membrane electrode assembly

Abstract

To provide a film electrode bonded body with excellent power generation capability and durability.SOLUTION: A film electrode bonded body includes a solid polymer electrolyte film, an anode catalyst layer disposed on one surface of the solid polymer electrolyte film, and a cathode catalyst layer disposed on the other surface of the solid polymer electrolyte film. The film electrode bonded body includes a metal ion selected from a cerium ion and a manganese ion, and a host compound that can form a clathrate compound with the metal ion. The cathode catalyst layer includes at least an electrode catalyst and a sulfonyl group containing polymer. The sulfonyl group containing polymer includes a constitutional unit (u1) with a sulfonyl group and a constitutional unit (u2) with a ring structure. The constitutional unit (u2) with a ring structure is at least one selected from a constitutional unit expressed by a formula (u2-1) and a constitutional unit expressed by a formula (u2-2).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a membrane electrode assembly. [Background technology]

[0002] Polymer electrolyte fuel cells (PEFCs) are attracting attention as fuel cells that generate electricity through an electrochemical reaction between fuel gas and oxidant gas. Because they can operate at room temperature and have a high output density, they are being actively researched as a form of fuel suitable for automotive applications.

[0003] A solid polymer fuel cell generally comprises a membrane electrode assembly (also referred to as "MEA") having a solid polymer electrolyte membrane as an electrolyte membrane, an anode catalyst layer disposed on one side of the solid polymer electrolyte membrane, and a cathode catalyst layer disposed on the other side of the solid polymer electrolyte membrane. The anode catalyst layer functions as a fuel electrode, and the cathode catalyst layer functions as an air electrode. Gas diffusion layers may also be disposed on both sides of the MEA; this configuration is called a membrane electrode gas diffusion layer assembly (also referred to as "MEGA").

[0004] Each electrode includes a catalyst layer, where an electrode reaction occurs due to the electrode catalyst contained in the catalyst layer. A three-phase interface where the electrolyte, catalyst, and reactant gas coexist is necessary for the electrode reaction to occur, and therefore the catalyst layer generally includes a catalyst and an electrolyte. The gas diffusion layer is a layer for supplying the reactant gas to the catalyst layer and exchanging electrons, and is made of a porous, electron-conductive material.

[0005] In polymer electrolyte fuel cells, hydrogen peroxide (H2O2) can be generated from water and oxygen in the catalyst layer during power generation, and hydroxyl radicals (·OH) can be generated from hydrogen peroxide. These hydrogen peroxide and hydroxyl radicals can cause deterioration of the polymer electrolyte membrane and electrolyte resins such as ionomers contained in the catalyst layer.

[0006] Therefore, a technology has been proposed to neutralize the hydrogen peroxide radicals generated during fuel cell power generation by incorporating a radical quenching agent such as cerium ions into the MEA. The neutralization of hydrogen peroxide radicals refers to the reaction of hydrogen peroxide radicals with water, for example.

[0007] For example, Patent Document 1 discloses a solid polymer electrolyte membrane made of a polymer electrolyte having sulfonic acid groups, the solid polymer electrolyte membrane comprising any one of the following (a) to (c): (a) cerium ions and an organic compound (X) capable of forming an inclusion compound with the cerium ions; (b) an inclusion compound (Y) made of the organic compound (X) that has encapsulated a cerium ion; and (c) at least one of the cerium ions and the organic compound (X), and the inclusion compound (Y). Patent Document 1 describes that the solid polymer electrolyte membrane of Patent Document 1 has excellent resistance to hydrogen peroxide or peroxide radicals. Although the reason for this is unclear, it is believed that the inclusion of cerium ions and the organic compound (X) in the electrolyte membrane causes at least a portion of them to form an inclusion compound, which then interacts with sulfonic acid groups (—SO—), resulting in ion exchange of a portion of the sulfonic acid groups with the inclusion compound (Y), forming a predetermined structure, thereby effectively improving the hydrogen peroxide or peroxide radical resistance of the polymer electrolyte membrane.

[0008] For example, Non-Patent Document 1 discloses a membrane electrode assembly (MEA) in which a coordination complex of 18-crown-6-ether / cerium ion (CRE / Ce) is embedded in a Nafion ionomer between the catalyst and the membrane. It is described (abstract, etc.) that Ce acts as a trap for HO- radicals, and CRE reduces the elution of cerium ions from the MEA during cell operation. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-130460 [Non-patent literature]

[0010] [Non-Patent Document 1] Vo Dinh Cong Tinh et al., "Enhancement of oxidative stability of PEM fuel cell by introduction of HO radical scavenger in Nafion ionomer", Journal of Membrane Science 613 (2020) 118517 Summary of the Invention [Problem to be solved by the invention]

[0011] As mentioned above, Patent Document 1 or Non-Patent Document 1 discloses a polymer electrolyte membrane or an anode catalyst layer containing cerium ions and 18-crown-6-ether as a radical quenching agent.

[0012] However, when a membrane electrode assembly containing cerium ions and 18-crown-6-ether was investigated, a decrease in performance was observed, revealing that there is room for improvement in terms of power generation performance and durability.

[0013] Therefore, an object of the present disclosure is to provide a membrane electrode assembly that is excellent in power generation performance and durability. [Means for solving the problem]

[0014] The present inventors conducted extensive research to solve the above-mentioned problems and found that the reason for the performance degradation was that 18-crown-6-ether contained in the membrane electrode assembly migrated to the cathode catalyst layer, poisoning the cathode catalyst and reducing the proton conductivity of the cathode ionomer. Further research led to the discovery that the performance degradation could be suppressed by using a sulfonyl group-containing polymer having a specific structure as an ionomer in the cathode catalyst layer, leading to the present disclosure.

[0015] Therefore, an example of the present embodiment is as follows. (1) A membrane electrode assembly having a solid polymer electrolyte membrane, an anode catalyst layer disposed on one surface of the solid polymer electrolyte membrane, and a cathode catalyst layer disposed on the other surface of the solid polymer electrolyte membrane, the membrane electrode assembly includes a metal ion selected from cerium ions and manganese ions, and a host compound capable of forming an inclusion compound with the metal ion; the cathode catalyst layer contains at least an electrode catalyst and a sulfonyl group-containing polymer, the sulfonyl group-containing polymer comprises a structural unit (u1) having a sulfonyl group and a structural unit (u2) having a ring structure, A membrane / electrode assembly, wherein the structural unit (u2) having a ring structure is at least one selected from a structural unit represented by the following formula (u2-1) and a structural unit represented by the following formula (u2-2): [ka] (In the formula, R 1 ~R 4 are each independently a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms), [ka] (In the formula, R 5 ~R 10 are each independently a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms. (2) The membrane / electrode assembly according to (1), wherein the structural unit (u1) having a sulfonyl group is represented by the following formula (u1): [ka] (In the formula, R F1 is -(CF2CF(CF3)O) h -(CF2) i -where h is an integer between 0 and 3, inclusive, and i is an integer between 1 and 10, inclusive. (3) The membrane / electrode assembly according to (1) or (2), wherein the structural unit (u2) having a ring structure is derived from at least one monomer selected from the group consisting of a monomer represented by the following formula (m2-1) and a monomer represented by the following formula (m2-2): [ka] (In the formula, R 1 ~R 4 are each independently a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms), [ka] (In the formula, R 5 ~R 10 are each independently a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms. (4) The membrane / electrode assembly according to any one of (1) to (3), wherein the structural unit (u1) having a sulfonyl group is derived from a monomer represented by the following formula (m1): [ka] (In the formula, R F1 is -(CF2CF(CF3)O) h -(CF2) i -where h is an integer between 0 and 3, inclusive, and i is an integer between 1 and 10, inclusive. (5) The membrane / electrode assembly according to any one of (1) to (4), wherein the sulfonyl group-containing polymer further contains a structural unit (u3) derived from a tetrafluoroethylene monomer. (6) The membrane / electrode assembly according to any one of (1) to (5), wherein the host compound is a crown ether compound. (7) The membrane / electrode assembly according to (6), wherein the host compound is a crown ether compound having an aromatic ring or an aliphatic ring. (8) The crown ether compound is dibenzo-15-crown-5-ether, benzo-18-crown-6-ether, dibenzo-18-crown-6-ether, benzo-21-crown-7-ether, dibenzo-21-crown-7-ether, benzo-24-crown-8-ether, dibenzo-24-crown-8-ether, cyclohexano-18-crown-6-ether, cyclohexano-21-crown-7-ether, cyclohexano-24-crown-8-ether, dicyclohexano-18-crown-6-ether, (6) or (7), wherein the membrane / electrode assembly is at least one compound selected from the group consisting of dicyclohexano-21-crown-7-ether, dicyclohexano-24-crown-8-ether, and compounds in which the aromatic ring or the aliphatic ring of these compounds is substituted with at least one substituent selected from a halogen atom, a hydroxy group, an amino group, a nitro group, a formyl group, an alkyl group having 1 to 6 carbon atoms, a hydroxyalkyl group having 1 to 6 carbon atoms, a carboxyalkyl group having 2 to 7 carbon atoms, and an aryl group having 6 to 14 carbon atoms. (9) The membrane / electrode assembly according to any one of (1) to (8), wherein the host compound and the metal ions are contained in the anode catalyst layer, the solid polymer electrolyte membrane, or both. (10) The membrane / electrode assembly according to any one of (1) to (9), wherein the host compound and the metal ions are added to the anode catalyst layer. (11) The membrane / electrode assembly according to any one of (1) to (10), wherein the host compound and at least a part of the metal ions form an inclusion compound. (12) A polymer electrolyte fuel cell comprising the membrane electrode assembly according to any one of (1) to (11). [Effects of the Invention]

[0016] The present disclosure makes it possible to provide a membrane electrode assembly that is excellent in power generation performance and durability. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic cross-sectional view for explaining an example of the configuration of a membrane electrode assembly and a polymer electrolyte fuel cell according to the present embodiment, and is a cross-sectional view of a main part of a fuel cell 10 as an example. DETAILED DESCRIPTION OF THE INVENTION

[0018] In this embodiment, A membrane electrode assembly having a solid polymer electrolyte membrane, an anode catalyst layer disposed on one surface of the solid polymer electrolyte membrane, and a cathode catalyst layer disposed on the other surface of the solid polymer electrolyte membrane, the membrane electrode assembly includes a metal ion selected from cerium ions and manganese ions, and a host compound capable of forming an inclusion compound with the metal ion; the cathode catalyst layer contains at least an electrode catalyst and a sulfonyl group-containing polymer, the sulfonyl group-containing polymer comprises a structural unit (u1) having a sulfonyl group and a structural unit (u2) having a ring structure, A membrane / electrode assembly, wherein the structural unit (u2) having a ring structure is at least one selected from a structural unit represented by the following formula (u2-1) and a structural unit represented by the following formula (u2-2): [ka] (In the formula, R 1 ~R 4 are each independently a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms), [ka] (In the formula, R 5 ~R 10 are each independently a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms.

[0019] This embodiment can provide a membrane / electrode assembly with excellent power generation performance and durability. In this embodiment, cerium ions and / or manganese ions, which function as radical quenchers, are added to the membrane / electrode assembly (e.g., an anode catalyst layer or a solid polymer electrolyte membrane). The cerium ions and / or manganese ions can capture and neutralize hydrogen peroxide radicals, thereby suppressing degradation of the membrane / electrode assembly. Furthermore, by adding a host compound for the metal ions to the membrane / electrode assembly, migration of the metal ions can be suppressed, thereby reducing uneven concentration in the in-plane direction. Furthermore, by using the highly oxygen-permeable sulfonyl group-containing polymer, which is a highly oxygen-permeable polymer, as an ionomer in the cathode catalyst layer, performance degradation due to catalyst poisoning in the cathode catalyst layer or reduced proton conductivity caused by migration of the host compound to the cathode catalyst layer can be suppressed. Therefore, the membrane / electrode assembly according to this embodiment can have excellent power generation performance and durability.

[0020] The configuration of this embodiment will be described below.

[0021] The solid polymer electrolyte membrane prevents the flow of electrons and gases, and also prevents the flow of protons (H + ) from the anode-side catalyst layer to the cathode-side catalyst layer. As the solid polymer electrolyte membrane in this embodiment, an electrolyte membrane having proton conductivity known in the art can be used. As the solid polymer electrolyte membrane, for example, a membrane formed from a fluororesin having sulfonic acid groups (such as Nafion (manufactured by DuPont), Flemion (manufactured by AGC), and Aciplex (manufactured by Asahi Kasei Corporation)) can be used.

[0022] The thickness of the solid polymer electrolyte membrane is not particularly limited, but is, for example, 5 μm to 50 μm from the viewpoint of improving proton conductivity.

[0023] The cathode catalyst layer functions as an air electrode (oxygen electrode).

[0024] The cathode catalyst layer contains at least an electrode catalyst (also simply referred to as a "catalyst") and an electrolyte. The electrode catalyst is preferably a metal-supported catalyst. In a metal-supported catalyst, a metal catalyst is supported on a carrier.

[0025] The carrier is not particularly limited and may be any carrier known in the art. Examples of the carrier include carbon materials such as carbon black, carbon nanotubes, and carbon nanofibers; and carbon compounds such as silicon carbide. One type of carrier may be used alone, or two or more types may be used in combination.

[0026] There are no particular limitations on the metal catalyst, so long as it exhibits catalytic activity in the reaction at the electrode. Air electrode (cathode): O2 + 4H + +4e - →2H2O Hydrogen electrode (anode): 2H2 → 4H + +4e -

[0027] The metal catalyst is not particularly limited, and examples thereof include platinum, palladium, rhodium, gold, silver, osmium, iridium, and alloys of two or more of these. The platinum alloy is also not particularly limited, and examples thereof include alloys of platinum with at least one of aluminum, chromium, manganese, iron, cobalt, nickel, gallium, zirconium, molybdenum, ruthenium, rhodium, palladium, vanadium, tungsten, rhenium, osmium, iridium, titanium, and lead. The metal catalyst may be used alone or in combination of two or more.

[0028] The content of the electrode catalyst in the cathode catalyst layer is not particularly limited, but is, for example, 3 to 40 mass % relative to the total mass of the catalyst layer.

[0029] The electrolyte used in the cathode catalyst layer is the sulfonyl group-containing polymer with high oxygen permeability. By using a sulfonyl group-containing polymer with high oxygen permeability, deterioration of the cathode catalyst layer due to migration of the host compound to the cathode catalyst layer can be suppressed. In this embodiment, the structural unit (u2) having a ring structure has a ring structure, which increases the free volume of the polymer and improves oxygen permeability. One speculation is that the hydrophobic ring structure contained in the ionomer prevents the host compound from flowing into the cathode catalyst layer. This speculation is not intended to limit the scope of this embodiment.

[0030] The structural unit (u2) having a ring structure can be derived from at least one monomer selected from the monomer represented by the following formula (m2-1) and the monomer represented by the following formula (m2-2).

[0031] [ka] (In the formula, R 1 ~R 4 are each independently a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms.

[0032] [ka] (In the formula, R 5 ~R 10 are each independently a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms.

[0033] As the monomer represented by formula (m2-1), the following monomers are preferred from the viewpoint of oxygen permeability.

[0034] [ka]

[0035] As the monomer represented by formula (m2-2), the following monomers are preferred from the viewpoint of oxygen permeability.

[0036] [ka]

[0037] From the viewpoint of high oxygen permeability, the structural unit (u1) having a sulfonyl group is preferably represented by the following formula (u1).

[0038] [ka] (In the formula, R F1 is -(CF2CF(CF3)O) h -(CF2) i -, where h is an integer between 0 and 3, inclusive, and i is an integer between 1 and 10, inclusive.

[0039] R F1 -(CF2CF(CF3)O) h -(CF2) i With regard to "-", it is preferred that the "-" on the left side indicates a bond to an oxygen atom, and the "-" on the right side indicates a bond to a sulfur atom of "SO3H".

[0040] The structural unit (u1) having a sulfonyl group can be derived from a monomer represented by the following formula (m1): The -SO2F group in the monomer represented by the following formula (m1) can be converted to a sulfonic acid group (-SO3H group) after the polymerization reaction.

[0041] [ka] (In the formula, R F1 is -(CF2CF(CF3)O) h -(CF2) i -, where h is an integer between 0 and 3, inclusive, and i is an integer between 1 and 10, inclusive.

[0042] R F1 -(CF2CF(CF3)O) h -(CF2) i Regarding "-", it is preferable that the "-" on the left side indicates a bond to an oxygen atom, and the "-" on the right side indicates a bond to a sulfur atom of "SO3H". F1 is, for example, a perfluoroalkyl group having 1 to 10 carbon atoms.

[0043] Examples of the polymerization method include well-known radical polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Polymerization may also be carried out in liquid or supercritical carbon dioxide. The polymerization is carried out under conditions that generate radicals. Methods for generating radicals include irradiation with radiation such as ultraviolet rays, gamma rays, and electron beams, and addition of a radical initiator. The polymerization temperature is usually 10 to 150°C, and preferably 15 to 100°C.

[0044] A method for converting -SO2F groups to sulfonic acid groups (-SO3H groups) includes hydrolyzing the -SO2F groups in the polymer to form sulfonate salts, and then converting the sulfonate salts to acid forms to convert them to sulfonic acid groups. Hydrolysis is carried out, for example, by contacting the polymer with a basic compound in a solvent. Examples of basic compounds include sodium hydroxide and potassium hydroxide. Examples of solvents include water and mixed solvents of water and polar solvents. Examples of polar solvents include alcohols (e.g., methanol, ethanol), dimethyl sulfoxide, etc.

[0045] The sulfonyl group-containing polymer may further contain a structural unit (u3) derived from a tetrafluoroethylene monomer.

[0046] The membrane electrode assembly according to this embodiment includes metal ions selected from cerium ions and manganese ions, and a host compound capable of forming an inclusion compound with the metal ions. The cerium ions and / or manganese ions function as radical quenchers, capturing and neutralizing hydrogen peroxide radicals, thereby suppressing deterioration of the membrane electrode assembly. Furthermore, by adding a host compound for the metal ions to the membrane electrode assembly, migration of the metal ions can be suppressed, thereby reducing uneven concentration in the in-plane direction.

[0047] The metal ions are selected from cerium ions and manganese ions. The cerium ions and manganese ions function as radical quenching agents. The radical quenching agents can facilitate the conversion of hydroxide radicals generated from hydrogen peroxide to hydroxide ions, thereby suppressing deterioration of the anode catalyst layer. For example, the reaction of cerium ions to convert hydroxide radicals to hydroxide ions is as follows: Ce 3+ + OH (hydroxyl radical) → Ce 4+ +OH - (hydroxide ion)

[0048] The cerium ion may be either +3 or +4 valent, and the manganese ion may be either +3 or +4 valent.

[0049] The cerium salt for obtaining cerium ions is not particularly limited, and examples thereof include cerium nitrate, cerium carbonate, cerium acetate, cerium chloride, cerium sulfate, diammonium cerium nitrate, and tetraammonium cerium sulfate. One type of cerium salt may be used alone, or two or more types may be used in combination. The cerium salt may be an organic metal complex salt. Examples of the organic metal complex salt include cerium acetylacetonate.

[0050] The manganese salt for obtaining manganese ions is not particularly limited, and examples thereof include manganese nitrate, manganese carbonate, manganese acetate, manganese chloride, manganese sulfate, etc. One type of manganese salt may be used alone, or two or more types may be used in combination.

[0051] In this embodiment, the host compound forms an inclusion compound with a cerium ion or manganese ion as a guest compound. The inclusion compound refers to an adduct in which the metal ion as a guest compound is included in the host compound. Examples of host compounds that form inclusion compounds include crown ether compounds, cyclodextrin compounds, and cyclophane compounds. One type of host compound may be used alone, or two or more types may be used in combination.

[0052] The host compound is not particularly limited as long as it is a compound that can form an inclusion compound with the metal ion. The host compound preferably has a cyclic structure, and the number of ring members in the cyclic structure is preferably 15 or more, and more preferably 18 or more. In one embodiment, the host compound is preferably a crown ether compound. The crown ether compound is a compound having a ring with a repeating structure of a (-CH2-CH2-Y-) unit or a (-CH2-CH2-CH2-Y-) unit, where Y is at least one heteroatom selected from O, S, N, and P. The crown ether compound captures a metal ion in this ring structure to form an inclusion compound. The number of ring members in the crown ether compound is preferably 15 or more, and more preferably 18 or more.

[0053] Examples of crown ether compounds include crown ethers and crown ether derivatives. Examples of crown ethers include 15-crown-5-ether, 18-crown-6-ether, 21-crown-7-ether, and 24-crown-8-ether. In this embodiment, the host compound is preferably a crown ether compound having an aromatic ring or an aliphatic ring. Crown ether compounds having an aromatic ring or an aliphatic ring have high hydrophobicity due to their structure, and therefore migrate less to the cathode catalyst layer. Examples of crown ether compounds having an aromatic ring or an aliphatic ring include dibenzo-15-crown-5-ether, benzo-18-crown-6-ether, dibenzo-18-crown-6-ether, benzo-21-crown-7-ether, dibenzo-21-crown-7-ether, benzo-24-crown-8-ether, dibenzo-24-crown-8-ether, cyclohexano-18-crown-6-ether, cyclohexano-21-crown-7-ether, cyclohexano-24-crown-8-ether, dicyclohexano-18-crown-6-ether, ether, dicyclohexano-21-crown-7-ether, dicyclohexano-24-crown-8-ether, and compounds in which the aromatic ring or aliphatic ring of these compounds is substituted with at least one substituent selected from halogen atoms (e.g., fluorine atoms or bromine atoms), hydroxy groups, amino groups, nitro groups, formyl groups, alkyl groups having 1 to 6 carbon atoms (e.g., methyl groups, ethyl groups, propyl groups, and butyl groups), hydroxyalkyl groups having 1 to 6 carbon atoms, carboxyalkyl groups having 2 to 7 carbon atoms, and aryl groups having 6 to 14 carbon atoms (e.g., phenyl groups). The number of substituents is, for example, 1 to 6, 1 to 5, 1 to 4, 1 to 3, 1 to 2, or 1. These compounds may be used alone or in combination of two or more.

[0054] In the membrane / electrode assembly of this embodiment, the host compound and at least a portion of the metal ions form an inclusion compound.

[0055] The host compound and metal ions can be contained in the anode catalyst layer, the solid polymer electrolyte membrane, or both.

[0056] The anode catalyst layer functions as a fuel electrode, that is, a hydrogen electrode.

[0057] When the anode catalyst layer contains a host compound and a metal ion, the anode catalyst layer contains at least an electrode catalyst, an electrolyte, a metal ion selected from cerium ions and manganese ions, and a host compound capable of forming an inclusion compound with the metal ion. The metal ion can facilitate the conversion of hydroxide radicals generated from hydrogen peroxide to hydroxide ions, thereby suppressing deterioration of the anode catalyst layer.

[0058] The electrode catalyst is not particularly limited, but for example, the above-mentioned materials can be used.

[0059] Ionomers are preferred as the electrolyte used in the anode catalyst layer. Ionomers, also known as cation exchange resins, exist as clusters formed from ionomer molecules. The ionomer is not particularly limited, but any ionomer known in the art can be used. Examples of ionomers include fluororesin-based electrolytes such as perfluorosulfonic acid resins; sulfonated plastic-based electrolytes such as sulfonated polyether ketones, sulfonated polyether sulfones, sulfonated polyether ether sulfones, sulfonated polysulfones, sulfonated polysulfides, and sulfonated polyphenylenes; and sulfoalkylated plastic-based electrolytes such as sulfoalkylated polyether ether ketones, sulfoalkylated polyether sulfones, sulfoalkylated polyether ether sulfones, sulfoalkylated polysulfones, sulfoalkylated polysulfides, and sulfoalkylated polyphenylenes. One type of electrolyte may be used alone, or two or more types may be used in combination.

[0060] The content of the metal ions and the host compound in the anode catalyst layer is preferably 0.1 to 20 mass% based on the total solid content of the anode catalyst layer. Regarding this content, the inclusion compound is considered to be a mixture of the metal ions and the host compound. That is, when the metal ions and the host compound are added to the anode catalyst layer separately or simply mixed together, even if an inclusion compound is formed in the polymer electrolyte, the amount of the inclusion compound is not taken into consideration, and only the total amount of the incorporated metal ions and the inclusion compound is included in the calculation. Furthermore, when an inclusion compound is formed in advance and then added to the anode catalyst layer, the amount of the inclusion compound is considered to be the total amount of the metal ions and the inclusion compound that formed the inclusion compound. Furthermore, when there are metal ions and the host compound that do not form an inclusion compound in addition to the metal ions and the host compound that form the inclusion compound, these are also included in the calculation.

[0061] In this embodiment, the molar ratio of the host compound to the metal ion ([moles of host compound] / [moles of metal ion]) is, for example, 0.1 to 10, preferably 0.2 to 7.5, and more preferably 0.4 to 5.0. That is, the content of the host compound is, for example, 0.1 to 10 mol, preferably 0.2 to 7.5 mol, and more preferably 0.4 to 5.0 mol per mol of the metal ion. In this relative ratio, the inclusion compound is also considered to be a mixture of the two, as described above.

[0062] When the solid polymer electrolyte membrane contains a host compound and metal ions, the solid polymer electrolyte membrane containing the host compound and metal ions can be obtained, for example, by the following method. (1) A solid polymer electrolyte membrane is immersed in a solution containing metal ions to exchange groups such as sulfonic acid groups with metal ions, and then immersed in a solution containing a host compound to incorporate the host compound into the membrane. (2) A method in which a compound containing a metal ion (e.g., a cerium salt) is added to a dispersion of a polymer electrolyte to ion-exchange groups such as sulfonic acid groups with metal ions, and then a solution or solid containing a host compound is added to the dispersion, and the resulting liquid is used for coating to form a film. (3) A method in which a compound containing a metal ion (e.g., a cerium salt) is reacted with a host compound in a solvent to form an inclusion compound, and then a solid polymer electrolyte membrane is immersed in a solution in which the inclusion compound is dissolved in a solvent to ion-exchange groups such as sulfonic acid groups with the inclusion compound, thereby incorporating the inclusion compound into the membrane. (4) A compound containing a metal ion (e.g., a cerium salt) is reacted with a host compound in a solvent to form an inclusion compound, and then the inclusion compound or a solution thereof is added to a dispersion of a polymer electrolyte, and the resulting liquid is used to form a film by coating.

[0063] [Method for manufacturing membrane electrode assembly] The catalyst layer can be formed, for example, by the steps of preparing a catalyst ink (e.g., about 10% solids concentration) containing an electrode catalyst, an ionomer, and a solvent, applying the catalyst ink to the surface of a substrate and volatilizing the solvent in the coating to form a catalyst layer on the surface of the substrate, and transferring the catalyst layer on the surface of the substrate to an electrolyte membrane. Alternatively, the catalyst layer can be formed by directly applying the catalyst ink to a solid polymer electrolyte membrane instead of a substrate. A membrane-electrode assembly can be produced by forming a cathode catalyst layer and an anode catalyst layer on the solid polymer electrolyte membrane.

[0064] Examples of methods for applying the catalyst ink include spraying, blade coating using a doctor blade or applicator, die coating, reverse roll coating, and intermittent die coating.

[0065] The anode catalyst layer may be formed by adding the metal ions and the host compound to a catalyst ink for forming the anode catalyst layer. Specifically, the catalyst ink for forming the anode catalyst layer may contain an electrode catalyst, an ionomer (e.g., an ionomer having a sulfonic acid group), the metal ions, a host compound, and a solvent. The metal ions and the host compound may be added separately or in the form of a complex of the two.

[0066] [Specific configurations of membrane electrode assembly and polymer electrolyte fuel cell] A solid polymer fuel cell has a membrane electrode assembly (MEA) as its basic unit, in which catalyst layers (electrodes) are bonded to both sides of a solid polymer electrolyte membrane. In solid polymer fuel cells, a gas diffusion layer is generally disposed on the outside of the catalyst layer. The gas diffusion layer supplies reactant gases and electrons to the catalyst layer, and is made of carbon paper, carbon cloth, or the like. The catalyst layer is the reaction site for electrode reactions.

[0067] The configurations of a membrane electrode assembly and a polymer electrolyte fuel cell will be described below with reference to FIG. 1. FIG. 1 is a schematic cross-sectional view illustrating an example of the configuration of a polymer electrolyte fuel cell according to this embodiment, showing a cross-sectional view of a main portion of a fuel cell 10 as an example. The polymer electrolyte fuel cell includes a stack of unit cells, each of which includes a power generation body and fuel cell separators disposed on both sides of the power generation body. A plurality of unit cells are stacked in the stacking direction, and the unit cells are electrically connected in series. As shown in FIG. 1, the fuel cell 10 includes a plurality of unit cells 1, which are basic units, stacked together. Each unit cell 1 is a polymer electrolyte 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). The unit cell 1 includes a membrane electrode & gas diffusion layer assembly (MEGA) 2 having gas diffusion layers (GDLs) 7 disposed on both sides thereof, and separators 3 in contact with the MEGA 2 to separate the MEGA 2. In this embodiment, the MEGA 2 is sandwiched between a pair of separators 3, 3.

[0068] The MEGA 2 includes a membrane electrode assembly (MEA) 4 and gas diffusion layers 7, 7 disposed on both sides thereof. The membrane electrode assembly 4 is composed of an electrolyte membrane 5 and a pair of electrodes 6, 6 bonded to sandwich the electrolyte membrane 5. The electrolyte membrane 5 is, for example, a proton-conductive ion-exchange membrane formed of a solid polymer material. The electrodes 6 include, for example, a porous carbon material supporting a catalyst 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 layers 7 are formed of a gas-permeable conductive material. Examples of gas-permeable conductive materials include porous carbon materials such as carbon paper or carbon cloth, or porous metal materials such as metal mesh or metal foam. In this embodiment, the anode electrode is formed of an anode catalyst layer, and the cathode electrode is formed of a cathode catalyst layer.

[0069] The MEGA 2 is the power generation part of the fuel cell 10, and the separator 3 is in contact with the gas diffusion layer 7 of the MEGA 2. If the gas diffusion layer 7 is not present, the membrane electrode assembly 4 is the power generation part, and in this case, the separator 3 is in contact with the membrane electrode assembly 4. Therefore, the power generation part of the fuel cell 10 includes the membrane electrode assembly 4 and is in contact with the separator 3.

[0070] The separator 3 is a plate-shaped member having a metal substrate (e.g., a stainless steel substrate). Metal substrates have excellent electrical conductivity and gas impermeability. In Fig. 1, the surface of the separator 3 facing the power generation section abuts against the gas diffusion layer 7 of the MEGA 2, and the other surface abuts against another adjacent separator 3.

[0071] The gas flow channel 21 defined between the gas diffusion layer 7 on one electrode (i.e., anode electrode) 6 side and the separator 3 is a flow channel through which a fuel gas flows, and the gas flow channel 22 defined between the gas diffusion layer 7 on the other electrode (i.e., cathode electrode) 6 side and the separator 3 is a flow channel through which an oxidant gas flows. When a fuel gas is supplied to one of the gas flow channels 21 facing each other via the cell 1 and an oxidant gas is supplied to the gas flow channel 22, an electrochemical reaction occurs in the cell 1, generating an electromotive force.

[0072] Furthermore, a given cell 1 and another adjacent cell 1 are arranged with the anode electrode 6 and cathode electrode 6 facing each other. The top of the rear surface of the separator 3 arranged along the anode electrode 6 of one cell 1 is in surface contact with the top of the rear surface of the separator 3 arranged along the cathode electrode 6 of the other cell 1. A refrigerant (e.g., water) that cools the cells 1 flows through a space (coolant flow path) 23 defined between the separators 3, 3 that are in surface contact between two adjacent cells 1. [Example]

[0073] The present embodiment will be described below using examples.

[0074] [Example 1] (Synthesis method) Perfluoro 2-ethyl-1,3-dioxole (PED) (5.07 g) and perfluorosulfonyl fluoride vinyl ether (PSVE-A) (28.79 g) were mixed and 0.05 mol% initiator was added. This mixture was subjected to freeze-degassing and nitrogen purge three times, and then allowed to react at room temperature for two days. The unreacted monomer was then removed by heating at 120°C under vacuum for 1 hour, yielding the desired fluorosulfonyl group-containing polymer (7.0 g). The equivalent mass of this fluorosulfonyl group-containing polymer was 810 g / mol. The -SO2F groups of the fluorosulfonyl group-containing polymer were converted to sulfonic acid groups (-SO3H groups), yielding the desired sulfonyl group-containing polymer. This sulfonyl group-containing polymer functions as a highly oxygen-permeable ionomer.

[0075] (equivalent mass of fluoropolymer (H)) 1.0 g of a fluorosulfonyl group-containing polymer and 10 mL of a water / methanol mixed solution containing sodium hydroxide at a concentration of 0.35 N were placed in a polycarbonate container and allowed to stand at 60°C for 40 hours, thereby converting the -SO2F groups of the fluorosulfonyl group-containing polymer to -SO3Na groups. The solution was back-titrated with 0.1 N hydrochloric acid using phenolphthalein as an indicator to determine the amount of sodium hydroxide in the solution, and the equivalent mass of the -SO3H type polymer of the fluoropolymer (H) was calculated. The equivalent mass in this case may sometimes be referred to as the equivalent mass of the polymer.

[0076] (Formation of cathode catalyst layer) A metal-supported catalyst serving as an electrode catalyst was dispersed in an ionomer solution prepared by dispersing the sulfonyl group-containing polymer in water and ethanol using a bead mill to prepare a catalyst ink. The mass ratio of water to ethanol in the catalyst ink (water / ethanol) was approximately 1. The resulting catalyst ink was applied to a polytetrafluoroethylene sheet and dried to form a cathode catalyst layer.

[0077] The Pt content in the cathode catalyst layer was 0.2 mg / cm 2 The mass ratio of ionomer to carbon (I / C) was 1.0. 30% Pt / Vulcan (registered trademark) (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., TEC10V30E) was used as catalyst particles.

[0078] (Formation of inclusion compounds (complexes)) 18-Crown-6-ether (18CRE) (2.64 g, 0.01 mol) and cerium(III) nitrate hexahydrate (4.34 g, 0.01 mol) were weighed into a 100 mL recovery flask, and ethanol (20 mL) and water (20 mL) were added. The mixture was stirred for 24 hours at room temperature. After removing the solvent using an evaporator, the mixture was vacuum dried at 60°C for 1 hour to obtain a white solid. FT-IR analysis confirmed that the peaks derived from the ether group were shifted to lower wavenumbers, confirming that CRE and Ce formed an inclusion compound.

[0079] (Formation of anode catalyst layer) The electrode catalyst used was 60 wt% Pt / Ketjen®. The electrode catalyst and the composite were dispersed in an ionomer solution (DE2020) containing water, ethanol, and Nafion® to prepare a catalyst ink. This catalyst ink was applied to a polytetrafluoroethylene sheet and dried to form an anode catalyst layer.

[0080] The Pt content of the anode catalyst layer is 0.1 mg / cm 2 , cerium ion concentration is 4 μg / cm 2 As described above, the host compound was contained in a Ce:ligand ratio of 1:1 mol. The mass ratio of ionomer to carbon (I / C) was 1.0.

[0081] (Fabrication of membrane electrode assembly) The obtained cathode catalyst layer and anode catalyst layer were thermally transferred onto both sides of a Nafion (registered trademark) membrane (NR211), respectively, to prepare a membrane electrode assembly E1. The thermal transfer conditions were 140°C and 50 kgf / cm 2 (4.90 MPa) for 5 min. The electrode area of ​​the membrane electrode assembly for the initial performance test was 1 cm × 1 cm (1 cm 2 The electrode area of ​​the membrane electrode assembly for the durability test was 3.6 × 3.6 cm (12.96 cm). 2 This membrane electrode assembly was sandwiched between paper diffusion layers (GDL) with water-repellent layers to prepare a test cell.

[0082] Comparative Example 1: A membrane / electrode assembly C1 was produced in the same manner as in Example 1, except that the anode catalyst layer was formed without adding a host compound and the cathode catalyst layer was formed using Aquivion (D79-25BS) as the ionomer solution. The equivalent mass of Aquivion was 790 g / mol.

[0083] Comparative Example 2: A membrane / electrode assembly C2 was produced in the same manner as in Example 1, except that the cathode catalyst layer was formed using Aquivion (D79-25BS) as the ionomer solution.

[0084] Comparative Example 3: A membrane / electrode assembly C3 was produced in the same manner as in Example 1, except that the anode catalyst layer was formed without adding a host compound.

[0085] [Example 2]: A membrane / electrode assembly E2 was produced in the same manner as in Example 1, except that benzo-18-crown-6-ether (B18CRE) (0.01 mol) was used instead of 18CRE (0.01 mol).

[0086] Comparative Example 4: A membrane / electrode assembly C4 was produced in the same manner as in Example 2, except that the cathode catalyst layer was formed using Aquivion (D79-25BS) as the ionomer solution.

[0087] [evaluation] (Initial performance test) The above test cell (electrode area: 1 cm 2 The current-voltage characteristics of the 1.0 A / cm 2 The voltage values ​​at are shown in Table 1 below. Low humidity environment (30% RH), sweep rate: 20 mA / s, cell temperature: 90°C, pressure: 150 kPa (abs), cathode gas type: air, cathode gas flow rate: 2.0 L / min, anode gas type: hydrogen, anode gas flow rate: 0.5 L / min.

[0088] (Durability test) The above test cell (electrode area: 12.96 cm 2The durability test was carried out in a highly humidified environment (90°C, 30% RH) at a cell temperature of 90°C, with hydrogen / air supplied and a current density of 0.05 A / cm. 2 The initial characteristics of the polymer electrolyte fuel cell in this case and the characteristics after a durability test load were evaluated. Hydrogen and air were humidified and supplied to the cell so that the anode side had a dew point of 67°C, and the cathode side had a dew point of 67°C. The cell voltage at the beginning of operation and the relationship between the cell voltage and the time elapsed after the start of operation were measured. The results are shown in Table 1 below. Under the above cell evaluation conditions, the cell voltage at the beginning of operation and after 300 hours had elapsed after the start of operation were also measured.

[0089] [Table 1]

[0090] [Consideration] In a comparison between Example 1 and Comparative Example 2, which are systems having an anode catalyst layer to which a host compound and cerium ions were added, Example 1, which used a highly oxygen-permeable ionomer, showed excellent power generation performance in the initial performance test, and also showed little deterioration in performance even after 300 hours in the durability test.

[0091] The upper and / or lower limit values ​​of the numerical ranges described herein can be arbitrarily combined to define a preferred range. For example, the upper and lower limit values ​​of the numerical ranges can be arbitrarily combined to define a preferred range, the upper limit values ​​of the numerical ranges can be arbitrarily combined to define a preferred range, and the lower limit values ​​of the numerical ranges can be arbitrarily combined to define a preferred range.

[0092] Although the present embodiment has been described in detail above, the specific configuration is not limited to this embodiment, and even if there are design changes within the scope that do not deviate from the gist of this disclosure, they are included in this disclosure. [Explanation of symbols]

[0093] 1: cell, 2: MEGA (power generation section), 3: separator (fuel cell separator), 4: membrane electrode assembly (MEA), 6: electrode, 7: gas diffusion layer, 10: fuel cell, 21, 22: gas flow path, 31: metal substrate, 32: tin oxide film

Claims

1. A membrane electrode assembly having a solid polymer electrolyte membrane, an anode catalyst layer disposed on one surface of the solid polymer electrolyte membrane, and a cathode catalyst layer disposed on the other surface of the solid polymer electrolyte membrane, the membrane electrode assembly includes a metal ion selected from cerium ions and manganese ions, and a host compound capable of forming an inclusion compound with the metal ion; the cathode catalyst layer contains at least an electrode catalyst and a sulfonyl group-containing polymer, the sulfonyl group-containing polymer comprises a structural unit (u1) having a sulfonyl group and a structural unit (u2) having a ring structure, The structural unit (u1) having a sulfonyl group is represented by the following formula (u1): 【Chemical 1】 (wherein R F1 is —(CF 2 CF(CF 3 )O) h —(CF 2 ) i —, h is an integer of 0 or more and 3 or less, and i is an integer of 1 or more and 10 or less). The structural unit (u2) having a ring structure is at least one selected from a structural unit represented by the following formula (u2-1) and a structural unit represented by the following formula (u2-2): 【Chemistry 2】 (In the formula, R １ ~R ４ are each independently a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms. 【Chemistry 3】 (In the formula, R ５ ~R １０ are each independently a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms. A membrane electrode assembly, wherein the host compound is 18-crown-6-ether or benzo-18-crown-6-ether.

2. 2. The membrane electrode assembly according to claim 1, wherein the host compound and the metal ions are contained in the anode catalyst layer, the solid polymer electrolyte membrane, or both.

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