Membrane electrode assembly and method for manufacturing membrane electrode assembly

Abstract

This membrane electrode assembly comprises a polymer electrolyte membrane and a pair of electrode catalyst layers, between which the polymer electrolyte membrane is sandwiched in the thickness direction. At least one of the two electrode catalyst layers is a catalyst layer of interest. The catalyst layer of interest comprises a catalyst, a polymer electrolyte, and a fibrous substance. In the catalyst layer of interest, the fiber proportion which is a mass ratio of the fibrous substance to the catalyst increases continuously or intermittently as the distance from the polymer electrolyte membrane in the thickness direction increases.

Description

Membrane electrode assembly, and method for manufacturing a membrane electrode assembly

[0001] This disclosure relates to a membrane electrode assembly used in a water electrolysis apparatus or an organic hydride electrolysis apparatus, and to a method for manufacturing a membrane electrode assembly.

[0002] In recent years, hydrogen-based energy has attracted attention as an energy source that does not emit carbon dioxide, in order to achieve carbon neutrality. Furthermore, a promising method for producing hydrogen is the electrolysis of water using renewable energy.

[0003] Generally, the following methods are known for water electrolysis: alkaline water electrolysis, proton exchange membrane (PEM) type water electrolysis, anion exchange membrane (AEM) type water electrolysis, and solid oxide type water electrolysis. Of these, PEM type water electrolysis is attracting attention as a method that enables miniaturization of water electrolysis equipment through high-efficiency operation, and AEM type water electrolysis is attracting attention as a method that can be expected to reduce manufacturing costs by using non-precious metal catalysts.

[0004] Typical PEM and AEM type water electrolysis apparatuses comprise a pair of main electrodes and a membrane electrode assembly positioned between these main electrodes. The membrane electrode assembly comprises a polymer electrolyte membrane and a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane in the thickness direction. In the case of the PEM type, a polymer electrolyte membrane having proton conductivity is used, while in the case of the AEM type, a polymer electrolyte membrane having anion conductivity is used (see, for example, Patent Document 1).

[0005] Furthermore, the use of organic hydrides is being considered to improve the efficiency of hydrogen transport and storage. The organic hydride electrolysis method replaces the hydrogen production in water electrolysis with the production of organic hydrides using hydrides, thereby simplifying the process and enabling low-cost synthesis of organic hydrides.

[0006] An example of an organic hydride electrolytic synthesis apparatus, similar to the water electrolysis apparatus described above, comprises a pair of main electrodes and a membrane electrode assembly positioned between these main electrodes. The membrane electrode assembly comprises a proton-conducting polymer electrolyte membrane and a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane in the thickness direction (see, for example, Patent Document 2).

[0007] Japanese Patent Publication No. 2019-83085, International Publication No. 2022 / 091361

[0008] Electrode catalyst layers are manufactured by applying and drying a coating solution containing materials for the electrode catalyst layer, such as a catalyst. In this manufacturing process, cracks are prone to occur near the surface of the electrode catalyst layer. When cracks occur in the electrode catalyst layer, the movement of ions and electrons is inhibited, and variations in the thickness of the electrode catalyst layer caused by cracks lead to uneven electrolytic reactions depending on the location within the plane. As a result, the occurrence of cracks in the electrode catalyst layer may lead to a decrease in electrolytic performance.

[0009] The following describes various embodiments of a membrane electrode assembly and a method for manufacturing a membrane electrode assembly to solve the above problems. [Embodiment 1] A membrane electrode assembly comprising a polymer electrolyte membrane and a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane in the thickness direction, wherein at least one of the pair of electrode catalyst layers is a target catalyst layer, the target catalyst layer comprises a catalyst, a polymer electrolyte, and a fibrous material, and in the target catalyst layer, the fiber ratio, which is the ratio of the mass of the fibrous material to the catalyst, increases continuously or intermittently as it moves away from the polymer electrolyte membrane in the thickness direction.

[0010] According to the above configuration, the difference in fiber ratio enhances the mechanical strength, particularly near the surface opposite the polymer electrolyte membrane in the target catalyst layer, thereby effectively suppressing crack formation and thickness variations. On the other hand, in the region near the polymer electrolyte membrane in the target catalyst layer, inhibition of the electrolytic reaction by the fibrous material is suppressed. Therefore, improvement in electrolytic performance is possible.

[0011] [Aspect 2] The target catalyst layer includes a plurality of layers having different mass ratios of the fibrous material to the catalyst. In the plurality of layers, the ratio increases as the layer is farther from the polymer electrolyte membrane. The membrane electrode assembly according to [Aspect 1]. According to the above configuration, a change in the fiber ratio in the target catalyst layer can be easily and accurately formed.

[0012] [Aspect 3] The plurality of layers are two layers or three layers. The membrane electrode assembly according to [Aspect 2]. According to the above configuration, while suppressing an increase in the load required for manufacturing the target catalyst layer, a change in the fiber ratio can be accurately formed.

[0013] [Aspect 4] The average fiber diameter of the fibrous material is 0.003 μm or more and 0.6 μm or less. The membrane electrode assembly according to any one of [Aspect 1] to [Aspect 3]. According to the above configuration, the effects of suppressing the occurrence of cracks and thickness variations in the target catalyst layer can be accurately obtained.

[0014] [Aspect 5] The ratio of the minimum value to the maximum value of the fiber ratio in the thickness direction of the target catalyst layer is 0.04 or more and 0.7 or less. The membrane electrode assembly according to any one of [Aspect 1] to [Aspect 4].

[0015] According to the above configuration, since a sufficient difference in the fiber ratio is obtained within the target catalyst layer, the above-described effects can be accurately obtained. On the other hand, since the difference in the fiber ratio within the target catalyst layer does not become too large, smooth progress of mass transfer is possible.

[0016] [Aspect 6] The fibrous material included in the target catalyst layer is any one of carbon fiber, cellulose nanofiber, and polybenzimidazole fiber. The membrane electrode assembly according to any one of [Aspect 1] to [Aspect 5]. According to the above configuration, the effects of suppressing the occurrence of cracks and thickness variations and the effect of improving electrolysis performance can be preferably obtained.

[0017] [Aspect 7] Each of the pair of electrode catalyst layers is the target catalyst layer, the electrode catalyst layer for the cathode contains polybenzimidazole fibers which are the fibrous substance, and the electrode catalyst layer for the anode contains cellulose nanofibers which are the fibrous substance, the membrane electrode assembly according to any one of [Aspect 1] to [Aspect 6]. According to the above configuration, the electrolysis performance is further enhanced.

[0018] [Aspect 8] The polymer electrolyte membrane has proton conductivity, the membrane electrode assembly according to any one of [Aspect 1] to [Aspect 7]. According to the above configuration, since the membrane electrode assembly can be used in a PEM water electrolysis device or an organic hydride electrolytic synthesis device, the versatility of the membrane electrode assembly is enhanced.

[0019] [Aspect 9] The membrane electrode assembly is used in a water electrolysis device, the membrane electrode assembly according to any one of [Aspect 1] to [Aspect 8]. According to the above configuration, the output of the water electrolysis device is enhanced.

[0020] [Aspect 10] The membrane electrode assembly is used in an organic hydride electrolytic synthesis device, the membrane electrode assembly according to any one of [Aspect 1] to [Aspect 8]. According to the above configuration, the output of the organic hydride electrolytic synthesis device is enhanced.

[0021] [Aspect 11] A method for manufacturing the membrane electrode assembly according to any one of [Aspect 1] to [Aspect 10], including forming a coating film by a doctor blade method or an inkjet method, and forming a layer included in the target catalyst layer from the coating film, a method for manufacturing a membrane electrode assembly.

[0022] According to the above manufacturing method, when using the doctor blade method, productivity can be improved by high-speed film formation, and when using the inkjet method, control of the pore distribution is possible.

[0023] According to the present disclosure, the generation of cracks and the thickness variation in the electrode catalyst layer can be suppressed.

[0024] Figure 1 is a diagram showing the cross-sectional structure of a membrane electrode assembly of an embodiment. Figure 2 is a table showing the configurations and evaluation results of Examples and Comparative Examples.

[0025] As used herein, the expression "at least one" means "one or more" of the desired options. For example, as used herein, "at least one" means "only one option" or "both of the two options" if there are two options. As another example, as used herein, "at least one" means "only one option" or "any combination of two or more options" if there are three or more options.

[0026] Hereinafter, an embodiment of a membrane electrode assembly and a method for manufacturing the membrane electrode assembly will be described with reference to the drawings. The membrane electrode assembly of this embodiment is used in any of the following: a PEM-type water electrolysis apparatus, an AEM-type water electrolysis apparatus, or an organic hydride electrolysis synthesis apparatus. Hereafter, these apparatuses will be collectively referred to as the target apparatus.

[0027] [Configuration of the membrane electrode assembly] As shown in Figure 1, the membrane electrode assembly 10 comprises a polymer electrolyte membrane 20 and a pair of electrode catalyst layers 30C and 30A.

[0028] The polymer electrolyte membrane 20 is sandwiched between the electrode catalyst layer 30C and the electrode catalyst layer 30A in the thickness direction. The electrode catalyst layer 30C is in contact with one of the two surfaces of the polymer electrolyte membrane 20, and the electrode catalyst layer 30A is in contact with the other of the two surfaces of the polymer electrolyte membrane 20.

[0029] The electrode catalyst layer 30C is used in the cathode of the device, and the electrode catalyst layer 30A is used in the anode of the device. The materials and configuration of the polymer electrolyte membrane 20 and the electrode catalyst layers 30C and 30A will be described in detail below.

[0030] <Materials and composition of the polymer electrolyte membrane> In the membrane electrode assembly 10 used in PEM-type water electrolysis apparatus and organic hydride electrolysis synthesizer, the polymer electrolyte membrane 20 is composed of a polymer electrolyte having proton conductivity. The proton-conducting polymer electrolyte has a proton-conducting functional group. An example of a proton-conducting functional group is a sulfo group (-SO ３ H), phosphonic acid group (-PO ３ H ２), a carboxyl group (-COOH). The proton-conductive functional group may have a form of a salt such as a metal.

[0031] As the polymer electrolyte membrane 20 having proton conductivity, specifically, a fluorine-based polymer electrolyte membrane or a hydrocarbon-based polymer electrolyte membrane can be used. Examples of the fluorine-based polymer electrolyte membrane include Nafion (registered trademark, manufactured by DuPont), Flemion (registered trademark, manufactured by Asahi Glass), Aciplex (registered trademark, manufactured by Asahi Kasei), Gore Select (registered trademark, manufactured by Gore), etc. Examples of the hydrocarbon-based polymer electrolyte membrane include a polymer electrolyte membrane composed of sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, sulfonated polyphenylene, etc.

[0032] In the membrane electrode assembly 10 used in the AEM type water electrolysis device, the polymer electrolyte membrane 20 is composed of a polymer electrolyte having anion conductivity. A typical example of anion conductivity is hydroxide ion (OH － ) conductivity.

[0033] The anion-conductive polymer electrolyte has an anion-conductive functional group. Examples of the anion-conductive functional group include ammonium groups such as quaternary ammonium groups (NR ４ ＋ ), primary to tertiary amino groups, phosphonium groups such as quaternary phosphonium groups (PR ４ ＋ ), sulfonium groups such as tertiary sulfonium groups (SR ３ ＋ ). The above R is an organic group such as an alkyl group or an aryl group. Specific examples of the quaternary ammonium group include trimethylammonium group, imidazolium group, pyridinium group, etc. A specific example of the amino group is dimethylamino group. The anion-conductive functional group may have a form of a salt such as a metal.

[0034] Examples of polymer electrolyte membranes with anionic conductivity include A201, A901 (both manufactured by Tokuyama), fumasep FAA, FAB (e.g., FAB-3, FAA-3-50, FAA-3-PK-130, FAA-3-PP-75, all manufactured by fumatech), Sustainion 37-50 (manufactured by Dioxide Materials), NEOSEPTA® ACM, AM-1, ACS, ACLE-5P, AHA, AMH (all manufactured by Astom), SELEMION® AMT, DSV, AAV, ASV, AHT, APS (all manufactured by Asahi Glass), Aciplex® A-501, A-231, A-101 (all manufactured by Asahi Kasei), and PiperION. A20-HCO ３ A40-HCO ３ A80-HCO ３ (All are made by Versogen), etc.

[0035] The thickness of the polymer electrolyte membrane 20 is not particularly limited, but is preferably 20 μm or more and 250 μm or less, and more preferably 20 μm or more and 80 μm or less. If the thickness of the polymer electrolyte membrane 20 is within the above range, it is possible to suppress a decrease in the mechanical durability of the polymer electrolyte membrane 20, and it is also possible to improve the electrolytic performance by reducing the resistance of protons or anions conducted by the polymer electrolyte membrane 20.

[0036] <Materials of the Electrode Catalyst Layer> The electrode catalyst layers 30C and 30A contain a catalyst, a polymer electrolyte, and a fibrous material. The catalyst has the function of promoting the reaction that occurs at the cathode or anode of the target device. Specifically, the cathode catalyst, which is used at the cathode, causes a reaction that generates hydrogen from water at the cathode of a water electrolysis device. The cathode catalyst also causes the hydrogenation of organic compounds at the cathode of an organic hydride electrolysis device. The anode catalyst, which is used at the anode, causes a reaction that generates oxygen from water at the anode of both the water electrolysis device and the organic hydride electrolysis device.

[0037] The electrode catalyst layers 30C and 30A should contain catalysts corresponding to the reaction at the electrodes of the apparatus in which the electrode catalyst layers 30C and 30A are used. Suitable cathode catalysts include, for example, precious metals such as platinum, palladium, ruthenium, iridium, rhodium, and osmium; non-precious metals such as nickel, cobalt, molybdenum, and manganese; and oxides of these precious and non-precious metals. Other preferred examples of cathode catalysts include platinum supported on carbon, platinum black, cerium dioxide supported on activated carbon, and nickel (Ni / CeO) ​​supported on lanthanum(III) oxide. ２ -La ２ O ３ Examples include carbon (C), Ni-Mo alloys, Ni-Fe-Co alloys, and Ni-Al-Mo alloys. These materials can be used as cathode catalysts, either individually or in combination of two or more types.

[0038] As anode catalysts, for example, metals included in the platinum group, metals other than the platinum group, alloys, oxides, complex oxides, and carbides of these metals can be used. Among these, ruthenium, rhodium, palladium, iridium, platinum, alloys containing at least one of these metals, and oxides of these metals are preferred due to their high catalytic activity. For example, iridium, platinum, rhodium, palladium, nickel and its oxides, alloys of iridium and ruthenium, and alloys of iridium and titanium dioxide are suitably used. In particular, iridium oxide (IrO) ｘ ) is widely used because it possesses outstanding catalytic activity.

[0039] Other preferred examples of anode catalysts include cobalt and copper composite oxides (e.g., CuCoO ３ CuCoO ｘ (x is a real number corresponding to the average oxidation state of the metal element), Cu ｘ Co ３－ｘ O ４ (x is a real number between 0 and 3), Cu ０．７ Co ２．３ O ４ (e.g., nickel and cobalt composite oxides (e.g., NiCo) ２ O ４(e.g., catalysts doped with iron in a nickel and cobalt composite oxide (NiCoO)) ｘ : Fe (x is a real number corresponding to the average oxidation state of the metal element), nickel and iron composite oxides (e.g., NiFe) ２ O ４ (e.g., ruthenium and lead composite oxides (e.g., Pb ２ Ru ２ O ６．５ (e.g., manganese, iron, and cerium composite oxides (e.g., Ce) ０．２ MnFe １．８ O ４ Examples include Ni-Fe alloys, Ni-Al alloys, etc. The above-mentioned materials can be used as anode catalysts, either individually or in combination of two or more types.

[0040] The catalyst may be in particulate form, for example. The average particle size of the primary particles of the particulate catalyst is preferably 100 nm or less, and more preferably 50 nm or less. If the average particle size is within the above range, the activity of the catalyst is further improved.

[0041] The catalyst may include a conductive support. In other words, the catalyst may consist of catalyst particles, which are particles of the metal or the like described above that exhibit catalytic activity, and a support that holds the catalyst particles. The support can be any material that is conductive and capable of supporting the catalyst particles without being eroded by them. Examples of such supports include carbon and TiO2. ２ ,Ti,SnoO ２ Sn is used. The average particle size of the support is preferably 10 nm or more. This facilitates the formation of electron conduction paths in the electrode catalyst layer. On the other hand, from the viewpoint of reducing the resistance of the electrode catalyst layer and increasing the amount of catalyst particles supported, the average particle size of the support is preferably 1000 nm or less, more preferably 100 nm or less, and even more preferably 50 nm or less. It is preferable that the cathode catalyst contains a support, while the anode catalyst does not need to contain a support.

[0042] In the above, the average particle size of the catalyst or support particles is the arithmetic mean of the equivalent circle diameters of 20 particles in the image observed by a scanning electron microscope (SEM).

[0043] The polymer electrolyte has proton conductivity or anionic conductivity, corresponding to the polymer electrolyte membrane 20. The polymer electrolyte can function as a binder that binds catalysts together, fibrous materials together, and catalysts together with fibrous materials. Furthermore, the polymer electrolyte can function as a binder that binds at least one of the catalyst and the fibrous material together with the polymer electrolyte membrane 20.

[0044] As the polymer electrolyte, the electrolyte exemplified as the electrolyte constituting the polymer electrolyte membrane 20 can be used. The polymer electrolyte contained in the electrode catalyst layers 30C and 30A may be the same electrolyte as that in the polymer electrolyte membrane 20, or it may be a different electrolyte from that in the polymer electrolyte membrane 20. In order to reduce the interfacial resistance between the polymer electrolyte membrane 20 and the electrode catalyst layers 30C and 30A, and to reduce the difference in the rate of dimensional change between the polymer electrolyte membrane 20 and the electrode catalyst layers 30C and 30A when humidity changes, it is preferable that the polymer electrolyte contained in the polymer electrolyte membrane 20 and the polymer electrolyte contained in the electrode catalyst layers 30C and 30A are the same electrolyte or have similar coefficients of thermal expansion.

[0045] From the viewpoint of improving the adhesion between the electrode catalyst layers 30C and 30A and the polymer electrolyte membrane 20, if the polymer electrolyte membrane 20 is composed of a fluorine-based polymer electrolyte, it is preferable that the electrode catalyst layers 30C and 30A also contain a fluorine-based polymer electrolyte. Furthermore, if the polymer electrolyte membrane 20 is composed of a hydrocarbon-based polymer electrolyte, it is preferable that the electrode catalyst layers 30C and 30A also contain a hydrocarbon-based polymer electrolyte. Furthermore, if the polymer electrolyte membrane 20 is composed of a hydroxide ion-conducting polymer electrolyte, it is preferable that the electrode catalyst layers 30C and 30A also contain a hydroxide ion-conducting polymer electrolyte.

[0046] The amount of polymer electrolyte in the electrode catalyst layers 30C and 30A is preferably 5 to 50 parts by mass, and more preferably 10 to 30 parts by mass, based on 100 parts by mass of catalyst. If the amount of polymer electrolyte is within the above range, electron conduction paths and proton or anion conduction paths are more easily formed in the electrode catalyst layers 30C and 30A, resulting in good electrolytic performance. If the catalyst contains a support, the amount of polymer electrolyte may be 40 to 80 parts by mass, based on 100 parts by mass of support.

[0047] The fibrous material can be any material that is not eroded by the catalyst and polymer electrolyte, and is preferably carbon fiber, polymer fiber, or a mixture thereof. The inclusion of the fibrous material suppresses the occurrence of cracks in the electrode catalyst layers 30C and 30A, and also suppresses variations in the thickness of the electrode catalyst layers 30C and 30A caused by surface irregularities due to cracks. Furthermore, the inclusion of the fibrous material can also improve the adhesion between the polymer electrolyte membrane 20 and the electrode catalyst layers 30C and 30A. This makes it possible to suppress the generation of voids due to delamination between the polymer electrolyte membrane 20 and the electrode catalyst layers 30C and 30A, and suppresses the increase in interfacial resistance of the membrane electrode assembly 10 caused by these voids. For these reasons, the membrane electrode assembly 10 of this embodiment can suitably suppress the deterioration of electrolytic performance in water electrolysis devices and organic hydride electrolytic synthesis devices.

[0048] The constituent materials of fibrous materials may contain Lewis acidic or Lewis basic functional groups in their molecular structure. This makes it easier for polymer electrolytes to be present around the fibrous material. Examples of fibrous materials with Lewis acidic functional groups include carbon fibers and polymer fibers containing hydroxyl groups, carbonyl groups, sulfonic acid groups, and phosphite groups. Examples of fibrous materials with Lewis basic functional groups include polymer fibers with imide structures, azole structures, etc.

[0049] For example, when a polymer electrolyte has proton conductivity, if the fibrous material contains Lewis acidic functional groups, hydrogen bonding occurs between the Lewis acidic functional groups and proton-conducting sites such as sulfonyl groups contained in the polymer electrolyte, making it easier for the polymer electrolyte to be present around the fibrous material. On the other hand, if the fibrous material contains Lewis basic functional groups, acidic proton-conducting sites such as sulfonyl groups contained in the polymer electrolyte bond with the Lewis basic functional groups through acid-base bonding, making it easier for the polymer electrolyte to be present around the fibrous material. Since the bonding force of acid-base bonding is stronger than that of hydrogen bonding, it is preferable for the fibrous material to contain Lewis basic functional groups. In particular, it is preferable for the fibrous material to have an azole structure. An azole structure is a heterogeneous five-membered ring structure containing one or more nitrogen atoms, such as an imidazole structure or an oxazole structure. Specifically, the fibrous material may be composed of compounds having a benzoazole structure, such as a benzimidazole structure or a benzoxazole structure. Examples of such compounds are polymer compounds such as polybenzimidazole and polybenzoxazole.

[0050] Furthermore, the constituent materials of the fibrous material may include functional groups capable of forming hydrogen bonds. A functional group capable of forming hydrogen bonds is a functional group that can form hydrogen bonds with other functional groups. Preferably, the fibrous material is a fiber made of a polymer compound having functional groups capable of forming hydrogen bonds in its repeating units. The functional groups capable of forming hydrogen bonds may function as hydrogen bond donors or as hydrogen bond acceptors.

[0051] Examples of functional groups that function as hydrogen bond donors include hydroxyl groups (-OH) and groups with N-H bonds. In these functional groups, the electron-rich oxygen or nitrogen atoms are directly bonded to hydrogen, so the hydrogen atom functions as a hydrogen bond donor. Examples of functional groups that function as hydrogen bond acceptors include carbonyl groups (>C=O), groups with ether bonds (-O-), groups with ester bonds (-COO-), functional groups with oxygen atoms such as hydroxyl groups (-OH), and amino groups (-NH). ２ ), amide group (-CO-NH ２Functional groups having nitrogen atoms such as ) and -CF ３ These are functional groups containing fluorine atoms. In these functional groups, electron-rich oxygen, nitrogen, or fluorine atoms bond with hydrogen, so the oxygen, nitrogen, or fluorine atom functions as an acceptor for hydrogen bonding. Note that hydroxyl groups and N-H bonds can function as either donors or acceptors for hydrogen bonding.

[0052] From the viewpoint of promoting the formation of hydrogen bonds between fibrous materials, it is preferable that the fibrous material has at least one of a hydroxyl group and an N-H bond as a functional group capable of forming hydrogen bonds. Alternatively, it is preferable that the fibrous material has a functional group that functions as a hydrogen bond donor and a functional group that functions as a hydrogen bond acceptor.

[0053] Because the fibrous material has functional groups capable of forming hydrogen bonds, the fibrous material in the electrode catalyst layers 30C and 30A can suitably form a three-dimensional network structure through hydrogen bonding and physical entanglement of fibers. As a result, cracks are less likely to occur in the electrode catalyst layers 30C and 30A, and durability is enhanced.

[0054] Furthermore, since hydrogen bonding can occur between functional groups in fibrous materials and oxygen atoms in proton-conducting functional groups of polymer electrolytes, or nitrogen atoms and hydrogen atoms in anion-conducting functional groups, the polymer electrolytes are more likely to be present around the fibrous material, thereby promoting the formation of proton or anion conduction paths.

[0055] In order to efficiently form a three-dimensional network structure with a small amount of fibrous material added, it is preferable that the fibrous material is a fiber made of a polymer compound containing two or more functional groups capable of forming hydrogen bonds in the repeating unit.

[0056] Specific examples of such fibrous materials include cellulose nanofibers, chitin nanofibers, and chitosan nanofibers. It is preferable that the fibrous material be dispersible in water or alcohol.

[0057] Examples of cellulose nanofibers include cellulose nanofibers without substituted hydroxyl groups, cellulose nanofibers in which at least a portion of the hydroxyl groups are substituted with carboxyl groups, acetyl groups or their derivatives, or carboxymethyl groups, cellulose nanofibers in which at least a portion of the hydroxyl groups are substituted with alkyl groups having 1 to 10 carbon atoms or their derivatives, sulfonated cellulose nanofibers, cellulose sulfate nanofibers, and cellulose phosphate nanofibers. The electrode catalyst layers 30C and 30A may contain multiple types of these.

[0058] Furthermore, the fibrous material may be polymer fibers such as polyacrylonitrile nanofibers, polylactic acid nanofibers, or polycaprolactone nanofibers, and these polymer fibers may also be fibers into which functional groups capable of forming the aforementioned hydrogen bonds have been introduced.

[0059] The shape of the fibrous material is not particularly limited; for example, it may have a hollow structure or a solid structure. The average fiber diameter of the fibrous material is not particularly limited, but is preferably 0.003 μm or more and 0.6 μm or less, and more preferably 0.005 μm or more and 0.4 μm or less. If the average fiber diameter of the fibrous material is within the above range, the occurrence of cracks and variations in thickness in the electrode catalyst layers 30C and 30A can be effectively suppressed. Furthermore, the effect of improving the adhesion between the polymer electrolyte membrane 20 and the electrode catalyst layers 30C and 30A can be more favorably obtained. Therefore, it is possible to improve the durability of the electrolytic performance, that is, to maintain the electrolytic performance over the long term.

[0060] The fiber diameter of a fibrous material can be obtained, for example, by measuring the diameter of the fibrous material exposed in a cross-sectional image of the electrode catalyst layer using a scanning electron microscope. If the fibrous material is cut obliquely in the cross-section, an elliptical cross-section is obtained, in which case the fiber diameter can be obtained by measuring the diameter of a perfect circle fitted along the minor axis of the cross-section. If the surface of the fiber, rather than the cross-section, is exposed, the fiber diameter can be obtained by measuring the width of the exposed fiber perpendicular to its major axis. The average fiber diameter is the arithmetic mean of the fiber diameters obtained at at least 20 measurement points. Known methods such as ion milling and ultramicrotomes can be used to expose the cross-section of the electrode catalyst layer.

[0061] The average fiber length of the fibrous material is preferably 0.5 μm to 100 μm, and more preferably 1 μm to 40 μm. If the average fiber length is 1 μm or more, the entanglement of the fibrous material does not become too weak, thereby increasing the mechanical strength of the electrode catalyst layers 30C and 30A, and effectively suppressing crack formation and thickness variations. If the average fiber length is 40 μm or less, the entanglement of the fibrous material does not become too strong, resulting in good dispersibility of the fibrous material.

[0062] The fiber length of a fibrous material can be obtained, for example, by observing a cross-sectional image of an electrode catalyst layer using a scanning electron microscope, extracting the fibrous material whose entire length is exposed in the cross-section, and measuring its length. The average fiber length is the arithmetic mean of the fiber lengths obtained from measuring at least 20 or more fibrous materials.

[0063] The amount of fibrous material in the electrode catalyst layers 30C and 30A is preferably 1 to 40 parts by mass, and more preferably 2 to 20 parts by mass, based on 100 parts by mass of catalyst. If the amount of fibrous material is within the above range, an intertwined structure of the fibrous material is suitably formed, thereby effectively suppressing the occurrence of cracks and variations in thickness in the electrode catalyst layers 30C and 30A. If the catalyst contains a support, the amount of fibrous material may be 10 to 50 parts by mass, based on 100 parts by mass of support.

[0064] <Configuration of the Electrode Catalyst Layer> In this embodiment, the fiber ratio Rf is the ratio of the mass of the fibrous material to the mass of the catalyst in the electrode catalyst layers 30C and 30A, and is defined for a region that includes a cross-section parallel to the surface in contact with the polymer electrolyte membrane 20. That is, for each region, the fiber ratio Rf is determined using the masses of the catalyst and fibrous material contained in that region by the following formula (Equation 1). Fiber ratio Rf = Mass of fibrous material / Mass of catalyst ... (Equation 1)

[0065] In the target catalyst layer, which is at least one of the electrode catalyst layer 30C and electrode catalyst layer 30A, the fiber ratio Rf increases continuously or intermittently as it moves away from the polymer electrolyte membrane 20 in the thickness direction.

[0066] For example, the target catalyst layer comprises multiple layers with different fiber ratios Rf, where the fiber ratio Rf increases with increasing distance from the polymer electrolyte membrane 20 in the thickness direction. In this case, the fiber ratio Rf increases intermittently. A specific example of this configuration is described below.

[0067] Figure 1 illustrates a configuration in which each of the electrode catalyst layer 30C and electrode catalyst layer 30A is a target catalyst layer, and each electrode catalyst layer 30C, 30A comprises multiple layers. Specifically, the electrode catalyst layer 30C comprises a first catalyst layer 31C and a second catalyst layer 32C. The first catalyst layer 31C and the second catalyst layer 32C are arranged in this order in the direction away from the polymer electrolyte membrane 20. In other words, the first catalyst layer 31C is in contact with the polymer electrolyte membrane 20, and the second catalyst layer 32C is laminated on the side opposite to the polymer electrolyte membrane 20 relative to the first catalyst layer 31C. The first catalyst layer 31C has a surface in contact with the polymer electrolyte membrane 20 in the electrode catalyst layer 30C, and the second catalyst layer 32C has the outermost surface in the electrode catalyst layer 30C that is opposite to the polymer electrolyte membrane 20.

[0068] Each of the first catalyst layer 31C and the second catalyst layer 32C contains a catalyst, a polymer electrolyte, and a fibrous material. The second catalyst layer 32C has a higher ratio of fibrous material to catalyst than the first catalyst layer 31C. In this configuration, the fiber ratio Rf in the electrode catalyst layer 30C is constant within the first catalyst layer 31C, increases at the interface between the first catalyst layer 31C and the second catalyst layer 32C, and remains constant within the second catalyst layer 32C. In other words, the fiber ratio Rf increases intermittently.

[0069] Similarly, in the electrode catalyst layer 30A, the first catalyst layer 31A and the second catalyst layer 32A are arranged in this order, moving away from the polymer electrolyte membrane 20, and the second catalyst layer 32A has a larger proportion of fibrous material to catalyst than the first catalyst layer 31A. As a result, the fiber ratio Rf in the electrode catalyst layer 30A increases intermittently as it moves away from the polymer electrolyte membrane 20 in the thickness direction.

[0070] Furthermore, the target catalyst layer does not necessarily have a clear interface separating multiple layers, and the fiber ratio Rf may increase continuously as it moves away from the polymer electrolyte membrane 20 in the thickness direction. Also, at least one of the electrode catalyst layer 30C and electrode catalyst layer 30A may be the target catalyst layer, and when only one of the electrode catalyst layer 30C and electrode catalyst layer 30A is the target catalyst layer, the other electrode catalyst layer may, for example, have a constant fiber ratio Rf throughout the entire electrode catalyst layer, or it may not contain any fibrous material.

[0071] As described above, by including fibrous material in the target catalyst layer, an intertwined structure of fibrous material is formed within the target catalyst layer, thereby increasing its mechanical strength. This suppresses the occurrence of cracks and variations in thickness within the target catalyst layer. In particular, this effect is highly pronounced when the average fiber diameter of the fibrous material is between 0.003 μm and 0.6 μm.

[0072] Here, cracks tend to occur in the outermost region of the electrode catalyst layers 30C and 30A, near the surface opposite to the polymer electrolyte membrane 20. On the other hand, fibrous material is not essential for the electrolytic reaction, and excess fibrous material can be a factor in inhibiting the electrolytic reaction. In the target catalyst layer of this embodiment, the fiber ratio Rf increases as the thickness increases away from the polymer electrolyte membrane 20, so the ratio of fibrous material is increased in the outermost region where cracks are likely to occur, thereby increasing the mechanical strength. On the other hand, in the region near the polymer electrolyte membrane 20, the ratio of fibrous material is lower than in the outermost region, so the electrolytic reaction can be promoted compared to the case where the ratio of fibrous material is high throughout the target catalyst layer. Therefore, it is possible to improve the electrolytic performance while accurately suppressing the occurrence of cracks and variations in thickness in the target catalyst layer.

[0073] In at least one of the anode and cathode of a water electrolysis apparatus and an organic hydride electrolytic synthesis apparatus, gases such as oxygen and hydrogen are generated in response to the supply of liquids such as water. As a result, the volume of the products relative to the supply increases significantly, and the electrode catalyst layer is subjected to considerable force. Therefore, by increasing the strength of the outermost region of the electrode catalyst layer facing the product flow path, it is possible to accurately improve the durability of the membrane electrode assembly 10.

[0074] Furthermore, the larger the fiber ratio Rf, the more pores are formed by the entanglement of fibrous material, resulting in a less dense structure within the target catalyst layer. Conversely, the smaller the fiber ratio Rf, the fewer pores there are, resulting in a denser structure within the target catalyst layer. In the target catalyst layer of this embodiment, the fiber ratio Rf increases with increasing thickness from the polymer electrolyte membrane 20, resulting in a relatively dense structure in the region near the polymer electrolyte membrane 20 and a relatively sparse structure in the outermost region. Consequently, the diffusivity of reactants and products in the electrolytic reaction is enhanced.

[0075] The ratio Rr (Rfn / Rfm) of the minimum fiber ratio Rfn to the maximum fiber ratio Rfm in the thickness direction of the target catalyst layer is preferably 0.04 or more and 0.7 or less. For example, in the case of the electrode catalyst layer 30C illustrated in Figure 1, the ratio Rr is the value of the fiber ratio Rf of the first catalyst layer 31C relative to the fiber ratio Rf of the second catalyst layer 32C.

[0076] If the ratio Rr is 0.04 or higher, the difference in the ratio of fibrous material between the high and low fiber ratio Rf regions does not become too large, thus suppressing the inhibition of ion and electron movement or the diffusion of reactants and products. If the ratio Rr is 0.7 or lower, a sufficient difference in the ratio of fibrous material between the high and low fiber ratio Rf regions is obtained, so the effects of the change in fiber ratio Rf described above are accurately obtained.

[0077] Furthermore, regarding fiber density, which is the mass of fibrous material per unit volume, the fiber density in the region with a high fiber ratio Rf is greater than the fiber density in the region with a low fiber ratio Rf. In the target catalyst layer, it can be said that the fiber density increases continuously or intermittently as the thickness increases away from the polymer electrolyte membrane 20. Typically, in an electrode catalyst layer, the amount of catalyst is determined to allow for the smooth progress of the electrolytic reaction, and the ratio of other materials to the catalyst is determined. Therefore, by defining the proportion of fibrous material in the electrode catalyst layer using the fiber ratio Rf, which is the ratio of fibrous material to catalyst, it is possible to accurately define the composition of the electrode catalyst layer. In the target catalyst layer, the mass of catalyst per unit volume may change, but this change is small compared to the change in fiber density.

[0078] [Method for Manufacturing a Membrane Electrode Assembly] The method for manufacturing the membrane electrode assembly 10 will be described below. The method for manufacturing the membrane electrode assembly 10 includes a catalyst ink preparation step and a electrode catalyst layer formation step 30C, 30A. Each step will be described in order.

[0079] (Preparation of catalyst ink) The catalyst ink used to form the electrode catalyst layers 30C and 30A comprises at least a catalyst, a polymer electrolyte, and a solvent. When forming electrode catalyst layers 30C and 30A containing fibrous material, the catalyst ink further comprises fibrous material. To form a target catalyst layer in which the fiber ratio Rf changes, multiple catalyst inks with different ratios of fibrous material to catalyst are prepared.

[0080] The solvent does not corrode other components of the catalyst ink and dissolves the polymer electrolyte or disperses it as a fine gel. The solvent may be, for example, alcohols, ketone solvents, ether solvents, or other polar solvents. Examples of alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, and pentanol. Examples of ketone solvents include acetone, methyl ethyl ketone, pentanone, methyl isobutyl ketone, heptanone, cyclohexanone, methylcyclohexanone, acetonylacetone, and diisobutyl ketone. Examples of ether solvents include tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene, and dibutyl ether. Examples of polar solvents include dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, diacetone alcohol, and 1-methoxy-2-propanol.

[0081] The solvent may be a mixed solvent containing two or more of the materials mentioned above. The solvent may also contain water. Water has a high affinity for polymer electrolytes. When using a lower alcohol as the solvent, it is preferable to use a mixed solvent of the lower alcohol and water to reduce the risk of ignition. The amount of water added to the solvent is not particularly limited, as long as it does not cause separation of the polymer electrolyte, resulting in turbidity or gelation. The catalyst ink may further contain additives such as dispersants.

[0082] The catalyst ink may be subjected to a dispersion treatment. The viscosity of the catalyst ink and the size of the particles contained in the catalyst ink can be controlled by the conditions of the dispersion treatment. The method of dispersion treatment is not particularly limited. For example, dispersion treatments include treatment by ball mill and roll mill, treatment by shear mill, treatment by wet mill, ultrasonic dispersion treatment, etc. Homogenizers that stir by centrifugal force may also be used for dispersion treatment. The longer the dispersion treatment time, the more the aggregates of particles contained in the catalyst ink are broken down, and the smaller the pore volume in the electrode catalyst layers 30C and 30A tends to become.

[0083] The solid content in the catalyst ink is preferably 1% by mass or more and 50% by mass or less. If the solid content is 1% by mass or more, the decrease in the film formation rate is suppressed, and thus the decrease in productivity is suppressed. If the solid content is 50% by mass or less, the viscosity of the catalyst ink is prevented from becoming excessively high, and thus the occurrence of cracks in the electrode catalyst layers 30C and 30A is suppressed.

[0084] (Formation of electrode catalyst layer) The electrode catalyst layers 30C and 30A are formed by applying catalyst ink to a substrate to form a coating film and then drying the coating film. A transfer sheet or a polymer electrolyte membrane 20 can be used as the substrate.

[0085] The transfer sheet can be any sheet made of a material with good transfer properties; for example, a sheet made of a fluororesin can be used. Examples of fluororesins include ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA), and polytetrafluoroethylene (PTFE).

[0086] Furthermore, the transfer sheet may be made of a polymer compound such as polyimide, polyethylene terephthalate, polyamide, polysulfone, polyethersulfone, polyphenylene sulfide, polyether / etherketone, polyetherimide, polyarylate, or polyethylene naphthalate.

[0087] The method for applying the catalyst ink is not particularly limited, and any known application method may be used. Suitable application methods include the doctor blade method, die coating method, curtain coating method, dipping method, spray coating method, screen printing method, roll coating method, and inkjet method, as these allow for the application of the catalyst ink to the substrate with a uniform film thickness. Of these, the doctor blade method is preferred because it can form a large-area coating film at high speed and is suitable for forming thick coating films. The inkjet method is preferred because it allows for control of the pore distribution in the catalyst layer formed from the coating film and is suitable for forming thin coating films.

[0088] The drying method for the coating film is not particularly limited as long as it can volatilize the solvent, and methods such as ovens, hot plates, hot air drying, and far-infrared radiation can be used. The drying temperature and drying time can be appropriately selected depending on the materials constituting the catalyst ink. The drying temperature of the coating film may be, for example, 40°C to 200°C, and preferably 40°C to 120°C. The drying time of the coating film may be, for example, 0.5 minutes to 1 hour, and preferably 1 minute to 30 minutes.

[0089] When the substrate for forming the electrode catalyst layers 30C and 30A is a transfer sheet, the electrode catalyst layers 30C and 30A are bonded to the polymer electrolyte membrane 20 by thermocompression bonding, and then the transfer sheet is peeled off from the electrode catalyst layers 30C and 30A. This forms the membrane electrode assembly 10.

[0090] When the substrate for forming the electrode catalyst layers 30C and 30A is a polymer electrolyte membrane 20, the electrode catalyst layers 30C and 30A are formed directly on the surface of the polymer electrolyte membrane 20. This forms the membrane electrode assembly 10.

[0091] When forming a target catalyst layer in which the fiber ratio Rf changes, multiple catalyst inks with different ratios of fibrous material to catalyst are sequentially applied to the substrate. Specifically, if the substrate is a transfer sheet, the application of the catalyst ink to form a coating film and the drying of the coating film are carried out in order from the layer with the largest ratio of fibrous material. This forms a target catalyst layer consisting of multiple layers. Subsequently, by bonding the target catalyst layer to the polymer electrolyte membrane 20, a membrane electrode assembly 10 is obtained that has a target catalyst layer in which the fiber ratio Rf increases as it moves away from the polymer electrolyte membrane 20.

[0092] When the substrate is a polymer electrolyte membrane 20, the formation of a coating film by applying catalyst ink and the drying of the coating film are carried out in order from the smallest proportion of fibrous material. This forms a membrane electrode assembly 10 having multiple layers, with a target catalyst layer in which the fiber ratio Rf increases as it moves away from the polymer electrolyte membrane 20.

[0093] In a configuration where the target catalyst layer comprises multiple layers, the first layer is formed using the first catalyst ink, and then the second layer is formed by applying the second catalyst ink to the surface of the first layer. Therefore, even if cracks occur in the first layer, they can be covered by the second layer. Consequently, the impact of cracks on electrolytic performance can be reduced.

[0094] Regarding the drying process in forming the target catalyst layer, after applying the first catalyst ink to form a coating film, the second catalyst ink may be applied to form a coating film without performing a drying process, and these coating films may be dried. Alternatively, after applying the first catalyst ink to form a coating film, the coating film may be partially dried by leaving some solvent in the coating film, and then the second catalyst ink may be applied to form a coating film, and these coating films may be dried. By not completely drying the coating film after forming the first coating film, the first and second layers can be made to adhere closely together. By controlling the drying process in this way, it is possible to form an electrode catalyst layer in which the fiber ratio Rf changes continuously.

[0095] When forming a target catalyst layer from multiple layers, the same coating method may be used for each layer, or different coating methods may be used. For example, the first layer may be formed using a doctor blade method or a die-coating method, the second layer may be formed using an inkjet method while the first layer is semi-dried, and then these layers may be dried. This manufacturing method allows the first and second layers to adhere closely together. Furthermore, by forming the first layer using a doctor blade method that can form coatings at high speed, and forming the second layer using an inkjet method that allows control of pore distribution, it is possible to obtain a target catalyst layer with high diffusivity of reactants and products near the surface while increasing production efficiency.

[0096] [Examples] The above-described membrane electrode assembly will be explained using specific examples and comparative examples. (Example 1) <Preparation of Cathode Catalyst Ink> The catalyst, fibrous material, and polymer electrolyte shown below were mixed in a solvent and dispersed in a planetary ball mill for 30 minutes to prepare a cathode catalyst ink, which is a catalyst ink for forming an electrode catalyst layer for the cathode. The catalyst includes catalyst particles and a support. A mixed solvent of ultrapure water and 1-propanol was used as the solvent. The volume ratio of ultrapure water to 1-propanol in the solvent was 1:1. The solid content in the cathode catalyst ink was adjusted to 10% by mass. - Catalyst: Platinum-supported carbon (product code "TEC10E50E": manufactured by Tanaka Kikinzoku Kogyo, platinum support density: 50% by mass) - Fibrous material: Carbon fiber (product name "VGCF-H": manufactured by Resonac, average fiber diameter: 0.15 μm) - Polymer electrolyte: Nafion (product name "Nafion® DE2020": manufactured by Fujifilm Wako Pure Chemical Industries)

[0097] In the preparation process for the cathode catalyst ink, a first cathode catalyst ink and a second cathode catalyst ink were prepared by changing the mixing ratio of the materials. In the first cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.1. In the first cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:10:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:20:60 by mass. In the second cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.2. In the second cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:20:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:40:60 by mass.

[0098] <Preparation of Anode Catalyst Ink> The catalyst, fibrous material, and polymer electrolyte shown below were mixed in a solvent and dispersed in a planetary ball mill for 30 minutes to prepare anode catalyst ink, which is a catalyst ink for forming the electrode catalyst layer for the anode. A mixed solvent of ultrapure water and 1-propanol was used as the solvent. The volume ratio of ultrapure water to 1-propanol in the solvent was 1:1. The solid content of the anode catalyst ink was adjusted to 10% by mass. The fibrous material, polybenzimidazole fiber, was obtained by dissolving polybenzimidazole in dimethylacetamide, forming fibers using electrospinning, and then grinding. ・Catalyst: Iridium oxide (product number "TEC77100": manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) ・Fibrous material: Polybenzimidazole fiber (average fiber diameter: 0.3 μm) ・Polymer electrolyte: Nafion (product name "Nafion® DE2020": manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd.)

[0099] In the preparation process for the anode catalyst ink, a first anode catalyst ink and a second anode catalyst ink were prepared by changing the mixing ratio of the materials. In the first anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst was 0.04, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte was 100:4:20 by mass. In the second anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst was 0.08, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte was 100:8:24 by mass.

[0100] <Fabrication of Membrane Electrode Assembly> A Nafion membrane (trade name "N115": manufactured by DuPont) was used as the polymer electrolyte membrane. The first cathode catalyst ink was applied to one side of the polymer electrolyte membrane using the doctor blade method, and the coating was dried in an air atmosphere at 70°C for 2 minutes. This formed the first catalyst layer. Subsequently, the second cathode catalyst ink was applied on the first catalyst layer using the doctor blade method, and the coating was dried in an air atmosphere at 80°C for 10 minutes. This formed the second catalyst layer, creating a two-layer electrode catalyst layer for the cathode. The coating amounts of the first and second cathode catalyst inks per unit area were set to a catalyst mass ratio of 1:1, and the catalyst load in the cathode electrode catalyst layer was 0.2 mg / cm². ２ I adjusted it so that it would work.

[0101] The first anode catalyst ink was applied to the other surface of the polymer electrolyte membrane using the doctor blade method, and the coating was dried in an air atmosphere at 70°C for 2 minutes. This formed the first catalyst layer. Subsequently, the second anode catalyst ink was applied on the first catalyst layer using the doctor blade method, and the coating was dried in an air atmosphere at 80°C for 10 minutes. This formed the second catalyst layer, creating a two-layer electrode catalyst layer for the anode. The application rate of the first anode catalyst ink and the second anode catalyst ink per unit area was 1:1 in terms of catalyst mass ratio, and the catalyst load in the electrode catalyst layer for the anode was 0.5 mg / cm². ２ I adjusted it so that it would work.

[0102] As described above, the membrane electrode assembly of Example 1 was obtained. In Example 1, in both the cathode electrode catalyst layer and the anode electrode catalyst layer, the fiber ratio Rf increases in steps as it moves away from the polymer electrolyte membrane. In each electrode catalyst layer, the ratio Rr of the minimum value to the maximum value of the fiber ratio Rf is 0.5.

[0103] (Example 2) The film electrode assembly of Example 2 was obtained using the same materials and process as in Example 1, except that the mixing ratio of the materials for the cathode catalyst ink and the anode catalyst ink was changed.

[0104] In the first cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.02. In the first cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:2:20 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:4:40 by mass. In the second cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.2. In the second cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:20:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:40:60 by mass.

[0105] In the first anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.02, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:2:20 by mass. In the second anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.1, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:10:24 by mass.

[0106] In Example 2, the fiber ratio Rf increases stepwise as it moves away from the polymer electrolyte membrane in both the cathode electrode catalyst layer and the anode electrode catalyst layer. In the cathode electrode catalyst layer, the ratio Rr of the minimum fiber ratio Rf to the maximum fiber ratio Rf is 0.1, and in the anode electrode catalyst layer, the ratio Rr of the minimum fiber ratio Rf to the maximum fiber ratio Rf is 0.2.

[0107] (Example 3) The film electrode assembly of Example 3 was obtained using the same materials and process as in Example 1, except that the mixing ratio of the materials for the cathode catalyst ink and the anode catalyst ink was changed.

[0108] In the first cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.02. In the first cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:2:20 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:4:40 by mass. In the second cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.1. In the second cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:10:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:20:60 by mass.

[0109] In the first anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.04, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:4:20 by mass. In the second anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.2, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:20:30 by mass.

[0110] In Example 3, the fiber ratio Rf of the cathode electrode catalyst layer and the anode electrode catalyst layer increases in steps as they move away from the polymer electrolyte membrane. In each electrode catalyst layer, the ratio Rr of the minimum value of the fiber ratio Rf to the maximum value is 0.2.

[0111] (Example 4) The film electrode assembly of Example 4 was obtained using the same materials and process as in Example 1, except that the mixing ratio of the materials for the cathode catalyst ink and the anode catalyst ink was changed.

[0112] In the first cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.02. In the first cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:2:20 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:4:40 by mass. In the second cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.4. In the second cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:40:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:80:60 by mass.

[0113] In the first anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.02, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:2:20 by mass. In the second anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.4, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:40:24 by mass.

[0114] In Example 4, the fiber ratio Rf of the cathode electrode catalyst layer and the anode electrode catalyst layer increases in steps as they move away from the polymer electrolyte membrane. In each electrode catalyst layer, the ratio Rr of the minimum value of the fiber ratio Rf to the maximum value is 0.05.

[0115] (Example 5) The film electrode assembly of Example 5 was obtained using the same materials and process as in Example 1, except that the mixing ratio of the materials for the cathode catalyst ink and the anode catalyst ink was changed.

[0116] In the first cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.24. In the first cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:24:20 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:48:40 by mass. In the second cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.4. In the second cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:40:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:80:60 by mass.

[0117] In the first anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.24, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:24:20 by mass. In the second anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.4, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:40:24 by mass.

[0118] In Example 5, the fiber ratio Rf of the cathode electrode catalyst layer and the anode electrode catalyst layer increases in steps as they move away from the polymer electrolyte membrane. In each electrode catalyst layer, the ratio Rr of the minimum value of the fiber ratio Rf to the maximum value is 0.6.

[0119] (Example 6) <Preparation of Cathode Catalyst Ink> The catalyst, fibrous material, and polymer electrolyte shown below were mixed in a solvent and dispersed in a planetary ball mill for 30 minutes to prepare a cathode catalyst ink. The catalyst includes catalyst particles and a support. A mixed solvent of ultrapure water and 1-propanol was used as the solvent. The volume ratio of ultrapure water to 1-propanol in the solvent was 1:1. The solid content in the cathode catalyst ink was adjusted to 10% by mass. ・Catalyst: Platinum-supported carbon (product number "TEC10E50E": manufactured by Tanaka Kikinzoku Kogyo, platinum support density: 50% by mass) ・Fibrous material: Polybenzimidazole fiber (average fiber diameter: 0.3 μm) ・Polymer electrolyte: Nafion (product name "Nafion (registered trademark) DE2020": manufactured by Fujifilm Wako Pure Chemical Industries)

[0120] In the preparation process for the cathode catalyst ink, a first cathode catalyst ink and a second cathode catalyst ink were prepared by changing the mixing ratio of the materials. In the first cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.1. In the first cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:10:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:20:60 by mass. In the second cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.2. In the second cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:20:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:40:60 by mass.

[0121] <Preparation of Anode Catalyst Ink> The catalyst, fibrous material, and polymer electrolyte listed below were mixed in a solvent and dispersed in a planetary ball mill for 30 minutes to prepare the anode catalyst ink. A mixed solvent of ultrapure water and 1-propanol was used as the solvent. The volume ratio of ultrapure water to 1-propanol in the solvent was 1:1. The solid content in the anode catalyst ink was adjusted to 10% by mass. • Catalyst: Iridium oxide (product code "TEC77100": manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) • Fibrous material: Cellulose nanofiber (average fiber diameter: 0.01 μm) • Polymer electrolyte: Nafion (product name "Nafion (registered trademark) DE2020": manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0122] In the preparation process for the anode catalyst ink, a first anode catalyst ink and a second anode catalyst ink were prepared by changing the mixing ratio of the materials. In the first anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst was 0.04, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte was 100:4:20 by mass. In the second anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst was 0.08, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte was 100:8:24 by mass.

[0123] <Fabrication of Membrane Electrode Assembly> A Nafion membrane (trade name "N115": manufactured by DuPont) was used as the polymer electrolyte membrane. The first cathode catalyst ink was applied to one side of the polymer electrolyte membrane using the doctor blade method, and the coating was dried in an air atmosphere at 60°C for 2 minutes. This formed the first catalyst layer. Subsequently, the second cathode catalyst ink was applied on the first catalyst layer using the inkjet method, and the coating was dried in an air atmosphere at 80°C for 5 minutes. This formed the second catalyst layer, creating a two-layer electrode catalyst layer for the cathode. The coating amounts of the first and second cathode catalyst inks per unit area were set to a catalyst mass ratio of 1:1, and the catalyst load in the cathode electrode catalyst layer was 0.2 mg / cm². ２ I adjusted it so that it would work.

[0124] The first anode catalyst ink was applied to the other side of the polymer electrolyte membrane using a doctor blade method, and the coating was dried in an air atmosphere at 60°C for 2 minutes. This formed the first catalyst layer. Subsequently, the second anode catalyst ink was applied on the first catalyst layer using an inkjet method, and the coating was dried in an air atmosphere at 80°C for 10 minutes. This formed the second catalyst layer, creating a two-layer electrode catalyst layer for the anode. The coating amounts of the first anode catalyst ink and the second anode catalyst ink per unit area were set to a catalyst mass ratio of 2:1, and the catalyst load in the electrode catalyst layer for the anode was 0.5 mg / cm². ２ I adjusted it so that it would work.

[0125] Based on the above, the membrane electrode assembly of Example 6 was obtained. In Example 6, in both the cathode electrode catalyst layer and the anode electrode catalyst layer, the fiber ratio Rf increases in steps as it moves away from the polymer electrolyte membrane. In each electrode catalyst layer, the ratio Rr of the minimum value to the maximum value of the fiber ratio Rf is 0.5.

[0126] (Example 7) The film electrode assembly of Example 7 was obtained using the same materials and process as in Example 6, except that the mixing ratio of the materials for the cathode catalyst ink and the anode catalyst ink was changed.

[0127] In the first cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.02. In the first cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:2:20 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:4:40 by mass. In the second cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.2. In the second cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:20:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:40:60 by mass.

[0128] In the first anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.02, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:2:20 by mass. In the second anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.1, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:10:24 by mass.

[0129] In Example 7, the fiber ratio Rf increases in a stepwise manner as it moves away from the polymer electrolyte membrane in both the cathode electrode catalyst layer and the anode electrode catalyst layer. In the cathode electrode catalyst layer, the ratio Rr of the minimum value of the fiber ratio Rf to the maximum value is 0.1, and in the anode electrode catalyst layer, the ratio Rr of the minimum value of the fiber ratio Rf to the maximum value is 0.2.

[0130] (Example 8) The film electrode assembly of Example 8 was obtained using the same materials and process as in Example 6, except that the mixing ratio of the materials for the cathode catalyst ink and the anode catalyst ink was changed.

[0131] In the first cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.02. In the first cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:2:20 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:4:40 by mass. In the second cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.1. In the second cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:10:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:20:60 by mass.

[0132] In the first anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.04, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:4:20 by mass. In the second anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.2, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:20:30 by mass.

[0133] In Example 8, the fiber ratio Rf of the cathode electrode catalyst layer and the anode electrode catalyst layer increases in steps as they move away from the polymer electrolyte membrane. In each electrode catalyst layer, the ratio Rr of the minimum value of the fiber ratio Rf to the maximum value is 0.2.

[0134] (Example 9) The film electrode assembly of Example 9 was obtained using the same materials and process as in Example 6, except that the mixing ratio of the materials for the cathode catalyst ink and the anode catalyst ink was changed.

[0135] In the first cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.02. In the first cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:2:20 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:4:40 by mass. In the second cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.4. In the second cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:40:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:80:60 by mass.

[0136] In the first anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.02, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:2:20 by mass. In the second anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.4, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:40:24 by mass.

[0137] In Example 9, the fiber ratio Rf of the cathode electrode catalyst layer and the anode electrode catalyst layer increases in steps as they move away from the polymer electrolyte membrane. In each electrode catalyst layer, the ratio Rr of the minimum value of the fiber ratio Rf to the maximum value is 0.05.

[0138] (Example 10) The film electrode assembly of Example 10 was obtained using the same materials and process as in Example 6, except that the mixing ratio of the materials for the cathode catalyst ink and the anode catalyst ink was changed.

[0139] In the first cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.24. In the first cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:24:20 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:48:40 by mass. In the second cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.4. In the second cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:40:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:80:60 by mass.

[0140] In the first anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.24, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:24:20 by mass. In the second anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.4, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:40:24 by mass.

[0141] In Example 10, the fiber ratio Rf of the cathode electrode catalyst layer and the anode electrode catalyst layer increases in steps as they move away from the polymer electrolyte membrane. In each electrode catalyst layer, the ratio Rr of the minimum value of the fiber ratio Rf to the maximum value is 0.6.

[0142] (Example 11) <Preparation of Cathode Catalyst Ink> A cathode catalyst ink was prepared using the same materials and process as in Example 6. In the preparation process of the cathode catalyst ink, the mixing ratio of the materials was changed to prepare a first cathode catalyst ink, a second cathode catalyst ink, and a third cathode catalyst ink. In the first cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst was 0.1. In the first cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte was 100:10:30 by mass, i.e., the ratio of the carrier:fibrous material:polymer electrolyte = 100:20:60 by mass. In the second cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst was 0.15. In the second cathode catalyst ink, the mixing ratio of catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:15:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:30:60 by mass. In the third cathode catalyst ink, the ratio of the mass of fibrous material to the mass of catalyst is 0.2. In the third cathode catalyst ink, the mixing ratio of catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:20:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:40:60 by mass.

[0143] <Preparation of Anode Catalyst Ink> An anode catalyst ink was prepared using the same materials and process as in Example 6. In the preparation of the anode catalyst ink, the mixing ratio of the materials was changed to prepare a first anode catalyst ink, a second anode catalyst ink, and a third anode catalyst ink. In the first anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst was 0.04, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte was 100:4:20 by mass. In the second anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst was 0.06, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte was 100:6:24 by mass. In the third anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.08, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:8:24 by mass.

[0144] <Fabrication of Membrane Electrode Assembly> A Nafion membrane (trade name "N115": manufactured by DuPont) was used as the polymer electrolyte membrane. The first cathode catalyst ink was applied to one side of the polymer electrolyte membrane by inkjet method, and the coating was dried in an air atmosphere at 60°C for 1 minute. This formed the first catalyst layer. Subsequently, the second cathode catalyst ink was applied on the first catalyst layer by inkjet method, and the coating was dried in an air atmosphere at 60°C for 1 minute. This formed the second catalyst layer. Furthermore, the third cathode catalyst ink was applied on the second catalyst layer by inkjet method, and the coating was dried in an air atmosphere at 80°C for 5 minutes. This formed the third catalyst layer, creating a three-layer electrode catalyst layer for the cathode. The coating amounts per unit area of ​​the first cathode catalyst ink, the second cathode catalyst ink, and the third cathode catalyst ink are set to a catalyst mass ratio of 1:1:1, and the catalyst load in the cathode electrode catalyst layer is 0.2 mg / cm². ２ I adjusted it so that it would work.

[0145] A first anode catalyst ink was applied to the other side of the polymer electrolyte membrane using an inkjet method, and the coating was dried in an air atmosphere at 60°C for 1 minute. This formed the first catalyst layer. Subsequently, a second anode catalyst ink was applied on the first catalyst layer using an inkjet method, and the coating was dried in an air atmosphere at 60°C for 1 minute. This formed the second catalyst layer. Furthermore, a third anode catalyst ink was applied on the second catalyst layer using an inkjet method, and the coating was dried in an air atmosphere at 80°C for 10 minutes. This formed the third catalyst layer, creating a three-layer electrode catalyst layer for the anode. The application rates of the first, second, and third anode catalyst inks per unit area were set to a catalyst mass ratio of 1:1:1, and the catalyst load in the electrode catalyst layer for the anode was 0.5 mg / cm². ２ I adjusted it so that it would work.

[0146] Based on the above, the membrane electrode assembly of Example 11 was obtained. In Example 11, in both the cathode electrode catalyst layer and the anode electrode catalyst layer, the fiber ratio Rf increases in steps as it moves away from the polymer electrolyte membrane. In each electrode catalyst layer, the ratio Rr of the minimum value to the maximum value of the fiber ratio Rf is 0.5.

[0147] (Example 12) The film electrode assembly of Example 12 was obtained using the same materials and process as in Example 11, except that the mixing ratio of the materials for the cathode catalyst ink and the anode catalyst ink was changed.

[0148] In the first cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.02. In the first cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:2:20 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:4:40 by mass. In the second cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.1. In the second cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:10:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:20:60 by mass. In the third cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.2. In the third cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:20:30 by mass, which means the carrier:fibrous material:polymer electrolyte is 100:40:60 by mass.

[0149] In the first anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.02, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:2:20 by mass. In the second anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.05, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:5:24 by mass. In the third anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.1, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:10:24 by mass.

[0150] In Example 12, the fiber ratio Rf increases in a stepwise manner as it moves away from the polymer electrolyte membrane in both the cathode electrode catalyst layer and the anode electrode catalyst layer. In the cathode electrode catalyst layer, the ratio Rr of the minimum value of the fiber ratio Rf to the maximum value is 0.1, and in the anode electrode catalyst layer, the ratio Rr of the minimum value of the fiber ratio Rf to the maximum value is 0.2.

[0151] (Example 13) The film electrode assembly of Example 13 was obtained using the same materials and process as in Example 11, except that the mixing ratio of the materials for the cathode catalyst ink and the anode catalyst ink was changed.

[0152] In the first cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.02. In the first cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:2:20 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:4:40 by mass. In the second cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.05. In the second cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:5:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:10:60 by mass. In the third cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.1. In the third cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:10:30 by mass, which means the carrier:fibrous material:polymer electrolyte is 100:20:60 by mass.

[0153] In the first anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.04, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:4:20 by mass. In the second anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.1, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:10:30 by mass. In the third anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.2, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:20:30 by mass.

[0154] In Example 13, the fiber ratio Rf of the cathode electrode catalyst layer and the anode electrode catalyst layer increases in steps as they move away from the polymer electrolyte membrane. In each electrode catalyst layer, the ratio Rr of the minimum value of the fiber ratio Rf to the maximum value is 0.2.

[0155] (Example 14) The film electrode assembly of Example 14 was obtained using the same materials and process as in Example 11, except that the mixing ratio of the materials for the cathode catalyst ink and the anode catalyst ink was changed.

[0156] In the first cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.02. In the first cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:2:20 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:4:40 by mass. In the second cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.2. In the second cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:20:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:40:60 by mass. In the third cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.4. In the third cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:40:30 by mass, which means the carrier:fibrous material:polymer electrolyte is 100:80:60 by mass.

[0157] In the first anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.02, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:2:20 by mass ratio. In the second anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.2, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:20:24 by mass ratio. In the third anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.4, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:40:24 by mass ratio.

[0158] In Example 14, the fiber ratio Rf of the cathode electrode catalyst layer and the anode electrode catalyst layer increases in steps as they move away from the polymer electrolyte membrane. In each electrode catalyst layer, the ratio Rr of the minimum value of the fiber ratio Rf to the maximum value is 0.05.

[0159] (Example 15) The film electrode assembly of Example 15 was obtained using the same materials and process as in Example 11, except that the mixing ratio of the materials for the cathode catalyst ink and the anode catalyst ink was changed.

[0160] In the first cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.24. In the first cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:24:20 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:48:40 by mass. In the second cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.3. In the second cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is catalyst:fibrous material:polymer electrolyte = 100:30:25 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:60:50 by mass. In the third cathode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.4. In the third cathode catalyst ink, the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:40:30 by mass, which means the carrier:fibrous material:polymer electrolyte is 100:80:60 by mass.

[0161] In the first anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.24, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:24:20 by mass. In the second anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.3, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:30:22 by mass. In the third anode catalyst ink, the ratio of the mass of the fibrous material to the mass of the catalyst is 0.4, and the mixing ratio of the catalyst, fibrous material, and polymer electrolyte is 100:40:24 by mass.

[0162] In Example 15, the fiber ratio Rf of the cathode electrode catalyst layer and the anode electrode catalyst layer increases in steps as they move away from the polymer electrolyte membrane. In each electrode catalyst layer, the ratio Rr of the minimum value of the fiber ratio Rf to the maximum value is 0.6.

[0163] (Comparative Example 1) One type of cathode catalyst ink was prepared using the same materials and process as in Example 1. Specifically, the components of the first cathode catalyst ink and the components of the second cathode catalyst ink, with the same mixing ratio as in Example 1, were mixed at once in a ratio such that the mass ratio of catalysts in these catalyst inks was 1:1, and a dispersion treatment was performed to obtain a cathode catalyst ink. In the cathode catalyst ink, the mixing ratio of catalyst, fibrous material, and polymer electrolyte was catalyst:fibrous material:polymer electrolyte = 100:15:30 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:30:60 by mass.

[0164] A single type of anode catalyst ink was prepared using the same materials and process as in Example 1. Specifically, the components of the first anode catalyst ink and the components of the second anode catalyst ink, with the same mixing ratio as in Example 1, were mixed at once in a ratio such that the mass ratio of catalysts in these catalyst inks was 1:1, and then dispersed to obtain an anode catalyst ink. In the anode catalyst ink, the mixing ratio of catalyst, fibrous material, and polymer electrolyte was 100:6:22 by mass.

[0165] A Nafion film (trade name "N115": manufactured by DuPont) was used as the polymer electrolyte membrane. Cathode catalyst ink was applied to one side of the polymer electrolyte membrane using the doctor blade method, and the coating was dried in an air atmosphere at 80°C for 10 minutes. This formed an electrode catalyst layer for the cathode. The amount of cathode catalyst ink applied was such that the catalyst load on the cathode electrode catalyst layer was 0.2 mg / cm². ２ I adjusted it so that it would work.

[0166] Anode catalyst ink was applied to the other side of the polymer electrolyte membrane using a doctor blade method, and the coating was dried in an air atmosphere at 80°C for 10 minutes. This formed an electrode catalyst layer for the anode. The amount of anode catalyst ink applied was such that the catalyst load in the electrode catalyst layer for the anode was 0.5 mg / cm². ２ The adjustments were made to achieve the above. As a result, the film electrode assembly of Comparative Example 1 was obtained. In Comparative Example 1, the fiber ratio Rf is constant in both the cathode electrode catalyst layer and the anode electrode catalyst layer.

[0167] (Comparative Example 2) One type of cathode catalyst ink was prepared using the same materials and process as in Example 1. Specifically, the components of the first cathode catalyst ink and the components of the second cathode catalyst ink, with the same mixing ratio as in Example 2, were mixed at once in a ratio such that the mass ratio of catalysts in these catalyst inks was 1:1, and a dispersion treatment was performed to obtain a cathode catalyst ink. In the cathode catalyst ink, the mixing ratio of catalyst, fibrous material, and polymer electrolyte was Catalyst:Fibrous Material:Polymer Electrolyte = 100:11:25 by mass, that is, Carrier:Fibrous Material:Polymer Electrolyte = 100:22:50 by mass.

[0168] A single type of anode catalyst ink was prepared using the same materials and process as in Example 1. Specifically, the components of the first anode catalyst ink and the components of the second anode catalyst ink, with the same mixing ratio as in Example 2, were mixed at once in a ratio such that the mass ratio of catalysts in these catalyst inks was 1:1, and a dispersion treatment was performed to obtain an anode catalyst ink. In the anode catalyst ink, the mixing ratio of catalyst, fibrous material, and polymer electrolyte was 100:6:22 by mass.

[0169] A cathode electrode catalyst layer and an anode electrode catalyst layer were formed using the same process as in Comparative Example 1. Thus, the film electrode assembly of Comparative Example 2 was obtained. In Comparative Example 2, the fiber ratio Rf was constant in both the cathode electrode catalyst layer and the anode electrode catalyst layer.

[0170] (Comparative Example 3) One type of cathode catalyst ink was prepared using the same materials and process as in Example 1. Specifically, the components of the first cathode catalyst ink and the components of the second cathode catalyst ink, with the same mixing ratio as in Example 3, were mixed at once in a ratio such that the mass ratio of catalyst in these catalyst inks was 1:1, and a dispersion treatment was performed to obtain a cathode catalyst ink. In the cathode catalyst ink, the mixing ratio of catalyst, fibrous material, and polymer electrolyte was catalyst:fibrous material:polymer electrolyte = 100:6:25 by mass, that is, carrier:fibrous material:polymer electrolyte = 100:12:50 by mass.

[0171] A single type of anode catalyst ink was prepared using the same materials and process as in Example 1. Specifically, the components of the first anode catalyst ink and the components of the second anode catalyst ink, according to the mixing ratio of Example 3, were mixed at once in a ratio such that the mass ratio of catalysts in these catalyst inks was 1:1, and a dispersion treatment was performed to obtain an anode catalyst ink. In the anode catalyst ink, the mixing ratio of catalyst, fibrous material, and polymer electrolyte was 100:12:25 by mass.

[0172] A cathode electrode catalyst layer and an anode electrode catalyst layer were formed using the same process as in Comparative Example 1. Thus, the film electrode assembly of Comparative Example 3 was obtained. In Comparative Example 3, the fiber ratio Rf was constant in both the cathode electrode catalyst layer and the anode electrode catalyst layer.

[0173] (Comparative Example 4) Cathode catalyst ink and anode catalyst ink were obtained using the same materials and process as in Comparative Example 1, except that no fibrous material was added to either the cathode catalyst ink or the anode catalyst ink.

[0174] In cathode catalyst inks, the mixing ratio of catalyst to polymer electrolyte is catalyst:polymer electrolyte = 100:30 by mass, which means the carrier:polymer electrolyte = 100:60 by mass. In anode catalyst inks, the mixing ratio of catalyst to polymer electrolyte is catalyst:polymer electrolyte = 100:22 by mass.

[0175] An attempt was made to form an electrode catalyst layer for the cathode and an electrode catalyst layer for the anode using the same process as in Comparative Example 1. However, large cracks occurred in the electrode catalyst layer, and the electrode catalyst layer peeled off from the polymer electrolyte membrane, making it impossible to form an electrode catalyst layer on the polymer electrolyte membrane.

[0176] (Comparative Example 5) Cathode catalyst ink and anode catalyst ink were obtained using the same materials and process as in Comparative Example 2, except that no fibrous material was added to either the cathode catalyst ink or the anode catalyst ink.

[0177] In cathode catalyst inks, the mixing ratio of catalyst to polymer electrolyte is catalyst:polymer electrolyte = 100:25 by mass, which means the mass ratio of carrier:polymer electrolyte = 100:50. In anode catalyst inks, the mixing ratio of catalyst to polymer electrolyte is catalyst:polymer electrolyte = 100:22 by mass.

[0178] An attempt was made to form an electrode catalyst layer for the cathode and an electrode catalyst layer for the anode using the same process as in Comparative Example 1. However, large cracks occurred in the electrode catalyst layer, and the electrode catalyst layer peeled off from the polymer electrolyte membrane, making it impossible to form an electrode catalyst layer on the polymer electrolyte membrane.

[0179] (Comparative Example 6) Cathode catalyst ink and anode catalyst ink were obtained using the same materials and process as in Comparative Example 3, except that no fibrous material was added to either the cathode catalyst ink or the anode catalyst ink.

[0180] In cathode catalyst inks, the mixing ratio of catalyst to polymer electrolyte is catalyst:polymer electrolyte = 100:25 by mass, which means the mass ratio of carrier:polymer electrolyte = 100:50. In anode catalyst inks, the mixing ratio of catalyst to polymer electrolyte is catalyst:polymer electrolyte = 100:25 by mass.

[0181] An attempt was made to form an electrode catalyst layer for the cathode and an electrode catalyst layer for the anode using the same process as in Comparative Example 1. However, large cracks occurred in the electrode catalyst layer, and the electrode catalyst layer peeled off from the polymer electrolyte membrane, making it impossible to form an electrode catalyst layer on the polymer electrolyte membrane.

[0182] (Evaluation Method) <Evaluation of Crack Amount> To evaluate the amount of cracks in the electrode catalyst layer, the contrast value using transmitted light was measured. When transmitted light is shone from the back of the laminate, defects such as cracks and pinholes appear white because more light is transmitted through them. Therefore, the contrast between the black and white areas when shone with transmitted light can be used to determine the amount of cracks.

[0183] For the examples and comparative examples, images were obtained by irradiating the laminates with transmitted light, for both laminates in which a cathode electrode catalyst layer was formed on a polymer electrolyte membrane and laminates in which an anode electrode catalyst layer was formed on a polymer electrolyte membrane. The contrast value was defined as the ratio of black pixels to white pixels in the image. In the evaluation of the amount of cracks, a contrast value of 10 was used. ３ If the above conditions are met, it is classified as "A" (no cracks), and the contrast value is 10. ３ If the value was less than the specified value, it was classified as "B" (cracked).

[0184] <Evaluation of Thickness Variation of Electrode Catalyst Layers> For the examples and comparative examples, the thickness variation of the electrode catalyst layers was evaluated by observing the cross-sections of the electrode catalyst layers for both the cathode and anode.

[0185] A cryocrosssection polisher (manufactured by JEOL) was used to expose the cross-section, and the cross-section was observed using a scanning electron microscope (SU8010: manufactured by Hitachi High-Technologies). During the cross-sectional observation, the thickness of the electrode catalyst layer was measured at more than 10 observation points to determine the uniformity of the thickness. The uniformity U (%) was calculated using the following formula (Equation 2), where Tm is the maximum thickness, Tn is the minimum thickness, and TA is the average thickness at the observation points: U = {(Tm - Tn) / TA} × 100 ... (Equation 2)

[0186] In evaluating the variation in the thickness of the electrode catalyst layer, a uniformity U of 5% or less was classified as "A" (no variation), and a uniformity U exceeding 5% was classified as "B" (variation present).

[0187] <Evaluation of Electrolytic Performance> The electrolytic performance of the membrane electrode assembly was evaluated for both the example and comparative example when used in a PEM-type water electrolysis apparatus and when used in an organic hydride electrolytic synthesis apparatus.

[0188] In evaluating the electrolytic performance of a PEM-type water electrolysis apparatus, a Pt-plated Ti mesh was incorporated as a power supply on both sides of the membrane electrode assembly to create an electrolytic cell for evaluation. The electrolytic cell was then subjected to a current density of 0 to 4.0 A / cm² at 50°C. ２The voltage is applied in stages to change the current density to 3.0 A / cm². ２ The voltage at which this occurred was measured. In a PEM-type water electrolysis apparatus, when water and voltage are supplied, oxygen and protons are generated from the water in the anode electrode catalyst layer, and the generated protons are converted into hydrogen in the cathode electrode catalyst layer. Pure water was used as the water.

[0189] In the evaluation of the electrolysis performance of the PEM type water electrolysis device, the current density was 3.0 A / cm². ２ In this case, a voltage of 1.85V or less was classified as good ("A"), a voltage exceeding 1.85V but 1.9V or less was classified as somewhat good ("B"), and a voltage exceeding 1.9V was classified as poor ("C").

[0190] In evaluating the electrolytic performance of an organic hydride electrolytic synthesis apparatus, a Pt-plated Ti mesh was incorporated as a power supply on both sides of the membrane electrode assembly to fabricate an electrolytic cell for evaluation. The current density of the electrolytic cell was then measured at 60°C, ranging from 0 to 2.0 A / cm². ２ The voltage is applied in stages to change the current density to 1.0 A / cm². ２ The voltage at which this occurs was measured. In an organic hydride electrolytic synthesis apparatus, when water, organic matter, and voltage are supplied, oxygen and protons are generated from water in the anode electrode catalyst layer, and the generated protons hydrogenate the organic matter in the cathode electrode catalyst layer to produce an organic hydride. Toluene was used as the organic matter, and methylcyclohexane was generated as the organic hydride.

[0191] In evaluating the electrolytic performance of an organic hydride electrolytic synthesis apparatus, a current density of 1.0 A / cm² was used. ２ In this case, a voltage of 1.75V or less was classified as good ("A"), a voltage exceeding 1.75V but 1.8V or less was classified as somewhat good ("B"), and a voltage exceeding 1.8V was classified as poor ("C").

[0192] (Evaluation Results) Figure 2 shows the type of fibrous material, the layer configuration of the electrode catalyst layer, the ratio Rr of the minimum value to the maximum value of the fiber ratio Rf, and the evaluation results for each example and comparative example. Note that comparative examples 4 to 6 were not evaluated because, as described above, an electrode catalyst layer could not be formed on the polymer electrolyte membrane.

[0193] Regarding the type of fibrous material, "CF" indicates carbon fiber, "PBI" indicates polybenzimidazole fiber, and "CNF" indicates cellulose nanofiber. Regarding the layer structure of the electrode catalyst layer, "L1" indicates a two-layer structure consisting of a first catalyst layer and a second catalyst layer formed by the doctor blade method, and "L2" indicates a two-layer structure consisting of a first catalyst layer formed by the doctor blade method and a second catalyst layer formed by the inkjet method. "L3" indicates a three-layer structure consisting of a first catalyst layer, a second catalyst layer, and a third catalyst layer formed by the inkjet method, and "L4" indicates a single-layer structure formed by the doctor blade method. Regarding the evaluation of electrolysis performance, "WE" indicates the evaluation of the electrolysis performance of a PEM-type water electrolysis apparatus, and "ES" indicates the evaluation of the electrolysis performance of an organic hydride electrolysis synthesizer.

[0194] As shown in Figure 2, in Examples 1 to 15, where the fiber ratio Rf in the electrode catalyst layer increases with distance from the polymer electrolyte membrane, it was confirmed that crack occurrence and variations in the thickness of the electrode catalyst layer were suppressed, resulting in good electrolytic performance.

[0195] On the other hand, in Comparative Examples 1 to 3, where the fiber ratio Rf is constant, crack occurrence is suppressed compared to Comparative Examples 4 to 6, which do not contain fibrous material. However, the results for each evaluation were not as high as those obtained in Examples 1 to 15. In Comparative Examples 1, 2, and 3, and in Examples 1, 2, and 3, the ratio of fibrous material throughout the entire electrode catalyst layer is the same. However, in Comparative Examples 1, 2, and 3, the fiber ratio Rf is more uniform than in Examples 1, 2, and 3. As a result, the ratio of fibrous material in the outermost region of the electrode catalyst layer is smaller compared to Examples 1, 2, and 3, and the ratio of fibrous material in the region near the polymer electrolyte membrane is larger compared to Examples 1, 2, and 3. Therefore, it is thought that the effects of suppressing crack occurrence, suppressing thickness variation, and improving electrolytic performance are not as pronounced as in Examples 1, 2, and 3.

[0196] Among Examples 1 to 15, Examples 6 to 15 showed particularly high electrolytic performance. In Examples 6 to 15, polybenzimidazole fibers are used in the cathode electrode catalyst layer, resulting in higher catalyst dispersibility in the cathode catalyst ink compared to Examples 1 to 5, which used carbon fibers. This leads to high catalytic activity and improved electrolytic performance. Furthermore, in Examples 6 to 15, cellulose nanofibers are used in the anode electrode catalyst layer, increasing the viscosity of the anode catalyst ink compared to Examples 1 to 5, which used polybenzimidazole fibers. This suppresses the penetration of the ink into the first layer of the coating when forming the second layer. This also improves electrolytic performance.

[0197] As described above using the examples, the membrane electrode assembly of the above embodiment provides the following effects: (1) In the target catalyst layer, the fiber ratio Rf increases continuously or intermittently as it moves away from the polymer electrolyte membrane in the thickness direction. As a result, the mechanical strength is particularly increased in the outermost region of the target catalyst layer, so that crack occurrence and thickness variations are effectively suppressed. On the other hand, in the region of the target catalyst layer near the polymer electrolyte membrane, inhibition of the electrolytic reaction by fibrous material is suppressed. Therefore, it is possible to improve the electrolytic performance.

[0198] Furthermore, when one of the pair of electrode catalyst layers is the target catalyst layer, the above-mentioned effects are obtained for the target catalyst layer, and it can be said that crack occurrence and thickness variation are suppressed compared to when neither of the pair of electrode catalyst layers is the target catalyst layer. To further improve electrolytic performance, it is preferable that both of the pair of electrode catalyst layers are the target catalyst layers.

[0199] (2) The target catalyst layer comprises multiple layers having different mass ratios of fibrous material to catalyst. With this configuration, changes in the fiber ratio in the target catalyst layer can be easily and accurately formed. If the above multiple layers consist of two or three layers, changes in the fiber ratio can be accurately formed while keeping the burden required for manufacturing the target catalyst layer low.

[0200] (3) If the average fiber diameter of the fibrous material is 0.003 μm or more and 0.6 μm or less, the effect of suppressing crack generation and thickness variation in the target catalyst layer can be accurately obtained. (4) If the ratio of the minimum value to the maximum value of the fiber ratio in the thickness direction of the target catalyst layer is 0.04 or more and 0.7 or less, a sufficient difference in fiber ratio can be obtained within the target catalyst layer, and the above effect can be accurately obtained. On the other hand, since the difference in fiber ratio within the target catalyst layer does not become too large, smooth mass transfer can proceed.

[0201] (5) If the fibrous material is any of carbon fiber, cellulose nanofiber, or polybenzimidazole fiber, the effects of suppressing crack formation and thickness variation, and improving electrolytic performance can be preferably obtained. In particular, if the electrode catalyst layer for the cathode contains polybenzimidazole fiber and the electrode catalyst layer for the anode contains cellulose nanofiber, the electrolytic performance can be further enhanced.

[0202] (6) If the polymer electrolyte membrane has proton conductivity, the membrane electrode assembly can be used in a PEM water electrolysis apparatus or an organic hydride electrolysis synthesis apparatus, thereby increasing the versatility of the membrane electrode assembly.

[0203] (7) By using the membrane electrode assembly in a water electrolysis apparatus, the output of the water electrolysis apparatus can be improved. By using the membrane electrode assembly in an organic hydride electrolysis synthesizer, the output of the organic hydride electrolysis synthesizer can be improved.

[0204] (8) The layers included in the target catalyst layer are formed from coatings deposited by the doctor blade method or the inkjet method. The doctor blade method allows for high-speed film deposition and improved productivity, while the inkjet method allows for control of the pore distribution.

[0205] [Note] The technical concepts that can be understood from the above embodiments and examples are described below. If the target catalyst layer contains a fibrous material, even if the fiber ratio Rf does not increase as it moves away from the polymer electrolyte membrane in the thickness direction, the effect of suppressing crack occurrence and thickness variation can be obtained compared to the case where the target catalyst layer does not contain a fibrous material.

[0206] Furthermore, if the region in the target catalyst layer, within a region within 1 / 3 of the thickness of the target catalyst layer in the thickness direction from the side opposite to the polymer electrolyte membrane, includes a region where the fiber ratio Rf is maximum, then the effect of suppressing crack generation in the outermost region can be obtained. In this case, the region where the fiber ratio Rf is minimum does not have to be near the polymer electrolyte membrane; in other words, the fiber ratio Rf does not have to increase monotonically in the thickness direction.

[0207] Furthermore, if the target catalyst layer contains a region within one-third of its thickness in the thickness direction from the surface in contact with the polymer electrolyte membrane, where the fiber ratio Rf is minimized, the inhibition of the electrolytic reaction by fibrous material is suppressed, thereby improving electrolytic performance. In this case, the region where the fiber ratio Rf is maximized does not have to be the outermost region; in other words, the fiber ratio Rf does not have to increase monotonically in the thickness direction.

[0208] <Note 1> A membrane electrode assembly comprising a polymer electrolyte membrane and a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane in the thickness direction, wherein at least one of the pair of electrode catalyst layers is a target catalyst layer, the target catalyst layer comprises a catalyst, a polymer electrolyte, and a fibrous material, and the target catalyst layer includes a region in the thickness direction from the surface opposite to the polymer electrolyte membrane, within a region of 1 / 3 of the thickness of the target catalyst layer, in which the fiber ratio, which is the ratio of the mass of the fibrous material to the catalyst, is maximized in the thickness direction.

[0209] According to the above configuration, the inclusion of fibrous material in the target catalyst layer suppresses crack formation and thickness variations. Furthermore, the mechanical strength is particularly enhanced near the surface opposite the polymer electrolyte membrane in the target catalyst layer, thereby effectively suppressing crack formation and thickness variations.

[0210] <Note 2> A membrane electrode assembly comprising a polymer electrolyte membrane and a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane in the thickness direction, wherein at least one of the pair of electrode catalyst layers is a target catalyst layer, the target catalyst layer comprises a catalyst, a polymer electrolyte, and a fibrous material, and the target catalyst layer includes a region within 1 / 3 of the thickness of the target catalyst layer in the thickness direction from the surface in contact with the polymer electrolyte membrane, in which the fiber ratio, which is the ratio of the mass of the fibrous material to the catalyst, is minimized in the thickness direction.

[0211] According to the above configuration, the inclusion of fibrous material in the target catalyst layer suppresses crack formation and variations in thickness. Furthermore, in the region near the polymer electrolyte membrane, inhibition of the electrolytic reaction by the fibrous material is suppressed, thus improving electrolytic performance.

[0212] 10... Membrane electrode assembly 20... Polymer electrolyte membrane 30C, 30A... Electrode catalyst layer 31C, 31A... First catalyst layer 32C, 32A... Second catalyst layer

Claims

1. A membrane electrode assembly comprising a polymer electrolyte membrane and a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane in the thickness direction, wherein at least one of the pair of electrode catalyst layers is a target catalyst layer, the target catalyst layer comprises a catalyst, a polymer electrolyte, and a fibrous material, and in the target catalyst layer, the fiber ratio, which is the ratio of the mass of the fibrous material to the catalyst, increases continuously or intermittently as it moves away from the polymer electrolyte membrane in the thickness direction.

2. The membrane electrode assembly according to claim 1, wherein the target catalyst layer comprises a plurality of layers having different mass ratios of the fibrous material to the catalyst, and in the plurality of layers, the ratio is larger for layers further away from the polymer electrolyte membrane.

3. The film electrode assembly according to claim 2, wherein the plurality of layers consist of two or three layers.

4. The membrane electrode assembly according to claim 1, wherein the average fiber diameter of the fibrous material is 0.003 μm or more and 0.6 μm or less.

5. The membrane electrode assembly according to claim 1, wherein the ratio of the minimum value to the maximum value of the fiber ratio in the thickness direction of the target catalyst layer is 0.04 or more and 0.7 or less.

6. The membrane electrode assembly according to claim 1, wherein the fibrous material contained in the target catalyst layer is any one of carbon fibers, cellulose nanofibers, and polybenzimidazole fibers.

7. The membrane electrode assembly according to claim 1, wherein each of the pair of electrode catalyst layers is the target catalyst layer, the electrode catalyst layer for the cathode contains polybenzimidazole fibers which are the fibrous material, and the electrode catalyst layer for the anode contains cellulose nanofibers which are the fibrous material.

8. The membrane electrode assembly according to claim 1, wherein the polymer electrolyte membrane is proton conductive.

9. The membrane electrode assembly is a membrane electrode assembly according to any one of claims 1 to 8, used in a water electrolysis apparatus.

10. The membrane electrode assembly is a membrane electrode assembly according to any one of claims 1 to 8, used in an organic hydride electrolytic synthesis apparatus.

11. A method for manufacturing a membrane electrode assembly according to any one of claims 1 to 8, comprising forming a coating film by a doctor blade method or an inkjet method, and forming a layer contained in the target catalyst layer from the coating film.

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