Membrane electrode assemblies and polymer electrolyte fuel cells

Abstract

The present invention provides a film electrode assembly with high carbon corrosion resistance. [Solution] The membrane electrode assembly comprises an anode-side electrode catalyst layer, a solid polymer electrolyte membrane, and a cathode-side electrode catalyst layer in this order. The anode-side electrode catalyst layer and the cathode-side electrode catalyst layer each contain catalyst particles, a carbon support carrying the catalyst particles, and a polymer electrolyte, and the volume density of the anode-side electrode catalyst layer is smaller than the volume density of the cathode-side electrode catalyst layer.

Description

[Technical Field]

[0001] This invention relates to a membrane electrode assembly used in a polymer electrolyte fuel cell. [Background technology]

[0002] In recent years, fuel cells have attracted attention as an effective solution to environmental and energy problems. A fuel cell oxidizes a fuel such as hydrogen using an oxidizing agent such as oxygen, and converts the resulting chemical energy into electrical energy. Fuel cells are classified into alkaline, phosphoric acid, polymer, molten carbonate, and solid oxide types depending on the type of electrolyte used. Polymer electrolyte fuel cells (PEFCs) are expected to have applications as portable power sources, household power sources, and automotive power sources due to their low-temperature operation, high power density, and the possibility of miniaturization and weight reduction.

[0003] The membrane electrode assembly of a polymer electrolyte fuel cell (PEFC) has a structure in which a polymer electrolyte membrane is sandwiched between a fuel electrode (anode) and an air electrode (cathode). Electricity is generated by supplying a fuel gas containing hydrogen to the fuel electrode side and an oxidizing gas containing oxygen to the air electrode side.

[0004] It is known that the air electrode becomes highly charged during fuel cell startup, and if the carbon support corrodes as a result, the power generation characteristics of the fuel cell will decrease. Carbon dioxide is produced when carbon reacts with water, and the carbon support corrodes and disappears. In other words, if there is a large amount of moisture present in the air electrode at this time, the corrosion of the carbon support will progress more easily. To improve the durability of fuel cells, it is necessary to improve the drainage from the air electrode.

[0005] One method for improving drainage from the air electrode is to utilize the reverse diffusion of water from the air electrode to the fuel electrode via a solid polymer electrolyte membrane. [Prior art documents] [Patent Documents]

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] As a condition for facilitating the reverse diffusion of water from the air electrode to the fuel electrode, it is necessary that the amount of water that the fuel electrode can hold is large. In Patent Document 1, as a method for promoting the reverse diffusion of water from the cathode - side electrode catalyst layer (air electrode) to the anode - side electrode catalyst layer (fuel electrode), it has been proposed to make the catalyst layer thickness of the anode - side electrode catalyst layer larger than the cathode - side electrode catalyst layer thickness.

[0008] Also, in Patent Document 2, studies have been made on the density of the electrode catalyst layer. However, there is still room for improvement in the reverse diffusion of water even in these technologies.

[0009] In Patent Document 3, by performing system control of gas switching supplied to the cathode, corrosion of the cathode is suppressed. However, implementing such a system increases the operating cost of the fuel cell. Therefore, cathode corrosion resistance of the membrane - electrode assembly itself is also required.

[0010] The present invention has been made in view of such circumstances, and an object thereof is to provide a membrane - electrode assembly with high carbon corrosion durability.

Means for Solving the Problems

[0011] 2] [1] A membrane - electrode assembly comprising an anode - side electrode catalyst layer, a solid polymer electrolyte membrane, and a cathode - side electrode catalyst layer in this order, The anode-side electrode catalyst layer and the cathode-side electrode catalyst layer each contain catalyst particles, a carbon support carrying the catalyst particles, and a polymer electrolyte, respectively. A film electrode assembly in which the volume density of the anode-side electrode catalyst layer is smaller than that of the cathode-side electrode catalyst layer. [2] The film electrode assembly according to [1], wherein at least one of the anode-side electrode catalyst layer and the cathode-side electrode catalyst layer further comprises a fibrous material. [3] The film electrode assembly according to [1] or [2], wherein the ratio of the volume density of the cathode-side electrode catalyst layer to the volume density of the anode-side electrode catalyst layer is 1.2 or more and 2.0 or less. [4] The membrane electrode assembly according to any one of [1] to [3], wherein the mass of the polymer electrolyte per unit area contained in the anode-side electrode catalyst layer is greater than the mass of the polymer electrolyte per unit area contained in the cathode-side electrode catalyst layer. [5] The membrane electrode assembly according to [4], wherein the ratio of the mass of the polymer electrolyte per unit area contained in the cathode electrode catalyst layer to the mass of the polymer electrolyte per unit area contained in the anode electrode catalyst layer is 0.2 or more and 0.7 or less. [6] The volume density of the anode side electrode catalyst layer is 400 mg / cm³ 3 Larger 900 mg / cm³ 3 A smaller membrane electrode assembly as described in any one of items [1] to [5]. [7] The volume density of the cathode side electrode catalyst layer is 800 mg / cm³ 3 Larger 1600 mg / cm³ 3 A smaller membrane electrode assembly as described in any one of items [1] to [6]. [8] A membrane electrode assembly according to any one of items [1] to [7], for use in fuel cells. [9] A polymer electrolyte fuel cell comprising a membrane electrode assembly as described in any one of items [1] to [8]. [Effects of the Invention]

[0012] According to one aspect of the present invention, the back diffusion of water from the cathode-side electrode catalyst layer to the anode-side electrode catalyst layer via the polymer electrolyte membrane is enhanced, providing a membrane electrode assembly that generates electricity stably during long-term operation. More specifically, water generated in the cathode-side electrode catalyst layer due to high-power operation moves to the anode-side electrode catalyst layer, which has a lower volume density and is more receptive to water, via the polymer electrolyte membrane. This reduces the amount of water in the cathode-side electrode catalyst layer, thereby suppressing carbon corrosion within the cathode-side electrode catalyst layer. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view showing the structure of a membrane electrode assembly in one embodiment. [Figure 2] Figure 1 is a schematic diagram illustrating the structure of the electrode catalyst layer in the membrane electrode assembly shown. [Modes for carrying out the invention]

[0014] (Embodiment) Embodiments of the present invention will be described below with reference to the accompanying drawings. The embodiments shown below are illustrative and not limiting to the invention, and are not limited to the features described as embodiments. Various modifications can be made to the embodiments within the technical scope defined by the claims described in the patent claims. Also, the drawings are schematic, and the relationship between thickness and planar dimensions, the ratio of the thickness of each layer, etc., may differ from reality.

[0015] (Membrane electrode assembly) As shown in Figure 1, the membrane electrode assembly 10 comprises a solid polymer electrolyte membrane 11, a cathode-side electrode catalyst layer 12C, and an anode-side electrode catalyst layer 12A in that order.

[0016] When referring to both the cathode-side electrode catalyst layer 12C and the anode-side electrode catalyst layer 12A, it is simply written as "electrode catalyst layer 12". Also, "solid polymer electrolyte membrane" may be simply written as "polymer electrolyte membrane".

[0017] (Solid polymer electrolyte membrane) The solid polymer electrolyte membrane 11 is formed from a solid polymer. That is, the solid polymer electrolyte membrane 11 is composed of a polymer material having proton conductivity, and for example, a fluorine-based electrolyte membrane or a hydrocarbon-based polymer electrolyte membrane can be used. As a fluorine-based polymer electrolyte membrane, for example, Nafion (registered trademark) from Chemours, Forblue (registered trademark) from AGC Inc., Aciplex (registered trademark) from Asahi Kasei Corporation, Gore Select (registered trademark) from Gore, etc. can be used. As a hydrocarbon-based polymer electrolyte membrane, for example, electrolyte membranes such as sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used.

[0018] (electrode catalyst layer) The cathode-side electrode catalyst layer 12C is provided on one main surface of the solid polymer electrolyte membrane 11, and the anode-side electrode catalyst layer 12A is provided on the other main surface of the solid polymer electrolyte membrane 11. One side of both the cathode-side electrode catalyst layer 12C and the anode-side electrode catalyst layer 12A is in contact with the solid polymer electrolyte membrane 11. Although not mandatory, when viewed from a direction opposite to one of the surfaces of the solid polymer electrolyte membrane 11, the outer shape of the cathode-side electrode catalyst layer 12C and the outer shape of the anode-side electrode catalyst layer 12A may be approximately the same, or the outer shape of the electrode catalyst layer 12 on the later-formed surface may be larger than the outer shape of the surface formed first, and the outer shape of the solid polymer electrolyte membrane 11 may be larger than or equal to the outer shapes of these electrode catalyst layers 12. The shape of the solid polymer electrolyte membrane 11 and the electrode catalyst layer 12 are not particularly limited and may be, for example, rectangular or square.

[0019] Figure 2 is a schematic cross-sectional view showing the configuration of the electrode catalyst layer 12 in this embodiment. The electrode catalyst layer 12 includes catalyst particles 21, a carbon support 22, and a polymer electrolyte 23.

[0020] (Catalyst particles) The catalyst particles 21 are either cathode catalyst particles for performing a reduction reaction or anode catalyst particles for performing an oxidation reaction. The catalyst particles 21 may be formed from an alloy containing platinum, an oxide of platinum, a complex oxide containing platinum, etc. The alloy containing platinum can contain, for example, a white metal element other than platinum. The white metal elements are palladium (Pd), ruthenium (Ru), iridium (Ir), rhodium (Rh), and osmium (Os). The alloy containing platinum can contain, for example, iron (Fe), lead (Pt), copper (Cu), chromium (Cr), cobalt (Co), nickel (Ni), manganese (Mn), vanadium (V), molybdenum (Mo), gallium (Ga), and aluminum (Al), etc. The catalyst formed from the alloy containing platinum is preferable from the viewpoint that the metal contained in the catalyst particles 21 is less likely to elute in the oxidation-reduction reaction and the overvoltage in the oxidation-reduction reaction is low.

[0021] The particle size of the catalyst particles 21 is preferably within the range of 0.5 nm or more and 20 nm or less, and more preferably within the range of 1 nm or more and 5 nm or less. When the particle size of the catalyst particles 21 is 0.5 nm or more, the stability of the catalyst particles 21 is less likely to decrease. When the particle size of the catalyst particles 21 is 20 nm or less, the activity of the catalyst particles 21 is less likely to decrease.

[0022] (Coating amount (loading amount) of catalyst particles) The lower limit of the mass of the catalyst particles per unit area contained in the anode-side electrode catalyst layer may be 0.01 mg / cm 2 and is preferably 0.025 mg / cm 2 . The upper limit of the mass of the catalyst particles per unit area contained in the anode-side electrode catalyst layer may be 0.2 mg / cm 2 and is preferably 0.15 mg / cm 2 . The lower limit of the mass of the catalyst particles per unit area contained in the cathode-side electrode catalyst layer may be 0.1 mg / cm 2 and is preferably 0.15 mg / cm 2 . The upper limit for the mass of catalyst particles per unit area contained in the cathode-side electrode catalyst layer is 0.6 mg / cm². 2 It is acceptable for it to be 0.5 mg / cm³ 2 It is preferable that this be the case.

[0023] (Carbon carrier) The carbon support 22 supports catalyst particles 21. The carbon support 22 may be, for example, carbon particles or carbon fibers. It is particularly preferable that the carbon support be carbon particles. By selecting carbon particles as the carbon support, the surface area of ​​the support can be increased compared to when other supports are selected, so that the catalyst particles 21 can be supported at a high density. This makes it possible to improve the catalytic activity per carbon support 22.

[0024] When the carbon support 22 is made of carbon particles, its average particle size is preferably in the range of 10 nm to 3 μm, and more preferably in the range of 10 nm to 2 μm. By having a particle size of 10 nm or more for the carbon support 22, the carbon support 22 is prevented from being too small, thereby preventing the formation of electron conduction paths from becoming difficult. Also, by having a particle size of 3 μm or less for the carbon support 22, the carbon support 22 is prevented from being too large, thereby preventing the electrode catalyst layer 12 from becoming too thick. As a result, the resistance of the electrode catalyst layer 12 is prevented from increasing, and consequently, the output characteristics of the fuel cell equipped with the electrode catalyst layer 12 are prevented from deteriorating.

[0025] The specific surface area of ​​the carbon support 22 is 50 m². 2 / g or more 2000m 2 It is preferable that it be included in the range of / g or less, and 100m 2 / g or more 1500m 2 It is more preferable that the range is less than or equal to / g. The specific surface area of ​​the carbon support 22 is 50 m². 2 By having a density of 2000 m² or more, the catalyst particles 21 are supported at high density, thereby increasing the activity of the catalyst particles 21. In addition, the specific surface area of ​​the carbon support 22 is 2000 m². 2By keeping the amount below / g, the amount of micropores in the carbon support 22 can be suppressed, thereby improving gas diffusion within the carbon support 22. This suppresses an increase in the mass transport resistance of the electrode catalyst layer 12, and as a result, prevents a decrease in the output characteristics of the fuel cell equipped with the electrode catalyst layer 12.

[0026] The degree of graphitization of the carbon support 22 is preferably in the range of 20% to 80%. If the degree of graphitization of the carbon support 22 is 20% or less, the carbon corrosion resistance of the carbon support 22 may decrease significantly due to the operation and shutdown of the fuel cell. On the other hand, if the degree of graphitization of the carbon support 22 is 80% or more, the support of the catalyst particles 21 becomes unstable, and as the fuel cell is used continuously, the particle size of the catalyst particles 21 increases and the activity of the catalyst particles 21 decreases, which may reduce the output of the fuel cell.

[0027] There are no limitations on the ratio of carbon support to catalyst particles, but in the cathode-side electrode catalyst layer 12C, the mass ratio of carbon support to the total mass of carbon support and catalyst particles may be 25% or more, 30% or more, 80% or less, or 50% or less. In the anode-side electrode catalyst layer 12A, the mass ratio of the carbon support to the total mass of the carbon support and catalyst particles may be 60% or more, 70% or more, 95% or less, or 90% or less.

[0028] (Polymer electrolyte) The polymer electrolyte 23 may be, for example, a polymer material having proton conductivity. The polymer material having proton conductivity may be, for example, a fluororesin or a hydrocarbon resin. The fluororesin may be, for example, Nafion (manufactured by Chemours, registered trademark) or Aquivion (manufactured by Solvay, registered trademark). The hydrocarbon resin may be, for example, an engineering plastic or a resin in which a sulfonic acid group has been introduced into a copolymer of engineering plastics.

[0029] (Approximate weight of polymer electrolytes) Preferably, the mass Wa of the polymer electrolyte 23 per unit area contained in the anode-side electrode catalyst layer 12A is greater than the mass Wc of the polymer electrolyte 23 per unit area contained in the cathode-side electrode catalyst layer 12C. Since the polymer electrolyte 23 is a substance that can hold water, increasing the mass of the polymer electrolyte 23 per unit area contained in the anode-side electrode catalyst layer 12A increases the amount of water that the anode-side electrode catalyst layer 12A can hold, thus making it easier for water to reverse diffuse from the cathode-side electrode catalyst layer 12C through the solid polymer electrolyte membrane 11.

[0030] The ratio Wc / Wa of the mass of polymer electrolyte 23 per unit area in the cathode electrode catalyst layer 12C to the mass of polymer electrolyte 23 per unit area in the anode electrode catalyst layer 12A is preferably 0.2 or more and 0.7 or less. If Wc / Wa is less than 0.2, too much water generated in the cathode electrode catalyst layer 12C may move to the anode electrode catalyst layer 12A, resulting in insufficient wetting of the polymer electrolyte 23 in the cathode electrode catalyst layer 12C and a decrease in power generation characteristics. On the other hand, if Wc / Wa is greater than 0.7, the movement of water generated in the cathode electrode catalyst layer 12C to the anode electrode catalyst layer 12A may be insufficient, causing corrosion of the carbon support 22 in the cathode electrode catalyst layer 12C.

[0031] The mass Wa of the polymer electrolyte 23 per unit area contained in the anode electrode catalyst layer 12A is 0.15 mg / cm². 2 Larger 0.30 mg / cm³ 2 Smaller is preferable. 0.15 mg / cm³ 2 If the value is smaller, the amount of water that the anode-side electrode catalyst layer 12A can hold decreases, which can make it difficult for water to reverse diffuse from the cathode-side electrode catalyst layer 12C through the solid polymer electrolyte membrane 11. On the other hand, 0.30 mg / cm³ 2 If the value is greater than this, water may accumulate in the anode-side electrode catalyst layer 12A, which can lead to reduced power generation characteristics.

[0032] The mass Wc of the polymer electrolyte 23 per unit area contained in the cathode-side electrode catalyst layer 12C is 0.10 mg / cm². 2 Larger 0.22 mg / cm³ 2 A smaller value is preferable. 0.11 mg / cm³ 2 If the value is smaller, the proton conduction velocity within the cathode-side electrode catalyst layer 12C will decrease, which can lead to a decline in power generation characteristics. On the other hand, 0.22 mg / cm³ 2 If the value is greater than this, water may accumulate in the cathode-side electrode catalyst layer 12C, leading to flooding and potentially lowering the power generation characteristics.

[0033] (fibrous material) At least one of the anode-side electrode catalyst layer 12A and the cathode-side electrode catalyst layer 12C, preferably both, further preferably contain a fibrous material from the viewpoint of adjusting the volume density. The fibrous material 24 may be carbon fibers, polymer fibers, oxide fibers, or metal fibers. Examples of carbon fibers include carbon fibers, carbon nanotubes, and carbon nanohorns. Examples of polymer fibers include nanofibers of amine polymers such as imide structures and azole structures. Engineering plastic nanofibers are more preferred among polymer fibers. It is preferable that the fibrous material 24 is not dissolved or affected by the solution used in the catalyst ink and has heat resistance at temperatures higher than 120°C. Based on the above properties, the stability of the fibrous material 24 in the electrode catalyst layer can be expected.

[0034] The average fiber diameter of the fibrous material 24 is preferably 300 nm or less, and more preferably 200 nm or less. If the average fiber diameter of the fibrous material 24 is 300 nm or less, an appropriate fineness is ensured for the fibrous material to be contained in the electrode catalyst layer 12. If it is greater than 300 nm, the pore diameter and porosity in the electrode catalyst layer 12 formed by the fibrous material 24 may be too large, which may reduce the power generation characteristics of the film electrode assembly. Furthermore, if the average fiber diameter of the fibrous material 24 is 50 nm or more, an appropriate thickness is ensured, the strength of the electrode catalyst layer 12 is increased, and a crack generation suppression effect is obtained.

[0035] The average fiber length of the fibrous material 24 is preferably within the range of 0.7 μm to 40 μm, and more preferably within the range of 2 μm to 30 μm. By having the fiber length within this range, the strength of the electrode catalyst layer 12 can be increased, thereby suppressing the occurrence of cracks, and as a result, the durability of the electrode catalyst layer 12 against physical impact is improved. In addition, the number of pores formed in the electrode catalyst layer 12 can be increased, thereby reducing the mass transport resistance during power generation operation.

[0036] The mass of the fibrous material 24 in the anode-side electrode catalyst layer 12A may be 0.1 times or more, 0.5 times or more, 2.0 times or less, or 1.0 times or less of the mass of the carbon support. The mass of the fibrous material 24 in the cathode-side electrode catalyst layer 12C may be 0.01 times or more, 0.05 times or more, 0.5 times or less, or 0.3 times or less of the mass of the carbon support.

[0037] (Relationship between volume densities of electrode catalyst layers) In this embodiment, the volume density ρa of the anode-side electrode catalyst layer 12A is smaller than the volume density ρc of the cathode-side electrode catalyst layer 12C. Volume density is the mass per unit volume. If the volume density ρa of the anode-side electrode catalyst layer 12A is smaller than the volume density ρc of the cathode-side electrode catalyst layer 12C, the diffusion rate of water in the relatively lower-density anode-side electrode catalyst layer 12A increases. This makes the anode-side electrode catalyst layer 12A easier to dry out, allowing water generated in the cathode-side electrode catalyst layer 12C to easily move to the anode-side electrode catalyst layer 12A via the solid polymer electrolyte membrane 11. Conversely, if the volume density of the anode-side electrode catalyst layer 12A is greater than the volume density of the cathode-side electrode catalyst layer 12C, the diffusion rate of water in the relatively higher-density anode-side electrode catalyst layer 12A decreases, making it more difficult for water to be discharged to the outside. This can make it difficult for water generated in the cathode-side electrode catalyst layer 12C to move to the anode-side electrode catalyst layer 12A via the solid polymer electrolyte membrane 11.

[0038] The ratio (ρc / ρa) of the volume density ρc of the cathode electrode catalyst layer 12C to the volume density ρa of the anode electrode catalyst layer 12A is preferably 1.2 or more and 2.0 or less. If (ρc / ρa) is less than 1.2, the movement of water generated in the cathode electrode catalyst layer 12C to the anode electrode catalyst layer 12A will be insufficient, which may cause corrosion of the carbon support 22 in the cathode electrode catalyst layer 12C. On the other hand, if (ρc / ρa) is greater than 2.0, too much water generated in the cathode electrode catalyst layer 12C will move to the anode electrode catalyst layer 12A, which may cause insufficient wetting of the polymer electrolyte 23 in the cathode electrode catalyst layer 12C and a decrease in power generation characteristics.

[0039] The volume density ρa of the anode-side electrode catalyst layer 12A is 400 mg / cm³. 2 Larger 900 mg / cm³ 2 Smaller is preferable. The volume density ρa of the anode-side electrode catalyst layer 12A is 400 mg / cm³. 2 If the volume density is smaller, the volume of the anode-side electrode catalyst layer 12A becomes too large, which is disadvantageous in terms of mass diffusion and proton conduction, and can lead to a decrease in power generation characteristics. On the other hand, if the volume density ρa of the anode-side electrode catalyst layer 12A is 900 mg / cm³, 2If the value is larger, the pores in the anode-side electrode catalyst layer 12A decrease, which can reduce the rate at which water is discharged to the outside and decrease carbon corrosion resistance.

[0040] The volume density ρc of the cathode-side electrode catalyst layer 12C is 800 mg / cm³. 2 Larger 1600 mg / cm³ 2 Smaller is preferable. The volume density ρc of the cathode-side electrode catalyst layer 12C is 800 mg / cm³. 2 If it is smaller, the volume density of catalyst particles 21 in the cathode-side electrode catalyst layer 12C may be too low, and the power generation characteristics may deteriorate due to insufficient catalyst. On the other hand, if the volume density ρc of the cathode-side electrode catalyst layer 12C is 1600 mg / cm³ 2 If the value is larger, the pores in the cathode-side electrode catalyst layer 12C decrease, which can lead to a decrease in power generation characteristics due to flooding caused by water accumulation.

[0041] The volume density of the electrode catalyst layer 12 can be controlled by the manufacturing method of the membrane electrode assembly and the composition of the catalyst ink. A specific example of controlling the manufacturing method of the membrane electrode assembly is to directly coat the catalyst ink onto the solid polymer electrolyte membrane 11 and then dry it. This allows the solvent in the catalyst ink to volatilize from the side opposite to the side in contact with the solid polymer electrolyte membrane 11, thus forming many pores in the electrode catalyst layer 12. Alternatively, by adding a fibrous material 24 to the catalyst ink, the electrode catalyst layer 12 takes on a nonwoven fabric-like structure, resulting in the formation of many pores in the electrode catalyst layer 12.

[0042] As a concrete example of controlling the composition of the catalyst ink, adding a foaming agent to the catalyst ink can create more pores in the electrode catalyst layer 12. By creating more pores, the spatial occupancy rate of the catalyst particles 21 and polymer electrolyte 23 per unit volume decreases, and the volume density of the electrode catalyst layer 12 can be reduced. Alternatively, the amount of pores in the electrode catalyst layer 12 can be controlled by changing the material, fiber diameter, and fiber length of the fibrous material 24. Furthermore, by changing the ratio of catalyst particles 21 to carbon support 22, the volume density of the electrode catalyst layer 12 can be controlled without changing the amount of catalyst supported per unit area of ​​the electrode.

[0043] The electrode catalyst layer consists of catalyst particles, a carbon support, a polymer electrolyte, and optionally included fibrous material, which together account for 50% or more of the total mass, can account for 70% or more, can account for 90% or more, and can account for 95% or more.

[0044] (Method for manufacturing an electrode catalyst layer) The electrode catalyst layer 12 of this embodiment can be manufactured by preparing an electrode catalyst layer slurry, coating it onto a substrate, and drying it.

[0045] (Preparation of slurry for electrode catalyst layer) A slurry for the electrode catalyst layer is prepared by mixing the components constituting the electrode catalyst layer 12, namely the carbon support 22 on which catalyst particles 21 are supported, the polymer electrolyte 23, and an arbitrary fibrous material 24, with a dispersion medium.

[0046] The solvent used as the dispersion medium for the electrode catalyst layer slurry is not particularly limited, as long as it does not erode the components constituting the electrode catalyst layer 12 and can dissolve the polymer electrolyte 23 in a highly fluid state or disperse it as a fine gel. However, it is desirable that the solvent contains at least a volatile organic solvent. The solvent used as the dispersion medium for the electrode catalyst layer slurry may be water, alcohols, ketone solvents, ether solvents, polar solvents, etc. Specifically, water, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, and tert-butyl alcohol, ketones such as acetone, methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl amyl ketone, pentanone, heptanone, cyclohexanone, methylcyclohexanone, acetonylacetone, diethyl ketone, dipropyl ketone, and diisobutyl ketone, ether solvents such as tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene, and dibutyl ether, and polar solvents such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, diacetone alcohol, and 1-methoxy-2-propanol can be used as appropriate. The solvent may also be a mixed solvent obtained by mixing two or more of the above materials.

[0047] Furthermore, since dispersion media using lower alcohols have a high risk of ignition, it is preferable to use a mixed solvent of lower alcohol and water when using lower alcohols as dispersion media. In addition, the dispersion media may contain water that is compatible with the polymer electrolyte 23, that is, water with high affinity for the polymer electrolyte 23. The amount of water added to the dispersion media is not particularly limited as long as it does not cause the polymer electrolyte 23 to separate, become cloudy, or gel. A dispersant may be included in the slurry for the electrode catalyst layer in order to disperse the carbon support 22 on which the catalyst particles 21 are supported in the catalyst ink.

[0048] Furthermore, the slurry for the electrode catalyst layer may be subjected to dispersion treatment as needed. The dispersion treatment is not particularly limited as long as it can disperse each component contained in the slurry for the electrode catalyst layer. Examples include treatment with a planetary ball mill and roll mill, treatment with a shear mill, treatment with a wet mill, ultrasonic dispersion treatment, and treatment with a homogenizer.

[0049] (Coating and drying on the substrate) After applying the slurry for the electrode catalyst layer onto the substrate, the electrode catalyst layer 12 is formed by performing a drying process to volatilize the dispersion medium.

[0050] As a substrate used when forming the electrode catalyst layer 12, for example, a transfer substrate that is peeled off after transferring the electrode catalyst layer 12 to the solid polymer electrolyte membrane 11 is used. As a transfer substrate, for example, a resin film is used. Alternatively, the solid polymer electrolyte membrane 11 may be used as the substrate used when forming the electrode catalyst layer 12.

[0051] Methods for coating the substrate with a slurry for the electrode catalyst layer 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.

[0052] Examples of drying methods for the electrode catalyst layer slurry applied to the substrate include hot air drying and IR drying. The drying temperature of the electrode catalyst layer slurry may be in the range of 40°C to 200°C, preferably in the range of 60°C to 110°C. The drying time of the electrode catalyst layer slurry may be in the range of 0.5 minutes to 2 hours, preferably in the range of 1 minute to 30 minutes.

[0053] In a manufacturing method that uses a solid polymer electrolyte membrane 11 as the substrate for forming the electrode catalyst layer 12, the electrode catalyst layer 12 is formed directly on the surface of the solid polymer electrolyte membrane 11. Therefore, the adhesion between the solid polymer electrolyte membrane 11 and the electrode catalyst layer 12 is increased, and since pressurization for bonding the electrode catalyst layer 12 is unnecessary, the collapse of the electrode catalyst layer 12 and the increase in its volume density are suppressed. For this reason, it is preferable to use a solid polymer electrolyte membrane 11 as the substrate for forming the electrode catalyst layer 12.

[0054] Here, since the solid polymer electrolyte membrane 11 generally has the characteristic of having large degrees of swelling and shrinkage, when the solid polymer electrolyte membrane 11 is used as the substrate, the volume change of the substrate during the drying process of the coating film that becomes the electrode catalyst layer 12 is larger compared to when a transfer substrate is used as the substrate. For this reason, if the electrode catalyst layer 12 does not contain fibrous material 24, cracks are likely to occur in the electrode catalyst layer 12. In contrast, with the electrode catalyst layer 12 of this embodiment, even if the volume of the solid polymer electrolyte membrane 11, which is the substrate, changes significantly during the manufacturing process of the electrode catalyst layer 12, the inclusion of fibrous material 24 suppresses the occurrence of cracks, so a manufacturing method using the solid polymer electrolyte membrane 11 as the substrate for forming the electrode catalyst layer 12 can be used.

[0055] (Calculation of volume density) Volume density of electrode catalyst layer 12 (ρ[mg / cm³]) 3 ]) is the thickness of the electrode catalyst layer 12 (T [cm]) and the weight per unit area (W [mg / cm]) 2 It was calculated using ]). ρ=W / T (Equation 1)

[0056] (Thickness measurement) The thickness of the electrode catalyst layer 12 can be measured by observing the cross-section of the film electrode assembly 10 with a scanning electron microscope (SEM). Specifically, the film electrode assembly was cut to a size of approximately 0.5 cm × 0.5 cm and embedded in a photocurable resin (Aronics (manufactured by Toagosei Co., Ltd.)). The cross-section of the film electrode assembly was then prepared using a microtome equipped with a diamond knife. The prepared film electrode assembly was observed with a scanning electron microscope (SEM (SU-8020 (manufactured by Hitachi High-Tech Corporation))). At this time, platinum sputtering was performed on the observation surface for 10 seconds. An Upper detector SE was used as the detector, and observation was performed with an acceleration voltage of 10.0 kV, an emission of 10 uA, and a magnification of 2000x. Measurements were taken at nine locations on the electrode portion of the film electrode assembly. The average of these measurement results was defined as the thickness of the electrode catalyst layer.

[0057] (Weight measurement per unit area) The weight per unit area of ​​the electrode catalyst layer 12 can be determined from the amount of slurry applied to the electrode catalyst layer, or from its dry weight. When determining the weight of the electrode catalyst layer 12 from the amount applied, the solid content (mass%) of the slurry for the electrode catalyst layer must be determined in advance, and the weight can be calculated from the predetermined amount applied and the weight of the solid content. When determining the weight of the electrode catalyst layer 12 from its dry weight, the electrode catalyst layer 12 can be processed to a predetermined size, and its weight can be measured. Alternatively, a membrane electrode assembly 10, which has electrode catalyst layers 12 on both sides of a solid polymer electrolyte membrane 11, can be processed to a predetermined size, and its weight can be measured. Then, the anode-side electrode catalyst layer 12A or the cathode-side electrode catalyst layer 12C can be removed from the solid polymer electrolyte membrane 11 using tape or the like, and the weight can be measured again to determine the weight of the electrode catalyst layer 12. The electrode portion of the membrane electrode assembly has an area of ​​9 cm². 2 The material was punched out using a die. A solid polymer electrolyte membrane was punched out using the same die, and its weight was measured. The weight of the electrode catalyst layer was calculated from this difference. When measuring the weight of only the cathode-side electrode catalyst layer, the measurement was taken using a solid polymer electrolyte membrane with a catalyst layer that only contained the cathode-side electrode catalyst layer.

[0058] (Polymer fuel cell) In Figure 1, the polymer electrolyte fuel cell (cell) 100 has a cathode-side current collector 13C and an anode-side current collector 13A. Specifically, on both the outer sides in the stacking direction of the cathode-side electrode catalyst layer 12C and the anode-side electrode catalyst layer 12A of the membrane electrode assembly 10, the cathode-side electrode catalyst layer 12C, the solid polymer electrolyte membrane 11, and the anode-side electrode catalyst layer 12A are sandwiched between the cathode-side electrode catalyst layer 12C and the anode-side electrode catalyst layer 12A, with the cathode-side electrode catalyst layer 12C and the anode-side current collector 13A facing each other. The side of the cathode-side electrode catalyst layer 12C opposite to the solid polymer electrolyte membrane 11 is in contact with the cathode-side current collector 13C. The side of the anode-side electrode catalyst layer 12A opposite to the solid polymer electrolyte membrane 11 is in contact with the anode-side current collector 13A. The cathode-side current collector 13C and the anode-side current collector 13A can also function as separators, and the membrane electrode assembly 10, the cathode-side current collector 13C, and the anode-side current collector 13A constitute the polymer electrolyte fuel cell 100. The cathode-side current collector 13C and the anode-side current collector 13A can be made of any conductive material. Specifically, examples include carbon paper, carbon nonwoven fabric, oxides, and metal plates. Examples of metal plates include titanium sintered bodies. Carbon paper may be water-repellent, and oxides and metal plates may be plated with precious metals. It is preferable that the cathode-side current collector 13C and the anode-side current collector 13A are porous. The porous nature of the current collector 13 ensures that the air and fuel gas necessary for the fuel cell reaction are sufficiently supplied to the membrane electrode assembly. This can improve the mass transport resistance during power generation and potentially improve power generation performance. In a polymer electrolyte fuel cell (PEFC), electricity is generated when a fuel gas containing hydrogen is supplied to the anode electrode catalyst layer and an oxidizer gas containing oxygen is supplied to the cathode side.

[0059] The following describes examples based on the present invention, but these examples are not limited to the following examples and comparative examples.

[0060] (Examples) Examples will be described with reference to Tables 1 and 2.

[0061] (Fabrication of membrane electrode assembly) The method for fabricating the film electrode assembly in each example is described below.

[0062] (Example A1) First, as a cathode catalyst, a slurry for the cathode electrode catalyst layer was prepared by adding a 20% by mass concentration of Nafion (trademark registered) dispersion (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymer electrolyte and polymer fibers having an imide structure as a fibrous material to platinum catalyst-supported carbon (TEC10EA60TPM (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.)) powder, and using an appropriate solvent. The amount of polymer electrolyte was set to 0.6 times the mass of platinum in the catalyst particles, and the amount of fibrous material was set to 0.05 times the mass of the carbon support in the catalyst particles. The average fiber diameter of the fibrous material was confirmed to be 300 nm. Note that in TEC10EA60TPM, 40% of the powder mass is the mass of the carbon support.

[0063] The obtained slurry for the cathode-side electrode catalyst layer is loaded onto one side of a solid polymer electrolyte membrane (Nafion® membrane) with a platinum load of 0.25 mg / cm² per electrode area. 2 The material was coated using a die coating method. Subsequently, a laminate was obtained in which an electrode catalyst layer was formed on one side of the solid polymer electrolyte membrane by drying it in an 80°C furnace for 5 minutes.

[0064] Next, as an anode catalyst, a slurry for the anode electrode catalyst layer was prepared by adding a 20% by mass concentration Nafion (trademark registered) dispersion as a polymer electrolyte and carbon fibers (VGCF-H (Resonac Corporation)) as a fibrous material to platinum catalyst-supported carbon (TEC10EA40E (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.)) powder, and using an appropriate solvent. The amount of polymer electrolyte was set to 1.0 times the mass of platinum in the catalyst particles, and the amount of fibrous material was set to 1.00 times the mass of the carbon support in the catalyst particles. The average fiber diameter of the fibrous material was confirmed to be 150 nm. Note that in TEC10EA40E, 60% of the powder mass is the mass of the carbon support.

[0065] The obtained anode-side electrode catalyst layer slurry is then applied to the side of the Nafion® film that does not have a cathode-side electrode catalyst layer, with a platinum load of 0.10 mg / cm² per electrode area. 2 The film electrode assembly of Example A1 was obtained by coating using a die coating method. Then, it was dried in an 80°C oven for 5 minutes.

[0066] (Example A2) The film electrode assembly of Example A2 was obtained in the same manner as in Example A1, except that the amount of fibrous material in the slurry for the anode-side electrode catalyst layer was 1.50 times the mass of the carbon support in the catalyst particles.

[0067] (Example A3) The film electrode assembly of Example A3 was obtained in the same manner as in Example A1, except that the amount of fibrous material in the slurry for the anode-side electrode catalyst layer was 0.50 times the mass of the carbon support in the catalyst particles.

[0068] (Example A4) The film electrode assembly of Example A4 was obtained in the same manner as in Example A1, except that the amount of fibrous material in the slurry for the cathode-side electrode catalyst layer was 0.20 times the mass of the carbon support in the catalyst particles.

[0069] (Example A5) The film electrode assembly of Example A5 was obtained in the same manner as in Example A1, except that the amount of fibrous material in the slurry for the cathode-side electrode catalyst layer was 0.01 times the mass of the carbon support in the catalyst particles.

[0070] (Comparative Example A1) A film electrode assembly of Comparative Example A1 was obtained in the same manner as in Example A4, except that the amount of fibrous material in the slurry for the anode-side electrode catalyst layer was 0.50 times the mass of the carbon support in the catalyst particles.

[0071] (Comparative example A2) First, as an anode catalyst, a slurry for the anode electrode catalyst layer was prepared by adding a 20% by mass concentration Nafion (trademark registered) dispersion as a polymer electrolyte and carbon fibers (VGCF-H) as a fibrous material to platinum catalyst-supported carbon (TEC10EA40E) powder, and using an appropriate solvent. The amount of polymer electrolyte was set to 1.0 times the mass of platinum in the catalyst particles, and the amount of fibrous material was set to 0.50 times the mass of the carbon support in the catalyst particles. The average fiber diameter of the fibrous material was confirmed to be 150 nm.

[0072] The obtained anode electrode catalyst layer slurry is then loaded onto one side of the Nafion® film with a platinum load of 0.10 mg / cm² per electrode area. 2 The material was coated using a die coating method. It was then dried in an 80°C oven for 5 minutes. The dried electrolyte membrane with the catalyst layer was then pressurized using a hot press at 80°C and 2.8 MPa for 10 minutes to obtain a laminate in which an electrode catalyst layer was formed on one side of the solid polymer electrolyte membrane.

[0073] Next, as a cathode catalyst, a slurry for the cathode electrode catalyst layer was prepared by adding a 20% by mass concentration of Nafion (trademark registered) dispersion as a polymer electrolyte and polymer fibers having an imide structure as a fibrous material to platinum catalyst-supported carbon (TEC10EA60TPM) powder, and using an appropriate solvent. The amount of polymer electrolyte was set to 0.6 times the mass of platinum in the catalyst particles, and the amount of fibrous material was set to 0.05 times the mass of the carbon support in the catalyst particles. The average fiber diameter of the fibrous material was confirmed to be 300 nm.

[0074] The obtained slurry for the cathode-side electrode catalyst layer is loaded onto the side of the Nafion® film that does not have an anode-side electrode catalyst layer, with a platinum load of 0.25 mg / cm² per electrode area. 2 The material was coated using a die coating method. Subsequently, the film electrode assembly of Comparative Example A2 was obtained by drying it in an 80°C oven for 5 minutes.

[0075] (Evaluation of power generation characteristics) A gas diffusion layer (SIGRACET® 36BB, manufactured by SGL Corporation) was placed outside the electrode catalyst layer 12, and the power generation performance of fuel cells equipped with the membrane electrode assemblies of each embodiment and each comparative example was evaluated using a commercially available JARI standard cell. The power generation performance was evaluated according to the protocol specified by the New Energy and Industrial Technology Development Organization (NEDO) (Cell Evaluation and Analysis Protocol, July 2023, Test Name: IV Measurement Method / Overvoltage Separation Analysis Method). The cell temperature was set to 80°C. Hydrogen with a relative humidity of 88%RH was supplied to the anode, and air with a relative humidity of 42%RH was supplied to the cathode.

[0076] (Carbon corrosion resistance evaluation) A gas diffusion layer (SIGRACET® 36BB) was placed outside the electrode catalyst layer 12, and the power generation performance of fuel cells equipped with the membrane electrode assemblies of each embodiment and fuel cells equipped with the membrane electrode assemblies of each comparative example was evaluated using a commercially available JARI standard cell. Carbon corrosion resistance was evaluated according to the protocol specified by the New Energy and Industrial Technology Development Organization (NEDO) (Cell Evaluation and Analysis Protocol, July 2023, Test Name: Potential Cycle (Start-Stop) Test Method).

[0077] [Table 1]

[0078] Carbon corrosion resistance is 1.0 A / cm² in the power generation performance evaluation. 2 The number of cycles when the voltage value in is 0.4V or less Over 10,000 cycles: A 9999~7500 cycles: B 7499~5000 cycles: C 4999~2500 cycles: D Less than 2499 cycles: E This was the conclusion. A cycle of 2500 or more was considered good. Even if the rating is "E," there are no practical problems.

[0079] As shown in Table 1, all of Examples A1 to A5 exhibited good carbon corrosion resistance. This is thought to be because the volume density of the anode-side electrode catalyst layer was lower than that of the cathode-side electrode catalyst layer, which promoted the movement of water from the cathode-side electrode catalyst layer to the anode-side electrode catalyst layer via the solid polymer electrolyte membrane, thus facilitating back diffusion of water. In contrast, in Comparative Examples A1 and A2, the volume density of the anode-side electrode catalyst layer was higher than that of the cathode-side electrode catalyst layer, so the diffusion of water within the cathode-side electrode catalyst layer was more advantageous than the movement of water via the polymer electrolyte membrane, resulting in insufficient back diffusion.

[0080] Examples A1 and A5 showed improved carbon corrosion resistance. This is thought to be because the ρc / ρa was in the range of 1.2 to 2.0, resulting in a good balance of water movement from the cathode-side electrode catalyst layer to the anode-side electrode catalyst layer, thus improving carbon corrosion resistance.

[0081] In Comparative Examples A1 and A2, the carbon corrosion resistance performance decreased because the volume density of the anode-side electrode catalyst layer was greater than that of the cathode-side electrode catalyst layer. This is thought to be because when the volume density of the anode-side electrode catalyst layer is greater than that of the cathode-side electrode catalyst layer, back diffusion of water from the cathode-side electrode catalyst layer becomes less likely, water tends to accumulate in the cathode-side electrode catalyst layer, and carbon becomes more susceptible to corrosion.

[0082] (Example B1) First, as a cathode catalyst, a slurry for the cathode electrode catalyst layer was prepared by adding a 20% by mass concentration of Nafion (trademark registered) dispersion (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymer electrolyte and polymer fibers having an imide structure as a fibrous material, to platinum catalyst-supported carbon (TEC10EA60TPM) powder, and using an appropriate solvent. The amount of polymer electrolyte was set to 0.48 times the mass of platinum in the catalyst particles, and the amount of fibrous material was set to 0.05 times the mass of the carbon support in the catalyst particles. The average fiber diameter of the fibrous material was confirmed to be 300 nm.

[0083] The obtained slurry for the cathode-side electrode catalyst layer is placed on one side of a polymer electrolyte membrane (Nafion® membrane) with sealing material on both sides, with a platinum load of 0.25 mg / cm² per electrode area. 2 The material was coated using a die coating method. Subsequently, a laminate was obtained in which an electrode catalyst layer was formed on one side of the polymer electrolyte membrane by drying it in an 80°C furnace for 5 minutes.

[0084] Next, as an anode catalyst, a slurry for the anode electrode catalyst layer was prepared by adding a 20% by mass concentration Nafion (trademark registered) dispersion as a polymer electrolyte and carbon fiber (VGCF-H) as a fibrous material to platinum catalyst-supported carbon (TEC10EA30E (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.)) powder, and using an appropriate solvent. The amount of polymer electrolyte was 2.3 times the mass of platinum in the catalyst particles, and the amount of fibrous material was 1.00 times the mass of the carbon support in the catalyst particles. The average fiber diameter of the fibrous material was confirmed to be 150 nm.

[0085] The obtained anode electrode catalyst layer slurry is then applied to the cathode side of the Nafion® film, where the electrode catalyst layer is not formed, with a platinum load of 0.10 mg / cm² per electrode area. 2 The material was coated using a die coating method. Subsequently, the film electrode assembly of Example B1 was obtained by drying it in an 80°C oven for 5 minutes.

[0086] (Example B2) First, as a cathode catalyst, a slurry for the cathode electrode catalyst layer was prepared by adding a 20% by mass concentration of Nafion (trademark registered) dispersion as a polymer electrolyte and carbon fiber (VGCF-H) as a fibrous material to platinum catalyst-supported carbon (TEC10EA50E (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.)) powder, and using an appropriate solvent. The amount of polymer electrolyte was set to 0.80 times the mass of platinum in the catalyst particles, and the amount of fibrous material was set to 0.50 times the mass of the carbon support in the catalyst particles. Note that in TEC10EA50E, 50% of the powder mass is the mass of the carbon support.

[0087] The obtained slurry for the cathode side electrode catalyst layer is placed on one side of a solid polymer electrolyte membrane (Nafion® membrane) with sealing material on both sides, with a platinum load of 0.25 mg / cm² per electrode area. 2 The material was coated using a die coating method. Subsequently, a laminate was obtained in which an electrode catalyst layer was formed on one side of the solid polymer electrolyte membrane by drying it in an 80°C furnace for 5 minutes.

[0088] Next, as an anode catalyst, a slurry for the anode electrode catalyst layer was prepared by adding a 20% by mass concentration Nafion (trademark registered) dispersion as a polymer electrolyte and carbon fiber (VGCF-H) as a fibrous material to platinum catalyst-supported carbon (TEC10EA10E (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.)) powder, and using an appropriate solvent. The amount of polymer electrolyte was 9.0 times the mass of platinum in the catalyst particles, and the amount of fibrous material was 0.50 times the mass of the carbon support in the catalyst particles. Note that 90% of the mass of the TEC10EA10E powder is the mass of the carbon support.

[0089] The obtained anode-side electrode catalyst layer slurry is then applied to the side of the Nafion® film that does not have a cathode-side electrode catalyst layer, with a platinum load of 0.05 mg / cm² per electrode area. 2 The material was coated using a die coating method. Subsequently, the film electrode assembly of Example B2 was obtained by drying it in an 80°C oven for 5 minutes.

[0090] (Example B3) The membrane electrode assembly of Example B3 was obtained in the same manner as in Example B2, except that after forming the cathode-side electrode catalyst layer, the electrolyte membrane with the catalyst layer was pressurized using a hot press device at 80°C and 1.0 MPa for 5 minutes.

[0091] (Example B4) The film electrode assembly of Example B4 was obtained in the same manner as in Example B1, except that platinum catalyst-supported carbon (TEC10EA70TPM (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.)) powder was used as the cathode catalyst, and the polymer electrolyte was 0.36 times the mass of platinum in the catalyst particles. Note that in TEC10EA70TPM, 30% of the powder mass is the mass of the carbon support.

[0092] (Example B5) The membrane electrode assembly of Example B5 was obtained in the same manner as in Example B4, except that after forming the cathode-side electrode catalyst layer, the electrolyte membrane with the catalyst layer was pressurized using a hot press device at 80°C and 1.0 MPa for 5 minutes.

[0093] (Example B6) In the anode catalyst layer slurry, platinum-supported carbon (TEC10EA10E) powder is used as the anode catalyst, the polymer electrolyte is 9.0 times the mass of platinum in the catalyst particles, the amount of fibrous material is 1.50 times the mass of carbon support in the catalyst particles, and the amount of platinum supported during coating is 0.05 mg / cm² per electrode area. 2 The film electrode assembly of Example B6 was obtained using the same method as in Example B1, except for the difference described above.

[0094] (Example B7) In the anode catalyst layer slurry, platinum-supported carbon (TEC10EA40E) powder is used as the anode catalyst, the polymer electrolyte is 1.5 times the mass of platinum in the catalyst particles, and the amount of fibrous material is 1.00 times the mass of carbon support in the catalyst particles, and the amount of platinum supported during coating is 0.10 mg / cm² per electrode area. 2 The film electrode assembly of Example B7 was obtained using the same method as in Example B1, except for the difference described above.

[0095] [Table 2]

[0096] As shown in Table 2, carbon corrosion resistance was better in all of Examples B1 to B7 than in Example A1. This is thought to be because the Wc / Wa value became less than 1, meaning that the mass of polymer electrolyte per unit area contained in the anode electrode catalyst layer was greater than the mass of polymer electrolyte per unit area contained in the cathode electrode catalyst layer, thereby promoting water backdiffusion. In addition, Example B7 showed slightly worse results compared to Examples B1 to B6. This is thought to be because the Wc / Wa value was 0.8, which was not within the optimal range.

[0097] Examples B1 to B4 showed particularly good carbon corrosion resistance. This is thought to be because, in addition to optimizing Wc / Wa, ρc / ρa also reached optimal values, resulting in optimized wetting of the anode-side electrode catalyst layer and the cathode-side electrode catalyst layer.

[0098] As described above, according to this embodiment, the membrane electrode assembly has an electrode catalyst layer in which the volume density of the anode-side electrode catalyst layer is smaller than that of the cathode-side electrode catalyst layer. As a result, the back diffusion of water from the cathode-side electrode catalyst layer through the solid polymer electrolyte membrane is enhanced, thereby improving carbon corrosion resistance during fuel cell operation and making it possible to provide a membrane electrode assembly that generates power stably during long-term operation. [Industrial applicability]

[0099] This invention offers high durability and high industrial value because the volume density of the anode-side electrode catalyst layer of the membrane electrode assembly is lower than that of the cathode-side electrode catalyst layer. For example, it is extremely suitable for the manufacture of automotive fuel cells. [Explanation of Symbols]

[0100] 10...Membrane electrode assembly, 11...Solid polymer electrolyte membrane, 12A...Anode-side electrode catalyst layer, 12C...Cathode-side electrode catalyst layer, 24...Fibrous material, 21...Catalyst particles, 22...Carbon support, 23...Polymer electrolyte, 100...Solid polymer fuel cell (cell).

Claims

1. A membrane electrode assembly comprising an anode-side electrode catalyst layer, a solid polymer electrolyte membrane, and a cathode-side electrode catalyst layer in this order, The anode-side electrode catalyst layer and the cathode-side electrode catalyst layer each contain catalyst particles, a carbon support carrying the catalyst particles, and a polymer electrolyte, respectively. A film electrode assembly in which the volume density of the anode-side electrode catalyst layer is smaller than that of the cathode-side electrode catalyst layer.

2. The film electrode assembly according to claim 1, wherein at least one of the anode-side electrode catalyst layer and the cathode-side electrode catalyst layer further comprises a fibrous material.

3. The film electrode assembly according to claim 1 or 2, wherein the ratio of the volume density of the cathode-side electrode catalyst layer to the volume density of the anode-side electrode catalyst layer is 1.2 or more and 2.0 or less.

4. The membrane electrode assembly according to claim 1 or 2, wherein the mass of the polymer electrolyte per unit area contained in the anode-side electrode catalyst layer is greater than the mass of the polymer electrolyte per unit area contained in the cathode-side electrode catalyst layer.

5. The membrane electrode assembly according to claim 4, wherein the ratio of the mass of the polymer electrolyte per unit area contained in the cathode-side electrode catalyst layer to the mass of the polymer electrolyte per unit area contained in the anode-side electrode catalyst layer is 0.2 or more and 0.7 or less.

6. The volume density of the anode-side electrode catalyst layer is 400 mg / cm³. ３ Larger 900 mg / cm³ ３ A smaller film electrode assembly according to claim 1 or 2.

7. The volume density of the cathode-side electrode catalyst layer is 800 mg / cm³. ３ Larger 1600 mg / cm³ ３ A smaller film electrode assembly according to claim 1 or 2.

8. A membrane electrode assembly according to claim 1 or 2, for use in a fuel cell.

9. A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 1 or 2.

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