Laminate for water electrolysis device, membrane electrode assembly for water electrolysis device, and water electrolysis device

Abstract

Provided is a laminate for a water electrolysis device, the laminate including a polymer electrolyte membrane and an electrode catalyst layer provided on one surface of the polymer electrolyte membrane. The electrode catalyst layer contains a catalyst, a polymer electrolyte, and a fibrous material. The membrane electrode assembly for a water electrolysis device includes the aforementioned laminate for a water electrolysis device and a second electrode catalyst layer and includes the electrode catalyst layer, the polymer electrolyte membrane, and the second electrode catalyst layer in this order.

Description

Laminate for water electrolysis device, membrane electrode assembly for water electrolysis device, and water electrolysis device

[0001] The present disclosure relates to a laminate for a water electrolysis device, a membrane electrode assembly for a water electrolysis device, and a water electrolysis device.

[0002] In recent years, CO2 that can be produced from various resources has been used to achieve carbon neutrality. ２ The movement to utilize hydrogen as a free energy source as a primary energy source is accelerating. As a method for producing such hydrogen, a method of electrolyzing water using renewable energy is considered promising. Generally, alkaline water electrolysis and polymer electrolyte membrane (PEM) water electrolysis are known as methods for electrolyzing water. PEM water electrolysis in particular has attracted attention as a method that enables the miniaturization of water electrolysis equipment through highly efficient operation.

[0003] A PEM water electrolysis device generally includes a pair of main electrodes and a membrane electrode assembly provided between the pair of main electrodes. The membrane electrode assembly includes a stacked body in which a first electrode catalyst layer is provided on one surface of a proton-conductive solid polymer electrolyte membrane, and a second electrode catalyst layer provided so as to sandwich the solid polymer electrolyte membrane together with the first electrode catalyst layer.

[0004] The laminate is obtained by forming an electrode catalyst layer on one surface of a solid polymer electrolyte membrane, for example, by a coating method (see, for example, Patent Document 1 listed below).

[0005] Japanese Patent Application Laid-Open No. 2019-83085

[0006] However, the laminate described in Patent Document 1 may have cracks in the electrode catalyst layer, and there is room for improvement in terms of suppressing crack occurrence.

[0007] The present disclosure has been made in view of the above-described problems, and aims to provide a laminate for a water electrolysis device, a membrane electrode assembly for a water electrolysis device, and a water electrolysis device that can suppress the occurrence of cracks in an electrode catalyst layer.

[0008] The present inventors have conducted studies to solve the above-mentioned problems. First, when a composition for forming an electrode catalyst layer is applied to the surface of a solid polymer electrolyte membrane using a coating method, the solid polymer electrolyte membrane swells due to the penetration of moisture in the composition for forming an electrode catalyst layer. They suspected that excessive stress would be applied to the electrode catalyst layer due to the subsequent release of moisture when the solid polymer electrolyte membrane was dried, which could result in cracks in the electrode catalyst layer. As a result of further intensive research, the present inventors discovered that the above-mentioned problems could be solved by including a fibrous material in the electrode catalyst layer in addition to the catalyst and polymer electrolyte, leading to the present disclosure.

[0009] That is, a first aspect of the present disclosure provides a laminate for a water electrolysis apparatus, the laminate including a polymer electrolyte membrane and an electrode catalyst layer provided on one surface of the polymer electrolyte membrane, wherein the electrode catalyst layer contains a catalyst, a polymer electrolyte, and a fibrous material.

[0010] The laminate for a water electrolysis apparatus according to the present disclosure can suppress the occurrence of cracks in the electrode catalyst layer, thereby suppressing the disturbance of the potential distribution in the electrode catalyst layer when a voltage is applied to a membrane electrode assembly having the laminate in a water electrolysis apparatus, thereby suppressing a decrease in the water electrolysis performance of the water electrolysis apparatus and improving the durability of the water electrolysis apparatus.

[0011] The reason why the above-described laminate for a water electrolysis apparatus suppresses cracking in the electrode catalyst layer is believed to be as follows. Specifically, when the electrode catalyst layer is formed on one side of a polymer electrolyte membrane, the polymer electrolyte membrane swells due to the infiltration of moisture. Then, when the polymer electrolyte membrane is dried, the polymer electrolyte membrane shrinks due to the discharge of moisture, causing the electrode catalyst layer to shrink and applying excessive stress to the electrode catalyst layer. However, even if the electrode catalyst layer contains, in addition to the catalyst and polymer electrolyte, a fibrous material that is appropriately entangled with the catalyst and polymer electrolyte, disperses the stress. This is believed to be why cracking in the electrode catalyst layer is suppressed. Furthermore, when a voltage is applied to a membrane-electrode assembly including the laminate of the present disclosure for water electrolysis, oxygen gas or hydrogen gas generated in the electrode catalyst layer may cause localized excessive stress. Even in this case, the fibrous material contained in the electrode catalyst layer disperses such excessive stress. This is believed to be why cracking in the electrode catalyst layer is suppressed.

[0012] A second aspect of the present disclosure provides the laminate for a water electrolysis apparatus according to the first aspect, wherein the average fiber diameter of the fibrous material is in the range of 100 nm or more and 1 μm or less.

[0013] The laminate for a water electrolysis device further suppresses the occurrence of cracks in the electrode catalyst layer. The laminate for a water electrolysis device also improves the adhesion between the polymer electrolyte membrane and the electrode catalyst layer. This suppresses the occurrence of voids due to peeling between the polymer electrolyte membrane and the electrode catalyst layer, and further suppresses an increase in the resistance of the laminate due to these voids. From the above, the laminate for a water electrolysis device further suppresses a decrease in water electrolysis performance.

[0014] The reason why the laminate for a water electrolysis system can improve the adhesion between the polymer electrolyte membrane and the electrode catalyst layer is believed to be as follows: The stress applied to the electrode catalyst layer is effectively dispersed by the fibrous material, which makes it possible to reduce the shear force at the interface between the electrode catalyst layer and the polymer electrolyte membrane.

[0015] A third aspect of the present disclosure provides the laminate for a water electrolysis apparatus according to the first or second aspect, wherein the fibrous material is a material having the property of adsorbing the polymer electrolyte.

[0016] The above-described laminate for a water electrolysis apparatus further suppresses the occurrence of cracks in the electrode catalyst layer.

[0017] The reason why the above effect is obtained is thought to be as follows: The strength of the electrode catalyst layer is further increased by the fibrous material being adsorbed onto the polymer electrolyte.

[0018] A fourth aspect of the present disclosure provides a laminate for a water electrolysis apparatus according to any one of the first to third aspects, wherein the fibrous material includes at least one of carbon fiber and polymer fiber. In the laminate for a water electrolysis apparatus, the fibrous material makes the electrode catalyst layer less susceptible to cracking, thereby increasing the durability of the electrode catalyst layer.

[0019] A fifth aspect of the present disclosure provides the laminate for a water electrolysis device of the fourth aspect, wherein the polymer fibers have cation exchange groups.A sixth aspect of the present disclosure provides the laminate for a water electrolysis device of the fifth aspect, wherein the polymer electrolyte contained in the electrode catalyst layer is an ionomer.The laminate for a water electrolysis device has high proton conductivity due to a linear proton conductive network formed on the polymer fibers.Furthermore, since the polymer fibers have cation exchange groups, these cation exchange groups can ionic bond with the polymer electrolyte to strongly adsorb the polymer electrolyte, thereby further increasing the adhesion between the polymer fibers and the polymer electrolyte.Furthermore, since the polymer electrolyte adsorbed on the polymer fibers is an ionomer, a proton conductive path is formed by the ionomer, resulting in high water electrolysis performance in the water electrolysis device.

[0020] A seventh aspect of the present disclosure provides the laminate for a water electrolysis apparatus according to the fourth aspect, wherein the polymer fibers have proton conductivity. The laminate for a water electrolysis apparatus has proton conduction paths formed in the polymer fibers, improving proton conductivity in the electrode catalyst layer and imparting high electrolysis performance to the water electrolysis apparatus.

[0021] An eighth aspect of the present disclosure provides the laminate for a water electrolysis apparatus of the fourth aspect, wherein the electrode catalyst layer includes aggregates of the polymer fibers, the polymer fibers having an average fiber length of more than 20 μm, and voids surrounding the aggregates having a size of 20 μm or less. In this case, since the voids in the electrode catalyst layer are small, the occurrence of cracks in the electrode catalyst layer can be more sufficiently suppressed, and deterioration of water electrolysis performance can be suppressed.

[0022] A ninth aspect of the present disclosure provides the laminate for a water electrolysis apparatus according to the fourth aspect, wherein the electrode catalyst layer includes aggregates of the polymer fibers, the polymer fibers having an average fiber length of 20 μm or less, and the size of voids surrounding the aggregates is equal to or less than the average fiber length of the polymer fibers. In this case, since the voids in the electrode catalyst layer are small, the occurrence of cracks in the electrode catalyst layer can be more sufficiently suppressed, and as a result, deterioration of water splitting performance can be suppressed.

[0023] A tenth aspect of the present disclosure provides the laminate for a water electrolysis device according to the first aspect, wherein the electrode catalyst layer is a cathode-side electrode catalyst layer, the catalyst is supported on a conductive support, the fibrous material is carbon fiber, and the amount of the fibrous material is within a range of 5 to 50 parts by mass per 100 parts by mass of the support. In this case, the amount of carbon fiber is preferably within a range of 5 to 20 parts by mass per 100 parts by mass of the support. By setting the amount of carbon fiber within this range, an entangled structure of the carbon fibers is suitably formed, thereby further increasing the strength of the electrode catalyst layer. This makes it less likely that cracks will occur, and the carbon fiber plays a role in favorably supporting electronic conductivity within the electrode catalyst layer, resulting in good electrolysis performance.

[0024] An eleventh aspect of the present disclosure provides the laminate for a water electrolysis device according to the first aspect, wherein the electrode catalyst layer is a cathode-side electrode catalyst layer, the catalyst is supported on a conductive support, the fibrous material is polymeric fiber, and the amount of the fibrous material is within a range of 5 to 20 parts by mass per 100 parts by mass of the support. In this case, the amount of the polymeric fiber is preferably within a range of 5 to 20 parts by mass per 100 parts by mass of the support. By setting the amount of the polymeric fiber within this range, an entangled structure of the polymeric fibers is suitably formed, thereby further increasing the strength of the electrode catalyst layer. This makes it less likely that cracks will occur, and the polymeric fiber plays a role in favorably supporting electronic conductivity within the electrode catalyst layer, resulting in good electrolysis performance.

[0025] A twelfth aspect of the present disclosure provides the laminate for a water electrolysis apparatus according to the tenth or eleventh aspect, in which the carrier is carbon particles.

[0026] A thirteenth aspect of the present disclosure provides a water electrolysis device including a membrane electrode assembly and a pair of main electrodes disposed so as to sandwich the membrane electrode assembly, wherein the membrane electrode assembly has a laminate for a water electrolysis device on any one of the first to twelfth aspects, and a second electrode catalyst layer disposed on a surface of the polymer electrolyte membrane of the laminate for a water electrolysis device opposite to the electrode catalyst layer.

[0027] The water electrolysis device of the present disclosure includes the above-described laminate for a water electrolysis device, and therefore the occurrence of cracks in the electrode catalyst layer of the laminate is suppressed, thereby suppressing disturbance of the potential distribution in the electrode catalyst layer of the laminate included in the membrane electrode assembly when a voltage is applied between the pair of main electrodes, thereby suppressing deterioration of water electrolysis performance and improving durability.

[0028] Furthermore, even if a voltage is applied between a pair of main electrodes for water electrolysis, which in turn applies a voltage to the laminate included in the membrane electrode assembly and causes excessive stress in localized areas due to oxygen gas or hydrogen gas generated in the electrode catalyst layer, the fibrous material contained in the electrode catalyst layer is thought to disperse such excessive stress. This is thought to prevent cracks from occurring in the electrode catalyst layer. Therefore, this is also thought to improve the durability of the water electrolysis device.

[0029]

[0016] A fourteenth aspect of the present disclosure provides a membrane electrode assembly for a water electrolysis device, comprising the laminate for a water electrolysis device of the first aspect and a second electrode catalyst layer, the membrane electrode assembly comprising the electrode catalyst layer, the polymer electrolyte membrane, and the second electrode catalyst layer in this order, the second electrode catalyst layer being a cathode-side electrode catalyst layer, the electrode catalyst layer being an anode-side electrode catalyst layer, and the membrane electrode assembly for a water electrolysis device comprising a catalyst-containing material containing the catalyst, the polymer electrolyte, and the fibrous material. The membrane electrode assembly for a water electrolysis device can suppress the occurrence of cracks in the anode-side electrode catalyst layer. Therefore, the membrane electrode assembly of the present disclosure suppresses disturbance of the potential distribution in the anode-side electrode catalyst layer when a voltage is applied in the water electrolysis device, suppresses a deterioration in the water electrolysis performance of the water electrolysis device, and improves the durability of the water electrolysis device.

[0030] The reason why the above-described membrane electrode assembly for a water electrolysis system suppresses cracking in the anode-side electrode catalyst layer is believed to be as follows. Specifically, when the anode-side electrode catalyst layer is formed on one side of a polymer electrolyte membrane, the polymer electrolyte membrane swells due to moisture penetration. Then, when the polymer electrolyte membrane is dried, the polymer electrolyte membrane shrinks due to the discharge of moisture, which causes the anode-side electrode catalyst layer to shrink and apply excessive stress to the anode-side electrode catalyst layer. However, even if the anode-side electrode catalyst layer contains a fibrous material in addition to a catalyst-containing material and a polymer electrolyte, and the fibrous material is appropriately entangled, the stress is dispersed by the fibrous material. This is believed to be why cracking in the anode-side electrode catalyst layer is suppressed. Furthermore, when a voltage is applied to the membrane electrode assembly of the present disclosure for water electrolysis, oxygen gas generated in the anode-side electrode catalyst layer may locally generate excessive stress. Even in this case, the fibrous material contained in the anode-side electrode catalyst layer disperses such excessive stress. This is believed to be why cracking in the anode-side electrode catalyst layer is suppressed.

[0031] A fifteenth aspect of the present disclosure provides the membrane electrode assembly for a water electrolysis device of the fourteenth aspect, wherein the cathode-side electrode catalyst layer includes a catalyst-containing material, a polymer electrolyte, and a fibrous material. The membrane electrode assembly for a water electrolysis device can also suppress the occurrence of cracks in the cathode-side electrode catalyst layer. Therefore, the membrane electrode assembly of the present disclosure also suppresses the disturbance of the potential distribution in the cathode-side electrode catalyst layer when a voltage is applied to the water electrolysis device, thereby further suppressing a decrease in the water electrolysis performance of the water electrolysis device and further improving the durability of the water electrolysis device.

[0032] A sixteenth aspect of the present disclosure provides the membrane electrode assembly for a water electrolysis system of the fifteenth aspect, wherein the fibrous material of the cathode-side electrode catalyst layer includes at least one of carbon fiber and polymer fiber, and the fibrous material of the anode-side electrode catalyst layer includes polymer fiber. With the membrane electrode assembly for a water electrolysis system, cracks are particularly unlikely to occur in the cathode-side electrode catalyst layer and the anode-side electrode catalyst layer, and durability is likely to be high.

[0033] A seventeenth aspect of the present disclosure provides the membrane electrode assembly for a water electrolysis system of the sixteenth aspect, wherein the polymer fibers have proton conductivity. With this membrane electrode assembly for a water electrolysis system, in the electrode catalyst layer containing the proton-conducting polymer fibers, of the cathode-side electrode catalyst layer and the anode-side electrode catalyst layer, a linear proton-conducting network is formed, thereby increasing proton conductivity, thereby improving proton conductivity. As a result, voltage loss during water electrolysis in the water electrolysis system can be suppressed.

[0034] An eighteenth aspect of the present disclosure provides the membrane electrode assembly for a water electrolysis device of the sixteenth aspect, wherein the polymer fibers have cation exchange groups. A nineteenth aspect of the present disclosure provides the laminate for a water electrolysis device of the fifth aspect, wherein the polymer electrolyte included in the electrode catalyst layer is an ionomer. The membrane electrode assembly for a water electrolysis device has high proton conductivity due to a linear proton conductive network formed on the polymer fibers. Furthermore, since the polymer fibers have cation exchange groups, the cation exchange groups ionic bond with the polymer electrolyte, allowing the polymer electrolyte to be strongly adsorbed, thereby further enhancing adhesion between the polymer fibers and the polymer electrolyte. Furthermore, since the polymer electrolyte adsorbed on the polymer fibers is an ionomer, a proton conduction path is formed by the ionomer, resulting in high water electrolysis performance in the water electrolysis device.

[0035] A twentieth aspect of the present disclosure provides the membrane electrode assembly for a water electrolysis system according to any one of the fifteenth to nineteenth aspects, wherein the fibrous material in the cathode-side electrode catalyst layer is carbon fiber, the average fiber diameter of the fibrous material is in the range of 50 nm to 300 nm, and the average fiber length of the fibrous material is in the range of 1.0 μm to 20 μm. With the membrane electrode assembly for a water electrolysis system, an entangled structure of the fibrous material is suitably formed in the cathode-side electrode catalyst layer, thereby further increasing the strength of the cathode-side electrode catalyst layer and further suppressing the occurrence of cracks.

[0036] A twenty-first aspect of the present disclosure provides the membrane electrode assembly for a water electrolysis system according to any one of the fifteenth to twentieth aspects, wherein the fibrous material in the cathode-side electrode catalyst layer is polymeric fiber, the average fiber diameter of the fibrous material is in the range of 100 nm to 500 nm, and the average fiber length of the fibrous material is in the range of 1.0 μm to 40 μm. With the membrane electrode assembly for a water electrolysis system, an entangled structure of the fibrous material is suitably formed in the cathode-side electrode catalyst layer, thereby further increasing the strength of the cathode-side electrode catalyst layer and further suppressing the occurrence of cracks.

[0037] A twenty-second aspect of the present disclosure provides a membrane electrode assembly for a water electrolysis system according to any one of the fourteenth to twenty-first aspects, wherein the fibrous material in the anode-side electrode catalyst layer has an average fiber diameter in the range of 100 nm to 500 nm and an average fiber length in the range of 1.0 μm to 40 μm. With this membrane electrode assembly for a water electrolysis system, an entangled structure of the fibrous material is suitably formed in the anode-side electrode catalyst layer, thereby further increasing the strength of the anode-side electrode catalyst layer and further suppressing the occurrence of cracks.

[0038] A twenty-third aspect of the present disclosure provides the membrane electrode assembly for a water electrolysis system according to any one of the fifteenth to twenty-first aspects, wherein the catalyst-containing material in the cathode-side electrode catalyst layer is a catalyst-supported particle having a catalyst and a support that supports the catalyst, the fibrous material in the cathode-side electrode catalyst layer is carbon fiber, and the blending amount of the fibrous material is within a range of 0.3 to 1.5 times the mass of the support. In the membrane electrode assembly for a water electrolysis system, a structure in which the carbon fibers are entangled is suitably formed in the cathode-side electrode catalyst layer, thereby further increasing the strength of the cathode-side electrode catalyst layer and further suppressing the occurrence of cracks.

[0039] A twenty-fourth aspect of the present disclosure provides the membrane electrode assembly for a water electrolysis system of any of the fifteenth to twenty-first and twenty-third aspects, wherein the catalyst-containing material in the cathode-side electrode catalyst layer is a catalyst-supported particle having a catalyst and a support that supports the catalyst, the fibrous material in the cathode-side electrode catalyst layer is a polymer fiber, and the blending amount of the fibrous material is in the range of 0.05 to 0.3 times the mass of the support. With the membrane electrode assembly for a water electrolysis system, a structure in which carbon fibers are entangled is suitably formed in the cathode-side electrode catalyst layer, thereby further increasing the strength of the cathode-side electrode catalyst layer and further suppressing the occurrence of cracks.

[0040] A twenty-fifth aspect of the present disclosure provides the membrane electrode assembly for a water electrolysis system according to any one of the fourteenth to twenty-fourth aspects, wherein the content of the fibrous material in the anode-side electrode catalyst layer is in the range of 0.5 mass % to 20 mass %. In the membrane electrode assembly for a water electrolysis system, the amount of the fibrous material is suitable for inclusion in the anode-side electrode catalyst layer, and an entangled structure of the fibrous material is suitably formed, thereby further increasing the strength of the anode-side electrode catalyst layer and further suppressing the occurrence of cracks.

[0041] A twenty-sixth aspect of the present disclosure provides the membrane electrode assembly for a water electrolysis system according to any one of the fifteenth to twenty-fourth aspects, wherein a ratio R(DF1 / DF2) of the content of the fibrous material in the cathode-side electrode catalyst layer (DF1) to the content of the fibrous material in the anode-side electrode catalyst layer (DF2) is greater than 1. The membrane electrode assembly for a water electrolysis system further increases the strength of the anode-side electrode catalyst layer, and can further suppress deformation and cracking of the polymer electrolyte membrane when the anode-side electrode catalyst layer is formed after the cathode-side electrode catalyst layer is formed.

[0042] A twenty-seventh aspect of the present disclosure provides the membrane electrode assembly for a water electrolysis system of the twenty-sixth aspect, wherein the fibrous material in the cathode-side electrode catalyst layer is carbon fiber, and the ratio R is 5 to 30. In the membrane electrode assembly for a water electrolysis system, the ratio R being within the above range further enhances the strength of the anode-side electrode catalyst layer, and further suppresses deformation and cracking of the polymer electrolyte membrane when the anode-side electrode catalyst layer is formed after the cathode-side electrode catalyst layer is formed.

[0043] A twenty-eighth aspect of the present disclosure provides the membrane electrode assembly for a water electrolysis system of the twenty-sixth aspect, wherein the fibrous material in the cathode-side electrode catalyst layer is polymer fiber, and the ratio R is 1.1 to 15. In the membrane electrode assembly for a water electrolysis system, the ratio R being within the above range further enhances the strength of the anode-side electrode catalyst layer, and further suppresses deformation and cracking of the polymer electrolyte membrane when the anode-side electrode catalyst layer is formed after the cathode-side electrode catalyst layer is formed.

[0044] A twenty-ninth aspect of the present disclosure provides the membrane electrode assembly for a water electrolysis system according to any one of the fourteenth to twenty-eighth aspects, wherein in at least one of the cathode-side electrode catalyst layer and the anode-side electrode catalyst layer, the polymer electrolyte is an ionomer, and the fibrous material is an ionomer-adsorbed fiber having a property of adsorbing the ionomer. The membrane electrode assembly for a water electrolysis system increases the strength of the electrode catalyst layer in which the polymer electrolyte is an ionomer and the fibrous material is an ionomer-adsorbed fiber having a property of adsorbing the ionomer, and a water electrolysis system including the membrane electrode assembly can achieve high water electrolysis performance.

[0045] A thirtieth aspect of the present disclosure provides a water electrolysis device including a cathode, a membrane electrode assembly, and an anode, in this order, where the membrane electrode assembly is the membrane electrode assembly for a water electrolysis device of any one of the fourteenth to twenty-ninth aspects. The water electrolysis device of the present disclosure includes the above-described membrane electrode assembly for a water electrolysis device, and therefore, according to the water electrolysis device of the present disclosure, the occurrence of cracks in the anode-side electrode catalyst layer in the membrane electrode assembly is suppressed. Therefore, when a voltage is applied between the cathode and the anode, the potential distribution in the electrode catalyst layer included in the membrane electrode assembly is suppressed from being disturbed, thereby suppressing a decrease in water electrolysis performance and improving durability.

[0046] Furthermore, even if a voltage is applied between the cathode and anode for water electrolysis, thereby applying a voltage to the membrane electrode assembly and generating oxygen gas in the electrode catalyst layer, causing localized excessive stress, the fibrous material contained in the electrode catalyst layer is thought to disperse such excessive stress. This is thought to prevent cracks from occurring in the electrode catalyst layer. Therefore, this is also thought to improve the durability of the water electrolysis device.

[0047] According to the present disclosure, there are provided a laminate for a water electrolysis device, a membrane electrode assembly for a water electrolysis device, and a water electrolysis device that can suppress the occurrence of cracks in an electrode catalyst layer.

[0048] Fig. 4 is a cross-sectional view showing an embodiment of a laminate for a water electrolysis device according to the present disclosure. Fig. 5 is a cross-sectional view showing, in part and schematically, a main portion of the electrode catalyst layer of Fig. 1. Fig. 6 is a cross-sectional view showing an example of a catalyst-containing material of Fig. 2. Fig. 7 is a cross-sectional view showing an embodiment of a membrane electrode assembly for a water electrolysis device according to the present disclosure. Fig. 8 is a cross-sectional view showing, in part and schematically, a main portion of the second electrode catalyst layer of Fig. 4. Fig. 9 is a cross-sectional view showing an embodiment of a water electrolysis device according to the present disclosure. Fig. 10 is a cross-sectional view showing, in part and specifically, another example of the electrode catalyst layer of Fig. 1.

[0049] Hereinafter, embodiments of the present disclosure will be described in detail.

[0050] <Laminate for water electrolysis apparatus> First, one embodiment of a laminate for a water electrolysis apparatus according to the present disclosure will be described with reference to Figures 1 and 2. Figure 1 is a cross-sectional view showing one embodiment of a laminate for a water electrolysis apparatus according to the present disclosure, Figure 2 is a schematic and partial view of an example of an electrode catalyst layer in Figure 1, and Figure 3 is a cross-sectional view of an example of a catalyst-containing material in Figure 2.

[0051] 1 , a laminate 100 for a water electrolysis apparatus (hereinafter simply referred to as "laminate") includes a polymer electrolyte membrane 10 and an electrode catalyst layer 20 provided on one surface of the polymer electrolyte membrane 10. The electrode catalyst layer 20 includes a catalyst-containing material 21, a polymer electrolyte 22, and a fibrous material 23 (see FIG. 2 ). In this embodiment, the electrode catalyst layer 20 will be described as an electrode catalyst layer (cathode-side electrode catalyst layer) disposed on the cathode (reducing electrode) side.

[0052] According to the laminate 100, the electrode catalyst layer 20 contains the catalyst-containing material 21, the polymer electrolyte 22, and the fibrous material 23, and therefore it is possible to suppress the occurrence of cracks in the electrode catalyst layer 20. Therefore, when a voltage is applied to a membrane electrode assembly having the laminate 100 in a water electrolysis device, the potential distribution in the electrode catalyst layer 20 is suppressed from being disturbed, and it is possible to suppress a decrease in the water electrolysis performance of the water electrolysis device and improve the durability of the water electrolysis device.

[0053] The polymer electrolyte membrane 10 and the electrode catalyst layer 20 will be described in more detail below.

[0054] (Polymer Electrolyte Membrane) The polymer electrolyte membrane 10 is made of a polymer material having proton conductivity. Specific examples of such a polymer electrolyte membrane 10 include a fluorine-based polymer electrolyte membrane and a hydrocarbon-based polymer electrolyte membrane. Examples of fluorine-based polymer electrolyte membranes that can be used include Nafion (registered trademark) manufactured by DuPont, Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., Aciplex (registered trademark) manufactured by Asahi Kasei Corporation, and Gore Select (registered trademark) manufactured by Gore. Examples of hydrocarbon-based polymer electrolyte membranes that can be used include polymer electrolyte membranes such as sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, and sulfonated polyphenylene.

[0055] The thickness of the polymer electrolyte membrane 10 is not particularly limited, but is typically 20 to 250 μm, and preferably 20 to 80 μm. When the thickness of the polymer electrolyte membrane 10 is within this range, the mechanical durability of the polymer electrolyte membrane 10 can be maintained, and the proton resistance can be reduced, thereby improving the electrolysis performance. In other words, when the thickness of the polymer electrolyte membrane 10 is within this range, both the mechanical durability and high proton conductivity of the polymer electrolyte membrane 10 can be achieved, and the water electrolysis performance of the water electrolysis device can be improved.

[0056] (Electrode catalyst layer) The electrode catalyst layer 20 is an electrode catalyst layer disposed on the cathode side. The electrode catalyst layer 20 includes a catalyst-containing material 21, a polymer electrolyte 22, and a fibrous material 23.

[0057] (1) Catalyst-Containing Material The catalyst-containing material 21 contains a catalyst (hereinafter also referred to as "cathode catalyst") that undergoes a reduction reaction with protons. Examples of such cathode catalysts include metals in the platinum group, metals other than the platinum group, and alloys, oxides, and double oxides of these metals. Examples of metals in the platinum group include platinum, palladium, ruthenium, iridium, rhodium, and osmium. Examples of metals other than the platinum group include iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. Note that the term "double oxide" refers to an oxide containing two types of metals. The cathode catalyst is preferably composed of a metal in the platinum group. When the cathode catalyst is one or more metals selected from platinum, gold, palladium, rhodium, ruthenium, and iridium, it exhibits high activity, resulting in excellent electrode reactivity and enabling efficient and stable electrode reactions.

[0058] The catalyst is usually in particulate form. The average particle size of the particulate catalyst is preferably 20 nm or less, more preferably 5 nm or less. In this case, the activity of the catalyst is further improved. Furthermore, from the viewpoint of the stability of the catalyst activity, the average particle size of the particulate catalyst is preferably 0.5 nm or more, more preferably 1 nm or more.

[0059] 3, the catalyst-containing material 21 may further include, in addition to the catalyst 21a, a conductive support 21b that supports the catalyst 21a. That is, the catalyst-containing material 21 may be a catalyst-supporting particle. The support 21b may be any material that is conductive and can support the catalyst 21a without being eroded by the catalyst 21a. Carbon particles are preferably used as such a support 21b because they exhibit high electronic conductivity.

[0060] The carbon particles are not limited as long as they are fine particles, conductive, and not eroded by the catalyst 21a. Examples of the carbon particles that can be used include carbon black, graphite, activated carbon, carbon fiber, carbon nanotubes, and fullerene. The carbon black is at least one selected from the group consisting of acetylene black, furnace black, and ketjen black.

[0061] The average particle size of the carbon particles is preferably 10 nm or more. In this case, an electron conduction path is more easily formed in the electrode catalyst layer 20. Furthermore, from the viewpoint of reducing the resistance value of the electrode catalyst layer 20 and increasing the catalyst loading amount, the average particle size of the carbon particles is preferably within the range of 1,000 nm or less, and more preferably within the range of 100 nm or less. Here, the average particle size is the arithmetic mean value of the particle sizes of at least 20 carbon particles observed with a scanning electron microscope (SEM), and the particle size refers to the diameter when a carbon particle is approximated as a circle, and is determined by calculating the diameter when the cross-sectional area of ​​the carbon particle is taken as the area of ​​the circle.

[0062] The carrier 21b may be covered with a hydrophobic coating. The hydrophobic coating imparts hydrophobic properties to the carrier 21b and has gas permeability that allows hydrogen gas to pass through. From the viewpoint of improving gas permeability, the thickness of the hydrophobic coating is preferably 40 nm or less. From the viewpoint of improving the ability to discharge excess water, the thickness of the hydrophobic coating is preferably 2 nm or more.

[0063] An example of a material for the hydrophobic coating is a fluorine-based compound having at least one polar group. The polar group may be at least one selected from the group consisting of a hydroxyl group, an alkoxy group, a carboxyl group, an ester group, an ether group, a carbonate group, and an amide group. A hydrophobic coating having a polar group is easily fixed to the outermost surface of the support 21b. An example of the moiety other than the polar group in the fluorine-based compound is a fluoroalkyl skeleton.

[0064] (2) Polymer Electrolyte The polymer electrolyte 22 may be a proton-conductive polymer electrolyte. Specific examples of the polymer electrolyte 22 include fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes. Examples of fluorine-based polymer electrolytes include Nafion® materials manufactured by DuPont. Examples of hydrocarbon-based polymer electrolytes include sulfonated polyetherketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene. The polymer electrolyte 22 may be the same polymer electrolyte as the polymer electrolyte membrane 10, or may be a different polymer electrolyte from the polymer electrolyte membrane 10. However, considering the interfacial resistance at the interface between the polymer electrolyte membrane 10 and the electrode catalyst layer 20 and the dimensional change rate of the polymer electrolyte membrane 10 and the electrode catalyst layer 20 when humidity changes, it is preferable that the polymer electrolyte contained in the polymer electrolyte membrane 10 and the polymer electrolyte 22 contained in the electrode catalyst layer 20 be the same electrolyte or polymer electrolytes with similar thermal expansion coefficients.

[0065] For example, when increasing the adhesion between the electrode catalyst layer 20 and the polymer electrolyte membrane 10, if the constituent material of the polymer electrolyte 22 is a fluorine-based polymer electrolyte, it is preferable that the constituent material of the polymer electrolyte membrane 10 is also a fluorine-based polymer electrolyte. Also, if the constituent material of the polymer electrolyte 22 is a hydrocarbon-based polymer electrolyte, it is preferable that the constituent material of the polymer electrolyte membrane 10 is also a hydrocarbon-based polymer electrolyte.

[0066] (3) Fibrous Material The fibrous material 23 may be any material that is not corroded by the catalyst 21 a and the polymer electrolyte 22, and is preferably carbon fiber, polymer fiber, or a mixture thereof. The fibrous material 23 makes it difficult for cracks to occur in the electrode catalyst layer 20, and increases the durability of the electrode catalyst layer 20.

[0067] The fibrous material 23 may contain Lewis acidic or Lewis basic functional groups in its molecular structure. This facilitates the presence of the polymer electrolyte 22 in the vicinity of the fibrous material 23. Examples of the fibrous material 23 having Lewis acidic functional groups include carbon fiber and polymer fibers having hydroxyl groups, carbonyl groups, sulfonic acid groups, and phosphorous groups. Examples of the fibrous material 23 having Lewis basic functional groups include polymer fibers having imide structures or azole structures. Proton-conducting moieties, such as sulfonyl groups, contained in the polymer electrolyte 22 hydrogen bond with the Lewis acidic functional groups in the fibrous material 23, thereby facilitating the presence of the polymer electrolyte 22 in the vicinity of the fibrous material 23. On the other hand, if the fibrous material 23 contains basic functional groups, acidic proton-conducting moieties, such as sulfonyl groups, contained in the polymer electrolyte 22 bond via acid-base bonding, thereby facilitating the presence of the polymer electrolyte 22 in the vicinity of the fibrous material 23. Because acid-base bonds have a stronger bonding strength than hydrogen bonds, the fibrous material 23 preferably contains Lewis basic functional groups. Among these, it is preferable that the fibrous material 23 has an azole structure. An azole structure is a five-membered heterocyclic structure containing one or more nitrogen atoms, such as an imidazole structure or an oxazole structure. It is preferable that the material containing a nitrogen atom has a benzoazole structure such as a benzimidazole structure or a benzoxazole structure. Specific examples of materials containing a nitrogen atom include polymers such as polybenzimidazole and polybenzoxazole.

[0068] The shape of the fibrous material 23 is not particularly limited, and may be, for example, a hollow structure or a solid structure. The fibrous material 23 contained in the electrode catalyst layer 20 may be one of the above-mentioned examples, or a combination of two or more types.

[0069] The average fiber diameter of the fibrous material 23 is not particularly limited, but is preferably 100 nm or more and 1 μm or less, and more preferably 5 μm or more and 50 μm or less. In this case, the occurrence of cracks in the electrode catalyst layer 20 is further suppressed. The adhesion between the polymer electrolyte membrane 10 and the electrode catalyst layer 20 can also be improved. This can suppress the occurrence of voids due to peeling between the polymer electrolyte membrane 10 and the electrode catalyst layer 20, and further suppress the increase in resistance of the membrane electrode assembly due to these voids. From the above, the membrane electrode assembly can further suppress the deterioration of water electrolysis performance.

[0070] The average fiber diameter of the fibrous material 23 refers to the average value of diameters measured for the cross section of the exposed fibrous material 23 when the cross section of the electrode catalyst layer 20 is observed using a scanning electron microscope (SEM). When the fibrous material 23 is cut obliquely relative to its major axis, an elliptical cross section is obtained. In this case, the diameter refers to the diameter of a perfect circle fitted along the minor axis of the ellipse. Furthermore, when the cross section of the electrode catalyst layer 20 is observed using an SEM, the surface of the fibrous material 23 may be exposed rather than the cross section of the fibrous material 23. In this case, the diameter refers to the width of the fibers perpendicular to the major axis of the exposed fibrous material 23. The average fiber diameter of the fibrous material 23 refers to the arithmetic mean value of fiber diameters obtained by similar measurements at at least 20 observation points.

[0071] The average fiber diameter of the fibrous material 23 may be 10 nm or more and 1 μm or less, or 100 nm or more and 200 nm or less. When the average fiber diameter of the fibrous material 23 is within the above range, the occurrence of cracks in the electrode catalyst layer 20 is further suppressed. The adhesion between the polymer electrolyte membrane 10 and the electrode catalyst layer 20 can also be improved. This makes it possible to suppress the occurrence of voids due to peeling between the polymer electrolyte membrane 10 and the electrode catalyst layer 20, and further suppress an increase in the resistance of the membrane electrode assembly due to these voids. From the above, the laminate 100 and a membrane electrode assembly including the laminate 100 can further suppress a decrease in water electrolysis performance.

[0072] The cross section of the electrode catalyst layer 20 can be exposed by a known method such as ion milling or ultramicrotome.

[0073] The average fiber length of the fibrous material 23 is not particularly limited, but is preferably 500 nm or more, more preferably 1 μm or more. In this case, the fibrous material 23 becomes entangled, forming pores of appropriate size in the electrode catalyst layer 20 and improving the mechanical properties of the electrode catalyst layer 20. However, the average fiber length of the fibrous material 23 is preferably 100 μm or less, more preferably 40 μm or less. The average fiber length of the fibrous material 23 refers to the arithmetic mean value of the fiber lengths obtained by measuring the lengths of at least 10 fibrous material pieces 23. The average fiber length of the fibrous material 23 in the electrode catalyst layer 20 can be determined by performing particle size distribution measurement using a solution in which the electrode catalyst layer 20 is dissolved in a solvent. Specifically, the correlation between the average fiber length determined using an electron microscope and the peak position in the particle size distribution measurement is determined in advance, and the average fiber length of the fibrous material 23 in the electrode catalyst layer 20 is determined based on this correlation and the peak position determined by the particle size distribution measurement.

[0074] The fibrous material 23 may be a material that has the property of adsorbing the polymer electrolyte 22, or a material that does not have the property of adsorbing the polymer electrolyte 22, but is preferably a material that has the property of adsorbing the polymer electrolyte 22. In this case, when the fibrous material 23 is a material that adsorbs the polymer electrolyte 22, the occurrence of cracks in the electrode catalyst layer 20 is further suppressed. Note that the "substance that has the property of adsorbing the polymer electrolyte" refers to a material that can adsorb 10 mg or more of polymer electrolyte per 1 g of the fibrous material.

[0075] When the fibrous material 23 is carbon fiber, examples of the carbon fiber include carbon fiber, carbon nanotube, and carbon nanohorn. In particular, carbon nanofiber or carbon nanotube is suitable in terms of conductivity and dispersibility. The average fiber diameter of the carbon fiber is preferably 300 nm or less, and more preferably 200 nm or less. When the average fiber diameter of the carbon fiber is 300 nm or less, the appropriate fineness is ensured as a fiber material to be contained in the electrode catalyst layer 20. The average fiber diameter of the carbon fiber is preferably 50 nm or more, and more preferably 100 nm or more. In this case, the appropriate thickness of the carbon fiber is ensured, further increasing the strength of the electrode catalyst layer 20 and further suppressing the occurrence of cracks.

[0076] The average fiber length of the carbon fibers is preferably in the range of 1.0 μm to 20 μm. When the average fiber length of the carbon fibers is within this range, entanglement of the fibrous material 23 can form pores of appropriate size in the electrode catalyst layer 20, and the capillary force of the pores can balance the supply of reactants and the dissipation of product substances, thereby improving the water electrolysis performance of the water electrolysis device. Furthermore, when the average fiber length of the carbon fibers is within this range, the strength of the electrode catalyst layer 20 can be improved. In particular, when the average fiber diameter of the carbon fibers is in the range of 100 nm to 300 nm, the average fiber length of the carbon fibers is preferably in the range of 1.0 μm to 20 μm. In this case, an entangled structure of the fibrous material 23 is suitably formed in the electrode catalyst layer 20, thereby further increasing the strength of the electrode catalyst layer 20 and further suppressing the occurrence of cracks.

[0077] The amount of carbon fiber blended is preferably 10 parts by mass or more and 200 parts by mass or less, more preferably 20 parts by mass or more and 100 parts by mass or less, per 100 parts by mass of the catalyst. In this case, an entangled structure of the carbon fibers is suitably formed, thereby further increasing the strength of the electrode catalyst layer 20 and further suppressing the occurrence of cracks. When the catalyst-containing material 21 contains the support 21b, the amount of carbon fiber blended may be within a range of 30 parts by mass or more and 150 parts by mass or less, based on 100 parts by mass of the support 21b in the catalyst-containing material 21. In this case, an entangled structure of the carbon fibers is suitably formed in the electrode catalyst layer 20, thereby further increasing the strength of the electrode catalyst layer 20 and further suppressing the occurrence of cracks. In particular, the amount of carbon fiber blended is preferably within a range of 5 parts by mass or more and 50 parts by mass or less, per 100 parts by mass of the conductive support 21b. By setting the amount of carbon fiber blended within this range, an entangled structure of the carbon fibers is suitably formed, thereby further increasing the strength of the electrode catalyst layer 20. This makes it more difficult for cracks to occur, and the carbon fibers effectively support the electron conductivity in the electrode catalyst layer 20, thereby obtaining good electrolysis performance. The conductive support 1b is preferably carbon particles, which have good electron conductivity and are available at low cost.

[0078] When the fibrous material 23 is a polymer fiber, the polymer fiber may be an ionomer-adsorbed fiber, a conductive polymer nanofiber, or a proton-conductive polymer fiber.

[0079] The polymer fiber may be an ionomer-adsorbing fiber having a cation exchange group, such as a hydroxyl group, a carbonyl group, a sulfonic acid group, a phosphorous acid group, or an amino group.

[0080] The polymer fibers can be proton-conductive polymer fibers. In this case, proton conduction paths are formed in the polymer fibers, improving the proton conductivity in the electrode catalyst layer 20 and providing high electrolysis performance to the water electrolysis device. That is, the formation of a linear proton-conductive network in the electrode catalyst layer 20 increases the proton conductivity, thereby suppressing voltage loss during water electrolysis in the water electrolysis device. The proton-conductive polymer fibers can be polymer fibers obtained by processing a proton-conductive polymer into a fibrous form. Materials for forming the proton-conductive polymer fibers can include fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes.

[0081] Preferably, the polymer fiber is an ionomer-adsorbed fiber, and the polymer electrolyte is an ionomer. Here, the ionomer-adsorbed fiber is a fibrous material capable of adsorbing an ionomer as a polymer electrolyte. In this case, the strength of the electrode catalyst layer 20 is increased, and high water electrolysis performance is obtained in a water electrolysis device including a membrane electrode assembly having the laminate 100. The reasons for this are believed to be as follows: The entanglement of the ionomer-adsorbed fibers increases the strength of the electrode catalyst layer 20. In particular, the ionomer can be strongly adsorbed onto the surface of the ionomer-adsorbed fiber, further increasing the strength of the electrode catalyst layer 20. Furthermore, the ionomer forms a proton conduction path, resulting in high water electrolysis performance. In particular, when the ionomer-adsorbed fiber is a polymer fiber having cation exchange groups, proton conductivity is increased due to the linear proton conductive network formed on the polymer fiber. Furthermore, since the polymer fiber has cation exchange groups, these cation exchange groups can ionically bond with the polymer electrolyte, thereby strongly adsorbing the polymer electrolyte, thereby further increasing the adhesion between the polymer fiber and the polymer electrolyte.

[0082] When the polymer fiber is an ionomer-adsorbed fiber and the polymer electrolyte is an ionomer, the amount of ionomer adsorbed to the ionomer-adsorbed fiber is 10 mg or more per 1 g of the ionomer-adsorbed fiber, preferably 200 mg or more, and more preferably 500 mg or more. However, the amount of ionomer adsorbed to the ionomer-adsorbed fiber is preferably 4000 mg or less, and more preferably 2000 mg or less per 1 g of the ionomer-adsorbed fiber. The amount of ionomer adsorbed to the ionomer-adsorbed fiber can be determined by contacting the ionomer-adsorbed fiber with a dispersion in which an ionomer is dispersed at a predetermined concentration C1, filtering the dispersion with a predetermined filter (e.g., 0.3 to 0.5 μm diameter), measuring the ionomer concentration C2 in the filtrate, and calculating the ionomer concentration C2 minus C1.

[0083] The average fiber diameter of the polymer fibers is preferably 500 nm or less, and more preferably 400 nm or less. When the average fiber diameter of the polymer fibers is 500 nm or less, the polymer fibers are ensured to be appropriately thin as a fiber material to be contained in the electrode catalyst layer 20. Furthermore, the average fiber diameter of the polymer fibers is preferably 100 nm or more. In this case, the appropriate thickness of the polymer fibers is ensured, which increases the strength of the electrode catalyst layer 20 and further suppresses the occurrence of cracks.

[0084] Furthermore, when the fibrous material 7 is polymeric fiber, the average fiber length of the polymeric fiber is preferably in the range of 1.0 μm to 40 μm. If the average fiber length of the polymeric fiber is within the above numerical range, pores of an appropriate size can be formed in the cathode electrode catalyst layer. In particular, when the average fiber diameter of the polymeric fiber is in the range of 100 nm to 500 nm, the average fiber length of the polymeric fiber is preferably in the range of 1.0 μm to 40 μm. In this case, an entangled structure of the fibrous material 23 is suitably formed in the electrode catalyst layer 20, thereby further increasing the strength of the electrode catalyst layer 20 and further suppressing the occurrence of cracks.

[0085] The blending amount of the polymer fiber is preferably 1 part by mass or more and 20 parts by mass or less, more preferably 2 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the catalyst. In this case, an entangled structure of the polymer fiber is suitably formed, thereby further increasing the strength of the electrode catalyst layer 20 and further suppressing the occurrence of cracks. When the catalyst-containing material 21 contains the carrier 21b, the blending amount of the polymer fiber may be in the range of 5 parts by mass or more and 30 parts by mass or less, based on 100 parts by mass of the carrier 21b in the catalyst-containing material 21. That is, when the catalyst-containing material 21 contains the catalyst 21a and the conductive carrier 21b, the blending amount of the polymer fiber may be in the range of 5 parts by mass or more and 30 parts by mass or less, relative to 100 parts by mass of the conductive carrier 21b. In this case, an entangled structure of the carbon fiber is suitably formed in the electrode catalyst layer 20, thereby further increasing the strength of the electrode catalyst layer 20 and further suppressing the occurrence of cracks. In particular, the blending amount of the polymer fibers is preferably within a range of 5 parts by mass to 20 parts by mass relative to 100 parts by mass of the conductive support 21b. By setting the blending amount of the polymer fibers within this range, an entangled structure of the polymer fibers is suitably formed, and the strength of the electrode catalyst layer 20 is further increased. As a result, cracks are less likely to occur, and the polymer fibers effectively support the electronic conductivity within the electrode catalyst layer 20, resulting in good electrolysis performance. The conductive support 1b is preferably carbon particles, as they have good electronic conductivity and are inexpensively available.

[0086] As the polymer fiber, a polymer fiber having cation exchange groups can be used as an ionomer-adsorbed fiber. In this case, proton conductivity is increased due to the linear proton-conducting network formed on the polymer fiber. Furthermore, by having the polymer fiber have cation exchange groups, these cation exchange groups can ionically bond with the polymer electrolyte, allowing for strong adsorption of the polymer electrolyte, thereby further enhancing adhesion between the polymer fiber and the polymer electrolyte. Examples of cation exchange groups include hydroxyl groups, carbonyl groups, sulfonic acid groups, phosphorous groups, and amino groups.

[0087] As shown in FIG. 7 , the electrode catalyst layer 20 may include polymer fiber aggregates 26 obtained by entanglement of polymer fibers as the fibrous material 23. The electrode catalyst layer 20 may further include voids 25 surrounding the aggregates 26. In FIG. 7 , reference numeral 24 denotes a catalyst-containing material 21 and a polymer electrolyte 22. However, in this case, if the average fiber length of the polymer fibers is greater than 20 μm, the size of the voids 25 surrounding the aggregates 26 is preferably 20 μm or less. In this case, since the voids 25 in the electrode catalyst layer 20 are small, the occurrence of cracks in the electrode catalyst layer 20 can be more sufficiently suppressed, and the deterioration of water electrolysis performance is suppressed. The reason why the deterioration of water electrolysis performance is suppressed is thought to be as follows. That is, when the size of the voids 25 is 20 μm or less, the voids 25 are less likely to be formed by the aggregates 26 along the interface between the electrode catalyst layer 20 and the polymer electrolyte membrane 10, making it less likely that the conduction of electrons or protons will be hindered. Furthermore, since there will be almost no catalyst present near the aggregates 26, it is less likely that portions that cannot contribute to the water splitting reaction will be generated. The size of the voids 25 surrounding the aggregates 26 is more preferably 10 μm or less, and particularly preferably 5 μm or less. The size of the voids 25 is preferably 0 μm, but may be larger than the average fiber diameter of the polymer fibers constituting the aggregates. Furthermore, when the average fiber length of the polymer fibers is 20 μm or less, it is preferable that the size of the voids 25 surrounding the aggregates 26 be equal to or less than the average fiber length of the polymer fibers. In this case, since the voids 25 in the electrode catalyst layer 20 are small, the occurrence of cracks in the electrode catalyst layer 20 can be more sufficiently suppressed, thereby suppressing a decrease in water splitting performance. The size of the voids 25 surrounding the aggregates 26 is more preferably 0.5 times or less the average fiber length of the polymer fibers, and particularly preferably 0.25 times or less the average fiber length of the polymer fibers. The size of the voids 25 is preferably 0 times the average fiber length of the polymer fibers. Here, the size of the voids 25 refers to the average value of the maximum sizes of the voids 25 observed in each of three cross sections in the thickness direction of the electrode catalyst layer 20. The size of the voids 25 refers to the linear distance connecting one end of the voids 25 to the other end farthest from that end.

[0088] <Method for manufacturing laminate for water electrolysis device> The method for manufacturing the laminate 100 includes a catalyst ink preparation step of preparing a catalyst ink, and an electrode catalyst layer formation step of applying the catalyst ink to one surface of the polymer electrolyte membrane 10 to form the electrode catalyst layer 20.

[0089] <Catalyst ink preparation process (electrode catalyst layer forming composition preparation process)> In the catalyst ink preparation process, the components constituting the electrode catalyst layer 20, i.e., the catalyst-containing material 21, the polymer electrolyte 22, and the fibrous material 23, are mixed using a dispersion medium to prepare a catalyst ink.

[0090] The dispersion medium for the catalyst ink is not particularly limited as long as it does not corrode the components constituting the electrode catalyst layer 20 and can dissolve the polymer electrolyte 22 in a highly fluid state or disperse it as a fine gel. However, it is desirable that the dispersion medium contain at least a volatile organic solvent. The dispersion medium for the catalyst ink may be water, alcohols, ketones, other polar solvents, ether-based solvents, etc. Specific examples of alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, and tert-butyl alcohol. Examples of ketones include acetone, methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl amyl ketone, pentanone, heptanone, cyclohexanone, methylcyclohexanone, acetonylacetone, diethyl ketone, dipropyl ketone, and diisobutyl ketone. Examples of polar solvents other than water, alcohols, and ketones include dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, diacetone alcohol, 1-methoxy-2-propanol, etc. Examples of ether solvents include tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene, dibutyl ether, etc. The dispersion medium may also be a mixed solvent of two or more of the above-mentioned solvents.

[0091] Furthermore, when a lower alcohol is used as the dispersion medium, it is preferable to use a mixed solvent of a lower alcohol and water in order to further suppress ignition of the dispersion medium. Furthermore, when the polymer electrolyte 22 is an ionomer, it is preferable that the dispersion medium contains water that is compatible with the ionomer, i.e., water that has a high affinity for the ionomer. The water content of the dispersion medium is not particularly limited as long as it is sufficient to prevent the ionomer from separating and becoming cloudy or gelling. When the catalyst-containing material 21 has a carrier 21b that supports the catalyst 21a, the catalyst ink may contain a dispersant to disperse the catalyst-containing material 21 in the catalyst ink. Examples of dispersants include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants.

[0092] The solid content of the catalyst ink is preferably 50% by mass or less, which further suppresses the occurrence of cracks on the surface of the electrode catalyst layer 20. From the viewpoint of improving the film formation rate of the electrode catalyst layer 20, the solid content of the catalyst ink is more preferably 1% by mass or more.

[0093] In the catalyst ink preparation process, the components constituting the electrode catalyst layer 20 may be mixed using a dispersion medium, and then a dispersion treatment may be performed as needed. Furthermore, in the catalyst ink preparation process containing polymer fibers, the polymer fibers may be dispersed in a dispersion medium in advance, and then mixed with other materials, and a dispersion treatment may be performed as needed. The dispersion treatment is not particularly limited as long as it is a treatment that can disperse the components contained in the electrode catalyst layer 20. Examples of such treatments include treatment with a planetary ball mill and a roll mill, treatment with a shear mill, treatment with a wet mill, ultrasonic dispersion treatment, and treatment with a homogenizer.

[0094] <Electrode catalyst layer forming process> In the electrode catalyst layer forming process, for example, the catalyst ink obtained in the catalyst ink preparation process is applied to one surface of the polymer electrolyte membrane 10, and then a drying process is performed to volatilize the dispersion medium, thereby forming the electrode catalyst layer 20 and obtaining the laminate 100.

[0095] At this time, the electrode catalyst layer 20 is formed directly on the surface of the polymer electrolyte membrane 10. This improves adhesion between the polymer electrolyte membrane 10 and the electrode catalyst layer 20. Furthermore, since pressure is not required to bond the electrode catalyst layer 20, crushing of the electrode catalyst layer 20 is also prevented.

[0096] Note that the polymer electrolyte membrane 10 generally has the characteristic of being subject to large degrees of swelling and shrinkage, and therefore, when a catalyst ink is applied onto the polymer electrolyte membrane 10, the volume of the polymer electrolyte membrane 10 changes more significantly than when the catalyst ink is applied to a substrate to form an electrode catalyst layer 20, and then the electrode catalyst layer 20 is transferred to the polymer electrolyte membrane 10. Therefore, if the catalyst ink does not contain a fibrous substance 23, cracks are likely to occur in the electrode catalyst layer 20. In contrast, if the catalyst ink contains a fibrous substance 23, the occurrence of cracks in the electrode catalyst layer 20 is suppressed because the catalyst ink contains the fibrous substance 23, even if the volume of the polymer electrolyte membrane 10 changes significantly when the catalyst ink is applied directly onto the polymer electrolyte membrane 10.

[0097] The method for applying the catalyst ink is not particularly limited, and various application methods can be used. As the application method, from the viewpoint of applying the catalyst ink to the surface of the electrode catalyst layer 20 in a uniform film thickness, for example, a doctor blade method, a die coating method, a curtain coating method, a dipping method, a spray coating method, a screen printing method, a roll coating method, etc. can be preferably used.

[0098] The drying method used in the drying process is not particularly limited as long as it is a method that can volatilize the dispersion medium, and methods such as oven drying, hot plate drying, and far-infrared drying can be used. The drying temperature and drying time in the drying process can be appropriately selected depending on the materials that make up the catalyst ink. The drying temperature of the catalyst ink may be, for example, in the range of 40°C to 200°C, and preferably in the range of 40°C to 120°C. The drying time of the catalyst ink may be, for example, in the range of 0.5 minutes to 1 hour, and preferably in the range of 1 minute to 30 minutes.

[0099] Instead of forming the electrode catalyst layer 20 by applying the catalyst ink to the surface of the polymer electrolyte membrane 10 and then performing a drying process to volatilize the dispersion medium, the electrode catalyst layer 20 may be formed by applying the catalyst ink to the surface of a substrate other than the polymer electrolyte membrane 10 and then performing a drying process to volatilize the dispersion medium, and then bonding the electrode catalyst layer 20 to the polymer electrolyte membrane 10 and then performing a transfer process to peel off the substrate.

[0100] The substrate may be made of any material that has good transferability, and for example, a fluorine-based resin may be used. Examples of fluorine-based resins include ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA), and polytetrafluoroethylene (PTFE). Furthermore, organic polymer compounds other than fluorine-based resins, such as polyimide, polyethylene terephthalate, polyamide (Nylon (registered trademark)), polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide, polyarylate, and polyethylene naphthalate, may also be used as the substrate. The substrate may be in the form of either a sheet or a film. The transfer process may be, for example, a transfer method using thermocompression bonding.

[0101] <Membrane electrode assembly for water electrolysis apparatus> Next, a membrane electrode assembly for a water electrolysis apparatus according to the present disclosure will be described with reference to Fig. 4 and Fig. 5. Fig. 4 is a cross-sectional view showing one embodiment of a membrane electrode assembly for a water electrolysis apparatus according to the present disclosure, and Fig. 5 is a schematic partial view showing one example of an electrode catalyst layer provided in the laminate of Fig. 4.

[0102] As shown in FIG. 4 , a membrane electrode assembly 200 for a water electrolysis system (hereinafter simply referred to as a "membrane electrode assembly") includes a laminate 100 and a second electrode catalyst layer 30. The second electrode catalyst layer 30 is disposed so as to sandwich the polymer electrolyte membrane 10 together with the electrode catalyst layer 20 of the laminate 100. That is, the membrane electrode assembly 200 includes, in this order, the electrode catalyst layer 20, the polymer electrolyte membrane 10, and the second electrode catalyst layer 30. The electrode catalyst layer 20 includes a catalyst-containing material 21, a polymer electrolyte 22, and a fibrous material 23 (see FIG. 2 ), and the second electrode catalyst layer 30 includes a catalyst-containing material 31, a polymer electrolyte 32, and a fibrous material 33 (see FIG. 5 ). In this embodiment, the second electrode catalyst layer 30 will be described as an electrode catalyst layer (anode-side electrode catalyst layer) disposed on the anode (oxidizing electrode) side.

[0103] According to the membrane electrode assembly 200, the electrode catalyst layer 20 contains the catalyst-containing material 21, the polymer electrolyte 22, and the fibrous material 23, and the second electrode catalyst layer 30 contains the catalyst-containing material 31, the polymer electrolyte 32, and the fibrous material 33, thereby making it possible to suppress the occurrence of cracks in the electrode catalyst layer 20 and the second electrode catalyst layer 30. Therefore, when a voltage is applied to the membrane electrode assembly 200 in a water electrolysis device including the membrane electrode assembly 200, the potential distribution in the electrode catalyst layer 20 and the second electrode catalyst layer 30 is prevented from being disturbed, making it possible to suppress a decrease in the water electrolysis performance of the water electrolysis device and improve the durability of the water electrolysis device.

[0104] (Second Electrode Catalyst Layer) The second electrode catalyst layer 30 is an electrode catalyst layer disposed on the anode side, and contains a catalyst-containing material 31 , a polymer electrolyte 32 , and a fibrous material 33 .

[0105] (1) Catalyst-Containing Substance The catalyst-containing substance 31 is a catalyst-containing substance that performs an oxidation reaction. The catalyst-containing substance 31 contains a catalyst (hereinafter also referred to as "anode catalyst") for performing an oxidation reaction in the anode fluid. Ultrapure water or other water is used as the anode fluid. Examples of the anode catalyst include platinum group metals, metals other than the platinum group metals, and alloys, oxides, double oxides, and carbides of these metals. These can be used alone or in combination of two or more. Among the above anode catalysts, ruthenium, rhodium, palladium, iridium, platinum, and alloys containing at least one of these metals are preferred due to their high catalytic activity. A double oxide refers to an oxide containing two metals. The anode catalyst is preferably composed of a platinum group metal. One or more metals selected from platinum, gold, palladium, rhodium, ruthenium, and iridium exhibit high activity, resulting in excellent electrode reactivity and efficient and stable electrode reactions.

[0106] The catalyst-containing material 31 may further include, in addition to the catalyst, a conductive carrier that supports the catalyst. That is, the catalyst-containing material 31 may be catalyst-supporting particles. The carrier may be any material that is conductive and not eroded in an oxidizing atmosphere (i.e., resistant to oxidative loss). Examples of such carriers include titanium, tin, zirconium, or oxides containing two or more of these. The average particle size of the carrier is preferably 10 nm or more. In this case, an electron conduction path is more likely to be formed. However, from the viewpoint of reducing the resistance value of the second electrode catalyst layer 30 and increasing the amount of catalyst supported, the average particle size of the carrier is preferably 1000 nm or less, and more preferably 100 nm or less. Here, the average particle size is the average particle size determined from an SEM image, and is determined in the same manner as the average particle size of the carbon particles serving as the carrier 21b.

[0107] (2) Polymer Electrolyte and Fibrous Material The polymer electrolyte 32 is the same as the polymer electrolyte 22 of the electrode catalyst layer 20 described above, and the fibrous material 33 is the same as the fibrous material 23 of the electrode catalyst layer 20 described above.

[0108] However, it is preferable that the fibrous material 33 contains polymer fibers. In this case, cracks are particularly unlikely to occur in the anode catalyst layer 30, and durability is likely to be improved.

[0109] The average fiber diameter of the fibrous material 33 is preferably 500 nm or less, and more preferably 400 nm or less. When the average fiber diameter of the fibrous material 33 is 500 nm or less, the fibrous material 33 is ensured to be appropriately thin as a fibrous material to be contained in the anode electrode catalyst layer 30. The average fiber diameter of the fibrous material 33 is preferably 100 nm or more. In this case, the fibrous material 33 is ensured to have an appropriate thickness, which increases the strength of the anode electrode catalyst layer 30 and further suppresses the occurrence of cracks.

[0110] Furthermore, the average fiber length of the fibrous material 33 is preferably within the range of 1.0 μm or more and 40 μm or less. When the average fiber length of the fibrous material 33 is within the above numerical range, pores of a suitable size can be formed in the anode electrode catalyst layer 30. In particular, when the average fiber diameter of the fibrous material 33 is within the range of 100 nm or more and 500 nm or less, the average fiber length of the fibrous material 33 is preferably within the range of 1.0 μm or more and 40 μm or less. In this case, an entangled structure of the fibrous material 33 is suitably formed in the anode electrode catalyst layer 30, which further increases the strength of the anode electrode catalyst layer 30 and further suppresses the occurrence of cracks.

[0111] The content of the fibrous material 33 in the second electrode catalyst layer 30 is preferably in the range of 0.5 mass % to 20 mass %, and more preferably in the range of 5 mass % to 15 mass %. In this case, the amount of the fibrous material 33 is suitable for inclusion in the second electrode catalyst layer 30, and an entangled structure of the fibrous material 33 is suitably formed, thereby further increasing the strength of the second electrode catalyst layer 30 and further suppressing the occurrence of cracks.

[0112] The ratio R (DF2 / DF1) of the content rate (DF2) of the fibrous material 33 in the second electrode catalyst layer 30 to the content rate (DF1) of the fibrous material 23 in the electrode catalyst layer 20 may be greater than 1 or less than 1, but is preferably greater than 1. In this case, the strength of the second electrode catalyst layer 30 is further increased, and deformation and cracking of the polymer electrolyte membrane 10 can be further suppressed when the second electrode catalyst layer 30 is formed after the formation of the electrode catalyst layer 20.

[0113] When the fibrous material 23 in the electrode catalyst layer 20 is carbon fiber, the ratio R is more preferably 5 or more and 30 or less, and even more preferably 10 or more and 20 or less. When the ratio R is within the above range, the strength of the second electrode catalyst layer 30 is further increased, and deformation and cracking of the polymer electrolyte membrane 10 can be further suppressed when the second electrode catalyst layer 30 is formed after the electrode catalyst layer 20 is formed.

[0114] When the fibrous material 23 in the electrode catalyst layer 20 is a polymer fiber, the ratio R is more preferably 1.1 or more and 15 or less, and more preferably 1.5 or more and 7 or less. When the ratio R is within the above range, the strength of the second electrode catalyst layer 30 is further increased, and deformation and cracking of the polymer electrolyte membrane 10 can be further suppressed when the second electrode catalyst layer 30 is formed after the electrode catalyst layer 20 is formed.

[0115] When the second electrode catalyst layer 30 is viewed from above in a direction opposing one surface of the polymer electrolyte membrane 10, the shape of the second electrode catalyst layer 30 may be the same as or different from the shape of the electrode catalyst layer 20. Furthermore, when the second electrode catalyst layer 30 is viewed from above in a direction opposing one surface of the polymer electrolyte membrane 10, the area of ​​the second electrode catalyst layer 30 may be smaller than or equal to the area of ​​the polymer electrolyte membrane 10, but is usually smaller than the area of ​​the polymer electrolyte membrane 10.

[0116] <Method for manufacturing membrane electrode assembly for water electrolysis apparatus> The method for manufacturing the membrane electrode assembly 200 includes a catalyst ink preparation step of preparing a catalyst ink, and an electrode catalyst layer formation step of applying the catalyst ink to both surfaces of the polymer electrolyte membrane 10 to form the cathode electrode catalyst layer 20 and the anode electrode catalyst layer 30. That is, the method for manufacturing the membrane electrode assembly 200 differs from the method for manufacturing the laminate 100 described above in the catalyst ink preparation step and the electrode catalyst layer formation step.

[0117] <Catalyst Ink Preparation Step> The catalyst ink preparation step differs from the catalyst ink preparation step in the method for producing the laminate 100 in that the catalyst ink for forming the anode electrode catalyst layer is further prepared by mixing the components that make up the anode electrode catalyst layer 30, i.e., the catalyst-containing material 31, the polymer electrolyte 32, and the fibrous material 33, using a dispersion medium.

[0118] The dispersion medium for the catalyst ink is not particularly limited as long as it does not corrode the components constituting the anode-side electrode catalyst layer 30 and can dissolve the polymer electrolyte 32 in a highly fluid state or disperse it as a fine gel. However, it is desirable that the dispersion medium contains at least a volatile organic solvent. The dispersion medium for the catalyst ink may be water, alcohols, ketones, other polar solvents, ether-based solvents, etc. Specific examples of alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, and tert-butyl alcohol. Examples of ketones include acetone, methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl amyl ketone, pentanone, heptanone, cyclohexanone, methylcyclohexanone, acetonylacetone, diethyl ketone, dipropyl ketone, and diisobutyl ketone. Examples of polar solvents other than water, alcohols, and ketones include dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, diacetone alcohol, 1-methoxy-2-propanol, etc. Examples of ether solvents include tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene, dibutyl ether, etc. The dispersion medium may also be a mixed solvent of two or more of the above-mentioned solvents.

[0119] Furthermore, when a lower alcohol is used as the dispersion medium, it is preferable to use a mixed solvent of a lower alcohol and water in order to further suppress ignition of the dispersion medium. Furthermore, when the polymer electrolyte 32 is an ionomer, it is preferable that the dispersion medium contains water that is compatible with the ionomer, i.e., water that has a high affinity for the ionomer. The amount of water contained in the dispersion medium is not particularly limited as long as it is sufficient to prevent the ionomer from separating and becoming cloudy or gelling.

[0120] When the catalyst-containing material 31 has a carrier that supports the catalyst, the catalyst ink for forming the anode-side electrode catalyst layer may contain a dispersant to disperse the catalyst-containing material 31 in the catalyst ink. Examples of the dispersant include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants.

[0121] The solid content of the catalyst ink is preferably 50% by mass or less, which further suppresses the occurrence of cracks on the surface of the anode electrode catalyst layer 30. From the viewpoint of improving the film formation rate of the anode electrode catalyst layer 30, the solid content of the catalyst ink is more preferably 1% by mass or more.

[0122] In the catalyst ink preparation step, the components constituting the anode electrode catalyst layer 30 may be mixed using a dispersion medium, and then a dispersion treatment may be carried out as necessary. The dispersion treatment is not particularly limited as long as it is a treatment that can disperse the components contained in the anode electrode catalyst layer 30. Examples of such treatments include treatment with a planetary ball mill and a roll mill, treatment with a shear mill, treatment with a wet mill, ultrasonic dispersion treatment, and treatment with a homogenizer.

[0123] <Electrode catalyst layer forming step> The electrode catalyst layer forming step differs from the electrode catalyst layer forming step in the manufacturing method of the laminate 100 in that the electrode catalyst layer forming step involves applying a catalyst ink for forming an anode-side electrode catalyst layer to the surface of the polymer electrolyte membrane 10 opposite the electrode catalyst layer 20 to form the anode-side electrode catalyst layer 30. In the electrode catalyst layer forming step, the catalyst ink for forming the anode-side electrode catalyst layer obtained in the catalyst ink preparation step is applied to the other surface of the polymer electrolyte membrane 10, and then a drying treatment is performed to volatilize the dispersion medium, thereby forming the anode-side electrode catalyst layer 30 and obtaining the membrane electrode assembly 200.

[0124] At this time, the anode electrode catalyst layer 30 is formed directly on the surface of the polymer electrolyte membrane 10. This improves adhesion between the polymer electrolyte membrane 10 and the anode electrode catalyst layer 30. Furthermore, since pressure is not required to bond the anode electrode catalyst layer 30, crushing of the anode electrode catalyst layer 30 is also prevented.

[0125] Note that the polymer electrolyte membrane 10 generally has the characteristic of being subject to large degrees of swelling and shrinkage. Therefore, when a catalyst ink is applied to the polymer electrolyte membrane 10, the volume of the polymer electrolyte membrane 10 changes more significantly than when the catalyst ink is applied to a substrate to form the anode electrode catalyst layer 30, and then the anode electrode catalyst layer 30 is transferred to the polymer electrolyte membrane 10. Therefore, if the catalyst ink does not contain a fibrous material 23, cracks are likely to occur in the anode electrode catalyst layer 30. In contrast, if the catalyst ink contains a fibrous material 33, the occurrence of cracks in the anode electrode catalyst layer 30 is suppressed because the catalyst ink contains the fibrous material 33, even if the volume of the polymer electrolyte membrane 10 changes significantly when the catalyst ink is applied directly to the polymer electrolyte membrane 10.

[0126] The method for applying the catalyst ink is not particularly limited, and various application methods can be used. As the application method, from the viewpoint of applying the catalyst ink to the surface of the cathode-side electrode catalyst layer 20 or the anode-side electrode catalyst layer 30 in a uniform film thickness, for example, a doctor blade method, a die coating method, a curtain coating method, a dipping method, a spray coating method, a screen printing method, a roll coating method, etc. can be preferably used.

[0127] The drying method used in the drying process is not particularly limited as long as it is a method that can volatilize the dispersion medium, and methods such as oven drying, hot plate drying, and far-infrared drying can be used. The drying temperature and drying time in the drying process can be appropriately selected depending on the materials that make up the catalyst ink. The drying temperature of the catalyst ink may be, for example, in the range of 40°C to 200°C, and preferably in the range of 40°C to 120°C. The drying time of the catalyst ink may be, for example, in the range of 0.5 minutes to 1 hour, and preferably in the range of 1 minute to 30 minutes.

[0128] Instead of forming the anode-side electrode catalyst layer 30 by applying the catalyst ink to the surface of the polymer electrolyte membrane 10 and then performing a drying process to volatilize the dispersion medium, the catalyst ink may be applied to the surface of a substrate other than the polymer electrolyte membrane 10 and then performing a drying process to volatilize the dispersion medium to form the anode-side electrode catalyst layer 30, and then the anode-side electrode catalyst layer 30 may be bonded to the polymer electrolyte membrane 10 and then a transfer process may be performed to peel off the substrate.

[0129] The substrate may be made of any material that has good transferability, and for example, a fluorine-based resin may be used. Examples of fluorine-based resins include ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA), and polytetrafluoroethylene (PTFE). Furthermore, organic polymer compounds other than fluorine-based resins, such as polyimide, polyethylene terephthalate, polyamide (Nylon (registered trademark)), polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide, polyarylate, and polyethylene naphthalate, may also be used as the substrate. The substrate may be in the form of either a sheet or a film. The transfer process may be, for example, a transfer method using thermocompression bonding.

[0130] <Water Electrolysis Apparatus> An embodiment of the water electrolysis apparatus of the present disclosure will be described with reference to FIG. 6 . FIG. 6 is a cross-sectional view showing the embodiment of the water electrolysis apparatus of the present disclosure. As shown in FIG. 6 , the water electrolysis apparatus 300 of this embodiment includes a membrane electrode assembly 200, a pair of main electrodes 310 and 320 sandwiching the membrane electrode assembly 200, and a DC power supply (not shown) electrically connected to the main electrodes 310 and 320. The main electrode 310 is a cathode and is bonded to the electrode catalyst layer 20 of the membrane electrode assembly 200. The main electrode 320 is an anode and is bonded to the second electrode catalyst layer 30 of the membrane electrode assembly 200. That is, the water electrolysis apparatus 300 of this embodiment includes, in this order, the cathode 310, the membrane electrode assembly 200, and the anode 320. The membrane electrode assembly 200 includes a stack 100 and a second electrode catalyst layer 30. The second electrode catalyst layer 30 is provided so as to sandwich the polymer electrolyte membrane 10 together with the electrode catalyst layer 20 of the laminate 100. That is, the membrane electrode assembly 200 includes the cathode electrode catalyst layer 20, the polymer electrolyte membrane 10, and the anode electrode catalyst layer 30, in this order, with the cathode electrode catalyst layer 20 disposed opposite the cathode 310 and the anode electrode catalyst layer 30 disposed opposite the anode 320.

[0131] The water electrolysis device 300 includes the above-described membrane electrode assembly 200, and therefore the water electrolysis device 300 suppresses the occurrence of cracks in the electrode catalyst layer 20 and the second electrode catalyst layer 30 in the membrane electrode assembly 200. Therefore, when a voltage is applied between the pair of main electrodes 310, 320 from a power source while water is supplied to the main electrode 320, which serves as an anode, the potential distribution in the electrode catalyst layer 20 and the second electrode catalyst layer 30 of the membrane electrode assembly 200 is suppressed from being disturbed, the water electrolysis performance of the water electrolysis device 300 is suppressed from being deteriorated, and the durability of the water electrolysis device 300 is improved.

[0132] More specifically, the water electrolysis device 300 includes the above-described membrane electrode assembly 200, and the anode-side electrode catalyst layer 30 in the membrane electrode assembly 200 contains the catalyst-containing material 31, the polymer electrolyte 32, and the fibrous material 33. Therefore, the water electrolysis device 300 can suppress the occurrence of cracks in the anode-side electrode catalyst layer 30. Therefore, when a voltage is applied to the membrane electrode assembly 200 in the water electrolysis device 300, the potential distribution in the anode-side electrode catalyst layer 30 is suppressed from being disturbed, the water electrolysis performance of the water electrolysis device 300 is suppressed from being deteriorated, and the durability of the water electrolysis device 300 can be improved. Furthermore, in the membrane electrode assembly 200, the cathode-side electrode catalyst layer 20 also contains the catalyst-containing material 21, the polymer electrolyte 22, and the fibrous material 23, so the occurrence of cracks in the cathode-side electrode catalyst layer 20 can also be suppressed. Therefore, when a voltage is applied to the membrane electrode assembly 200 in the water electrolysis device 300, the potential distribution in the cathode-side electrode catalyst layer 20 is prevented from being disturbed, and the water electrolysis performance of the water electrolysis device 300 is prevented from being reduced, thereby further improving the durability of the water electrolysis device 300.

[0133] The laminate for a water electrolysis apparatus according to the present disclosure is not limited to the laminate 100 of the above embodiment. For example, in the laminate 100, the electrode catalyst layer 20 is provided on the polymer electrolyte membrane 10, but a second electrode catalyst layer 30 may be provided instead of the electrode catalyst layer 20.

[0134] Furthermore, the membrane electrode assembly for a water electrolysis apparatus according to the present disclosure is not limited to the membrane electrode assembly 200 of the above embodiment. For example, in the membrane electrode assembly 200, both the cathode electrode catalyst layer 20 and the anode electrode catalyst layer 30 contain a fibrous material, but the cathode electrode catalyst layer 20 does not necessarily need to contain a fibrous material.

[0135] The contents of the present disclosure will be explained in more detail below using examples, but the present disclosure is not limited to the following examples.

[0136] Example 1A First, a catalyst-supported powder consisting of a carbon support (product number "TEC61E54", manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.; PtRu support amount: 54% by mass) supporting PtRu as a catalyst, a dispersion containing Nafion® as a polymer electrolyte (product name "Nafion® DE2020", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and carbon fiber (product name "VGCF-H", manufactured by Showa Denko K.K.) as a fibrous material were mixed in a solvent, and the mixture was dispersed for 30 minutes using a planetary ball mill to prepare a catalyst ink. The solvent for the catalyst ink was a mixed solvent of ultrapure water and 1-propanol. The volume ratio of ultrapure water to 1-propanol was 1:1. The catalyst ink was prepared so that the solids content in the catalyst ink was 10% by mass. The amount of fibrous material was 50 parts by mass per 100 parts by mass of the support. The average fiber diameter of the fibrous material was confirmed to be 150 nm and the average fiber length was 6 μm. A Nafion (registered trademark) membrane (trade name "N117", manufactured by DuPont) was prepared as a polymer electrolyte membrane. Next, using a slit die coater, the catalyst ink was applied to one main surface of the polymer electrolyte membrane so that the total amount of Pt and Ru supported per area of ​​the main surface was 0.5 mg / cm. ２ The catalyst ink was applied by die coating so that the catalyst ink was 0.01 mm thick. The catalyst ink was then dried in an oven at 80°C to remove the solvent component, yielding a laminate of an electrode catalyst layer and a polymer electrolyte membrane. When the laminate obtained in this manner was visually observed, no cracks were found in the electrode catalyst layer of Example 1A. Furthermore, no peeling of the electrode catalyst layer from the polymer electrolyte membrane was observed in the laminate. Furthermore, when a cross section of the laminate in the thickness direction was observed with an SEM to check the state of the agglomerates of the fibrous material in the electrode catalyst layer, no voids due to the agglomerates were found.

[0137] Example 2A First, a catalyst ink was prepared by mixing a dispersion containing iridium oxide as a catalyst, Nafion® as a polymer electrolyte (trade name "Nafion® DE2020", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and nitrogen-containing polymer fibers as a fibrous material in a solvent. The mixture was then dispersed for 30 minutes using a planetary ball mill. A mixed solvent of ultrapure water and 1-propanol was used as the solvent for the catalyst ink. The volume ratio of ultrapure water to 1-propanol was 1:1. The catalyst ink was prepared so that the solid content of the catalyst ink was 10% by mass. The amount of fibrous material was 2 parts by mass per 100 parts by mass of the carrier. The average fiber diameter of the fibrous material was confirmed to be 400 nm, and the average fiber length was confirmed to be 25 μm. A laminate of an electrode catalyst layer and an electrolyte membrane was then obtained in the same manner as in Example 1A. Visual inspection of the resulting laminate revealed no cracks in the electrode catalyst layer of Example 2A. Furthermore, in the laminate, no peeling of the electrode catalyst layer from the polymer electrolyte membrane was observed. Furthermore, when the cross section of the laminate in the thickness direction was observed with an SEM to check the state of the agglomerates of the fibrous material in the electrode catalyst layer, no voids due to the agglomerates were observed.

[0138] Example 3A First, a catalyst-supported powder consisting of a carbon support (product number "TEC61E54", manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.; PtRu support amount: 54% by mass) supporting PtRu as a catalyst, a dispersion containing Nafion® as a polymer electrolyte (product name "Nafion® DE2020", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and polymer fibers containing nitrogen atoms as a fibrous material were mixed in a solvent, and the mixture was subjected to a dispersion treatment using a high-pressure disperser for 30 minutes to prepare a catalyst ink. The polymer fibers were previously dispersed in the dispersion medium using the high-pressure disperser. The solvent for the catalyst ink was a mixed solvent of ultrapure water and 1-propanol. The volume ratio of ultrapure water to 1-propanol was 1:1. The catalyst ink was prepared so that the solids content in the catalyst ink was 10% by mass. The amount of fibrous material was 5 parts by mass per 100 parts by mass of the support. The average fiber diameter of the fibrous material was confirmed to be 200 nm and the average fiber length was confirmed to be 20 μm. A Nafion (registered trademark) membrane (trade name "N117", manufactured by DuPont) was prepared as a polymer electrolyte membrane. Next, using a slit die coater, the catalyst ink was applied to one main surface of the polymer electrolyte membrane so that the total amount of Pt and Ru supported per area of ​​the main surface was 0.5 mg / cm. ２ The catalyst ink was applied by die coating so that the thickness of the electrode catalyst layer was 100 μm. The catalyst ink was then dried in an oven at 80°C to remove the solvent component, yielding a laminate of an electrode catalyst layer and a polymer electrolyte membrane. When the laminate thus obtained was observed, no cracks were found in the electrode catalyst layer of Example 3A. Furthermore, no peeling of the electrode catalyst layer from the polymer electrolyte membrane was observed in the laminate. Furthermore, when the cross section of the laminate in the thickness direction was observed with an SEM to check the state of the agglomerates of the fibrous material in the electrode catalyst layer, no voids due to the agglomerates were found.

[0139] Example 4A A laminate of an electrode catalyst layer and an electrolyte membrane was obtained in the same manner as in Example 3A, except that a high-speed stirrer was used instead of a high-pressure disperser as the device used for the dispersion treatment when preparing the catalyst ink. Visual inspection of the laminate thus obtained revealed no cracks in the electrode catalyst layer of Example 4A. Furthermore, no peeling of the electrode catalyst layer from the polymer electrolyte membrane was observed in the laminate. Meanwhile, a cross section of the laminate in the thickness direction was observed using an SEM to confirm the state of the aggregates of the fibrous material in the electrode catalyst layer. It was confirmed that numerous aggregates were present, with voids of approximately 40 μm in size surrounding the aggregates.

[0140] Example 5A A laminate of an electrode catalyst layer and an electrolyte membrane was obtained in the same manner as in Example 3A, except that the dispersion treatment was performed using an ultrasonic disperser when preparing the catalyst ink. Visual inspection of the laminate thus obtained revealed no cracks in the electrode catalyst layer of Example 5A. Furthermore, no peeling of the electrode catalyst layer from the polymer electrolyte membrane was observed in the laminate. Meanwhile, the cross section of the laminate in the thickness direction was observed with an SEM to confirm the state of the agglomerates of the fibrous material in the electrode catalyst layer. It was confirmed that agglomerates were present and that voids of 5 μm in size had formed surrounding the agglomerates.

[0141] Example 6A A laminate of an electrode catalyst layer and an electrolyte membrane was obtained in the same manner as in Example 3A, except that the catalyst ink was prepared by simultaneously mixing the catalyst-supported powder, dispersion, and fibrous material in a solvent without dispersing the fibrous material in a dispersion medium beforehand, and then performing a dispersion process for 30 minutes using a high-pressure disperser. Visual observation of the resulting laminate revealed no cracks in the electrode catalyst layer of Example 6A. Furthermore, the laminate also showed no peeling of the electrode catalyst layer from the polymer electrolyte membrane. Meanwhile, a cross section of the laminate in the thickness direction was observed using an SEM to confirm the state of the aggregates of the fibrous material in the electrode catalyst layer. It was confirmed that aggregates were present and that voids of approximately 40 μm in size had formed surrounding the aggregates.

[0142] Example 7A A laminate of an electrode catalyst layer and an electrolyte membrane was obtained in the same manner as in Example 3A, except that a bead mill was used instead of a high-pressure disperser as the device used for the dispersion treatment when preparing the catalyst ink. Visual inspection of the laminate thus obtained revealed no cracks in the electrode catalyst layer of Example 7A. Furthermore, no peeling of the electrode catalyst layer from the polymer electrolyte membrane was observed in the laminate. Meanwhile, a cross section of the laminate in the thickness direction was observed using an SEM to confirm the state of the aggregates of the fibrous material in the electrode catalyst layer. The presence of aggregates and deformation of the fibrous material were also observed. It was also confirmed that voids of approximately 5 μm in size were formed surrounding the aggregates.

[0143] (Comparative Example 1A) A laminate of an electrode catalyst layer and an electrolyte membrane was obtained in the same manner as in Example 1A, except that the fibrous material was not included. Visual inspection of the thus obtained laminate revealed that cracks had occurred in the electrode catalyst layer of Comparative Example 1. Furthermore, partial peeling of the electrode catalyst layer from the polymer electrolyte membrane was observed in the laminate.

[0144] Example 8A A laminate of an electrode catalyst layer and an electrolyte membrane was obtained in the same manner as in Example 1A, except that the blending amount of the fibrous material was 5 parts by mass per 100 parts by mass of the carrier. When the laminate obtained in this manner was visually observed, no cracks were found in the electrode catalyst layer of Example 8A.

[0145] Example 9A A laminate of an electrode catalyst layer and an electrolyte membrane was obtained in the same manner as in Example 1A, except that the blending amount of the fibrous material was 25 parts by mass per 100 parts by mass of the carrier. When the laminate obtained in this manner was visually observed, no cracks were found in the electrode catalyst layer of Example 9A.

[0146] Example 10A A laminate of an electrode catalyst layer and an electrolyte membrane was obtained in the same manner as in Example 1A, except that the blending amount of the fibrous material was 75 parts by mass relative to 100 parts by mass of the carrier. When the laminate obtained in this manner was visually observed, no cracks were found in the electrode catalyst layer of Example 10A.

[0147] <Evaluation of Electrolysis Performance> (Fabrication of Membrane Electrode Assembly) First, a dispersion containing iridium oxide as a catalyst and Nafion® as a polymer electrolyte (product name "Nafion® DE2020", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and polymer fibers containing nitrogen atoms as a fibrous material were mixed in a solvent and dispersed for 30 minutes using a planetary ball mill to prepare a catalyst ink for forming an anode-side electrode catalyst layer. A mixed solvent of ultrapure water and 1-propanol was used as the solvent for the catalyst ink. The volume ratio of ultrapure water to 1-propanol was 1:1. The catalyst ink was prepared so that the solid content in the catalyst ink was 10% by mass. The amount of the fibrous material was 2 parts by mass per 100 parts by mass of the carrier. The average fiber diameter of the fibrous material was confirmed to be 400 nm and the average fiber length to be 25 μm. Furthermore, it was confirmed that the amount of polymer electrolyte adsorbed on the fibrous material was 10 mg or more per 1 g of the fibrous material.

[0148] Next, using a slit die coater, the catalyst ink for forming an anode-side electrode catalyst layer was applied to the other main surface of the polymer electrolyte membrane of the laminate produced in Examples 1A, 8A to 10A, and Comparative Example 1A, on which the cathode-side electrode catalyst layer was not formed, so that the amount of iridium oxide carried per area of ​​the main surface was 1.0 mg / cm ２ The catalyst ink was applied by die coating so that the dispersion medium in the catalyst ink was 0.01g / cm2. The catalyst ink was then dried in an oven at 80°C to remove the dispersion medium. In this way, an anode-side electrode catalyst layer was formed on the polymer electrolyte membrane of the laminate, and a membrane electrode assembly for a water electrolysis device was obtained. The membrane electrode assembly thus obtained was placed between a cathode and an anode to obtain a structure, which was then immersed in water to prepare a water electrolysis device. The electrolysis performance of this water electrolysis device was evaluated. Specifically, the electrolysis performance was evaluated by applying a voltage of 1 A / cm2 to the membrane electrode assembly. ２ The evaluation was based on the voltage value (electrolysis voltage value) measured when a current of 100 kJ / s flows. The results are shown in Table 1. Note that the closer the voltage is to the theoretical electrolysis voltage of water, the higher the performance, and normally the voltage will be higher than the theoretical electrolysis voltage due to various resistance components.

[0149] The results shown in Table 1 indicate that Example 10A, in which the amount of fibrous material was 75 parts by mass relative to 100 parts by mass of the carrier, exhibited a high electrolysis voltage of 1.98 V. In contrast, Examples 1A, 8A, 9A, and Comparative Example 1A exhibited low electrolysis voltages of 1.95 V or less, and thus exhibited good electrolysis performance. The results shown in Table 1 suggest that the amount of fibrous material relative to 100 parts by mass of the carrier was 5 parts by mass or more and 50 parts by mass or less, thereby forming a proton conduction path by the ionomer or reducing the formation of voids in the electrode catalyst layer and reducing resistance, thereby improving water electrolysis performance. Thus, it can be seen that, in the water electrolysis layer laminate, when the amount of fibrous material relative to 100 parts by mass of the carrier is 5 parts by mass or more and 50 parts by mass or less, good electrolysis performance can be achieved while suppressing cracks in the electrode catalyst layer. Note that, as described above, no cracks were observed in the electrode catalyst layer in Examples 1A and 8A to 10A, which suggests that a decrease in electrolysis performance can be suppressed and the durability of the water electrolysis device can be improved. On the other hand, in Comparative Example 1A, as described above, cracks occurred in the electrode catalyst layer, and it is considered that the electrode catalyst layer was severely deteriorated, the deterioration of electrolysis performance could not be suppressed, and the durability of the water electrolysis device could not be improved.

[0150]

[0151] Example 1B (Formation of Cathode-Side Electrode Catalyst Layer) First, the following catalyst-containing material, dispersion containing a polymer electrolyte, and fibrous material were mixed in a dispersion medium and dispersed for 30 minutes using a planetary ball mill. In this way, a catalyst ink for forming a cathode-side electrode catalyst layer was prepared. The catalyst ink was prepared so that the solid content in the catalyst ink was 10% by mass. The amount of fibrous material was 1.0 times the mass of the support in the catalyst-containing material, and the amount of polymer electrolyte was 0.8 times the mass of the support in the catalyst-containing material. The average fiber diameter of the fibrous material was confirmed to be 150 nm and the average fiber length to be 15 μm. Furthermore, it was confirmed that the amount of polymer electrolyte adsorbed on the fibrous material was 10 mg or more per 1 g of fibrous material. Catalyst-containing material: catalyst-supported particles made of a carbon support supporting PtRu (product number "TEC61E54", manufactured by Tanaka Kikinzoku Kogyo K.K., PtRu support amount: 54% by mass) Polymer electrolyte (ionomer)-containing dispersion: dispersion containing Nafion (registered trademark), a fluorine-based polymer electrolyte (product name "Nafion (registered trademark) DE2020", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Fibrous material: carbon fiber (product name "VGCF-H", manufactured by Showa Denko K.K.) Dispersion medium: mixed solvent of ultrapure water and 1-propanol (water:1-propanol=1:1 (volume ratio))

[0152] Next, using a slit die coater, the catalyst ink for forming a cathode-side electrode catalyst layer was coated on one main surface of a Nafion (registered trademark) membrane (product name "N117", manufactured by DuPont) as a polymer electrolyte membrane so that the total amount of Pt and Ru supported per area of ​​the main surface was 0.5 mg / cm. ２ The catalyst ink was then dried in an oven at 80° C. to remove the solvent component from the catalyst ink, thereby obtaining a laminate of the electrode catalyst layer and the polymer electrolyte membrane.

[0153] (Formation of Anode-Side Electrode Catalyst Layer) Separately, the following catalyst, a dispersion containing a polymer electrolyte, and a fibrous material were mixed in a dispersion medium and dispersed for 30 minutes using a planetary ball mill. In this way, a catalyst ink for forming an anode-side electrode catalyst layer was prepared. The catalyst ink was prepared so that the solid content in the catalyst ink was 10% by mass. The amount of the fibrous material was 0.01 times the mass of the anode-side electrode catalyst layer, and the amount of the polymer electrolyte was 0.2 times the mass of the catalyst. The average fiber diameter of the fibrous material was confirmed to be 200 nm and the average fiber length to be 25 μm. Furthermore, it was confirmed that the amount of polymer electrolyte adsorbed on the fibrous material was 10 mg or more per 1 g of the fibrous material. Catalyst: iridium oxide powder Dispersion containing polymer electrolyte (ionomer): Dispersion containing Nafion (registered trademark), a fluorine-based polymer electrolyte (trade name "Nafion (registered trademark) DE2020", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Fibrous material (ionomer-adsorbed fiber): Polymer fiber (cation exchange group: sulfonic acid group) Dispersion medium: Mixed solvent of ultrapure water and 1-propanol (water:1-propanol=1:1 (volume ratio))

[0154] Next, using a slit die coater, the catalyst ink for forming an anode-side electrode catalyst layer was applied to the other main surface of the polymer electrolyte membrane of the laminate, on which the cathode-side electrode catalyst layer was not formed, so that the amount of iridium oxide carried per area of ​​the main surface was 1.0 mg / cm ２ The catalyst ink was applied by die coating so that the dispersion medium in the catalyst ink was removed by drying in an oven at 80° C. In this manner, an anode-side electrode catalyst layer was formed on the polymer electrolyte membrane of the laminate, thereby obtaining a membrane electrode assembly for a water electrolysis system.

[0155] Example 2B A membrane electrode assembly for a water electrolysis system was obtained in the same manner as in Example 1B, except that polymer fibers (cation exchange groups: sulfonic acid groups) were used as the fibrous material instead of carbon fibers when preparing the catalyst ink for forming the cathode-side electrode catalyst layer. The amount of the fibrous material was set to 0.05 times the mass of the cathode-side electrode catalyst layer. The fibrous material was confirmed to have an average fiber diameter of 200 nm and an average fiber length of 25 μm. It was also confirmed that the amount of polymer electrolyte adsorbed on the fibrous material was 10 mg or more per 1 g of the fibrous material.

[0156] Example 3B A membrane electrode assembly for a water electrolysis system was obtained in the same manner as in Example 2B, except that the amount of fibrous material used in preparing the catalyst ink for forming a cathode-side electrode catalyst layer was 0.5 times the mass of the support in the catalyst-containing material for the cathode-side electrode catalyst layer, and the amount of fibrous material used in preparing the catalyst ink for forming an anode-side electrode catalyst layer was 0.1 times the mass of the anode-side electrode catalyst layer. Example 4B (Preparation of Catalyst Ink for Forming a Cathode-Side Electrode Catalyst Layer) First, the following catalyst-containing material, a dispersion containing a polymer electrolyte, and a fibrous material were mixed in a dispersion medium, and the mixture was subjected to a dispersion treatment for 30 minutes using a planetary ball mill. In this manner, a catalyst ink for forming a cathode-side electrode catalyst layer was prepared. The catalyst ink was prepared so that the solid content in the catalyst ink was 10% by mass. The amount of fibrous material was 0.5 times the mass of the carrier in the catalyst-containing material, and the amount of polymer electrolyte was 0.8 times the mass of the carrier in the catalyst-containing material. It was also confirmed that the average fiber diameter of the fibrous material was 150 nm and the average fiber length was 15 μm. It was confirmed that the amount of polymer electrolyte adsorbed on the fibrous material was 10 mg or more per 1 g of the fibrous material. Catalyst-containing carrier: catalyst-supported particles made of a carbon carrier supporting PtRu (product number "TEC61E54", manufactured by Tanaka Kikinzoku Kogyo K.K., PtRu support amount: 54 mass%) Polymer electrolyte (ionomer)-containing dispersion: dispersion containing Nafion (registered trademark), a fluorine-based polymer electrolyte (product name "Nafion (registered trademark) DE2020", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Fibrous material: carbon fiber (product name "VGCF-H", manufactured by Showa Denko K.K.) Dispersion medium: mixed solvent of ultrapure water and 1-propanol (water:1-propanol=1:1 (volume ratio))

[0157] (Preparation of catalyst ink for forming anode-side electrode catalyst layer) The following catalyst-containing material, dispersion liquid containing a polymer electrolyte, and fibrous material were mixed in a dispersion medium and dispersed for 30 minutes using a planetary ball mill. In this way, a catalyst ink for forming an anode-side electrode catalyst layer was prepared. The catalyst ink was prepared so that the solid content in the catalyst ink was 10% by mass. The amount of fibrous material was 0.2 times the mass of the support in the catalyst-containing material, and the amount of polymer electrolyte was 0.4 times the mass of the support in the catalyst-containing material. The average fiber diameter of the fibrous material was confirmed to be 200 nm and the average fiber length was 25 μm. It was confirmed that the amount of polymer electrolyte adsorbed on the fibrous material was 10 mg or more per 1 g of fibrous material. Catalyst-containing material: catalyst-supported particles in which iridium oxide is supported on a titanium oxide support. Dispersion containing polymer electrolyte (ionomer): dispersion containing Nafion (registered trademark), a fluorine-based polymer electrolyte (trade name "Nafion (registered trademark) DE2020", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). Fibrous material (ionomer-adsorbed fiber): ion exchange resin as polymer fiber (cation exchange group: sulfonic acid group). Dispersion medium: mixed solvent of ultrapure water and 1-propanol (water:1-propanol=1:1 (volume ratio)).

[0158] (Production of Electrode Catalyst Layer) Two polytetrafluoroethylene (PTFE) sheets were prepared as substrates, and these were used as a first substrate and a second substrate. Then, a catalyst ink for forming an anode-side electrode catalyst layer was applied to one surface of the first substrate using a doctor blade method, and the applied film was dried in an air atmosphere at 80°C, thereby producing an anode-side electrode catalyst layer. At this time, the catalyst loading amount in the anode-side electrode catalyst layer was 0.3 mg / cm. ２ The amount of catalyst ink applied was adjusted so that the anode-side electrode catalyst layer was 0.3 mg / cm. The cathode-side electrode catalyst layer was then manufactured by applying the catalyst ink for forming a cathode-side electrode catalyst layer to one surface of the second substrate using a doctor blade method and drying the applied film in an air atmosphere at 80°C. The cathode-side electrode catalyst layer was manufactured by applying the catalyst ink for forming a cathode-side electrode catalyst layer to one surface of the second substrate using a doctor blade method and drying the applied film in an air atmosphere at 80°C. The amount of catalyst loaded in the cathode-side electrode catalyst layer was adjusted so that the amount of catalyst loaded in the cathode-side electrode catalyst layer was 0.3 mg / cm. ２The amount of the catalyst ink to be applied was adjusted so that the cathode-side electrode catalyst layer was formed.

[0159] (Fabrication of Membrane Electrode Assembly) A portion of the anode-side electrode catalyst layer formed on the first substrate was punched out together with the first substrate. At this time, the size of the anode-side electrode catalyst layer punched out together with the first substrate was 5 cm x 5 cm. The punched-out anode-side electrode catalyst layer was then disposed on one main surface of a 183 μm-thick polymer electrolyte membrane made of a fluorine-based polymer electrolyte (Nafion (registered trademark) 117). Also, a portion of the cathode-side electrode catalyst layer formed on the second substrate was punched out together with the second substrate. At this time, the size of the cathode-side electrode catalyst layer punched out together with the second substrate was 5 cm x 5 cm. The punched-out cathode-side electrode catalyst layer was then disposed on the other main surface of the polymer electrolyte membrane. The anode-side electrode catalyst layer and the cathode-side electrode catalyst layer were then transferred at a transfer temperature of 130°C and a thickness of 5.0 x 10 ６ The polymer electrolyte membrane was transferred onto the polymer electrolyte membrane by hot pressing under a transfer pressure of 100 Pa to obtain a membrane electrode assembly.

[0160] Example 5B A membrane electrode assembly was obtained in the same manner as in Example 4B, except that polymer fibers having nitrogen atoms (average fiber diameter: 15 nm, cation exchange group: sulfonic acid group) were used as the fibrous material in the catalyst ink for forming an anode-side electrode catalyst layer. It was confirmed that the amount of polymer electrolyte (ionomer) adsorbed on the fibrous material (ionomer-adsorbed fiber) was 10 mg or more per 1 g of the fibrous material.

[0161] Example 6B A membrane electrode assembly was obtained in the same manner as in Example 4B, except that polymer fibers having nitrogen atoms (average fiber diameter: 800 nm, cation exchange group: sulfonic acid group) were used as the fibrous material in the catalyst ink for forming an anode-side electrode catalyst layer. It was confirmed that the amount of polymer electrolyte (ionomer) adsorbed on the fibrous material (ionomer-adsorbed fiber) was 10 mg or more per 1 g of the fibrous material.

[0162] Example 7B A membrane electrode assembly was obtained in the same manner as in Example 4B, except that polymer fibers having nitrogen atoms (average fiber diameter: 300 nm, cation exchange group: amino group) were used as the fibrous material in the catalyst ink for forming an anode-side electrode catalyst layer. It was confirmed that the amount of polymer electrolyte (ionomer) adsorbed on the fibrous material (ionomer-adsorbed fiber) was 10 mg or more per 1 g of the fibrous material.

[0163] Example 8B A membrane electrode assembly was obtained in the same manner as in Example 1B, except that polymer fibers having nitrogen atoms (average fiber diameter: 200 nm, cation exchange group: sulfonic acid group) were used as the fibrous material in the catalyst ink for forming a cathode-side electrode catalyst layer. It was confirmed that the amount of polymer electrolyte (ionomer) adsorbed on the fibrous material (ionomer-adsorbed fiber) was 10 mg or more per 1 g of the fibrous material.

[0164] Comparative Example 1B A membrane / electrode assembly was obtained in the same manner as in Example 4B, except that no fibrous material was added when preparing the catalyst ink for forming the anode-side electrode catalyst layer.

[0165] <Evaluation of crack occurrence> For the membrane electrode assemblies of Examples 1B to 8B and Comparative Example 1B, the state of crack occurrence was confirmed by observing the surface of the anode-side electrode catalyst layer with a microscope (magnification: 200x). In this evaluation, the occurrence of cracks 10 μm or longer was marked as "×", and the absence of cracks 10 μm or longer was marked as "◯". The results are shown in Table 2.

[0166]

[0167] 10...polymer electrolyte membrane, 20...electrode catalyst layer, 21, 31...catalyst-containing material, 21a...catalyst, 21b...carrier, 22, 32...polymer electrolyte, 23, 33...fibrous material, 25...void, 26...aggregate, 30...second electrode catalyst layer (anode side electrode catalyst layer), 100...laminated body, 200...membrane electrode assembly, 300...water electrolysis device.

Claims

1. A laminate for a water electrolysis apparatus comprising a polymer electrolyte membrane and an electrode catalyst layer provided on one surface of the polymer electrolyte membrane, The electrode catalyst layer comprises a catalyst, a polymer electrolyte, and a fibrous material, and is a laminate for a water electrolysis apparatus.

2. The laminate for a water electrolysis apparatus according to claim 1, wherein the average fiber diameter of the fibrous material is in the range of 100 nm to 1 μm.

3. The laminate for a water electrolysis apparatus according to claim 1 or 2, wherein the fibrous material is a material having the property of adsorbing the polymer electrolyte.

4. The laminate for a water electrolysis apparatus according to claim 1 or 2, wherein the fibrous material includes at least one of carbon fibers and polymer fibers.

5. The laminate for a water electrolysis apparatus according to claim 4, wherein the polymer fiber has a cation exchange group.

6. The laminate for a water electrolysis apparatus according to claim 5, wherein the polymer electrolyte contained in the electrode catalyst layer is an ionomer.

7. The laminate for a water electrolysis apparatus according to claim 4, wherein the polymer fiber has proton conductivity.

8. The electrode catalyst layer includes the aggregate of polymer fibers, The laminate for a water electrolysis apparatus according to claim 4, wherein the average fiber length of the polymer fibers is greater than 20 μm, and the size of the void surrounding the aggregate is 20 μm or less.

9. The electrode catalyst layer includes the aggregate of polymer fibers, The laminate for a water electrolysis apparatus according to claim 4, wherein the average fiber length of the polymer fibers is 20 μm or less, and the size of the void surrounding the aggregate is less than or equal to the average fiber length of the polymer fibers.

10. The electrode catalyst layer is the cathode-side electrode catalyst layer, The catalyst is supported on a conductive carrier, and the fibrous material is carbon fiber. The laminate for a water electrolysis apparatus according to claim 1, wherein the amount of the fibrous material is within the range of 5 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the carrier.

11. The electrode catalyst layer is the cathode-side electrode catalyst layer, The catalyst is supported on a conductive carrier, and the fibrous material is a polymer fiber. The laminate for a water electrolysis apparatus according to claim 1, wherein the amount of the fibrous material is within the range of 5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the carrier.

12. The laminate for a water electrolysis apparatus according to claim 10 or claim 11, wherein the carrier is carbon particles.

13. A membrane electrode assembly and The membrane electrode assembly comprises a pair of main electrodes provided so as to sandwich the aforementioned membrane electrode assembly, The aforementioned film electrode assembly, A laminate for a water electrolysis apparatus according to any one of claims 1, 2, 10, and 11, A water electrolysis apparatus having a second electrode catalyst layer provided on the surface of the polymer electrolyte membrane of the laminate for the water electrolysis apparatus that is opposite to the electrode catalyst layer.

14. A membrane electrode assembly for a water electrolysis apparatus comprising a laminate for a water electrolysis apparatus according to claim 1 and a second electrode catalyst layer, wherein the electrode catalyst layer, the polymer electrolyte membrane, and the second electrode catalyst layer are arranged in this order, The second electrode catalyst layer is the cathode-side electrode catalyst layer, The electrode catalyst layer is an anode-side electrode catalyst layer, and the membrane electrode assembly for a water electrolysis apparatus comprises a catalyst-containing substance containing the catalyst, the polymer electrolyte, and the fibrous substance.

15. The membrane electrode assembly for a water electrolysis apparatus according to claim 14, wherein the cathode-side electrode catalyst layer comprises a catalyst-containing substance, a polymer electrolyte, and a fibrous substance.

16. The fibrous material in the cathode-side electrode catalyst layer comprises at least one of carbon fibers and polymer fibers. The membrane electrode assembly for a water electrolysis apparatus according to claim 15, wherein the fibrous material of the anode-side electrode catalyst layer includes polymer fibers.

17. The membrane electrode assembly for a water electrolysis apparatus according to claim 16, wherein the polymer fiber has proton conductivity.

18. The membrane electrode assembly for a water electrolysis apparatus according to claim 16, wherein the polymer fiber has a cation exchange group.

19. The membrane electrode assembly for a water electrolysis apparatus according to claim 18, wherein the polymer electrolyte contained in the anode-side electrode catalyst layer and the cathode-side electrode catalyst layer is an ionomer.

20. The fibrous material in the cathode-side electrode catalyst layer is carbon fiber. The average fiber diameter of the fibrous material is in the range of 50 nm to 300 nm. The membrane electrode assembly for a water electrolysis apparatus according to claim 15 or 16, wherein the average fiber length of the fibrous material is in the range of 1.0 μm or more and 20 μm or less.

21. The fibrous material in the cathode-side electrode catalyst layer is a polymer fiber. The average fiber diameter of the fibrous material is in the range of 100 nm to 500 nm. The membrane electrode assembly for a water electrolysis apparatus according to any one of claims 15 to 19, wherein the average fiber length of the fibrous material is in the range of 1.0 μm or more and 40 μm or less.

22. The average fiber diameter of the fibrous material in the anode-side electrode catalyst layer is in the range of 100 nm to 500 nm. The membrane electrode assembly for a water electrolysis apparatus according to any one of claims 14 to 19, wherein the average fiber length of the fibrous material is in the range of 1.0 μm or more and 40 μm or less.

23. The catalyst-containing material in the cathode-side electrode catalyst layer is a catalyst-supported particle having the catalyst and a carrier that supports the catalyst. The fibrous material in the cathode-side electrode catalyst layer is carbon fiber. The membrane electrode assembly for a water electrolysis apparatus according to claim 15 or 16, wherein the amount of the fibrous material is within the range of 0.3 times or more and 1.5 times the mass of the carrier.

24. The catalyst-containing material in the cathode-side electrode catalyst layer is a catalyst-supported particle having the catalyst and a carrier that supports the catalyst. The fibrous material in the cathode-side electrode catalyst layer is a polymer fiber. The membrane electrode assembly for a water electrolysis apparatus according to any one of claims 15 to 19, wherein the amount of the fibrous material is within the range of 0.05 times or more and 0.3 times or less the mass of the carrier.

25. The membrane electrode assembly for a water electrolysis apparatus according to any one of claims 15 to 19, wherein the content of the fibrous material in the anode-side electrode catalyst layer is in the range of 0.5% by mass or more and 20% by mass or less.

26. The membrane electrode assembly for a water electrolysis apparatus according to any one of claims 15 to 19, wherein the ratio R(DF1 / DF2) of the content of the fibrous material in the cathode-side electrode catalyst layer to the content of the fibrous material in the anode-side electrode catalyst layer (DF2) is greater than 1.

27. The fibrous material in the cathode-side electrode catalyst layer is carbon fiber. The membrane electrode assembly for a water electrolysis apparatus according to claim 26, wherein the ratio R is 5 or more and 30 or less.

28. The fibrous material in the cathode-side electrode catalyst layer is a polymer fiber. The membrane electrode assembly for a water electrolysis apparatus according to claim 26, wherein the ratio R is 1.1 or more and 15 or less.

29. A membrane electrode assembly for a water electrolysis apparatus according to any one of claims 15 to 19, wherein in at least one of the cathode-side electrode catalyst layer and the anode-side electrode catalyst layer, the polymer electrolyte is an ionomer, and the fibrous material is an ionomer-adsorbing fiber having the property of adsorbing the ionomer.

30. The cathode, film electrode assembly, and anode are provided in this order. The aforementioned film electrode assembly, A water electrolysis apparatus, which is a membrane electrode assembly for a water electrolysis apparatus according to any one of claims 14 to 19.