JP2019083112A - Membrane electrode assembly for fuel cell and manufacturing method thereof, and solid polymer fuel cell - Google Patents

Abstract

To provide an electrode catalyst layer for fuel cell improving water retention under low humidification condition without blocking removal of water produced by electrode reaction, and showing high power generation performance even under low humidification condition, the electrode catalyst layer being able to be manufactured at a low cost.SOLUTION: At least one electrode catalyst layer, out of a pair of electrode catalyst layers 2, 3 sandwiching a polymer electrolyte membrane 1, is provided with at least two electrode catalyst parts, i.e., a first electrode catalyst part 2a (or 3a) provided on the inlet side of gas, and a second electrode catalyst part 2b (or 3b) provided on the outlet side of gas, where the mass ratio of a fibrous material to carbon particles in the second electrode catalyst part 2b (or 3b) is larger than the mass ratio of the fibrous material to carbon particles in the first electrode catalyst part 2a (or 3a) in the membrane electrode assembly for fuel cell.SELECTED DRAWING: Figure 1

Description

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

A fuel cell is a power generation system that uses a hydrogen-containing fuel gas and an oxygen-containing oxidant gas to cause the reverse reaction of water electrolysis at a catalyst-containing electrode to generate electricity simultaneously with heat. This power generation system has features such as high efficiency, low environmental load, and low noise as compared with the conventional power generation system, and is attracting attention as a future clean energy source. There are several types of fuel cells depending on the type of ion conductor used, and a cell using a proton conductive polymer membrane is called a polymer electrolyte fuel cell.
Among fuel cells, polymer electrolyte fuel cells can be used at around room temperature, and their use in automotive power sources and home stationary power sources is expected to be promising. In recent years, various types of polymer electrolyte fuel cells have been proposed. Research and development is underway. In a polymer electrolyte fuel cell, a membrane electrode assembly (Membrane Electrode Assembly: hereinafter sometimes referred to as MEA) in which a pair of electrode catalyst layers are disposed on both sides of a polymer electrolyte membrane is sandwiched by a pair of separator plates. Battery.

In one separator plate, a gas flow path for supplying a fuel gas containing hydrogen is formed in one of the pair of electrodes, and in the other separator plate, oxidation is performed including oxygen in the other of the pair of electrodes. A gas flow path for supplying the agent gas is formed.
Here, the electrode to which the fuel gas is supplied is a fuel electrode, and the electrode to which the oxidant gas is supplied is an air electrode. These electrodes are provided with an electrode catalyst layer formed by laminating a polymer electrolyte and carbon particles carrying a catalyst such as a platinum-based noble metal, and a gas diffusion layer having both gas permeability and electron conductivity. . In addition, these electrodes are disposed such that the gas diffusion layer faces the separator.

For the electrode catalyst layer, efforts have been made to improve the gas diffusivity in order to improve the power density of the fuel cell. The pores in the electrode catalyst layer are located ahead from the separator plate through the gas diffusion layer and play a role of a passage for transporting a plurality of substances. The fuel electrode not only smoothly supplies the fuel gas to the three-phase interface which is the reaction site of the oxidation reduction, but also functions to supply water for conducting the generated protons smoothly in the polymer electrolyte membrane. The air electrode, together with the supply of the oxidant gas, functions to smoothly remove the water produced by the electrode reaction.
In the polymer electrolyte fuel cell, the phenomenon of so-called "flooding" in which the power generation reaction is stopped due to the obstruction of the substance transport at the fuel electrode and the air electrode is prevented. For this reason, the structure which improves drainage property until now is examined (for example, refer patent document 1, patent document 2, patent document 3, and patent document 4).

Moreover, although the subject for practical use of a polymer electrolyte fuel cell includes the improvement of power density and durability, etc., the biggest subject is cost reduction (cost reduction).
One way to reduce costs is to reduce the number of humidifiers. Perfluorosulfonic acid membranes and hydrocarbon-based membranes are widely used as polymer electrolyte membranes located at the center of membrane electrode assemblies. And, in order to obtain excellent proton conductivity, water management close to a saturated water vapor pressure atmosphere is required, and at present, water is supplied from the outside by a humidifier. Therefore, for the purpose of low power consumption and simplification of the system, development of a polymer electrolyte membrane showing sufficient proton conductivity even under low humidification conditions that does not require a humidifier has been promoted. .

However, in the case of the electrode catalyst layer having enhanced drainage performance, the polymer electrolyte is dried up under low humidification conditions, so it is necessary to optimize the structure of the electrode catalyst layer to improve the water retention. Heretofore, in order to improve the water retentivity of the fuel cell under low humidification conditions, for example, a method of sandwiching a humidity control film between the electrode catalyst layer and the gas diffusion layer has been devised.
For example, Patent Document 5 describes a method in which a humidity control film composed of conductive carbonaceous powder and polytetrafluoroethylene exhibits a humidity control function to prevent dry-up.
Patent Document 6 describes a method of providing a groove on the surface of a catalyst electrode layer in contact with a polymer electrolyte membrane. In the method described in Patent Document 6, by forming a groove having a width of 0.1 to 0.3 mm on the surface of the catalyst electrode layer, a decrease in power generation performance under low humidification conditions is suppressed.

Unexamined-Japanese-Patent No. 2006-120506 Unexamined-Japanese-Patent No. 2006-332041 JP 2007-87651A JP 2007-80726 A Unexamined-Japanese-Patent No. 2006-252948 Japanese Patent Application Publication No. 2007-141588

According to the methods described in Patent Documents 5 and 6, it is possible to enhance the drainage of the electrode catalyst layer (do not inhibit the removal of water generated by the electrode reaction), and at the same time, to retain water of the electrode catalyst layer under low humidification conditions. Can be expected to improve. However, fuel cells using the electrode catalyst layer obtained by these methods have room for improvement in terms of power generation performance under low humidification conditions and durability. In addition, these methods are complicated, and there is also a problem that the production cost of the electrode catalyst layer is high.
The present invention focuses on the above points, and the water retention under low humidification conditions is improved without inhibiting the removal of water generated by the electrode reaction, and high power generation even under low humidification conditions An object of the present invention is to provide a fuel cell membrane electrode assembly exhibiting performance and durability.

  In order to solve the problems, one aspect of the present invention is that a polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers, and at least one of the pair of electrode catalyst layers is the polymer electrolyte membrane A gas having a first electrode catalyst portion and a second electrode catalyst portion facing each other and flowing into the electrode catalyst layer as a relative arrangement of the first electrode catalyst portion and the second electrode catalyst portion And the second electrode catalyst portion is disposed at the outlet side of the flow direction, and the first electrode catalyst portion is disposed at the inlet side of the flow direction. The second electrode catalyst portion includes a catalyst-supporting particle consisting of carbon particles supporting a catalyst, a fibrous substance having an average fiber length of 1 μm to 15 μm, and a polymer electrolyte, and the above-mentioned carbon particle Regarding the mass ratio of fibrous material, the second electrode It is characterized in that the mass ratio of the catalyst part is larger than the mass ratio of the first electrode catalyst part.

  According to one aspect of the present invention, a membrane electrode for a fuel cell, which has improved water retention under low humidification conditions and exhibits high power generation performance even under low humidification conditions without inhibiting removal of water generated by electrode reaction. A conjugate can be provided. As a result, according to one aspect of the present invention, a fuel cell membrane electrode assembly having the above effects can be manufactured at low cost.

It is a disassembled perspective view which shows typically the membrane electrode assembly of embodiment of this invention. It is a disassembled perspective view which shows typically the structure of the polymer electrolyte fuel cell provided with the membrane electrode assembly of FIG.

Embodiment
Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. The present invention is not limited to the embodiments described below, and modifications such as design changes can be made based on the knowledge of those skilled in the art, and such modifications can be made. Is also within the scope of the present invention.

[Membrane electrode assembly]
First, the membrane electrode assembly 11 according to the present embodiment will be described.
As shown in FIG. 1, the membrane electrode assembly 11 comprises a polymer electrolyte membrane 1 and an electrode catalyst layer 2 sandwiching the polymer electrolyte membrane 1 from the upper and lower surfaces of the polymer electrolyte membrane 1 (in FIG. And an electrode catalyst layer 3 (shown below in FIG. 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 located on the inlet side of the gas flowing into the electrode catalyst layer and a second electrode located on the outlet side of the gas And a catalyst portion 2b. Similarly, the electrode catalyst layer 3 shown on the lower side in the drawing has a first electrode catalyst portion 3a located on the gas inlet side and a second electrode catalyst portion 3b located on the gas outlet side.

At least one of the two electrode catalyst layers 2 and 3 has the following configurations (a) and (b). It is preferable that the two electrode catalyst layers 2 and 3 satisfy the following configuration.
(A) A catalyst supporting particle, a fibrous substance, and a polymer electrolyte. The average fiber length of the fibrous material is 1 μm or more and 15 μm or less.
(B) The mass ratio of fibrous material to carbon particles in the second electrode catalyst portion 2b (or 3b) is based on the mass ratio of fibrous material to carbon particles in the first electrode catalyst portion 2a (or 3a) Too big.

  The electrode catalyst layers 2 and 3 having the above-mentioned configurations (a) and (b) are high in such a manner that the generation of cracks in the electrode catalyst layer causing the deterioration of durability is suppressed by the entanglement of highly crystalline fibrous substances. Durability and mechanical properties are obtained. If the average fiber length of the fibrous material is less than 1 μm, the mechanical properties may be deteriorated because the entanglement of the fibrous material is weak. When the average fiber length of the fibrous material exceeds 15 μm, the fibrous material may not be dispersed as ink because the entanglement of the fibrous material is strong.

  Further, by increasing the mass ratio of the fibrous material to the carbon particles, the number of pores formed in the electrode catalyst layer by the fibrous material is increased, and the removal of water is promoted. In the membrane electrode assembly 11, the mass ratio of the fibrous substance to the carbon particles in the first electrode catalyst portion 2a (or 3a) provided on the gas inlet side is the second electrode catalyst portion 2b (on the gas outlet side) Or 3b) compared to the smaller. For this reason, the water retentivity is enhanced by the first electrode catalyst portion 2a (or 3a) provided on the gas inlet side, and the removal of water is promoted in the second electrode catalyst portion 2b (or 3b) provided on the gas outlet side. ing. Thus, the membrane electrode assembly 11 has both the drainage property of the water generated by the electrode reaction and the water retention property under the low humidification condition.

The electrode catalyst layers 2 and 3 having the above configurations (a) and (b) preferably further have the following configuration (c).
(C) The mass ratio of the fibrous substance to the carbon particles in the first electrode catalyst portion 2a (or 3a) is in the range of 0.1 or more and 1.2 or less, and the second electrode catalyst portion 2b (or The mass ratio of the fibrous material to the carbon particles in 3b) is in the range of 0.2 or more and 2.5 or less.
If the mass ratio of fibrous material to carbon particles in the first electrode catalyst portion 2a (or 3a) is less than 0.1, the entanglement of the fibrous material is weak, so the first electrode catalyst portion 2a (or The mechanical properties of 3a) may be degraded. In addition, when the mass ratio of the fibrous material to the carbon particles in the first electrode catalyst portion 2a (or 3a) exceeds 1.2, it may be difficult to retain water and the proton conductivity may be reduced.

When the mass ratio of fibrous material to carbon particles in the second electrode catalyst portion 2b (or 3b) is less than 0.2, it is difficult to remove water because the number of pores formed by the fibrous material is small It may be In addition, when the mass ratio of the fibrous material to the carbon particles in the second electrode catalyst portion 2b (or 3b) exceeds 2.5, it may be difficult to retain water and the proton conductivity may be reduced.
Unlike the case where the low humidity is achieved by applying a conventional humidity control film or forming a groove on the surface of the electrode catalyst layer, the membrane electrode assembly 11 does not show deterioration in power generation characteristics due to an increase in interface resistance. Therefore, the polymer electrolyte fuel cell provided with the membrane electrode assembly 11 has a remarkable effect of having high power generation characteristics even under low humidification conditions, as compared with the polymer electrolyte fuel cell provided with the conventional membrane electrode assembly. Play.

Polymer Electrolyte Fuel Cell
Next, a polymer electrolyte fuel cell provided with the membrane electrode assembly 11 of the embodiment will be described with reference to FIG.
As shown in FIG. 2, the polymer electrolyte fuel cell 12 is opposed to the gas diffusion layer 4 on the air electrode side disposed so as to face the electrode catalyst layer 2 of the membrane electrode assembly 11 and the electrode catalyst layer 3. And a gas diffusion layer 5 on the fuel electrode side arranged to The electrode catalyst layer 2 and the gas diffusion layer 4 form an air electrode (cathode) 6. The electrode catalyst layer 3 and the gas diffusion layer 5 form a fuel electrode (anode) 7.
In addition, a pair of separators 10a and 10b made of a conductive and impermeable material, provided with gas flow paths 8a and 8b for gas flow and cooling water flow paths 9a and 9b for cooling water flow, It is disposed outside the diffusion layers 4 and 5, respectively.

For example, hydrogen gas is supplied as fuel gas from the gas flow path 8b of the separator 10b on the fuel electrode 7 side. On the other hand, for example, oxygen gas is supplied as an oxidant gas from the gas flow path 8a of the separator 10a on the air electrode 6 side. By causing electrode reaction between hydrogen of the fuel gas and oxygen of the oxidant gas in the presence of the catalyst, an electromotive force can be generated between the fuel electrode and the air electrode.
In the polymer electrolyte fuel cell 12, the polymer electrolyte membrane 1, the two electrode catalyst layers 2 and 3, and the gas diffusion layers 4 and 5 are sandwiched between a pair of separators 10a and 10b. The polymer electrolyte fuel cell 12 is a single cell fuel cell, but a plurality of cells may be stacked via the separator 10a or the separator 10b to form a polymer electrolyte fuel cell.

[Method of producing membrane electrode assembly]
Next, an example of a method of manufacturing 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 manufacturing step, catalyst portion forming step and lamination step.
The catalyst ink production step is a step of producing a catalyst ink comprising catalyst-supporting particles consisting of carbon particles carrying a catalyst, an average fiber length of a fibrous substance of 1 μm to 15 μm, a polymer electrolyte, and a solvent. In the catalyst ink preparation step, two kinds of catalyst inks having different mass ratios of fibrous material to carbon particles are prepared. A catalyst ink having a small mass ratio of the fibrous material to carbon particles is used as a first catalyst ink, and a catalyst ink having a large mass ratio of the fibrous material to carbon particles is used as a second catalyst ink.

In the catalyst portion forming step, a first catalyst ink is applied to a substrate and dried to form a first electrode catalyst portion 2a (or 3a), and a second catalyst ink is used as a substrate. It has the 2nd process of forming the 2nd electrode catalyst part 2b (or 3b) by making it apply and drying.
In the catalyst portion forming step, the coating is performed such that the application region of the first catalyst ink and the application region of the second catalyst ink overlap with the substrate.
In the laminating step, the electrode catalyst layer formed on the base material is attached and laminated on the polymer electrolyte membrane 1. In the stacking step, the first electrode catalyst portion is set to the inlet side of the flow direction and the second electrode catalyst portion is set to the outlet side of the flow direction in the flow direction of the gas flowing into the electrode catalyst layer. Paste it. In addition, when a base material is the polymer electrolyte membrane 1, a lamination process will be performed by performing a catalyst part formation process.

By attaching the electrode catalyst layers 2 and 3 to the upper and lower surfaces of the polymer electrolyte membrane 1, the membrane electrode assembly 11 is obtained. Both of the electrode catalyst layers 2 and 3 may be manufactured by the method described above, or one may be manufactured by the method described above and the other may be manufactured by a conventional method.
Here, the first step in the step of producing the first catalyst ink in the catalyst ink producing step and the first step in the catalyst portion forming step correspond to the first step, and the second catalyst in the catalyst ink producing step The second step of the step of producing the ink and the step of forming the catalyst portion corresponds to the second step.

[Detailed description]
Hereinafter, the membrane electrode assembly 11 and the polymer electrolyte fuel cell 12 will be described in more detail.
The polymer electrolyte membrane 1 may be one having proton conductivity, and a fluorine-based polymer electrolyte membrane or a hydrocarbon-based polymer electrolyte membrane can be used. As an example of a fluorine-based polymer electrolyte membrane, Nafion (registered trademark) manufactured by DuPont, Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., Aciplex (registered trademark) manufactured by Asahi Kasei Corp., Gore Select (registered trademark) manufactured by Gore Etc. can be used.

Further, as the hydrocarbon-based polymer electrolyte membrane, an electrolyte membrane of sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, sulfonated polyphenylene, or the like can be used. In particular, Nafion (registered trademark) -based materials manufactured by DuPont can be suitably used as the polymer electrolyte membrane 1.
The electrode catalyst layers 2 and 3 are formed on both sides of the polymer electrolyte membrane 1 using a catalyst ink. The catalyst ink for the electrode catalyst layers 2 and 3 contains catalyst supporting particles, a polymer electrolyte and a solvent. In addition, the catalyst ink used for at least one of the electrode catalyst layers 2 and 3 contains two types of compositions including catalyst-supporting particles, a fibrous substance, a polymer electrolyte, and a solvent, and the mass ratio of the fibrous substance to carbon particles is different. Use

  The polymer electrolyte contained in the catalyst ink may be any one having proton conductivity, and the same material as that of the polymer electrolyte membrane 1 can be used, and a fluorine-based polymer electrolyte and a hydrocarbon-based polymer electrolyte can be used. It can be used. As an example of a fluorine-based polymer electrolyte, Nafion (registered trademark) -based material manufactured by DuPont can be used. Further, as the hydrocarbon-based polymer electrolyte, electrolytes such as sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, sulfonated polyphenylene and the like can be used. In particular, Nafion (registered trademark) manufactured by DuPont can be suitably used as the fluorine-based polymer electrolyte.

As a catalyst used in the present embodiment (hereinafter sometimes referred to as catalyst particles or catalyst), platinum group elements, metals, alloys or oxides of the metals, composite oxides, etc. can be used. Examples of platinum group elements include platinum, palladium, ruthenium, iridium, rhodium and osmium, and examples of metals include iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium and aluminum. The term "multiple oxide" as used herein means an oxide composed of two types of metals.
When the catalyst particles are one or more metals selected from platinum, gold, palladium, rhodium, ruthenium, and iridium, they are excellent in electrode reactivity and efficiently and stably perform electrode reactions. it can. When the catalyst particles are one or more metals selected from platinum, gold, palladium, rhodium, ruthenium, and iridium, the polymer electrolyte fuel cell 12 provided with the electrode catalyst layers 2 and 3 is It is preferable because it exhibits high power generation characteristics.

Moreover, 0.5 nm or more and 20 nm or less are preferable, and, as for the average particle diameter of the catalyst particle mentioned above, 1 nm or more and 5 nm or less are more preferable. Here, the average particle size is an average particle size obtained from an X-ray diffraction method if it is a catalyst supported on a carrier such as carbon particles. In addition, if the catalyst is not supported on the carrier, it is the arithmetic mean particle size obtained from particle size measurement. When the average particle diameter of the catalyst particles is in the range of 0.5 nm or more and 20 nm or less, the activity and stability of the catalyst are preferably improved.
Carbon particles are generally used as the electron conductive powder (support) supporting the above-mentioned catalyst. The type of carbon particles is not limited as long as it is particulate and conductive and is not dependent on a catalyst, but carbon black, graphite, graphite, activated carbon, carbon fiber, carbon nanotubes, fullerene may be used Can.

The average particle diameter of the carbon particles is preferably about 10 nm or more and 1000 nm or less, and more preferably 10 nm or more and 100 nm or less. Here, the average particle size is an average particle size obtained from a SEM image. When the average particle diameter of the carbon particles is in the range of 10 nm to 1000 nm, the activity and stability of the catalyst are improved, which is preferable. It is preferable because an electron conduction path is easily formed, and the gas diffusivity of the two electrode catalyst layers 2 and 3 and the utilization of the catalyst are improved.
As the fibrous material, conductive fibers can be used. Examples of conductive fibers include carbon nanofibers, carbon nanotubes, and vapor grown carbon fibers. As an example of the vapor grown carbon fiber, VGCF (registered trademark) manufactured by Showa Denko K. K. can be used. In addition, an electrolyte fiber obtained by processing a polymer electrolyte into a fiber may be used. The proton conductivity can be improved by using an electrolyte fiber. These fibrous substances may be used alone or in combination of two or more, and conductive fibers and electrolyte fibers may be used together.

  The solvent used as a dispersion medium for the catalyst ink is not particularly limited as long as it can dissolve the polymer electrolyte in a highly fluid state or disperse as a fine gel without eroding the catalyst material-supporting particles and the polymer electrolyte. It is not a thing. However, the solvent preferably contains at least a volatile organic solvent. Examples of the solvent used as a dispersion medium for the catalyst ink include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, alcohols such as isobutyl alcohol, tert-butyl alcohol and pentanol, and acetone Ketone solvents such as methyl ethyl ketone, pentanone, methyl isobutyl ketone, heptanone, cyclohexanone, methyl cyclohexanone, acetonyl acetone, diisobutyl ketone, etc., ether solvents such as tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene, dibutyl ether, etc. Dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, diacetone alcohol , It can be used polar solvents such as 1-methoxy-2-propanol. Moreover, you may use the mixed solvent which mixed 2 or more types among the above-mentioned materials as a solvent.

Moreover, since the thing using a lower alcohol as a solvent used as a dispersion medium of a catalyst ink has a high danger of ignition, when using a lower alcohol, it is preferable to set it as the mixed solvent with water. Furthermore, water that is compatible with the polymer electrolyte (water with high affinity) may be included. The amount of water added is not particularly limited as long as the polymer electrolyte is not separated to cause white turbidity or gelation.
A dispersant may be contained in the catalyst ink in order to disperse the catalyst material supporting particles. As a dispersing agent, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant etc. can be mentioned.

  Examples of anionic surfactants include alkyl ether carboxylates, ether carboxylates, alkanoyl sarcosines, alkanoyl glutamates, acyl glutamates, oleic acid / N-methyl taurine, potassium oleate / diethanolamine salts, alkyl ether sulfates / triols Ethanolamine salt, polyoxyethylene alkyl ether sulfate triethanolamine salt, amine salt of specially modified polyether ester acid, amine salt of higher fatty acid derivative, amine salt of specially modified polyester acid, amine salt of high molecular weight polyether ester acid Amine salts of specially modified phosphoric esters, high molecular weight polyester acid amidoamine salts, amidoamine salts of special fatty acid derivatives, alkylamine salts of higher fatty acids, amides of high molecular weight polycarboxylic acids Minates, carboxylic acid type surfactants such as sodium laurate, sodium stearate, sodium oleate, dialkyl sulfosuccinates, dialkyl sulfosuccinates, 1,2-bis (alkoxycarbonyl) -1-ethane sulfonates, Alkyl sulfonates, alkyl sulfonates, paraffin sulfonates, α-olefin sulfonates, linear alkyl benzene sulfonates, alkyl benzene sulfonates, polynaphthyl methane sulfonates, polynaphthyl methane sulfonates, naphthalene sulfonate-formalin condensates, alkyl naphthalene sulfonates, alkanoyl Methyl taurine, lauryl sulfate sodium salt, cetyl sulfate sodium salt, stearyl sulfate sodium salt, oleyl sulfate S Sulfonic acid type surfactants such as ter sodium salt, lauryl ether sulfuric acid ester salt, sodium alkyl benzene sulfonate, oil-soluble alkyl benzene sulfonic acid salt, α-olefin sulfonic acid salt, alkyl sulfuric acid ester salt, sulfuric acid alkyl salt, alkyl sulfate, alkyl Ether sulfate, polyoxyethylene alkyl ether sulfate, alkyl polyethoxy sulfate, polyglycol ether sulfate, alkyl polyoxyethylene sulfate, sulfated surfactant such as sulfated oil, highly sulfated oil, phosphoric acid (mono or Di) alkyl salts, (mono or di) alkyl phosphates, (mono or di) alkyl phosphoric acid ester salts, phosphoric acid alkylpolyoxyethylene salts, alkyl ether phosphates, alkyl polyethoxy. Acid salt, polyoxyethylene alkyl ether, phosphoric acid alkylphenyl polyoxyethylene salt, alkylphenyl ether phosphate, alkylphenyl polyethoxy phosphate, polyoxyethylene alkylphenyl ether phosphate, higher alcohol phosphoric acid monoester Disodium salt, higher alcohol phosphoric acid diester disodium salt, phosphoric acid ester type surfactants such as zinc dialkyl dithiophosphate, etc. may be mentioned.

  Examples of cationic surfactants include benzyldimethyl {2- [2- (P-1,1,3,3-tetramethylbutylphenoxy) ethoxy] ethyl} ammonium chloride, octadecylamine acetate, tetradecylamine acetate Octadecyl trimethyl ammonium chloride, tallow trimethyl ammonium chloride, dodecyl trimethyl ammonium chloride, coconut trimethyl ammonium chloride, hexadecyl trimethyl ammonium chloride, behenyl trimethyl ammonium chloride, coconut dimethyl benzyl ammonium chloride, tetradecyl dimethyl benzyl ammonium chloride, octadecyl dimethyl benzyl ammonium chloride , Dioleyl dimethyl ammonium chloride, 1-hydroxyethyene -2- tallow imidazoline quaternary salt, 2-heptadecenyl-hydroxyethyl imidazoline, stearamide ethyl diethylamine acetate, stearamide ethyl diethylamine hydrochloride, triethanolamine monostearate formate, alkyl pyridinium salt, higher alkyl amine Ethylene oxide adduct, polyacrylamide amine salt, modified polyacrylamide amine salt, perfluoroalkyl quaternary ammonium iodide and the like can be mentioned.

  As an example of amphoteric surfactants, dimethyl coconut betaine, dimethyl lauryl betaine, sodium lauryl aminoethyl glycine, sodium lauryl amino propionate, stearyl dimethyl betaine, lauryl dihydroxyethyl betaine, amido betaine, imidazolinium betaine, lecithin, 3- [ Examples include sodium ω-fluoroalkanoyl-N-ethylamino] -1-propanesulfonic acid, N- [3- (perfluorooctanesulfonamido) propyl] -N, N-dimethyl-N-carboxymethylene ammonium betaine and the like.

  Examples of nonionic surfactants include coconut fatty acid diethanolamide (1: 2 type), coconut fatty acid diethanolamide (1: 1 type), bovine fatty acid diethanolamide (1: 2 type), bovine fatty acid diethanolamide (1: 1 type) Type), oleic acid diethanolamide (1: 1 type), hydroxyethyl lauryl amine, polyethylene glycol lauryl amine, polyethylene glycol coyl amine, polyethylene glycol stearyl amine, polyethylene glycol tallow amine, polyethylene glycol tallow propylene diamine, polyethylene glycol dioleyl amine, Dimethyl lauryl amine oxide, dimethyl stearyl amine oxide, dihydroxyethyl lauryl amine oxide, perfluoroalkyl amine oxide, polyvinyl pyro Don, higher alcohol ethylene oxide adduct, alkylphenol ethylene oxide adduct, fatty acid ethylene oxide adduct, polypropylene glycol ethylene oxide adduct, fatty acid ester of glycerin, fatty acid ester of pentaerythritol, fatty acid ester of Sorbit, fatty acid ester of sorbitan, The fatty acid ester of sugar etc. are mentioned.

Among the above-described surfactants, a sulfonic acid type surfactant can be suitably used as a dispersant, in consideration of the dispersion effect of carbon, the change of the catalyst performance due to the remaining of the dispersant, and the like. Examples of sulfonic acid type surfactants include alkyl benzene sulfonic acid, oil soluble alkyl benzene sulfonic acid, α-olefin sulfonic acid, sodium alkyl benzene sulfonate, oil soluble alkyl benzene sulfonate, α-olefin sulfonate and the like.
Pore volume generally decreases as the amount of polyelectrolyte in the catalyst ink is increased. On the other hand, when the amount of carbon particles in the catalyst ink is increased, the pore volume is increased. Also, the use of dispersants reduces the pore volume.

  In addition, the catalyst ink is subjected to dispersion processing as needed. 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. Distributed processing can be performed by employing various devices. In particular, the method of distributed processing is not limited. For example, as the dispersion treatment, treatment with a ball mill or roll mill, treatment with a shear mill, treatment with a wet mill, ultrasonic dispersion treatment and the like can be mentioned. Moreover, you may employ | adopt the homogenizer etc. which stir by a centrifugal force. The pore volume is reduced as the dispersion time of the dispersion time is broken, the aggregates of the catalyst supporting particles are broken.

  If the solid content in the catalyst ink is too large, the viscosity of the catalyst ink becomes high, so that the surface of the electrode catalyst layers 2 and 3 is easily cracked. On the other hand, when the solid content in the catalyst ink is too small, the film forming rate is very slow, and the productivity is lowered. Therefore, the solid content in the catalyst ink is preferably 1% by mass (wt%) or more and 50% by mass or less. The solid content is composed of catalyst material-supporting particles and a polymer electrolyte, but when the content of catalyst material-supporting particles in the solid content is increased, the viscosity becomes high even with the same solid content. On the other hand, when the content of the catalyst substance-supporting particles in the solid content is reduced, the viscosity decreases even at the same solid content. Therefore, the proportion of the catalyst substance-supporting particles in the solid content is preferably 10% by mass to 80% by mass. The viscosity of the catalyst ink is preferably about 0.1 cP to 500 cP (0.0001 Pa · s to 0.5 Pa · s), preferably 5 cP to 100 cP (0.005 Pa · s to 0.1 Pa · s). Is more preferred. The viscosity can also be controlled by adding a dispersant at the time of dispersing the catalyst ink.

In addition, the catalyst ink may contain a pore forming agent. The pore forming agent can be removed after the formation of the electrode catalyst layer to form pores. Examples thereof include acids and alkalis, substances soluble in water, substances to be sublimated such as camphor, and substances to be thermally decomposed. If the pore forming agent is a substance soluble in warm water, it may be removed by water generated at the time of power generation.
Examples of the pore-forming agent soluble in acid, alkali and water include acid-soluble inorganic salts, inorganic salts soluble in alkaline aqueous solution, metals soluble in acid or alkali, water-soluble inorganic salts, water-soluble organic compounds and the like. Examples of acid-soluble inorganic salts include calcium carbonate, barium carbonate, magnesium carbonate, magnesium sulfate, magnesium oxide and the like. Alumina, silica gel, silica sol etc. are mentioned as an inorganic salt soluble in alkaline aqueous solution. Metals soluble in acid or alkali include aluminum, zinc, tin, nickel, iron and the like. Examples of water-soluble inorganic salts include sodium chloride, potassium chloride, ammonium chloride, sodium carbonate, sodium sulfate, monosodium phosphate and the like. Examples of water-soluble organic compounds include polyvinyl alcohol and polyethylene glycol. Moreover, although the pore making agent mentioned above may be used individually by 1 type or in combination of 2 or more types, it is preferable to use in combination of 2 or more types.

As a coating method for coating the catalyst ink on the substrate, a doctor blade method, a dipping method, a screen printing method, a roll coating method, or the like can be adopted.
A transfer sheet can be used as a base material used for manufacture of the electrode catalyst layers 2 and 3.
The transfer sheet used as the substrate may be made of a material having good transferability, and, for example, a fluorine-based resin can be used. As a fluorine resin, ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE) Etc. can be mentioned. Moreover, a polymer sheet and a polymer film can also be used as a transfer sheet. Examples of materials for polymer sheet and polymer film include polyimide, polyethylene terephthalate, polyamide (nylon (registered trademark)), polysulfone, polyether sulfone, polyphenylene sulfide, polyether / ether ketone, polyether imide, and polyarylate And polyethylene naphthalate can be used. When a transfer sheet is used as the substrate, the transfer sheet is peeled off after the polymer electrolyte membrane 1 is bonded to the electrode membrane which is a coating after solvent removal, and the electrode catalyst is formed on both sides of the polymer electrolyte membrane 1. The membrane electrode assembly 11 can be provided with the layers 2 and 3.

As the gas diffusion layers 4 and 5, a material having gas diffusivity and conductivity can be used. For example, as the gas diffusion layers 4 and 5, porous carbon materials such as carbon cloth, carbon paper, and non-woven fabric can be used.
As the separator 10 (10a, 10b), a carbon type or metal type can be used. The gas diffusion layers 4 and 5 and the separators 10 (10a and 10b) may be integrally formed. When the separators 10 (10a, 10b) or the electrode catalyst layers 2, 3 perform the function of 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.

  Hereinafter, the method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell in the present embodiment will be described with reference to specific examples and comparative examples, but the present embodiment is limited by the following examples and comparative examples. It is not something to be done.

<Others>
In the electrode catalyst layers 2 and 3 of the membrane electrode assembly 11 according to the present embodiment, the mass ratio of the fibrous substance to the carbon particles in the first electrode catalyst portion 2a (or 3a) provided on the gas inlet side The mass ratio of the second electrode catalyst portion 2b (or 3b) provided on the outlet side is smaller than that of the second electrode catalyst portion 2b (or 3b). According to this configuration, the water retentivity is enhanced by the first electrode catalyst portion 2a (or 3a) provided on the gas inlet side, and the second electrode catalyst portion 2b (or 3b) provided on the gas outlet side It can promote the removal of water.

It is preferable to make the mass ratio in the second electrode catalyst portion 2b (or 3b) twice or more the mass ratio in the first electrode catalyst portion 2a (or 3a).
Therefore, it is possible to increase the water retentivity without inhibiting the removal of water generated by the electrode reaction and the like, and to obtain high power generation characteristics even under low humidification conditions.
In the membrane electrode assembly 11 of the present embodiment, if the mass ratio of the fibrous material to the carbon particles is different between the first electrode catalyst portion 2a (or 3a) and the second electrode catalyst portion 2b (or 3b). It can be realized by

For this reason, high power generation characteristics can be obtained without significant change of the manufacturing process and the like and without a significant increase in cost.
In the above-mentioned embodiment, although the case where the 1st electrode catalyst part and the 2nd electrode catalyst part were provided in each of electrode catalyst layers 2 and 3 was explained, it does not restrict to this, and electrode catalyst layer Each of 2 and 3 may be provided with three or more electrode catalyst parts. When three or more electrode catalyst parts are provided in each of the electrode catalyst layers 2 and 3, the mass ratio of the fibrous material to the carbon particles is closer to the upstream side of the gas than the electrode catalyst part on the gas downstream side. It is preferable to make it smaller.

For example, the third electrode catalyst portion is formed as a mixing portion in which the catalyst ink for the first electrode catalyst portions 2a and 3a and the catalyst ink for the second electrode catalyst portions 2b and 3b are mixed. However, the third electrode catalyst portion may be composed of a composition different from the above-described configurations (a) and (b). However, when it comprises from composition different from the above-mentioned composition (a) and (b), it is preferred to make the 3rd electrode catalyst part into 20% or less of the area of the whole electrode catalyst layer. In addition, the boundary between the electrode catalyst portions may not be linear in plan view. The boundary may have a serpentine shape or the like.
In the membrane electrode assembly 11, the first electrode catalyst portion and the second electrode catalyst portion are formed only on one of the electrode catalyst layers 2 and 3 out of the electrode catalyst layers 2 and 3 formed on both sides of the polymer electrolyte membrane 1. An electrode catalyst portion may be provided.

When the first electrode catalyst portion and the second electrode catalyst portion are provided only in one of the electrode catalyst layers 2 and 3, the electrode catalyst layer having two electrode catalyst portions is an air electrode (where water is generated due to an electrode reaction) It is preferable to arrange on the cathode side. However, it is more preferable that the electrode catalyst layer having two electrode catalyst parts be formed on both sides of the polymer electrolyte membrane 1 from the viewpoint of water retention of the polymer electrolyte under low humidification conditions.
Further, in FIG. 1, the first electrode catalyst portion and the second electrode catalyst portion of the electrode catalyst layer 2 or 3 are divided into two by the same area (area ratio of the first electrode catalyst portion to the electrode catalyst layer 2 Shows an example of 50%), but is not limited thereto.

  The area ratio of the first electrode catalyst portion to the electrode catalyst layer 2 or 3 is preferably 15% or more and 60% or less from the viewpoint of gas reactivity. If the area ratio of the first electrode catalyst portion to the electrode catalyst layer 2 or 3 is less than 15%, the water retention effect under the low humidity condition is weak, and high power generation characteristics can not be obtained. In addition, when the area ratio of the first electrode catalyst portion to the electrode catalyst layer 2 or 3 exceeds 60%, the phenomenon of power generation reaction is stopped due to the obstruction of the material transport in the fuel electrode and the air electrode, so high power generation No property is obtained.

Next, examples of the invention relating to the present embodiment will be described.
[Adjustment of catalyst ink]
25 mass% polymer electrolyte solution containing a platinum-supported carbon catalyst having a mass density of 30 mass%, a fibrous material having an average fiber length of 1.5 μm, and a polymer electrolyte having an ion exchange capacity of 1.4 meq / g The mixture was mixed in a solvent and dispersed for 30 minutes in a planetary ball mill to prepare a first catalyst ink. The first catalyst ink has a mass ratio of the fibrous substance to the carbon particles of 0.3, and the mass ratio of the carbon particles to the fibrous substance and the polymer electrolyte is 1: 0.3: 1. .3.

Next, 25% by mass of a platinum-supported carbon catalyst having a supported density of 30% by mass, a fibrous material having an average fiber length of 1.5 μm, and a polymer electrolyte having an ion exchange capacity of 1.4 meq / g The molecular electrolyte solution was mixed in a solvent, and dispersion treatment was performed for 30 minutes in a planetary ball mill to prepare a second catalyst ink. The second catalyst ink has a mass ratio of the fibrous substance to the carbon particles of 0.5, and the mass ratio of the carbon particles, the fibrous substance and the polymer electrolyte is 1: 0.5: 1. .5.
The solvent of each catalyst ink was 1: 1 in the volume ratio of ultrapure water and 1-propanol. In addition, the solid content in each catalyst ink was adjusted to be 8% by mass.

[Formation of electrode catalyst layer]
The prepared catalyst ink was applied by a doctor blade method to a substrate of a polytetrafluoroethylene (PTFE) sheet, and dried at 80 ° C. in an air atmosphere. The coating amount of the first catalyst ink is adjusted so that the supported amount of platinum is 0.1 mg / cm ² as the fuel electrode (anode), and the supported amount of platinum is 0.3 mg / cm ² as the air electrode (cathode). To form an electrode catalyst layer (first electrode catalyst portion). In addition, the coating amount of the second catalyst ink is adjusted so that the supported amount of platinum is 0.1 mg / cm ² as the fuel electrode (anode), and the supported amount of platinum is 0.3 mg / cm ² as the air electrode (cathode). To form an electrode catalyst layer (second electrode catalyst part).

[Fabrication of membrane electrode assembly]
The substrate on which each electrode catalyst layer is formed is punched out to 5 cm × 2.5 cm, and the first electrode catalyst portion is disposed on the gas inlet side, and the second electrode catalyst portion is disposed on the gas outlet side. , 5 cm × 5 cm as an electrode catalyst layer. This electrode catalyst layer was disposed on both sides of the polymer electrolyte membrane 1 and hot pressing was performed under the conditions of a transfer temperature of 130 ° C. and a transfer pressure of 5.0 × 10 ⁶ Pa to obtain a membrane electrode assembly 11.

Comparative Example
[Adjustment of catalyst ink]
25 mass including a platinum-supported carbon catalyst having a mass density of 30% by mass, a fibrous substance having an average fiber length of 1.5 μm, and a polymer electrolyte having an ion exchange capacity of 1.4 meq / g as a polymer electrolyte solution % Polymer electrolyte solution was mixed in a solvent, and dispersion treatment was performed for 30 minutes with a planetary ball mill to prepare a catalyst ink. In the catalyst ink, the composition ratio of the carbon particles, the fibrous substance and the polymer electrolyte is 1: 0.4: 1.4 in mass ratio as the composition ratio of the mass ratio of the fibrous substance to the carbon particles is 0.4. did. The solvent of the catalyst ink was 1: 1 in the volume ratio of ultrapure water and 1-propanol. In addition, the solid content in the catalyst ink was adjusted to 8% by mass.
Thus, a catalyst ink was obtained. This catalyst ink is obtained by mixing and dispersing all components of the first catalyst ink and the second catalyst ink in the example at one time.

[Formation of electrode catalyst layer]
The prepared catalyst ink was applied by a doctor blade method to a substrate of a polytetrafluoroethylene (PTFE) sheet, and dried at 80 ° C. in an air atmosphere. The coating amount of the catalyst ink is adjusted so that the supported amount of platinum is 0.1 mg / cm ² as the fuel electrode (anode) and the supported amount of platinum is 0.3 mg / cm ² as the air electrode (cathode). Formed.
[Fabrication of membrane electrode assembly]
The substrate on which each electrode catalyst layer is formed is punched out to 5 cm × 5 cm, and this electrode catalyst layer is disposed on both sides of the polymer electrolyte membrane, under conditions of transfer temperature 130 ° C., transfer pressure 5.0 × 10 ⁶ Pa Hot pressing was performed to obtain a membrane electrode assembly.

<Evaluation>
[Power generation characteristics]
A carbon paper is pasted together as a gas diffusion layer so as to sandwich each membrane electrode assembly obtained in the example and the comparative example, installed in a power generation evaluation cell, and a current / voltage measurement using a fuel cell measuring device. went. The cell temperature at the time of measurement was 80 ° C., and the operating conditions were full humidification and low humidification shown below. In addition, hydrogen was used as the fuel gas, air was used as the oxidant gas, and flow 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 result〕
The membrane electrode assembly produced in the example exhibited superior power generation performance under the low humidification operating condition than the membrane electrode assembly produced in the comparative example. In addition, the membrane electrode assembly manufactured in the example had the power generation performance at the same level as the full humidification operating condition even under the low humidification operating condition. In particular, the power generation performance near the current density of 0.5 A / cm ² was improved. The cell voltage at a current density of 0.5 A / cm ² of the membrane electrode assembly manufactured in the example is 0.27 V compared to the cell voltage at a current density of 0.5 A / cm ² of the membrane electrode assembly manufactured in the comparative example. It showed high power generation characteristics.

From the results of the power generation characteristics of the membrane electrode assembly manufactured in the example and the membrane electrode assembly manufactured in the comparative example, the membrane electrode assembly of the example has a higher water retention, and the power generation characteristic under the low humidification operating condition is It has been confirmed that the power generation characteristics equivalent to the full humidification operating conditions are exhibited.
In addition, under the full humidification operating conditions, the cell voltage at a current density of 0.5 A / cm ² of the membrane electrode assembly produced in the example is the current density of 0.5 A / cm of the membrane electrode assembly produced in the comparative example. ^It showed a power generation characteristic 0.18 V higher than the cell voltage at ² .
From the results of the power generation characteristics of the membrane electrode assembly fabricated in the example and the membrane electrode assembly fabricated in the comparative example, the membrane electrode assembly fabricated in the example has high diffusivity of the reaction gas and is generated by the electrode reaction. It was confirmed that the removal of water was not inhibited.

  As mentioned above, although the embodiment of the present invention has been described in detail, the present invention is not limited to the above embodiment in fact, and the present invention is included in the present invention even if there are changes within the scope of the present invention.

DESCRIPTION OF SYMBOLS 1: Polymer electrolyte membrane 2: electrode catalyst layer 2a: first electrode catalyst unit 2b: second electrode catalyst unit 3: electrode catalyst layer 3a: first electrode catalyst unit 3b: second electrode catalyst unit 4: Gas diffusion layer 5 ... gas diffusion layer 6 ... air electrode (cathode)
7 ... Fuel electrode (anode)
8, 8a, 8b: gas flow channels 9, 9a, 9b: cooling water flow channels 10, 10a, 10b: separators 11: membrane electrode assembly 12: solid polymer fuel cell

Claims (5)

The polymer electrolyte membrane is sandwiched between a pair of 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,
As the relative arrangement of the first electrode catalyst portion and the second electrode catalyst portion, the inlet direction of the first electrode catalyst portion with respect to the flow direction of the gas flowing into the electrode catalyst layer And the second electrocatalyst portion is disposed at the outlet side of the flow direction,
Each of the first electrode catalyst portion and the second electrode catalyst portion includes catalyst-supporting particles consisting of carbon particles supporting a catalyst, a fibrous substance having an average fiber length of 1 μm to 15 μm, and a polymer electrolyte. Including
Regarding a mass ratio of the fibrous material to the carbon particles, a mass ratio of the second electrode catalyst portion is larger than a mass ratio of the first electrode catalyst portion. . The mass ratio in the first electrode catalyst portion is in the range of 0.1 or more and 1.2 or less,
The fuel cell membrane electrode assembly according to claim 1, wherein the mass ratio of the second electrode catalyst portion is in the range of 0.2 or more and 2.5 or less. The polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers,
Among the pair of electrode catalyst layers, at least one of the electrode catalyst layers comprises catalyst-supporting particles consisting of carbon particles supporting a catalyst, a fibrous substance having an average fiber length of 1 μm to 15 μm, and a polymer electrolyte Including
The mass ratio of the fibrous substance to the carbon particles in at least one of the pair of electrode catalyst layers is from the inlet side to the outlet side in the flow direction of the gas flowing into the electrode catalyst layer. What is claimed is: 1. A fuel cell membrane electrode assembly characterized by being continuously or stepwise increased.   A polymer electrolyte fuel cell comprising the fuel cell membrane electrode assembly according to any one of claims 1 to 3. A method of manufacturing a fuel cell membrane electrode assembly according to claim 1, wherein
A first catalyst ink is prepared by dispersing a catalyst-supporting particle comprising carbon particles supporting a catalyst, a fibrous substance having an average fiber length of 1 μm to 15 μm and a polymer electrolyte in a solvent, and the first catalyst ink After applying to a base material and drying to form the first electrode catalyst portion;
A second catalyst ink is prepared by dispersing, in a solvent, catalyst-supporting particles comprising carbon particles supporting a catalyst, a fibrous substance having an average fiber length of 1 μm to 15 μm, and a polymer electrolyte, and the second catalyst ink A second step of applying to the above-mentioned substrate and then drying to form the above-mentioned second electrode catalyst portion;
And laminating the electrode catalyst layer having the first and second electrode catalyst parts formed in the first and second steps on a polymer electrolyte membrane,
Performing the application such that the application region of the first catalyst ink and the application region of the second catalyst ink do not overlap the substrate;
In the stacking step, the first electrode catalyst portion is on the inlet side of the flow direction and the second electrode catalyst portion is on the outlet side of the flow direction with respect to the flow direction of the gas flowing into the electrode catalyst layer. Set as
The mass ratio of the fibrous substance to the carbon particles in the second catalyst ink is adjusted to be larger than the mass ratio of the fibrous substance to the carbon particles in the first catalyst ink The manufacturing method of the membrane electrode assembly for fuel cells characterized by the above-mentioned.

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