylimidazolium trifluoromethanesulfonate, 1-methyl-3-n-octylimidazolium tetrafluoroborate, 1-methyl-3-propylimidazolium bromide, 1-methyl-3-propylimidazolium tetrafluoroborate,1-Methyl-3-pentylimidazolium bromide, 1-methyl-3-n-octylimidazolium bis(trifluoromethanesulfonyl)imide, 1-methyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butylpyridinium tetrafluoroborate, 1-butyl-4-methylpyridinium tetrafluoroborate, 1-butylpyridinium bis(trifluoromethanesulfonyl)imide, 1-butyl-4-methylpyridinium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3- Methylpyridinium ethyl sulfate, 1-ethyl-3-(hydroxymethyl)pyridinium ethyl sulfate, 1-ethyl-3-methylpyridinium bis(trifluoromethanesulfonyl)imide, triethylpentylammonium bis(trifluoromethanesulfonyl)imide, diethyl(methyl)propylammonium bis(fluorosulfonyl)imide, diethyl(2-methoxyethyl)methylammonium bis(fluorosulfonyl)imide, ethyl(2-methoxyethyl)dimethylammonium bis(fluorosulfonyl)imide ethyl(2-methoxyethyl)dimethylammonium bis(trifluoromethanesulfonyl)imide, ethyl(3-methoxypropyl)dimethylammonium bis(trifluoromethanesulfonyl)imide, ethyl(dimethyl)(2-phenylethyl)ammonium bis(trifluoromethanesulfonyl)imide, methyltri-n-octylammonium bis(trifluoromethanesulfonyl)imide, tributylmethylammonium bis(trifluoromethanesulfonyl)imide, trimethylpropylammonium bis(trifluoromethanesulfonyl)imide, tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide, 1-allyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide, 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate, 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide,1-(2-methoxyethyl)-1-methylpyrrolidinium bis(fluorosulfonyl), imide, 1-butyl-1-methylpiperidinium bis(trifluoromethanesulfonyl)imide, 1-methyl-1-propylpiperidinium bis(fluorosulfonyl)imide, or triethylsulfonium bis(trifluoromethanesulfonyl)imide, or a combination of the aforementioned ionic liquids.

[0063] <Metal catalyst> The metal catalyst may be any catalyst that is responsible for the electrolytic reaction in the catalyst layer that electrochemically synthesizes ammonia. Examples of the metal catalyst include metal catalysts that are used in a single composition and metal catalysts that are used in a mixture of multiple metal components such as alloy catalysts.

[0064] Specific examples of the metal catalyst include platinum catalyst, gold catalyst, silver catalyst, ruthenium catalyst, iridium catalyst, rhodium catalyst, palladium catalyst, osmium catalyst, tungsten catalyst, lead catalyst, iron catalyst, chromium catalyst, cobalt catalyst, nickel catalyst, manganese catalyst, vanadium catalyst, molybdenum catalyst, gallium catalyst, aluminum catalyst, and alloys thereof, or combinations of the above metal catalysts. Preferred examples of the metal catalyst include platinum catalyst, gold catalyst, ruthenium catalyst, iridium catalyst, rhodium catalyst, palladium catalyst, molybdenum catalyst, alloys thereof, and combinations of the above metal catalysts.

[0065] In the alloy of a metal catalyst and another metal, the metal constituting the alloy with the metal catalyst is not particularly limited as long as it is other than the selected metal catalyst, and examples thereof include boron, magnesium, aluminum, silicon, calcium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, strontium, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, indium, tin, antimony, barium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, gold, lead, bismuth, lanthanum, cerium, etc. These may be used alone or in combination of two or more.

[0066] In the core-shell type metal catalyst, the core is made of a metal other than platinum, and the shell is platinum. The metal used for the core is not particularly limited as long as it is other than the selected metal catalyst, and examples thereof include nickel, copper, palladium, silver, gold, iridium, titanium, iron, cobalt, ruthenium, osmium, chromium, molybdenum, and tungsten. These may be used alone or in combination of two or more.

[0067] As the metal catalyst, it is possible to use metal nanoparticles formed from a surfactant or the like, or metal particles, metal nanoparticles, metal films, metal foils, etc. having self-organized portions formed by bonding between metal and thiol using a thiol compound. Examples of the thiol compound include R 1 -SH(R 1 is defined as follows.) 1 is R 1Taking into consideration the boiling point of -SH, ease of isolation by chromatography, etc., the organic group is not particularly limited and may be any appropriate one, but is preferably an organic group having 1 to 20 carbon atoms, and more preferably an organic group having 6 to 16 carbon atoms. Examples of the organic group include a hydrocarbon group, a chain saturated hydrocarbon group, a chain unsaturated hydrocarbon group, a cyclic saturated hydrocarbon group, a cyclic unsaturated hydrocarbon group, an aromatic hydrocarbon group, and groups in which a part of the carbon-carbon bond of these groups is interrupted by a heteroatom or substituted by a substituent containing a heteroatom.

[0068] Specific examples of the thiol compound include 2-methylbenzenethiol, 3-methylbenzenethiol, 4-methylbenzenethiol, phenylmethanethiol, 1-butanethiol, 1-decanethiol, 1-dodecanethiol, 1-heptanethiol, 1-hexadecanethiol, 1-hexanethiol, 1-nonanethiol, 1-octadecanethiol, 1-octanethiol, 1-pentadecanethiol, 1-pentanethiol, 1-propanethiol, 1-tetradecanethiol, 1-undecanethiol, 1 1-Mercaptoundecyl trifluoroacetate, 1H,1H,2H,2H-perfluorodecanethiol, 2-ethylhexanethiol, 2-methyl-1-propanethiol, 2-methyl-2-propanethiol, 3-methyl-1-butanethiol, methyl 3-mercaptopropionate, tert-dodecyl mercaptan, (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide, (11-mercaptoundecyl)hexa(ethylene glycol), (11-mercaptoundecyl) 11-mercaptoundecyl)tetra(ethylene glycol), 1-(11-mercaptoundecyl)imidazole, 1-mercapto-2-propanol, 11-(1H-pyrrol-1-yl)undecane-1-thiol, 11-amino-1-undecanethiol hydrochloride, 11-mercapto-1-undecanol, 11-mercaptoundecanamide, 11-mercaptoundecanoic acid, 11-mercaptoundecylhydroquinone, 11-mercaptoundecylphosphonic acid, 12-mercaptododecanoic acid, 16-amino-1-hexadecanoic acid 16-mercaptohexadecanamide, 16-mercaptohexadecanoic acid, 3-amino-1-propanethiol hydrochloride, 3-chloro-1-propanethiol, 3-mercapto-1-propanol, 3-mercaptopropionic acid, 6-amino-1-hexanethiol hydrochloride, 6-mercapto-1-hexanol, 6-mercaptohexanoic acid, 8-amino-1-octanethiol hydrochloride, 8-mercapto-1-octanol, 8-mercaptooctanoic acid, 9-mercapto-1-nonanol, triethylenediamine Ethylene glycol mono-11-mercaptoundecyl ether, 1,4-butanediol diacetate, [11-(methylcarbonylthio)undecyl]hexa(ethylene glycol), [11-(methylcarbonylthio)undecyl]tetra(ethylene glycol), [11-(methylcarbonylthio)undecyl]tri(ethylene glycol)acetic acid, hexa(ethylene glycol) mono-11-(acetylthio)undecyl ether, S,S'-[1,4-phenylenebis(2,1-ethynediyl-4,1-phenylene)]bis(thioacetate), S-[4-[2-[4-(2-phenylethynyl)phenyl]ethynylphenyl]thioacetate, S-(10-undecyl)thioacetate, S-(11-bromoundecyl)thioacetate, S-(4-azidobutyl)thioacetate, S-(4-bromobutyl)thioacetate, S-(4-cyanobutyl)thioacetate, 1,1',4',1''-terphenyl-4-thiol, 1,4- Benzenedimethanethiol, 1-adamantanethiol, 1-naphthalenethiol, 2-phenylethanethiol, 4'-bromo-4-mercaptophenyl, 4'-mercaptophenylcarbonitrile, 4,4'-bis(mercaptomethyl)biphenyl, 4,4'-dimercaptostilbene, 4-(6-mercaptohexyloxy)benzyl alcohol, 4-mercaptobenzoic acid, 9-fluorenylmethylthiol, 9-mercapto Examples of the mercaptoethylimidazole include fluorene, biphenyl-4,4-dithiol, biphenyl-4-thiol, cyclohexanethiol, cyclopentanethiol, p-terphenyl-4,4″-dithiol, thiophenol, aminoethanethiol, aminopropanethiol, aminobutanethiol, methylaminoethanethiol, isopropylethylaminoethanethiol, dimethylaminoethanethiol, diethylaminoethanethiol, dibutylaminoethanethiol, mercaptoethylimidazole, mercaptopropylimidazole, mercaptobutylimidazole, mercaptohexylimidazole, mercaptotriazole, mercaptoethyltriazole, mercaptopropyltriazole, mercaptobutyltriazole, mercaptohexyltriazole, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropyltrimethoxysilane.

[0069] <Oxide catalyst> The oxide catalyst may be any catalyst that is responsible for the electrolytic reaction in the catalyst layer that electrochemically synthesizes ammonia. Examples of the oxide catalyst include oxide catalysts that use metal oxides of typical elements, transition metal oxides, or oxide catalysts that use a mixture of multiple metal oxides, and the oxide catalyst may be used as a carrier for the catalyst used in the electrolytic reaction in the catalyst layer.

[0070] Specific examples of the oxide catalyst include iridium (IV) oxide powder catalyst, iridium oxide catalyst, aluminum oxide, zirconium oxide, titanium oxide, vanadium oxide, chromium oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide, copper oxide, zinc oxide, niobium pentoxide, molybdenum oxide, cerium oxide, samarium oxide, ruthenium oxide, rhodium oxide, silver oxide, tantalum oxide, tungsten oxide, osmium oxide, iridium oxide, indium oxide, platinum oxide, gold oxide, magnesium oxide, silica, silica-alumina, silica-magnesia, combinations of the above oxide catalysts, and combinations of the above metal catalysts.

[0071] <Metal complex> The metal complex is not particularly limited as long as it is responsible for the electrolytic reaction in the catalyst layer that electrochemically synthesizes ammonia, and may be responsible for capturing nitrogen molecules when the nitrogen molecules react in the vicinity of the electrode and then providing protons and electrons for reduction, and may be a compound in which the nitrogen molecules are coordinated at the metal center of the metal complex. The compound is sometimes called a nitrogen complex. Specifically, since the discovery of [Ru(NH3)5N2]2+ described in the non-patent literature Chem. Commun., 1965, pp. 621-622, for the first time in 1965, nitrogen complexes have been reported in the non-patent literature Science, 1968, vol. 159, pp. 320-322; J. Am. Chem. Soc., 1968, vol. 90, pp. 3263-3264; J. Am. Chem. Soc., 1968, vol. 90, pp. 5295-5296; Chem. Lett., 1993, vol. 22, pp. 1329-1332; Polyhedron, 1996, vol. 24, pp. 4421-4423; and Chem. Rev., 2004, vol. 104, pp. 385-401, and these can be cited as examples of the nitrogen complexes described above.

[0072] More specifically, examples of the metallocene compounds include a molybdenum nitrogen complex having a triamide monoamine tetradentate ligand described in Science 2003, vol. 301, pp. 76-78, an iron nitrogen complex having a triphosphine borane tetradentate ligand described in Nature 2013, vol. 501, pp. 84-87, a metallocene compound represented by bis(cyclopentadienyl)titanium dichloride described in Japanese Patent No. 5729022, and a half metallocene compound. Metallocene compounds have two rings such as cyclopentadiene, benzene, cyclooctatetraene, and derivatives thereof, and a metal atom is sandwiched between the rings, and are sometimes called sandwich compounds. Half metallocene compounds have one ring and are sometimes called open sandwich compounds.

[0073] Examples of metallocene compounds include bis(cyclopentadienyl)titanium dichloride, μ-chloro-μ-methylene[bis(cyclopentadienyl)titanium]dimethylaluminum, bis(cyclopentadienyl)zirconium dichloride, bis(cyclopentadienyl)zirconium chloride hydride, bis(butylcyclopentadienyl)zirconium(IV) dichloride, decamethylzirconocene dichloride bis(pentamethylcyclopentadienyl)zirconium(IV) dichloride, 1,1'-isopropylidene zirconocene dichloride, hafnocene dichloride, 1,1'-dipropyl hafnocene dichloride bis(propylcyclopentadienyl)hafnocene dichloride, and 1,1'-dipropyl hafnocene dichloride bis(propylcyclopentadienyl)hafnocene dichloride. Examples of the half metallocene compounds include cyclopentadienyltitanium(IV) trichloride, (pentamethylcyclopentadienyl)titanium(IV) trichloride, (indenyl)titanium(IV) trichloride, trichloro(indenyl)titanium(IV), cyclopentadienylzirconium(IV) trichloride, dimethylsilylbis(1-indenyl)zirconium dichloride, rac-dimethylsilylbis(1-indenyl)zirconium dichloride, ethylenebis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, ra Examples of the dichloride include c-ethylenebis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride. Among these, bis(cyclopentadienyl)titanium dichloride, bis(cyclopentadienyl)zirconium dichloride, rac-dimethylsilylbis(1-indenyl)zirconium dichloride, and rac-ethylenebis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride are preferred.

[0074] In addition to the above-mentioned metal complexes, those having a metal complex supported thereon can also be used. For example, a complex having a vinyl group represented by formula (S1) described in the non-patent literature Journal of Organometallic Chemistry, Vol. 655, pp. 167-171, 2002, is radically polymerized with styrene to produce a compound represented by formula (S2): [ka] Furthermore, the form in which the metallocene compound is supported on a polymer is described, for example, in the non-patent literature, Comprehensive Organometallic Chemistry III (2007), pages 728 to 738, and it is also possible to use a form in which the metallocene compound is supported on a polymer.

[0075] <<Anode electrode catalyst>> Examples of the anode electrode catalyst include the same catalyst carriers as those described in the cathode electrode catalyst, and examples of the catalyst include the metal catalysts and oxide catalysts described in the cathode electrode catalyst. It is also possible to use a combination of a plurality of these catalysts. Depending on the conditions of the electrolytic reaction and the electrolyte membrane, the catalyst carriers and catalysts described below can be set and used as the anode electrode catalyst. As the anode catalyst, platinum catalysts and iridium oxide catalysts are preferred. Furthermore, an anode gas diffusion electrode (manufactured by Chemix Corporation, with an iridium oxide coating weight of 2 mg / cm) fabricated with the anode electrode catalyst, anode catalyst layer, and an anode gas diffusion layer can be used. 2 The weight of the Nafion solid content is 0.8 mg / cm 2It is also possible to obtain and use iridium oxide and Nafion solids, and the weight per unit area can be adjusted.

[0076] <<Method for producing gas diffusion electrodes and membrane electrode assemblies>> The method for producing the gas diffusion electrode and the membrane electrode assembly of the present invention will be described. The gas diffusion electrode and the membrane electrode assembly in FIG. 3 are simulated diagrams before thermocompression bonding, and the gas diffusion electrode and the membrane electrode assembly 2 in FIG. 4 are simulated diagrams after thermocompression bonding. It is sufficient to produce a gas diffusion electrode in a state in which a catalyst layer 11 containing a material for a cathode catalyst layer and a cathode electrode catalyst 12 (black circles in FIG. 3 and FIG. 4, which may be an unsupported cathode catalyst 12) are arranged between an electrolyte membrane 102 and a cathode gas diffusion layer 104, and after thermocompression bonding, the catalyst layer 11 and the cathode electrode catalyst 12 are arranged in the same thin layer region, and a cathode catalyst layer 103 is produced. The anode catalyst layer 203 can be produced by a production method based on the production of MEA for water electrolysis, fuel cells, etc., which are known techniques. In the region of the anode gas diffusion layer 204, the anode catalyst layer 203, and the electrolyte membrane 102, it is possible to perform bonding using an electrolyte similar to the electrolyte membrane. Preferably, the cathode gas diffusion layer 104, the cathode catalyst layer 103, and the electrolyte membrane 102 are bonded using the cathode catalyst layer material of the present invention. The bonding can be performed using any device capable of thermocompression bonding, and is preferably performed using a hot press device or a precision heating and pressing device.

[0077] <<Preparation of catalyst layer containing cathode catalyst layer material>> In the gas diffusion electrode shown in FIG. 3 and FIG. 4, the catalyst layer 11 containing the material for the cathode catalyst layer is prepared by preparing and applying an ink for the catalyst layer using at least one material selected from the group consisting of materials for the cathode catalyst layer according to the type of electrolyte membrane and the catalyst support, and then thermocompressing the ink to prepare the catalyst layer containing the material for the cathode catalyst layer in the gas diffusion electrode. In the preparation of the ink for the catalyst layer, it is also possible to adjust the ink by adding a binder, a conductive carbon material, an ionic liquid, etc., in addition to the selected material for the cathode catalyst layer. The ink for the catalyst layer can be applied to one side of the electrolyte membrane 102, one side of the cathode gas diffusion layer 104, or one side of the electrolyte membrane and one side of the cathode gas diffusion layer. When a catalyst supported on a catalyst support such as carbon is used as the cathode electrode catalyst 12, the supported catalyst may be added to the ink for the catalyst layer to adjust the ink.

[0078] <Preparation of Catalyst Layer Containing Cathode Catalyst Layer Material A> Examples of methods for supporting the cathode catalyst 12 on one side of the cathode gas diffusion layer 104 include sputtering deposition, arc plasma deposition, electron beam deposition, thermal heating deposition, and pulse laser deposition, and the amount of catalyst supported can be appropriately adjusted by controlling the deposition conditions in consideration of the type of catalyst. The cathode catalyst 12 shown in FIG. 5 is directly supported on the cathode gas diffusion layer 104 via a gas diffusion electrode 401 (hereinafter sometimes abbreviated as "GDE"), and the ink for the catalyst layer, which is the catalyst layer 11 containing the material for the cathode catalyst layer, is applied and then thermocompressed to produce a gas diffusion electrode.

[0079] <Preparation of Catalyst Layer Containing Cathode Catalyst Layer Material B> When a catalyst supported on a catalyst carrier such as carbon is used as the cathode electrode catalyst 12, for example, a commercially available electrode catalyst that is a platinum catalyst supported on carbon (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., platinum content: 46.5 wt %, product name "TEC10E50E") can be used. A gas diffusion electrode can be produced by preparing and applying an ink for a catalyst layer made of a catalyst layer 11 containing a material for a cathode catalyst layer and a platinum catalyst supported on carbon, and then thermocompressing the ink. The surface to which the ink for the catalyst layer is applied is the one side of the electrolyte membrane 102 when passing through the catalyst coated membrane 402 (hereinafter sometimes abbreviated as "CCM") shown in Figure 6, and can be produced via the catalyst coated membrane 402 (hereinafter sometimes abbreviated as "CCM") described in the gas diffusion electrode 4. Furthermore, when passing through the gas diffusion electrode 403 described in the gas diffusion electrode 5 shown in Figure 7, the ink is applied to one side of the cathode gas diffusion layer 104.

[0080] <Cathode catalyst layer materials> The cathode catalyst layer material will be described. The cathode catalyst layer material may be any material that is responsible for ion conduction, electron conduction, and ion and electron conduction in the electrolytic reaction in the catalyst layer that electrochemically synthesizes ammonia, and may be any material that is responsible for transporting raw materials, nitrogen gas, products, electrolytes, reaction solutions, etc. related to ammonia electrolytic synthesis. Examples of the ions include protons, hydroxonium ions, ammonium ions, hydroxide ions, etc., and when the environment in which the catalyst layer is placed is acidic, it is preferable to use a material that can supply at least one type of ion, which is a proton or a hydroxonium ion, and when the environment in which the catalyst layer is placed is alkaline, it is preferable to use a material that can supply hydroxide ions. Examples of raw materials and products related to ammonia electrolytic synthesis include nitrogen gas, water, protons, hydroxonium ions, ammonia, ammonium ions, hydroxide ions, etc. Examples of the cathode catalyst layer material group include a polymer electrolyte, a sintered body of a mixture containing a nitrogen-containing compound component and a conductive carbon material (abbreviated as sintered body A), and the like.

[0081] <Polymer electrolyte> Examples of the polymer electrolyte include those described in the above catalyst carrier. From the viewpoint of acid-base affinity with ammonium ions, preferred polymer electrolytes are those having a functional group of a weak acid, and specific examples thereof include a fluorine-based polymer electrolyte having a perfluorocarboxylic acid, a fluorine-based polymer electrolyte having a perfluorocarboxylic acid, and a methacrylic copolymer containing a carboxyl group. Examples of the functional group of a weak acid include a carboxyl group, a hydroxyl group, and a phenolic hydroxyl group. The pKa value of DuPont's Nafion (registered trademark), a fluoropolymer electrolyte having perfluorosulfonic acid groups, is -6 (Non-patent literature: Membrane, 2002, Vol. 27, No. 3, pp. 131-138), while the pKa value of a carboxyl group is 4 to 5, the pKa value of a hydroxyl group is 16 to 17, and the pKa value of a phenolic hydroxyl group is 8 to 11 (Non-patent literature: March Organic Chemistry (Vol. 1), 2003, pp. 234-235), where pKa is the acid dissociation constant and is an index that quantitatively expresses the strength of an acid and the ease with which hydrogen ions dissociate.

[0082] In the cathode catalyst layer, under strong acidic conditions such as sulfonic acid groups, the generated ammonia becomes ammonium ions, which tend to have a strong affinity with the anion site of the highly acidic sulfonic acid groups, whereas under weak acidic conditions such as carboxyl groups, phenolic hydroxyl groups, and hydroxyl groups, the affinity between the anion site of the weak acid functional group and ammonium ions weakens, and it is believed that ammonium ions in the vicinity of the anion site of the weak acid functional group are more likely to be exchanged with hydroxonium ions, water, etc., and as a result, it is believed that ammonium ions that have completed the reaction are more easily discharged from the cathode catalyst layer, and the next supply of nitrogen gas and protons also progresses.

[0083] <Fired body A> The calcined body A is a calcined body produced by calcining a mixture containing a conductive carbon material containing a nitrogen-containing compound, an aromatic compound having a phenolic hydroxyl group, or both. It is a material designed to transport raw materials and products related to ion conduction and electrolytic synthesis.

[0084] Examples of the nitrogen-containing compound include urea, aromatic urea compounds, guanidine compounds, triazine-based heterocyclic compounds, and nitrogen-containing condensed ring compounds. Examples of the aromatic urea compound include phenylurea, benzylurea, N-ethyl-N'-phenylurea, p-ethoxyphenylurea, N,N'-diphenylurea, N,N-diphenylurea, tetraphenylurea, and benzoylurea. Examples of the guanidine compound include guanidine, methylguanidine, nitroguanidine, aminoguanidine, biguanide, dicyandiamide, carbamoylguanidine, glycocyamine, creatine, N,N'-diphenylguanidine, and triphenylguanidine, and guanidine and aminoguanidine are preferred. Examples of the triazine-based heterocyclic compound include 1,3,5-triazine, cyanuric chloride, cyanuric acid, trimethyl cyanurate, methyl isocyanurate, ethyl isocyanurate, melamine, melem, melam, ammeline, ammelide, benzoguanamine, methylguanamine, 1,3,5-trimethyltriazine, 1,3,5-triphenyltriazine, amerine, ameride, thiocyanuric acid, diaminomercaptotriazine, diaminomethyltriazine, diaminophenyltriazine, and diaminoisopropoxytriazine, and melamine is preferred.

[0085] The conductive carbon material may be any material that is responsible for electron conduction in the catalyst layer that electrochemically synthesizes ammonia, and examples of such materials include carbon black, carbon nanotubes, and graphene nanoplatelets. These materials may be used alone or in combination of two or more. Examples of carbon black include Ketjen black, Examples of carbon black include EC, channel black, oil furnace black, Vulcan, furnace black, thermal black, acetylene black, lamp black, graphitized black, and black oxide. Since they have good electrical conductivity, acetylene black, Ketjen black, and Ketjen black EC are preferred, and Ketjen black and Ketjen black EC are more preferred. Carbon black may be used alone or in combination of two or more. Carbon black may be surface-treated. Specific examples of carbon black include Denka Black (manufactured by Denka Company); LACK PEARLS (registered trademark) 2000, VULCAN (registered trademark) XC-72, VULCAN (registered trademark) P, and TERLING (registered trademark) C (manufactured by Cabot Corporation); Asahi HS-500, Asahi #8, Asahi #15, Asahi #15HS, Asahi #22K, Asahi Thermal, Asahi #35, Asahi #50, Asahi #50U, Asahi #50HG, Asahi #51, Asahi #52, Asahi #55, Asahi #60U, Asahi #60HN, Asahi #65, Asahi F-200GS, Asahi #70, Asahi #80, Asahi #95, Asahi AX-015, and Asahi #15HS (manufactured by Asahi Carbon); and Ketjen Black. Examples include EC300J, Carbon ECP, Ketjen black EC600JD, Carbon ECP600JD (manufactured by Lion Specialty Chemicals); Ketjen black EC, Ketjen black EC-600JD (manufactured by Ketjen black International); Carbon black CP (manufactured by Aldrich), TOKABLACK #5500, TOKABLACK #4500, TOKABLACK #4400, Aqua-black 001 (manufactured by Tokai Carbon), etc.

[0086] Examples of carbon nanotubes include single-walled nanotubes and multi-walled carbon nanotubes obtained by vapor phase growth, catalytic vapor phase growth, catalytic chemical vapor growth, chemical vapor growth, super multiplication, catalytic carbon deposition, arc discharge, laser evaporation, etc., and these can take any shape such as needle-like, coil-like, tubular, etc. Carbon nanotubes have a shape formed by rolling one surface of carbon hexagonal mesh graphite into a cylindrical shape, and examples of the carbon nanotube include multi-walled carbon nanotubes rolled in three or more layers (multi-walled carbon nanotubes), single-walled carbon nanotubes (single-walled carbon nanotubes: SWNT) rolled in one layer with one surface of graphite, double-walled carbon nanotubes (double-walled carbon nanotubes: DWNT) rolled in two layers, and vapor-grown carbon fiber (VGCF, a registered trademark of Showa Denko KK). Specifically, supergrowth method CNT (manufactured by the New Energy and Industrial Technology Development Organization), eDIPS-CNT (manufactured by the New Energy and Industrial Technology Development Organization), SWNT series (manufactured by Meijo Nanocarbon Co., Ltd.: trade name), VGCF (registered trademark) series such as VGCF, VGCF-H, VGCF-X (manufactured by Showa Denko K.K.: registered trademark), FloTube series (manufactured by CNano Technology Co., Ltd.: trade name), AMC (manufactured by Ube Industries, Ltd.: trade name), NANOCYL NC7000 series (manufactured by Nanocyl SA: trade name), Baytubes (manufactured by Bayer: trade name), GRAPHISTRENGTH (manufactured by Arkema: trade name), MWNT7 (manufactured by Hodogaya Chemical Co., Ltd.: trade name), Hyperion CNT (manufactured by Hypeprion Catalysis International: trade name), etc. are mentioned. VGCF (registered trademark) series such as VGCF, VGCF-H, VGCF-X, etc. are preferred. The carbon nanotubes may be used alone or in combination of two or more. The carbon nanotubes may be surface-treated. Furthermore, carbon black and carbon nanotubes may be used in combination.

[0087] Examples of graphene nanoplatelets include xGnP (registered trademark: manufactured by XG Sciences) such as xGnP C-grade (750), xGnP Dispersion, xGnP R-grade, xGnP graphene nanoplatelets-grade C-500, xGnP graphene nanoplatelets-grade C-300, and xGnP M-5, graphene nanoplatelets manufactured by Cheap Tubes, and graphene nanoplatelets manufactured by Strem.

[0088] The aromatic compound having a phenolic hydroxyl group is a monocyclic aromatic compound, and examples of phenols having three phenolic hydroxyl groups include pyrogallol, 1,2,4-benzenetriol, phloroglucinol, 2-methylphloroglucinol, m-xylose, and the like. Examples of the phenols having four phenolic hydroxyl groups as monocyclic aromatic compounds include 1,2,3,5-benzenetetraol or 1,2,4,5-benzenetetraol. Examples of the phenols having six phenolic hydroxyl groups as monocyclic aromatic compounds include hexahydroxybenzene. Examples of the phenolic hydroxyl groups as monocyclic aromatic compounds include 3-6 phenols having 3-6 phenolic hydroxyl groups, and the monocyclic aromatic compounds are more preferably phenols having three phenolic hydroxyl groups, and phloroglucinol represented by the following formula (I) is particularly preferred. [ka] Examples of the condensed polycyclic aromatic compounds include naphthalene, azulene, heptalene, biphenylene, acenaphthylene, fluorene, phenalene, phenanthrene, anthracene, aceanthrylene, triphenylene, pyrene, chrysene, tetracene, perylene, pentacene, picene, and coronene, and naphthalene, anthracene, and triphenylene are preferred. Examples of the condensed polycyclic aromatic compounds having a phenolic hydroxyl group include 1,2-dihydroxynaphthalene, 1,3-dihydroxynaphthalene, 1,4-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,4-dihydroxynaphthalene, 2,5-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, 1,3,8-trihydroxynaphthalene, 9,10-anthracene, and Examples of the hydroxyl group include ellagic acid and 2,3,6,7,10,11-hexahydroxytriphenylene, and the like. Preferred examples include 2,6-dihydroxynaphthalene, 1,3,8-trihydroxynaphthalene, 9,10-anthracene, ellagic acid, and 2,3,6,7,10,11-hexahydroxytriphenylene, and more preferred examples include ellagic acid represented by the following formula (II) and 2,3,6,7,10,11-hexahydroxytriphenylene represented by the following formula (III). [ka] The aromatic compound having a phenolic hydroxyl group may be used alone or in combination of two or more. The aromatic compound having a phenolic hydroxyl group, whether monocyclic or condensed polycyclic, preferably has three or more phenolic hydroxyl groups, more preferably has 3 to 6 phenolic hydroxyl groups, and is presumed to be capable of forming a three-dimensional polymer.

[0089] The manufacturing method of the calcined body A will be described. The calcined body A is a material having a nitrogen-containing compound and a phenolic hydroxyl group. The carbon material is obtained by calcining a mixture containing a conductive carbon material containing an aromatic compound having a phenolic hydroxyl group or both. The calcination temperature may be a temperature at which the nitrogen-containing compound and the aromatic compound having a phenolic hydroxyl group can be polymerized or carbonized, and is preferably 150 to 1000°C, more preferably 200 to 800°C, and even more preferably 250 to 600°C. Calcination is performed at the calcination temperature for preferably 1 to 10 hours, more preferably 1 to 5 hours. Calcination can be performed in air or in an inert gas, and examples of the inert gas include nitrogen and argon.

[0090] <Structure of fired body A> The nitrogen-containing compound component of the raw material and the aromatic compound having a phenolic hydroxyl group of the preferred raw material may be contained in the fired body in the form of the mother nucleus structure of the raw material. Alternatively, at least a part of the raw material nitrogen-containing compound component and the preferred raw material aromatic compound having a phenolic hydroxyl group may be contained in the fired body as a three-dimensional polymer. The raw material nitrogen-containing compound component and the preferred raw material aromatic compound having a phenolic hydroxyl group may undergo a thermal condensation reaction and a thermal polymerization reaction by firing to form a three-dimensional polymer of an aromatic compound having a phenolic hydroxyl group and a three-dimensional polymer of a nitrogen-containing compound constituting the raw material nitrogen-containing compound component, respectively. When a thermal condensation reaction and a thermal polymerization reaction occur in three dimensions, the raw material aromatic compound having a phenolic hydroxyl group has three or more phenolic hydroxyl groups, and the nitrogen-containing compound constituting the raw material nitrogen-containing compound component has three or more functional groups.

[0091] A three-dimensional polymer of an aromatic compound having a phenolic hydroxyl group is, for example, represented by the following formula (a) when phloroglucinol represented by the following formula (I) is used as a raw material. [ka]

[0092] A three-dimensional polymer of a nitrogen-containing compound is produced, for example, by calcining melamine (i) as a raw material, while eliminating ammonia, through ammonia-eliminating condensation products such as melam represented by the following formula (ii), melem represented by the following formula (iii), a compound represented by the following formula (iv) or formula (v), and melon represented by the following formula (vi), formula (vii) or formula (viii). [ka] The three-dimensional polymer of the nitrogen-containing compound may have a structure in which a large number of structures such as (i) to (viii) are linked together, for example, as represented by the following formula (ix). By proceeding with the polymerization reaction, the structure becomes a layered structure of g-C3N4, which is graphite-like carbon nitride represented by the following formula (x). [ka]

[0093] The structure of graphitic carbon nitride can be understood from the following non-patent literature. (Non-Patent Document A) Industrial Chemistry Journal, 1963, Vol. 66, No. 6, pp. 804-809 (Non-Patent Document B) Chem.Eur.J. 2007, Vol. 13, pp. 4969-4980

[0094] In the calcined body A, the reaction to form a three-dimensional polymer having a large number of phenolic hydroxyl groups, as shown in formula (a), and the reaction to form a three-dimensional polymer having a large number of amino groups, as shown in formula (ix), are presumed to be orthogonal reactions, and it is believed that each three-dimensional polymer is formed independently.

[0095] The fired body A is a conductive carbon material having a surface layer on which a large number of phenolic compounds represented by the formula (a) are formed. It is presumed that the cathode catalyst layer exhibits both electronic and ionic conductivity because it has a structure of a three-dimensional polymer having hydroxyl groups, or a three-dimensional polymer having a large number of amino groups as shown in formula (ix), or both.

[0096] <Ink for catalyst layer> Examples of materials to be added to the ink for the catalyst layer containing the cathode catalyst layer material include a binder, a conductive carbon material, and an ionic liquid.

[0097] <Binder: Material added to ink for catalyst layer> The binder may be capable of binding materials capable of conducting ions and electrons, supported catalysts, or materials added to the ink when the ink is applied and the solvent component is distilled off to form a catalyst layer, and may further be capable of binding the solid content of the ink to the surfaces of the electrolyte membrane and the gas diffusion layer. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), hydrophilic polymers, fluorine-based sulfonic acid polymers such as Nafion (registered trademark, manufactured by DuPont Co., Ltd.), Aquivion (registered trademark, manufactured by Solvay K.K.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.). A hydrophilic polymer exhibits hydrophilicity by containing polar or charged functional groups in the polymer, and has many functional groups in the polymer that have a strong interaction with water. Examples of functional groups that have a strong interaction with water include ionic groups, hydroxy groups, amino groups, amide groups, and ether groups. In addition, the weight average molecular weight measured by gel permeation chromatography is 10,000 to 3,000,000, preferably 20,000 to 2,000,000, and more preferably 30,000 to 1,500,000. Specific examples include polyvinyl alcohol, polyacrylamide, polyethyleneimine, polyacrylic acid, polyvinylpyrrolidone, polypyridine, poly(4-vinylpyridine), poly(2-vinylpyridine), and poly(4-vinylpyridine-co-styrene), and these may be used alone or in combination of two or more. Among these, polyvinyl alcohol, polyvinylpyrrolidone, poly(4-vinylpyridine) and poly(2-vinylpyridine) are preferred, and polyvinylpyrrolidone is more preferred.

[0098] <Conductive carbon material: Material added to ink for catalyst layer> The conductive carbon material may be any material that is responsible for electron conduction in the catalyst layer that electrochemically synthesizes ammonia, and examples of the conductive carbon material include those described above as the conductive carbon material for the fired body A.

[0099] <Ionic liquid: Material added to ink for catalyst layer> Examples of the ionic liquid include those described above as the catalyst carrier.

[0100] <Solvent used in ink for catalyst layer> Examples of the solvent used in the ink for the catalyst layer include water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, pentanol, dimethyl sulfoxide, and N,N-dimethylformamide. As the solvent, water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and isobutyl alcohol are preferred. Two or more of the above-mentioned solvents can also be mixed and used. From the viewpoint of preventing re-aggregation of the ink and facilitating application, and further preventing the solvent from remaining in the catalyst layer, the solvent used in the catalyst ink is more preferably water, ethanol, 1-propanol, and 2-propanol.

[0101] <Electrolyte membrane> Examples of the electrolyte membrane include polymer electrolyte membranes and reinforced membranes, and in addition to cation exchange membranes and anion exchange membranes, bipolar membranes and mosaic charged membranes are composite charged membranes in which the structures of cation exchange membranes and anion exchange membranes exist in one membrane due to differences in the fixed charge structure in one membrane, and can be arbitrarily selected and used in the ammonia production apparatus of this embodiment. Specific examples of such electrolyte membranes include DuPont's Nafion Membrane (registered trademark), Solvay's Aquivion Membrane (registered trademark), AGC's Flemion Membrane (registered trademark), Asahi Kasei's Aciplex (registered trademark), Dow's Dow Membrane (registered trademark), sulfonated polyether ketone polymer membranes, sulfonated polyether sulfone polymer membranes, sulfonated polyether ether sulfone polymer membranes, sulfonated polysulfide polymer membranes, sulfonated polyphenylene polymer membranes, and perfluorosulfonate membranes using a polytetrafluoroethylene (PTFE) porous body as a reinforcing material. Examples of such membranes include GoreSelect Membrane (registered trademark) from Gore Japan LLC, which is impregnated with a phosphate polymer, membranes reinforced with PTFE woven fabric, membranes using a porous polyethylene (PE) or porous polypropylene (PP) as a reinforcing material (for example, as described in patent document WO98 / 20063), fibril-reinforced membranes using PTFE fibrils (for example, as described in patent document US2001-026883A1 and non-patent document Industrial Materials, 2001, vol. 49, p. 31), Neosepta (registered trademark) from Astom Corporation, Selemion Membrane (registered trademark) from AGC Corporation, Aciplex Membrane (registered trademark) from Asahi Kasei Corporation, Fumasep Membrane (registered trademark) from FUMATECH BWT GmbH, and fumapem Membrane (registered trademark) from FUMATECH BWT GmbH.

[0102] As the electrolyte membrane 102 which is a cation exchange membrane, Nafion membrane (registered trademark) of DuPont, Aquivion membrane (registered trademark) of Solvay, and Gore Select membrane (registered trademark) of Gore Japan LLC are preferred, and as the electrolyte membrane 302 which is an anion exchange membrane, FAP-450 membrane and FAA-3 membrane of Fumasep membrane (registered trademark) of FUMATECH BWT GmbH, ASVN membrane and AHO membrane of Selemion membrane (registered trademark) of AGC are preferred.

[0103] The electrolyte contained in the electrolytic solution in the method for producing ammonia will be described. Examples of the electrolyte include cations such as proton, lithium ion, sodium ion, potassium ion, imidazolium ion, pyridinium ion, quaternary ammonium ion, phosphonium ion, pyrrolidinium ion, and phosphonium ion, which may be used alone or in combination, and anions such as chloride ion, bromide ion, iodide ion, tetrafluoroborate, trifluoro(trifluoromethyl)borate, dimethylphosphate ion, diethylphosphate ion, hexafluorophosphate, tris(pentafluoroethyl)trifluorophosphate, trifluoroacetate, methylsulfate, trifluoromethanesulfonate, bis(trifluoromethanesulfonyl)imide, perchlorate ion, sulfate ion, and nitrate ion, which may be used alone or in combination. The electrolyte may be used alone or in combination.

[0104] Examples of the quaternary ammonium ion in the electrolyte include triethylpentylammonium ion, diethyl(methyl)propylammonium ion, methyltri-n-octylammonium ion, trimethylpropylammonium ion, cyclohexyltrimethylammonium ion, diethyl(2-methoxyethyl)-methylammonium ion, ethyl(2-methoxyethyl)-dimethylammonium ion, ethyl(3-methoxypropyl)dimethyl-ammonium ion, ethyl(dimethyl)(2-phenylethyl)-ammonium ion, tetramethylammonium ion, tetraethylammonium ion, triethylpentylammonium ion, tetra-n-butylammonium ion, diethyl(methyl)propylammonium ion, methyltri-n-octylammonium ion, trimethylpropylammonium ion, cyclohexyltrimethylammonium ion, diethyl(2-methoxyethyl)-methylammonium ion, ethyl(2 -methoxyethyl)-dimethylammonium ion, ethyl(3-methoxypropyl)dimethyl-ammonium ion, ethyl(dimethyl)(2-phenylethyl)-ammonium ion, etc.

[0105] Specific examples of the imidazolium ion, pyridinium ion, phosphonium ion, pyrrolidinium ion and phosphonium ion in the electrolyte include those mentioned above.

[0106] The cation, which is an electrolyte contained in the electrolytic solution, is preferably a proton, an imidazolium ion, or a pyrrolidinium ion, and the anion, which is an electrolyte, is preferably a perchlorate ion or a sulfate ion.

[0107] It goes without saying that the present invention is not limited to the above-described embodiment, and can be embodied in various forms within the technical scope of the present invention.

[0108] [Synthesis Example 1: Production of fired body (1)] Ketjen Black EC (Lion Corporation, EC300J, 1.00 g), melamine (Nissan Chemical Industries, 0.50 g), and phloroglucinol (Tokyo Chemical Industry, 0.50 g) were mixed in a mortar and placed in an alumina crucible. The crucible was placed in a tabletop high-speed heating electric furnace MSFT-1520-P-TR (Yamada Electric Co., Ltd.), heated at 10°C per minute, and fired at a firing temperature of 400°C for 2 hours. After firing, a black fired product (1.32 g, 66% recovery when the charged weight is 100%) was obtained.

[0109] [Example 1] 1. Gas diffusion electrode ("GDE-Cathode-1") The cathode electrode catalyst 12 was prepared on the carbon paper (manufactured by Toray Industries, product name "TGP-H-060H") that was the cathode gas diffusion layer 104. Using a reactive magnetron sputtering device (manufactured by Sanyu Electronics, SRS-7000T), a film was formed on the carbon paper at a rate of 0.636 nm / sec. The film formation conditions were as follows: target: molybdenum (φ106 mm, purity 99.95%), power: DC 300 W, atmosphere: argon (pressure 1 Pa). In this way, a 2.8 × 2.8 cm3 substrate supporting molybdenum catalyst (1.8 mg) was prepared. 2 The gas diffusion electrode 401 was designated as "GDE-Cathode-1A". The ink for the catalyst layer was prepared using the sintered body (1) and 2-propanol (manufactured by Wako Pure Chemical Industries, Ltd.). The ink for the catalyst layer was prepared by adding the sintered body and 2-propanol in this order to a glass vial, and irradiating the dispersion solution with ultrasonic waves for 30 minutes using an ultrasonic cleaner ASU-6 manufactured by AS ONE Corporation with the oscillation power set to High. Specifically, the ink was prepared as "ink 1A" consisting of the sintered body (1) (30 mg) and 2-propanol (1.2 mL). Next, the "ink 1A" was applied to the gas diffusion electrode 401 "GDE-Cathode-1A" and the ink solvent was dried to prepare the cathode gas diffusion electrode 403 as "GDE-Cathode-1".

[0110] The anode catalyst layer 203 was prepared as follows. An ink for preparing the anode catalyst layer 203 was prepared as "ink 1B" as follows. "Ink 1B" was prepared using a carbon black-supported platinum catalyst (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., platinum content: 46.5% by weight, product name "TEC10E50E", hereinafter abbreviated as carbon-supported platinum catalyst) as an electrode catalyst, deionized water, ethanol, and a Nafion dispersion solution (manufactured by Fujifilm Wako Pure Chemical Industries, product name "5% Nafion dispersion solution DE520 CS type") as an electrode catalyst. The carbon-supported platinum catalyst, deionized water, Nafion dispersion solution, and ethanol were added in this order to a glass vial, and the obtained dispersion solution was irradiated with ultrasonic waves set to 40% output using an ultrasonic homogenizer Smurt NR-50M manufactured by Microtech Nithion Co., Ltd. for 30 minutes to prepare "ink 1B". Ink 1B, a carbon-supported platinum catalyst (100.0 mg), a Nafion dispersion solution (837 μL, 38.9 mg of Nafion solids), deionized water (0.6 mL), and ethanol (5 mL) were prepared. Next, this "Ink 1B" was applied to a carbon paper (manufactured by Toray Industries, product name "TGP-H-060H") that was the anode gas diffusion layer 204 and fixed to a hop plate at 80°C, and the ink solvent was dried. The amount of application was 1 cm. 2 The amount of platinum per unit area was adjusted to 1.0 mg. In this way, a 2.8 × 2.8 cm2 sample was prepared, coated with 7.8 mg of platinum catalyst, a metal catalyst. 2 The anode gas diffusion electrode was fabricated as "GDE-Aode-1".

[0111] 2. Membrane electrode assembly (preparation of "MEA-1") A membrane electrode assembly "MEA-1" consisting of an electrolyte membrane 102, a cathode gas diffusion electrode 403 "GDE-Cathode-1" and an anode gas diffusion electrode "GDE-Aode-1" was produced as follows. The ion exchange membrane used for the electrolyte membrane 102 was a commercially available DuPont Nafion 212 membrane (registered trademark) (film thickness 50 μm, 5 cm × 4 cm). After placing "GDE-Cathode-1" on one side of the electrolyte membrane and "GDE-Anode-1" on the other side, the membrane was thermocompressed using a precision heating and pressing device (CYPT10, manufactured by Shinto Kogyo Co., Ltd.) under the conditions of upper and lower plate temperatures of 134°C, load of 5.4 kN, and compression time of 240 seconds to produce the membrane electrode assembly "MEA-1".

[0112] 3. Construction of ammonia electrochemical synthesis device A stainless steel current collector with 25 circular holes of 2.5 mm in diameter was attached to both sides of the obtained "MEA-1" together with a Teflon (registered trademark) sheet serving as a gasket to an electrolytic cell, and a production apparatus (manufactured by Nissan Chemical Industries, Ltd.) having the configuration shown in the schematic diagram of FIG. 1 and ammonia production apparatus 300 in FIG. 8 were assembled.

[0113] 4. Ammonia production using electrochemical synthesis equipment Using the production apparatus as described above, ammonia was electrolytically synthesized by constant potential electrolysis under the following conditions. Temperature of the device body: 25 to 28°C (room temperature) Power supply 101: Versa STAT4 manufactured by Princeton Applied Research was used to perform constant potential electrolysis and measure voltage and current. Reaction conditions: -2.3V constant potential electrolysis, 1 hour Cathode electrolyte tank 303: Nitrogen was bubbled into an aqueous sulfuric acid solution (0.02 mol / L, 6 mL) at 10 mL / min. Anode electrolyte tank 313: Sulfuric acid solution (0.02 mol / L, 6 mL) Ammonia collection tank 308: sulfuric acid aqueous solution (0.02 mol / L, 10 mL) Reaction conditions: -2.3V constant potential electrolysis Ammonia was quantified using Thermo Scientific Dionex ion chromatography (IC) system, Dionex Integrion manufactured by Thermo. The amount of ammonia produced was calculated by quantifying the amount of ammonia in the sulfuric acid aqueous solution in the dilute sulfuric acid aqueous solution tank 308 for ammonia collection and in the sulfuric acid aqueous solution in the cathode electrolyte tank 303. The amount of ammonia produced was 0.36 μmol.

[0114] [Example 2] 1. Gas diffusion electrode ("GDE-Cathode-2") The cathode catalyst layer 103 was produced as follows. The ink for producing the cathode catalyst layer 103 was called "ink 2A" and was produced as follows. A carbon-supported platinum catalyst (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., platinum content: 46.5% by weight, product name "TEC10E50E") as an electrode catalyst, a fired body (1), polyvinylpyrrolidone (manufactured by Tokyo Kasei Co., Ltd., K30, weight average molecular weight 40,000), a Nafion dispersion solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name "5% Nafion dispersion solution DE520 CS type"), and 2-propanol (manufactured by Wako Pure Chemical Industries, Ltd.) were mixed in this order. After adding the above, ultrasonic homogenizer Smurt NR-50M was used to irradiate ultrasonic waves at 40% output for 30 minutes to prepare "ink 2A". Specifically, the following ingredients were set: carbon-supported platinum catalyst (100.0 mg), Nafion dispersion solution (276.0 mg, Nafion solid content 13.8 mg), fired body (1) (48.6 mg), polyvinylpyrrolidone (6.6 mg), and 2-propanol (4 mL). Next, this "ink 2A" was applied to carbon paper (manufactured by Toray Industries, product name "TGP-H-060H"), which was the cathode gas diffusion layer 104 and fixed to a hop plate at 80°C, and the ink solvent was dried. The amount of application was 1 cm. 2 The amount of platinum per unit area was adjusted to 1.0 mg. In this way, a 2.8 × 2.8 cm2 sample was prepared, coated with 7.8 mg of platinum catalyst, a metal catalyst. 2 Ammonia production by electrolysis was carried out in the same manner as in Example 1, except that the anode gas diffusion electrode was prepared as "GDE-Cathode-2." The amount of ammonia produced was 0.41 μmol.

[0115] [Comparative Example 1] The cathode catalyst layer 103 was prepared as follows. It was prepared in the same manner as "Ink 1B" prepared in Example 1, and the ink was applied to carbon paper (manufactured by Toray Industries, product name "TGP-H-060H") in the same manner, with the amount of ink applied adjusted, to obtain a 2.8 x 2.8 cm2 layer coated with platinum catalyst (1.8 mg) as a metal catalyst and Nafion (7.8 mg) as a solid content. 2 Except for preparing the cathode gas diffusion electrode 403 as "GDE-Cathode-1C", ammonia was produced by electrolysis in the same manner as in Example 1. The amount of ammonia produced was 0.11 μmol.

[0116] Comparing the amount of ammonia generated in Example 2 with that in Comparative Example 1, there was an improvement of about four times. This is presumably due to the improvement effect of the gas diffusion electrode of the present invention, which uses a material selected from the group of materials for the cathode catalyst layer. [Industrial Applicability]

[0117] The gas diffusion electrode of the present invention can be used as an electrode member of an ammonia production apparatus that electrochemically synthesizes ammonia using nitrogen gas and water as raw materials, and can also be used in ammonia production methods. [Explanation of symbols]

[0118] 1 Schematic diagram showing the configuration of the gas diffusion electrode and membrane electrode assembly 2 Schematic diagram showing the structure of the gas diffusion electrode and membrane electrode assembly after thermocompression bonding 2 3 Schematic diagram showing the configuration of the gas diffusion electrode and membrane electrode assembly 3 4 Schematic diagram showing the configuration of the gas diffusion electrode and membrane electrode assembly 4 5 Schematic diagram showing the configuration of the gas diffusion electrode and membrane electrode assembly. 11 Catalyst layer including a material for a cathode catalyst layer 12 Cathode electrode catalyst 100 A manufacturing device that electrochemically synthesizes ammonia using nitrogen gas and water as raw materials. 101 Power supply 102 Electrolyte membrane (cation exchange membrane) 103 Cathode catalyst layer 104 Cathode gas diffusion layer 105 Cathode separator 106 Cathode side flow path (connected to various supply devices) 107 Cathode side flow path (connected to the recovery tank and exhaust device) 200 A manufacturing device that electrochemically synthesizes ammonia using nitrogen gas and water as raw materials. 203 Anode catalyst layer 204 Anode gas diffusion layer 205 Anode separator 206 Anode side flow path (connected to various supply devices) 207 Anode side flow path (connected to the recovery tank and exhaust device) 300 A manufacturing device that electrochemically synthesizes ammonia using nitrogen gas and water as raw materials. 301 Piping 302 Electrolyte membrane (anion exchange membrane) 303 Cathode side electrolyte tank 304 Cathode side electrolyte 313 Anode side electrolyte tank 314 Anode side electrolyte 305 Nitrogen gas mass flow controller 306 Nitrogen cylinder regulator 307 Nitrogen Cylinder 308 Ammonia collection tank 309 Draft device 401 Gas diffusion electrode consisting of cathode catalyst and cathode gas diffusion layer 402 Catalyst-coated membrane consisting of cathode catalyst layer and electrolyte membrane 403 Gas diffusion electrode consisting of cathode catalyst layer and cathode gas diffusion layer

Claims

1. A gas diffusion electrode comprising a catalyst layer including a material for a cathode catalyst layer and a cathode electrode catalyst.

2. 2. The gas diffusion electrode according to claim 1, wherein the material for the cathode catalyst layer is at least one selected from the group consisting of polymer electrolytes and sintered bodies of mixtures containing a nitrogen-containing compound component and a conductive carbon material.

3. 3. The gas diffusion electrode according to claim 1, further comprising a catalyst layer comprising a material for a cathode catalyst layer, the material being formed by using a material for a cathode catalyst layer and an ink for a catalyst layer containing a cathode electrode catalyst.

4. The gas diffusion electrode according to any one of claims 1 to 3, wherein an additive component to the ink for the catalyst layer containing the material for the cathode catalyst layer and the cathode electrode catalyst is at least one selected from the group consisting of a binder, a conductive carbon material, and an ionic liquid.

5. 3. The gas diffusion electrode according to claim 1, further comprising a catalyst layer containing a material for a cathode catalyst layer, the catalyst layer being formed using an ink for a catalyst layer containing the material for a cathode catalyst layer.

6. 6. The gas diffusion electrode according to claim 1, wherein an additive component to an ink for a catalyst layer containing a material for a cathode catalyst layer is at least one selected from the group consisting of a binder, a conductive carbon material, and an ionic liquid.

7. The method for producing a gas diffusion electrode according to any one of claims 1 to 6, further comprising the step of producing a catalyst layer containing a material for a cathode catalyst layer in the process for producing the gas diffusion electrode.

8. A membrane electrode assembly comprising the gas diffusion electrode according to any one of claims 1 to 6.

9. An ammonia producing apparatus for electrochemically synthesizing ammonia, comprising the membrane electrode assembly according to claim 8.

Images