Fuel cell

Abstract

The present embodiment relates to a fuel cell comprising at least a membrane electrode assembly having an electrolyte membrane, an anode catalyst layer disposed on one surface of the electrolyte membrane, and a cathode catalyst layer disposed on the other surface of the electrolyte membrane, the cathode catalyst layer contains at least an electrochemical oxygen reduction electrode catalyst that contains a catalyst metal having oxygen reduction activity and a modifier that modifies the catalyst metal, and the modifier is at least one type selected from the group consisting of nitrogen-containing cyclic organic compounds and polymers thereof. At least one selected from the group consisting of the electrolyte membrane, the anode catalyst layer, and the cathode catalyst layer contains a decomposition inhibitor that inhibits the decomposition of the modifier.

Description

Technical Field

[0001] This disclosure relates to a fuel cell. Background Technology

[0002] Fuel cells generate electricity through an electrochemical reaction between hydrogen and oxygen. The only byproduct of power generation from fuel cells is, in principle, water. Therefore, they have attracted attention as a clean power generation system with virtually no impact on the Earth's environment. A fuel cell is constructed using a membrane electrode gas diffusion layer junction (hereinafter also referred to as "MEGA") as its basic unit, with electrode catalyst layers disposed on both sides of an electrolyte membrane, and a gas diffusion layer disposed on the outside of each electrode catalyst layer. The binder between the electrolyte membrane and the electrode catalyst layers typically uses a polymeric electrolyte with ion-exchange groups (hereinafter also referred to as "ionomer" or "ion-crosslinked polymer"). During fuel cell operation, an electromotive force is generated by supplying hydrogen-containing fuel gas to the electrode catalyst layer on the anode (fuel electrode) side and oxygen-containing oxidizing gas to the electrode catalyst layer on the cathode (air electrode) side. The hydrogen oxidation reaction occurs at the anode, and the oxygen reduction reaction occurs at the cathode, supplying an electromotive force to an external circuit. Therefore, the electrode catalyst layer at the cathode uses an oxygen reduction catalyst with oxygen reduction capabilities. In order to provide high-performance and highly durable oxygen reduction catalysts that can be used in the electrode catalyst layer of the cathode of fuel cells, various electrochemical oxygen reduction electrode catalysts have been developed.

[0003] For example, Japanese Patent Application Publication No. 2023-121010 discloses a catalyst composition comprising a platinum-based catalyst and a salt modified by the platinum-based catalyst, wherein the salt is composed of a 1,3,5-triazine derivative cation and a perfluoroalkylsulfonyl imide anion represented by the following general formula (1).

[0004] International Publication No. 2019 / 221156 discloses an electrochemical oxygen reduction catalyst containing platinum-containing nanoparticles and at least one of melamine compounds, thiocyanuric acid compounds, and polymers using the aforementioned melamine compounds or thiocyanuric acid compounds as monomers.

[0005] International Publication No. 2021 / 090746 discloses an electrochemical oxygen reduction catalyst containing platinum nanoparticles and at least one selected from polymers with melamine compounds as monomers and thiol melamine compounds, wherein the polymers with melamine compounds as monomers are polymers having repeating units represented by general formula (1), and the thiol melamine compounds are thiol melamine compounds represented by general formula (2). Summary of the Invention

[0006] As described above, an electrochemical oxygen reduction electrode catalyst having a catalyst metal modified with various nitrogen-containing cyclic organic compounds or their polymers has been developed for use in the electrode catalyst layer of the cathode of a fuel cell. It is known that modifying the surface of an oxygen-reducing catalyst with nitrogen-containing cyclic organic compounds such as melamine improves the catalyst's performance, particularly its initial voltage. Specifically, it is known that in fuel cells using this catalyst in the cathode (air electrode), performance is particularly improved in the low-load region where the catalyst performance contributes significantly. Operation in the low-load region is the most fundamental operating condition due to the low consumption of hydrogen as fuel and the ability to operate efficiently.

[0007] However, it has been found that fuel cells using catalysts containing nitrogen-containing cyclic organic compounds as modifiers exhibit a rapid voltage drop rate when continuously operated in low-load regions. Therefore, there is room for improvement in the performance related to the voltage drop rate in fuel cells using catalysts containing nitrogen-containing cyclic organic compounds as modifiers.

[0008] Therefore, the purpose of this disclosure is to provide a fuel cell with good voltage and its retention rate.

[0009] The inventors have conducted various studies on methods for solving the above-mentioned problems and have found that the accelerated voltage drop in fuel cells using catalysts containing nitrogen-containing cyclic organic compounds as modifiers at the cathode is due to catalyst poisoning caused by the decomposition of the modifier and its associated decomposition products. Specifically, it is believed that catalyst poisoning occurs due to the decomposition of the modifier during the following process, resulting in catalyst poisoning from these decomposition products.

[0010] (1) Hydrogen peroxide is generated in MEA

[0011] (2) In the Fenton reaction, hydrogen peroxide generates OH radicals.

[0012] (3) Decomposition of the modifier caused by OH free radicals

[0013] (4) Catalyst poisoning due to decomposition products leads to a decrease in catalyst performance.

[0014] Therefore, the inventors discovered that by including a decomposition inhibitor that inhibits the decomposition of the modifier in the fuel cell, the voltage retention rate can be improved, thus completing this disclosure.

[0015] Therefore, examples of this embodiment are described below.

[0016] [1] A fuel cell comprising at least a membrane electrode assembly having an electrolyte membrane, an anode catalyst layer disposed on one side of the electrolyte membrane, and a cathode catalyst layer disposed on the other side of the electrolyte membrane.

[0017] The aforementioned cathode catalyst layer comprises at least an electrochemical oxygen reduction electrode catalyst, wherein the electrochemical oxygen reduction electrode catalyst contains a catalyst metal with oxygen reduction activity and a modifier that modifies the catalyst metal.

[0018] The aforementioned modifier is selected from at least one nitrogen-containing cyclic organic compound and its polymer.

[0019] At least one of the electrolyte membrane, the anode catalyst layer, and the cathode catalyst layer contains a decomposition inhibitor that inhibits the decomposition of the above-mentioned modifier.

[0020] [2] According to the fuel cell described in [1], the above-mentioned decomposition inhibitor is a free radical quencher, which is a metal or metal complex, metal salt, metal oxide or metal ion.

[0021] [3] The fuel cell according to any one of [1] to [2], wherein the above-mentioned decomposition inhibitor is at least one metal ion selected from cerium ions and manganese ions.

[0022] [4] The fuel cell according to any one of [1] to [3], wherein the nitrogen-containing cyclic organic compound is a compound of the following formula (1):

[0023]

[0024] In formula (1), R1, R2 and R3 are each independently a hydrogen atom, halogen atom, amino, hydroxyl, nitrile, amide, thiol, sulfonyl, carboxyl, phosphate, ketone, aldehyde, ester, phenyl, phenol, alkyl, cycloalkyl, alkenyl, alkoxy, alkylamino, alkylsulfonic acid, perfluoroalkyl, alkenylamino, alkenylsulfonic acid, or perfluoroalkenyl. These groups may be substituted by fluorine, chlorine, bromine or iodine atoms, and at least one carbon atom of these groups may be substituted by oxygen, sulfur or nitrogen atoms.

[0025] [5] The fuel cell according to any one of [1] to [4], wherein the catalyst metal having oxygen reduction activity comprises at least one selected from platinum, platinum alloys and platinum-containing composites.

[0026] According to this disclosure, a fuel cell with good voltage and its retention rate can be provided. Attached Figure Description

[0027] Hereinafter, the features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described with reference to the accompanying drawings, wherein the same symbols denote the same elements.

[0028] Figure 1This is a cross-sectional schematic diagram used to illustrate the configuration example of the membrane electrode gas diffusion layer junction and the fuel cell of this embodiment, and is a cross-sectional view of the main part of the fuel cell 10 as an example. Detailed Implementation

[0029] This embodiment is a fuel cell, comprising at least a membrane electrode assembly having an electrolyte membrane, an anode catalyst layer disposed on one side of the electrolyte membrane, and a cathode catalyst layer disposed on the other side of the electrolyte membrane. The cathode catalyst layer contains at least an electrochemical oxygen reduction electrode catalyst, comprising an oxygen reduction-active catalyst metal and a modifier modifying the catalyst metal. The modifier is at least one selected from nitrogen-containing cyclic organic compounds and their polymers, and includes a decomposition inhibitor to suppress the decomposition of the modifier.

[0030] This embodiment provides a fuel cell with excellent voltage and voltage retention. In this fuel cell, excellent initial voltage is achieved by using an electrode catalyst comprising a catalyst metal with oxygen reduction activity modified by a modifier (a nitrogen-containing cyclic organic compound and / or its polymer) in the cathode catalyst layer. It has been confirmed that the nitrogen-containing cyclic organic compound or its polymer, as a modifier, activates the catalyst metal; therefore, using a catalyst metal modified by this modifier at the cathode improves power generation performance (initial voltage). On the other hand, as described above, when using a catalyst modified by the aforementioned modifier, catalyst poisoning occurs due to the decomposition of the modifier and its associated decomposition products, resulting in a faster rate of voltage decrease during operation, i.e., a lower voltage retention rate. Therefore, in this embodiment, the fuel cell, such as the membrane electrode assembly or the membrane electrode gas diffusion layer assembly, contains a decomposition inhibitor that suppresses the decomposition of the modifier. This suppresses the decomposition of the modifier in the cathode catalyst layer, thereby suppressing catalyst poisoning and improving the voltage retention rate.

[0031] The structure of this embodiment will be described below.

[0032] fuel cells

[0033] The fuel cell of this embodiment includes at least a membrane electrode assembly, which has an electrolyte membrane, an anode catalyst layer disposed on one side of the electrolyte membrane, and a cathode catalyst layer disposed on the other side of the electrolyte membrane. Alternatively, the fuel cell of this embodiment may also include at least a membrane electrode gas diffusion layer assembly, which includes: an electrolyte membrane, an anode catalyst layer disposed on one side of the electrolyte membrane, a cathode catalyst layer disposed on the other side of the electrolyte membrane, an anode-side gas diffusion layer disposed on the surface of the anode catalyst layer opposite to the electrolyte membrane, and a cathode-side gas diffusion layer disposed on the surface of the cathode catalyst layer opposite to the electrolyte membrane.

[0034] The following is for reference Figure 1 The specific configurations of the membrane electrode assembly, the membrane electrode gas diffusion layer assembly, and the fuel cell (e.g., a solid polymer fuel cell) are described.

[0035] Fuel cells (such as solid polymer fuel cells) use a membrane electrode assembly (MEA) as their basic unit, in which catalyst layers (electrodes) are bonded to both sides of an electrolyte membrane. Catalyst layers (electrodes) are bonded to both sides of the electrolyte membrane (e.g., a solid polymer electrolyte membrane). Additionally, a gas diffusion layer can be disposed outside the catalyst layers, and the fuel cell can use a membrane electrode gas diffusion layer assembly (MEGA) as its basic unit. The gas diffusion layer supplies reactant gases and electrons to the catalyst layers and can be made of materials such as carbon paper or carbon cloth. Furthermore, the catalyst layer forms the reaction field for the electrode reactions.

[0036] The following is for reference Figure 1 The composition of the membrane electrode assembly, the membrane electrode gas diffusion layer assembly, and the solid polymer fuel cell is described. Figure 1 This is a cross-sectional schematic diagram used to explain an example of the structure of the solid polymer fuel cell of this embodiment, and is a cross-sectional view of the main part of the fuel cell 10 as an example. The solid polymer fuel cell has a stack of single cells consisting of a power generator and fuel cell separators disposed on both sides of the power generator. Multiple single cells are stacked in the stacking direction, and the single cells are connected in series. Figure 1As shown, the fuel cell 10 has multiple single cells 1 stacked as basic units. Each single cell 1 is a solid polymer fuel cell that generates an electromotive force through an electrochemical reaction between an oxidant gas (e.g., air) and a fuel gas (e.g., hydrogen). Each single cell 1 includes: a membrane electrode gas diffusion layer assembly (MEGA) 2 with gas diffusion layers (GDL) 7 disposed on both sides, and a separator 3 that contacts the MEGA 2 in a manner that divides the MEGA 2. It should be noted that in this embodiment, the MEGA 2 is held by a pair of separators 3, 3.

[0037] MEGA2 comprises a membrane electrode assembly (MEA) 4 and gas diffusion layers 7, 7 disposed on both sides thereof. The MEA 4 consists of an electrolyte membrane 5 and a pair of electrodes 6, 6 joined together to hold the electrolyte membrane 5. The electrolyte membrane 5 is, for example, a proton-conducting ion exchange membrane formed of a solid polymer material. The electrodes 6 contain, for example, porous carbon raw materials supported on catalysts such as platinum. The electrode 6 disposed on one side of the electrolyte membrane 5 functions as an anode, and the electrode 6 on the other side functions as a cathode. The gas diffusion layer 7 is formed of a permeable conductive component. Examples of permeable conductive components include porous carbon materials such as carbon paper or carbon cloth, or porous metal materials such as metal mesh or foamed metal. For example, the anode electrode is formed of an anode catalyst layer, and the cathode electrode is formed of a cathode catalyst layer.

[0038] Electrolyte membranes impede the flow of electrons and gases and allow protons (H+) generated at the anode to pass through. + This refers to the function of the electrolyte membrane migrating from the anode catalyst layer to the cathode catalyst layer. As the electrolyte membrane in this embodiment, a proton-conducting electrolyte membrane known in the art can be used. As a solid polymer electrolyte membrane, for example, a membrane formed from a fluoropolymer with sulfonic acid groups (such as Nafion (DuPont), FORBLUE (AGC), and Aciplex (Asahi Kasei)) can be used. In this embodiment, the electrolyte membrane may also contain a decomposition inhibitor.

[0039] There is no particular limitation on the thickness of the electrolyte membrane; for example, from the viewpoint of improving proton conductivity, it can be 5 μm to 50 μm.

[0040] The cathode catalyst layer functions as the air electrode (oxygen electrode). In this embodiment, the cathode catalyst layer contains at least an electrochemical oxygen reduction electrode catalyst, which includes an oxygen-reducing catalyst metal and a modifier that modifies the catalyst metal. The modifier is selected from at least one nitrogen-containing cyclic organic compound and its polymers. In this embodiment, the cathode catalyst layer may contain a decomposition inhibitor.

[0041] In electrochemical oxygen reduction electrode catalysts, the catalyst metal can be any metal that has oxygen reduction activity (oxygen reduction catalytic energy). Examples of catalyst metals include platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium. The catalyst metal may contain only one of the metals listed above, or it may be contained in the form of an alloy of two or more metals. Furthermore, the catalyst metal may also be an oxide, nitride, sulfide, or phosphide of the metals listed above. Preferably, the catalyst metal contains at least one metal selected from platinum, platinum alloys, and platinum-containing complexes. In the case of platinum alloys and platinum-containing composites, metals other than platinum can be included, for example, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium. Platinum alloys and platinum-containing composites may contain two or more of the metals exemplified above. By including the catalyst metals exemplified above, the electrochemical oxygen reduction electrode catalyst can exhibit high proton conductivity.

[0042] The content of the catalyst metal relative to the total mass of the electrochemical oxygen reduction electrode catalyst is typically in the range of 1 to 70% by mass, preferably in the range of 18 to 65% by mass. Furthermore, when the catalyst metal is a platinum alloy or a platinum-containing composite, the content of metals other than platinum relative to the total mass of the catalyst metal is typically in the range of 0.11 to 60 atomic% by mass. By including the catalyst metal in the above-mentioned ranges, the electrochemical oxygen reduction electrode catalyst can exhibit high proton conductivity.

[0043] The particle size (particle diameter) of catalyst metals is typically in the range of 1 to 100 nm.

[0044] In electrochemical oxygen reduction electrode catalysts, the composition and content of catalyst metals can be determined by, for example, dissolving and extracting the catalyst metals contained in the electrochemical oxygen reduction electrode catalyst, and analyzing the metal elements contained in the extract using thermogravimetric analysis (IG) or inductively coupled plasma atomic emission spectrometry (ICP).

[0045] In electrochemical oxygen reduction electrode catalysts, the particle size of the catalyst metal can be determined, for example, by measuring the crystallite size using X-ray diffraction and calculating the average crystallite size. Alternatively, the particle size of the catalyst metal can be determined by measuring the particle size of 100 to 1000 catalyst metal particles using electron microscopy and calculating their average value (average particle size).

[0046] In electrochemical oxygen reduction electrode catalysts, the catalyst metal is modified by a modifier. The state in which the catalyst metal is modified by a modifier refers to the state in which the modifier adsorbs, supports, or contacts at least a portion of the catalyst metal.

[0047] In this embodiment, the modifier is selected from at least one nitrogen-containing cyclic organic compound and its polymers. By using an electrochemical oxygen reduction electrode catalyst containing this modifier in the cathode catalyst layer, the power generation performance (initial voltage) can be improved, especially the performance in the low-load region where the catalyst performance contributes significantly.

[0048] The nitrogen equivalent of nitrogen-containing cyclic organic compounds is typically in the range of 20–270 g / equivalent, preferably in the range of 20–70 g / equivalent. The nitrogen equivalent of a nitrogen-containing cyclic organic compound is defined by the following formula: Nitrogen equivalent (g / equivalent) = Molecular weight of the nitrogen-containing organic compound (g / mol) / Mass of nitrogen atoms contained in one molecule of the nitrogen-containing organic compound (molN / mol). In the case of polymers containing nitrogen-containing cyclic organic compounds, the nitrogen equivalent of the monomers contained in the polymer is sufficient as long as it falls within the range illustrated above.

[0049] Examples of nitrogen-containing cyclic organic compounds include pyridine, pyrrole, thiazole, and isothiazole. azole, isotonic azole, imidazole, imidazoline, pyrazole, 1,3,5-triazine, pyrimidine, pyridazine, pyrazine, indole, quinoline, isoquinoline, purine, benzimidazole, benzo[a] Zyrazoles, benzothiazoles, tetrazolium, tetrazines, triazoles, carbazoles, acridine, quinoxaline, and quinazoline. The nitrogen-containing cyclic organic compounds exemplified above may have one or more substituted or unsubstituted amines or amino groups (e.g., primary, secondary, tertiary, or quaternary ammonium cations), hydroxyl groups, halogens (e.g., fluorine, chlorine, bromine, or iodine), nitriles, amides, imides, thiols, sulfonyl groups, carboxyl groups, phosphonyl groups, ketones, aldehydes, esters, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkynyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted cycloalkenyl groups, substituted or unsubstituted cycloalkynyl groups, substituted or unsubstituted heterocyclic alkyl groups, substituted or unsubstituted... Cycloalkylalkyl, substituted or unsubstituted heterocycloalkylalkyl, substituted or unsubstituted aryl, substituted or unsubstituted arylalkyl, substituted or unsubstituted heteroaryl, substituted or unsubstituted heteroarylalkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted cycloalkoxy, substituted or unsubstituted heterocycloalkoxy, substituted or unsubstituted arylalkoxy, substituted or unsubstituted arylaloxy, substituted or unsubstituted arylolefin, substituted or unsubstituted heteroaryloxy, substituted or unsubstituted heteroarylalkoxy, or substituted or unsubstituted acyloxy as cyclic groups. The number of carbon atoms in the groups exemplified above is typically in the range of 1 to 10 when in a chain form and typically in the range of 3 to 16 when in a cyclic form. When the groups exemplified above are substituted, the substituents are preferably selected from one or more groups exemplified above.

[0050] In addition, nitrogen-containing cyclic organic compounds are preferably compounds of the following formula (1).

[0051]

[0052] [In formula (1), R1, R2, and R3 are each independently a hydrogen atom, halogen atom, amino group, hydroxyl group, nitrile group, amide group, thiol group, sulfonyl group, carboxyl group, phosphate group, ketone group, aldehyde group, ester group, phenyl group, phenolic group, alkyl group, cycloalkyl group, alkenyl group, alkoxy group, alkylamino group, alkylsulfonic acid group, perfluoroalkyl group, alkenylamino group, alkenylsulfonic acid group, or perfluoroalkenyl group. These groups may be substituted by fluorine, chlorine, bromine, or iodine atoms, and at least one carbon atom of these groups may be substituted by oxygen, sulfur, or nitrogen atoms.]

[0053] In formula (1), the alkyl group can be straight-chain or branched, and its carbon number is, for example, 1 to 10. The cycloalkyl group has, for example, 3 to 10 carbon atoms. The alkenyl group can be straight-chain or branched, and its carbon number is, for example, 2 to 10. The alkoxy group can be straight-chain or branched, and its carbon number is, for example, 1 to 10. The alkylamino group can be a primary amino group or a secondary amino group, i.e., containing -NH (alkyl) and -N (alkyl)2, each "alkyl" group being independently straight-chain or branched, and its carbon number is, for example, 1 to 10. The alkyl group of the alkylsulfonic acid group can be straight-chain or branched, and its carbon number is, for example, 1 to 10. The alkyl group of the perfluoroalkyl group can be straight-chain or branched, and its carbon number is, for example, 1 to 10. Alkenyl amino groups can be primary or secondary amino groups, i.e., containing -NH (alkenyl) and -N (alkenyl)2, each "alkenyl" group being independently linear or branched, with each having an independent number of carbon atoms, for example, 1 to 10. Alkenyl sulfonic acid groups can have linear or branched alkenyl groups, with an example number of carbon atoms, for example, 1 to 10. Perfluoroalkenyl groups can have linear or branched alkenyl groups, with an example number of carbon atoms, for example, 1 to 10.

[0054] The modifier is preferably melamine (1,3,5-triazine-2,4,6-triamine), cyanuric acid diamide (Ammeline), cyanuric acid monoamide (Ammelide), cyanuric acid or triazine (1,2,3-triazine, 1,2,4-triazine or 1,3,5-triazine) or its derivatives, or polymers thereof, preferably melamine or its derivatives (nitrogen equivalent 21 g / equivalent), cyanuric acid diamide, cyanuric acid monoamide, 1,3,5-triazine or its derivatives (nitrogen equivalent 27 g / equivalent), thiocyanuric acid or its derivatives (nitrogen equivalent 59 g / equivalent), cyanuric acid or its derivatives (nitrogen equivalent 34 g / equivalent), 2,4,6-tris[bis(methoxymethyl)amino]-1,3,5-triazine ( The copolymers of melamine-formaldehyde copolymers, such as 6-(dibutylamino)-1,3,5-triazine-2,4-dithiol (nitrogen equivalent 65 g / equivalent), 6-(dibutylamino)-1,3,5-triazine (nitrogen equivalent 30 g / equivalent), or 2,4,6-tris(pentafluoroethyl)-1,3,5-triazine (nitrogen equivalent 145 g / equivalent) or polymers using these monomers, or methylated poly(melamine-co-formaldehyde) (nitrogen equivalent 20-40 g / equivalent) or isobutylated poly(melamine-co-formaldehyde) (nitrogen equivalent 20-40 g / equivalent), are preferred to be 1,3,5-triazine, cyanuric acid monoamide, melamine, or melamine-formaldehyde copolymers.

[0055] Polymers containing nitrogen-containing cyclic organic compounds include, for example, homopolymers or copolymers comprising at least one of the nitrogen-containing cyclic organic compounds exemplified above as monomers. In the case of polymers containing nitrogen-containing cyclic organic compounds, the degree of polymerization is preferably in the range of 1 to 10,000, more preferably in the range of 10 to 10,000.

[0056] The polymer containing nitrogen-containing cyclic organic compounds in this embodiment is, for example, a polymer obtained by polycondensation of a compound comprising formula (1) and an aldehyde such as formaldehyde, acetaldehyde, or propionaldehyde. Formaldehyde is a preferred aldehyde. The polymer is preferably obtained by polycondensation of melamine and formaldehyde. There are no particular limitations on the manufacturing method of the polymer; for example, it can be obtained by known methods.

[0057] The content of the modifier, expressed as a mass ratio (modifier / catalyst metal) relative to the mass of the catalyst metal in the electrochemical oxygen reduction electrode catalyst, is typically in the range of 0.001 to 0.1, preferably in the range of 0.005 to 0.1. By including the modifier in the above-mentioned range, the electrochemical oxygen reduction electrode catalyst can exhibit high proton conductivity.

[0058] The composition and content of the modifier can be determined by, for example, dissolving and extracting the modifier contained in the electrochemical oxygen reduction electrode catalyst, and analyzing the components contained in the extract using elemental analysis, various chromatographic methods, ultraviolet-visible spectroscopy (UV-Vis), infrared spectroscopy (IR), or nuclear magnetic resonance (NMR).

[0059] In electrochemical oxygen reduction electrode catalysts, modifiers are typically disposed on the surface of the catalyst metal, for example, on the surface of a coated catalyst metal. In this case, it is preferable that at least a portion of the modifier forms bonds with the catalyst metal. Furthermore, the modification rate of the modifier on the surface of the catalyst metal relative to the total surface area of ​​the catalyst metal is preferably less than 28% area, and more preferably in the range of 5 to 20% area. By configuring the modifier as described above, the electrochemical oxygen reduction electrode catalyst can exhibit high durability.

[0060] In an electrochemical oxygen reduction electrode catalyst, the modification rate of the modifier on the surface of the catalyst metal is defined as the percentage of the surface area of ​​the modified catalyst metal relative to the total surface area of ​​the catalyst metal. The modification rate of the modifier on the surface of the catalyst metal can be determined, for example, by the following steps: The modifier contained in the electrochemical oxygen reduction electrode catalyst is dissolved to obtain a catalyst metal with the modifier removed. The surface area of ​​the modified catalyst metal (i.e., the total surface area of ​​the catalyst metal) is measured using, for example, gas-phase adsorption or electrochemical adsorption. The surface area of ​​the unmodified catalyst metal contained in the electrochemical oxygen reduction electrode catalyst is measured using the same method. The value obtained by subtracting the surface area of ​​the unmodified catalyst metal from the total surface area of ​​the catalyst metal is the surface area of ​​the modified catalyst metal. The modification rate of the modifier on the surface of the catalyst metal is calculated based on the obtained value.

[0061] Electrochemical oxygen reduction electrode catalysts typically have a support on which a catalyst metal is supported. In one embodiment, the electrode catalyst is a metal-supported catalyst in which catalytically active metal particles are supported on a support. Examples of supports include conductive carbon and oxides, as well as mixtures of one or more of these. The carbon is preferably carbon black (acetylene black, Ketjen black, and furnace black, etc.), activated carbon, lead black, glassy carbon, graphite, graphene, carbon fiber, carbon nanotubes, carbon nitride, carbon sulfide, carbon phosphide, channel black, drum black, disc black, oil furnace black, gas furnace black, lamp black, thermal cracking black, or Cabot black, or a mixture of one or more of these. The oxide is preferably titanium oxide, niobium oxide, tin oxide, tungsten oxide, or molybdenum oxide, or a mixture of one or more of these. The support is preferably carbon, more preferably carbon black.

[0062] The carrier is preferably a carrier with fine pores, and more preferably a carbon carrier with fine pores.

[0063] As a method for supporting catalyst metals on a support, conventional methods can be used. For example, a method can be described as follows: Particulate catalyst metals are mixed in a support dispersion containing the support, filtered, washed, and then dispersed in ethanol or the like, followed by drying using a vacuum pump or the like. After drying, heat treatment can be performed as needed.

[0064] The carrier can be either a primary particle or a secondary particle. The particle size of the primary particles in the carrier is typically in the range of 5–5000 nm.

[0065] In electrochemical oxygen reduction electrode catalysts, the composition, content, and particle size of the support can be determined, for example, by the same method used to determine the composition, content, and particle size of the catalyst metal described above.

[0066] The cathode catalyst layer may contain a binder. The binder is typically a polymeric electrolyte (ionomer) with ion-exchange groups. Examples of ion-exchange groups in the polymeric electrolyte include sulfonic acid groups, phosphate groups, and quaternary ammonium cation groups. Examples of polymers constituting the polymeric electrolyte include polymers primarily composed of perfluorocarbons, polyetheretherketones, and polybenzimidazoles. A perfluorocarbon sulfonic acid polymer is preferred as the binder.

[0067] As an ionomer, an ionomer having sulfonic acid groups is preferred. Ionomers, also known as cation exchange resins, exist in the form of clusters formed by ionomer molecules. There is no particular limitation on the ionomer; for example, ionomers known in the art can be used. Examples of ionomers include fluoropolymers such as perfluorosulfonic acid polymers; sulfonated resin ionomers such as sulfonated polyetherketones, sulfonated polyarylene ether sulfonates, sulfonated polyether ether sulfonates, sulfonated polysulfones, sulfonated polysulfides, and sulfonated polyphenylene ethers; and sulfonated resin ionomers such as sulfonated alkylated polyether etherketones, sulfonated polyether sulfonates, sulfonated polyether ether sulfonates, sulfonated polysulfones, sulfonated polysulfides, and sulfonated polyphenylene ethers. Among these, fluoropolymer ionomers are preferred. One type of ionomer can be used alone, or two or more can be used in combination.

[0068] The content of the electrochemical oxygen reduction electrode catalyst (electrode catalyst) in the cathode catalyst layer is not particularly limited, for example, it is 3 to 70% by mass relative to the total mass of the catalyst layer.

[0069] Modifiers can be incorporated into the metal-supported catalyst, for example, by adding a mixed modifier together with particulate catalyst metal to a support dispersion in which a support is dispersed. Therefore, in this embodiment, the electrode catalyst is preferably a metal-supported catalyst comprising a catalyst metal, a support supporting the catalyst metal, and the aforementioned modifier. Furthermore, the catalyst ink used to form the cathode catalyst layer may contain the aforementioned modifier. Specifically, the catalyst ink used to form the cathode catalyst layer may comprise an electrode catalyst, a binder (e.g., an ionomer), a solvent, and the aforementioned modifier.

[0070] The following describes the manufacturing method of the electrochemical oxygen reduction electrode catalyst. The manufacturing method of the electrochemical oxygen reduction electrode catalyst includes a modification step, and may include a preparation step and an electrode catalyst layer fabrication step, depending on the requirements.

[0071] Preparation process

[0072] This step includes preparing the catalyst metal and modifying agents. It also typically includes preparing the support and binder. Additionally, this step may prepare extra materials such as solvents and substrates as needed.

[0073] The catalyst metal, support, and binder prepared in this process can be any material having the characteristics described above. For example, the catalyst metal prepared in this process can be supported on the support described above.

[0074] The modifying agent prepared in this process contains at least a nitrogen-containing cyclic organic compound or its polymer. The modifying agent can be any material having the characteristics described above.

[0075] In this process, for each material, you can prepare materials with specified characteristics yourself, or you can purchase commercially available products.

[0076] Finishing process

[0077] This process includes modifying the catalyst metal by mixing it with a modifier. In this process, a binder may also be mixed in addition to the catalyst metal and modifier, if necessary. Additionally, in this process, a decomposition inhibitor may also be mixed in addition to the catalyst metal and modifier, if necessary.

[0078] In this process, the catalyst metal, modifier, and, if necessary, support or binder are typically mixed with a solvent. There are no particular limitations on the solvent; any liquid can be used. Examples of solvents include water and alcohols, as well as mixtures of one or more of them. Examples of alcohols include methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol (tert-butanol), diacetone alcohol, ethylene glycol, and propylene glycol.

[0079] In this process, there is no particular limitation on the method of mixing the materials. Examples of mixing methods include ultrasonic homogenizers, air jet mills, bead mills, ball mills, high-speed shear mills, and Primix. The specific conditions of the mixing methods exemplified above (e.g., stirring speed, stirring time, rotation speed, etc.) are not particularly limited and can be appropriately set within any range.

[0080] This process may include a vacuum degassing treatment, where the resulting mixture is degassed under vacuum conditions as needed. In this case, the specific conditions of the vacuum degassing treatment (e.g., pressure and treatment time) are not particularly limited and can be appropriately set within any range. The vacuum degassing treatment can be performed multiple times.

[0081] In this process, the electrochemical oxygen reduction electrode catalyst can be obtained by removing the solvent from the resulting mixture. The removal of the solvent is not particularly limited and can be carried out by any method such as heating and drying or filtration.

[0082] Alternatively, when performing the electrode catalyst layer fabrication process described below, the mixture obtained in this process can be used as a catalyst ink containing an electrochemical oxygen reduction electrode catalyst in the electrode catalyst layer fabrication process. In this case, the mixture obtained in this process can be used as is, or it can be used by further adding the solvents exemplified above.

[0083] By implementing this process, the catalyst metal can be modified with a modifier.

[0084] Electrode catalyst layer fabrication process

[0085] This process involves coating the surface of a substrate with a catalyst ink containing an electrochemical oxygen reduction electrode catalyst obtained in the modification process.

[0086] There are no particular limitations on the substrate used in this process; any material such as polytetrafluoroethylene (PTFE), electrolyte membranes with ion exchange groups, carbon fibers, and metal fibers can be used.

[0087] In this process, there is no particular limitation on the coating method of the catalyst ink. Examples of coating methods include molding, spin coating, screen printing, squeegee application, blade application, spraying, and applicator application. The specific conditions for the coating methods exemplified above are not particularly limited and can be appropriately set within any range.

[0088] In this process, solvent is typically removed from the coated catalyst ink. Solvent removal is not particularly limited and can be carried out by any method, such as heating and drying. Specific conditions for solvent removal (e.g., temperature, pressure, and processing time) are not particularly limited and can be appropriately set within any range.

[0089] By performing this process, an electrochemical oxygen reduction electrode catalyst can be obtained in the form of an electrode catalyst layer disposed on the surface of a substrate. In this case, the film thickness of the electrode catalyst layer is typically in the range of 5 to 30 μm. Furthermore, the content of the catalyst metal in the electrode catalyst layer, expressed as a percentage by mass relative to the total area of ​​the electrode catalyst layer, is typically 0.1 to 0.6 mg / cm³. 2 The range.

[0090] In this embodiment, the membrane electrode gas diffusion layer junction includes a decomposition inhibitor that suppresses the decomposition of the aforementioned modifier. The modifier decomposes under the operating environment of the fuel cell, and the resulting decomposition products poison the catalyst, leading to a faster rate of voltage drop. Therefore, in this embodiment, at least a portion of the membrane electrode gas diffusion layer junction contains a decomposition inhibitor that suppresses the decomposition of the modifier. This suppresses the decomposition of the modifier in the cathode catalyst layer, thereby inhibiting catalyst poisoning and, consequently, improving voltage retention.

[0091] The decomposition inhibitor need only be included within the fuel cell, and may be contained in any of the components constituting the fuel cell. Furthermore, it is preferable to include it in any component of the membrane electrode assembly, specifically, at least one selected from the electrolyte membrane, the anode catalyst layer, and the cathode catalyst layer. Additionally, it is preferable to include it in any component of the membrane electrode gas diffusion layer assembly, for example, preferably at least one selected from the electrolyte membrane, the anode catalyst layer, the cathode catalyst layer, the anode-side gas diffusion layer, and the cathode-side gas diffusion layer.

[0092] For example, when adding a decomposition inhibitor to the anode or cathode catalyst layer, a specified amount of the decomposition inhibitor (e.g., cerium nitrate) is added together with the metal support, binder, modifier, and solvent during the catalyst ink preparation process, thereby making the decomposition inhibitor present in the anode or cathode catalyst layer. Similarly, when adding a decomposition inhibitor to an electrolyte membrane, the decomposition inhibitor is present in the electrolyte membrane by immersing it in a solution (e.g., an aqueous solution) of a specified concentration of the decomposition inhibitor (e.g., cerium nitrate) for a specified time. When adding it to the anode-side or cathode-side gas diffusion layer, the decomposition inhibitor is present in the gas diffusion layer by adding a specified amount of the decomposition inhibitor (e.g., cerium oxide) to the MPL (Micro Porous Layer) paste.

[0093] Decomposition inhibitors are, for example, free radical quenchers that are metals or metal complexes, metal salts, metal oxides, or metal ions. Examples of free radical quenchers include at least one metal ion selected from cerium ions and manganese ions. Cerium ions and manganese ions function as free radical quenchers. A technique has been proposed to render hydrogen peroxide free radicals generated during fuel cell power generation harmless by incorporating free radical quenchers such as cerium ions into the membrane electrode gas diffusion layer junction. The harmlessness of hydrogen peroxide free radicals refers, for example, to the reaction of hydrogen peroxide free radicals to water. This free radical quencher facilitates the conversion of hydroxyl radicals generated from hydrogen peroxide to hydroxide ions and can inhibit the decomposition of decomposition inhibitors. For example, the reaction of hydroxyl radicals to hydroxide ions based on cerium ions is described below.

[0094] Ce 3+ +·OH (hydroxyl radical) → Ce 4+ +OH － (hydroxide ions)

[0095] Cerium ions can have either a +3 or +4 oxidation state. Manganese ions can also have either a +3 or +4 oxidation state.

[0096] There are no particular limitations on the cerium salts used to obtain cerium ions; examples include cerium nitrate, cerium carbonate, cerium acetate, cerium chloride, cerium sulfate, diammonium nitrate, or tetraammonium sulfate. A single cerium salt can be used alone, or in combination of two or more. Cerium salts can be organometallic complexes. Examples of organometallic complexes include cerium acetylacetonate.

[0097] There are no particular limitations on the manganese salts used to obtain manganese ions; examples include manganese nitrate, manganese carbonate, manganese acetate, manganese chloride, or manganese sulfate. A single manganese salt can be used alone, or in combination of two or more.

[0098] When an electrolyte membrane (especially a solid polymer electrolyte membrane) contains metal ions that act as decomposition inhibitors, an electrolyte membrane containing metal ions can be obtained, for example, by the following methods.

[0099] (1) A method of immersing a solid polymer electrolyte membrane in a solution containing metal ions to exchange sulfonic acid groups and other group ions for metal ions.

[0100] (2) A method of coating a film by adding a compound containing metal ions (e.g., cerium salt) to a dispersion of a polymer electrolyte to exchange sulfonic acid groups and other groups for metal ions.

[0101] There are no particular restrictions on the content of the decomposition inhibitor, for example, it can be 0.1–20 μg / cm³. 2 Specifically, there are no particular limitations on the content of the decomposition inhibitor in the electrolyte membrane, anode catalyst layer, cathode catalyst layer, anode-side gas diffusion layer, or cathode-side gas diffusion layer; for example, it can be 0.1–20 μg / cm³. 2 .

[0102] The anode catalyst layer functions as the fuel electrode, i.e., the hydrogen electrode.

[0103] The anode catalyst layer comprises at least an electrode catalyst and a binder. The binder is preferably an ionomer, and more preferably an ionomer having sulfonic acid groups. Examples of ionomers having sulfonic acid groups include the aforementioned ionomers. In this embodiment, the anode catalyst layer may contain a decomposition inhibitor. In one embodiment, the anode catalyst layer may contain a decomposition inhibitor in addition to the electrode catalyst and the ionomer.

[0104] There are no particular limitations on the electrode catalyst; for example, it can be a metal-supported catalyst in which catalytically active metal particles are supported on a support.

[0105] There are no particular limitations on ionomers containing sulfonic acid groups; for example, ionomers containing perfluorosulfonic acid groups and other ion-conducting polymeric electrolyte resins can be cited. Specific examples of ionomers containing sulfonic acid groups include Nafion and Aquivion (Solvay Corporation).

[0106] As described above, the fuel cell of this embodiment can be based on a membrane electrode gas diffusion layer assembly. The gas diffusion layer functions to uniformly supply the gas (oxidizing gas or fuel gas) from the separator to the catalyst layer. Furthermore, it is desirable for the gas diffusion layer to have excellent conductivity, serving as an electronic conduction path between the catalyst layer and the separator.

[0107] The anode-side gas diffusion layer is disposed on the surface of the anode catalyst layer and on the side opposite to the electrolyte membrane, and the cathode-side gas diffusion layer is disposed on the surface of the cathode catalyst layer and on the side opposite to the electrolyte membrane.

[0108] There are no particular limitations on the gas diffusion layer; for example, it can have a gas diffusion layer substrate and an MPL (MicroPorous Layer). The gas diffusion layer is also not particularly limited; for example, it can include a conductive porous substrate such as carbon fiber nonwoven fabric or carbon fiber woven fabric, and an MPL mainly composed of conductive particles and polymer resin. The conductive porous substrate is, for example, made of carbon fiber. Alternatively, the gas diffusion layer substrate can also be a metal porous body such as a metal mesh or foamed metal. The MPL can be formed, for example, by containing conductive carbon particles and a polymer resin (e.g., a water-repellent resin). Examples of water-repellent resins include polytetrafluoroethylene, polyethylene, or polypropylene. The MPL can be formed by coating the gas diffusion layer substrate with an MPL paste, which is a mixture of conductive carbon particles, a polymer resin (e.g., a water-repellent resin), an adhesive, and a solvent such as water. The MPL paste can be formed as needed through a drying or calcination process after coating. Two gas diffusion layers (cathode-side gas diffusion layer and anode-side gas diffusion layer) are respectively disposed on both sides of the membrane electrode assembly in a manner that connects the MPL to the membrane electrode assembly.

[0109] In this embodiment, the MPL may contain the aforementioned decomposition inhibitor. For example, by including the decomposition inhibitor in the MPL paste, the decomposition inhibitor can be contained within the MPL.

[0110] The thickness of the gas diffusion layer is, for example, 50 to 1000 μm, preferably 100 to 500 μm.

[0111] Method for manufacturing membrane electrode gas diffusion layer junction

[0112] The catalyst layer can be formed, for example, by the following steps: preparing a catalyst ink containing an electrode catalyst (e.g., a solid content concentration of about 10%), forming a catalyst layer on the substrate surface by coating the catalyst ink onto the substrate surface and allowing the solvent in the coating to evaporate, and transferring the catalyst layer on the substrate surface to the electrolyte membrane. Alternatively, the catalyst layer can be formed by directly coating the catalyst ink onto the electrolyte membrane instead of the substrate. A membrane electrode assembly can be fabricated by forming a cathode catalyst layer and an anode catalyst layer on the electrolyte membrane. Furthermore, a membrane electrode gas diffusion layer assembly can be fabricated by distributing two gas diffusion layers (a cathode-side gas diffusion layer and an anode-side gas diffusion layer) on both sides of the membrane electrode assembly. In this embodiment, the cathode catalyst layer is formed containing the aforementioned modifier. The catalyst ink used to form the anode catalyst layer and / or cathode catalyst layer can contain the aforementioned decomposition inhibitor.

[0113] Examples of coating methods for catalyst inks include spraying, scraping with a doctor blade or applicator, die coating, reverse roller coating, and intermittent die coating.

[0114] In summary, this embodiment provides a fuel cell with good voltage and its retention rate. Such a fuel cell can be appropriately used, for example, in automobiles, ships, or trains.

[0115] The following describes this implementation method using examples.

[0116] Preparation of Electrode Catalyst 1 (containing Modifier)

[0117] A metal-supported catalyst (electrode catalyst 1) was prepared, comprising platinum-cobalt alloy particles as the catalyst metal (0.13 atm of metals other than platinum, average particle size: 3-4 nm), a polymer containing 1,3,5-triazine-2,4,6-triamine as a monomer (trade name: poly(melamine-co-formaldehyde) methylation solution, manufactured by Merck), and carbon (commercially available acetylene black) as a support (metal loading ratio: 40 wt%).

[0118] The ratio of the mass of the modifier to the mass of the carbon carrier (mass of modifier / mass of carrier), calculated based on the amount of material fed, is 0.02.

[0119] Preparation of Electrode Catalyst 2 (without modifier)

[0120] A metal-supported catalyst (electrode catalyst 2) was prepared, comprising platinum-cobalt alloy particles as the catalyst metal (metal ratio other than platinum 0.13 atm, average particle size: 3-4 nm) and carbon (commercially available acetylene black) as the support (metal loading ratio: 40 wt%).

[0121] Preparation of cathode catalyst ink (containing modifiers and decomposition inhibitors)

[0122] Electrode catalyst 1 (containing a modifier) ​​was dispersed in an ionomer solution (NafionDE2020) containing water, cerium nitrate as a decomposition inhibitor, and ethanol using a bead mill to prepare a cathode catalyst ink (containing a modifier and a decomposition inhibitor). The water / alcohol mass ratio in this catalyst ink was approximately 1.

[0123] Preparation of cathode catalyst ink (containing modifier)

[0124] Without adding cerium nitrate as a decomposition inhibitor, the cathode catalyst ink (containing a modifier) ​​is prepared using the same method as described in [Preparation of cathode catalyst ink (containing a modifier and a decomposition inhibitor)].

[0125] Preparation of cathode catalyst ink (−)

[0126] Electrode catalyst 2 (without modifier) ​​is added instead of electrode catalyst 1 (containing modifier). In addition, cerium nitrate, which is a decomposition inhibitor, is not added. Otherwise, the cathode catalyst ink (-) is prepared using the same method as described in [Preparation of cathode catalyst ink (containing modifier and decomposition inhibitor)].

[0127] Preparation of catalyst ink for anodes (containing decomposition inhibitors)

[0128] As the electrode catalyst, a platinum-supported carbon catalyst (TEC10E30E, carbon supported with 30% platinum, manufactured by Tanaka Precious Metals Industry Co., Ltd.) was used. This electrode catalyst was dispersed in an ionomer solution (DE2020) containing water, cerium nitrate (as a decomposition inhibitor), ethanol, and Nafion (registered trademark) to prepare an anode catalyst ink (containing a decomposition inhibitor).

[0129] Preparation of catalyst ink (−) for anodes

[0130] Without adding cerium nitrate as a decomposition inhibitor, the anode catalyst ink (-) is prepared using the same method as described in [Preparation of anode catalyst ink (containing decomposition inhibitor)].

[0131] Preparation of electrolyte membranes (containing decomposition inhibitors)

[0132] Electrolyte membranes (containing decomposition inhibitors) are prepared by immersing Nafion (registered trademark) membrane (NR211) in an aqueous solution of cerium nitrate.

[0133] Preparation of electrolyte membrane (−)

[0134] Nafion (registered trademark) membrane (NR211) is used as the electrolyte membrane (-).

[0135] Preparation of the cathode-side gas diffusion layer (containing decomposition inhibitors)

[0136] A cathode-side gas diffusion layer (containing decomposition inhibitor) is prepared by coating the surface of carbon paper with an MPL paste containing carbon particles, cerium nitrate as a decomposition inhibitor, polytetrafluoroethylene and solvent, and then drying it.

[0137] Preparation of the cathode-side gas diffusion layer (−)

[0138] Without adding cerium nitrate as a decomposition inhibitor, the cathode-side gas diffusion layer (-) is prepared using the same method as described in [Preparation of cathode-side gas diffusion layer (containing decomposition inhibitor)].

[0139] Preparation of the anode-side gas diffusion layer (containing decomposition inhibitors)

[0140] An MPL paste containing carbon particles, cerium nitrate (as a decomposition inhibitor), polytetrafluoroethylene, and a solvent is coated onto the surface of carbon paper made of carbon fiber and dried to prepare an anode-side gas diffusion layer (containing a decomposition inhibitor).

[0141] Preparation of the anode-side gas diffusion layer (−)

[0142] Without adding cerium nitrate as a decomposition inhibitor, the anode-side gas diffusion layer (-) is prepared using the same method as described in [Preparation of Anode-Side Gas Diffusion Layer (Containing Decomposition Inhibitor)].

[0143] Example 1

[0144] Formation of cathode catalyst layer

[0145] The cathode catalyst layer is formed by coating a polytetrafluoroethylene sheet with a catalyst ink (containing modifiers and decomposition inhibitors) and then drying it. The Pt unit area weight of the cathode catalyst layer is 0.2 mg / cm³. 2 The mass ratio (I / C) of the ionomer to the carrier is 1.0. The concentration of cerium nitrate is 3 μg / cm³. 2 .

[0146] Formation of the anode catalyst layer

[0147] The anode catalyst layer is formed by coating a polytetrafluoroethylene sheet with catalyst ink (−) and then drying it. The Pt unit area weight of the anode catalyst layer is 0.1 mg / cm³. 2 The mass ratio of ionomer to carbon (I / C) is 1.0.

[0148] Fabrication of membrane electrode gas diffusion layer bonding

[0149] The obtained cathode catalyst layer and anode catalyst layer were each thermally transferred to both sides of the electrolyte membrane (-) to fabricate a membrane electrode assembly. The thermal transfer conditions were 140°C and 50 kgf / cm². 2 (4.90 MPa), 5 min. The electrode area of ​​the membrane electrode assembly is 1 cm × 1 cm (1 cm 2 The membrane electrode assembly was clamped with a cathode-side gas diffusion layer (-) and an anode-side gas diffusion layer (-) with the MPL on the membrane electrode assembly side to form a membrane electrode gas diffusion layer assembly, which served as the test cell E1.

[0150] Example 2

[0151] The membrane electrode gas diffusion layer assembly was fabricated using cathode catalyst ink (containing a modifier), anode catalyst ink (containing a decomposition inhibitor), an electrolyte membrane (-), a cathode-side gas diffusion layer (-), and an anode-side gas diffusion layer (-), except that it was fabricated in the same manner as in Example 1, as the test cell E2.

[0152] Example 3

[0153] The membrane electrode gas diffusion layer assembly was fabricated using cathode catalyst ink (containing a modifier), anode catalyst ink (-), electrolyte membrane (containing a decomposition inhibitor), cathode-side gas diffusion layer (-), and anode-side gas diffusion layer (-), except that it was fabricated in the same manner as in Example 1, as the test cell E3.

[0154] Example 4

[0155] The membrane electrode gas diffusion layer assembly was fabricated using the same procedure as in Example 1, except that a cathode catalyst ink (containing a modifier), an anode catalyst ink (-), an electrolyte membrane (-), a cathode-side gas diffusion layer (-), and an anode-side gas diffusion layer (containing a decomposition inhibitor). This assembly served as the test cell E4.

[0156] Example 5

[0157] The membrane electrode gas diffusion layer assembly was fabricated using the same procedure as in Example 1, except that a cathode catalyst ink (containing a modifier), an anode catalyst ink (-), an electrolyte membrane (-), a cathode-side gas diffusion layer (containing a decomposition inhibitor), and an anode-side gas diffusion layer (-). This assembly served as the test cell E5.

[0158] Comparative Example 1

[0159] The membrane electrode gas diffusion layer assembly was fabricated using the same procedure as in Example 1, except that it consisted of cathode catalyst ink (-), anode catalyst ink (-), electrolyte membrane (-), cathode-side gas diffusion layer (-), and anode-side gas diffusion layer (-).

[0160] Comparative Example 2

[0161] The membrane electrode gas diffusion layer assembly was fabricated using cathode catalyst ink (-), anode catalyst ink (-), an electrolyte membrane (containing a decomposition inhibitor), a cathode-side gas diffusion layer (-), and an anode-side gas diffusion layer (-), except that it was fabricated in the same manner as in Example 1, as the test cell C2.

[0162] Comparative Example 3

[0163] The membrane electrode gas diffusion layer assembly was fabricated using cathode catalyst ink (containing a modifier), anode catalyst ink (-), electrolyte membrane (-), cathode-side gas diffusion layer (-), and anode-side gas diffusion layer (-), except that it was fabricated in the same manner as in Example 1, as the test cell C3.

[0164] Performance Evaluation

[0165] Using a membrane electrode gas diffusion layer conjugate (electrode area: 1 cm²) 2 Battery cell evaluation was conducted under low humidity conditions (80°C, 30% RH), with air supplied to the air electrode at a pressure of 150 kPa and hydrogen supplied to the hydrogen electrode at a rate of 2.0 L / min. The flow rate was 0.2 A / cm². 2 The voltage was initially set as the initial performance (V), and the voltage after 1 hour was taken as the post-endurance performance (V). The results are shown in Table 1.

[0166] (Table 1)

[0167]

[0168] The upper and / or lower limits of the numerical ranges described in this specification can be arbitrarily combined to define the preferred range. For example, the upper and lower limits of the numerical ranges can be arbitrarily combined to define the preferred range; the upper limits of the numerical ranges can be arbitrarily combined with each other to define the preferred range; and the lower limits of the numerical ranges can be arbitrarily combined with each other to define the preferred range.

[0169] The above describes the embodiment in detail, but the specific configuration is not limited to this embodiment. The design can be changed within the scope of the spirit of this disclosure, and they are all included in this disclosure.

Claims

1. A fuel cell comprising at least a membrane electrode assembly having an electrolyte membrane, an anode catalyst layer disposed on one face of the electrolyte membrane, and a cathode catalyst layer disposed on the other face of the electrolyte membrane, the cathode catalyst layer comprising at least an electrochemical oxygen reduction electrode catalyst containing a catalyst metal having oxygen reduction activity and a modifier modifying the catalyst metal, the modifier being at least one selected from the group consisting of nitrogen-containing cyclic organic compounds and polymers thereof, and a decomposition inhibitor inhibiting decomposition of the modifier contained in at least one selected from the group consisting of the electrolyte membrane, the anode catalyst layer, and the cathode catalyst layer. The decomposition inhibitor is a radical quencher, and the radical quencher is a metal or a metal complex, a metal salt, a metal oxide, or a metal ion. The decomposition inhibitor is at least one metal ion selected from the group consisting of cerium ions and manganese ions. The nitrogen-containing cyclic organic compound is a compound of the following formula (1): Formula (1) wherein R1, R2, and R3 are each independently a hydrogen atom, a halogen atom, an amino group, a hydroxyl group, a nitrile group, an amide group, a thiol group, a sulfo group, a carboxyl group, a phosphoric acid group, a ketone group, an aldehyde group, an ester group, a phenyl group, a phenol group, an alkyl group, a cycloalkyl group, an alkenyl group, an alkoxy group, an alkylamino group, an alkylsulfo group, a perfluoroalkyl group, an alkenylamino group, an alkenylsulfo group, or a perfluoroalkenyl group, each of which can be substituted with a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and at least one of the carbon atoms of each of these groups can be substituted with an oxygen atom, a sulfur atom, or a nitrogen atom.

2. The fuel cell of claim 1, wherein, The catalyst metal having oxygen reduction activity contains at least one selected from the group consisting of platinum, platinum alloys, and platinum-containing composites.

3. The fuel cell of claim 1, wherein, ​ 4. The fuel cell of claim 1, wherein, ​ ​ 5. The fuel cell of claim 1, wherein, ​

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