Electrode catalyst layer, membrane electrode assembly, and solid polymer fuel cell

Abstract

An electrode catalyst layer (20) that is used by being bonded to a polymer electrolyte membrane and that contains catalyst-supporting particles (21) that contain a carrier and a catalyst supported on the carrier, a polymer electrolyte (22) that contains fluorine atoms, and two or more types of fibrous substances. The fibrous material includes one or more types of conductive fibrous material (23) and one or more types of non-conductive fibrous material (24), and when the content of the carrier is 100 parts by mass, the content of the conductive fibrous material (23) is 5-50 parts by mass, and the content of the non-conductive fibrous material (24) is 5-20 parts by mass.

Description

Technical Field

[0001] The present invention relates to an electrode catalyst layer, a membrane electrode assembly, and a solid polymer fuel cell. Background Art

[0002] As a countermeasure to the increasing environmental load on the earth, the demand for creating cleaner energy is increasing. Fuel cells are a power generation system that generates electricity through a chemical reaction between hydrogen and oxygen and only emits water. Fuel cells are highly expected to be a future energy source.

[0003] Fuel cells are classified into alkaline type, phosphoric acid type, solid polymer type, molten carbonate type, and solid oxide type according to the type of electrolyte. Since solid polymer fuel cells can be used at room temperature, they are expected to be widely used as power sources for vehicles and homes. Therefore, research and development for practical applications of solid polymer fuel cells, such as improving power generation performance and durability and reducing costs, is in full swing.

[0004] The solid polymer fuel cell has: a polymer electrolyte membrane with proton conductivity, a fuel electrode as an anode, and an air electrode as a cathode. In the thickness direction of the polymer electrolyte membrane, the fuel electrode and the air electrode sandwich the polymer electrolyte membrane. The fuel electrode has an electrode catalyst layer that separates the fuel gas into protons and electrons. The air electrode has an electrode catalyst layer that oxidizes the protons transported through the polymer electrolyte membrane with an oxygen-containing oxidant and receives electrons from an external circuit. The electrode catalyst layers of the fuel electrode and the air electrode contain catalyst substances such as platinum-based precious metals, carriers that support the catalyst substances, and polymer electrolytes.

[0005] The solid polymer fuel cell is a single cell with a structure in which a gas diffusion layer and a separator are arranged on the surface of each electrode catalyst layer of the fuel electrode and the air electrode on the opposite side of the polymer electrolyte membrane as the basic structure, and a plurality of such single cells are stacked. The gas diffusion layer is a layer with conductivity for uniform diffusion of the reaction gas. The separator is a component having a gas flow path and a cooling water flow path, and is responsible for outputting electrons to the external circuit, and is arranged on the outside of the gas diffusion layer. Hereinafter, the structure in which the fuel electrode and the air electrode are formed on both sides of the polymer electrolyte membrane is referred to as a membrane electrode assembly.

[0006] The polymer electrolyte fuel cell generates electricity by supplying a fuel gas containing hydrogen to a fuel electrode and an oxidant gas containing oxygen to an air electrode, and electrode reactions represented by the following formulas 1 and 2 occur in the fuel electrode and the air electrode.

[0007] Fuel electrode: H 2 → 2H + +2e- ··· (Formula 1)

[0008] Air electrode: 1 / 2O 2 + 2H + +2e - → H 2 O··· (Formula 2)

[0009] As shown in Formula 1, the fuel gas supplied to the fuel electrode is separated into protons and electrons by the catalyst material contained in the electrode catalyst layer of the fuel electrode. The separated protons pass through the humidified polymer electrolyte and polymer electrolyte membrane contained in the electrode catalyst layer of the fuel electrode and move to the air electrode. The separated electrons are output from the fuel electrode to the external circuit, pass through the external circuit and move to the air electrode. As shown in Formula 2, in the air electrode, the oxidant gas reacts with the protons and electrons moved from the fuel electrode to generate water. The electrons pass through the external circuit to generate current.

[0010] However, the following problems can be cited: the electrode catalyst layer of the fuel cell is usually formed of a thin film with a thickness of less than 100 μm, and cracks, i.e., so-called cracks, are generated in the electrode catalyst layer during manufacturing, which becomes a problem. Due to the generation of cracks, the proton conduction path and the electron conduction path in the electrode catalyst layer are cut off, and the power generation performance and durability are reduced. In order to solve this problem, as a technology for improving the bonding strength of the electrode catalyst layer, the technology disclosed in Patent Document 1 is known.

[0011] In Patent Document 1, a fibrous substance such as hydrophilic carbon whiskers is added to an electrode catalyst layer to improve the bonding strength of the electrode catalyst layer.

[0012] Prior art literature

[0013] Patent Literature

[0014] Patent Document 1: Japanese Patent No. 4065862 Summary of the invention

[0015] Problems to be solved by the invention

[0016] However, in the conventional fuel cell using the electrode catalyst layer disclosed in Patent Document 1, there is still room for improvement in terms of initial power generation performance and durability performance.

[0017] When a fibrous substance is added to the electrode catalyst layer, protons cannot be conducted on the fibrous substance, so the proton conduction resistance in the electrode catalyst layer increases, and the power generation performance of the membrane electrode assembly sometimes decreases. In particular, under low humidification conditions, the water content of the polymer electrolyte decreases, so the proton conduction resistance sometimes increases significantly.

[0018] On the other hand, when the ratio of the polymer electrolyte in the electrode catalyst layer is increased in order to improve proton conductivity, the electron conductivity in the electrode catalyst layer cannot be ensured, or the water discharged during power generation at a high current density cannot be discharged outside the system due to water retention in the polymer electrolyte, resulting in reduced power generation performance.

[0019] Therefore, it is necessary to exert power generation performance while suppressing the amount of polymer electrolyte in the catalyst layer to a small amount. Therefore, it is very important to appropriately construct electron conduction paths and proton conduction paths in the electrode catalyst layer to which the fibrous substance is added.

[0020] An object of the present invention is to provide a polymer electrolyte fuel cell using an electrode catalyst layer containing a fibrous substance, while achieving high initial power generation performance and improving durability performance.

[0021] Means for solving problems

[0022] After intensive research, the inventors found that by including multiple fibrous materials in the electrode catalyst layer, both proton conductivity and electron conductivity can be achieved. In addition, the inventors obtained the following insight: when the content of multiple fibrous materials exists in a certain range, the durability performance can be greatly improved while maintaining high initial power generation performance.

[0023] In order to solve the above-mentioned problems, one embodiment of the present invention provides an electrode catalyst layer, which is an electrode catalyst layer used in conjunction with a polymer electrolyte membrane, comprising catalyst-loaded particles, a polymer electrolyte containing fluorine atoms, and two or more fibrous substances, wherein the catalyst-loaded particles include a carrier and a catalyst loaded on the carrier, the fibrous substance includes one or more conductive fibrous substances and one or more non-conductive fibrous substances, and when the content of the carrier is set to 100 parts by mass, the content of the conductive fibrous substance is not less than 5 parts by mass and not more than 50 parts by mass, and the content of the non-conductive fibrous substance is not less than 5 parts by mass and not more than 20 parts by mass.

[0024] The conductive fibrous material may be carbon fiber.

[0025] The non-conductive fibrous material may be a high molecular polymer fiber.

[0026] The high molecular polymer fiber may be a high molecular polymer fiber having a basic functional group in its molecular structure.

[0027] The basic functional group may contain nitrogen.

[0028] The non-conductive fibrous material may be a high molecular polymer fiber having an imide structure or an azole structure.

[0029] Another aspect of the present invention provides a membrane electrode assembly comprising a polymer electrolyte membrane and a pair of electrode catalyst layers arranged on both sides of the polymer electrolyte membrane in a thickness direction, wherein either or both of the pair of electrode catalyst layers are the electrode catalyst layers of one aspect of the present invention.

[0030] Another embodiment of the present invention provides a solid polymer fuel cell comprising: a membrane electrode assembly having an electrode catalyst layer according to one embodiment of the present invention, a pair of gas diffusion layers arranged on both sides of the membrane electrode assembly in the thickness direction, and a pair of separators opposite to each other sandwiching the membrane electrode assembly and the pair of gas diffusion layers.

[0031] Effects of the Invention

[0032] According to the present invention, by containing a plurality of fibrous substances in a predetermined range in an electrode catalyst layer containing a fibrous substance, it is expected that high initial power generation performance of a solid polymer fuel cell can be achieved while also improving durability performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] [ Figure 1 ] is a cross-sectional view showing a membrane electrode assembly according to one embodiment.

[0034] [ Figure 2 ] is a diagram schematically showing the structure of an electrode catalyst layer constituting a membrane electrode assembly according to one embodiment.

[0035] [ Figure 3 ] is a cross-sectional view showing the structure of catalyst-supported particles contained in an electrode catalyst layer according to one embodiment.

[0036] [ Figure 4 ] is a disassembled perspective view showing a solid polymer fuel cell according to one embodiment. DETAILED DESCRIPTION

[0037] Reference Figures 1 to 4 , an embodiment of an electrode catalyst layer, a membrane electrode assembly, and a solid polymer fuel cell is described. For easy understanding, the various figures of the accompanying drawings are appropriately exaggerated. In addition, the composition and materials of the electrode catalyst layer, membrane electrode assembly, solid polymer fuel cell, and their manufacturing methods of the present invention are not limited to the composition and materials described below, and include all materials and compositions that are analogized to have the same function.

[0038] [Membrane Electrode Assembly]

[0039] like Figure 1As shown, the membrane electrode assembly 10 includes a polymer electrolyte membrane 11 , a cathode electrode catalyst layer 12C, and an anode electrode catalyst layer 12A.

[0040] The polymer electrolyte membrane 11 is a solid polymer electrolyte membrane. The polymer electrolyte membrane 11 is formed of, for example, a polymer material having proton conductivity. Examples of polymer materials having proton conductivity include fluororesins and hydrocarbon resins. Examples of fluororesins include Nafion (manufactured by DuPont, registered trademark), Flemion (manufactured by AGC, registered trademark), and Gore-Selet (manufactured by Gore, registered trademark). Examples of hydrocarbon resins include engineering plastics and engineering plastics into which sulfonic acid groups are introduced.

[0041] The cathode electrode catalyst layer 12C is an electrode catalyst layer constituting an air electrode as a cathode and is bonded to one surface of the polymer electrolyte membrane 11. The cathode electrode catalyst layer 12C is a layer for oxidizing protons transported via the polymer electrolyte membrane 11 with an oxygen-containing oxidant and receiving electrons from an external circuit.

[0042] The anode electrode catalyst layer 12A is an electrode catalyst layer constituting a fuel electrode as an anode, and is bonded to the surface of the polymer electrolyte membrane 11 opposite to the surface bonded to the cathode electrode catalyst layer 12C. The anode electrode catalyst layer 12A is a layer for separating fuel gas into protons and electrons.

[0043] In addition, hereinafter, the cathode-side electrode catalyst layer 12C and the anode-side electrode catalyst layer 12A may be simply referred to as “electrode catalyst layers”.

[0044] [Electrode catalyst layer]

[0045] The cathode electrode catalyst layer 12C and the anode electrode catalyst layer 12A constituting the membrane electrode assembly 10 are Figure 2 The electrode catalyst layer (hereinafter referred to as the "first electrode catalyst layer") 20 of the structure shown. It should be noted that either the cathode side electrode catalyst layer 12C or the anode side electrode catalyst layer 12A may be the first electrode catalyst layer 20, and the other may be Figure 2 An electrode catalyst layer having a different structure (hereinafter referred to as a "second electrode catalyst layer").

[0046] That is, by making at least one of the cathode side electrode catalyst layer 12C and the anode side electrode catalyst layer 12A the first electrode catalyst layer, the effect of improving the initial power generation performance and the durability performance can be obtained. It should be noted that, from the viewpoint of improving the above-mentioned effect, when only one of the cathode side electrode catalyst layer 12C and the anode side electrode catalyst layer 12A is used as the first electrode catalyst layer, it is preferred that the cathode side electrode catalyst layer 12C constituting the air electrode is used as the first electrode catalyst layer.

[0047] (First Electrode Catalyst Layer)

[0048] like Figure 2 As shown, the first electrode catalyst layer 20 includes catalyst-supported particles 21, a polymer electrolyte 22, a conductive fibrous material 23, and a non-conductive fibrous material 24. The first electrode catalyst layer 20 may include other known components contained in the electrode catalyst layer of a fuel cell as arbitrary components.

[0049] <Catalyst Supported Particles>

[0050] like Figure 3 As shown, the catalyst-supporting particle 21 includes a catalyst 21 a and a carrier 21 b that supports the catalyst 21 a.

[0051] As the catalyst 21a, for example, a metal contained in the platinum group, a metal other than the platinum group, or an alloy, oxide, composite oxide, or carbide thereof can be used. As the metal contained in the platinum group, for example, platinum, palladium, ruthenium, iridium, rhodium, and osmium can be listed. As the metal other than the platinum group, for example, gold, iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum can be listed. Among these, platinum, gold, palladium, rhodium, ruthenium, and alloys thereof are highly active as catalysts and are suitable.

[0052] It should be noted that the catalyst 21 a constituting the catalyst-supporting particles 21 may be only one of the above examples, or may be a combination of two or more.

[0053] The average particle size of the catalyst 21a is preferably 0.5 nm or more and 20 nm or less, and more preferably 1 nm or more and 5 nm or less. By setting the average particle size of the catalyst 21a to be 0.5 nm or more, the decrease in stability can be suppressed. In addition, by setting the average particle size of the catalyst 21a to be 20 nm or less, the decrease in activity can be suppressed.

[0054] In addition, in this specification, the arithmetic mean particle diameter calculated|required by particle size measurement is defined as an average particle diameter.

[0055] The carrier 21b is a material that is conductive, not corroded by the catalyst 21a, and capable of supporting the catalyst 21a. Examples of the material constituting the carrier 21b include carbon materials such as carbon black, graphite, black lead, activated carbon, carbon nanotubes, carbon nanofibers, and fullerene.

[0056] It should be noted that the carrier 21 b constituting the catalyst-supporting particles 21 may be only one of the above examples, or may be a combination of two or more.

[0057] The shape of the carrier 21b is not particularly limited, and may be, for example, a particle shape or a fiber shape. It should be noted that from the perspective of smoothly transferring the electrons generated on the surface of the catalyst 21a to the outside of the system, the carrier 21b is preferably in a shape capable of supporting the catalyst 21a on its outer surface.

[0058] The average particle size of the carrier 21b is preferably 10 nm or more and 1000 nm or less, and more preferably 10 nm or more and 100 nm or less. By setting the average particle size of the carrier 21b to be 10 nm or more, it is easy to form an electron conduction path in the electrode catalyst layer. In addition, by setting the average particle size of the carrier 21b to be 1000 nm or less, the increase in resistance caused by the increase in the thickness of the first electrode catalyst layer 20 can be suppressed.

[0059] <Polymer electrolyte>

[0060] As the polymer electrolyte 22, a substance having proton conductivity is used. As the substance having proton conductivity, for example, fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes can be listed. As the fluorine-based polymer electrolyte, for example, a fluorine-based polymer electrolyte having a tetrafluoroethylene skeleton represented by Nafion (registered trademark) manufactured by DuPont can be listed. As the hydrocarbon-based polymer electrolyte, for example, sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, and sulfonated polyphenylene can be listed.

[0061] It should be noted that, as the polymer electrolyte 22 constituting the first electrode catalyst layer 20 , only one of the above examples may be used, or two or more of them may be used in combination.

[0062] For example, when the content of the support 21 b in the first electrode catalyst layer 20 is 100 parts by mass, the content of the polymer electrolyte in the first electrode catalyst layer 20 is preferably 40 parts by mass or more and 140 parts by mass or less.

[0063] By setting the content of the polymer electrolyte to 40 parts by mass or more, the decrease in proton conductivity caused by the defect in the proton conduction path can be suppressed. As a result, it is easy to ensure the balance between proton conductivity and electron conductivity in the first electrode catalyst layer 20. By setting the content of the polymer electrolyte to 140 parts by mass or less, the catalyst 21a of the catalyst-supported particles 21 can be appropriately exposed. As a result, the catalyst activity of the first electrode catalyst layer 20 is improved.

[0064] <Fibrous substances>

[0065] As the conductive fibrous material 23, it can be a material that is not affected by the catalyst 21a and the polymer electrolyte 22, and preferably has a conductive material, such as carbon fiber. As carbon fiber, for example, VGCF (Vapor Grown Carbon Fiber) and CNT (Carbon Nano Tube) can be listed. Through the conductive fibrous material 23, it is difficult to generate cracks in the electrode catalyst layer, and the physical durability is improved. In addition, since the conductive fibrous material assists the electron conduction path in the first electrode catalyst layer, the electrical durability is also improved.

[0066] The non-conductive fibrous material 24 may be a material that is not affected by the catalyst 21a and the polymer electrolyte 22, and for example, a polymer fiber may be used. Examples of the polymer fiber include nanofibers of amine polymers such as an imide structure or an azole structure.

[0067] The non-conductive fibrous material 24 may contain a basic functional group in the molecular structure of its material. Thus, the polymer electrolyte 22 is easily present around the non-conductive fibrous material 24. As the non-conductive fibrous material 24 having a basic functional group, polymer fibers having an imide structure or an azole structure, etc., can be cited. The azole structure refers to a 5-membered heterocyclic structure containing more than one nitrogen, such as an imidazole structure and an oxazole structure. The non-conductive fibrous material is preferably a polymer fiber having a benzoxazole structure such as a benzimidazole structure and a benzoxazole structure. As a specific example of a polymer, polymers such as polybenzimidazole and polybenzoxazole can be cited.

[0068] When the non-conductive fibrous material 24 has a basic functional group, the acidic proton conductive sites such as sulfonyl groups contained in the polymer electrolyte 22 are bonded by acid and base, so that the polymer electrolyte 22 is likely to exist around the non-conductive fibrous material 24. Compared with hydrogen bonds, the binding force of acid-base bonds is stronger, so the non-conductive fibrous material 24 preferably contains a basic functional group.

[0069] Examples of the acidic functional group include a carbonyl group and the like, and examples of the basic functional group include an amine group containing a pyridine, imide structure, azole structure and the like.

[0070] That is, since the non-conductive fibrous substance 24 has a basic functional group containing a nitrogen atom in its molecular structure, the polymer electrolyte 22 is likely to be present in the periphery.

[0071] The shapes of the conductive fibrous material 23 and the non-conductive fibrous material 24 are not particularly limited, and they may be, for example, hollow structures or solid structures.

[0072] It should be noted that, as the conductive fibrous material 23 and the non-conductive fibrous material 24 constituting the first electrode catalyst layer 20 , only one of the above examples may be used, or two or more thereof may be used in combination.

[0073] In addition, in a fuel cell, the result of the cell reaction is that the amount of generated water generated in the electrode catalyst layer is proportional to the amount of chemical reaction. Therefore, in the case of power generation at a high current density, the amount of generated water increases. When the generated water cannot be fully discharged outside the electrode catalyst layer, the generated water retained in the electrode catalyst layer may block the diffusion path of the gas. In this case, the phenomenon that the reaction gas cannot reach the active point and the power generation performance is significantly reduced is overflow (flooding).

[0074] By using the conductive fibrous material 23 and the non-conductive fibrous material 24 as constituent materials of the first electrode catalyst layer 20 , an appropriate space is ensured in the first electrode catalyst layer 20 , and drainage of the generated water can be promoted.

[0075] When the content of the support 21 b in the first electrode catalyst layer 20 is 100 parts by mass, the content of the conductive fibrous substance 23 in the first electrode catalyst layer 20 is preferably 5 parts by mass or more and 50 parts by mass or less.

[0076] By setting the content of the conductive fiber-like substance 23 to 5 parts by mass or more, a network of the conductive fiber-like substances 23 can be formed, and the electrode catalyst layer can be easily formed. Thus, the construction of the electron conduction path in the electrode catalyst layer and the structural reinforcement of the electrode catalyst layer can be fully carried out. As a result, the power generation performance and durability of the fuel cell are improved. By setting the content of the conductive fiber-like substance 23 to 50 parts by mass or less, the increase in resistance caused by the increase in the thickness of the first electrode catalyst layer 20 can be suppressed.

[0077] When the content of the support 21 b in the first electrode catalyst layer 20 is 100 parts by mass, the content of the non-conductive fibrous substance 24 in the first electrode catalyst layer 20 is preferably 5 parts by mass or more and 20 parts by mass or less.

[0078] By setting the content of the non-conductive fibrous material 24 to 5 parts by mass or more, a network of the non-conductive fibrous materials 24 can be formed, and the electrode catalyst layer can be easily formed. Thus, the construction of the proton conduction path in the electrode catalyst layer and the structural reinforcement of the electrode catalyst layer can be fully carried out. As a result, the power generation performance of the fuel cell is improved. By setting the content of the non-conductive fibrous material 24 to 20 parts by mass or less, the increase in resistance caused by the increase in the thickness of the first electrode catalyst layer 20 can be suppressed.

[0079] (Second Electrode Catalyst Layer)

[0080] As the second electrode catalyst layer, a known electrode catalyst layer applied to a membrane electrode assembly can be used. As the second electrode catalyst layer, for example, an electrode catalyst layer that is different from the first electrode catalyst layer 20 in that it does not contain a polymer fiber (non-conductive fibrous material) and has the same other structure as the first electrode catalyst layer 20 can be cited.

[0081] It should be noted that the above-mentioned materials used as constituent components of the first electrode catalyst layer and the second electrode catalyst layer may be the same when used for the cathode electrode catalyst layer 12C and the anode electrode catalyst layer 12A, or may be at least partially different.

[0082] [Solid polymer fuel cell]

[0083] Next, the structure of a solid polymer fuel cell having a membrane electrode assembly 10 is described. Hereinafter, as an example of a solid polymer fuel cell, a single-cell solid polymer fuel cell is described. The solid polymer fuel cell is not limited to a single-cell structure, but may also have a structure in which a plurality of single cells are stacked.

[0084] like Figure 4 As shown, the polymer electrolyte fuel cell 30 includes a membrane electrode assembly 10, a pair of gas diffusion layers 31a, 31b, and a pair of separators 32a, 32b.

[0085] The gas diffusion layers 31a and 31b are layers for uniformly diffusing the reaction gas. The gas diffusion layer 31a is arranged to face the cathode-side electrode catalyst layer 12C of the membrane electrode assembly 10. The gas diffusion layer 31b is arranged to face the anode-side electrode catalyst layer 12A of the membrane electrode assembly 10. The pair of gas diffusion layers 31a and 31b sandwich the membrane electrode assembly 10 in the thickness direction of the membrane electrode assembly 10.

[0086] The cathode-side electrode catalyst layer 12C and the gas diffusion layer 31a form an air electrode as a cathode, and the anode-side electrode catalyst layer 12A and the gas diffusion layer 31b form a fuel electrode as an anode.

[0087] The gas diffusion layers 31a and 31b are made of a material having electron conductivity and gas diffusivity. As the material constituting the gas diffusion layers 31a and 31b, for example, a porous carbon material can be used. Examples of the porous carbon material include carbon cloth, carbon paper, and nonwoven fabric.

[0088] The separators 32a and 32b are components that output electrons to an external circuit and are disposed outside the gas diffusion layer 31b. The pair of separators 32a and 32b sandwich the membrane electrode assembly 10 and the pair of gas diffusion layers 31a and 31b in the thickness direction of the membrane electrode assembly 10.

[0089] The separators 32a and 32b have gas flow paths 33a and 33b and cooling water flow paths 34a and 34b. The gas flow paths 33a and 33b are flow paths for circulating the reaction gas and are formed on the surfaces of the separators 32a and 32b facing the gas diffusion layers 31a and 31b. The cooling water flow paths 34a and 34b are flow paths for circulating cooling water and are formed on the surfaces of the separators 32a and 32b on the opposite side of the surfaces facing the gas diffusion layers 31a and 31b.

[0090] The separators 32a and 32b are formed of a material having electrical conductivity and gas impermeability. Examples of materials constituting the separators 32a and 32b include carbon materials and metal materials. In addition, the material constituting the separators 32a and 32b is preferably a material having a certain degree of strength and good formability.

[0091] The gas flow path 33a of the separator 32a facing the gas diffusion layer 31a constituting the air electrode is supplied with an oxidant gas as a reaction gas. The oxidant gas is, for example, air or oxygen. The gas flow path 33b of the separator 32b facing the gas diffusion layer 31b constituting the fuel electrode is supplied with a fuel gas as a reaction gas. The fuel gas is, for example, hydrogen.

[0092] In the solid polymer fuel cell 30, a fuel gas containing hydrogen is supplied to the fuel electrode, and an oxidant gas containing oxygen is supplied to the air electrode, so that the electrode reactions shown in the following formulas 1 and 2 occur in the fuel electrode and the air electrode to generate electricity. In addition, the solid polymer fuel cell is used in combination with related devices such as a gas supply device and a cooling device.

[0093] Fuel electrode: H 2 →2H + +2e - ···(Formula 1)

[0094] Air electrode: 1 / 2O 2 +2H + +2e - →H 2 O···(Formula 2)

[0095] [Method for producing membrane electrode assembly]

[0096] Next, a method for manufacturing the membrane electrode assembly 10 will be described.

[0097] The method for producing the membrane electrode assembly 10 includes a preparation step of preparing a catalyst ink and a formation step of forming an electrode catalyst layer using the catalyst ink.

[0098] (Preparation process)

[0099] In the preparation step, the catalyst ink is prepared by mixing the components constituting the electrode catalyst layer using a dispersion medium.

[0100] The dispersion medium is not particularly limited as long as it can disperse the components constituting the electrode catalyst layer. As the dispersion medium, for example, water, alcohol, ketones or mixtures thereof can be listed. Specifically, water can be used appropriately; alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, tert-butanol; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl amyl ketone, amyl ketone, heptanone, cyclohexanone, methylcyclohexanone, acetonyl acetone, diethyl ketone, dipropyl ketone, diisobutyl ketone, etc.

[0101] The catalyst ink may also contain a dispersant for dispersing the components constituting the electrode catalyst layer in a favorable manner. Examples of the dispersant include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants.

[0102] Examples of the anionic surfactant include alkyl ether carboxylates, ether carboxylates, alkanoyl sarcosines, alkanoyl glutamates, acyl glutamates, oleic acid / N-methyltaurine, potassium oleate / diethanolamine salts, alkyl ether sulfate / triethanolamine salts, polyoxyethylene alkyl ether sulfate / triethanolamine salts, amine salts of specially modified polyether ester acids, amine salts of higher fatty acid derivatives, amine salts of specially modified polyester acids, amine salts of high molecular weight polyether ester acids, amine salts of specially modified phosphate esters, and high molecular weight polyester acid amide amine salts. , amidoamine salts of special fatty acid derivatives, alkylamine salts of higher fatty acids, amidoamine salts of high molecular weight polycarboxylic acids, sodium laurate, sodium stearate, sodium oleate and other carboxylic acid type surfactants; dialkyl sulfosuccinates, dialkyl sulfosuccinates, 1,2-bis(alkoxycarbonyl)-1-ethanesulfonates, alkyl sulfonates, alkyl sulfonates, alkane sulfonates, α-olefin sulfonates, linear alkylbenzene sulfonates, alkylbenzene sulfonates, polynaphthalene methanesulfonates, polynaphthalene methanesulfonates, naphthalene sulfonate-formalin condensates, alkyl Sulfonic acid surfactants such as naphthalene sulfonate, alkanoyl methyl taurate, sodium dodecyl sulfate, sodium hexadecyl sulfate, sodium octadecyl sulfate, sodium oleyl sulfate, sodium dodecyl ether sulfate, sodium alkylbenzene sulfonate, oil-soluble alkylbenzene sulfonate, α-olefin sulfonate, etc.; alkyl sulfate ester salts, alkyl sulfate salts, alkyl sulfate esters, alkyl ether sulfate esters, polyoxyethylene alkyl ether sulfate esters, alkyl polyethoxy sulfates, polyethylene glycol ether sulfates, alkyl polyoxyethylene sulfates, sulfated oils, highly sulfated oils Sulfate-type surfactants such as (mono- or di-)alkyl phosphates, (mono- or di-)alkyl phosphate esters, (mono- or di-)alkyl phosphate ester salts, alkyl polyoxyethylene phosphate salts, alkyl ether phosphates, alkyl polyethoxy / phosphates, polyoxyethylene alkyl ethers, alkylphenyl / polyoxyethylene phosphate salts, alkylphenyl ether / phosphate esters, alkylphenyl / polyethoxy / phosphates, polyoxyethylene / alkylphenyl / ether phosphate esters, higher alcohol monoester disodium salts, higher alcohol diester disodium salts, dialkyl zinc dithiophosphates and other phosphate-type surfactants.

[0103] Examples of the cationic surfactant include benzyldimethyl{2-[2-(P-1,1,3,3-tetramethylbutylphenoxy)ethoxy]ethyl}ammonium chloride, octadecylamine acetate, tetradecylamine acetate, octadecyltrimethylammonium chloride, tallow trimethylammonium chloride, dodecyltrimethylammonium chloride, coconut trimethylammonium chloride, hexadecyltrimethylammonium chloride, behenyltrimethylammonium chloride, coconut dimethylbenzyl ammonium chloride, tetradecyldimethylbenzyl ammonium chloride, octadecyldimethylbenzyl ammonium chloride, dioleyldimethylammonium chloride, 1-hydroxyethyl-2-tallow imidazoline quaternary salt, 2-heptadecenyl-hydroxyethyl imidazoline, stearamidoethyldiethylamine acetate, stearamidoethyldiethylamine hydrochloride, triethanolamine monostearate formate, alkyl pyridinium salts, higher alkylamine ethylene oxide adducts, polyacrylamide amine salts, modified polyacrylamide amine salts, and perfluoroalkyl quaternary ammonium iodides.

[0104] Examples of the amphoteric surfactant include dimethyl coconut betaine, dimethyl lauryl betaine, sodium laurylaminoethyl glycinate, sodium laurylaminopropionate, stearyl dimethyl betaine, lauryl dihydroxyethyl betaine, amido betaine, imidazolium betaine, lecithin, sodium 3-[ω-fluoroalkanoyl-N-ethylamino]-1-propanesulfonate, and N-[3-(perfluorooctylsulfonamide)propyl]-N,N-dimethyl-N-carboxymethylene ammonium betaine.

[0105] Examples of the nonionic surfactant include coconut fatty acid diethanolamide (1:2 type), coconut fatty acid diethanolamide (1:1 type), tallow fatty acid diethanolamide (1:2 type), tallow fatty acid diethanolamide (1:1 type), oleic acid diethanolamide (1:1 type), hydroxyethyl laurylamine, polyethylene glycol laurylamine, polyethylene glycol coconut amine, polyethylene glycol stearylamine, polyethylene glycol tallowamine, polyethylene glycol tallow propylenediamine, polyethylene glycol dioleylamine, dimethyl laurylamine oxide, dimethyl stearylamine oxide, dihydroxyethyl laurylamine oxide, perfluoroalkylamine oxide, polyvinyl pyrrolidone, higher alcohol ethylene oxide adducts, alkylphenol ethylene oxide adducts, fatty acid ethylene oxide adducts, polypropylene glycol ethylene oxide adducts, fatty acid esters of glycerol, fatty acid esters of pentaerythritol, fatty acid esters of sorbitol, fatty acid esters of sorbitan, and fatty acid esters of sucrose.

[0106] Among the above-mentioned surfactants, sulfonic acid-type surfactants such as alkylbenzenesulfonic acid, oil-soluble alkylbenzenesulfonic acid, α-olefinsulfonic acid, sodium alkylbenzenesulfonate, oil-soluble alkylbenzenesulfonate, and α-olefinsulfonate can be preferably used as the dispersant, because they are excellent in the carbon dispersion effect and are unlikely to cause changes in catalyst performance due to dispersant residue.

[0107] The dispersion method in the preparation process is not particularly limited as long as it can disperse the components contained in the catalyst ink, and a known dispersion method can be used. As a known dispersion method, for example, a method using a planetary ball mill, a bead mill or an ultrasonic homogenizer can be cited. In addition, the mixing ratio of each component in the catalyst ink and the dispersion medium can be appropriately selected according to the coating property and the required power generation performance.

[0108] (Formation process)

[0109] In the forming step, the catalyst ink obtained in the preparation step is applied to a substrate, and then a drying process is performed to volatilize the dispersion medium, thereby forming a coating-like electrode catalyst layer. As the substrate, a polymer electrolyte membrane 11, a transfer substrate, or a gas diffusion layer 31a, 31b can be used.

[0110] The coating method for coating the catalyst ink on the substrate is not particularly limited, and a known coating method applied when coating a slurry-like mixture on the substrate with a uniform film thickness can be used. Examples of known coating methods include die coating, rod coating, spray coating, dipping, and screen printing. Among these, die coating is preferably used because the viscosity range of the catalyst ink that can be coated is relatively wide and the coating can be performed with high film thickness uniformity.

[0111] The drying method used in the drying process is not particularly limited as long as it is a method that can volatilize the dispersion medium, and known drying methods such as methods utilizing an oven, a hot plate, and far infrared rays can be used. In addition, the drying temperature and drying time in the drying process can be appropriately selected according to the materials used in the electrode catalyst layer and the substrate. In addition, when a transfer substrate is used as a substrate, the electrode catalyst layer formed on the transfer substrate is transferred from the transfer substrate to the polymer electrolyte membrane 11. As a transfer method at this time, for example, a transfer method based on thermal compression bonding can be used.

[0112] The transfer substrate is not particularly limited as long as it is a substrate that can demould the formed electrode catalyst layer and transfer it to the polymer electrolyte membrane. As the transfer substrate, for example, a fluororesin film can be used. The transferability of the fluororesin film is excellent. As fluororesins constituting the fluororesin film, for example, ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE) can be listed.

[0113] When a polymer electrolyte membrane 11 or a transfer substrate is used as a transfer substrate, a membrane electrode assembly 10 can be obtained by providing electrode catalyst layers on both sides of the polymer electrolyte membrane 11. Then, by stacking the obtained membrane electrode assembly 10, gas diffusion layers 31a, 31b, and separators 32a, 32b, a solid polymer fuel cell 30 can be obtained.

[0114] In addition, when the gas diffusion layers 31a and 31b are used as the transfer substrate, the membrane electrode assembly 10 having the gas diffusion layers 31a and 31b can be obtained by stacking the polymer electrolyte membrane 11 and the gas diffusion layers 31a and 31b having the electrode catalyst layers. Then, the separators 32a and 32b are stacked on the obtained membrane electrode assembly 10 to obtain the solid polymer fuel cell 30.

[0115] It should be noted that the electrode catalyst layer manufacturing method when manufacturing the cathode electrode catalyst layer 12C and the electrode catalyst layer manufacturing method when manufacturing the anode electrode catalyst layer 12A may be the same or different.

[0116] Example

[0117] Next, the above-mentioned embodiment will be described in more detail with reference to examples and comparative examples. It should be noted that the present invention is not limited to the configurations of the examples.

[0118] [No.1 (Example)]

[0119] First, a catalyst ink is prepared by dispersing a mixed solution containing catalyst-supported particles, a polymer electrolyte, a conductive fibrous material, a non-conductive fibrous material, and a dispersion medium.

[0120] The amount of the polymer electrolyte to be added was set to 70 parts by mass relative to 100 parts by mass of the carrier content of the catalyst-supported particles (hereinafter referred to as "the amount of the catalyst-supported particles added based on the carrier content"). The amount of the conductive fibrous substance to be added was set to 5 parts by mass relative to 100 parts by mass of the catalyst-supported particles added based on the carrier content. The amount of the non-conductive fibrous substance to be added was set to 5 parts by mass relative to 100 parts by mass of the catalyst-supported particles added based on the carrier content.

[0121] The amount of the dispersion medium added was such that the solid content concentration of the catalyst ink was 10% by mass. Zirconia balls with a diameter of 3 mm were used in a planetary ball mill for 600 min. -1 The dispersion treatment was carried out at a rotation speed of 100 rpm for 60 minutes.

[0122] The details of each component used in the catalyst ink are as follows.

[0123] Catalyst supported particles: platinum supported carbon catalyst (carbon: platinum = 1:1, mass ratio)

[0124] Polymer electrolyte: Fluorine-based polymer electrolyte (dispersion liquid of "Nafion (registered trademark)" manufactured by FUJIFILM Wako Pure Chemical Corporation)

[0125] Conductive fibrous material: Carbon fiber ("VGCF-H" manufactured by Showa Denko Packaging Co., Ltd.) Non-conductive fibrous material: High molecular polymer fiber containing an azole structure (fiber diameter 300 nm × fiber length 10 μm)

[0126] Dispersion medium: a mixture of water and 1-propanol in a mass ratio of 1:1

[0127] Next, the prepared catalyst ink was applied to one side of a polymer electrolyte membrane (Nafion (registered trademark) 211 manufactured by Dupont) using a die coater to form a 50 mm long x 50 mm wide quadrilateral coating. The amount of catalyst ink applied was set so that the platinum loading was 0.3 mg / cm 2 Next, the dispersion medium contained in the coating film was volatilized in an oven heated to 80° C., thereby forming a cathode-side electrode catalyst layer.

[0128] Next, the prepared catalyst ink was applied to the surface of the polymer electrolyte membrane opposite to the surface on which the cathode electrode catalyst layer was formed, forming a 50 mm long x 50 mm wide square coating. The amount of catalyst ink applied was set so that the platinum loading amount was 0.1 mg / cm 2 Next, the dispersion medium contained in the coating film was volatilized in an oven heated to 80° C., thereby forming an anode-side electrode catalyst layer, thereby obtaining a membrane electrode assembly of Example 1.

[0129] [No.2 (Example)]

[0130] A membrane electrode assembly of No. 2 was obtained by the same method as No. 1 except that the amount of the non-conductive fibrous substance was 20 parts by mass based on 100 parts by mass of the catalyst-supported particles calculated as a carrier.

[0131] [No.3 (Example)]

[0132] A membrane electrode assembly of No. 3 was obtained by the same method as No. 1 except that the amount of the conductive fibrous substance blended was 50 parts by mass based on 100 parts by mass of the catalyst-supported particles blended in terms of the carrier.

[0133] [No.4 (Example)]

[0134] The membrane electrode assembly No. 4 was obtained by the same method as No. 1, except that the amount of the conductive fibrous material was set to 50 parts by mass relative to 100 parts by mass of the catalyst-loaded particles calculated as the carrier, and the amount of the non-conductive fibrous material was set to 20 parts by mass relative to 100 parts by mass of the catalyst-loaded particles calculated as the carrier.

[0135] [No.5 (Comparative Example)]

[0136] A membrane electrode assembly of No. 5 was obtained by the same method as No. 1 except that the amount of the conductive fibrous substance blended was 2 parts by mass based on 100 parts by mass of the catalyst-supported particles blended in terms of the carrier.

[0137] [No.6 (Comparative Example)]

[0138] A membrane electrode assembly of No. 6 was obtained by the same method as No. 1 except that the amount of the conductive fibrous substance blended was 60 parts by mass based on 100 parts by mass of the catalyst-supported particles blended in terms of the carrier.

[0139] [No.7 (Comparative Example)]

[0140] A membrane electrode assembly of No. 7 was obtained by the same method as No. 1 except that the amount of the non-conductive fibrous substance was 2 parts by mass based on 100 parts by mass of the catalyst-supported particles calculated as a carrier.

[0141] [No.8 (Comparative Example)]

[0142] A membrane electrode assembly of No. 8 was obtained by the same method as No. 1 except that the amount of the non-conductive fibrous substance was 30 parts by mass based on 100 parts by mass of the catalyst-supported particles calculated as a carrier.

[0143] [No.9 (Comparative Example)]

[0144] The membrane electrode assembly No. 9 was obtained by the same method as No. 1, except that the amount of the conductive fibrous material was set to 2 parts by mass relative to 100 parts by mass of the catalyst-loaded particles calculated as the carrier, and the amount of the non-conductive fibrous material was set to 2 parts by mass relative to 100 parts by mass of the catalyst-loaded particles calculated as the carrier.

[0145] [No.10 (Comparative Example)]

[0146] The membrane electrode assembly No. 10 was obtained by the same method as No. 1, except that the amount of the conductive fibrous material was set to 60 parts by mass relative to 100 parts by mass of the catalyst-loaded particles calculated as the carrier, and the amount of the non-conductive fibrous material was set to 30 parts by mass relative to 100 parts by mass of the catalyst-loaded particles calculated as the carrier.

[0147] [Evaluation of initial power generation performance]

[0148] For each of the membrane electrode assemblies No. 1 to 10, carbon paper as a gas diffusion layer was pasted in a manner of clamping the membrane electrode assembly to produce a sample. Each sample was set in a power generation evaluation cell, and the current and voltage were measured using a fuel cell measuring device. The cell temperature during the measurement was set to 80°C. The humidification conditions were set to: the relative humidity on the anode side was 90% RH, and the relative humidity on the cathode side was 30% RH. In addition, hydrogen was used as the fuel gas and air was used as the oxidant gas. At this time, hydrogen was allowed to flow at a flow rate at which the hydrogen utilization rate became 80%, and air was allowed to flow at a flow rate at which the oxygen utilization rate became 40%. It should be noted that the back pressure was set to 50 kPa.

[0149] [Evaluation of durability]

[0150] In the durability measurement, the same sample as that used in the evaluation of the initial power generation performance was used to perform a potential cycle test described in the "Battery Evaluation and Analysis Procedure" issued by the New Energy and Industrial Technology Development Organization (NEDO), and the same power generation evaluation as above was performed before and after, thereby evaluating the current density to be 1.5 A / cm 2 The voltage drop when

[0151] The measured initial power generation performance and durability performance of each membrane electrode assembly are shown in Table 1. 2 The voltage at the time of the test is 0.65V or more" and the current density after the endurance test is 1.5A / cm 2 The voltage drop is within 100 mV when the current density is 1.5 A / cm2, which is applicable to both passenger cars that value initial power generation performance and commercial vehicles that value durability performance. Therefore, in Table 1, "0" indicates that the current density is 1.5 A / cm2. 2 The voltage at the time of the endurance test is 0.65 V or more, "×" indicates that the voltage is less than 0.65 V, and "0" indicates that the current density after the endurance test is 1.5 A / cm 2 The voltage drop is within 100 mV when the voltage is lowered, and "×" is used to indicate the voltage drop is greater than 100 mV.

[0152] [Table 1]

[0153]

[0154] As shown in Table 1, in No. 1 to 4 that satisfy one embodiment of the present invention (when the content of the carrier is set to 100 parts by mass, the content of the conductive fibrous material is from 5 parts by mass to 50 parts by mass, and the content of the non-conductive fibrous material is from 5 parts by mass to 20 parts by mass), good results are obtained in terms of initial power generation performance and durability performance (applicable to both passenger cars that emphasize initial power generation performance and commercial vehicles that emphasize durability performance).

[0155] In No. 5 in which the content of the conductive fibrous substance was less than 5 parts by mass, it was found that the desired performance could not be exhibited in terms of durability.

[0156] In No. 6 in which the content of the conductive fibrous substance was more than 50 parts by mass, the desired performance could not be exhibited in terms of initial power generation performance.

[0157] In No. 7 in which the content of the non-conductive fibrous material was less than 5 parts by mass, the desired performance could not be exhibited in terms of initial power generation performance.

[0158] In No. 8 in which the content of the non-conductive fibrous substance was more than 20 parts by mass, the performance proposed in terms of the initial power generation performance was not achieved.

[0159] In No. 9, in which the content of the conductive fibrous substance was less than 5 parts by mass and the content of the non-conductive fibrous substance was also less than 5 parts by mass, both the initial power generation performance and the durability performance could not exhibit the desired performance.

[0160] In No. 10, in which the content of the conductive fibrous material was more than 50 parts by mass and the content of the non-conductive fibrous material was more than 20 parts by mass, the desired performance could not be achieved in terms of initial power generation performance.

[0161] From the results of No. 1 to 4, it can be seen that when the content of the conductive fibrous material and the non-conductive fibrous material satisfies the constitution of one embodiment of the present invention, good power generation performance can be obtained. In addition, from the results of No. 5 and No. 9, it can be seen that when the amount of the conductive fibrous material added is less than the constitution of one embodiment of the present invention, good durability performance cannot be obtained. In addition, from the results of No. 6, 7, 8, and 10, it can be seen that when the content of the conductive fibrous material is more than the constitution of one embodiment of the present invention, or when the content of the non-conductive fibrous material is outside the constitution of one embodiment of the present invention, good power generation performance cannot be obtained.

[0162] Thus, the mechanism for obtaining this effect is inferred as follows. The conductive fibrous material is contained in order to improve the electron conductivity in the electrode catalyst layer, and the non-conductive fibrous material is contained in order to improve the proton conductivity in the electrode catalyst layer. When the conductive fibrous material is less than the structure of one embodiment of the present invention, the conductive fibrous material cannot make up for the electron conductivity of the carrier deteriorated during the durability test, thereby reducing the durability. When the conductive fibrous material is more than the structure of one embodiment of the present invention, although the electron conductivity can be made up, the film thickness becomes too thick to generate resistance, and the initial power generation performance is reduced.

[0163] On the other hand, when the non-conductive fibrous material is less than the configuration of one embodiment of the present invention, the construction of proton conductivity cannot be assisted, and the initial power generation performance is reduced. When the non-conductive fibrous material is more than the present embodiment, the film thickness becomes too thick and resistance is generated, and the initial power generation performance is reduced. That is, it is believed that when the content of the conductive fibrous material and the non-conductive fibrous material satisfies the configuration of one embodiment of the present invention, appropriate assistance of electron conductivity and proton conductivity is performed, so that both the initial power generation performance and the durability performance can be improved.

[0164] The above description shows that, in the electrode catalyst layer including the fibrous substance, by making the contents of the plurality of fibrous substances fall within the range of the configuration of one embodiment of the present invention, it is possible to achieve high initial power generation performance and improve durability performance.

[0165] Explanation of symbols

[0166] 10…membrane electrode assembly, 11…polymer electrolyte membrane, 12C…cathode side electrode catalyst layer, 12A…anode side electrode catalyst layer, 20…first electrode catalyst layer, 21…catalyst-supported particles, 21a…catalyst, 21b…support, 22…polymer electrolyte, 23…conductive fibrous material, 24…non-conductive fibrous material, 30…solid polymer fuel cell, 31a, 31b…gas diffusion layer, 32a, 32b…partition, 33a, 33b…gas flow path, 34a, 34b…cooling water flow path.

Claims

1. An electrode catalyst layer, which is used in conjunction with a polymer electrolyte membrane, The invention comprises catalyst-supported particles, a polymer electrolyte containing fluorine atoms, and two or more fibrous substances. The catalyst-supported particles include a carrier and a catalyst supported on the carrier. The fibrous material includes one or more conductive fibrous materials and one or more non-conductive fibrous materials. When the content of the carrier is 100 parts by mass, the content of the conductive fibrous substance is 5 parts by mass or more and 50 parts by mass or less, and the content of the non-conductive fibrous substance is 5 parts by mass or more and 20 parts by mass or less.

2. The electrode catalyst layer according to claim 1, wherein The conductive fibrous material is carbon fiber.

3. The electrode catalyst layer according to claim 1 or 2, wherein: The non-conductive fibrous material is a high molecular polymer fiber.

4. The electrode catalyst layer according to claim 3, wherein: The high molecular polymer fiber is a high molecular polymer fiber having a basic functional group in its molecular structure.

5. The electrode catalyst layer according to claim 4, wherein The basic functional group contains nitrogen.

6. The electrode catalyst layer according to claim 1 or 2, wherein: The non-conductive fibrous material is a high molecular polymer fiber having an imide structure or an azole structure.

7. A membrane electrode assembly comprising a polymer electrolyte membrane and a pair of electrode catalyst layers arranged on both sides of the polymer electrolyte membrane in a thickness direction, Either one or both of the pair of electrode catalyst layers is the electrode catalyst layer according to any one of claims 1 to 6.

8. A solid polymer fuel cell comprising: The membrane electrode assembly according to claim 7, a pair of gas diffusion layers disposed on both sides of the membrane electrode assembly in the thickness direction, and A pair of separators are disposed opposite to each other with the membrane electrode assembly and the pair of gas diffusion layers interposed therebetween.

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