Catalyst layer-attached electrolyte membrane, method for producing catalyst layer-attached electrolyte membrane, membrane electrode assembly, and water electrolysis device

Abstract

Provided is a catalyst layer-attached electrolyte membrane comprising an electrolyte membrane, a first catalyst layer, and a second catalyst layer in this order, wherein the first catalyst layer is an inorganic layer including a metal catalyst, the second catalyst layer is an inorganic layer or an organic layer including a metal catalyst, and the metal catalyst included in the first catalyst layer and the metal catalyst included in the second catalyst layer contain the same group element.

Description

Electrolyte membrane with catalyst layer, method for manufacturing electrolyte membrane with catalyst layer, membrane electrode assembly, and water electrolysis device

[0001] The present disclosure relates to an electrolyte membrane with a catalyst layer, a method for manufacturing an electrolyte membrane with a catalyst layer, a membrane electrode assembly, and a water electrolysis device.

[0002] In recent years, the utilization of hydrogen has attracted attention from the perspective of utilizing renewable energy. As one of the hydrogen production methods, solid polymer electrolysis can be mentioned. In solid polymer electrolysis, in recent years, a membrane with a catalyst layer (CCM: Catalyst Coated Membrane) in which electrode catalyst layers containing a catalyst for water electrolysis and a solid electrolyte (for example, an ionomer resin) are formed on both sides of a solid polymer membrane (PEM: Polymer Electoron Membrane), which is an ion exchange membrane, is used as a member constituting a water electrolysis device.

[0003] For example, Japanese Patent Application Laid-Open No. 2018-153770 describes a coating method in which a coating liquid containing a combustible material is applied to a conveyed long strip-shaped electrolyte membrane at an application portion while conveying the electrolyte membrane, and the coating liquid applied by the application portion is dried at a drying portion.

[0004] Japanese Patent Application Laid-Open No. 2008-258155 describes a membrane electrode composite having an anode electrode and a cathode electrode on both sides of an electrolyte membrane, the anode electrode being composed of an electrode base material and a catalyst layer, the catalyst layer being composed of at least metal particles, metal-supported particles, and a polymer binder, and the weight ratio of the metal particles, metal-supported particles, and polymer binder being greater than 4 / 1 and less than 10 / 1.

[0005] Regarding the electrolyte membrane with a catalyst layer, there may be a case where it is required to further improve the adhesion between the electrolyte membrane and the catalyst layer.

[0006] The problem to be solved by one embodiment of the present disclosure has been made in view of the above circumstances, and it is to provide an electrolyte membrane with a catalyst layer having excellent adhesion between the electrolyte membrane and the catalyst layer, and a method for manufacturing an electrolyte membrane with a catalyst layer. Further, the problem to be solved by another embodiment of the present disclosure is to provide a membrane electrode assembly including the above electrolyte membrane with a catalyst layer, and a water electrolysis device.

[0007] This disclosure includes the following embodiments: <1> A catalyst-layered electrolyte membrane comprising an electrolyte membrane, a first catalyst layer, and a second catalyst layer in this order, wherein the first catalyst layer is an inorganic layer containing a metal catalyst, the second catalyst layer is an inorganic or organic layer containing a metal catalyst, and the metal catalyst contained in the first catalyst layer and the metal catalyst contained in the second catalyst layer contain elements of the same group. <2> The catalyst-layered electrolyte membrane according to <1>, wherein the first catalyst layer has a porosity of 30% to 80%. <3> The catalyst-layered electrolyte membrane according to <1> or <2>, wherein the first catalyst layer has a surface resistivity of 0.2 Ω to 100 Ω. <4> The catalyst-layered electrolyte membrane according to any one of <1> to <3>, wherein the thickness of the first catalyst layer is 30 nm or more. <5> The catalyst-layered electrolyte membrane according to any one of <1> to <4>, wherein the first catalyst layer is a vapor-deposited film layer and the second catalyst layer is a coated layer. <6> A catalyst-layered electrolyte membrane according to any one of <1> to <5>, comprising an intermediate layer with a thickness of 5 nm or more between the first catalyst layer and the second catalyst layer. <7> A catalyst-layered electrolyte membrane according to any one of <1> to <6>, wherein both the first catalyst layer and the second catalyst layer contain platinum group elements. <8> A catalyst-layered electrolyte membrane according to <6>, wherein both the intermediate layer and the second catalyst layer contain organic components, and the content of organic components in the intermediate layer is less than the content of organic components in the second catalyst layer. <9> A catalyst-layered electrolyte membrane according to <6>, wherein the intermediate layer contains components contained in the first catalyst layer and components contained in the second catalyst layer. <10> A method for producing a catalyst-layered electrolyte membrane, comprising the steps of: forming a first catalyst layer on an electrolyte membrane using a vapor deposition method; and applying a composition for forming a second catalyst layer on the first catalyst layer to form a second catalyst layer. <11> A membrane electrode assembly comprising a catalyst-layered electrolyte membrane according to any one of <1> to <9>. <12> A water electrolysis apparatus including the membrane electrode assembly described in <11>.

[0008] According to one embodiment of the present disclosure, an electrolyte membrane with a catalyst layer exhibiting excellent adhesion between the electrolyte membrane and the catalyst layer, and a method for manufacturing the electrolyte membrane with a catalyst layer are provided. Furthermore, according to another embodiment of the present disclosure, a membrane electrode assembly including the above-mentioned electrolyte membrane with a catalyst layer, and a water electrolysis apparatus are provided.

[0009] In this disclosure, numerical ranges indicated using "~" mean ranges that include the numbers before and after "~" as the minimum and maximum values, respectively. In this disclosure, the term "process" is included not only in the sense of an independent process, but also in the sense of a process that is not clearly distinguishable from other processes, as long as the intended purpose of that process is achieved. In numerical ranges described in stages in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Also, in numerical ranges described in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the value shown in the example. In this disclosure, two or more preferred forms or combinations of embodiments are considered more preferred forms or embodiments.

[0010] [Electrolyte membrane with catalyst layer] The electrolyte membrane with catalyst layer according to this disclosure comprises an electrolyte membrane, a first catalyst layer, and a second catalyst layer in this order, wherein the first catalyst layer is an inorganic layer containing a metal catalyst, and the second catalyst layer is an inorganic or organic layer containing a metal catalyst, and the metal catalyst contained in the first catalyst layer and the metal catalyst contained in the second catalyst layer contain elements of the same group.

[0011] Conventionally, an organic layer has been formed on an electrolyte membrane by coating it with a catalyst layer-forming composition containing an organic compound. However, catalyst layer-forming compositions containing organic compounds usually contain an organic solvent to dissolve or disperse the organic compound in the liquid, and the organic solvent penetrates into the electrolyte membrane. The present inventors have found that when an organic layer is formed on the electrolyte membrane, the adhesion between the electrolyte membrane and the catalyst layer is insufficient. The electrolyte membrane with a catalyst layer according to this disclosure comprises an electrolyte membrane, a first catalyst layer, and a second catalyst layer in this order, wherein the first catalyst layer is an inorganic layer containing a metal catalyst. The second catalyst layer is an inorganic or organic layer containing a metal catalyst, and the metal catalyst contained in the first catalyst layer and the metal catalyst contained in the second catalyst layer contain elements of the same group. It has been found that this configuration provides excellent adhesion between the electrolyte membrane and the catalyst layer.

[0012] Japanese Patent Publication No. 2018-153770 and Japanese Patent Publication No. 2008-258155 do not contain any descriptions focusing on an inorganic layer containing a metal catalyst as the first catalyst layer.

[0013] (Electrolyte membranes) Examples of electrolyte membranes include fluorine-based electrolyte membranes and hydrocarbon-based electrolyte membranes. Specifically, examples of electrolyte membranes include perfluorocarbon sulfonic acid polymers represented by Nafion (registered trademark), poly(meth)acrylates having phosphate groups in their side chains, heat-resistant aromatic polymers such as sulfonated polyether ether ketones, sulfonated polyether ketones, sulfonated polyether sulfones, sulfonated polysulfones, sulfonated polysulfones, sulfonated polybenzimidazoles, sulfonated polystyrene, sulfonated polyoxetanes, sulfonated polyimides, sulfonated polyphenylene sulfide, sulfonated polyphenylene oxide, and sulfonated polyphenylene membranes.

[0014] The thickness of the electrolyte membrane is preferably 30 μm to 250 μm, and more preferably 50 μm to 200 μm. The thickness of the electrolyte membrane is measured by the method described in JIS K 7130:1999.

[0015] (First catalyst layer) The first catalyst layer is placed on at least one surface of the electrolyte membrane.

[0016] The first catalyst layer is an inorganic layer containing a metal catalyst.

[0017] An inorganic layer refers to a layer that is substantially free of carbon atoms. "Substantially free of carbon atoms" means that organic components are not intentionally added during the formation of the layer, although organic components may inevitably be present. In elemental analysis, the carbon atom content in the inorganic layer is preferably 3 at% or less, and more preferably 1 at% or less.

[0018] Examples of metal catalysts include platinum, gold, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and other metals and alloys thereof. From the viewpoint of catalytic activity and durability, the metal catalyst contained in the first catalyst layer preferably contains platinum or iridium, and more preferably iridium.

[0019] The first catalyst layer preferably has a porosity of 30% to 80%, and more preferably 40% to 60%. If the porosity is 30% or more, the stress applied to the first catalyst layer is reduced, and the occurrence of cracks is suppressed. If the porosity is 80% or less, the strength of the first catalyst layer is maintained, and the occurrence of cracks is suppressed.

[0020] The porosity in the first catalyst layer is measured by the following method: The sample is cut into sections, the cross-section is observed using a scanning electron microscope (SEM), and a cross-sectional SEM image is obtained. Image processing is performed on the portion of the obtained SEM image corresponding to the catalyst to determine the area ratio of the voids.

[0021] The thickness of the first catalyst layer is preferably 30 nm or more, and more preferably 50 nm or more. The upper limit of the thickness of the first catalyst layer is not particularly limited, but from the viewpoint of suppressing cracking caused by internal stress in the inorganic layer, it is preferably 200 nm.

[0022] When the thickness of the first catalyst layer is 30 nm or more, the adhesion between the first catalyst layer and the electrolyte membrane is improved.

[0023] The thickness of the first catalyst layer is measured by the method described in JIS K 7130:1999.

[0024] The first catalyst layer preferably has a surface resistivity of 0.2 Ω to 100 Ω, and more preferably 1 Ω to 50 Ω. A surface resistivity of 0.2 Ω to 100 Ω results in good affinity with the electrolyte membrane and superior adhesion between the electrolyte membrane and the first catalyst layer.

[0025] In this disclosure, surface resistivity is a value measured using a surface resistance meter in accordance with JIS K 7194:1994. Surface resistivity is expressed in units of "Ω per square (Ω / □)", and the dimensions of the electrodes may be taken into consideration when calculating the resistance value.

[0026] The first catalyst layer is preferably a vapor-deposited layer. A vapor-deposited layer means a layer formed by a vapor deposition method. The fact that the first catalyst layer is a vapor-deposited layer can be confirmed by carbon component analysis of the surface by ESCA (X-ray photoelectron spectroscopy).

[0027] Examples of vapor phase deposition methods include sputtering, vacuum deposition, and chemical vapor deposition. Among these, sputtering is preferred as the vapor phase deposition method.

[0028] (Second catalyst layer) The second catalyst layer is placed on top of the first catalyst layer.

[0029] The second catalyst layer is an inorganic or organic layer containing a metal catalyst.

[0030] When the second catalyst layer is an inorganic layer containing a metal catalyst, the preferred embodiment of the second catalyst layer is the same as the preferred embodiment of the first catalyst layer. When the second catalyst layer is an organic layer containing a metal catalyst, it is preferable that it contains both a metal catalyst and a resin.

[0031] Examples of metal catalysts include platinum, gold, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and other metals and alloys thereof. From the viewpoint of catalytic activity and durability, the metal catalyst contained in the second catalyst layer preferably contains platinum or iridium, and more preferably iridium.

[0032] The resin is preferably a polymer having a proton-donating group. Examples of resins include perfluorocarbon sulfonic acid polymers represented by Nafion®, poly(meth)acrylates having phosphate groups in the side chains, heat-resistant aromatic polymers such as sulfonated polyether ether ketones, sulfonated polyether ketones, sulfonated polyether sulfones, sulfonated polysulfones, sulfonated polysulfones, and sulfonated polybenzimidazole; sulfonated polystyrene, sulfonated polyoxetane, sulfonated polyimide, sulfonated polyphenylene sulfide, sulfonated polyphenylene oxide, and sulfonated polyphenylene.

[0033] In the electrolyte membrane with a catalyst layer according to this disclosure, the metal catalyst contained in the first catalyst layer and the metal catalyst contained in the second catalyst layer include elements of the same group. In this disclosure, elements of the same group include not only groups of elements belonging to the same group in the periodic table, but also groups of elements that have similar properties to each other. The concept of elements of the same group includes noble metals, iron group elements, and platinum group elements.

[0034] In particular, from the viewpoint of improving catalytic performance and durability, it is preferable that both the first catalyst layer and the second catalyst layer contain platinum group elements.

[0035] Platinum group elements are elements located in the 5th and 6th periods, and groups 8, 9, and 10 of the periodic table. In other words, platinum group elements are ruthenium, rhodium, palladium, osmium, iridium, or platinum.

[0036] The second catalyst layer is preferably a coated layer. A coated layer means a layer formed by coating. The fact that the second catalyst layer is a coated layer can be confirmed by surface ESCA (X-ray photoelectron spectroscopy).

[0037] The thickness of the second catalyst layer is not particularly limited, but is preferably 1 μm or more, and more preferably 2 μm or more. The upper limit of the thickness of the second catalyst layer is not particularly limited, but is preferably 15 μm from the viewpoint of suppressing the occurrence of cracks due to drying shrinkage.

[0038] (Intermediate layer) The electrolyte membrane with a catalyst layer according to this disclosure may include layers other than the first catalyst layer and the second catalyst layer on the electrolyte membrane. Specifically, the electrolyte membrane with a catalyst layer according to this disclosure preferably includes an intermediate layer with a thickness of 5 nm or more between the first catalyst layer and the second catalyst layer.

[0039] The presence of an intermediate layer improves the adhesion between the first catalyst layer and the second catalyst layer.

[0040] Both the intermediate layer and the second catalyst layer contain organic components, and it is preferable that the content of organic components in the intermediate layer is less than the content of organic components in the second catalyst layer. Examples of organic components include the resins mentioned above.

[0041] For example, by applying a composition for forming a second catalyst layer containing an organic component onto the first catalyst layer, a part of the organic component penetrates into the first catalyst layer, and an intermediate layer is formed between the first catalyst layer and the second catalyst layer.

[0042] The intermediate layer preferably contains components contained in the first catalyst layer and components contained in the second catalyst layer. By the intermediate layer containing components contained in the first catalyst layer and components contained in the second catalyst layer, the adhesion between the first catalyst layer and the second catalyst layer is further improved.

[0043] The intermediate layer existing between the first catalyst layer and the second catalyst layer is specified by the following method. Using the etching ESCA method, elemental analysis is performed from the second catalyst layer side toward the first catalyst layer. The intermediate layer is defined as the position from where the amount of a specific component (for example, an organic component) contained in the second catalyst layer starts to decrease to where the specific component is no longer detected. Note that the fact that the specific component is no longer detected means that it cannot be measured due to being buried in the detection limit of the analyzer or the background measurement value.

[0044] From the viewpoint of adhesion, the thickness of the intermediate layer is preferably 5 nm or more, and more preferably 10 nm or more. Also, from the viewpoint of suppressing the occurrence of cracks due to the mixing of different materials, the thickness of the intermediate layer is preferably 30 nm or less.

[0045] Further, the electrolyte membrane with a catalyst layer according to the present disclosure may include a first catalyst layer and a second catalyst layer on one surface of the electrolyte membrane, and a third catalyst layer on the other surface of the electrolyte membrane.

[0046] The third catalyst layer is preferably an organic layer containing a metal catalyst, and preferably contains a metal catalyst and a resin.

[0047] Examples of metal catalysts include platinum, gold, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and other metals and alloys thereof. From the viewpoint of catalytic activity and durability, the metal catalyst contained in the third catalyst layer preferably contains platinum or iridium, and more preferably platinum.

[0048] The metal catalyst may be supported on a carbon material. Examples of carbon materials include carbon black, activated carbon, coke, natural graphite, and artificial graphite. Specifically, examples include Ketjenblack, Vulcan black, acetylene black, carbon fibers, single-wall carbon nanotubes, multi-wall carbon nanotubes, graphitized Ketjenblack, graphitized Vulcan black, and graphitized acetylene black.

[0049] A preferred embodiment of the resin that may be included in the third catalyst layer is the same as a preferred embodiment of the resin that may be included in the second catalyst layer.

[0050] The thickness of the third catalyst layer is not particularly limited, but is preferably 1 μm or more, and more preferably 5 μm or more. The upper limit of the thickness of the third catalyst layer is not particularly limited, but is preferably 20 μm from the viewpoint of suppressing the occurrence of cracks due to drying shrinkage.

[0051] [Method for manufacturing an electrolyte membrane with a catalyst layer] The method for manufacturing an electrolyte membrane with a catalyst layer according to the present disclosure includes the steps of forming a first catalyst layer on an electrolyte membrane using a vapor deposition method (hereinafter also referred to as the "first catalyst layer formation step") and forming a second catalyst layer by applying a composition for forming a second catalyst layer on the first catalyst layer (hereinafter also referred to as the "second catalyst layer formation step").

[0052] (First catalyst layer formation step) In the first catalyst layer formation step, a first catalyst layer is formed on the electrolyte membrane using a vapor deposition method.

[0053] Details of the electrolyte membrane are as described above.

[0054] Examples of vapor phase deposition methods include sputtering, vacuum deposition, and chemical vapor deposition. Among these, sputtering is preferred as the vapor phase deposition method.

[0055] In the sputtering method, the pressure is preferably 0.1 Pa to 2 Pa. The film deposition time is, for example, 60 seconds to 500 seconds.

[0056] The first catalyst layer preferably contains a metal catalyst. Details of the metal catalyst contained in the first catalyst layer are as described above.

[0057] (Second catalyst layer formation step) In the second catalyst layer formation step, a composition for forming the second catalyst layer is applied to the first catalyst layer to form the second catalyst layer.

[0058] The composition for forming the second catalyst layer preferably includes a metal catalyst, a resin, and a solvent. Details of the metal catalyst and resin that may be included in the second catalyst layer are as described above.

[0059] Examples of solvents include water, methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol.

[0060] The composition for forming the second catalyst layer may be a solution or a dispersion.

[0061] The application method is not particularly limited, and known application methods can be used.

[0062] Examples of coating equipment include bar coaters, screen printers, doctor blades, reverse coaters, die coaters, spray coaters, gravure coaters, and comma coaters.

[0063] After applying the second catalyst layer forming composition, the applied second catalyst layer forming composition may be dried. The drying method is not particularly limited, and known drying methods 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.

[0064] The method for manufacturing an electrolyte membrane with a catalyst layer according to this disclosure preferably includes the steps of forming a first catalyst layer on one surface of the electrolyte membrane by a first catalyst layer formation step, forming a second catalyst layer by a second catalyst layer formation step, and then forming a third catalyst layer on the other surface of the electrolyte membrane.

[0065] The step of forming the third catalyst layer preferably includes the steps of: applying a composition for forming the third catalyst layer onto a temporary support to produce a transfer substrate having the third catalyst layer (hereinafter also referred to as the "transfer substrate production step"); arranging the transfer substrate on the electrolyte membrane on which the first catalyst layer and the second catalyst layer are formed, such that the electrolyte membrane and the third catalyst layer are in contact, and performing thermocompression bonding between the electrolyte membrane and the transfer substrate (hereinafter also referred to as the "thermocompression bonding step"); and peeling off the temporary support (hereinafter also referred to as the "temporary support peeling step").

[0066] (Transfer substrate preparation process) The temporary support is not particularly limited as long as it is a substrate capable of holding the catalyst layer and can be peeled off after the thermocompression bonding process.

[0067] Examples of temporary supports include polymer films such as polyimide, polyethylene terephthalate, polycarboxylic acid aramid, polyamide (nylon), polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyetherimide, polyacrylate, and polyethylene naphthalate. Alternatively, the temporary support may be a fluororesin film such as ethylene tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroperfluoroalkyl vinyl ether copolymer, or polytetrafluoroethylene (PTFE).

[0068] The thickness of the temporary support is not particularly limited, but is preferably 250 μm or less, and more preferably 50 μm or less. The lower limit of the thickness is, for example, 30 μm.

[0069] The thickness of the temporary support is measured by the method described in JIS K 7130:1999.

[0070] The composition for forming the third catalyst layer preferably contains a metal catalyst, a resin, and a solvent.

[0071] Examples of metal catalysts include platinum, gold, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and other metals and alloys thereof. From the viewpoint of catalytic activity and durability, the metal catalyst included in the composition for forming the third catalyst layer preferably contains platinum or iridium, and more preferably platinum.

[0072] The metal catalyst may be supported on a carbon material. Examples of carbon materials include carbon black, activated carbon, coke, natural graphite, and artificial graphite. Specifically, examples include Ketjenblack, Vulcan black, acetylene black, carbon fibers, single-wall carbon nanotubes, multi-wall carbon nanotubes, graphitized Ketjenblack, graphitized Vulcan black, and graphitized acetylene black.

[0073] Preferred embodiments of the resin and solvent that may be included in the third catalyst layer forming composition are the same as preferred embodiments of the resin and solvent that may be included in the second catalyst layer forming composition.

[0074] The details of the method for applying the third catalyst layer forming composition are the same as those for applying the second catalyst layer forming composition.

[0075] After applying the third catalyst layer forming composition, the applied third catalyst layer forming composition may be dried. The drying method is not particularly limited, and known drying methods 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.

[0076] (Thermocompression bonding process) In the thermocompression bonding process, a transfer substrate is placed on the electrolyte membrane on which the first catalyst layer and the second catalyst layer are formed, so that the electrolyte membrane and the third catalyst layer are in contact, and thermocompression bonding is performed between the electrolyte membrane and the transfer substrate. As a result, the temporary support, the third catalyst layer, the electrolyte membrane, the first catalyst layer, and the second catalyst layer are laminated in this order.

[0077] The thermocompression bonding process can be carried out using a known thermocompression bonding apparatus, for example, by pressing a heating element against the material or by sandwiching it between heating elements. Examples of heating elements include a heating plate, a heating block, and a heating roll. Alternatively, a laminator equipped with a pair of heating rolls may be used, and the material may be passed between the pair of rolls to perform the thermocompression bonding.

[0078] The temperature for heat sealing is preferably 80°C to 200°C, and more preferably 130°C to 180°C. The pressure for heat sealing is preferably 0.1 MPa to 5 MPa, and more preferably 0.5 MPa to 3 MPa.

[0079] (Temporary support removal process) The method for removing the temporary support is not particularly limited and can be carried out by a method that is generally known.

[0080] By peeling off the temporary support, a catalyst-layered electrolyte membrane is obtained in which the third catalyst layer, electrolyte membrane, first catalyst layer, and second catalyst layer are stacked in that order.

[0081] A step of heating the transfer substrate and electrolyte membrane may be included before the thermocompression bonding process. Heating the transfer substrate and electrolyte membrane softens the catalyst layer contained in the transfer substrate, improving adhesion to the electrolyte membrane. The means of heating the transfer substrate and electrolyte membrane are not particularly limited, and known heating methods can be used. The heating temperature of the transfer substrate is, for example, 50°C to 200°C. The heating temperature of the electrolyte membrane is, for example, 50°C to 150°C.

[0082] [Membrane Electrode Assembly] The membrane electrode assembly according to this disclosure includes an electrolyte membrane with a catalyst layer according to this disclosure. Specifically, the electrolyte membrane with a catalyst layer according to this disclosure preferably comprises an anode catalyst layer, an electrolyte membrane, and a cathode catalyst layer in this order, and the membrane electrode assembly according to this disclosure preferably comprises an anode gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode gas diffusion layer.

[0083] Examples of gas diffusion layers include porous carbon materials and porous metal materials. Examples of porous carbon materials include carbon paper, carbon cloth, carbon mesh, and nonwoven carbon fabric. Examples of porous metal materials include metal mesh, foamed metal, metal fabric, sintered metal, and nonwoven metal fabric. Examples of metals include titanium, aluminum, nickel, nickel-chromium alloys, copper and its alloys, silver, aluminum alloys, zinc alloys, lead alloys, titanium, niobium, tantalum, iron, stainless steel, gold, and platinum.

[0084] The membrane electrode assembly according to this disclosure includes an electrolyte membrane with a catalyst layer according to this disclosure, and therefore offers excellent productivity.

[0085] [Water electrolysis apparatus] The water electrolysis apparatus according to this disclosure includes a membrane electrode assembly according to this disclosure. In particular, the water electrolysis apparatus according to this disclosure is preferably a solid polymer type water electrolysis apparatus.

[0086] The present disclosure will be further explained below with reference to examples. The materials, amounts used, proportions, and details of each process shown in the following examples may be modified as appropriate, as long as they do not deviate from the spirit of this disclosure. Therefore, the scope of this disclosure is not limited to the specific examples shown below.

[0087] [Example 1] <First Catalyst Layer Formation Process> A first catalyst layer with a thickness of 50 nm was formed on an electrolyte membrane (product name "Nafion® N115", manufactured by DuPont, thickness 127 μm, 15 mm square) by sputtering. The first catalyst layer was an inorganic layer consisting of an iridium oxide layer. Film deposition target: Ir Film deposition pressure: 1.3 Pa Film deposition gas Ar: O ２ = 7:3 Deposition time: 100 seconds

[0088] <Second Catalyst Layer Formation Process> 3.96 g of iridium oxide (manufactured by Furuya Metals Co., Ltd.), 2.58 g of a 1:1 mixture of isopropyl alcohol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and methanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as dispersion solvents, and 4.5 g of 20% by mass Nafion® dispersion solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were weighed in a nitrogen-purged glove box and placed into a vial (solid content concentration 44% by mass, approximately 10% by volume). The turbid material removed from the glove box was stirred in a rotary homogenizer at 2000 rpm (revolutions per minute) for 30 minutes to obtain a dispersion, which was used as the composition for forming the second catalyst layer.

[0089] On the electrolyte membrane on which the first catalyst layer was formed, the areas of the electrolyte membrane other than the coated area were masked using the doctor blade method, and the composition for forming the second catalyst layer was applied and dried at 90°C for 10 minutes. As a result, the first and second catalyst layers were formed on the electrolyte membrane in that order. The second catalyst layer was an organic layer containing iridium oxide and resin. The thickness of the second catalyst layer was 2.5 μm. Furthermore, by performing SEM observation of the cross-section, it was confirmed that an intermediate layer was formed between the first and second catalyst layers.

[0090] <Third Catalyst Layer Formation Process> 6.17 g of platinum-supported carbon (manufactured by Tanaka Kikinzoku Co., Ltd.), 37.95 g of a 1:1 mixture of isopropyl alcohol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and methanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as dispersion solvents, and 18.35 g of 20% by mass Nafion® dispersion solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were weighed in a nitrogen-purged glove box and placed into vials. (Solid content concentration 16% by mass, approximately 7% by volume) The turbidity removed from the glove box was stirred in a rotary homogenizer at 2000 rpm (revolutions per minute) for 30 minutes to obtain a dispersion, which was used as the composition for forming the third catalyst layer.

[0091] A PTFE film (product name "Nitoflon No. 900 UL", manufactured by Nitto Denko Corporation, 50 μm thick, 1.5 cm x 1.5 cm) was used as a temporary support, onto which a composition for forming the third catalyst layer was applied using the doctor blade method and dried at 90°C for 10 minutes. This resulted in a transfer substrate with a 15 μm thick third catalyst layer formed on the temporary support. The solvent content in the third catalyst layer of the transfer substrate was 1% by mass.

[0092] A transfer substrate was placed on the electrolyte membrane, on which the first and second catalyst layers were formed, so that the electrolyte membrane and the third catalyst layer were in contact.

[0093] The electrolyte membrane and transfer substrate were preheated at 100°C for 3 minutes using a heating plate heated by a heater.

[0094] Using a thermal laminator, the electrolyte film and the transfer substrate were heat-pressed together at a temperature of 160°C and a press pressure of 1 MPa.

[0095] The temporary support was peeled off using an adhesive roll. This resulted in an electrolyte membrane with catalyst layers, in which the third catalyst layer, electrolyte membrane, first catalyst layer, and second catalyst layer were laminated in that order.

[0096] [Example 2] An electrolyte membrane with a catalyst layer was obtained in the same manner as in Example 1, except that the deposition pressure of the first catalyst layer was set to 0.2 Pa.

[0097] [Example 3] An electrolyte membrane with a catalyst layer was obtained in the same manner as in Example 1, except that the deposition pressure of the first catalyst layer was set to 1.5 Pa.

[0098] [Example 4] The film-forming gas for the first catalyst layer is Ar:O ２ An electrolyte membrane with a catalyst layer was obtained in the same manner as in Example 1, except that the ratio was set to 9:1.

[0099] [Example 5] The film-forming gas for the first catalyst layer is Ar:O ２ An electrolyte membrane with a catalyst layer was obtained in the same manner as in Example 1, except that the ratio was set to 6:4.

[0100] [Example 6] An electrolyte membrane with a catalyst layer was obtained in the same manner as in Example 1, except that the film formation time for the first catalyst layer was set to 30 seconds.

[0101] [Example 7] An electrolyte membrane with a catalyst layer was obtained in the same manner as in Example 1, except that the second catalyst layer was formed in the same manner as the third catalyst layer. Specifically, the composition for forming the second catalyst layer was applied to a temporary support using the doctor blade method and dried at 90°C for 10 minutes. This resulted in obtaining a transfer substrate on which a second catalyst layer with a thickness of 15 μm was formed on the temporary support. The transfer substrate was placed on the electrolyte membrane on which the first catalyst layer was formed so that the first catalyst layer and the second catalyst layer were in contact. The electrolyte membrane and the transfer substrate were heat-pressed together using a thermal laminator at a temperature of 160°C and a press pressure of 1 MPa. When the electrolyte membrane with a catalyst layer was observed in the same manner as in Example 1, it was confirmed that there was no intermediate layer between the first catalyst layer and the second catalyst layer.

[0102] [Example 8] A second catalyst layer with a thickness of 100 nm was formed on the electrolyte membrane on which the first catalyst layer was formed by sputtering in the same manner as in the first catalyst layer formation step. The second catalyst layer was an inorganic layer consisting of an iridium oxide layer. Film formation target: Ir Film formation pressure: 1.3 Pa Film formation gas Ar: O ２ = 7:3 Film formation time: 100 seconds When the electrolyte membrane with catalyst layer was observed in the same manner as in Example 1, it was confirmed that there was no intermediate layer between the first catalyst layer and the second catalyst layer.

[0103] [Comparative Example 1] An electrolyte membrane with a catalyst layer was obtained in the same manner as in Example 1, except that the formation of the first catalyst layer and the second catalyst layer was modified as follows. The first catalyst layer forming composition and the second catalyst layer forming composition were prepared without using a dispersion solvent, and furthermore, a 20% by mass Nafion® dispersion solution was heated to evaporate the solvent. The obtained first catalyst layer forming composition and the second catalyst layer forming composition had a solid content concentration of 50% by volume or more. The obtained first catalyst layer forming composition was applied to the electrolyte membrane and dried. The first catalyst layer was an organic layer containing iridium oxide and resin. The obtained second catalyst layer forming composition was applied to the first catalyst layer and dried. The second catalyst layer was an organic layer containing iridium oxide and resin. Furthermore, by performing SEM observation of the cross-section, it was confirmed that an intermediate layer was formed between the first catalyst layer and the second catalyst layer.

[0104] The porosity and surface resistivity of the first catalyst layer were measured. The measurement results are shown in Table 1.

[0105] The resulting electrolyte membrane with a catalyst layer was used to evaluate its adhesion and cracking properties.

[0106] <Adhesion> Cross-cut adhesion was evaluated in accordance with JIS-K5600-5-6. The evaluation criteria were as follows: A: No peeling occurred. B: Some peeling occurred, but it was less than 5% of the total area. C: Peeling occurred in more than 5% of the total area.

[0107] <Cracks> A surface-emitting light source was placed beneath the electrolyte membrane with a catalyst layer, and an image of the light intensity distribution was captured from above using a CCD camera (4K-CCD (resolution 30 μm)). If there was leakage of transmitted light, the light intensity in the obtained image was high. Leakage of transmitted light means that cracks have occurred in the electrolyte membrane with a catalyst layer. Therefore, the presence or absence of cracks was determined based on the high light intensity in the obtained image. The evaluation criteria were as follows: A: No cracks occurred. B: Cracks occurred.

[0108]

[0109] In the intermediate layer column in Table 1, "Y" indicates that an intermediate layer has been formed, and "N" indicates that an intermediate layer has not been formed.

[0110] As shown in Table 1, Examples 1 to 8 are provided with an electrolyte membrane, a first catalyst layer, and a second catalyst layer in this order. The first catalyst layer is an inorganic layer containing a metal catalyst, and the second catalyst layer is an inorganic or organic layer containing a metal catalyst. Since the metal catalyst contained in the first catalyst layer and the metal catalyst contained in the second catalyst layer contain elements of the same group, it was found that the adhesion between the electrolyte membrane and the catalyst layer is excellent.

[0111] Furthermore, the disclosure of Japanese Patent Application No. 2024-171065, filed on September 30, 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 noted to be incorporated by reference.

Claims

1. An electrolyte membrane with a catalyst layer comprising an electrolyte membrane, a first catalyst layer, and a second catalyst layer in this order, wherein the first catalyst layer is an inorganic layer containing a metal catalyst, the second catalyst layer is an inorganic or organic layer containing a metal catalyst, and the metal catalyst contained in the first catalyst layer and the metal catalyst contained in the second catalyst layer contain elements of the same group.

2. The electrolyte membrane with a catalyst layer according to claim 1, wherein the first catalyst layer has a porosity of 30% to 80%.

3. The electrolyte membrane with a catalyst layer according to claim 1, wherein the first catalyst layer has a surface resistivity of 0.2 Ω to 100 Ω.

4. The electrolyte membrane with a catalyst layer according to claim 1, wherein the thickness of the first catalyst layer is 30 nm or more.

5. The electrolyte membrane with a catalyst layer according to claim 1, wherein the first catalyst layer is a vapor-deposited film layer and the second catalyst layer is a coated layer.

6. The electrolyte membrane with a catalyst layer according to claim 1, further comprising an intermediate layer with a thickness of 5 nm or more between the first catalyst layer and the second catalyst layer.

7. The electrolyte membrane with catalyst layers according to claim 1, wherein both the first catalyst layer and the second catalyst layer contain platinum group elements.

8. The electrolyte membrane with a catalyst layer according to claim 6, wherein both the intermediate layer and the second catalyst layer contain an organic component, and the content of the organic component in the intermediate layer is less than the content of the organic component in the second catalyst layer.

9. The catalyst layer-equipped electrolyte membrane according to claim 6, wherein the intermediate layer contains the components contained in the first catalyst layer and the components contained in the second catalyst layer.

10. A method for producing an electrolyte membrane with a catalyst layer, comprising the steps of: forming a first catalyst layer on an electrolyte membrane using a vapor deposition method; and applying a composition for forming a second catalyst layer on the first catalyst layer to form a second catalyst layer.

11. A membrane electrode assembly comprising an electrolyte membrane with a catalyst layer according to any one of claims 1 to 9.

12. A water electrolysis apparatus comprising the membrane electrode assembly described in claim 11.

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