JP7533194B2 - Membrane electrode assembly for fuel cells and polymer electrolyte fuel cells - Google Patents

Description

The present invention relates to a membrane electrode assembly for a fuel cell and a polymer electrolyte fuel cell.

A fuel cell is a power generation system that uses a fuel gas containing hydrogen and an oxidant gas containing oxygen to generate electricity as well as heat by inducing a reverse reaction in the electrolysis of water at electrodes containing a catalyst. Compared to conventional power generation methods, this power generation system has features such as high efficiency, low environmental impact, and low noise, and is attracting attention as a clean energy source of the future. There are several types of fuel cells depending on the type of ion conductor used, and fuel cells that use a proton-conducting polymer membrane are called solid polymer fuel cells.

Among fuel cells, solid polymer fuel cells can be used at around room temperature, and are therefore seen as promising for use as vehicle power sources and stationary home power sources, and in recent years, various research and development efforts have been conducted on them. Solid polymer fuel cells are cells in which a membrane electrode assembly (hereinafter sometimes referred to as MEA), in which a pair of electrode catalyst layers are arranged on both sides of a polymer electrolyte membrane, is sandwiched between a pair of separators.

One of the separators has a gas flow path formed therein for supplying a fuel gas containing hydrogen to one of the electrodes, and the other separator has a gas flow path formed therein for supplying an oxidizer gas containing oxygen to the other of the electrodes.
Here, the one electrode to which the fuel gas is supplied is referred to as the fuel electrode, and the other electrode to which the oxidant gas is supplied is referred to as the air electrode. These electrodes are provided with an electrode catalyst layer having a polymer electrolyte, carbon particles (catalyst-supported particles) supporting a catalyst such as a platinum-based precious metal, and a gas diffusion layer having both gas permeability and electronic conductivity. The gas diffusion layer constituting these electrodes is disposed so as to face the separator, i.e., between the electrode catalyst layer and the separator.

In order to improve the output density of fuel cells, efforts have been made to improve the gas diffusion properties of the electrode catalyst layer. One of these efforts concerns the pores in the electrode catalyst layer. The pores in the electrode catalyst layer are located beyond the separator through the gas diffusion layer, and act as passages to transport multiple substances. At the fuel electrode, the pores not only smoothly supply fuel gas to the three-phase interface, which is the site of the oxidation-reduction reaction, but also supply water to smoothly conduct the generated protons within the polymer electrolyte membrane. At the air electrode, the pores not only supply oxidant gas, but also smoothly remove water generated in the electrode reaction.

In solid polymer electrolyte fuel cells, it is necessary to prevent a phenomenon known as "flooding," in which the power generation reaction stops due to impeded material transport at the fuel electrode and air electrode. For this reason, configurations that improve drainage have been studied (see, for example, Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4).

Furthermore, while issues to be overcome in order to commercialize solid polymer fuel cells include improving output density and durability, the greatest issue is reducing costs (cost reduction).
One of the ways to reduce costs is to reduce the number of humidifiers. Perfluorosulfonic acid membranes and hydrocarbon membranes are widely used for the polymer electrolyte membrane, which is located at the center of the membrane electrode assembly. In order to obtain excellent proton conductivity, moisture management close to a saturated water vapor pressure atmosphere is required, and currently moisture is supplied from the outside using a humidifier. Therefore, in order to reduce power consumption and simplify the system, development is underway for a polymer electrolyte membrane that shows sufficient proton conductivity even under low humidity conditions so that a humidifier is not required.

However, in an electrode catalyst layer with improved drainage, the polymer electrolyte dries up under low humidity conditions, so it is necessary to optimize the electrode catalyst layer structure and improve water retention. To date, methods have been devised to improve the water retention of fuel cells under low humidity conditions, for example, by sandwiching a humidity adjustment film between the electrode catalyst layer and the gas diffusion layer.
For example, Patent Document 5 describes a method in which a humidity adjusting film made of conductive carbonaceous powder and polytetrafluoroethylene exhibits a humidity adjusting function and prevents drying up.

Patent Document 6 also describes a method of providing grooves on the surface of the catalyst electrode layer that contacts the polymer electrolyte membrane. In the method described in Patent Document 6, grooves with a width of 0.1 to 0.3 mm are formed on the surface of the catalyst electrode layer, thereby suppressing the deterioration of power generation performance under low humidification conditions.

JP 2006-120506 A JP 2006-332041 A JP 2007-87651 A JP 2007-80726 A JP 2006-252948 A JP 2007-141588 A

However, the power generation performance of the electrode catalyst layers described in these patent documents is insufficient, and further improvement in power generation performance has been desired.
The present invention aims to provide a membrane electrode assembly for a fuel cell having an electrode catalyst layer which, when used in a polymer electrolyte fuel cell, has improved water retention under low humidification conditions without inhibiting the removal of water generated in an electrode reaction, and exhibits high power generation performance even under low humidification conditions.

According to one aspect of the present invention, there is provided a membrane electrode assembly for a fuel cell in which a polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers, and the pair of electrode catalyst layers are sandwiched from the outside by a pair of separators that form a gas flow path between the electrode catalyst layers, at least one of the pair of electrode catalyst layers has a first electrode catalyst part and a second electrode catalyst part that face the polymer electrolyte membrane, the first electrode catalyst part is an electrode catalyst part for the inlet side of the gas flow path, and the second electrode catalyst part is an electrode catalyst part for the outlet side of the gas flow path, each of the first electrode catalyst part and the second electrode catalyst part includes a catalyst-supported particle made of carbon particles on which a catalyst is supported, a fibrous material, and a polymer electrolyte, the fibrous material is composed of a hydrophobic fibrous material and a hydrophilic fibrous material, and the mass ratio of the hydrophobic fibrous material to the fibrous material is such that the mass ratio of the second electrode catalyst part is greater than the mass ratio of the first electrode catalyst part.

According to another aspect of the present invention, there is provided a polymer electrolyte fuel cell comprising the fuel cell membrane electrode assembly of the above aspect, a pair of gas diffusion layers sandwiching the fuel cell membrane electrode assembly, and a pair of separators disposed opposite each other and sandwiching the fuel cell membrane electrode assembly and the pair of gas diffusion layers.

According to the present invention, it is possible to provide an electrode catalyst layer that exhibits high power generation characteristics when used in a polymer electrolyte fuel cell.

FIG. 2 is an exploded perspective view showing an example of a membrane electrode assembly for a fuel cell according to one embodiment of the present invention, and is an exploded perspective view showing a schematic structure of the membrane electrode assembly having an electrode catalyst layer for a fuel cell. 1 is an exploded perspective view showing a schematic example of the structure of a polymer electrolyte fuel cell to which the present invention is applied;

<Embodiment>
Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.
Here, the drawings are schematic, and the relationship between thickness and planar dimensions, the thickness ratio of each layer, etc. are different from the actual ones. In addition, the embodiments shown below are examples of configurations for embodying the technical idea of the present disclosure, and the technical idea of the present disclosure is not limited to the materials, shapes, structures, etc. of the components described below. The technical idea of the present disclosure can be modified in various ways within the technical scope defined by the claims described in the claims.

[Membrane Electrode Assembly]
First, the membrane electrode assembly 11 according to this embodiment will be described.
As shown in FIG. 1, the membrane electrode assembly 11 includes a polymer electrolyte membrane 1, and an electrode catalyst layer 2 (shown on the upper side in FIG. 1) and an electrode catalyst layer 3 (shown on the lower side in FIG. 1) that sandwich the polymer electrolyte membrane 1 from the upper and lower sides of the polymer electrolyte membrane 1. Furthermore, the two electrode catalyst layers 2 and 3 of the membrane electrode assembly 11 are divided into two regions in the planar direction of the polymer electrolyte membrane 1. More specifically, the electrode catalyst layer 2 shown on the upper side in FIG. 1 has a first electrode catalyst portion 2a arranged on the inlet side of the gas flowing into the electrode catalyst layer 2, and a second electrode catalyst portion 2b arranged on the outlet side of the gas. Similarly, the electrode catalyst layer 3 shown on the lower side in FIG. 1 has a first electrode catalyst portion 3a located on the inlet side of the gas flowing into the electrode catalyst layer 3, and a second electrode catalyst portion 3b located on the outlet side of the gas.

At least one of the two electrode catalyst layers 2, 3 has the following configurations (a) and (b). It is preferable that both of the two electrode catalyst layers 2, 3 satisfy the following configurations (a) and (b).
(a) The catalyst support includes a catalyst-supporting particle, a fibrous material, and a polymer electrolyte, the fibrous material being composed of a hydrophobic fibrous material and a hydrophilic fibrous material.
(b) The mass ratio of the hydrophobic fibrous material to the fibrous material in the second electrode catalyst portion 2b (or 3b) is greater than the mass ratio of the hydrophobic fibrous material to the fibrous material in the first electrode catalyst portion 2a (or 3a).
The average fiber length of the entire fibrous material including the hydrophobic fibrous material and the hydrophilic fibrous material is preferably within the range of 0.7 μm or more and 30 μm or less, and more preferably within the range of 10 μm or more and 20 μm or less.

The fiber mass, which is the sum of the mass of the hydrophobic fibrous material and the mass of the hydrophilic fibrous material, is preferably 0.05 to 0.4 times the mass of the carrier in the catalyst-supported particle, and more preferably 0.2 to 0.3 times. If the fiber mass is less than 0.05 times the mass of the carrier in the catalyst-supported particle, it is estimated that the water generated by the electrode reaction cannot be sufficiently drained in the high current range due to the small number of pores formed in the electrode catalyst layer, and the diffusibility of the reaction gas may not be improved. Also, if it exceeds 0.4 times, it is estimated that the number of pores formed in the electrode catalyst layer may be large, making it difficult to increase the water retention under low humidification conditions.

The mass of the polymer electrolyte is preferably 0.3 to 1.0 times the mass of the carrier in the catalyst-supported particle, and more preferably 0.5 to 0.8 times. If the mass of the polymer electrolyte is less than 0.3 times the mass of the carrier in the catalyst-supported particle, it is estimated that the water generated in the electrode reaction cannot be sufficiently drained in the high current range due to the small number of pores formed in the electrode catalyst layer, and the diffusibility of the reaction gas may not be improved. Also, if it exceeds 1.0 times, it is estimated that the number of pores formed in the electrode catalyst layer may be large, making it difficult to increase water retention under low humidification conditions.

The inventors of the present application have confirmed that the first electrode catalyst part 2a (or 3a) having the above-mentioned configuration has water retention under low humidification conditions, and that the second electrode catalyst part 2b (or 3b) does not inhibit the removal of water generated by the electrode reaction. The detailed mechanism is speculated as follows, but the present invention is not limited to the mechanism described below.

The electrode catalyst layers 2 and 3 having the above-mentioned configurations (a) and (b) have high durability and mechanical properties, such as suppressing the occurrence of cracks in the electrode catalyst layer that cause a decrease in durability, due to the entanglement of the fibrous material. If the average fiber length of the fibrous material is less than 0.7 μm, the entanglement of the fibrous material is weak, and the mechanical properties may decrease. Also, if the average fiber length of the fibrous material exceeds 30 μm, the entanglement of the fibrous material is strong, and the ink may not be able to be dispersed.

In addition, in the second electrode catalyst part 2b (or 3b) provided on the gas outlet side, the mass ratio of the hydrophobic fibrous material to the fibrous material is increased, thereby increasing the hydrophobicity of the pores formed in the electrode catalyst layer and facilitating water removal. On the other hand, in the first electrode catalyst part 2a (or 3a) provided on the gas inlet side, the mass ratio of the hydrophobic fibrous material to the fibrous material is decreased, thereby increasing the hydrophilicity of the pores formed in the electrode catalyst layer, thereby achieving both water retention under low humidification conditions.

The electrode catalyst layers 2, 3 having the above configurations (a) and (b) preferably further have the following configuration (c).
(c) In the first electrode catalyst part 2a (or 3a), the mass ratio of the hydrophobic fibrous material to the fibrous material (mass of hydrophobic fibrous material/mass of fibrous material) is in the range of 0.1 or more and 0.45 or less, and in the second electrode catalyst part 2b (or 3b), the mass ratio of the hydrophobic fibrous material to the fibrous material (mass of hydrophobic fibrous material/mass of fibrous material) is in the range of 0.55 or more and 0.9 or less.

The mass ratio of the hydrophobic fibrous material to the fibrous material in the first electrode catalyst portion 2a (or 3a) is preferably 0.1 or more and 0.45 or less, and more preferably 0.2 or more and 0.35 or less.
Furthermore, with regard to the mass ratio of hydrophobic fibrous material to fibrous material, the mass ratio (mass of hydrophobic fibrous material/mass of fibrous material) in the second electrode catalyst part 2b (or 3b) is preferably 0.55 or more and 0.9 or less, and more preferably 0.65 or more and 0.8 or less.

If the mass ratio of hydrophobic fibrous material to fibrous material in the first electrode catalyst portion 2a (or 3a) is less than 0.1, the hydrophilicity of the pores formed in the electrode catalyst layer may become excessively high, making it difficult to remove water.
If the mass ratio of the hydrophobic fibrous material to the fibrous material in the second electrode catalyst portion 2b (or 3b) exceeds 0.9, it becomes difficult to retain water under low humidification conditions, and proton conductivity may decrease.
Furthermore, if the mass ratio of hydrophobic fibrous material to fibrous material in the first electrode catalyst part 2a (or 3a) exceeds 0.45, or if the mass ratio of hydrophobic fibrous material to fibrous material in the second electrode catalyst part 2b (or 3b) is less than 0.55, the difference between hydrophobicity and hydrophilicity in the pores formed in the electrode catalyst layer becomes small, making it difficult to exhibit high power generation performance.

[Polymer electrolyte fuel cell]
Next, a polymer electrolyte fuel cell including a membrane electrode assembly 11 according to one embodiment of the present invention will be described with reference to FIG.
2 includes a membrane electrode assembly 11, a pair of gas diffusion layers 4 and 5, and a set of separators 10a and 10b. The gas diffusion layer 5 is disposed so as to face the electrode catalyst layer 2 of the assembly 11. The gas diffusion layer 5 is disposed so as to face the electrode catalyst layer 3. The electrode catalyst layer 2 and the gas diffusion layer 4 form an air electrode. The electrode catalyst layer 3 and the gas diffusion layer 5 form a fuel electrode (anode, negative electrode) 7.

The pair of separators 10a, 10b are disposed on the outside of the gas diffusion layers 4 and 5, that is, on the opposite side of the gas diffusion layers 4 and 5 from the side facing the membrane electrode assembly 11. That is, the membrane electrode assembly 11 is sandwiched between one separator 10a, 10b in the thickness direction of the membrane electrode assembly 11. The separators 10a, 10b each have gas flow paths 8a, 8b for gas flow formed on the surface facing the gas diffusion layers 4 and 5, and cooling water flow paths 9a, 9b for cooling water flow formed on the surface opposite to the surface facing the gas diffusion layers 4 and 5. The separators 10a, 10b are formed of a material having electrical conductivity and impermeability.

A fuel gas, for example, hydrogen gas, is supplied to the gas flow passage 8b of the separator 10b facing the fuel electrode 7. On the other hand, an oxidizer gas, for example, oxygen gas, is supplied to the gas flow passage 8a of the separator 10a facing the air electrode 6. An electromotive force can be generated between the fuel electrode 7 and the air electrode 6 by causing an electrode reaction between the hydrogen fuel gas and the oxygen oxidizer gas in the presence of a catalyst.
In the solid polymer fuel cell 12, a pair of separators 10a, 10b sandwich a polymer electrolyte membrane 1, a pair of electrode catalyst layers 2, 3, and a pair of gas diffusion layers 4, 5. The solid polymer fuel cell 12 shown in Fig. 2 is an example of a fuel cell having a single cell structure, but the solid polymer fuel cell may have a structure in which a plurality of cells are stacked with the separator 10a or the separator 10b interposed therebetween.

[Method for producing membrane electrode assembly]
Next, an example of a method for producing the membrane electrode assembly 11 having the above configurations (a), (b), and (c) will be described.
The membrane electrode assembly 11 having the above configurations (a), (b), and (c) is manufactured by a method including the following catalyst ink preparation step, catalyst portion formation step, and lamination step.
The catalyst ink preparation process is a process for producing a catalyst ink that includes catalyst-supported particles made of carbon particles carrying a catalyst, a fibrous material including a hydrophobic fibrous material and a hydrophilic fibrous material, a polymer electrolyte, and a solvent. In the catalyst ink preparation process, two types of catalyst inks with different mass ratios of hydrophobic fibrous material to fibrous material are prepared. The catalyst ink with a smaller mass ratio of hydrophobic fibrous material to fibrous material was designated as the first catalyst ink, and the catalyst ink with a larger mass ratio of hydrophobic fibrous material to fibrous material was designated as the second catalyst ink.

The catalyst part formation process includes a first step of forming a first electrode catalyst part 2a (or 3a) by applying a first catalyst ink to a substrate and drying it, and a second step of forming a second electrode catalyst part 2b (or 3b) by applying a second catalyst ink to the substrate and drying it.
In the catalyst portion forming step, the first catalyst ink and the second catalyst ink are applied to the substrate so that the application area of the first catalyst ink does not overlap with the application area of the second catalyst ink, thereby forming an electrode catalyst layer 2 (or 3) having a first electrode catalyst portion 2a (or 3a) and a second electrode catalyst portion 2b (or 3b).

The lamination step is a step of laminating the electrode catalyst layer 2 (or 3) formed on the substrate on the polymer electrolyte membrane 1. In the lamination step, the electrode catalyst layer 2 (or 3) is attached so that the first electrode catalyst part 2a (or 3a) is on the inlet side of the gas flow direction and the second electrode catalyst part 2b (or 3b) is on the outlet side of the gas flow direction with respect to the gas flow direction flowing into the electrode catalyst layer 2 (or 3). When the substrate is the polymer electrolyte membrane 1, that is, when the electrode catalyst layer 2 (or 3) is formed directly on the polymer electrolyte membrane 1, the lamination step is performed by carrying out the catalyst part formation step.
The electrode catalyst layers 2, 3 are attached to the upper and lower surfaces of the polymer electrolyte membrane 1 to obtain a membrane electrode assembly 11. Both of the electrode catalyst layers 2, 3 may be produced by the above-mentioned method, or one of them may be produced by the above-mentioned method and the other by a conventional method.

Detailed Description
The membrane electrode assembly 11 and the polymer electrolyte fuel cell 12 will be described in more detail below.
The polymer electrolyte membrane 1 may be any membrane having proton conductivity, for example, a fluorine-based polymer electrolyte membrane or a hydrocarbon-based polymer electrolyte membrane. Examples of the fluorine-based polymer electrolyte membrane include Nafion (registered trademark) manufactured by DuPont, Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., Aciplex (registered trademark) manufactured by Asahi Kasei Corporation, and Gore Select (registered trademark) manufactured by W. L. Gore and Associates, Inc.

As the hydrocarbon-based polymer electrolyte membrane, for example, electrolyte membranes made of sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, sulfonated polyphenylene, etc. are usable. In particular, it is preferable to use a Nafion (registered trademark)-based material manufactured by DuPont as the polymer electrolyte membrane 1.
The electrode catalyst layers 2, 3 are formed using a catalyst ink on both sides of the polymer electrolyte membrane 1. The catalyst ink for the electrode catalyst layers 2, 3 contains catalyst-supported particles made of carbon particles supporting a catalyst, fibrous materials including a hydrophobic fibrous material and a hydrophilic fibrous material, a polymer electrolyte, and a solvent, and uses two types of compositions with different mass ratios of the hydrophobic fibrous material to the fibrous material.

The polymer electrolyte contained in the catalyst ink may be any material that has proton conductivity. The polymer electrolyte may be made of the same material as the polymer electrolyte membrane 1. The polymer electrolyte may be, for example, a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte. The fluorine-based polymer electrolyte may be, for example, a Nafion (registered trademark)-based material manufactured by DuPont. The hydrocarbon-based polymer electrolyte may be, for example, a sulfonated polyether ketone, a sulfonated polyether sulfone, a sulfonated polyether ether sulfone, a sulfonated polysulfide, or a sulfonated polyphenylene. In particular, it is preferable to use a Nafion (registered trademark)-based material manufactured by DuPont as the fluorine-based polymer electrolyte.

The catalyst used in this embodiment (hereinafter sometimes referred to as catalyst particles or catalyst) may be a platinum group element, a metal, an alloy, an oxide, or a double oxide of the metal. Examples of the platinum group element include platinum, palladium, ruthenium, iridium, rhodium, and osmium, and examples of the metal include iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. The double oxide referred to here means an oxide made of two types of metals.
When the catalyst particles are one or more metals selected from platinum, gold, palladium, rhodium, ruthenium, and iridium, the electrode reactivity is excellent and the electrode reaction can be efficiently and stably performed. When the catalyst particles are one or more metals selected from platinum, gold, palladium, rhodium, ruthenium, and iridium, the polymer electrolyte fuel cell 12 having the electrode catalyst layers 2 and 3 exhibits high power generation characteristics, which is preferable.

Carbon particles are generally used as the electron conductive powder that supports the above-mentioned catalyst, i.e., the carrier. The type of carbon particles is not limited as long as they are fine particles, conductive, and are not affected by the catalyst. Examples of carbon particles that can be used include carbon black, graphite, activated carbon, carbon fiber, carbon nanotubes, and fullerene.
The average particle diameter of the carbon particles is preferably within the range of 10 nm to 1000 nm, and more preferably within the range of 10 nm to 100 nm. Here, the average particle diameter is the average particle diameter obtained from a SEM image. When the average particle diameter of the carbon particles is within the range of 10 nm to 1000 nm, the activity and stability of the catalyst are improved, which is preferable. In addition, when the average particle diameter of the carbon particles is within the range of 10 nm to 1000 nm, an electron conduction path is easily formed, and the gas diffusion properties and catalyst utilization rate of the two electrode catalyst layers 2 and 3 are improved, which is preferable.

The above-mentioned catalyst-supporting particles may be provided with a hydrophobic coating. In other words, the particles supporting the catalyst may be covered with a hydrophobic coating. In this case, it is preferable that the hydrophobic coating has a thickness that allows the reaction gas to pass through sufficiently. Specifically, the thickness of the hydrophobic coating is preferably 40 nm or less. If the thickness is greater than 40 nm, the supply of the reaction gas to the active points may be hindered. On the other hand, if the hydrophobic coating is 40 nm or less, the reaction gas can pass through the hydrophobic coating sufficiently, and therefore the catalyst-supporting particles can be provided with hydrophobicity.
In addition, the thickness of the hydrophobic coating covering the catalyst-supporting particles is preferably a thickness that sufficiently repels the generated water. Specifically, the thickness of the hydrophobic coating is preferably 2 nm or more. If the hydrophobic coating is thinner than this, the generated water may accumulate, and the supply of the reaction gas to the active points may be hindered. That is, by having the hydrophobic coating have a thickness of 2 nm or more, the accumulation of the generated water is suppressed, and thus the supply of the reaction gas to the active points is prevented from being hindered.

The hydrophobic coating covering the catalyst-supported particles is formed, for example, from a fluorine-based compound having at least one polar group. Examples of polar groups include hydroxyl groups, alkoxy groups, carboxyl groups, ester groups, ether groups, carbonate groups, and amide groups. The presence of the polar group allows the fluorine-based compound to be fixed to the outermost surface of the electrode catalyst layer. The portion of the fluorine-based compound other than the polar group is preferably a structure consisting of fluorine and carbon because of its high hydrophobicity and chemical stability. However, the hydrophobic coating is not limited to such a structure as long as it has sufficient hydrophobicity and chemical stability.

The hydrophobic fibrous material is not particularly limited as long as it has hydrophobicity, and conductive fibers can be used. Examples of conductive fibers include carbon nanofibers, carbon nanotubes, and vapor-grown carbon fibers. Examples of vapor-grown carbon fibers include VGCF (registered trademark) manufactured by Showa Denko K.K. These hydrophobic fibrous materials may be used alone or in combination of two or more.
The hydrophilic fibrous material is not particularly limited as long as it has hydrophilicity, and a conductive fiber made to have hydrophilicity may be used, or a conductive fiber that does not have hydrophilicity may be imparted with hydrophilicity. Examples of a method for imparting hydrophilicity include ozone or oxygen plasma treatment, electrolytic oxidation, and mixed acid treatment. These hydrophilic fibrous materials may be used alone or in combination of two or more kinds.

The solvent used as the dispersion medium of the catalyst ink is not particularly limited as long as it does not corrode the catalyst-supported particles made of carbon particles carrying a catalyst, the fibrous material made of hydrophobic fibrous material and hydrophilic fibrous material, and the polymer electrolyte, and can dissolve the polymer electrolyte in a highly fluid state or disperse it as a fine gel. However, it is preferable that the solvent contains at least a volatile organic solvent. The solvent used as the dispersion medium of the catalyst ink may be alcohols, ketone-based solvents, ether-based solvents, polar solvents, etc. Alcohols may be, for example, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, pentanol, etc. Ketone-based solvents may be, for example, acetone, methyl ethyl ketone, pentanone, methyl isobutyl ketone, heptanone, cyclohexanone, methyl cyclohexanone, acetonyl acetone, diisobutyl ketone, etc. The ether solvent may be, for example, tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene, dibutyl ether, etc. The polar solvent may be, for example, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, diacetone alcohol, 1-methoxy-2-propanol, etc. The solvent may also be a mixed solvent in which two or more of the above-mentioned materials are mixed.

In addition, since a dispersion medium using a lower alcohol has a high risk of ignition, it is preferable to use a mixed solvent of a lower alcohol and water when using a lower alcohol as the dispersion medium. Furthermore, the dispersion medium may contain water that is compatible with the polymer electrolyte, i.e., water that has a high affinity for the polymer electrolyte. The amount of water added to the dispersion medium is not particularly limited as long as the polymer electrolyte does not separate and become cloudy or gel.
In order to disperse the catalyst-supported carbon particles in the catalyst ink, the catalyst ink may contain a dispersant, such as an anionic surfactant, a cationic surfactant, an amphoteric surfactant, or a nonionic surfactant.

Examples of anionic surfactants include alkyl ether carboxylates, ether carboxylates, alkanoyl sarcosines, alkanoyl glutamates, acyl glutamates, oleic acid/N-methyl taurine, potassium oleate/diethanolamine salt, alkyl ether sulfate/triethanolamine salt, polyoxyethylene alkyl ether sulfate/triethanolamine salt, amine salts of special modified polyether ester acids, amine salts of higher fatty acid derivatives, amine salts of special modified polyester acids, amine salts of high molecular weight polyether ester acids, amine salts of special modified phosphate esters, amide amine salts of high molecular weight polyester acids, amide amine salts of special fatty acid derivatives, etc. salts, alkylamine salts of higher fatty acids, amidoamine salts of high molecular weight polycarboxylic acids, carboxylic acid surfactants such as sodium laurate, sodium stearate, and sodium oleate, dialkyl sulfosuccinates, dialkyl sulfosuccinates, 1,2-bis(alkoxycarbonyl)-1-ethanesulfonates, alkyl sulfonates, alkyl sulfonates, paraffin sulfonates, α-olefin sulfonates, linear alkylbenzene sulfonates, alkylbenzene sulfonates, polynaphthylmethanesulfonates, polynaphthylmethanesulfonates, naphthalenesulfonate-formalin condensates, alkylnaphthalenesulfonates, alkanoyl Sulfonic acid surfactants such as methyl tauride, sodium lauryl sulfate, sodium cetyl sulfate, sodium stearyl sulfate, sodium oleyl sulfate, lauryl ether sulfate, sodium alkylbenzene sulfonate, oil-soluble alkylbenzene sulfonate, and α-olefin sulfonate; sulfate ester surfactants such as alkyl sulfate, alkyl sulfate, alkyl ether sulfate, polyoxyethylene alkyl ether sulfate, alkyl polyethoxy sulfate, polyglycol ether sulfate, alkyl polyoxyethylene sulfate, sulfated oil, and highly sulfated oil. , (mono- or di-)alkyl phosphate salts, (mono- or di-)alkyl phosphate salts, (mono- or di-)alkyl phosphate ester salts, alkyl polyoxyethylene phosphate salts, alkyl ether phosphates, alkyl polyethoxy phosphate salts, polyoxyethylene alkyl ethers, alkyl phenyl polyoxyethylene phosphate salts, alkyl phenyl ether phosphates, alkyl phenyl polyethoxy phosphate salts, polyoxyethylene alkyl phenyl ether phosphates, higher alcohol phosphate monoester disodium salts, higher alcohol phosphate diester disodium salts, and zinc dialkyl dithiophosphates.

Examples of cationic surfactants include benzyldimethyl{2-[2-(P-1,1,3,3-tetramethylbutylphenoxy)ethoxy]ethyl}ammonium chloride, octadecylamine acetate, tetradecylamine acetate, octadecyltrimethylammonium chloride, beef tallow trimethylammonium chloride, dodecyltrimethylammonium chloride, coconut trimethylammonium chloride, hexadecyltrimethylammonium chloride, behenyltrimethylammonium chloride, coconut dimethylbenzyl ammonium chloride, tetradecyldimethylbenzyl Examples include ammonium chloride, octadecyldimethylbenzylammonium chloride, dioleyldimethylammonium chloride, 1-hydroxyethyl-2-beef tallow imidazoline quaternary salt, 2-heptadecenyl-hydroxyethyl imidazoline, stearamidoethyl diethylamine acetate, stearamidoethyl diethylamine hydrochloride, triethanolamine monostearate formate, alkylpyridinium salt, higher alkylamine ethylene oxide adduct, polyacrylamide amine salt, modified polyacrylamide amine salt, perfluoroalkyl quaternary ammonium iodide, etc.

Examples of amphoteric surfactants include dimethyl coconut betaine, dimethyl lauryl betaine, sodium lauryl aminoethyl glycine, sodium lauryl aminopropionate, stearyl dimethyl betaine, lauryl dihydroxyethyl betaine, amido betaine, imidazolinium betaine, lecithin, sodium 3-[ω-fluoroalkanoyl-N-ethylamino]-1-propanesulfonate, N-[3-(perfluorooctanesulfonamido)propyl]-N,N-dimethyl-N-carboxymethylene ammonium betaine, etc.

Examples of nonionic surfactants include coconut fatty acid diethanolamide (1:2 type), coconut fatty acid diethanolamide (1:1 type), cow fatty acid diethanolamide (1:2 type), cow 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 tallow amine, polyethylene glycol tallow propylene diamine, polyethylene glycol dioleylamine, dimethyl laurylamine oxide, dimethyl stearylamine oxide, dihydroxyethyl laurylamine oxide, perfluoroalkylamine oxide, polyvinylpyrrolidone, higher alcohol ethylene oxide adducts, alkylphenol ethylene oxide adducts, fatty acid ethylene oxide adducts, polypropylene glycol ethylene oxide adducts, fatty acid esters of glycerin, fatty acid esters of pentaerythritol, fatty acid esters of sorbitol, fatty acid esters of sorbitan, fatty acid esters of sugar, etc.

Among the surfactants mentioned above, sulfonic acid type surfactants such as alkylbenzene sulfonic acid, oil-soluble alkylbenzene sulfonic acid, α-olefin sulfonic acid, sodium alkylbenzene sulfonate, oil-soluble alkylbenzene sulfonate, and α-olefin sulfonate are suitable as dispersants from the viewpoints of the carbon dispersion effect and the change in catalyst performance due to residual dispersant.

The catalyst ink may be subjected to a dispersion process as necessary. The viscosity of the catalyst ink and the size of the particles contained in the catalyst ink can be controlled by the conditions of the dispersion process of the catalyst ink. The dispersion process can be performed using various devices. In particular, the method of the dispersion process is not limited. For example, the dispersion process may be performed using a ball mill or a roll mill, a shear mill, a wet mill, or an ultrasonic dispersion process. A homogenizer that stirs by centrifugal force may also be used for the dispersion process. As the dispersion time for which the catalyst ink is subjected to the dispersion process increases, the aggregates of the catalyst-supported particles are destroyed, and the pore volume becomes smaller in the electrode catalyst layer formed using the catalyst ink.

If the solid content in the catalyst ink is too high, the viscosity of the catalyst ink increases, and cracks are likely to occur on the surfaces of the electrode catalyst layers 2 and 3. On the other hand, if the solid content in the catalyst ink is too low, the film formation rate is very slow, and productivity decreases. Therefore, the solid content in the catalyst ink is preferably 1% by mass (wt%) or more and 50% by mass or less. That is, by having the solid content in the catalyst ink be 1% by mass or more, it is possible to prevent the film formation rate from becoming excessively slow, and thereby to prevent a decrease in productivity. By having the solid content in the catalyst ink be 50% by mass or less, the viscosity of the catalyst ink is prevented from becoming excessively high, and thus the occurrence of cracks on the surfaces of the electrode catalyst layers 2 and 3 is prevented.
The method for applying the catalyst ink onto the substrate may be a doctor blade method, a dipping method, a screen printing method, a roll coating method, or the like.
As the substrate used in producing the electrode catalyst layers 2 and 3, a transfer sheet can be used.

The transfer sheet used as the substrate may be made of any material having good transferability, such as fluororesin. Examples of fluororesin include ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkylvinylether copolymer (PFA), polytetrafluoroethylene (PTFE), and the like. Polymer sheets and polymer films may also be used as the transfer sheet. Materials for the polymer sheets and polymer films include polyimide, polyethylene terephthalate, polyamide (nylon (registered trademark)), polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide, polyarylate, and polyethylene naphthalate. When a transfer sheet is used as the substrate, the electrode membrane, which is a coating film after removing the solvent, is bonded to the polymer electrolyte membrane 1, and then the transfer sheet is peeled off to form a membrane electrode assembly 11 having electrode catalyst layers 2 and 3 on both sides of the polymer electrolyte membrane 1.

A material having gas diffusibility and electrical conductivity can be used for the gas diffusion layers 4 and 5. For example, the gas diffusion layers 4 and 5 can be made of a porous carbon material such as carbon cloth, carbon paper, or nonwoven fabric.
The separator 10 (10a, 10b) may be of a carbon type or a metal type. The gas diffusion layers 4, 5 and the separator 10 (10a, 10b) may each be integral with each other. In addition, when the separator 10 (10a, 10b) or the electrode catalyst layers 2, 3 function as the gas diffusion layers 4, 5, the gas diffusion layers 4, 5 may be omitted.
The polymer electrolyte fuel cell 12 can be manufactured by assembling a gas supply device, a cooling device, and other associated devices.

<Other Effects>
In the electrode catalyst layers 2 and 3 of the membrane electrode assembly 11 according to this embodiment, the mass ratio of the hydrophobic fibrous material to the fibrous material in the first electrode catalyst portion 2a (or 3a) provided on the gas inlet side is made smaller than the mass ratio in the second electrode catalyst portion 2b (or 3b) provided on the gas outlet side.
According to this configuration, the first electrode catalyst part 2a (or 3a) provided on the gas inlet side can increase water retention, and the second electrode catalyst part 2b (or 3b) provided on the gas outlet side can promote water removal, making it possible to obtain high power generation characteristics even under low humidification conditions.

Therefore, high power generation characteristics can be obtained without any significant changes to the manufacturing process or a significant increase in costs.
In the above embodiment, a case has been described in which a first electrode catalyst portion and a second electrode catalyst portion are provided in each of the electrode catalyst layers 2 and 3, but the present invention is not limited thereto, and three or more electrode catalyst portions may be provided in each of the electrode catalyst layers 2 and 3. When three or more electrode catalyst portions are provided in each of the electrode catalyst layers 2 and 3, it is preferable that the mass ratio of the hydrophobic fibrous material to the fibrous material is smaller closer to the upstream side of the gas than that of the electrode catalyst portion on the downstream side of the gas.

For example, the third electrode catalyst portion is formed as a mixture of the catalyst ink for the first electrode catalyst portion 2a, 3a and the catalyst ink for the second electrode catalyst portion 2b, 3b. However, the third electrode catalyst portion may be composed of a composition different from the above-mentioned configurations (a) and (b). However, when composed of a composition different from the above-mentioned configurations (a) and (b), the third electrode catalyst portion is preferably 20% or less of the area of the entire electrode catalyst layer. In addition, the boundary between each electrode catalyst portion does not have to be linear in plan view. The boundary may be a meandering shape or the like.
In addition, in the membrane electrode assembly 11, of the electrode catalyst layers 2 and 3 formed on both sides of the polymer electrolyte membrane 1, only one of the electrode catalyst layers 2 or 3 may be provided with a first electrode catalyst portion and a second electrode catalyst portion.

When the first electrode catalyst portion and the second electrode catalyst portion are provided only on one of the electrode catalyst layers 2 or 3, the electrode catalyst layer having the two electrode catalyst portions is preferably disposed on the air electrode (cathode) side where water is generated by the electrode reaction. However, from the viewpoint of water retention in the polymer electrolyte under low humidification conditions, it is more preferable that the electrode catalyst layer having the two electrode catalyst portions is formed on both sides of the polymer electrolyte membrane 1.
In addition, FIG. 1 shows an example in which the first electrode catalyst portion and the second electrode catalyst portion of the electrode catalyst layer 2 or 3 are divided into two portions with equal areas (the area ratio of the first electrode catalyst portion to the electrode catalyst layer 2 is 50%), but is not limited to this.

From the viewpoint of gas reactivity, it is preferable that the area ratio of the first electrode catalyst part to the electrode catalyst layer 2 or 3 is 15% or more and 60% or less. If the area ratio of the first electrode catalyst part to the electrode catalyst layer 2 or 3 is less than 15%, the water retention effect under low humidification conditions is weak, and high power generation characteristics cannot be obtained. Furthermore, if the area ratio of the first electrode catalyst part to the electrode catalyst layer 2 or 3 exceeds 60%, a flooding phenomenon occurs in which the power generation reaction stops due to the impediment of material transport at the fuel electrode and air electrode, and high power generation characteristics cannot be obtained.

Next, examples of the present invention related to this embodiment will be described.
Hereinafter, the method for producing a membrane electrode assembly for a polymer electrolyte fuel cell according to the present embodiment will be described with reference to specific examples and comparative examples. However, the present embodiment is not limited to the following examples and comparative examples.

<Example>
[Preparation of catalyst ink]
A platinum-supported carbon catalyst with a support density of 30% by mass, a hydrophobic fibrous material (carbon fiber) and a hydrophilic fibrous material (oxidized carbon fiber) with an average fiber length of 1.5 μm, and a 20% by mass polymer electrolyte solution containing a polymer electrolyte with an ion exchange capacity of 1.4 meq/g were mixed in a solvent and dispersed for 30 minutes in a planetary ball mill to prepare a first catalyst ink. The first catalyst ink had a composition ratio of 0.3 by mass of the hydrophobic fibrous material to the fibrous material, a composition ratio of 0.7 by mass of the hydrophilic fibrous material to the fibrous material, and a compounding ratio of 1:0.3:0.8 by mass between the carbon particles, the fibrous material, and the polymer electrolyte.

Next, a platinum-supported carbon catalyst with a support density of 30% by mass, a hydrophobic fibrous material and a hydrophilic fibrous material with an average fiber length of 1.5 μm, and a 20% by mass polymer electrolyte solution containing a polymer electrolyte with an ion exchange capacity of 1.4 meq/g were mixed in a solvent, and a dispersion process was performed for 30 minutes using a planetary ball mill to prepare a second catalyst ink. The second catalyst ink had a composition ratio of 0.7 by mass of the hydrophobic fibrous material to the fibrous material, a composition ratio of 0.3 by mass of the hydrophilic fibrous material to the fibrous material, and a compounding ratio of 1:0.3:0.8 by mass between the carbon particles, the fibrous material, and the polymer electrolyte.
The solvent for each catalyst ink was ultrapure water and 1-propanol in a volume ratio of 1: 1. The solid content in each catalyst ink was adjusted to 8% by mass.

[Formation of Electrode Catalyst Layer]
The prepared catalyst ink was applied to a substrate of polytetrafluoroethylene (PTFE) sheet by the doctor blade method and dried at 80 ° C. in an air atmosphere. The amount of application of the first catalyst ink was adjusted so that the platinum loading amount was 0.1 mg / cm ² as the fuel electrode (anode) and the platinum loading amount was 0.3 mg / cm ² as the air electrode (cathode), forming an electrode catalyst layer (first electrode catalyst part). The amount of application of the second catalyst ink was adjusted so that the platinum loading amount was 0.1 mg / cm ² as the fuel electrode (anode) and the platinum loading amount was 0.3 mg / cm ² as the air electrode (cathode), forming an electrode catalyst layer (second electrode catalyst part).

[Preparation of Membrane Electrode Assembly]
The substrates on which the respective electrode catalyst layers were formed were punched out to 5 cm x 2.5 cm, and the first electrode catalyst part was positioned on the gas inlet side, and the second electrode catalyst part was positioned on the gas outlet side to obtain an electrode catalyst layer of 5 cm x 5 cm. These electrode catalyst layers were placed on both sides of the polymer electrolyte membrane 1, and hot pressed under conditions of a transfer temperature of 130°C and a transfer pressure of 5.0 x ¹⁰⁶ Pa to obtain a membrane electrode assembly 11.

Comparative Example
[Preparation of catalyst ink]
A platinum-supported carbon catalyst with a support density of 30% by mass, a hydrophobic fibrous material and a hydrophilic fibrous material with an average fiber length of 1.5 μm, and a 20% by mass polymer electrolyte solution containing a polymer electrolyte with an ion exchange capacity of 1.4 meq/g were mixed in a solvent, and a dispersion treatment was performed for 30 minutes using a planetary ball mill to prepare a catalyst ink. The catalyst ink had a composition ratio of 0.5 by mass of the hydrophobic fibrous material to the fibrous material, a composition ratio of 0.5 by mass of the hydrophilic fibrous material to the fibrous material, and a blending ratio of the carbon particles, the fibrous material, and the polymer electrolyte was 1:0.3:0.8 by mass. The solvent for the catalyst ink was ultrapure water and 1-propanol in a volume ratio of 1:1. The solid content in the catalyst ink was adjusted to 8% by mass for each.
This resulted in the production of a catalyst ink, which was obtained by mixing and dispersing all of the components of the first catalyst ink and the second catalyst ink in the examples at once.

[Formation of Electrode Catalyst Layer]
The prepared catalyst ink was applied to a polytetrafluoroethylene (PTFE) sheet substrate by a doctor blade method and dried in an air atmosphere at 80° C. The amount of catalyst ink applied was adjusted so that the fuel electrode (anode) had a platinum loading of 0.1 mg/ ^cm2 and the air electrode (cathode) had a platinum loading of 0.3 mg/ ^cm2 , forming an electrode catalyst layer.
[Preparation of Membrane Electrode Assembly]
The substrates on which the respective electrode catalyst layers were formed were punched out to 5 cm x 5 cm, and the electrode catalyst layers were placed on both sides of a polymer electrolyte membrane. Hot pressing was performed under conditions of a transfer temperature of 130°C and a transfer pressure of 5.0 x ¹⁰⁶ Pa to obtain membrane electrode assemblies.

<Evaluation>
[Power generation characteristics]
Carbon paper was attached as a gas diffusion layer so as to sandwich each of the membrane electrode assemblies obtained in the examples and comparative examples, and the assembly was placed in a power generation evaluation cell, and current and voltage measurements were performed using a fuel cell measurement device. The cell temperature during the measurements was 80°C, and the operating conditions were full humidification and low humidification as shown below. Hydrogen was used as the fuel gas and air as the oxidant gas, and flow rate control was performed with a constant utilization rate. The back pressure was 50 kPa.
[Operating conditions]
Condition 1 (full humidification): Relative humidity anode 100% RH, cathode 100% RH
Condition 2 (low humidity): Relative humidity: anode 30% RH, cathode 30% RH

[Measurement results]
The membrane electrode assembly prepared in the examples showed better power generation performance under low humidification operating conditions than the membrane electrode assembly prepared in the comparative examples. Moreover, the membrane electrode assembly prepared in the examples showed the same level of power generation performance under low humidification operating conditions as under full humidification operating conditions. In particular, the power generation performance was improved at a current density of about 1.5 A/cm ^2. The cell voltage of the membrane electrode assembly prepared in the examples at a current density of 1.5 A/cm ² showed a power generation characteristic 0.21 V higher than the cell voltage of the membrane electrode assembly prepared in the comparative examples at a current density of 1.5 A/cm ² .

From the results of the power generation characteristics of the membrane electrode assemblies prepared in the Examples and the membrane electrode assemblies prepared in the Comparative Examples, it was confirmed that the membrane electrode assemblies of the Examples had improved water retention and exhibited power generation characteristics under low humidification operating conditions that were equivalent to those under full humidification operating conditions.
Furthermore, under the operating condition of full humidification, the cell voltage of the membrane electrode assembly prepared in the example at a current density of 1.5 A/ ^cm2 exhibited a power generation characteristic that was 0.13 V higher than the cell voltage of the membrane electrode assembly prepared in the comparative example at a current density of 1.5 A/ ^cm2 .
From the results of the power generation characteristics of the membrane electrode assemblies prepared in the Examples and the membrane electrode assemblies prepared in the Comparative Examples, it was confirmed that the membrane electrode assemblies prepared in the Examples had high diffusibility of the reactant gas and did not inhibit the removal of water generated in the electrode reaction.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and even if the modifications do not deviate from the gist of the present invention, they are included in the present invention.

REFERENCE SIGNS LIST 1...polymer electrolyte membrane 2...electrode catalyst layer 2a...first electrode catalyst portion 2b...second electrode catalyst portion 3...electrode catalyst layer 3a...first electrode catalyst portion 3b...second electrode catalyst portion 4...gas diffusion layer 5...gas diffusion layer 6...air electrode (cathode)
7...Fuel electrode (anode)
8, 8a, 8b... Gas channels 9, 9a, 9b... Cooling water channels 10, 10a, 10b... Separator 11... Membrane electrode assembly 12... Polymer electrolyte fuel cell

Claims (6)

A membrane electrode assembly for a fuel cell, comprising: a polymer electrolyte membrane sandwiched between a pair of electrode catalyst layers; and the pair of electrode catalyst layers are sandwiched from outside by a pair of separators that form a gas flow path between the electrode catalyst layers,
at least one of the pair of electrode catalyst layers has a first electrode catalyst portion and a second electrode catalyst portion facing the polymer electrolyte membrane,
the first electrode catalyst portion is an electrode catalyst portion for an inlet side of the gas flow passage, and the second electrode catalyst portion is an electrode catalyst portion for an outlet side of the gas flow passage,
each of the first electrode catalyst portion and the second electrode catalyst portion includes a catalyst-supporting particle formed of a carbon particle on which a catalyst is supported, a fibrous material, and a polymer electrolyte;
The fibrous material is composed of a hydrophobic fibrous material and a hydrophilic fibrous material,
A membrane electrode assembly for a fuel cell, characterized in that the mass ratio of the hydrophobic fibrous material to the fibrous material in the second electrode catalyst portion is greater than the mass ratio of the first electrode catalyst portion. the mass ratio in the first electrode catalyst portion is within a range of 0.1 or more and 0.45 or less,
2. The membrane electrode assembly for a fuel cell according to claim 1, wherein the mass ratio in the second electrode catalyst portion is within a range of 0.55 to 0.9. The fuel cell membrane electrode assembly according to claim 1 or 2, characterized in that the average fiber length of the fibrous material including the hydrophobic fibrous material and the hydrophilic fibrous material is in the range of 0.7 μm to 30 μm. The fuel cell membrane electrode assembly according to any one of claims 1 to 3, characterized in that the fiber mass, which is the sum of the mass of the hydrophobic fibrous material and the mass of the hydrophilic fibrous material, is in the range of 0.05 to 0.4 times the mass of the carrier in the catalyst-supported particle. The fuel cell membrane electrode assembly according to any one of claims 1 to 4, characterized in that the mass of the polymer electrolyte is in the range of 0.3 to 1.0 times the mass of the carrier in the catalyst-supported particle. The fuel cell membrane electrode assembly according to any one of claims 1 to 5,
a pair of gas diffusion layers sandwiching the fuel cell membrane electrode assembly;
a pair of separators disposed opposite to each other and sandwiching the fuel cell membrane electrode assembly and the pair of gas diffusion layers;
A polymer electrolyte fuel cell comprising:

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