Solid polymer electrolyte membrane, membrane electrode assembly, water electrolysis device, method for producing hydrogen, and method for producing membrane electrode assembly

Abstract

Provided is a solid polymer electrolyte membrane which is capable of suppressing an increase in electrolytic voltage after water electrolysis is performed for a certain period, and in which pinholes are hardly generated.　This solid polymer electrolyte membrane includes: a fluorine-containing polymer having an ion exchange group; a platinum-containing material; aggregates of cerium oxide particles; and a woven fabric. The average particle diameter of the aggregates is 0.1-10 μm.

Description

Solid polymer electrolyte membrane, membrane electrode assembly, water electrolysis device, method for producing hydrogen, and method for producing membrane electrode assembly

[0001] The present disclosure relates to a solid polymer electrolyte membrane, a membrane electrode assembly, a water electrolysis device, a method for producing hydrogen, and a method for producing a membrane electrode assembly.

[0002] From the viewpoint of power-to-gas, i.e., converting surplus electricity into gas for storage and utilization, the use of a polymer electrolyte membrane (PEM) water electrolysis device has been considered. For example, Patent Literature 1 discloses a polymer electrolyte membrane (PEM) water electrolysis device having a membrane electrode assembly including an anode and a cathode each having a catalyst layer, and a solid polymer electrolyte membrane disposed between the anode and the cathode.

[0003] International Publication No. 2022 / 050363

[0004] In recent years, there has been a demand for further improvements in the performance of water electrolysis devices. The present inventors evaluated a water electrolysis device having a solid polymer electrolyte membrane as described in Patent Document 1 and found that it may be difficult to suppress both an increase in electrolysis voltage after water electrolysis for a certain period of time and the occurrence of pinholes.

[0005] The present disclosure has been made in view of the above-mentioned problems, and an object of one embodiment of the present invention is to provide a solid polymer electrolyte membrane, a membrane electrode assembly, a water electrolysis device, a method for producing hydrogen, and a method for producing a membrane electrode assembly that can suppress an increase in electrolysis voltage after water electrolysis for a certain period of time and are less likely to produce pinholes.

[0006] The present disclosure has the following aspects. [1] A solid polymer electrolyte membrane comprising a fluoropolymer having ion exchange groups, a platinum-containing material, aggregates containing cerium oxide particles, and a woven fabric, wherein the average particle size of the aggregates is 0.1 to 10 μm. [2] The solid polymer electrolyte membrane according to [1], wherein the average particle size of the aggregates is greater than 3 μm. [3] The solid polymer electrolyte membrane according to [1] or [2], wherein the ion exchange capacity of the fluoropolymer is 0.90 to 2.00 milliequivalents / gram dry resin. [4] A solid polymer electrolyte membrane according to [1] or [2], wherein the ion exchange capacity of the fluoropolymer is 0.90 to 2.00 milliequivalents / gram dry resin. [5] A solid polymer electrolyte membrane according to [1] or [2], wherein the ion exchange capacity of the solid polymer electrolyte membrane is 0.90 to 2.00 milliequivalents / gram dry resin. ２ The mass of the aggregate per cm is 0.010 mg / cm ２[5] The solid polymer electrolyte membrane according to any one of [1] to [4], wherein the platinum-containing material is unevenly distributed on one surface side of the solid polymer electrolyte membrane. [6] The solid polymer electrolyte membrane according to any one of [1] to [5], wherein the platinum-containing material is supported on a carrier. [7] The solid polymer electrolyte membrane according to any one of [1] to [6], wherein the ion exchange group of the fluoropolymer is a sulfonic acid type functional group. [8] The solid polymer electrolyte membrane according to any one of [1] to [7], wherein the fluoropolymer contains a unit represented by formula (1-1) described below. Formula (1-1)-[CF ２ -CF(-O-R ｆ１ -SO ３ M)] - In formula (1-1), R ｆ１is a perfluoroalkylene group which may contain an oxygen atom between carbon atoms, and M is a hydrogen atom, an alkali metal, or a quaternary ammonium cation. [9] The solid polymer electrolyte membrane according to any one of [1] to [8], wherein the woven fabric is made of a material selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, polyether ether ketone, and polyphenylene sulfide.

[10] A membrane electrode assembly comprising the solid polymer electrolyte membrane according to any one of [1] to [9], a cathode catalyst layer disposed on one side of the solid polymer electrolyte membrane, and an anode catalyst layer disposed on the other side of the solid polymer electrolyte membrane.

[11] A water electrolysis device comprising the membrane electrode assembly according to

[10] , a power supply unit connected to the cathode catalyst layer side and the anode catalyst layer side of the membrane electrode assembly, and a water supply unit which supplies water to the anode catalyst layer side.

[12] A method for producing hydrogen by electrolyzing water using the water electrolysis device according to

[11] .

[13] A method for producing a membrane electrode assembly including the solid polymer electrolyte membrane according to any one of [1] to [9], a cathode catalyst layer, and an anode catalyst layer, the method comprising forming the cathode catalyst layer on one side of the solid polymer electrolyte membrane, and forming the anode catalyst layer on the other side of the solid polymer electrolyte membrane.

[0007] According to one embodiment of the present invention, it is possible to provide a solid polymer electrolyte membrane, a membrane electrode assembly, a water electrolysis apparatus, a method for producing hydrogen, and a method for producing a membrane electrode assembly, which can suppress an increase in electrolysis voltage after water electrolysis for a certain period of time and are less likely to produce pinholes.

[0008] 1 is a schematic cross-sectional view of a solid polymer electrolyte membrane for illustrating a state in which platinum-containing substances are unevenly distributed. 2 is a cross-sectional view schematically showing an example of a membrane electrode assembly according to the present disclosure. 3 is a cross-sectional view schematically showing an example of a membrane electrode assembly according to the present disclosure.

[0009] The definitions of the following terms apply throughout the present specification and claims unless otherwise specified. An "ion exchange group" is a group that can exchange at least a portion of the ions contained in this group for other ions, and examples thereof include sulfonic acid functional groups and carboxylic acid functional groups. A "sulfonic acid functional ... ３ Here, the form of the sulfonate group is, for example, (—SO ３ － ) Ma ＋ , (-SO ３ － ) ２ Mb ２＋ , and (-SO ３ － ) ３ Mc ３＋ (However, Ma ＋ is an alkali metal ion or a quaternary ammonium cation, and Mb ２＋ is a divalent metal ion, Mc ３＋ is a trivalent metal ion.) When there are two ligands, the number of ion exchange groups is counted as two, and when there are three ligands, the number of ion exchange groups is counted as three. The "carboxylic acid type functional group" means a carboxylic acid group (-COOH) or a carboxylic acid salt group. Here, the form of the carboxylic acid salt group can be, for example, (-COO － ) Ma ＋ , (-COO － ) ２ Mb ２＋ , and (-COO － ) ３ Mc ３＋ (However, Ma ＋ is an alkali metal ion or a quaternary ammonium cation, and Mb ２＋ is a divalent metal ion, Mc ３＋is a trivalent metal ion.) Note that when there are two ligands, the number of ion exchange groups is counted as two, and when there are three ligands, the number of ion exchange groups is counted as three. A "precursor membrane" is a membrane containing a polymer having a group that can be converted into an ion exchange group. A "group that can be converted into an ion exchange group" means a group that can be converted into an ion exchange group by treatment such as hydrolysis or acidification. A "group that can be converted into a sulfonic acid functional group" means a group that can be converted into a sulfonic acid functional group by treatment such as hydrolysis or acidification. A "group that can be converted into a carboxylic acid functional group" means a group that can be converted into a carboxylic acid functional group by known treatment such as hydrolysis or acidification.

[0010] The term "unit" in a polymer refers to an atomic group based on one molecule of a monomer formed by polymerization of the monomer. The unit may be an atomic group formed directly by the polymerization reaction, or may be an atomic group in which a part of the atomic group is converted into a different structure by treating the polymer obtained by the polymerization reaction.

[0011] A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. In the numerical ranges described in stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the examples.

[0012] [Electrolyte Membrane] The solid polymer electrolyte membrane (hereinafter also simply referred to as "electrolyte membrane") of the present disclosure comprises a fluoropolymer having ion exchange groups (hereinafter also simply referred to as "fluoropolymer (I)"), a platinum-containing material, an aggregate containing cerium oxide particles, and a woven fabric, wherein the average particle size of the aggregate is 0.1 to 10 μm. Hereinafter, the aggregate containing cerium oxide particles and having an average particle size of 0.1 to 10 μm in the present disclosure will also be referred to as "the present aggregate."

[0013] The present inventors have found that an electrolyte membrane containing cerium oxide particle-containing agglomerates, where the agglomerates have an average particle size of less than 0.1 μm, tends to exhibit an increase in electrolysis voltage after a certain period of water electrolysis when applied to a water electrolysis device. Because the cerium oxide particles are small, their surface area increases. When water electrolysis is performed using such relatively small cerium oxide particles for a certain period of time (e.g., 500 hours), cerium is likely to be eluted from the cerium oxide particles over time. It is believed that the eluted cerium reduces the proton conductivity of the ionomer in the electrolyte membrane and catalyst layer, resulting in an increase in electrolysis voltage. Furthermore, the present inventors have found that an electrolyte membrane containing cerium oxide particle-containing agglomerates, where the agglomerates have an average particle size of more than 10 μm, tends to cause expansion of the mesh size of the woven fabric during operation of the water electrolysis device, and the expanded portions swell, resulting in pinholes. In such cases, it is believed that the use of the present agglomerates (agglomerates containing cerium oxide particles with an average particle size of 10 μm or less) can suppress expansion of the mesh size of the woven fabric, thereby reducing the occurrence of pinholes.

[0014] The electrolyte membrane may have a single layer structure or a multilayer structure. Specific embodiments of the electrolyte membrane having a multilayer structure include a laminated structure in which a plurality of electrolyte layers having different contents of at least one of the platinum-containing material and the present aggregate are stacked, and a laminated structure in which a plurality of electrolyte layers having different ion exchange capacities are stacked.

[0015] When the electrolyte membrane contains a platinum-containing material and the present aggregate in the same layer, this is preferable because hydroxyl radicals derived from hydrogen peroxide, which are generated when the platinum-containing material recombines hydrogen and oxygen, can be efficiently recovered by the cerium oxide contained in the present aggregate.

[0016] The platinum-containing material and the present aggregate contained in the electrolyte membrane may each be dispersed throughout the electrolyte membrane, or may be unevenly distributed on one surface side of the electrolyte membrane. When unevenly distributed on one surface side of the electrolyte membrane, it is preferable that at least one of the platinum-containing material and the present aggregate is unevenly distributed on one surface side of the electrolyte membrane, and it is preferable that at least the platinum-containing material of the platinum-containing material and the present aggregate is unevenly distributed on one surface side of the electrolyte membrane. Furthermore, the platinum-containing material and the present aggregate (i.e., both the platinum-containing material and the present aggregate) may be unevenly distributed on one surface side of the electrolyte membrane. When the electrolyte membrane is applied to a water electrolysis device, it is preferable to arrange the surface of the electrolyte membrane on which the platinum-containing material is unevenly distributed on the anode side, in order to suppress the occurrence of hydrogen crossover.

[0017] In this specification, the phrase "platinum-containing substances are unevenly distributed on one surface side of the electrolyte membrane" means that the concentration of the platinum-containing substances in a region from one surface (hereinafter also referred to as "surface A") of the electrolyte membrane to a predetermined depth position (hereinafter also referred to as "depth position B") before reaching the other surface (hereinafter also referred to as "surface C") is higher than the concentration of the platinum-containing substances in a region from surface C to depth position B. Furthermore, the phrase "the present aggregates are unevenly distributed on one surface side of the electrolyte membrane" means that the concentration of the present aggregates in a region from surface A to depth position B is higher than the concentration of cerium oxide in a region from surface C to depth position B. Furthermore, the phrase "platinum-containing substances and the present aggregates are unevenly distributed on one surface side of the electrolyte membrane" means that the concentration of the platinum-containing substances in a region from surface A to depth position B is higher than the concentration of the platinum-containing substances in a region from surface C to depth position B, and the concentration of the present aggregates in a region from surface A to depth position B is higher than the concentration of the present aggregates in a region from surface C to depth position B. Here, in one preferred embodiment in which the platinum-containing substance is unevenly distributed on one surface side of the electrolyte membrane, the platinum-containing substance is unevenly distributed at a depth position B, which is a depth position of 50% of the thickness of the electrolyte membrane from the surface A. ５０ The concentration of platinum-containing substances in the region from the surface C to the depth position B ５０ In one embodiment, the concentration of the platinum-containing material is higher than that in the region up to 10 ...

[0018] The state in which "platinum inclusions are unevenly distributed on one surface side of the electrolyte membrane" will be specifically explained using the example of FIG. 1. FIG. 1 is a cross-sectional schematic diagram of an electrolyte membrane for explaining the state in which platinum inclusions are unevenly distributed. In FIG. 1, the electrolyte membrane 1 has a surface A1, which is one surface, and a surface C1, which is the other surface. The depth position B1 is a distance T from the surface A1 toward the surface C1. Ｘ The distance T １ corresponds to the thickness of the electrolyte membrane 1, and the distance T Ｘ is the distance T １ For example, the length is X% of the distance T Ｘ is the distance T １ , the depth position B1 is the thickness of the electrolyte membrane 1 (distance T １ ) corresponds to a position where the thickness is 20% of the surface thickness of the electrolyte membrane. Region X represents the region from surface A1 to depth position B1, and region Y represents the region from surface C1 to depth position B1. If there are irregularities on the surface of the electrolyte membrane 1, the above distances are measured based on the position where the thickness of the electrolyte membrane 1 is minimum. In FIG. 1, if the concentration of the platinum-containing substance in region X is higher than the concentration of the platinum-containing substance in region Y, it can be said that "the platinum-containing substance is unevenly distributed on one surface side of the electrolyte membrane."

[0019] In order to obtain a more excellent effect of the present disclosure, the platinum-containing material contained in the electrolyte membrane is preferably present from one surface of the electrolyte membrane to a thickness position corresponding to 25%, particularly 20%, further 15%, and even further 10% of the thickness of the electrolyte membrane.Furthermore, it is preferable that the platinum-containing material contained in the electrolyte membrane is present only up to these thickness positions.

[0020] The positions of the platinum-containing substances and the agglomerates in the electrolyte membrane can be identified by element distribution using, for example, an energy dispersive X-ray analyzer (product name "QUANTAX FlatQUAD", manufactured by Bruker). Based on the obtained element distribution, the above-mentioned distance Tx can be calculated.

[0021] One example of a method for distributing the platinum-containing material unevenly on one surface of the electrolyte membrane is a method of obtaining an electrolyte membrane by laminating a first electrolyte layer containing the platinum-containing material and a second electrolyte layer having a lower platinum-containing material concentration than the first electrolyte layer or not containing the platinum-containing material. Another example is a method of immersing one surface of an electrolyte membrane not containing the platinum-containing material in a solution containing platinum ions, so that the platinum-containing material is contained between one surface of the electrolyte membrane and a predetermined depth position in the electrolyte membrane.

[0022] The thickness of the electrolyte membrane is preferably 30 μm or more, more preferably 60 μm or more, even more preferably 90 μm or more, and preferably 400 μm or less, more preferably 300 μm or less, even more preferably 200 μm or less, and particularly preferably 100 μm or less. Furthermore, since the aggregates may act as shields in the electrolyte membrane, creating areas where current is difficult to flow and increasing resistance, when the average particle size of the aggregates is 5 μm or more, the thickness of the electrolyte membrane is preferably 90 μm or more. When the average particle size of the aggregates is less than 5 μm, the thickness of the electrolyte membrane is preferably 60 μm or more. Furthermore, the upper limits of each are preferably within the thickness range of the electrolyte membrane described above. When the electrolyte membrane has a multilayer structure, the thickness of the electrolyte membrane refers to the total thickness of each layer. When the electrolyte membrane has a multilayer structure and includes the first electrolyte layer and the second electrolyte layer, the ratio of the thickness of the first electrolyte layer to the thickness of the second electrolyte layer (thickness of the first electrolyte layer / thickness of the second electrolyte layer) is preferably 0.02 or more, more preferably 0.05 or more, even more preferably 0.12 or more, particularly preferably 0.19 or more, and is preferably 0.80 or less, more preferably 0.50 or less, and even more preferably 0.30 or less. The thickness of the electrolyte membrane is measured using a magnified image (e.g., 100x) of the cross section of the electrolyte membrane taken with an optical microscope (product name "BX-51", manufactured by Olympus Corporation). If the surface of the electrolyte membrane is uneven, the thicknesses of 10 recessed portions on the electrolyte membrane and 10 raised portions on the electrolyte membrane are measured, and the arithmetic mean value of the thicknesses at the 20 points is taken as the thickness of the electrolyte membrane. However, if the raised portions contain threads that constitute the woven fabric, the thickness of the raised portions is the value obtained by subtracting the thickness of the threads present in the raised portions.

[0023] <Fluorine-containing polymer (I)> The electrolyte membrane contains a fluoropolymer (I). The ion exchange capacity of the fluoropolymer (I) is preferably 0.90 milliequivalents / gram dry resin or more, more preferably greater than 1.10 milliequivalents / gram dry resin, even more preferably 1.15 milliequivalents / gram dry resin or more, particularly preferably 1.20 milliequivalents / gram dry resin or more, and even more preferably 1.25 milliequivalents / gram dry resin or more, from the viewpoint of further reducing the electrolysis voltage when applied to a water electrolysis device. The ion exchange capacity of the fluoropolymer (I) is preferably 2.00 milliequivalents / gram dry resin or less, more preferably 1.50 milliequivalents / gram dry resin or less, even more preferably 1.43 milliequivalents / gram dry resin or less, and particularly preferably 1.35 milliequivalents / gram dry resin or less, from the viewpoint of the strength of the membrane / electrode assembly when wet. Only one type of fluoropolymer (I) may be used, or two or more types may be used in a laminated or mixed state.

[0024] The electrolyte membrane may contain a polymer other than the fluorine-containing polymer (I), but it is preferable that the polymer in the electrolyte membrane essentially consists of the fluorine-containing polymer (I). "Essentially consisting of the fluorine-containing polymer (I)" means that the content of the fluorine-containing polymer (I) is 95% by mass or more relative to the total mass of the polymers in the electrolyte membrane. The upper limit of the content of the fluorine-containing polymer (I) can be 100% by mass relative to the total mass of the polymers in the electrolyte membrane. Specific examples of polymers other than the fluorine-containing polymer (I) include one or more polyazole compounds selected from the group consisting of polymers of heterocyclic compounds containing one or more nitrogen atoms in the ring, and polymers of heterocyclic compounds containing one or more nitrogen atoms and oxygen atoms and / or sulfur atoms in the ring. Specific examples of polyazole compounds include polyimidazole compounds, polybenzimidazole compounds, polybenzobisimidazole compounds, polybenzoxazole compounds, polyoxazole compounds, polythiazole compounds, and polybenzothiazole compounds. In view of the oxidation resistance of the electrolyte membrane, specific examples of other polymers include polyphenylene sulfide resin and polyphenylene ether resin.

[0025] The fluoropolymer (I) has an ion-exchange group. Specific examples of the ion-exchange group include a sulfonic acid type functional group and a carboxylic acid type functional group, and the sulfonic acid type functional group is preferred from the viewpoint of further reducing the electrolysis voltage when the electrolyte membrane is applied to a water electrolysis device. Hereinafter, embodiments of the fluoropolymer having a sulfonic acid type functional group (hereinafter also referred to as "fluoropolymer (S)") will be mainly described in detail.

[0026] The fluorine-containing polymer (S) preferably contains a unit based on a fluorine-containing olefin and a unit having a sulfonic acid functional group and a fluorine atom. Examples of the fluorine-containing olefin include fluoroolefins having 2 to 3 carbon atoms and having one or more fluorine atoms in the molecule. Specific examples of the fluoroolefin include tetrafluoroethylene (hereinafter also referred to as "TFE"), chlorotrifluoroethylene, vinylidene fluoride, vinyl fluoride, and hexafluoropropylene. Among these, TFE is preferred from the viewpoints of the production cost of the monomer, reactivity with other monomers, and excellent properties of the resulting fluorine-containing polymer (S). One type of fluorine-containing olefin may be used alone, or two or more types may be used in combination.

[0027] As the unit having a sulfonic acid type functional group and a fluorine atom, a unit represented by formula (1) is preferred. ２ -CF(-L-(SO ３ M) ｎ )]-

[0028] L is an (n+1)-valent perfluorohydrocarbon group which may contain an etheric oxygen atom. The etheric oxygen atom may be located at a terminal of the perfluorohydrocarbon group or between carbon atoms. The (n+1)-valent perfluorohydrocarbon group preferably has 1 or more carbon atoms, more preferably 2 or more carbon atoms, and preferably 20 or less, more preferably 10 or less.

[0029] L is preferably an (n+1)-valent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom, more preferably a divalent perfluoroalkylene group which may contain an etheric oxygen atom, where n = 1, or a trivalent perfluoroaliphatic hydrocarbon group which may contain an etheric oxygen atom, where n = 2. The divalent perfluoroalkylene group may be either linear or branched.

[0030] M is a hydrogen atom, an alkali metal, or a quaternary ammonium cation. Multiple Ms may be the same or different. n is 1 or 2.

[0031] The unit represented by formula (1) is preferably a unit represented by formula (1-1), a unit represented by formula (1-2), a unit represented by formula (1-3) or a unit represented by formula (1-4), and more preferably a unit represented by formula (1-1). ２ -CF(-O-R ｆ１ -SO ３ M)] - Formula (1-2) - [CF ２ -CF(-R ｆ１ -SO ３ M) ]-

[0032]

[0033]

[0034] R ｆ１ is a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, and is preferably 20 or less, more preferably 10 or less.

[0035] R ｆ２ is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, and is preferably 20 or less, more preferably 10 or less.

[0036] R ｆ３is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, and is preferably 20 or less, more preferably 10 or less.

[0037] r is 0 or 1. m is 0 or 1. M is as defined above.

[0038] As the unit represented by formula (1-1) and the unit represented by formula (1-2), a unit represented by formula (1-5) is more preferred. ２ -CF(-(CF ２ ) ｘ -(OCF ２ CFY) ｙ -O-(CF ２ ) ｚ -SO ３ M)]—x is 0 or 1, y is an integer from 0 to 2, z is an integer from 1 to 4, and Y is F or CF ３ M is as described above.

[0039] Specific examples of the unit represented by formula (1-1) include the following units. In the formula, w is an integer of 1 to 8, and x is an integer of 1 to 5. The definition of M in the formula is as described above. -[CF ２ -CF(-O-(CF ２ ) ｗ -SO ３ M)]- -[CF ２ -CF(-O-CF ２ CF (CF ３ )-O-(CF ２ ) ｗ -SO ３ M)]- -[CF ２ -CF(-(O-CF ２ CF (CF ３ )) ｘ -SO ３ M) ]-

[0040] Specific examples of the unit represented by formula (1-2) include the following units. In the formula, w is an integer of 1 to 8. The definition of M in the formula is as described above. -[CF ２ -CF(-(CF２ ) ｗ -SO ３ M)]- -[CF ２ -CF (-CF ２ -O-(CF ２ ) ｗ -SO ３ M) ]-

[0041] The unit represented by formula (1-3) is preferably a unit represented by formula (1-3-1), where M is defined as above.

[0042]

[0043] R ｆ４ is a linear perfluoroalkylene group having 1 to 6 carbon atoms, and R ｆ５ is a single bond or a linear perfluoroalkylene group having 1 to 6 carbon atoms which may contain an oxygen atom between the carbon atoms. The definitions of r and M are as described above.

[0044] Specific examples of the unit represented by formula (1-3-1) include the following.

[0045]

[0046] As the unit represented by formula (1-4), a unit represented by formula (1-4-1) is preferred. ｆ１ , R ｆ２ and M are defined as above.

[0047]

[0048] Specific examples of the unit represented by formula (1-4-1) include the following.

[0049]

[0050] The unit having a sulfonic acid type functional group and a fluorine atom may be used alone or in combination of two or more.

[0051] The fluoropolymer (I) may contain units based on other monomers other than the units based on fluorine-containing olefin and the units having a sulfonic acid functional group and a fluorine atom. Specific examples of other monomers include CF２ = CFR ｆ６ (However, R ｆ６ is a perfluoroalkyl group having 2 to 10 carbon atoms, CF ２ =CF-OR ｆ７ (However, R ｆ７ is a perfluoroalkyl group having 1 to 10 carbon atoms, and CF ２ = CFO (CF ２ ) ｖ CF = CF ２ (wherein v is an integer of 1 to 3.) The content of units based on other monomers is preferably at most 30 mass % based on all units in the fluoropolymer (I) from the viewpoint of maintaining ion exchange performance.

[0052] The content of the fluoropolymer (I) is preferably from 95 to 100% by mass based on the total mass of the electrolyte membrane.

[0053] <Platinum-containing material> The electrolyte membrane contains a platinum-containing material. The platinum-containing material may contain platinum atoms, and specific examples of the platinum-containing material include platinum itself, platinum oxide, platinum-containing composite metal oxides, and platinum alloys. Specific examples of platinum-containing composite oxides include M ｘ Pt ３ O ４ (M is at least one metal atom selected from the group consisting of Li, Na, Mg, Ca, Zn, Cd, Co, Ni, Mn, Cu, Ag, Bi, and Ce, and x is greater than 0 and equal to or less than 1.) A specific example of a platinum alloy is an alloy containing platinum and at least one metal selected from the group consisting of transition metals and noble metals other than platinum.

[0054] Specific examples of the shape of the platinum-containing material include particles and sheets. When the platinum-containing material is particulate, it may be a core-shell type particle. An example of a core-shell type particle is a particle in which the core is carbon or contains a metal other than platinum, and the shell contains platinum atoms. When the platinum-containing material is particulate, the average particle diameter (D50) of the platinum-containing material is preferably 1 nm or more, more preferably 5 nm or more, even more preferably 10 nm or more, particularly preferably 100 nm or more, and preferably 10,000 nm or less, more preferably 5,000 nm or less, and even more preferably 3,000 nm or less. The average particle diameter of the platinum-containing material is the cumulative 50% diameter (D50) on a volume basis obtained by dispersing a dispersion containing the platinum-containing material and then measuring it using a particle size distribution analyzer, and the detailed measurement conditions are as follows. After dispersing a dispersion containing a platinum-containing material and a fluoropolymer (dispersing using a bead mill), the particle size distribution is measured using a laser diffraction particle size distribution analyzer (MT3300EXII-SDC, manufactured by Microtrackbell Corporation) to determine the volume-based cumulative 50% diameter of the platinum-containing material. The arithmetic mean value of the obtained three cumulative 50% diameters is used as D50. Alternatively, in a cross-sectional image of an electrolyte membrane taken using a scanning electron microscope (SEM), SEM-EDX (Energy Dispersive X-ray Spectroscopy), or TEM (Transmission Electron Microscope), the particle diameters of 20 arbitrarily selected different platinum-containing material particles may be measured, and the arithmetic mean value of the volume-based cumulative 50% diameter may be used as D50.

[0055] Electrolyte membrane 1cm ２ The mass of platinum content per unit mass is 0.010 mg / cm ２ More than 0.013 mg / cm is preferred. ２ More preferably, 0.015 mg / cm or more ２ More preferably, 0.050 mg / cm ２ The mass of the platinum-containing material is preferably 0.010 mg / cm or less. ２ If the mass of the platinum-containing material is 0.050 mg / cm or more, the occurrence of hydrogen crossover can be further suppressed. ２If the electrolyte membrane has a multi-layer structure, at least one electrolyte layer (preferably the above-mentioned first electrolyte layer) included in the electrolyte membrane has a thickness of 1 cm or less. ２ The mass of platinum content per unit area is 0.010 mg / cm ２ More than 0.013 mg / cm is preferred. ２ More preferably, 0.015 mg / cm or more ２ More preferably, 0.050 mg / cm ２ The mass of the platinum-containing material is preferably 0.013 mg / cm or less. ２ If the mass of the platinum-containing material is 0.050 mg / cm or more, the occurrence of hydrogen crossover can be further suppressed. ２ If the above ratio is less than 1, the electrolysis voltage can be reduced, and a low-cost membrane electrode assembly and water electrolysis device can be provided.

[0056] When the electrolyte membrane has a single layer structure, the mass ratio of the platinum-containing material to the fluoropolymer (I) in the electrolyte membrane (mass of platinum-containing material / mass of fluoropolymer (I)) is preferably 0.0005 to 0.0040. When the mass ratio is 0.0005 or more, the occurrence of hydrogen crossover can be further suppressed. When the mass ratio is 0.0040 or less, the electrolysis voltage can be further reduced, and a low-cost membrane electrode assembly and water electrolysis device can be provided. When the electrolyte membrane has a multilayer structure, the mass ratio of the platinum-containing material to the fluoropolymer (I) (mass of platinum-containing material / mass of fluoropolymer (I)) in at least one electrolyte layer (preferably the above-mentioned first electrolyte layer) contained in the electrolyte membrane is preferably 0.005 or more, more preferably 0.007 or more, even more preferably 0.014 or more, and preferably 0.024 or less. When the mass ratio is 0.005 or more, the occurrence of hydrogen crossover can be further suppressed. If the mass ratio is 0.024 or less, the electrolysis voltage can be lowered, and a low-cost membrane electrode assembly and water electrolysis device can be provided.

[0057] The platinum-containing material may be supported on a carrier. Specific examples of the carrier include carbon carriers such as carbon black powder, graphitized carbon, carbon fiber, and carbon nanotubes. When the platinum-containing material is supported on a carrier, the amount of the platinum-containing material supported is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and preferably 50% by mass or less, based on the total mass of the platinum-containing material and the carrier.

[0058] <Present Aggregate> The electrolyte membrane contains the present aggregate. The present aggregate is an aggregate containing cerium oxide particles having an average particle size of 0.1 to 10 μm. The aggregate containing cerium oxide particles preferably contains cerium oxide as a main component. The content of the cerium oxide particles in the present aggregate is preferably 80 mass % or more, more preferably 90 mass %, and even more preferably 95 mass % or more, relative to the total mass of the present aggregate, and may even be 100 mass %. In other words, the present aggregate may be an aggregate of cerium oxide particles. The cerium oxide is CeO ２ (Cerium (IV) oxide) or Ce ２ O ３ (cerium (III) oxide), and from the viewpoint of stability, CeO ２ Cerium oxide may be doped with polyvalent metal ions such as zirconium and praseodymium.

[0059] The average particle diameter (D50) of the present agglomerates is 0.1 μm or more, more preferably 0.6 μm or more, even more preferably 1 μm or more, and particularly preferably more than 3 μm. It is also 10 μm or less, more preferably 8 μm or less, even more preferably 6 μm or less, and particularly preferably 5 μm or less. When the D50 of the present agglomerates is within the above range, an increase in electrolysis voltage or the occurrence of pinholes after a certain period of water electrolysis can be further suppressed. The average particle diameter of the present agglomerates is measured by measuring the particle diameters of 20 arbitrarily selected different agglomerates in a cross-sectional image of the electrolyte membrane taken using SEM, SEM-EDX, or TEM, and the arithmetic mean value of the cumulative 50% diameters on a volume basis is taken as D50.

[0060] The average particle size of the present aggregates can be adjusted, for example, by adjusting the kneading conditions in the production method of the electrolyte membrane described below.

[0061] Electrolyte membrane 1cm ２ The mass of this aggregate per cm is 0.010 mg / cm ２ More than 0.029 mg / cm ２ More preferably, 0.043 mg / cm or more ２ More preferably, 0.088 mg / cm ２ More than 0.132 mg / cm is particularly preferred. ２ More than 1.000 mg / cm is most preferred. ２ Preferably, 0.500 mg / cm or less ２ More preferably, 0.300 mg / cm or less ２ It is more preferable that the mass of the aggregate is 0.010 mg / cm or less. ２ If the mass of the agglomerates is 0.300 mg / cm or more, the electrolyte membrane will have a whitish color, making it easier to find foreign matter present in the electrolyte membrane. As a result, when the electrolyte membrane is used in a water electrolysis device, the part of the electrolyte membrane where the foreign matter is present can be avoided, thereby suppressing the occurrence of pinholes in the electrolyte membrane due to the foreign matter. ２ If the above ratio is less than 1, the electrolysis voltage can be reduced, and a low-cost membrane electrode assembly and water electrolysis device can be provided.

[0062] <Woven Fabric> The electrolyte membrane includes a woven fabric composed of warp yarns and weft yarns (hereinafter, the warp yarns and weft yarns are collectively referred to as "yarns"). The woven fabric serves to improve the dimensional stability, strength, and handleability of the electrolyte membrane. The aperture ratio of the woven fabric is preferably 50% or more, more preferably 55% or more, even more preferably 60% or more, and particularly preferably 70% or more, from the viewpoint of further reducing the electrolysis voltage. Furthermore, from the viewpoint of further improving the strength of the membrane electrode assembly, it is preferably 90% or less, more preferably 80% or less. The aperture ratio of the woven fabric is calculated using the following formula (ε) based on the average diameter R1 of the yarns constituting the woven fabric and the average spacing P1 between adjacent yarns (hereinafter, also referred to as "pitch P1") among the yarns constituting the woven fabric. Here, the average yarn diameter R1 refers to the arithmetic mean value of the diameters of 10 different yarns arbitrarily selected based on a magnified image (e.g., 100x magnification) of the woven fabric surface obtained using a microscope. The pitch P1 refers to the arithmetic mean value of 10 different intervals arbitrarily selected based on a magnified image (for example, 100x) of the woven fabric surface obtained using a microscope. Opening ratio of woven fabric (%) = [P1 / (P1+R1)] ２ × 100 (ε)

[0063] The denier number of the yarn constituting the woven fabric is 2 or more, and from the viewpoint of obtaining better strength and dimensional stability of the membrane electrode assembly, it is preferably 10 or more, more preferably 15 or more, and from the viewpoint of further reducing the electrolysis voltage, it is preferably 60 or less, more preferably 50 or less, and even more preferably 20 or less. The denier number is the value expressed in grams of the mass of 9,000 m of yarn (g / 9000 m).

[0064] The density of the threads constituting the woven fabric is preferably 50 threads / inch or more, more preferably 70 threads / inch or more, and even more preferably 90 threads / inch or more, from the viewpoint of excellent strength and dimensional stability of the membrane electrode assembly, and is preferably 200 threads / inch or less, more preferably 150 threads / inch or less, and even more preferably 100 threads / inch or less, from the viewpoint of further reducing the electrolysis voltage.

[0065] The yarn constituting the woven fabric may be either a monofilament consisting of one filament or a multifilament consisting of two or more filaments, with monofilament being preferred.

[0066] The yarns constituting the woven fabric are preferably made of a material selected from the group consisting of polytetrafluoroethylene (hereinafter also referred to as "PTFE"), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (hereinafter also referred to as "PFA"), polyether ether ketone (hereinafter also referred to as "PEEK"), and polyphenylene sulfide (hereinafter also referred to as "PPS"), in view of superior durability of the yarns. The yarns constituting the woven fabric are preferably made of slit yarns in view of superior durability and strength of the yarns.

[0067] When the material constituting the woven fabric is PTFE, the weight of the woven fabric is 20 g / m from the viewpoint of an excellent balance between the strength and the handling property of the electrolyte membrane. ２ More than 30 g / m ２ More preferably, 40 g / m ２ When the material constituting the woven fabric is PFA, the weight per unit area of ​​the woven fabric is preferably 10 g / m or less, in view of an excellent balance between the strength and the handling properties of the electrolyte membrane. ２ More than 30 g / m ２ Preferably, 20 g / m or less ２ When the material constituting the woven fabric is PEEK, the weight of the woven fabric is preferably 5 g / m2 or less, in view of an excellent balance between the strength and the handling properties of the electrolyte membrane. ２ More than 40 g / m ２ Preferably, 30 g / m or less ２ When the material constituting the woven fabric is PPS, the weight per unit area of ​​the woven fabric is preferably 5 g / m or less, in view of an excellent balance between the strength and the handling properties of the electrolyte membrane. ２ More than 40 g / m ２ Preferably, 30 g / m or less ２ The following is more preferred:

[0068] The content of the woven fabric is preferably 3 mass % or more, more preferably 5 mass % or more, and is preferably 50 mass % or less, more preferably 40 mass % or less, and even more preferably 30 mass % or less, based on the total mass of the electrolyte membrane.

[0069] <Method for Producing Electrolyte Membrane> An example of a method for producing an electrolyte membrane is the following method. First, a mixture containing a polymer (hereinafter also referred to as "fluoropolymer (I')") of a fluorine-containing monomer having a group convertible to an ion-exchange group (hereinafter also referred to as "fluorine-containing monomer (I')"), a platinum-containing substance, and the present agglomerate is used to obtain a membrane P1 containing the fluorine-containing polymer (I'), the platinum-containing substance, and the present agglomerate. Next, the membrane P1, the woven fabric, and the membrane P1 are arranged in this order, and these are laminated using a laminating roll or a vacuum laminating device to obtain a precursor membrane, and then the groups convertible to ion-exchange groups in the precursor membrane are converted to ion-exchange groups to obtain an electrolyte membrane containing the fluorine-containing polymer (I), the platinum-containing substance, the present agglomerate, and the woven fabric. The mixture is preferably kneaded in advance using a stirrer. Examples of the stirrer include known stirrers such as a twin-screw extruder. The kneading conditions can be appropriately changed depending on the average particle size of the desired present agglomerate. For example, when the present agglomerate A is prepared under certain kneading conditions A using a twin-screw extruder, and the present agglomerate B having a smaller average particle size than the present agglomerate A is to be prepared, the present agglomerate B can be obtained by carrying out the kneading under conditions B in which the discharge rate under the kneading conditions A is reduced while the screw rotation speed is increased.

[0070] Another example of the method for producing an electrolyte membrane is the following method. First, groups convertible to ion-exchange groups in the fluoropolymer (I') are converted into ion-exchange groups to obtain the fluoropolymer (I). Next, a dispersion of the fluoropolymer (I), a platinum-containing substance, and the present agglomerate is dispersed, and the resulting woven fabric is impregnated with the dispersion, followed by drying to obtain an electrolyte membrane containing the fluoropolymer (I), the platinum-containing substance, the present agglomerate, and the woven fabric.

[0071] By these methods, an electrolyte membrane having a single layer structure (corresponding to the first electrolyte layer described above) can be obtained.

[0072] An example of a method for producing a multilayer electrolyte membrane is the following method. First, a membrane (precursor membrane) containing a fluoropolymer (I') and a woven fabric is produced. Next, groups in the precursor membrane that can be converted to ion-exchange groups are converted to ion-exchange groups to obtain an electrolyte membrane A containing a fluoropolymer (I) and a woven fabric. Alternatively, an electrolyte membrane B is obtained by a casting method using a dispersion in which a fluoropolymer (I), a platinum-containing substance, and the present agglomerate are dispersed. Next, the electrolyte membrane A and the electrolyte membrane B are arranged in this order, and laminated using a lamination roll or a vacuum lamination device to obtain an electrolyte membrane containing a fluoropolymer (I), a platinum-containing substance, the present agglomerate, and a woven fabric. This method provides an electrolyte membrane with a multilayer structure. In the multilayer electrolyte membrane obtained in this way, the platinum-containing substance and the present agglomerate are unevenly distributed on one surface side of the electrolyte membrane.

[0073] Another example of a method for producing a multilayer electrolyte membrane is a method in which a first electrolyte layer containing the fluoropolymer (I), the platinum-containing material, and the present aggregate is laminated with an electrolyte layer (corresponding to the second electrolyte layer described above) that does not contain the platinum-containing material or has a lower concentration of the platinum-containing material than the first electrolyte layer, and then hot-pressed. The woven fabric may be contained in at least one of the first electrolyte layer and the second electrolyte layer. This results in a multilayer electrolyte membrane. In the multilayer electrolyte membrane obtained in this manner, the platinum-containing material is unevenly distributed on one surface side of the electrolyte membrane.

[0074] The fluoropolymer (I') is preferably a polymer (hereinafter also referred to as "fluoropolymer (S')") of a fluoromonomer having a group that can be converted into a sulfonic acid type functional group (hereinafter also referred to as "fluoromonomer (S')"), and more preferably a copolymer of a fluorine-containing olefin and a monomer having a group that can be converted into a sulfonic acid type functional group and a fluorine atom. The fluoropolymer (S') will be described in detail below.

[0075] As the method for copolymerizing the fluoropolymer (S'), known methods such as solution polymerization, suspension polymerization and emulsion polymerization can be used.

[0076] Examples of the fluorine-containing olefin include those exemplified above, and TFE is preferred from the viewpoints of the production cost of the monomer, the reactivity with other monomers, and the excellent properties of the resulting fluorine-containing polymer (S). One type of fluorine-containing olefin may be used alone, or two or more types may be used in combination.

[0077] The fluorine-containing monomer (S') may be a compound having one or more fluorine atoms in the molecule, an ethylenic double bond, and a group that can be converted into a sulfonic acid functional group. As the fluorine-containing monomer (S'), a compound represented by formula (2) is preferred in terms of the production cost of the monomer, reactivity with other monomers, and excellent properties of the resulting fluorine-containing polymer (S). Formula (2) CF ２ =CF-L-(A) ｎ The definitions of L and n in formula (2) are as described above. A is a group that can be converted into a sulfonic acid functional group. The group that can be converted into a sulfonic acid functional group is preferably a functional group that can be converted into a sulfonic acid functional group by hydrolysis. Specific examples of groups that can be converted into a sulfonic acid functional group include -SO ２ F, -SO ２ Cl and -SO ２ Br. The n A's may be the same or different.

[0078] The compound represented by formula (2) is preferably a compound represented by formula (2-1), a compound represented by formula (2-2), a compound represented by formula (2-3), or a compound represented by formula (2-4). ２ =CF-O-R ｆ１ -A Formula (2-2) CF ２ =CF-R ｆ１ -A

[0079]

[0080] R in the formula ｆ１ , R ｆ２ , r and A are as defined above.

[0081]

[0082] R in the formula ｆ１, R ｆ２ , R ｆ３ , r, m and A are as defined above.

[0083] The compound represented by formula (2-1) and the compound represented by formula (2-1) are preferably compounds represented by formula (2-5): Formula (2-5) CF ２ =CF-(CF ２ ) ｘ -(OCF ２ CFY) ｙ -O-(CF ２ ) ｚ -SO ３ The definitions of x, y, z and Y in the formula F are as described above.

[0084] Specific examples of the compound represented by formula (2-1) include the following compounds. In the formula, w is an integer of 1 to 8, and x is an integer of 1 to 5. CF ２ =CF-O-(CF ２ ) ｗ -SO ２ FCF ２ =CF-O-CF ２ CF (CF ３ )-O-(CF ２ ) ｗ -SO ２ FCF ２ =CF-[O-CF ２ CF (CF ３ )] ｘ -SO ２ F

[0085] Specific examples of the compound represented by formula (2-2) include the following compounds: In the formula, w is an integer of 1 to 8. CF ２ =CF-(CF ２ ) ｗ -SO ２ FCF ２ =CF-CF ２ -O-(CF ２ ) ｗ -SO ２ F

[0086] The compound represented by formula (2-3) is preferably a compound represented by formula (2-3-1).

[0087]

[0088] R in the formula ｆ４ , R ｆ５ , r and A are as defined above.

[0089] Specific examples of the compound represented by formula (2-3-1) include the following.

[0090]

[0091] The compound represented by formula (2-4) is preferably a compound represented by formula (2-4-1).

[0092]

[0093] R in the formula ｆ１ , R ｆ２ and A are defined as above.

[0094] Specific examples of the compound represented by formula (2-4-1) include the following.

[0095]

[0096] The fluorine-containing monomer (S') may be used alone or in combination of two or more. In the production of the fluorine-containing polymer (S'), in addition to the fluorine-containing olefin and the fluorine-containing monomer (S'), other monomers may be further used. Examples of other monomers include those exemplified above.

[0097] The ion exchange capacity of the fluoropolymer (I') can be adjusted by changing the content of groups that can be converted into ion exchange groups in the fluoropolymer (I').

[0098] Specific examples of methods for converting groups in the precursor membrane that can be converted to ion-exchange groups into ion-exchange groups include methods of subjecting the precursor membrane to hydrolysis treatment, acidification treatment, etc. Among these, a method of contacting the precursor membrane with an alkaline aqueous solution is preferred.

[0099] Specific examples of the method for contacting the precursor film with the alkaline aqueous solution include immersing the precursor film in the alkaline aqueous solution and spraying the alkaline aqueous solution onto the surface of the precursor film. The temperature of the alkaline aqueous solution is preferably 30° C. or higher, more preferably 40° C. or higher, and preferably 100° C. or lower. The contact time between the precursor film and the alkaline aqueous solution is preferably 3 minutes or longer, more preferably 5 minutes or longer, and preferably 150 minutes or shorter, more preferably 50 minutes or shorter.

[0100] The alkaline aqueous solution preferably contains an alkali metal hydroxide, a water-soluble organic solvent, and water. Examples of alkali metal hydroxides include sodium hydroxide and potassium hydroxide. In this specification, the water-soluble organic solvent refers to an organic solvent that is easily soluble in water. Specifically, an organic solvent having a solubility of 0.1 g or more in 1000 mL of water (20°C) is preferred, and an organic solvent having a solubility of 0.5 g or more is more preferred. The water-soluble organic solvent preferably contains at least one selected from the group consisting of aprotic organic solvents, alcohols, and aminoalcohols, and more preferably contains an aprotic organic solvent. One water-soluble organic solvent may be used alone, or two or more water-soluble organic solvents may be used in combination.

[0101] Specific examples of aprotic organic solvents include dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone, with dimethyl sulfoxide being preferred. Specific examples of alcohols include methanol, ethanol, isopropanol, butanol, methoxyethoxyethanol, butoxyethanol, butylcarbitol, hexyloxyethanol, octanol, 1-methoxy-2-propanol, and ethylene glycol. Specific examples of aminoalcohols include ethanolamine, N-methylethanolamine, N-ethylethanolamine, 1-amino-2-propanol, 1-amino-3-propanol, 2-aminoethoxyethanol, 2-aminothioethoxyethanol, and 2-amino-2-methyl-1-propanol.

[0102] The concentration of the alkali metal hydroxide in the alkaline aqueous solution is preferably 1% by mass or more, more preferably 3% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less. The content of the water-soluble organic solvent in the alkaline aqueous solution is preferably 1% by mass or more, more preferably 3% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less. The concentration of water in the alkaline aqueous solution is preferably 39 to 80% by mass.

[0103] After the precursor film is brought into contact with the alkaline aqueous solution, a treatment for removing the alkaline aqueous solution may be carried out. As a method for removing the alkaline aqueous solution, for example, a method for washing the precursor film that has been brought into contact with the alkaline aqueous solution with water may be mentioned.

[0104] After contacting the precursor film with the alkaline aqueous solution, the resulting film may be contacted with an acidic aqueous solution to convert the ion exchange groups to an acid form. Specific examples of methods for contacting the precursor film with the acidic aqueous solution include immersing the precursor film in the acidic aqueous solution and spraying the acidic aqueous solution onto the surface of the precursor film. The acidic aqueous solution preferably contains an acid component and water. Specific examples of the acid component include hydrochloric acid and sulfuric acid.

[0105] [Membrane Electrode Assembly] The membrane electrode assembly of the present disclosure may include the electrolyte membrane described above. The membrane electrode assembly preferably includes the electrolyte membrane, a cathode catalyst layer disposed on one side of the electrolyte membrane, and an anode catalyst layer disposed on the other side of the electrolyte membrane.

[0106] 2 is a cross-sectional view schematically illustrating an example of a membrane electrode assembly according to the present disclosure. In the example of Fig. 2, the membrane electrode assembly 20 includes an anode 22 having a catalyst layer 26 and a gas diffusion layer 28, a cathode 24 having the catalyst layer 26 and the gas diffusion layer 28, and an electrolyte membrane 10 disposed between the anode 22 and the cathode 24 in contact with the catalyst layer 26.

[0107] Although the example of FIG. 2 shows a case where the electrolyte membrane has a single layer structure, the electrolyte membrane may have a multilayer structure. Specific examples and preferred embodiments of the multilayer electrolyte membrane are as described above. FIG. 3 is a cross-sectional view schematically illustrating an example of a membrane electrode assembly according to the present disclosure, illustrating a case where the electrolyte membrane has a multilayer structure. The structure of the membrane electrode assembly 120 of FIG. 3 is similar to the structure of the membrane electrode assembly 20 of FIG. 2 except that the electrolyte membrane 10 of FIG. 2 has an electrolyte membrane 100 instead of the electrolyte membrane 10. The electrolyte membrane 100 of FIG. 3 includes a first electrolyte layer 100A and a second electrolyte layer 100B arranged in this order from the anode 22 side to the cathode 24 side. The first electrolyte layer 100A includes a fluoropolymer (I), a platinum-containing material, and the present aggregate. The second electrolyte layer 100B includes the fluoropolymer (I) and the present aggregate. Note that the second electrolyte layer 100B has a lower concentration of the platinum-containing material than the first electrolyte layer, or does not include the platinum-containing material. At least one of the first electrolyte layer 100A and the second electrolyte layer 100B includes a woven fabric.

[0108] In the example of FIG. 3, the electrolyte membrane has a two-layer structure, but the electrolyte membrane may have a three-layer or more structure.

[0109] In the example of Figure 3, an example is shown in which only the platinum-containing material is unevenly distributed on one surface side of the electrolyte membrane, but the electrolyte membrane included in the membrane electrode assembly of the present disclosure may have both the platinum-containing material and the present aggregate unevenly distributed on one surface side.

[0110] <Anode and Cathode> The anode and cathode each have a catalyst layer. In the example of Figure 2, the anode 22 and cathode 24 each have a catalyst layer 26 and a gas diffusion layer 28.

[0111] Specific examples of the catalyst layer include a layer containing a catalyst and a polymer having an ion exchange group.Specific examples of the catalyst include a supported catalyst in which a carbon support supports a catalyst containing platinum, a platinum alloy, or a platinum having a core-shell structure, an iridium oxide catalyst, a composite oxide catalyst containing iridium and other metal elements, an alloy containing iridium oxide, and a catalyst containing iridium oxide having a core-shell structure.An example of the carbon support is carbon black powder.An example of the polymer having an ion exchange group is a fluorine-containing polymer having an ion exchange group, and for example, the above-mentioned fluorine-containing polymer (I) can be used.

[0112] Catalyst layer 1cm ２ The mass of the catalytic metal per ２ More than 0.2 mg / cm is preferred. ２ More preferably, 4 mg / cm ２ Preferably, less than 2 mg / cm ２ More preferably, 1 mg / cm or less ２ The following is more preferred: The mass ratio of the catalyst to the polymer having an ion-exchange group in the catalyst layer (mass of catalyst / mass of polymer having an ion-exchange group) is preferably 2 to 6.

[0113] The gas diffusion layer functions to rapidly diffuse gas generated from the catalyst layer out of the catalyst layer and as a current collector. Specific examples of gas diffusion layers include carbon paper, carbon cloth, carbon felt, sintered titanium oxide fiber, and sintered titanium oxide particle. The anode side has a high potential, and using carbon materials would result in oxidation. Therefore, it is preferable to use sintered titanium oxide fiber or sintered titanium oxide particle. The sintered titanium oxide may be plated with platinum or the like as needed. The cathode gas diffusion layer may be treated with PTFE or the like to be water-repellent. While the membrane electrode assembly in FIG. 2 includes a gas diffusion layer 28, the gas diffusion layer is an optional component and need not be included in the membrane electrode assembly.

[0114] The thickness of the anode and cathode is preferably 5 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 30 μm or less, and particularly preferably 15 μm or less. The thickness of the anode and cathode is measured using an image obtained by measuring a cross section cut in the thickness direction of the membrane electrode assembly with a laser microscope, and is the arithmetic average value of thicknesses at any 20 points.

[0115] <Method for Manufacturing Membrane Electrode Assembly> A method for manufacturing a membrane electrode assembly involves forming a cathode catalyst layer on one side of an electrolyte membrane and forming an anode catalyst layer on the other side of the electrolyte membrane. One example of a method for manufacturing a membrane electrode assembly involves using a laminate having an anode catalyst layer and a releasable substrate (e.g., an ETFE (ethylene-tetrafluoroethylene) sheet) and a laminate having a cathode catalyst layer and a releasable substrate (e.g., an ETFE sheet), bonding catalyst layers to both sides of the electrolyte membrane, and then peeling off the releasable substrate. The laminate may have a gas diffusion layer between the catalyst layer and the releasable substrate. In this case, the gas diffusion layer can be formed on the side of the catalyst layer opposite the electrolyte membrane. A method for manufacturing a catalyst layer includes applying a catalyst layer-forming coating liquid to a predetermined position (e.g., the surface of the releasable substrate) and drying it as necessary. The catalyst layer-forming coating liquid is a liquid in which a polymer having ion exchange groups and a catalyst are dispersed in a dispersion medium.

[0116] <Applications> The membrane electrode assembly of the present disclosure is suitably used in a solid polymer water electrolysis device.

[0117] [Water Electrolysis Apparatus and Hydrogen Production Method] The water electrolysis apparatus of the present disclosure may include the membrane electrode assembly described above. The water electrolysis apparatus preferably includes the membrane electrode assembly described above, a water supply unit that supplies water to the anode catalyst layer side, and a power supply unit electrically connected to the anode catalyst layer side and the cathode catalyst layer side. In the water electrolysis apparatus of the present disclosure, when a DC voltage is applied by the power supply unit while water is supplied to the anode catalyst layer side by the water supply unit, water is decomposed on the anode catalyst layer side to generate oxygen and protons. Furthermore, on the cathode catalyst layer side, protons that have migrated to the cathode catalyst layer side through the electrolyte membrane acquire electrons to generate hydrogen. The water electrolysis apparatus of the present disclosure may have the same configuration as a known water electrolysis apparatus (e.g., an oxygen recovery member that recovers generated oxygen, a hydrogen recovery member that recovers generated hydrogen), except for the components described above. Furthermore, the hydrogen production method of the present disclosure produces hydrogen by electrolyzing water (electrolyte) using the water electrolysis apparatus of the present disclosure. The hydrogen production method of the present disclosure uses the water electrolysis apparatus of the present disclosure, allowing efficient hydrogen production.

[0118] The present invention will be described in detail below with reference to examples. Examples 1 to 7, 10, and 11 are working examples, and Examples 8 and 9 are comparative examples. However, the present invention is not limited to these examples.

[0119] [Ion exchange capacity of fluoropolymer] The fluoropolymer was placed in a glove box filled with dry nitrogen for 24 hours, and the dry mass of the fluoropolymer was measured. Thereafter, the fluoropolymer was immersed in a 2 mol / L aqueous sodium chloride solution at 60°C for 1 hour. The fluoropolymer was washed with ultrapure water and then removed. The solution in which the fluoropolymer had been immersed was titrated with a 0.1 mol / L aqueous sodium hydroxide solution to determine the ion exchange capacity (milli-equivalent / gram dry resin) of the fluoropolymer.

[0120] [Thickness of Electrolyte Membrane] The thickness of the electrolyte membrane was measured using a magnified image (objective lens magnification: 50x) of a cross section of the electrolyte membrane photographed using a laser microscope (product name "VK-X1000", manufactured by Keyence Corporation) under conditions of a temperature of 23°C and a relative humidity of 50% RH.

[0121] [Average Particle Diameter of Aggregates] The average particle diameter of aggregates containing cerium oxide particles is the arithmetic mean value D50 of the cumulative 50% diameter on a volume basis, obtained by measuring the particle diameters of 20 random aggregates in a cross-sectional image of the electrolyte membrane photographed using SEM-EDX under the following conditions: <Measurement Conditions> Apparatus: SU6600 manufactured by Hitachi High-Technologies Corporation and Noran System 6 manufactured by Thermo Electronics, Inc. Acceleration voltage: 10 kV Working distance: ≈ 15 mm Probe current: medium

[0122] [Electrolysis Voltage Increase] The membrane electrode assembly was heat-treated at 150°C for 15 minutes and then set in a water electrolysis evaluation jig EH50-25 (manufactured by Greenlight Innovation). Next, to first fully hydrate the solid polymer electrolyte membrane and both electrode ionomers, pure water with a conductivity of 1.0 μS / cm or less, a temperature of 80°C, and atmospheric pressure was supplied to the anode and cathode sides at a flow rate of 50 mL / min for 12 hours. The cathode side was then purged with nitrogen. After the nitrogen purging, pure water with a conductivity of 1.0 μS / cm or less, a temperature of 80°C, and atmospheric pressure was supplied to the anode side at a flow rate of 50 mL / min. While the generated gas pressure on the cathode side was kept at atmospheric pressure, a current density of 2 A / cm was applied using a DC power supply PWR1600L manufactured by Kikusui Electronics Co., Ltd. ２ The test piece was operated for 500 hours at 400°C, and the voltage difference (voltage rise) between immediately after the start of operation and after 500 hours was evaluated. A, B, C, or D was preferable. A: When the voltage difference was less than 20 mV B: When the voltage difference was 20 mV or more and less than 30 mV C: When the voltage difference was 30 mV or more and less than 40 mV D: When the voltage difference was 40 mV or more and less than 50 mV E: When the voltage difference was 50 mV or more

[0123] [Pinholes] The membrane electrode assembly was heat-treated at 150°C for 15 minutes and then set in a water electrolysis evaluation jig EH50-25 (manufactured by Greenlight Innovation). Next, to first fully hydrate the solid polymer electrolyte membrane and both electrode ionomers, pure water with a conductivity of 1.0 μS / cm or less, a temperature of 80°C, and atmospheric pressure was supplied to the anode and cathode sides at a flow rate of 50 mL / min for 12 hours. The cathode side was then purged with nitrogen. After the nitrogen purging, pure water with a conductivity of 1.0 μS / cm or less, a temperature of 80°C, and atmospheric pressure was supplied to the anode side at a flow rate of 50 mL / min. While the generated gas pressure on the cathode side was set to 0.9 MPa, a current density of 2 A / cm was generated using a DC power supply PWR1600L manufactured by Kikusui Electronics Co., Ltd. ２ The fuel cell was operated for 1,000 hours at 1000 K. After operation, the number of pinholes (holes) in the electrolyte membrane of the membrane electrode assembly was counted using a pinhole inspection device (product name "TRS-70", manufactured by Sanko Electronics Laboratory Co., Ltd.). A rating of A or B is preferable. A: No pinholes were found. B: There were 1 to 2 pinholes. C: There were 3 or more pinholes.

[0124] [Example 1] First, CF ２ =CF ２ and a monomer (X) represented by the following formula (X) were copolymerized to obtain a fluoropolymer (I'-1) (ion exchange capacity: 1.25 meq / g dry resin). The ion exchange capacity in parentheses represents the ion exchange capacity of the fluoropolymer obtained when the fluoropolymer (I'-1) is hydrolyzed by the procedure described below. CF ２ =CF-O-CF ２ CF (CF ３ )-O-CF ２ CF ２ -SO ２ F...(X)

[0125] Next, a twin-screw extruder (manufactured by The Japan Steel Works, Ltd.) was used to extrude fluorine-containing polymer (I'-1), platinum black (Tanaka Kikinzoku K.K. "TEC90300", platinum-containing material), and cerium oxide (Fujifilm Wako Pure Chemical Industries, Ltd., primary particle size: less than 10 nm, CeO ２)) were kneaded to obtain a kneaded material. The kneading conditions were such that the discharge rate and screw rotation speed were adjusted so that the aggregates containing cerium oxide particles had the desired average particle size. For example, increasing the screw rotation speed while decreasing the discharge rate resulted in a smaller average particle size of the resulting aggregates. The kneaded material obtained in the heat mixing section of the twin-screw extruder was melted and extruded through a T-die, and the melt was adhered to a substrate made of a linear low-density polyethylene (LLDPE) film (melting point: 110 to 120°C), to obtain a film-attached substrate Y1 in which a film α1 (film thickness: 45 μm) was formed on the substrate.

[0126] In addition, 18.6 denier PFA yarns were used as the warp and weft yarns, and plain weaving was performed so that the density of the PFA yarns was 100 threads / inch to obtain a woven fabric A1. The weight of the woven fabric A1 was 16.3 g / m ２ The warp and weft were made of slit yarns.

[0127] The film-attached substrate Y1 / woven fabric A1 / film-attached substrate Y1 were stacked in this order. The film-attached substrate Y1 was positioned so that the film α1 of the film-attached substrate Y1 was in contact with the woven fabric A1. The stacked members were then subjected to a temperature of 160°C and a surface pressure of 30 MPa / m ２ After 10 minutes of heat and pressure bonding using a flat plate press, the substrates on both sides were peeled off at a temperature of 50 ° C. to obtain a precursor membrane. The precursor membrane was immersed in a solution of dimethyl sulfoxide / potassium hydroxide / water = 30.0 / 5.5 / 64.5 (mass ratio) at 95 ° C. for 30 minutes, and the groups convertible to sulfonic acid functional groups in the precursor membrane were hydrolyzed to K-type sulfonic acid functional groups, and then washed with water. The obtained membrane was then immersed in 1 M sulfuric acid, the terminal groups were converted from K-type to H-type, and then dried to obtain an electrolyte membrane 1 (thickness 90 μm) of Example 1.

[0128] CF ２ =CF ２and the above-mentioned monomer (X), and then hydrolyzed and acid-treated to obtain an acid-form fluoropolymer (ion exchange capacity: 1.10 meq / g dry resin). This fluoropolymer was dispersed in a water / ethanol solvent of 40 / 60 (mass%) at a solids concentration of 26.0 mass% to obtain a dispersion (hereinafter also referred to as "dispersion Y"). To the obtained dispersion Y (33.0 g), ethanol (18.06 g) and Zeorola-H (manufactured by Nippon Zeon, 10.58 g) were added, and the mixture was mixed for 5 minutes at 2200 rpm in a planetary centrifugal mixer (Thinky, Awatori Rentaro). To the mixed composition (54.06 g), ethanol (46.44 g) and water (75.75 g) were added, and a mixture of 74.8 mass% iridium and a specific surface area of ​​100 m was obtained. ２ 40.0 g of an iridium oxide catalyst (manufactured by Tanaka Kikinzoku Co., Ltd.) was added to the mixture. The resulting mixture was processed in a planetary bead mill (rotational speed: 300 rpm) for 90 minutes to obtain an anode catalyst ink with a solids concentration of 22 mass %. The anode catalyst ink was applied to an ETFE sheet so that the iridium concentration was 1.0 mg / cm. ２ The anode catalyst layer decal was obtained by applying the coating with an applicator so that the coating became smooth, followed by drying at 80° C. for 10 minutes and then heat treating at 150° C. for 15 minutes.

[0129] Water (59.4 g) and ethanol (39.6 g) were added to 11 g of a supported catalyst ("TEC10E50E" manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) in which 46% by mass of platinum was supported on carbon powder, and the mixture was mixed and pulverized using an ultrasonic homogenizer to obtain a catalyst dispersion. To the catalyst dispersion, a mixture (29.2 g) of dispersion Y (20.1 g), ethanol (11 g), and Zeorola-H (manufactured by Zeon Corporation) (6.3 g) was premixed and kneaded. Furthermore, water (3.66 g) and ethanol (7.63 g) were added to the resulting dispersion and mixed for 60 minutes using a paint conditioner to obtain a cathode catalyst ink with a solids concentration of 10.0% by mass. The cathode catalyst ink was applied to an ETFE sheet using a die coater, dried at 80°C, and further heat-treated at 150°C for 15 minutes, resulting in a platinum content of 0.4 mg / cm. ２ As a result, a cathode catalyst layer decal of 1000 nm was obtained.

[0130] The surface of the anode catalyst layer decal on which the catalyst layer is present was placed opposite one surface of the electrolyte membrane 1, and the surface of the cathode catalyst layer decal on which the catalyst layer is present was placed opposite the other surface of the electrolyte membrane 1. The anode catalyst layer, the electrolyte membrane 1, and the cathode catalyst layer were bonded together by hot pressing under conditions of a pressing temperature of 150°C and a pressure of 3 MPa for 10 minutes. After the temperature was lowered to 70°C, the pressure was released and the assembly was removed. The ETFE sheets of the anode catalyst layer decal and the cathode catalyst layer decal were peeled off, and the electrode area was reduced to 16 cm. ２ A membrane electrode assembly of 1000 sq. m was obtained. The obtained membrane electrode assembly was subjected to the above-mentioned respective evaluations. The results are shown in Table 1. When foreign matter was found when visually inspecting the electrolyte membrane 1, the foreign matter was removed from the electrolyte membrane 1 before fabricating the membrane electrode assembly. The same applies to the following examples.

[0131] [Examples 2 to 11] Each membrane electrode assembly was produced in the same procedure as in Example 1, except that the conditions were changed as shown in Table 1 and the kneading conditions were adjusted as follows. For example, the kneading conditions in Example 2 were a higher discharge rate than in Example 1 and a lower screw rotation speed. The kneading conditions in Example 3 were a higher discharge rate than in Example 2 and a lower screw rotation speed. The kneading conditions in Example 8 were a lower discharge rate than in Example 1 and an increased screw rotation speed. The kneading conditions in Example 9 were a higher discharge rate than in Example 5 and a lower screw rotation speed. In the other examples, the kneading conditions were similarly changed so that the aggregates containing cerium oxide particles had the average particle size shown in Table 1.

[0132] In the table, IEC (meq / g) indicates the ion exchange capacity (milliequivalents / gram of dry resin) of the fluoropolymer (I). ２ ) is 1 cm of electrolyte membrane ２ The mass of the platinum-containing particles per 1000 sieve is shown. The average particle size (μm) of the agglomerates indicates the average particle size of the agglomerates containing cerium oxide particles. The mass of the agglomerates (mg / cm ２ ) is 1 cm of electrolyte membrane ２ The mass of the agglomerate containing cerium oxide particles per 1000 sieve is shown.

[0133] The membrane electrode assemblies obtained in each example were used to evaluate the increase in electrolysis voltage and the occurrence of pinholes as described above. The results are shown in Table 1. Note that for examples that received an evaluation result of A in the pinhole evaluation described above (i.e., examples in which pinholes did not occur), an evaluation was performed in which the gas pressure generated on the cathode side was changed to 2 MPa, and it was confirmed that pinholes did not occur in this evaluation either.

[0134]

[0135] As shown in Table 1, it was confirmed that the electrolyte membrane of the present disclosure can suppress the increase in electrolysis voltage after water electrolysis for a certain period of time, and is less likely to develop pinholes.

[0136] The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2023-221212, filed on December 27, 2023, are hereby incorporated by reference as the disclosure of the specification of the present invention.

[0137] 1, 10, 100 Electrolyte membrane 20, 120 Membrane electrode assembly 22 Anode 24 Cathode 26 Catalyst layer 28 Gas diffusion layer 100A First electrolyte layer 100B Second electrolyte layer A1, C1 Surface B1 Depth position T １ , T Ｘ Distance X, Y area

Claims

1. A solid polymer electrolyte membrane comprising a fluorine-containing polymer having an ion-exchange group, a platinum-containing substance, an aggregate containing cerium oxide particles, and a woven fabric, wherein the average particle diameter of the aggregate is 0.1 to 10 μm.

2. The solid polymer electrolyte membrane according to claim 1, wherein the average particle diameter of the aggregate is more than 3 μm.

3. The solid polymer electrolyte membrane according to claim 1, wherein the ion-exchange capacity of the fluorine-containing polymer is 0.90 to 2.00 milliequivalents / gram of dry resin.

4. The mass of the aggregates per 1 cm of the solid polymer electrolyte membrane ２ is 0.010 mg / cm ２ or more. The solid polymer electrolyte membrane according to claim 1.

5. The solid polymer electrolyte membrane according to claim 1, wherein the platinum-containing substance is unevenly distributed on one surface side of the solid polymer electrolyte membrane.

6. The solid polymer electrolyte membrane according to claim 1, wherein the platinum-containing substance is supported on a carrier.

7. The solid polymer electrolyte membrane according to claim 1, wherein the ion-exchange group of the fluorine-containing polymer is a sulfonic acid type functional group.

8. The solid polymer electrolyte membrane according to claim 1, wherein the fluorine-containing polymer contains a unit represented by the formula (1-1). Formula (1-1) -[CF ２ -CF(-O-R ｆ１ -SO ３ M)]- In formula (1-1), R ｆ１ is a perfluoroalkylene group which may contain an oxygen atom between carbon atoms, and M is a hydrogen atom, an alkali metal or a quaternary ammonium cation.

9. The solid polymer electrolyte membrane according to claim 1, wherein the woven fabric is composed of a material selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, polyether ether ketone, and polyphenylene sulfide.

10. A membrane electrode assembly comprising the solid polymer electrolyte membrane according to any one of claims 1 to 9, a cathode catalyst layer disposed on one surface side of the solid polymer electrolyte membrane, and an anode catalyst layer disposed on the other surface side of the solid polymer electrolyte membrane.

11. A water electrolysis device comprising the membrane electrode assembly according to claim 10, a power supply unit connected to the cathode catalyst layer side and the anode catalyst layer side in the membrane electrode assembly, and a water supply unit for supplying water to the anode catalyst layer side.

12. A method for producing hydrogen by electrolyzing water with the water electrolysis device according to claim 11.

13. A method for manufacturing a membrane electrode assembly comprising the solid polymer electrolyte membrane according to any one of claims 1 to 9, a cathode catalyst layer, and an anode catalyst layer, the method comprising forming the cathode catalyst layer on one surface side of the solid polymer electrolyte membrane and forming the anode catalyst layer on the other surface side of the solid polymer electrolyte membrane.

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