Electrode catalyst layer

Abstract

To provide an electrode catalyst layer for a polymer fuel battery, in which drainage or a gas diffusion property can be improved, and a high output can be made.SOLUTION: An electrode catalyst layer bonded to a polymer fuel electrolyte membrane, includes: a catalysis 13; a conductive carrier 14 carrying the catalysis 13; a polymer electrolyte 15; and a fiber state material 16. In a first cross section as a cross section of a thickness direction, a distance between the adjacent first fiber state materials is 0.30 μm or more and 8 μm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electrode catalyst layer constituting a membrane electrode assembly for a polymer fuel cell.

Background Art

[0002] In recent years, fuel cells have attracted attention as effective solutions to environmental and energy problems. A fuel cell oxidizes a fuel such as hydrogen using an oxidant such as oxygen, and converts the accompanying chemical energy into electrical energy. [[ID=...]]Fuel cells are classified into alkaline, phosphoric acid, polymer, molten carbonate, solid oxide, etc. according to the type of electrolyte. Polymer electrolyte fuel cells (PEFC) operate at low temperatures, have high power densities, and can be miniaturized and lightened, so they are expected to be applied as portable power sources, household power sources, and vehicle-mounted power sources.

[0003] A polymer electrolyte fuel cell (PEFC) includes a membrane electrode assembly in which a polymer electrolyte membrane as an electrolyte membrane is sandwiched between a pair of electrodes composed of a fuel electrode (anode) and an air electrode (cathode). By supplying a fuel gas containing hydrogen to the fuel electrode side and an oxidant gas containing oxygen to the air electrode side, power is generated by the following electrochemical reaction.

[0004] Anode: H2 → 2H , + , - , + , - + 2e - ···(1) Cathode: 1 / 2O2 + 2H + + 2e - s → H2O ···(2) The anode and the cathode each have a laminated structure of an electrode catalyst layer and a gas diffusion layer. The fuel gas supplied to the anode-side electrode catalyst layer becomes protons and electrons by the electrode catalyst (Reaction 1). Protons pass through the polymer electrolyte and the polymer electrolyte membrane in the anode-side electrode catalyst layer and move to the cathode. Electrons move to the cathode through an external circuit.A reaction occurs in the cathode-side electrode catalyst layer where protons, electrons, and an oxidant gas supplied from the outside react to generate water (Reaction 2). Thus, power is generated when electrons pass through the external circuit.

[0005] Currently, there is a demand for fuel cells that exhibit high power output characteristics in order to reduce the cost of fuel cells. However, fuel cells generate a large amount of water during high-power operation, which causes water to overflow into the electrode catalyst layer and gas diffusion layer, resulting in footing that hinders gas supply. When footing occurs, there is a problem in that the output of the fuel cell drops significantly.

[0006] To address the above issues, Patent Documents 1 and 2 propose catalyst layers containing carbon or carbon fibers of different particle sizes. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 10-241703 [Patent Document 2] Patent No. 5537178 [Overview of the project] [Problems that the invention aims to solve]

[0008] Patent documents 1 and 2 state that by including different carbon materials, pores are created within the electrode catalyst layer, which is expected to improve drainage and gas diffusion. However, increasing the porosity within the electrode catalyst layer increases its thickness, lengthening the distance electrons or protons travel and increasing resistance. This reduces power generation performance. Furthermore, while there are descriptions of the size, shape, and content of the carbon materials, there is no description of the structure of the catalyst layer, and its effects have not been specifically verified. The invention was made in view of these circumstances, and aims to provide an electrode catalyst layer for polymer fuel cells that can improve drainage and gas diffusion and enable high output. [Means for solving the problem]

[0009] To solve the above problems, one aspect of the present invention provides an electrode catalyst layer bonded to a polymer electrolyte membrane, comprising a catalyst, a conductive carrier supporting the catalyst, a polymer electrolyte, and a fibrous material, wherein the distance between adjacent first fibrous material portions in a first cross-section, which is a cross-section in the thickness direction, is 0.30 μm or more and 8 μm or less. [Effects of the Invention]

[0010] According to one aspect of the present invention, it is possible to provide a catalyst layer for polymer fuel cells that can improve drainage and gas diffusion without unnecessarily increasing the thickness, and that can achieve high output. [Brief explanation of the drawing]

[0011] [Figure 1] This figure schematically shows the structure of the electrode catalyst layer in a membrane electrode assembly according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view illustrating the structure of an electrode catalyst layer according to one embodiment of the present invention. [Figure 3] This is a cross-sectional view illustrating the structure of a membrane electrode assembly according to one embodiment of the present invention. [Figure 4] This is an exploded perspective view showing the internal structure of a single cell of a polymer electrolyte fuel cell according to one embodiment of the present invention. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below with reference to the drawings. It should be noted that the present invention is not limited to the embodiments described below, and modifications such as changes in design can be made based on the knowledge of those skilled in the art, and such modified embodiments are also included within the scope of the present invention.

[0013] (electrode catalyst layer) As shown in Figure 1, the electrode catalyst layers 2 and 3 for polymer fuel cells according to this embodiment consist of a catalyst 13, a conductive carrier 14 supporting the catalyst 13, a polymer electrolyte 15, and a fibrous material 16. In addition, as shown in FIG. 2, in the first cross-section obtained by cutting the electrode catalyst layers 2 and 3 in the thickness direction of the electrode catalyst layer, the distance between any fibrous material and another fibrous material adjacent to the fibrous material is set to be 0.30 μm or more and 8 μm or less. That is, in the first cross-section, the distance between adjacent fibrous materials is set to be 0.30 μm or more and 8 μm or less. By including the fibrous material 16, the electrode catalyst layers 2 and 3 can be formed without cracks, and the pores in the electrode catalyst layers 2 and 3 can be increased. Further, since the distance between the respective fibrous materials 16 is maintained within the above-mentioned predetermined range, the fibrous material 16 can be efficiently utilized, and it is possible to prevent the thickness of the electrode catalyst layers from increasing or the movement distance of electrons or protons from becoming long. Also, in the second cross-section orthogonal to the first cross-section, it is preferable that the distance between adjacent fibrous materials 16 is 0.30 μm or more and 8 μm or less. When set in this way, the effect of the fibrous material 16 can be obtained in all directions of the electrode catalyst layers 2 and 3.

[0014] The distance between the fibrous materials 16 can be obtained, for example, by measuring the distance between the centers of the exposed cross-sections of the respective exposed fibrous materials 16 when observing a cross-section of the electrode catalyst layers 2 and 3 as shown in FIG. 2 using a scanning electron microscope (SEM). That is, in the present embodiment, the distance between the fibrous materials 16 refers to the separation distance between the centers of the cross-sections of the two fibrous materials 16. When the fibrous material 16 is cut obliquely in the cross-section, the shape of the exposed cross-section may be elliptical. In that case, the distance between the fibrous materials 16 can be obtained by measuring with the center of a perfect circle fitted along the minor axis. The observation magnification in the scanning electron microscope (SEM) is preferably 6000 times in terms of being able to measure the distance between the fibrous materials 16 in the entire catalyst layer, and it is preferable to measure all the fibrous materials 16.

[0015] As a method for exposing the cross-section of the electrode catalyst layers 2 and 3, for example, ion milling, ultramicrotome, etc. can be used. When performing the process of exposing the cross-section, in order to reduce the damage to the polymer electrolyte membrane 1 and the polymer electrolyte 15 constituting the electrode catalyst layers 2 and 3, it is preferable to perform the process while cooling the membrane electrode assembly 12. Particularly in terms of obtaining a clear cross-section, it is preferable to use cryo-ion milling.

[0016] The thickness of the electrode catalyst layers 2 and 3 is preferably 30 μm or less, and more preferably 10 μm. When the thickness is greater than 30 μm, the resistance of the electrode catalyst layers 2 and 3 increases, and the output decreases. Also, cracks are likely to occur in the electrode catalyst layers 2 and 3, which is not preferable. The thickness of the electrode catalyst layers 2 and 3 is preferably 1 μm or more. When the thickness is less than 1 μm, variations in layer thickness are likely to occur, and the internal catalyst 13 and polymer electrolyte 15 are likely to become non-uniform. Cracks on the surface of the electrode catalyst layers 2 and 3 and non-uniformity in thickness are likely to have an adverse effect on the durability when used as a fuel cell and operated over a long period, which is not preferable. Also, in the electrode catalyst layers 2 and 3, the concentration of generated water due to power generation is likely to increase, flooding is likely to occur, and the power generation performance decreases, which is not preferable.

[0017] [ <Polymer electrolyte> The polymer electrolyte 15 may be any material having ion conductivity. However, considering the adhesion between the electrode catalyst layers 2 and 3 and the polymer electrolyte membrane, it is preferable to select a material of the same quality as the polymer electrolyte membrane. For the polymer electrolyte 15, for example, fluorine-based resins or hydrocarbon-based resins can be used. For example, as the fluorine-based resin, Nafion (manufactured by Chemours, registered trademark), and as the hydrocarbon-based resin, engineering plastics or those obtained by introducing a sulfonic acid group into its copolymer, etc. can be mentioned.

[0018] <0000 ><Catalyst> As catalyst 13, platinum group elements, metals or alloys thereof, or oxides, complex oxides, etc., can be used. Examples of platinum group elements include platinum, palladium, ruthenium, iridium, rhodium, and osmium. Examples of metals include iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. Among these, platinum or platinum alloys are preferred as catalyst 13. Furthermore, the particle size of these catalysts 13 is preferably 0.5 to 20 nm, as too large a particle size reduces the activity of catalyst 13, and too small a particle size reduces the stability of catalyst 13. More preferably, it is 1 to 5 nm.

[0019] <Conductive carrier> Any conductive carrier 14 can be used as long as it is in particulate form, conductive, and not affected by the catalyst 13. Carbon particles are an example of a conductive carrier 14. The particle size of the conductive carrier 14 is preferably around 10 to 1000 nm. If it is too small, it becomes difficult to form electron conduction paths, and if it is too large, the electrode catalyst layers 2 and 3 become thicker, increasing resistance and degrading the output characteristics. More preferably, it is between 10 and 100 nm. Furthermore, by supporting the catalyst 13 on a conductive carrier 14 with a high surface area, the catalyst 13 can be supported at high density, improving catalytic activity.

[0020] <Fibrous material> The fibrous material 16 can be any material that can maintain its fibrous shape without being affected by the catalyst 13 and the polymer electrolyte 15. In order to reduce the resistance of the electrode catalyst layers 2 and 3, the fibrous material 16 is preferably one that exhibits electronic conductivity or proton conductivity. As the fibrous material 16 exhibiting electronic conductivity, carbon fibers, carbon nanofibers, and carbon nanotubes can be used. Preferably, carbon nanofibers and carbon nanotubes are used. Examples of fibrous materials 16 exhibiting proton conductivity include fibers obtained by processing polymer electrolytes into fibers. Suitable polymer electrolytes include fluororesins and hydrocarbon resins. For example, fluororesins include Nafion (a registered trademark of Chemours), and hydrocarbon resins include engineering plastics or copolymers thereof into which sulfonic acid groups have been introduced. Acid-doped polybenzoazoles, which exhibit proton conductivity through acid doping, can also be suitably used.

[0021] Furthermore, the fibrous material 16 may also include resin fibers having basic functional groups capable of interacting with acidic substances in their main chain skeleton or side chain functional groups. These interact with the acidic substances contained in the polymer electrolyte 15, causing the surface of the resin fibers to be coated with the polymer electrolyte, thereby enabling them to exhibit proton conductivity. Examples of basic functional groups capable of interacting with acidic substances include =N- groups, -NH2 groups, >NH groups, >N- groups, ammonium groups, amine derivatives, pyridine derivatives, imidazole derivatives, and imidazolium groups. Specific examples of resin fibers include polybenzimidazole (PBI), polybenzoxazole, polybenzothioazole, polyvinylimidazole, and polyallylamine. In particular, from the viewpoint of proton conductivity and processing, polybenzimidazole (PBI) having an azole structure is preferred.

[0022] The fiber diameter of the fibrous material 16 is preferably 0.5 to 500 nm, and more preferably 10 to 300 nm. By setting it within this range, the pores in the electrode catalyst layers 2 and 3 can be increased, enabling higher power output.

[0023] The fiber length of the fibrous material 16 is preferably 1 to 200 μm, and more preferably 1 to 50 μm. By setting it within this range, the strength of the electrode catalyst layers 2 and 3 can be increased, and crack formation during formation can be suppressed. In addition, the pore size within the electrode catalyst layers 2 and 3 can be increased, enabling higher power output.

[0024] (Membrane electrode assembly) The membrane electrode assembly 12 for polymer electrolyte fuel cell in this embodiment has a structure like the cross-sectional view shown in Figure 3, for example. This membrane electrode assembly 12 has a structure comprising a polymer electrolyte membrane 1, a cathode-side electrode catalyst layer 2 formed on one side of the polymer electrolyte membrane 1, and an anode-side electrode catalyst layer 3 formed on the other side of the polymer electrolyte membrane 1. One or both of the cathode-side electrode catalyst layer 2 and the anode-side electrode catalyst layer 3 consist of the electrode catalyst layers of this embodiment described above.

[0025] (Polymer electrolyte fuel cell) As shown in Figure 4, in this embodiment of the polymer electrolyte fuel cell, the cathode-side electrode catalyst layer 2 and the anode-side electrode catalyst layer 3 of the membrane electrode assembly 12 of this embodiment are opposed to an air electrode-side gas diffusion layer 4 and a fuel electrode-side gas diffusion layer 5, respectively. As a result, the cathode-side electrode catalyst layer 2 and the air electrode-side gas diffusion layer 4 constitute an air electrode 6, and the anode-side electrode catalyst layer 3 and the fuel electrode-side gas diffusion layer 5 constitute a fuel electrode 7. A single-cell polymer electrolyte fuel cell 11 is formed by sandwiching the air electrode 6 and the fuel electrode 7 with a pair of separators 10. The pair of separators 10 is made of a conductive and gas-impermeable material and includes a gas channel 8 for reaction gas flow that is positioned facing the air electrode-side gas diffusion layer 4 or the fuel electrode-side gas diffusion layer 5, and a cooling water channel 9 for cooling water flow that is positioned on the main surface opposite the gas channel 8.

[0026] This polymer electrolyte fuel cell 11 generates electricity when an oxidizing agent such as air or oxygen is supplied to the air electrode 6 through the gas passage 8 of one separator 10, and a fuel gas containing hydrogen or an organic fuel is supplied to the fuel electrode 7 through the gas passage 8 of the other separator 10.

[0027] (Method for manufacturing an electrode catalyst layer) The electrode catalyst layer can be manufactured by preparing a catalyst layer slurry and then coating and drying the prepared catalyst layer slurry on a substrate or the like.

[0028] The catalyst layer slurry consists of a catalyst 13, a conductive carrier 14, a polymer electrolyte 15, a fibrous material 16, and a solvent. Carbon fibers can be used as an example of the fibrous material 16. The solvent is not particularly limited, but one that can disperse or dissolve the polymer electrolyte 15 is preferable. Commonly used solvents include water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol and other alcohols, acetone, methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl amyl ketone, pentanone, heptanone, cyclohexanone, methylcyclohexanone, acetonylacetone, diethyl ketone, dipropyl ketone, diisobutyl ketone and other ketones, tetrahydrofuran, tetrahydropyran, dioxane, diethylene glycol dimethyl alcohol Ethers such as ethers, anisole, methoxytoluene, diethyl ether, dipropyl ether, and dibutyl ether; amines such as isopropylamine, butylamine, isobutylamine, cyclohexylamine, diethylamine, and aniline; esters such as propyl formate, isobutyl formate, amyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, isopentyl acetate, methyl propionate, ethyl propionate, and butyl propionate; and other solvents such as acetic acid, propionic acid, dimethylformamide, dimethylacetamide, and N-methylpyrrolidone may also be used. Examples of glycol and glycol ether solvents include ethylene glycol, diethylene glycol, propylene glycol, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diacetone alcohol, 1-methoxy-2-propanol, and 1-ethoxy-2-propanol.

[0029] Methods for coating the catalyst layer slurry include, but are not limited to, the doctor blade method, die coating method, dipping method, screen printing method, laminator roll coating method, and spray method.

[0030] Drying methods for the catalyst layer slurry include hot air drying and IR drying. The drying temperature is 40 to 200°C, preferably 40 to 120°C. The drying time is 0.5 minutes to 1 hour, preferably 1 minute to 30 minutes.

[0031] Here, setting the distance between fibrous materials within the electrode catalyst layer to between 0.30 μm and 8 μm can be achieved by adjusting conditions such as the amount of carbon fiber added, the fiber length, the heating temperature for drying, the temperature gradient, and the pressure applied in the film thickness direction until the electrode catalyst layer is dried.

[0032] (Method for manufacturing a membrane electrode assembly) Methods for manufacturing a membrane electrode assembly include forming an electrode catalyst layer on a transfer substrate or gas diffusion layer and then forming the electrode catalyst layer on a polymer electrolyte membrane by thermocompression bonding, or forming the catalyst layer directly on the polymer electrolyte membrane. The method of forming the catalyst layer directly on the polymer electrolyte membrane is preferred because it provides high adhesion between the polymer electrolyte membrane and the catalyst layer, and there is no risk of the catalyst layer being crushed.

[0033] As described above, the electrode catalyst layer of this embodiment comprises a catalyst, a conductive carrier supporting the catalyst, a polymer electrolyte, and a fibrous material, and in the first cross-section, which is a cross-section in the thickness direction of the catalyst layer, the distance between the fibrous materials is 0.30 μm or more and 8 μm or less. This configuration allows for improved drainage and gas diffusion without unnecessarily increasing the thickness of the electrode catalyst layer, and provides an electrode catalyst layer for polymer fuel cells that enables high output. Furthermore, the electrode catalyst layer of this embodiment is extremely suitable for application to, for example, a polymer electrolyte fuel cell.

[0034] (others) This disclosure may also take the following form: (1) An electrode catalyst layer bonded to a polymer electrolyte membrane, The material comprises a catalyst, a conductive carrier supporting the catalyst, a polymer electrolyte, and a fibrous material. An electrode catalyst layer in which, in a first cross-section which is a cross-section in the thickness direction, the distance between adjacent first fibrous materials is 0.30 μm or more and 8 μm or less. (2) In the second cross-section perpendicular to the first cross-section, the distance between adjacent fibrous materials is 0.30 μm or more and 8 μm or less. (3) The fibrous material exhibits at least one of either electronic conductivity or proton conductivity. (4) The above fibrous material contains an azole structure. (5) The content of the fibrous material in the electrode catalyst layer is 1% by weight or more and 15% by weight or less. (6) The thickness of the electrode catalyst layer is 1 μm or more and 30 μm or less. [Examples]

[0035] Next, an example based on this embodiment will be described. [Calculation of distance between fibrous materials] A cross-section of the electrode catalyst layer was obtained using cryo-ion milling, and a cross-sectional image of the electrode catalyst layer (6000x magnification) was obtained using a scanning electron microscope (SEM). The distance between each fibrous material was measured from the image. The method for determining the distance was the same as described in the embodiment. [Evaluation of power generation characteristics] A gas diffusion layer (SIGRACET(R) 22BC, manufactured by SGL Corporation) was placed outside the electrode catalyst layer, and the power generation characteristics were evaluated using a commercially available JARI standard cell. The cell temperature was set to 80°C, and hydrogen (100% RH) was supplied to the anode and air (100% RH) to the cathode.

[0036] [Example 1] In Embodiment 1, 20 g of platinum-supported carbon (TEC10E50E, manufactured by Tanaka Kikinzoku Co., Ltd.) was placed in a container, water was added and mixed, then 1-propanol, an electrolyte (Nafion® dispersion, Wako Pure Chemical Industries, Ltd.), and 10 g of carbon nanofiber (Showa Denko Corporation, trade name "VGCF", fiber diameter approximately 150 nm, fiber length approximately 10 μm) were added and stirred to obtain a catalyst layer slurry. The obtained catalyst layer slurry was coated onto a polymer electrolyte membrane (Chemours, Nafion 212) by die coating and dried in a furnace to obtain a membrane electrode assembly having the electrode catalyst layer of Example 1. The composition of the catalyst layer slurry and the drying temperature were adjusted so that the distance between fibrous materials was between 0.30 μm and 8 μm.

[0037] [Example 2] The electrode catalyst layer (cathode) of Example 2 was prepared using the same procedure as in Example 1, except that a resin fiber having an azole structure (fiber diameter approximately 200 nm, fiber length approximately 20 μm) was used as the fibrous material. [Example 3] A film electrode assembly having the electrode catalyst layer (cathode) of Example 3 was obtained using the same procedure as in Example 1, except that the amount of fibrous material was increased. [Comparative Example 1] A film electrode assembly having the electrode catalyst layer (cathode) of Comparative Example 1 was obtained using the same procedure as in Example 3, except that the stirring time when preparing the slurry for the catalyst layer was shortened. [Comparative Example 2] A membrane electrode assembly having the electrode catalyst layer (cathode) of Comparative Example 2 was obtained using the same procedure as in Example 1, except that the electrode catalyst layer was coated onto a PET substrate and transferred to the electrolyte membrane by thermocompression bonding. [Comparative Example 3] A film electrode assembly having the electrode catalyst layer (cathode) of Comparative Example 3 was obtained using the same procedure as in Example 1, except that the slurry composition and coating amount were adjusted so that the thickness of the electrode catalyst layer was less than 1 μm. [Comparative Example 4] A film electrode assembly having the electrode catalyst layer (cathode) of Comparative Example 4 was obtained using the same procedure as in Example 1, except that the slurry composition and coating amount were adjusted so that the thickness of the electrode catalyst layer exceeded 30 μm. [Comparative Example 5] A film electrode assembly having the electrode catalyst layer of Comparative Example 5 was obtained using the same procedure as in Example 1, except that no fibrous material was added.

[0038] (evaluation) The electrode catalyst layers of Examples 1-3 and Comparative Examples 1-5 were observed under a microscope (magnification: 200x) to evaluate the presence or absence of cracks larger than 10 μm. The evaluation results are shown in Table 1.

[0039] [Table 1]

[0040] As shown in Table 1, when no fibrous material was added (Comparative Example 5), many cracks occurred. In contrast, when a fibrous material was added, as in the Examples and Comparative Examples 1-4, the catalyst layer was free of cracks.

[0041] Furthermore, the electrode catalyst layers of Examples 1-3 and Comparative Examples 1-4 were evaluated for their thickness, distance between fibrous materials, and power generation characteristics. The evaluation results are shown in Table 2. In Examples 1 and 2, the distance between fibrous materials was between 0.30 μm and 8 μm in the cross-section perpendicular to the cross-section (second cross-section) shown in Table 2 (first cross-section). Here, the mass of the catalyst added to each electrode catalyst layer is adjusted to be the same, but the thickness of each electrode catalyst layer differs due to differences in other components.

[0042] [Table 2]

[0043] From Tables 1 and 2, it was found that by having a catalyst, a conductive carrier supporting the catalyst, a polymer electrolyte, and fibrous material, and by having a distance of 0.30 μm to 8 μm between the fibrous material particles in the first cross-section in the thickness direction, cracks do not occur in the membrane electrode assembly, and even if the materials contained in the electrode catalyst layer are the same (Example 1, Comparative Example 2), drainage and gas diffusion are improved, and an electrode catalyst layer for polymer fuel cells capable of high output can be provided. [Explanation of Symbols]

[0044] 1 Polymer electrolyte membrane 2. Cathode-side electrode catalyst layer 3. Anode-side electrode catalyst layer 4. Gas diffusion layer on the air electrode side 5. Gas diffusion layer on the fuel electrode side 6. Air pole 7 Fuel electrode 8 Gas flow path 9 Cooling water channel 10 Separators 11 Solid polymer fuel cell 12 Membrane electrode assembly 13 Catalyst 14 Conductive carrier 15 Polyelectrolyte 16. Fibrous material

Claims

1. An electrode catalyst layer bonded to a polymer electrolyte membrane and used in a fuel cell, The above electrode catalyst layer is at least one of the anode-side electrode catalyst layer and the cathode-side electrode catalyst layer. The material comprises a catalyst, a conductive carrier supporting the catalyst, a polymer electrolyte, and a fibrous material. In the first cross-section, which is a cross-section in the thickness direction, the distance between adjacent first fibrous materials is 0.30 μm or more and 8 μm or less. The above fibrous material is a substance that exhibits proton conductivity and contains an azole structure. The thickness of the electrode catalyst layer is 1 μm or more and 30 μm or less. An electrode catalyst layer characterized by the following features.

2. In the second cross-section perpendicular to the first cross-section described above, the distance between adjacent fibrous materials is 0.30 μm or more and 8 μm or less. The electrode catalyst layer according to claim 1.

3. The content of the fibrous material in the electrode catalyst layer is 1% by weight or more and 15% by weight or less. The electrode catalyst layer according to claim 1 or 2.

4. The content of the fibrous material in the electrode catalyst layer is 1% by weight or more and 15% by weight or less, The total content of the catalyst and the conductive carrier supporting the catalyst in the electrode catalyst layer is 50% by weight. The content of the polymer electrolyte in the electrode catalyst layer is 25% by weight. The electrode catalyst layer according to claim 1 or 2.

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