Solid polymer fuel cells

Abstract

To provide a membrane-electrode assembly and a solid polymer fuel cell which allow a satisfactory power generating performance to be gained in a plurality of environments different in humidification condition.SOLUTION: A membrane-electrode assembly 10 comprises: a polyelectrolyte membrane 11; a pair of electrode catalyst layers 12A, 12C in contact with faces of the polyelectrolyte membrane 11, between which the polyelectrolyte membrane 11 is located; a fuel electrode diffusion layer 13A which is a gas diffusion layer laminated on one of the pair of electrode catalyst layers 12A, 12C and forming a fuel electrode; and an air electrode diffusion layer 13C which is a gas diffusion layer laminated the other of the pair of electrode catalyst layers 12A, 12C and forming an air electrode. Gurley value indicative of an air impermeability of a thickness direction in the air electrode diffusion layer 13C is equal to or smaller than 80 sec. and smaller than Gurley value indicative of an air impermeability of a thickness direction in the fuel electrode diffusion layer 13A.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention , solid This invention relates to polymer electrolyte fuel cells. [Background technology]

[0002] Fuel cells are attracting attention as a type of battery that can contribute to solving environmental and energy problems. Fuel cells generate electricity by utilizing a chemical reaction between a fuel such as hydrogen and an oxidant such as oxygen. Among fuel cells, polymer electrolyte fuel cells can be operated at low temperatures and can be made compact, so they are expected to be used as portable power sources, household power sources, and vehicle power sources.

[0003] A polymer electrolyte fuel cell includes a membrane electrode assembly having a fuel electrode (anode), an air electrode (cathode), and a polymer electrolyte membrane sandwiched between the fuel electrode and the air electrode. Each of the fuel electrode and the air electrode includes a laminate of an electrode catalyst layer and a gas diffusion layer. A fuel gas containing hydrogen is supplied to the fuel electrode, and an oxidant gas containing oxygen is supplied to the air electrode. As a result, electrode reactions occur at the fuel electrode and the air electrode, as shown in the following (Equation 1) and (Equation 2), generating electricity. Fuel electrode: H2→ 2H + + 2e - ...(Formula 1) Air electrode: 1 / 2O2+ 2H + + 2e - → H2O (Eq. 2)

[0004] That is, as shown in Equation 1, protons and electrons are generated from the fuel gas supplied to the anode due to the action of the catalyst contained in the electrode catalyst layer. The protons are conducted by the polymer electrolyte contained in the electrode catalyst layer and polymer electrolyte membrane, and move through the polymer electrolyte membrane to the air cathode. The electrons are extracted from the anode to an external circuit, and move through the external circuit to the air cathode. At the air cathode, as shown in Equation 2, the oxidant gas reacts with the protons and electrons that have moved from the anode to produce water. In this way, current is generated as the electrons pass through the external circuit.

[0005] To improve the output of a polymer electrolyte fuel cell, it is important to improve the gas diffusion in the membrane electrode assembly and the drainage of water produced during power generation. For example, in Patent Document 1, the gas diffusion of the electrode catalyst layer is improved by incorporating carbon particles of different particle sizes into the electrode catalyst layer. In Patent Document 2, the gas diffusion and drainage of the electrode catalyst layer are improved by controlling the proportion and fiber length of the carbon fibers incorporated into the electrode catalyst layer. In Patent Document 3, the drainage of the gas diffusion layer is improved by controlling the size of the carbon powder incorporated into the gas diffusion layer. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-241703 [Patent Document 2] Patent No. 5537178 [Patent Document 3] International Publication No. 2017 / 170355 Summary of the Invention [Problem to be solved by the invention]

[0007] In addition to improving output, polymer electrolyte fuel cells are expected to be able to operate in a variety of environments, including low- and high-humidity environments. To achieve this, it is important to maintain an appropriate amount of moisture in the membrane electrode assembly so that it does not become too dry, while improving the drainage properties of the membrane electrode assembly. In particular, because the conditions regarding moisture, such as whether or not water is generated during power generation, differ between the anode and cathode, there is a need for improvements in membrane electrode assemblies that take into account the differences between the anode and cathode. [Means for solving the problem]

[0008] A membrane electrode assembly for solving the above problems includes a polymer electrolyte membrane, a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane and in contact with a surface of the polymer electrolyte membrane, an anode diffusion layer which is a gas diffusion layer laminated on one of the pair of electrode catalyst layers to form an anode, and an cathode diffusion layer which is a gas diffusion layer laminated on the other of the pair of electrode catalyst layers to form an anode, wherein the cathode diffusion layer has a Gurley value which indicates the air permeation resistance in the thickness direction and is 80 seconds or less and is smaller than the Gurley value which indicates the air permeation resistance in the thickness direction of the anode diffusion layer.

[0009] This configuration promotes the drainage of generated water at the air electrode, thereby suppressing flooding, while at the fuel electrode, moisture escapes more slowly than at the air electrode, preventing drying. As a result, the moisture content of the membrane electrode assembly is properly balanced, enabling good power generation performance in both low-humidity and high-humidity environments.

[0010] In the above configuration, the electrode catalyst layer may include a catalyst material, carbon particles, aggregates of a polymer electrolyte, and a fibrous material. According to the above-mentioned configuration, since the electrode catalyst layer contains a fibrous material, the strength of the electrode catalyst layer is increased, making it less susceptible to cracking, and further improving the durability of the membrane electrode assembly and the power generation performance of the fuel cell.

[0011] In the above configuration, the fibrous material contained in the electrode catalyst layer may be at least one of an electron conductive fiber and a proton conductive fiber. According to the above configuration, the electrode catalyst layer contains polymer electrolyte fibers, thereby improving the proton conductivity in the electrode catalyst layer, and the electrode catalyst layer contains electron-conductive fibers, thereby improving the electron conductivity in the electrode catalyst layer.

[0012] In the above configuration, the electrode catalyst layer may contain carbon fibers as the fibrous material, and the carbon fibers contained in the electrode catalyst layer may be at least one of carbon nanotubes and carbon nanofibers. According to the above configuration, the electronic conductivity of the electrode catalyst layer is suitably increased.

[0013] A polymer electrolyte fuel cell that solves the above problem includes the above membrane electrode assembly and a pair of separators that sandwich the membrane electrode assembly.

[0014] According to the above configuration, good power generation performance can be obtained in a plurality of environments with different humidification conditions. [Effects of the Invention]

[0015] According to the present invention, good power generation performance can be obtained in a plurality of environments with different humidification conditions. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is a diagram showing a cross-sectional structure of a membrane electrode assembly according to one embodiment of the membrane electrode assembly. [Figure 2] FIG. 2 is a diagram schematically illustrating an electrode catalyst layer according to an embodiment. [Figure 3] FIG. 1 is an exploded perspective view showing a polymer electrolyte fuel cell according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of a membrane electrode assembly and a polymer electrolyte fuel cell will be described with reference to FIGS. [Membrane electrode assembly] The structure of the membrane electrode assembly will be described with reference to FIGS.

[0018] 1, the membrane electrode assembly 10 includes a polymer electrolyte membrane 11, a pair of electrode catalyst layers, and a pair of gas diffusion layers. The pair of electrode catalyst layers is an anode catalyst layer 12A and an air cathode catalyst layer 12C. The pair of gas diffusion layers is an anode diffusion layer 13A and an air cathode diffusion layer 13C.

[0019] Polymer electrolyte membrane 11 is sandwiched between anode catalyst layer 12A and cathode catalyst layer 12C. Anode catalyst layer 12A is in contact with one of the two surfaces of polymer electrolyte membrane 11, and cathode catalyst layer 12C is in contact with the other of the two surfaces of polymer electrolyte membrane 11.

[0020] Anode diffusion layer 13A is laminated on anode catalyst layer 12A, and cathode diffusion layer 13C is laminated on cathode catalyst layer 12C. In other words, the laminate of polymer electrolyte membrane 11, anode catalyst layer 12A, and cathode catalyst layer 12C is sandwiched between anode diffusion layer 13A and cathode diffusion layer 13C.

[0021] Anode catalyst layer 12A and anode diffusion layer 13A constitute the anode of the polymer electrolyte fuel cell, while cathode catalyst layer 12C and anode diffusion layer 13C constitute the cathode of the polymer electrolyte fuel cell.

[0022] When viewed from a position facing one surface of polymer electrolyte membrane 11, anode catalyst layer 12A, cathode catalyst layer 12C, anode diffusion layer 13A, and cathode diffusion layer 13C have substantially the same external shape. Polymer electrolyte membrane 11 is larger than catalyst layers 12A and 12C and diffusion layers 13A and 13C. There are no particular limitations on the external shape of polymer electrolyte membrane 11, catalyst layers 12A and 12C, and diffusion layers 13A and 13C, and each may have, for example, a rectangular shape.

[0023] The polymer electrolyte membrane 11 includes a polymer electrolyte. The polymer electrolyte used in the polymer electrolyte membrane 11 may be any polymer electrolyte having proton conductivity, such as a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte. Examples of fluorine-based polymer electrolytes 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 Aquivion (registered trademark: manufactured by Solvay). Examples of hydrocarbon-based polymer electrolytes include sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, sulfonated polyphenylene, sulfonated polyimide, and acid-doped polybenzazoles.

[0024] Fig. 2 shows a schematic diagram of the electrode catalyst layer of this embodiment. As shown in Fig. 2, anode catalyst layer 12A and cathode catalyst layer 12C each contain a catalyst material 21, carbon particles 22, and polymer electrolyte aggregates 23. Furthermore, anode catalyst layer 12A and cathode catalyst layer 12C each may contain a fibrous material 24. In catalyst layers 12A and 12C, aggregates 23 and fibrous material 24 are positioned around dispersed carbon particles 22, and voids H1 are formed between these components.

[0025] Examples of catalyst material 21 include platinum group elements such as platinum, palladium, ruthenium, iridium, rhodium, and osmium, metals such as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum, and alloys, oxides, and composite oxides thereof. Platinum or a platinum alloy is particularly preferred for catalyst material 21. The average particle size of catalyst material 21 is preferably 0.5 nm or more and 20 nm or less, and more preferably 1 nm or more and 5 nm or less. If the average particle size of catalyst material 21 is equal to or greater than the lower limit, the catalyst's stability is enhanced. If the average particle size of catalyst material 21 is equal to or less than the upper limit, the catalyst's activity is enhanced.

[0026] The carbon particles 22 may be any carrier that is particulate, electrically conductive, and resistant to the catalyst. Examples of carbon materials used for the carbon particles 22 include powdered carbon materials such as carbon black, graphite, activated carbon, carbon nanotubes, and fullerenes. The average particle size of the carbon particles 22 is preferably 10 nm to 1000 nm, and more preferably 10 nm to 100 nm. When the average particle size of the carbon particles 22 is equal to or greater than the lower limit, an electron conduction path is easily formed in the catalyst layers 12A and 12C. When the average particle size of the carbon particles 22 is equal to or less than the upper limit, the catalyst layers 12A and 12C can be formed thin enough to prevent excessive resistance, thereby preventing a decrease in the output of the fuel cell.

[0027] The catalyst substance 21 is preferably supported on carbon particles 22. When the carbon material supporting the catalyst substance 21 is in particulate form, the area of ​​the carbon material that can support the catalyst substance 21 can be increased, and the catalyst substance 21 can be supported on the carbon material at a high density. This makes it possible to improve catalytic activity.

[0028] The polymer electrolyte aggregates 23 are lumps formed by the aggregation of ionomer polymer electrolytes due to cohesive forces, including Coulomb forces and van der Waals forces acting between ionomers.

[0029] The polymer electrolyte constituting the aggregates 23 may be any polymer electrolyte having proton conductivity, such as a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte. Examples of fluorine-based polymer electrolytes 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 Aquivion (registered trademark: manufactured by Solvay). Examples of hydrocarbon-based polymer electrolytes include sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, sulfonated polyphenylene, sulfonated polyimide, and acid-doped polybenzazoles.

[0030] When the polymer electrolyte constituting the aggregates 23 and the polymer electrolyte constituting the polymer electrolyte membrane 11 are the same type of electrolyte, the adhesion of the catalyst layers 12A, 12C to the polymer electrolyte membrane 11 is improved.

[0031] The fibrous material 24 is an electron-conductive fiber or a proton-conductive fiber. The catalyst layers 12A, 12C contain the fibrous material 24, which increases the strength of the catalyst layers 12A, 12C, making it easier to form the catalyst layers 12A, 12C and reducing the likelihood of cracks occurring in the catalyst layers 12A, 12C. Furthermore, the durability of the membrane electrode assembly 10 and the power generation performance of the fuel cell can be improved.

[0032] The electron conductive fiber is, for example, a carbon fiber. The carbon fiber is a fibrous structure containing carbon as a constituent element. The carbon material used as the carbon fiber is, for example, a fibrous carbon material made of carbon fiber, carbon nanofiber, carbon nanotube, or the like. In particular, it is preferable to use a carbon nanofiber or a carbon nanotube.

[0033] Proton-conductive fibers are fibers made by processing a polymer electrolyte having proton conductivity into a fibrous form. The polymer electrolyte constituting the proton-conductive fibers may be, for example, a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte. Examples of fluorine-based polymer electrolytes 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 Aquivion (registered trademark: manufactured by Solvay). Examples of hydrocarbon-based polymer electrolytes include sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, sulfonated polyphenylene, sulfonated polyimide, and acid-doped polybenzazoles.

[0034] If the polymer electrolytes constituting the polymer electrolyte membrane 11, the aggregates 23, and the proton-conductive fibers are the same type of electrolyte, the adhesion of the catalyst layers 12A and 12C to the polymer electrolyte membrane 11 is improved.

[0035] The fibrous material 24 contained in the catalyst layers 12A, 12C may be composed of only electron conductive fibers or only proton conductive fibers. Alternatively, the fibrous material 24 contained in the catalyst layers 12A, 12C may include both electron conductive fibers and proton conductive fibers. Furthermore, the catalyst layers 12A, 12C may not include the fibrous material 24.

[0036] The average fiber diameter of the fibrous material 24 is preferably 0.5 nm or more and 500 nm or less, and more preferably 10 nm or more and 300 nm or less. If the average fiber diameter is within the above range, pores Hl are appropriately formed in the catalyst layers 12A and 12C, thereby improving the output of the fuel cell.

[0037] The average fiber length of the fibrous material 24 is preferably 1 μm or more and 200 μm or less, and more preferably 1 μm or more and 50 μm or less. If the average fiber length is within the above range, the strength of the catalyst layers 12A, 12C is appropriately increased, thereby preventing cracks from occurring during the formation of the catalyst layers 12A, 12C. Furthermore, pores H1 are appropriately formed in the catalyst layers 12A, 12C, thereby improving the output of the fuel cell.

[0038] When catalyst layers 12A, 12C contain carbon fibers, catalyst material 21 may be supported by the carbon fibers. Alternatively, catalyst material 21 may be supported by both carbon fibers and carbon particles 22. However, it is preferable that carbon particles 22 support catalyst material 21, because gaps formed by the carbon fibers serve as drainage paths for water produced by power generation, improving the drainage properties of catalyst layers 12A, 12C.

[0039] The thickness of the catalyst layers 12A, 12C is preferably 30 μm or less, and more preferably 10 μm or less. If the thickness of the catalyst layers 12A, 12C is within the above range, an increase in the resistance of the catalyst layers 12A, 12C is suppressed, thereby suppressing a decrease in the power generation performance of the fuel cell. Furthermore, because the catalyst layers 12A, 12C are not too thick, cracks are less likely to occur.

[0040] The thickness of catalyst layers 12A, 12C is preferably 5 μm or more. If the thickness of catalyst layers 12A, 12C is 5 μm or more, thickness variations within catalyst layers 12A, 12C are unlikely to occur, thereby suppressing uneven distribution of catalyst material 21 and polymer electrolyte within catalyst layers 12A, 12C. Furthermore, an increase in the proportion of water produced by power generation within catalyst layers 12A, 12C is suppressed, thereby suppressing a decrease in the power generation performance of the fuel cell. By suppressing cracks on the surfaces of the catalyst layers 12A, 12C and unevenness in thickness, the durability of the membrane electrode assembly 10 during long-term use of the fuel cell is improved.

[0041] The diffusion layers 13A and 13C are layered bodies that allow gas to pass through. The diffusion layers 13A and 13C preferably include a carbon substrate. The carbon substrate may be, for example, carbon paper, carbon cloth, or carbon felt. The carbon substrate is preferably treated to be water-repellent to improve drainage.

[0042] Furthermore, the diffusion layers 13A and 13C preferably include a microporous layer, which is a layer made of a porous material, in addition to the carbon substrate. The material of the microporous layer is, for example, a mixture of a fluororesin such as polytetrafluoroethylene (PTFE), perfluoroethylene-propene copolymer (FEP), or tetrafluoroethylene-ethylene copolymer (ETFE) with a carbon material such as carbon black particles, carbon fiber, or graphite.

[0043] The thickness of the diffusion layers 13A, 13C is preferably 5 μm or more and 500 μm or less. If the thickness of the diffusion layers 13A, 13C is 5 μm or more, the gas diffusion and drainage properties of the diffusion layers 13A, 13C are improved. Furthermore, if the thickness of the diffusion layers 13A, 13C is 500 μm or less, an increase in the electrical resistance of the diffusion layers 13A, 13C is suppressed.

[0044] The Gurley value, which indicates the air permeation resistance in the thickness direction of the cathode diffusion layer 13C, is 80 seconds or less and is smaller than the Gurley value of the anode diffusion layer 13A. The Gurley value is the time required for a specified volume of air to permeate per unit area and unit pressure difference, and is a parameter expressed in hours per 100 mL, and is measured according to the measurement method specified in JIS P8117:2009.

[0045] The air electrode generates water during power generation, which tends to result in excess moisture, while the fuel electrode tends to dry out more easily than the air electrode. The greater air permeability of the air electrode diffusion layer 13C than the fuel electrode diffusion layer 13A promotes drainage of generated water at the air electrode, preventing flooding. The fuel electrode, however, is less susceptible to moisture escape than the air electrode, preventing excessive dryness. As a result, the moisture content of the membrane electrode assembly 10 is properly balanced, enabling sufficient fuel cell output in both low-humidity and high-humidity environments.

[0046] To enhance this effect, the difference in Gurley value between air electrode diffusion layer 13C and anode diffusion layer 13A is preferably 10 seconds or more. Furthermore, if the difference in Gurley value between air electrode diffusion layer 13C and anode diffusion layer 13A is 40 seconds or less, the difference in gas diffusivity between air electrode diffusion layer 13C and anode diffusion layer 13A is kept to a level that does not affect the progress of the electrode reaction.

[0047] If the Gurley value of the air electrode diffusion layer 13C is 80 seconds or less, the gas diffusibility and drainage properties of the air electrode diffusion layer 13C are sufficient. The Gurley value, which indicates the air permeability resistance in the thickness direction of the anode diffusion layer 13A, is not particularly limited, but is preferably 100 seconds or less. If the Gurley value of the anode diffusion layer 13A is 100 seconds or less, the anode is prevented from drying out as described above, while the gas diffusibility of the anode diffusion layer 13A is favorably obtained. The Gurley values ​​of the diffusion layers 13A and 13C can be adjusted by the material and thickness of the diffusion layers 13A and 13C, the proportion of voids contained in the diffusion layers 13A and 13C, and the like.

[0048] [Polymer electrolyte fuel cell] The configuration of a polymer electrolyte fuel cell including the above-described membrane electrode assembly 10 will be described with reference to FIG.

[0049] 3, the polymer electrolyte fuel cell 30 includes a membrane electrode assembly 10 and a pair of separators 31A and 31C. The polymer electrolyte fuel cell 30 may further include a pair of gaskets 34A and 34C.

[0050] The membrane electrode assembly 10 is sandwiched between separators 31A and 31C. Separators 31A and 31C are made of a conductive and gas-impermeable material. Separator 31A faces anode diffusion layer 13A, and separator 31C faces cathode diffusion layer 13C. A gas flow path 32A is formed on the surface of separator 31A facing anode diffusion layer 13A, and a cooling water flow path 33A is formed on the surface opposite anode diffusion layer 13A. Similarly, a gas flow path 32C is formed on the surface of separator 31C facing cathode diffusion layer 13C, and a cooling water flow path 33C is formed on the surface opposite cathode diffusion layer 13C.

[0051] Gasket 34A surrounds the outer peripheries of anode catalyst layer 12A and anode diffusion layer 13A between polymer electrolyte membrane 11 and separator 31A. Gasket 34C surrounds the outer peripheries of cathode catalyst layer 12C and cathode diffusion layer 13C between polymer electrolyte membrane 11 and separator 31C. Gaskets 34A and 34C function to prevent gas supplied to catalyst layers 12A and 12C and diffusion layers 13A and 13C from leaking outside solid polymer fuel cell 30. Gaskets 34A and 34C may be one of the components of membrane electrode assembly 10.

[0052] During operation of the polymer electrolyte fuel cell 30, a fuel gas such as hydrogen flows through the gas flow channel 32A of the separator 31A, and an oxidant gas such as oxygen flows through the gas flow channel 32C of the separator 31C. Cooling water flows through the cooling water flow channels 33A and 33C of the separators 31A and 31C. The fuel gas is supplied from the gas flow channel 32A to the fuel electrode, and the oxidant gas is supplied from the gas flow channel 32C to the air electrode, causing an electrode reaction and generating an electromotive force between the fuel electrode and the air electrode. An organic fuel such as methanol may be supplied to the fuel electrode.

[0053] The polymer electrolyte fuel cell 30 may be used in the form of a single cell as shown in FIG. 3, or multiple polymer electrolyte fuel cells 30 may be stacked and connected in series to be used as a single fuel cell.

[0054] [Method for manufacturing membrane electrode assembly] A method for manufacturing the membrane electrode assembly 10 will now be described. The catalyst layers 12A and 12C are formed by applying a catalyst layer slurry containing the materials for the catalyst layers 12A and 12C to a substrate to form a coating film, and then drying the coating film.

[0055] The solvent for the catalyst layer slurry is not particularly limited, and examples of the solvent include 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 propyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl amyl ketone, pentanone, heptanone, cyclohexanone, methylcyclohexanone, acetonylacetone, diethyl ketone, dipropyl ketone, and diisobutyl ketone, tetrahydrofuran, tetrahydropyran, dioxane, and diethylene glycol dimethyl ether. Examples of the solvent include ethers such as ether, anisole, methoxytoluene, diethyl ether, dipropyl ether, and dibutyl ether, amines such as isopropylamine, butylamine, isobutylamine, cyclohexylamine, diethylamine, and aniline, esters such as propyl formate, isobutyl formate, amyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, isopentyl acetate, methyl propionate, ethyl propionate, and butyl propionate, acetic acid, propionic acid, dimethylformamide, dimethylacetamide, and N-methylpyrrolidone. Examples of glycol and glycol ether solvents include ethylene glycol, diethylene glycol, propylene glycol, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diacetone alcohol, 1-methoxy-2-propanol, and 1-ethoxy-2-propanol.

[0056] The substrate for forming the catalyst layers 12A, 12C may be, for example, a transfer substrate that is peeled off after transferring the catalyst layers 12A, 12C to the polymer electrolyte membrane 11. The transfer substrate may be, for example, a resin film. The substrate for forming the catalyst layers 12A, 12C may be the polymer electrolyte membrane 11 or the diffusion layers 13A, 13C.

[0057] The method for applying the catalyst layer slurry to the substrate is not particularly limited, and examples of the application method include a doctor blade method, a die coating method, a dipping method, a screen printing method, a laminator roll coating method, and a spray method.

[0058] The coating film, which is the catalyst layer slurry applied to the substrate, can be dried by, for example, hot air drying, IR drying, etc. The drying temperature is preferably about 40° C. to 200° C., and more preferably about 40° C. to 120° C. The drying time is preferably about 0.5 minutes to 1 hour, and more preferably about 1 minute to 30 minutes.

[0059] When the substrate for forming the catalyst layers 12A and 12C is a transfer substrate, the catalyst layers 12A and 12C are bonded to the polymer electrolyte membrane 11 by thermocompression bonding, and then the transfer substrate is peeled off from the catalyst layers 12A and 12C. Then, the diffusion layers 13A and 13C are pressure-bonded to the catalyst layers 12A and 12C on the polymer electrolyte membrane 11. In this way, the membrane electrode assembly 10 is formed.

[0060] When the substrates for forming the catalyst layers 12A and 12C are the diffusion layers 13A and 13C, the catalyst layers 12A and 12C supported by the diffusion layers 13A and 13C are joined to the polymer electrolyte membrane 11 by thermocompression bonding, thereby forming the membrane electrode assembly 10.

[0061] When the substrate for forming the catalyst layers 12A and 12C is the polymer electrolyte membrane 11, the catalyst layers 12A and 12C are formed directly on the surfaces of the polymer electrolyte membrane 11, and then the diffusion layers 13A and 13C are pressure-bonded to the catalyst layers 12A and 12C, thereby forming the membrane electrode assembly 10.

[0062] A manufacturing method using the polymer electrolyte membrane 11 as the substrate for forming the catalyst layers 12A and 12C can achieve high adhesion between the polymer electrolyte membrane 11 and the catalyst layers 12A and 12C. Furthermore, because pressure is not required to bond the catalyst layers 12A and 12C, crushing of the catalyst layers 12A and 12C is also suppressed. However, because the polymer electrolyte membrane 11 has a large swelling and shrinking property, when the 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 catalyst layers 12A and 12C is larger than when a transfer substrate or diffusion layer 13A and 13C is used as the substrate. Therefore, if the catalyst layers 12A and 12C contain a fibrous material 24, the occurrence of cracks is suppressed, and the catalyst layers 12A and 12C can be suitably formed even when the polymer electrolyte membrane 11 is used as the substrate. The polymer electrolyte fuel cell 30 is manufactured by assembling separators 31A and 31C to the membrane electrode assembly 10, and further providing a gas supply mechanism and the like.

[0063] [Example] The above-mentioned membrane electrode assembly and polymer electrolyte fuel cell will be described using specific examples and comparative examples.

[0064] Example 1 Platinum-supported carbon (TEC10E50E: manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was used as the carbon particles carrying the catalytic material. 20 g of platinum-supported carbon was added to water and mixed, and then a polymer electrolyte dispersion (Nafion dispersion: manufactured by Wako Pure Chemical Industries, Ltd.) and 1-propanol were added and stirred to prepare a slurry for the catalyst layer.

[0065] The catalyst layer slurry was applied to a polyethylene terephthalate substrate and the coating was dried to form two electrode catalyst layers. The electrode catalyst layers were then transferred from the polyethylene terephthalate substrate to a polymer electrolyte membrane (Nafion 212, manufactured by DuPont) so that the electrode catalyst layers were disposed on both sides of the polymer electrolyte membrane. During the transfer, the polymer electrolyte membrane and the electrode catalyst layers were thermocompression bonded at 120°C.

[0066] Gas diffusion layers with different gas permeabilities were laminated on the two electrode catalyst layers to obtain the membrane electrode assembly of Example 1. The gas diffusion layer was a laminate of a carbon substrate and a microporous layer. The Gurley value of the gas diffusion layer at the fuel electrode was 68 seconds, and the Gurley value of the gas diffusion layer at the air electrode was 47 seconds.

[0067] Example 2 Except for changing the gas diffusion layer, the membrane electrode assembly of Example 2 was obtained using the same materials and process as in Example 1. In Example 2, the Gurley value of the gas diffusion layer of the fuel electrode was 90 seconds, and the Gurley value of the gas diffusion layer of the air electrode was 75 seconds.

[0068] Example 3 Except for changing the gas diffusion layer, the membrane electrode assembly of Example 3 was obtained using the same materials and process as in Example 1. In Example 3, the Gurley value of the gas diffusion layer of the fuel electrode was 61 seconds, and the Gurley value of the gas diffusion layer of the air electrode was 50 seconds.

[0069] Example 4 Except for changing the gas diffusion layer, the membrane electrode assembly of Example 4 was obtained using the same materials and process as in Example 1. In Example 4, the Gurley value of the gas diffusion layer of the fuel electrode was 41 seconds, and the Gurley value of the gas diffusion layer of the air electrode was 5 seconds.

[0070] Example 5 A membrane / electrode assembly of Example 5 was obtained using the same materials and steps as in Example 1, except that 10 g of carbon fiber was added to the catalyst layer slurry. Carbon nanofibers (VGCF: manufactured by Showa Denko K.K.) were used as the carbon fibers. The carbon fibers had an average fiber diameter of approximately 150 nm and an average fiber length of approximately 10 μm.

[0071] (Comparative Example 1) Except for changing the gas diffusion layer, the membrane electrode assembly of Comparative Example 1 was obtained using the same materials and process as in Example 1. In Comparative Example 1, the Gurley value of the gas diffusion layer of the fuel electrode was 90 seconds, and the Gurley value of the gas diffusion layer of the air electrode was 85 seconds.

[0072] (Comparative Example 2) Except for changing the gas diffusion layer, a membrane electrode assembly of Comparative Example 2 was obtained using the same materials and process as in Example 1. In Comparative Example 2, the Gurley values ​​of the gas diffusion layers of the fuel electrode and the air electrode were both 75 seconds.

[0073] (Comparative Example 3) Except for changing the gas diffusion layer, a membrane electrode assembly of Comparative Example 3 was obtained using the same materials and process as in Example 1. In Comparative Example 3, the Gurley value of the gas diffusion layer of the fuel electrode was 50 seconds, and the Gurley value of the gas diffusion layer of the air electrode was 61 seconds.

[0074] <Evaluation> In accordance with the "Cell Evaluation and Analysis Protocol" published by the New Energy and Industrial Technology Development Organization (NEDO), a JARI standard cell was used as the evaluation unit cell. The cell was constructed by placing gaskets and separators on both sides of the membrane electrode assembly and clamping it down to a specified pressure. IV measurements were then performed as described in the "Cell Evaluation and Analysis Protocol." The IV measurements were performed under three humidification conditions: Condition 1, Condition 2, and Condition 3. Condition 2 was the standard condition; Condition 1 was a low-humidity condition in which the relative humidity of the air electrode was changed from the standard condition to 30% RH; and Condition 3 was a high-humidity condition in which the relative humidity of both the fuel electrode and the air electrode was changed from the standard condition to 100% RH.

[0075] <Evaluation results> Table 1 shows the Gurley value of the gas diffusion layer and the evaluation results of the power generation performance under each condition for each example and comparative example. 2 When the voltage was 0.65V or more, it was indicated by "◎", when the voltage was 0.60V or more and less than 0.65V, it was indicated by "◯", and when the voltage was less than 0.60V, it was indicated by "×".

[0076] [Table 1]

[0077] As shown in Table 1, in Examples 1 to 5, in which the Gurley value of the gas diffusion layer of the air electrode was 80 seconds or less and smaller than the Gurley value of the gas diffusion layer of the fuel electrode, it was confirmed that good power generation performance was obtained under low humidity conditions, standard conditions, and high humidity conditions. Furthermore, a comparison between Example 1 and Example 5 suggests that the electrode catalyst layer containing a fibrous material can improve output, particularly under high humidity conditions.

[0078] On the other hand, in Comparative Example 1, the Gurley value of the gas diffusion layer of the air electrode was smaller than that of the gas diffusion layer of the fuel electrode, but exceeded 80 seconds, and sufficient power generation performance was not obtained under high-humidity conditions. This is thought to be due to the insufficient air permeability of the gas diffusion layer of the air electrode, which leads to insufficient drainage at the air electrode under more humid conditions, resulting in a decrease in output under high-humidity conditions.

[0079] Furthermore, in Comparative Example 2, in which the Gurley values ​​of the air electrode gas diffusion layer and the anode gas diffusion layer are the same, sufficient power generation performance is not obtained under high-humidity conditions, and in Comparative Example 3, in which the anode gas diffusion layer has a smaller Gurley value than the cathode gas diffusion layer, sufficient power generation performance is not obtained under standard conditions as well as high-humidity conditions. These results are thought to be due to the fact that the air permeability of the air electrode gas diffusion layer is insufficient compared to that of the anode gas diffusion layer, which disrupts the balance of moisture content in the membrane electrode assembly and results in a decrease in output.

[0080] As described above using the examples, the membrane electrode assembly and polymer electrolyte fuel cell of the above embodiment provide the following effects. (1) The Gurley value of the air electrode diffusion layer 13C is 80 seconds or less and is smaller than the Gurley value of the anode diffusion layer 13A. This configuration promotes drainage of generated water at the air electrode, thereby suppressing flooding, while at the anode, moisture escapes more slowly than at the air electrode, preventing drying. As a result, the moisture content of the membrane electrode assembly 10 is properly balanced, enabling good power generation performance in both low-humidity and high-humidity environments.

[0081] (2) The catalyst layers 12A, 12C contain the fibrous material 24, which increases the strength of the catalyst layers 12A, 12C, making them less susceptible to cracking. Furthermore, the durability of the membrane electrode assembly 10 and the power generation performance of the fuel cell can be improved.

[0082] (3) When the catalyst layers 12A, 12C contain proton-conductive polymer electrolyte fibers, the proton conductivity of the catalyst layers 12A, 12C is enhanced. On the other hand, when the catalyst layers 12A, 12C contain carbon fibers, the electronic conductivity of the catalyst layers 12A, 12C is enhanced. Furthermore, when the carbon material constituting the carbon fibers is at least one of carbon nanotubes and carbon nanofibers, the electronic conductivity of the catalyst layers 12A, 12C is suitably enhanced. [Explanation of symbols]

[0083] 10...Membrane electrode assembly 11...Polymer electrolyte membrane 12A…Fuel electrode catalyst layer 12C: Air electrode catalyst layer 13A...Anode diffusion layer 13C...Air electrode diffusion layer 21...catalyst material 22...Carbon particles 23…aggregate 24...Fibrous materials 30...Polymer fuel cell 31A, 31C...Separator 34A, 34C...Gasket

Claims

1. A polymer electrolyte fuel cell comprising a membrane electrode assembly and a pair of separators sandwiching the membrane electrode assembly, in which a fuel gas containing hydrogen is supplied to the fuel electrode and an oxidant gas is supplied to the air electrode, The membrane electrode assembly is a polymer electrolyte membrane; a pair of electrode catalyst layers that sandwich the polymer electrolyte membrane and are in contact with the surfaces of the polymer electrolyte membrane; an anode diffusion layer which is a gas diffusion layer laminated on one of the pair of electrode catalyst layers to constitute the anode; an air electrode diffusion layer which is a gas diffusion layer laminated on the other of the pair of electrode catalyst layers to constitute the air electrode, the anode diffusion layer has a two-layer structure of a carbon substrate and a microporous layer, and faces one of the pair of separators; the air electrode diffusion layer has a two-layer structure of a carbon substrate and a microporous layer, and faces the other of the pair of separators; a Gurley value, which indicates the air resistance in the thickness direction of the air electrode diffusion layer, of 5 seconds or more and 80 seconds or less, which is smaller than the Gurley value, which indicates the air resistance in the thickness direction of the anode diffusion layer; The Gurley value of the anode diffusion layer is 100 seconds or less, and the difference between the Gurley value of the anode diffusion layer and the Gurley value of the cathode diffusion layer is 40 seconds or less. Polymer electrolyte fuel cell.

2. The electrode catalyst layer includes a catalyst material, carbon particles, polymer electrolyte aggregates, and a fibrous material. The polymer electrolyte fuel cell according to claim 1 .

3. The fibrous material contained in the electrode catalyst layer is at least one of an electron conductive fiber and a proton conductive fiber. The polymer electrolyte fuel cell according to claim 2 .

4. the electrode catalyst layer contains carbon fiber, which is the fibrous material, The carbon fibers contained in the electrode catalyst layer are at least one of carbon nanotubes and carbon nanofibers. The polymer electrolyte fuel cell according to claim 2 or 3.

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