Electrolyte membrane laminate, and method for producing electrolyte membrane laminate

Abstract

Provided are an electrolyte membrane laminate and a use therefor, said electrolyte membrane laminate comprising an electrolyte membrane and two or more catalyst layers laminated on the electrolyte membrane, wherein at least one pair of adjacent catalyst layers has an interface present therebetween.

Description

Electrolyte membrane laminate and method for manufacturing the electrolyte membrane laminate

[0001] The present disclosure relates to an electrolyte membrane laminate and a method for manufacturing an electrolyte membrane laminate.

[0002] In recent years, the use of hydrogen has been attracting attention from the viewpoint of utilizing renewable energy, etc. One method for producing hydrogen is solid polymer water electrolysis. In solid polymer water electrolysis, a catalyst-coated membrane (CCM) has recently been used as a component constituting a water electrolysis device. The catalyst-coated membrane (CCM) has an electrode catalyst layer containing a water electrolysis catalyst and a solid electrolyte (e.g., an ionomer resin) formed on both sides of a solid polymer electron membrane (PEM), which is an ion exchange membrane.

[0003] For example, Japanese Patent Application Laid-Open No. 2007-103291 describes a method for producing a membrane / electrode assembly for a direct methanol fuel cell, which comprises the following steps: a first step of applying a slurry containing a carbon material, a catalytic metal, and a cation exchange resin onto a sheet and drying it to produce a first laminate (3) of a catalyst layer and a sheet; a second step of applying a slurry containing a carbon material, a catalytic metal, and a cation exchange resin solution onto a conductive porous body and drying it to produce a second laminate (6) of a catalyst layer and a conductive porous body; a third step of bonding the first laminate (3) to at least one side of a cation exchange membrane so that the catalytic layer of the first laminate (3) contacts the cation exchange membrane, and then peeling off the sheet to produce a membrane / electrode assembly; and a fourth step of bonding the second laminate (6) to the membrane / electrode assembly so that the catalytic layer of the second laminate (6) contacts the catalytic layer of the membrane / electrode assembly. Japanese Patent Laid-Open Publication No. 2006-344426 describes a polymer electrolyte fuel cell in which a membrane electrode assembly, in which a pair of catalyst layers are arranged on both sides of a solid polymer electrolyte membrane, is sandwiched between separators having gas flow paths, and the catalyst layer includes at least an electrode catalyst in which catalyst particles are supported on a carbon support, and a solid polymer electrolyte, and at least one of the catalyst layers is formed by stacking a catalyst layer (1) in contact with the solid polymer electrolyte membrane and having no cracks, and a catalyst layer (2) having cracks, in the thickness direction of the membrane electrode assembly, and in at least one of catalyst layers (1) and (2), the crystallinity of the carbon support increases from the inlet side to the outlet side of the gas flow path.

[0004] In water electrolysis devices and fuel cells, it is necessary to increase the amount of catalyst per unit area in order to improve performance. When the amount of catalyst per unit area is increased, it is necessary to suppress the occurrence of defects in the catalyst layer.

[0005] The problem to be solved by one embodiment of the present disclosure has been made in view of the above circumstances, and is to provide an electrolyte membrane laminate having a larger catalyst amount per unit area and fewer defects (particularly cracks) than conventional ones, and a method for manufacturing the same.

[0006] The present disclosure includes the following aspects. <1> An electrolyte membrane laminate comprising an electrolyte membrane and two or more catalyst layers laminated on the electrolyte membrane, wherein an interface exists between at least one of the adjacent catalyst layers. <2> The electrolyte membrane laminate according to <1>, wherein a mixed layer exists between the electrolyte membrane and the catalyst layer adjacent to the electrolyte membrane. <3> The electrolyte membrane laminate according to <2>, wherein the mixed layer has a thickness of 0.1 μm to 1 μm. <4> The electrolyte membrane laminate according to any one of <1> to <3>, comprising an electrolyte membrane, a first catalyst layer, and a second catalyst layer in this order, wherein the amount of catalyst contained in the first catalyst layer is greater than the amount of catalyst contained in the second catalyst layer. <5> A method for producing an electrolyte membrane laminate, comprising the steps of: preparing a first transfer substrate having a first catalyst layer on a first temporary support; placing the first transfer substrate on an electrolyte membrane so that the electrolyte membrane and the first catalyst layer are in contact with each other, and performing a first thermocompression bonding between the electrolyte membrane and the first transfer substrate; peeling off the first temporary support and forming the first catalyst layer on the electrolyte membrane; preparing a second transfer substrate having a second catalyst layer on a second temporary support; placing the second transfer substrate on the first catalyst layer so that the first catalyst layer and the second catalyst layer are in contact with each other, and performing a second thermocompression bonding between the electrolyte membrane with the first catalyst layer formed on it and the second transfer substrate; and peeling off the second temporary support and forming the second catalyst layer on the first catalyst layer. <6> A method for producing an electrolyte membrane laminate according to <5>, wherein the content of a solvent in the second catalyst layer of the second transfer substrate is 1% by mass to 10% by mass with respect to the total amount of the second catalyst layer. <7> The method for producing an electrolyte membrane laminate according to <5> or <6>, wherein in the step of arranging the second transfer substrate, the second catalyst layer is superposed on the entire surface of the first catalyst layer. <8> The method for producing an electrolyte membrane laminate according to any one of <5> to <7>, further comprising a step of heating the electrolyte membrane and the first transfer substrate before the step of thermocompression bonding the electrolyte membrane and the first transfer substrate. <9> The method for producing an electrolyte membrane laminate according to any one of <5> to <8>, further comprising a step of heating the electrolyte membrane on which the first catalyst layer has been formed and the second transfer substrate before the step of thermocompression bonding the electrolyte membrane on which the first catalyst layer has been formed and the second transfer substrate.<10> A method for producing an electrolyte membrane laminate according to any one of <5> to <9>, comprising the steps of: performing first thermocompression bonding on both surfaces of an electrolyte membrane; forming a first catalyst layer on the electrolyte membrane; performing second thermocompression bonding; and forming a second catalyst layer on the electrolyte membrane. <11> A method for producing an electrolyte membrane laminate according to any one of <5> to <10>, further comprising the step of heating the electrolyte membrane on which the first catalyst layer and the second catalyst layer have been formed, after the step of forming the second catalyst layer on the first catalyst layer.

[0007] According to one embodiment of the present disclosure, an electrolyte membrane laminate having a larger catalyst amount per unit area and fewer defects (particularly cracks) than conventional ones, and a method for manufacturing the same, are provided.

[0008] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples. In the present disclosure, a combination of two or more preferred embodiments or aspects is a more preferred embodiment or aspect.

[0009] [Electrolyte Membrane Stack] The electrolyte membrane stack according to the present disclosure includes an electrolyte membrane and two or more catalyst layers stacked on the electrolyte membrane, and an interface exists between at least one of the adjacent catalyst layers.

[0010] Conventionally, a method for increasing the amount of catalyst per unit area has been used in which a catalyst-containing ink is repeatedly applied to an electrolyte membrane and dried. In an electrolyte membrane laminate obtained by such a method, no interface is formed between the stacked catalyst layers. Meanwhile, cracks tend to occur in the stacked catalyst layers due to drying shrinkage. In contrast, the electrolyte membrane laminate according to the present disclosure includes two or more catalyst layers, thereby increasing the amount of catalyst per unit area compared to conventional methods. Furthermore, the presence of an interface between at least one of the adjacent catalyst layers reduces defects (particularly cracks). Japanese Patent Application Laid-Open Nos. 2007-103291 and 2006-344426 do not mention the interface between adjacent catalyst layers.

[0011] (Electrolyte Membrane) Examples of the electrolyte membrane include a fluorine-based electrolyte membrane and a hydrocarbon-based electrolyte membrane. Specific examples of the electrolyte membrane include perfluorocarbon sulfonic acid polymers such as Nafion (registered trademark), poly(meth)acrylates having phosphoric acid groups in their side chains, heat-resistant aromatic polymers such as sulfonated polyether ether ketones, sulfonated polyether ketones, sulfonated polyether sulfones, sulfonated polysulfones, and sulfonated polybenzimidazoles, sulfonated polystyrenes, sulfonated polyoxetanes, sulfonated polyimides, sulfonated polyphenylene sulfides, sulfonated polyphenylene oxides, and sulfonated polyphenylene membranes.

[0012] The thickness of the electrolyte membrane is preferably 30 μm to 250 μm, and more preferably 50 μm to 200 μm, and is measured by the method described in JIS K 7130:1999.

[0013] (Catalyst Layer) The catalyst layer is a layer containing a catalyst. The catalyst layer preferably contains a catalyst and a binder.

[0014] Examples of the catalyst include metals such as platinum, gold, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum, and alloys thereof. From the viewpoints of catalytic activity and durability, the catalyst preferably contains platinum.

[0015] The catalyst is preferably supported on a carbon material, such as carbon black, activated carbon, coke, natural graphite, and artificial graphite, and more specifically, ketjen black, vulcan black, acetylene black, carbon fiber, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphitized ketjen black, graphitized vulcan black, and graphitized acetylene black.

[0016] The binder is preferably a polymer having a proton-donating group. Examples of the binder include perfluorocarbon sulfonic acid polymers such as Nafion (registered trademark), poly(meth)acrylates having phosphoric acid groups in their side chains, heat-resistant aromatic polymers such as sulfonated polyether ether ketones, sulfonated polyether ketones, sulfonated polyether sulfones, sulfonated polysulfones, and sulfonated polybenzimidazoles; sulfonated polystyrenes, sulfonated polyoxetanes, sulfonated polyimides, sulfonated polyphenylene sulfides, sulfonated polyphenylene oxides, and sulfonated polyphenylenes.

[0017] The catalyst layers are stacked on the electrolyte membrane. The number of catalyst layers stacked on the electrolyte membrane is two or more, and preferably three or more. The number of stacked catalyst layers is, for example, six or less.

[0018] The types of catalysts contained in the two or more catalyst layers stacked on the electrolyte membrane may be the same or different, but from the viewpoint of improving performance based on a specific catalyst, it is preferable that the types of catalysts are the same.

[0019] The amount of catalyst contained in each catalyst layer is not particularly limited. When an electrolyte membrane laminate includes an electrolyte membrane, a first catalyst layer, and a second catalyst layer in this order, the amount of catalyst contained in the first catalyst layer is preferably greater than the amount of catalyst contained in the second catalyst layer, from the viewpoint of suppressing wrinkles. The amount of catalyst contained in each catalyst layer can be controlled, for example, by the thickness of the catalyst layer.

[0020] The thickness of the entire catalyst layer (total thickness of two or more catalyst layers) is not particularly limited, but from the viewpoint of ensuring the loading amount, it is preferably 10 μm to 50 μm, and more preferably 15 μm to 30 μm.

[0021] The thickness of each catalyst layer is not particularly limited, but is preferably 5 μm to 15 μm from the viewpoint of suppressing defects and wrinkles.

[0022] The thickness of the catalyst layer is measured by the method described in JIS K 7130:1999.

[0023] -Interface- In the electrolyte membrane laminate according to the present disclosure, an interface exists between at least one of the adjacent catalyst layers. For example, when a first catalyst layer and a second catalyst layer are stacked in this order on the electrolyte membrane, an interface exists between the two catalyst layers. When a first catalyst layer, a second catalyst layer, and a third catalyst layer are stacked in this order on the electrolyte membrane, an interface exists at least between the first catalyst layer and the second catalyst layer and between the second catalyst layer and the third catalyst layer, and it is preferable that an interface exists in both.

[0024] In an electrolyte membrane stack in which there is an interface between at least one of the adjacent catalyst layers, the occurrence of defects is suppressed.

[0025] The presence or absence of an interface between adjacent catalyst layers is determined by the following method: A cross section of an electrolyte membrane laminate is observed with a scanning electron microscope (SEM). If a continuous boundary line can be confirmed between the catalyst layers, it is determined that an interface exists. If the boundary line is broken or cannot be confirmed, it is determined that no interface exists.

[0026] - Mixed Layer - A mixed layer is preferably present between the electrolyte membrane and the catalyst layer adjacent to the electrolyte membrane. The presence of the mixed layer improves adhesion between the electrolyte membrane and the catalyst layer.

[0027] The mixed layer between the electrolyte membrane and the catalyst layer adjacent to the electrolyte membrane is identified by the following method. Elemental analysis is performed from the catalyst layer side toward the electrolyte membrane using the etching ESCA method. The mixed layer is defined as the area from the position where the amount of a specific metal contained in the catalyst layer begins to decrease to the position where the specific metal is no longer detected. Note that the term "no longer detectable" means that the specific metal has reached the detection limit of the analytical device or is buried in background measurement values ​​and is therefore no longer measurable.

[0028] From the viewpoint of suppressing wrinkles, the thickness of the mixed layer is preferably 0.1 μm to 1 μm, and more preferably 0.3 μm to 0.8 μm.

[0029] The electrolyte membrane laminate according to the present disclosure may have two or more catalyst layers laminated on one side of the electrolyte membrane, or may have two or more catalyst layers laminated on each of both sides of the electrolyte membrane.

[0030] When two or more catalyst layers are laminated on each of the two surfaces of the electrolyte membrane, there is an interface between at least one of the adjacent catalyst layers on either surface of the electrolyte membrane.

[0031] [Method for manufacturing an electrolyte membrane laminate] A method for manufacturing an electrolyte membrane laminate according to the present disclosure includes: a step of preparing a first transfer substrate having a first catalyst layer on a first temporary support (hereinafter also referred to as a "first transfer substrate preparation step"); a step of arranging the first transfer substrate on the electrolyte membrane so that the electrolyte membrane and the first catalyst layer are in contact with each other, and performing a first thermocompression bonding between the electrolyte membrane and the first transfer substrate (hereinafter also referred to as a "first compression bonding step"); a step of peeling off the first temporary support and forming a first catalyst layer on the electrolyte membrane (hereinafter also referred to as a "first peeling step"); a step of preparing a second transfer substrate having a second catalyst layer on a second temporary support (hereinafter also referred to as a "second transfer substrate preparation step"); and a step of arranging the second transfer substrate on the first catalyst layer so that the first catalyst layer and the second catalyst layer are in contact with each other, and performing a second thermocompression bonding between the electrolyte membrane on which the first catalyst layer has been formed, and the second transfer substrate (hereinafter also referred to as a "second compression bonding step"); and a step of peeling off the second temporary support and forming a second catalyst layer on the first catalyst layer (hereinafter also referred to as a "second support peeling step").

[0032] <First Transfer Substrate Preparation Step> The method for producing an electrolyte membrane laminate according to the present disclosure includes a step of preparing a first transfer substrate having a first catalyst layer on a first temporary support.

[0033] (First Transfer Substrate) The first transfer substrate has a first temporary support and a first catalyst layer formed on the first temporary support. The first temporary support is not particularly limited as long as it is a substrate that can hold the first catalyst layer and can be peeled off after the thermocompression bonding step.

[0034] Examples of the first temporary support include polymer films such as polyimide, polyethylene terephthalate, polypalvanic acid aramid, polyamide (nylon), polysulfone, polyethersulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyetherimide, polyacrylate, polyethylene naphthalate, etc. The first temporary support may also be a film of a fluororesin such as ethylene tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroperfluoroalkylvinyl ether copolymer, polytetrafluoroethylene (PTFE), etc.

[0035] The thickness of the first temporary support is not particularly limited, but is preferably 250 μm or less, more preferably 50 μm or less. The lower limit of the thickness is, for example, 30 μm.

[0036] The thickness of the first temporary support is measured by the method described in JIS K 7130:1999.

[0037] The method for providing the first catalyst layer on the first temporary support is not particularly limited, and may be a method of bonding the first temporary support and a sheet for the catalyst layer, or a method of applying a first catalyst-containing dispersion onto the first temporary support and drying it.

[0038] From the viewpoint of productivity, the transfer substrate is preferably produced by applying the first catalyst-containing dispersion onto the first temporary support and drying the same. The application method is not particularly limited, and any known application method can be used.

[0039] Examples of the coating device include a bar coater, a screen printer, a doctor blade, a reverse coater, a die coater, a spray coater, a gravure coater, and a comma coater.

[0040] The first catalyst-containing dispersion preferably contains a catalyst, a binder, and a solvent.

[0041] Details of the catalyst and binder are as described above.

[0042] Examples of solvents include water, methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol.

[0043] The method for drying the first catalyst-containing dispersion after coating it on the first temporary support is not particularly limited, and any known drying method can be used. The drying temperature is, for example, 25° C. to 130° C. The drying time is, for example, 1 minute to 1 hour.

[0044] The content of the solvent in the first catalyst layer of the first transfer substrate is preferably 1% by mass to 10% by mass, and more preferably 2% by mass to 5% by mass, relative to the total amount of the first catalyst layer. When the content of the solvent in the first catalyst layer of the first transfer substrate is within the above range, the adhesion between the first catalyst layer and the electrolyte membrane is improved. When the first transfer substrate is produced by applying the first catalyst-containing dispersion onto the first temporary support, the content of the solvent in the first catalyst layer of the first transfer substrate can be adjusted by changing the drying conditions.

[0045] The content of the solvent contained in the first catalyst layer of the first transferring substrate is measured using a method such as component identification using a combination of gas chromatography and a detector.

[0046] <First thermocompression bonding step> The method for manufacturing an electrolyte membrane laminate according to the present disclosure includes a step of placing a first transfer substrate on the electrolyte membrane so that the electrolyte membrane and the first catalyst layer are in contact with each other, and performing first thermocompression bonding between the electrolyte membrane and the first transfer substrate.

[0047] The first thermocompression bonding step can be performed using a known thermocompression bonding device, for example, by pressing a heating member against the laminate, sandwiching the laminate between heating members, etc. Examples of the heating member include a hot plate, a hot block, and a hot roll. A laminator equipped with a pair of hot rolls may be used, and the laminate may be passed between the pair of rolls to perform thermocompression bonding.

[0048] The temperature for thermocompression bonding is preferably 80° C. to 200° C., more preferably 130° C. to 180° C. The pressure for thermocompression bonding is preferably 0.1 MPa to 5 MPa, more preferably 0.5 MPa to 3 MPa.

[0049] <First Temporary Support Peeling Step> The method for producing an electrolyte membrane laminate according to the present disclosure includes the steps of peeling off the first temporary support and forming a first catalyst layer on the electrolyte membrane.

[0050] The method for peeling off the first temporary support is not particularly limited, and can be carried out by a commonly known method.

[0051] <Step of Preparing Second Transfer Substrate> The method for producing an electrolyte membrane laminate according to the present disclosure includes a step of preparing a second transfer substrate having a second catalyst layer on a second temporary support.

[0052] The preferred embodiments of the second temporary support are the same as those of the first temporary support. The method for providing the second catalyst layer on the second temporary support is the same as the method for providing the first catalyst layer on the first temporary support.

[0053] The content of the solvent in the second catalyst layer of the second transfer substrate is preferably 1% by mass to 10% by mass, and more preferably 2% by mass to 5% by mass, relative to the total amount of the second catalyst layer. When the content of the solvent in the second catalyst layer of the second transfer substrate is within the above range, the adhesion between the first catalyst layer and the second catalyst layer is improved. When the second transfer substrate is produced by applying the second catalyst-containing dispersion onto the second temporary support, the content of the solvent in the second catalyst layer of the second transfer substrate can be adjusted by changing the drying conditions.

[0054] <Second thermocompression bonding step, second temporary support peeling step> The method for manufacturing an electrolyte membrane laminate according to the present disclosure includes the steps of: placing a second transfer substrate on the first catalyst layer so that the first catalyst layer and the second catalyst layer are in contact with each other; and performing second thermocompression bonding between the electrolyte membrane on which the first catalyst layer has been formed and the second transfer substrate. The method for manufacturing an electrolyte membrane laminate according to the present disclosure also includes the steps of peeling off the second temporary support and forming the second catalyst layer on the first catalyst layer.

[0055] In the second transfer substrate placement step, it is preferable to overlay the second catalyst layer on the entire surface of the first catalyst layer, which increases the overall thickness of the catalyst layer and increases the amount of catalyst per unit area.

[0056] A preferred embodiment of the thermocompression bonding in the second thermocompression bonding step is the same as a preferred embodiment of the thermocompression bonding in the first thermocompression bonding step. A method for peeling off the second temporary support in the second temporary support peeling step is the same as a method for peeling off the first temporary support in the first temporary support peeling step.

[0057] According to the method for manufacturing an electrolyte membrane laminate according to the present disclosure, a first catalyst layer and a second catalyst layer are formed on an electrolyte membrane by a transfer method, which allows for a larger amount of catalyst per unit area than conventional methods, and is expected to result in improved performance.

[0058] Furthermore, according to the method for manufacturing an electrolyte membrane laminate according to the present disclosure, the first catalyst layer and the second catalyst layer are formed on the electrolyte membrane by a transfer method, thereby forming an interface between the first catalyst layer and the second catalyst layer. By using the transfer method, it is possible to suppress the occurrence of cracks due to drying shrinkage. Furthermore, the presence of an interface between the first catalyst layer and the second catalyst layer makes it difficult for cracks to propagate between the catalyst layers.

[0059] The method for producing an electrolyte membrane laminate according to the present disclosure may include other steps in addition to the steps described above.

[0060] A step of heating the first transfer substrate and the electrolyte membrane may be performed before the first thermocompression bonding step. By heating the first transfer substrate and the electrolyte membrane, the first catalyst layer included in the first transfer substrate softens, improving adhesion to the electrolyte membrane. The heating means for the first transfer substrate and the electrolyte membrane is not particularly limited, and known heating means can be used. The heating temperature for the first transfer substrate is, for example, 50°C to 200°C. The heating temperature for the electrolyte membrane is, for example, 50°C to 150°C.

[0061] A step of heating the electrolyte membrane on which the first catalyst layer has been formed and the second transfer substrate may be performed before the second thermocompression bonding step. By heating the electrolyte membrane on which the first catalyst layer has been formed and the second transfer substrate, the first catalyst layer included in the first transfer substrate softens, improving adhesion to the electrolyte membrane. The heating means for the first transfer substrate and the electrolyte membrane is not particularly limited, and known heating means can be used. The heating temperature for the first transfer substrate is, for example, 50°C to 200°C. The heating temperature for the electrolyte membrane is, for example, 50°C to 150°C.

[0062] Preferably, the method further comprises, after the second temporary support peeling step, a step of heating the electrolyte membrane on which the first catalyst layer and the second catalyst layer have been formed. By reheating, the uniformity of the thickness of the entire catalyst layer is improved.

[0063] Furthermore, in the method for manufacturing an electrolyte membrane laminate according to the present disclosure, it is preferable to perform the first thermocompression bonding step, the first temporary support peeling step, the second thermocompression bonding step, and the second temporary support peeling step on both surfaces of the electrolyte membrane.

[0064] The steps performed on one side of the electrolyte membrane may be the same as or different from the steps performed on the other side of the electrolyte membrane.

[0065] The present invention will be explained in more detail below with reference to examples. The materials, amounts used, ratios, details of each step, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. Note that "parts" are all based on mass.

[0066] Example 1 First Transfer Substrate Preparation Step 7.2 g of a platinum-carbon black-supported catalyst (product name "TEC10E50", manufactured by Tanaka Kikinzoku Kogyo Kogyo) and 47.6 g of IPA (isopropanol) were stirred and mixed in a disperser to prepare a platinum-carbon black-supported catalyst dispersion. 21 g of a 20 mass % polymer dispersion (product name "Nafion (registered trademark) D-2020, manufactured by Chemours) was added to the dispersion, and the mixture was stirred and mixed in the disperser to obtain a catalyst layer dispersion A.

[0067] The catalyst layer dispersion A was applied by doctor blade onto a PTFE film (product name "Nitoflon No. 900 UL", manufactured by Nitto Denko Corporation, thickness 50 μm, 20 cm × 20 cm) used as a temporary support, and dried at 90°C for 10 minutes. This resulted in a first transfer substrate having a first catalyst layer of 10 μm thickness formed on the temporary support. The content of solvent in the first catalyst layer of the first transfer substrate was 1 mass%.

[0068] <Transfer substrate placement step> A first transfer substrate was placed on an electrolyte membrane (product name "Nafion (registered trademark) N115", manufactured by DuPont, thickness 127 μm, 120 cm square) so that the electrolyte membrane and the first catalyst layer were in contact with each other.

[0069] <Preheating Step> Using a hot plate heated by a heater, the electrolyte membrane and the first transfer substrate were preheated at a temperature of 100° C. for 3 minutes.

[0070] <First Thermocompression Bonding Step> Using a thermal laminator, the electrolyte membrane and the first transfer substrate were thermocompression bonded together at a temperature of 160° C. and a pressing pressure of 1 MPa.

[0071] <First Temporary Support Peeling Step> The temporary support was peeled off using an adhesive roll, and the first catalyst layer was transferred onto the electrolyte membrane, thereby obtaining an electrolyte membrane on which the first catalyst layer was formed.

[0072] <Second Transfer Substrate Preparation Step> A second transfer substrate having a second catalyst layer with a thickness of 10 μm formed on a temporary support was obtained in the same manner as in the first transfer substrate preparation step.

[0073] <Transfer Substrate Arrangement Step> The first transfer substrate was arranged so that the electrolyte membrane on which the first catalyst layer was formed and the second catalyst layer were in contact with each other.

[0074] <Preheating Step> Using a hot plate heated by a heater, the electrolyte membrane on which the first catalyst layer had been formed in advance and the second transfer substrate were heated at a temperature of 100° C. for 3 minutes.

[0075] <Second Thermocompression Bonding Step> Using a thermal laminator, the electrolyte membrane on which the first catalyst layer had been formed and the second transfer substrate were thermocompression bonded together at a temperature of 160° C. and a pressing pressure of 1 MPa.

[0076] <Second temporary support peeling step> The temporary support was peeled off using an adhesive roll, and the second catalyst layer was transferred onto the first catalyst layer. Thereafter, the mixture was heated at a temperature of 90°C for 3 minutes to obtain an electrolyte membrane laminate in which the first catalyst layer and the second catalyst layer were formed on the electrolyte membrane.

[0077] [Example 2] A third transfer substrate was obtained by forming a third catalyst layer having a thickness of 10 μm on a temporary support using the same method as in the first transfer substrate preparation step. Thereafter, an electrolyte membrane laminate was obtained by forming the first catalyst layer, the second catalyst layer, and the third catalyst layer on the electrolyte membrane using the same method as in the formation of the first and second catalyst layers.

[0078] [Example 3] A first transfer substrate and a second transfer substrate were obtained in the same manner as in Example 1, except that catalyst layer dispersion A was applied onto a temporary support and dried at 90°C for 3 minutes. The content of the solvent in the first catalyst layer of the first transfer substrate was 9 mass%. The content of the solvent in the second catalyst layer of the second transfer substrate was 9 mass%. Then, an electrolyte membrane laminate was obtained in the same manner as in Example 1, except that the first transfer substrate and second transfer substrate were used.

[0079] [Example 4] A first transfer substrate and a second transfer substrate were obtained in the same manner as in Example 1, except that the catalyst layer dispersion was applied to a temporary support and dried for 10 minutes, followed by vacuum drying at 90°C for 60 minutes. The solvent content in the first catalyst layer of the first transfer substrate was 0.1 mass%. The solvent content in the second catalyst layer of the second transfer substrate was 0.1 mass%. An electrolyte membrane laminate was then obtained in the same manner as in Example 1, except that the first transfer substrate and second transfer substrate were used.

[0080] Example 5 An electrolyte membrane laminate was obtained in the same manner as in Example 1, except that the thickness of the second catalyst layer was changed to 5 μm.

[0081] [Example 6] A first transfer substrate and a second transfer substrate were obtained in the same manner as in Example 1, except that catalyst layer dispersion A was applied to a temporary support and dried, and then dried at 90°C for 30 seconds. The solvent content in the first catalyst layer of the first transfer substrate was 15% by mass. The solvent content in the second catalyst layer of the second transfer substrate was 15% by mass. Then, an electrolyte membrane laminate was obtained in the same manner as in Example 1, except that the first transfer substrate and second transfer substrate were used.

[0082] Example 7 An electrolyte membrane laminate was obtained in the same manner as in Example 1, except that the preheating step was not carried out.

[0083] [Comparative Example 1] The catalyst layer dispersion A was applied onto an electrolyte membrane by a doctor blade method, and dried for 10 minutes at 90° C. This resulted in an electrolyte membrane laminate in which a first catalyst layer having a thickness of 20 μm was formed on the electrolyte membrane.

[0084] [Comparative Example 2] Catalyst layer dispersion A was applied onto an electrolyte membrane by doctor blade application and dried at 90°C for 10 minutes. This resulted in an electrolyte membrane laminate in which a first catalyst layer having a thickness of 10 µm was formed on the electrolyte membrane. Furthermore, catalyst layer dispersion A was applied onto the first catalyst layer by doctor blade application and dried at 90°C for 10 minutes. This resulted in an electrolyte membrane laminate in which a first catalyst layer and a second catalyst layer were formed on the electrolyte membrane.

[0085] <<Measurement and Evaluation>> -Interface between catalyst layers- A cross section of the electrolyte membrane laminate was observed with a scanning electron microscope (SEM). When a continuous boundary line was confirmed between the catalyst layers, it was determined that an interface existed. When the boundary line was broken or when the boundary line could not be confirmed, it was determined that no interface existed. In Table 1, when it was determined that an interface existed, it was recorded as "present," and when it was determined that no interface existed, it was recorded as "absent."

[0086] -Thickness of mixed layer- Elemental analysis was performed using an etching ESCA method from the first catalyst layer side toward the electrolyte membrane. The mixed layer was defined as the region from the position where the amount of Pt in the first catalyst layer began to decrease to the position where Pt was no longer detected, and the thickness was measured.

[0087] -Cracks- The surface of the catalyst layer in the electrolyte membrane laminate was observed under a microscope. Evaluation was made based on the following evaluation criteria: A: No cracks B: Cracks present locally C: Cracks present over the entire surface

[0088] - Pinholes - The surface of the catalyst layer in the electrolyte membrane laminate was observed under a microscope and evaluated based on the following criteria: A: No pinholes. B: Pinholes present.

[0089] Appearance The surface of the catalyst layer in the obtained electrolyte membrane laminate was visually observed and evaluated based on the following criteria: A: No wrinkles. B: Wrinkles present.

[0090]

[0091] As shown in Table 1, Examples 1 to 7 each comprised an electrolyte membrane and two or more catalyst layers stacked on the electrolyte membrane, and an interface was present between at least one of the adjacent catalyst layers, resulting in a larger catalyst amount per unit area than in the past and suppressing the occurrence of defects. In Comparative Examples 1 and 2, no interface was present between the catalyst layers, and cracks were confirmed as defects. Furthermore, the occurrence of pinholes was also observed in Comparative Example 1.

[0092] Example 100 A first catalyst layer and a second catalyst layer were formed on one surface of an electrolyte membrane in the same manner as in Example 1. Next, a first catalyst layer and a second catalyst layer were formed on the other surface of the electrolyte membrane in the same manner as in Example 1, except that catalyst layer dispersion B was used instead of catalyst layer dispersion A. In this way, an electrolyte membrane laminate in which catalyst layers were formed on both surfaces of the electrolyte membrane was obtained.

[0093] -Dispersion liquid B for catalyst layer- IrO ２ 7.35 g of catalyst (manufactured by Furuya Metal Co., Ltd.) and 12.25 g of IPA were mixed and stirred in a disperser to form IrO ２ A catalyst dispersion was prepared. 5.25 g of a 20 mass % polymer dispersion (product name: Nafion (registered trademark) D-2020, manufactured by Chemours) was added to the dispersion, and the mixture was stirred and mixed using a disperser to obtain a catalyst layer dispersion B.

[0094] In Example 100, the surfaces (two sides) of the catalyst layer in the electrolyte membrane laminate were visually inspected for cracks, pinholes, and appearance, and all were rated as A.

[0095] The disclosure of Japanese Patent Application No. 2024-036317, filed on March 8, 2024, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated to be incorporated by reference.

Claims

1. An electrolyte membrane stack comprising: an electrolyte membrane; and two or more catalyst layers stacked on the electrolyte membrane, wherein an interface exists between at least one of the adjacent catalyst layers.

2. The electrolyte membrane stack according to claim 1, wherein a mixed layer is present between the electrolyte membrane and a catalyst layer adjacent to the electrolyte membrane.

3. The electrolyte membrane laminate according to claim 2, wherein the thickness of the mixed layer is 0.1 μm to 1 μm.

4. An electrolyte membrane laminate according to any one of claims 1 to 3, comprising an electrolyte membrane, a first catalyst layer, and a second catalyst layer in this order, wherein the amount of catalyst contained in the first catalyst layer is greater than the amount of catalyst contained in the second catalyst layer.

5. A method for manufacturing an electrolyte membrane laminate, comprising the steps of: preparing a first transfer substrate having a first catalyst layer on a first temporary support; placing the first transfer substrate on an electrolyte membrane so that the electrolyte membrane and the first catalyst layer are in contact with each other, and performing a first thermocompression bonding between the electrolyte membrane and the first transfer substrate; peeling off the first temporary support and forming a first catalyst layer on the electrolyte membrane; preparing a second transfer substrate having a second catalyst layer on a second temporary support; placing the second transfer substrate on the first catalyst layer so that the first catalyst layer and the second catalyst layer are in contact with each other, and performing a second thermocompression bonding between the electrolyte membrane on which the first catalyst layer has been formed and the second transfer substrate; and peeling off the second temporary support and forming a second catalyst layer on the first catalyst layer.

6. The method for producing an electrolyte membrane laminate according to claim 5, wherein the content of the solvent in the second catalyst layer of the second transfer substrate is 1% by mass to 10% by mass relative to the total amount of the second catalyst layer.

7. A method for manufacturing an electrolyte membrane laminate according to claim 5 or claim 6, wherein in the step of placing the second transfer substrate, the second catalyst layer is superimposed on the entire surface of the first catalyst layer.

8. A method for manufacturing an electrolyte membrane laminate according to claim 5 or claim 6, further comprising a step of heating the electrolyte membrane and the first transfer substrate before the step of thermocompression bonding the electrolyte membrane and the first transfer substrate.

9. A method for manufacturing an electrolyte membrane laminate according to claim 5 or claim 6, further comprising a step of heating the electrolyte membrane on which the first catalyst layer has been formed and the second transfer substrate before the step of thermocompression bonding the electrolyte membrane on which the first catalyst layer has been formed and the second transfer substrate.

10. A method for manufacturing an electrolyte membrane laminate as described in claim 5 or claim 6, comprising the steps of: performing the first thermocompression bonding on both sides of the electrolyte membrane; forming a first catalyst layer on the electrolyte membrane; performing the second thermocompression bonding; and forming a second catalyst layer on the electrolyte membrane.

11. A method for manufacturing an electrolyte membrane stack according to claim 5 or claim 6, further comprising, after the step of forming a second catalyst layer on the first catalyst layer, a step of heating the electrolyte membrane on which the first catalyst layer and the second catalyst layer have been formed.