JP6862827B2 - Electrode catalyst layer for fuel cells and its manufacturing method - Google Patents

Description

The present invention relates to an electrode catalyst layer for a fuel cell and a method for producing the same.

A fuel cell is a power generation system that uses a fuel gas containing hydrogen and an oxidant gas containing oxygen to cause an inverse reaction of electrolysis of water at an electrode containing a catalyst to generate electricity at the same time as heat. This power generation system has features such as high efficiency, low environmental load, and low noise as compared with the conventional power generation method, and is attracting attention as a clean energy source in the future. There are several types depending on the type of ionic conductor used, and a battery using a proton conductive polymer membrane is called a polymer electrolyte fuel cell.

Among fuel cells, polymer electrolyte fuel cells can be used near room temperature, so their use in in-vehicle power supplies and household power supplies is expected to be promising. In recent years, various researches and developments have been carried out. There is. In a polymer electrolyte fuel cell, a membrane electrode assembly (hereinafter sometimes referred to as MEA) in which a pair of electrode catalyst layers are arranged on both sides of a polymer electrolyte membrane is sandwiched between a pair of separator plates. It is a battery.
One separator plate is formed with a gas flow path for supplying a fuel gas containing hydrogen to one of the electrodes, and the other separator plate is provided with an oxidant gas containing oxygen to the other electrode. A gas flow path is formed for this purpose.
Here, the above-mentioned other electrode to which the fuel gas is supplied is referred to as a fuel electrode, and the above-mentioned one electrode to which the oxidizing agent gas is supplied is referred to as an air electrode. These electrodes include 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. .. Further, these electrodes are arranged so that the gas diffusion layer faces the separator.

For the electrode catalyst layer, efforts have been made to increase the gas diffusivity in order to improve the output density of the fuel cell. The pores in the electrode catalyst layer are located ahead of the separator plate through the gas diffusion layer and serve as 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 field of redox, but also functions to supply water for smoothly conducting the generated protons in the polymer electrolyte membrane. The air electrode functions to smoothly remove the water generated by the electrode reaction as well as to supply the oxidant gas.
In the polymer electrolyte fuel cell, in order to prevent the so-called "flooding" phenomenon in which the power generation reaction is stopped due to the obstruction of substance transport at the fuel electrode and the air electrode, a configuration for improving drainage has been studied. For example, see Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4).

In addition, issues for practical use of polymer electrolyte fuel cells include improvement of output density and durability, but the biggest issue is cost reduction (cost reduction).
One of the means of reducing the cost is to reduce the number of humidifiers. A perfluorosulfonic acid film or a hydrocarbon-based film is widely used for the polymer electrolyte membrane located at the center of the membrane electrode assembly. In order to obtain excellent proton conductivity, it is necessary to control the moisture content close to the saturated water vapor pressure atmosphere, and at present, the moisture is supplied from the outside by a humidifier. Therefore, in order to reduce power consumption and simplify the system, a polymer electrolyte membrane that exhibits sufficient proton conductivity even under low humidification conditions that does not require a humidifier is being developed. ..

However, in the electrode catalyst layer with improved drainage, the polymer electrolyte dries up under low humidification conditions, so it is necessary to optimize the electrode catalyst layer structure and improve water retention. So far, in order to improve the water retention of the fuel cell under low humidity 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 a 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 the catalyst electrode layer in contact with the polymer electrolyte membrane. In this method, a groove having a width of 0.1 to 0.3 mm is formed on the surface of the catalyst electrode layer to suppress a decrease in power generation performance under low humidification conditions.

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

According to the methods described in Patent Documents 5 and 6, the drainage property of the electrode catalyst layer is enhanced (does not hinder the removal of water generated by the electrode reaction), and at the same time, the water retention of the electrode catalyst layer under low humidification conditions is achieved. Can be expected to improve. However, the fuel cell using the electrode catalyst layer obtained by these methods has room for improvement in terms of power generation performance under low humidification conditions. Further, these methods are complicated, and there is also a problem that the manufacturing cost of the electrode catalyst layer is high.
An object of the present invention is an electrode catalyst layer for a fuel cell, which does not hinder the removal of water generated by an electrode reaction, has improved water retention under low humidification conditions, and exhibits high power generation performance even under low humidification conditions. To provide products that can be manufactured at low cost.

The first aspect of the present invention is an electrode catalyst layer for a fuel cell having the following configurations (1) and (2).
(1) A catalyst-supported particle composed of a carrier on which a catalyst is supported, carbon particles, and a first polymer electrolyte and a second polymer electrolyte having different ion exchange capacities are contained in a mixed state. The ion exchange capacity of the first polymer electrolyte is larger than the ion exchange capacity of the second polymer electrolyte.
(2) The first polymer electrolyte exists at a position close to the catalyst-supporting particles, and the second polymer electrolyte exists at a position away from the catalyst-supporting particles.

A second aspect of the present invention is a method for producing an electrode catalyst layer for a fuel cell having the following configurations (10) to (30).
(10) The first step of producing a catalyst ink containing catalyst-supported particles, carbon particles, a polymer electrolyte, and a solvent composed of a catalyst-supported carrier, and the catalyst ink is applied onto a substrate to dry the solvent. This includes a second step of forming the electrode catalyst layer.
(20) As the polymer electrolyte, the first polymer electrolyte and the second polymer electrolyte having different ion exchange capacities are used, and the ion exchange capacity of the first polymer electrolyte is the ion exchange capacity of the second polymer electrolyte. Greater.
In the (30) first step, (31) the first polymer electrolyte solution containing the first polymer electrolyte and the catalyst-supporting particles are mixed in a solvent, and the catalyst-supporting particles are dispersed. A second ink is prepared through the steps of producing an ink and (32) a process of mixing a second polymer electrolyte solution containing a second polymer electrolyte and carbon particles in a solvent to disperse the carbon particles. It has a step of mixing the first ink and the second ink, and a step of dispersing the solvent-supporting particles and the carbon particles.

According to the first aspect of the present invention, the electrode for a fuel cell shows improved water retention under low humidification conditions and high power generation performance even under low humidification conditions without inhibiting the removal of water generated by the electrode reaction. A catalyst layer is provided. According to the second aspect of the present invention, the electrode catalyst layer for a fuel cell of the first aspect can be manufactured at low cost.

It is an exploded perspective view which shows typically the membrane electrode assembly which has the electrode catalyst layer of embodiment of this invention. It is an exploded 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 accompanying 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 are added. The form of is also included in the scope of the present invention.

[Membrane electrode assembly]
First, a membrane electrode assembly having an electrode catalyst layer according to the embodiment of the present invention will be described with reference to FIG.
The membrane electrode assembly 11 shown in FIG. 1 has an electrode catalyst layer 2 (shown on the upper side in FIG. 1) that sandwiches the polymer electrolyte membrane 1 and the polymer electrolyte membrane 1 from the upper and lower surfaces of the polymer electrolyte membrane 1. And an electrode catalyst layer 3 (shown on the lower side in FIG. 1). Further, in the membrane electrode assembly 11, the two electrode catalyst layers 2 and 3 include catalyst-supporting particles and a polymer electrolyte.
At least one of the two electrode catalyst layers 2 and 3 has the following configurations (a) and (b).
(a) Includes catalyst-supported particles, carbon particles, a polymer electrolyte, and a first polymer electrolyte and a second polymer electrolyte having different ion exchange capacities. The ion exchange capacity of the first polymer electrolyte is larger than the ion exchange capacity of the second polymer electrolyte.
(b) The first polymer electrolyte is located close to the catalyst-supported particles, and the second polymer electrolyte is located away from the catalyst-supported particles.

The electrode catalyst layers 2 and 3 having the above configurations (a) and (b) can undergo electrode reaction even under low humidification conditions because the first polymer electrolyte having a large ion exchange capacity is present at a position close to the catalyst-supporting particles. The generated water can be retained. Further, the diffusivity of the reaction gas can be enhanced by the presence of the second polymer electrolyte having a small ion exchange capacity at a position away from the catalyst-supporting particles (that is, at a position close to the carbon particles).

The electrode catalyst layers 2 and 3 having the above configurations (a) and (b) preferably have the following configuration (c).
(c) The ion exchange capacity of the first polymer electrolyte is 0.9 meq / g or more and 3.0 meq / g or less, and the ion exchange capacity of the second polymer electrolyte is 0.8 meq / g or more and 2.8 meq / g. It is less than or equal to g.
When the ion exchange capacity of the first polymer electrolyte is less than 0.9 meq / g, it becomes difficult to retain water in the polymer electrolyte in the vicinity of the catalyst-supporting particles, and the catalytic activity may decrease. Further, when the ion exchange capacity of the first polymer electrolyte exceeds 3.0 meq / g, the polymer electrolyte in the vicinity of the catalyst-supporting particles retains water excessively, making it difficult to secure the diffusivity of the reaction gas. May become.

When the ion exchange capacity of the second polymer electrolyte is less than 0.8 meq / g, it becomes difficult to retain water in the polymer electrolyte in the vicinity of the carbon particles, and the proton conductivity may decrease. Further, when the ion exchange capacity of the second polymer electrolyte exceeds 3.0 meq / g, the polymer electrolyte that is not close to the catalyst-supporting particles retains water excessively, making it difficult to secure the diffusivity of the reaction gas. May become.
In the membrane electrode assembly 11, unlike the case where the conventional humidity control film is applied or the humidity is reduced by forming grooves on the surface of the electrode catalyst layer, the power generation characteristics are not deteriorated due to the increase in the interfacial resistance. As a result, according to the polymer electrolyte fuel cell provided with the membrane electrode assembly 11, the power generation characteristics under low humidification conditions are higher than those of the conventional polymer electrolyte fuel cell provided with the membrane electrode assembly. Become.

[Proton electrolyte fuel cell]
Next, the polymer electrolyte fuel cell provided with the membrane electrode assembly 11 of the embodiment will be described with reference to FIG.
The polymer electrolyte fuel cell 12 shown in FIG. 2 has a gas diffusion layer 4 on the air electrode side arranged so as to face the electrode catalyst layer 2 of the membrane electrode assembly 11 so as to face the electrode catalyst layer 3. It includes a gas diffusion layer 5 on the fuel electrode side to be arranged. 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.

Further, a set 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 are gas. It is arranged outside the diffusion layers 4 and 5, respectively.
For example, hydrogen gas is supplied as the 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 oxidizing agent gas from the gas flow path 8a of the separator 10a on the air electrode 6 side. By causing an electrode reaction between hydrogen as a fuel gas and oxygen as an oxidant gas in the presence of a catalyst, an electromotive force can be generated between the fuel electrode and the air electrode.
In the polymer electrolyte fuel cell 12, a set of separators 10a and 10b is sandwiched between a polymer electrolyte membrane 1, two electrode catalyst layers 2 and 3, and a gas diffusion layer 4 and 5. Although the polymer electrolyte fuel cell 12 is a fuel cell having a single cell structure, a plurality of cells may be laminated via a separator 10a or a separator 10b to form a polymer electrolyte fuel cell.

[Manufacturing method of electrode catalyst layer]
Next, a method for producing the electrode catalyst layers 2 and 3 having the above configurations (a) and (b) will be described.
The electrode catalyst layers 2 and 3 having the above configurations (a) and (b) are manufactured by a method including the following first step and second step.
The first step is a step of producing a catalyst ink containing catalyst-supporting particles, carbon particles, a polymer electrolyte, and a solvent, which consist of a carrier on which a catalyst is supported. In the first step, as the polymer electrolyte, a first polymer electrolyte and a second polymer electrolyte having different ion exchange capacities are used. The ion exchange capacity of the first polymer electrolyte is larger than the ion exchange capacity of the second polymer electrolyte.

The first step has the following three steps. In the first step, the first polymer electrolyte solution containing the first polymer electrolyte and the catalyst-supporting particles are mixed in a solvent, and the catalyst-supporting particles are dispersed to prepare the first ink. It is a process. The second step is a step of mixing a second polymer electrolyte solution containing the second polymer electrolyte and carbon particles in a solvent and dispersing the carbon particles to prepare a second ink. is there. The third step is a step of mixing the first ink and the second ink to disperse the catalyst-supported particles and the carbon particles.
The second step is a step of forming the electrode catalyst layers 2 and 3 by applying the catalyst ink obtained in the first step onto the substrate and drying the solvent.
Further, 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 can be obtained. Both of the electrode catalyst layers 2 and 3 may be manufactured by the above-mentioned method, or one may be manufactured by the above-mentioned method and the other may be manufactured by the conventional method.

[Details]
Hereinafter, the electrode joint 11 and the polymer electrolyte fuel cell 12 will be described in more detail.
The polymer electrolyte membrane 1 may be any one having proton conductivity, and a fluorine-based polymer electrolyte membrane and a hydrocarbon-based polymer electrolyte membrane can be used. Examples of fluorine-based polymer electrolyte membranes include DuPont's Nafion (registered trademark), Asahi Glass Co., Ltd.'s Flemion (registered trademark), Asahi Kasei Corporation's AGClex (registered trademark), and Gore's Gore Select (registered trademark). Etc. can be used.
Further, as the hydrocarbon-based polymer electrolyte membrane, an electrolyte membrane such as a sulfonated polyether ketone, a sulfonated polyether sulfone, a sulfonated polyether ether sulfone, a sulfonated polysulfide, or a sulfonated polyphenylene can be used. In particular, as the polymer electrolyte membrane 1, a Nafion (registered trademark) -based material manufactured by DuPont can be preferably used.

The electrode catalyst layers 2 and 3 are formed on both surfaces of the polymer electrolyte membrane 1 using catalyst ink. The catalyst ink for the electrode catalyst layers 2 and 3 contains catalyst-supporting particles, a polymer electrolyte, and a solvent. The catalyst ink used for at least one of the electrode catalyst layers 2 and 3 contains catalyst-supporting particles, carbon particles, two types of polymer electrolytes having different ion exchange capacities, and a solvent.
The polymer electrolyte contained in the catalyst ink may be any as long as it has proton conductivity, and the same material as that of the polymer electrolyte film 1 can be used, and a fluorine-based polymer electrolyte and a hydrocarbon-based polymer electrolyte can be used. Can be used. As an example of the fluorine-based polymer electrolyte, Nafion (registered trademark) -based material manufactured by DuPont can be used. Further, as the hydrocarbon-based polymer electrolyte, an electrolyte such as a sulfonated polyether ketone, a sulfonated polyether sulfone, a sulfonated polyether ether sulfone, a sulfonated polysulfide, or a sulfonated polyphenylene can be used. In particular, as the fluorine-based polymer electrolyte, a Nafion (registered trademark) -based material manufactured by DuPont can be preferably used.

Examples of the catalyst used in the present embodiment (hereinafter, may be referred to as catalyst particles or catalyst) include platinum, palladium, ruthenium, iridium, rhodium, osmium, and other platinum group elements, as well as iron, lead, copper, chromium, cobalt, and the like. Metals such as nickel, manganese, vanadium, molybdenum, gallium or aluminum or alloys, oxides or double oxides thereof can be used. The compound oxide referred to here refers to 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, the electrode reactivity is excellent and the electrode reaction can be performed efficiently and stably. 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 It is preferable because it exhibits high power generation characteristics.
The average particle size of the catalyst particles described above is preferably 0.5 nm or more and 20 nm or less, and more preferably 1 nm or more and 5 nm or less. Here, the average particle size is the average flow size obtained by the X-ray diffraction method if the catalyst is supported on a carrier such as carbon particles. If the catalyst is not supported on a carrier, it is the arithmetic mean flow diameter obtained from the particle size measurement. When the average particle size 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 improved, which is preferable.

Carbon particles are generally used as the electron-conducting powder (carrier) that carries the above-mentioned catalyst. The type of carbon particles is not limited as long as it is fine particles, has conductivity, and is not affected by a catalyst, but carbon black, graphite, graphite, activated carbon, carbon fiber, carbon nanotubes, and fullerenes should be used. Can be done.
The average particle size 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 the average flow diameter obtained from the SEM image. When the average particle size of the carbon particles is in the range of 10 nm or more and 1000 nm or less, 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 diffusibility of the two electrode catalyst layers 2 and 3 and the utilization rate of the catalyst are improved.
As the carbon particles (carbon particles that do not support a catalyst) contained in the second ink, the above-mentioned general carbon particles are used.

The solvent used as the dispersion medium for the catalyst ink is particularly limited as long as it does not erode the catalyst-supporting particles or the polymer electrolyte and can dissolve the polymer electrolyte in a highly fluid state or disperse it as a fine gel. It's not a thing. However, it is desirable that the solvent contains at least a volatile organic solvent.
Examples of solvents used as dispersion media for catalytic inks include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, pentanol and other alcohols, and acetone. , Methyl ethyl ketone, Pentanone, Methyl isobutyl ketone, Heptanone, Cyclohexanone, Methylcyclohexanone, Acetenylacetone, Diisobutylketone and other ketone solvents, tetrahydrofuran, Dioxane, Diethylene glycol dimethyl ether, Anisole, methoxytoluene, Dibutyl ether and other ether solvents, etc. Polar solvents such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, diacetone alcohol, 1-methoxy-2-propanol and the like can be used. Further, as the solvent, a mixed solvent in which two or more kinds of the above-mentioned materials are mixed may be used.

Further, as the solvent used as the dispersion medium of the catalyst ink, the solvent using the lower alcohol has a high risk of ignition. Therefore, when the lower alcohol is used, it is preferable to use a mixed solvent with water. Further, water having a good affinity with the polymer electrolyte (water having a high affinity) may be contained. The amount of water added is not particularly limited as long as the polymer electrolyte does not separate and cause cloudiness or gelation.
The catalyst ink may contain a dispersant in order to disperse the catalyst-supported particles. Examples of the dispersant include anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants and the like.

Examples of anionic surfactants include alkyl ether carboxylate, ether carboxylate, alkanoyl zarcosine, alkanoyl glutamate, acyl glutamate, oleic acid / N-methyltaurine, potassium oleate / diethanolamine salt, alkyl ether sulfate tri. Ethanolamine salt, polyoxyethylene alkyl ether sulfate triethanolamine salt, special modified polyether ester acid amine salt, higher fatty acid derivative amine salt, special modified polyester acid amine salt, high molecular weight polyether ester acid amine salt , Special modified phosphate amine salt, high molecular weight polyesteric acid amidamine salt, special fatty acid derivative amidamine salt, higher fatty acid alkylamine salt, high molecular weight polycarboxylic acid amidamine salt, sodium laurate, sodium stearate, oleic acid Carboxylic acid type surfactants such as sodium, dialkyl sulfosuccinate, dialkyl sulfosuccinate, 1,2-bis (alkoxycarbonyl) -1-ethanesulfonate, alkylsulfonate, alkylsulfonate, paraffin sulfonate, α-olefin sulfonate, linear alkylbenzene sulfonate, alkylbenzene sulfonate, polynaphthylmethane sulfonate, polynaphthylmethane sulfonate, naphthalene sulfonate-formalin condensate, alkylnaphthalene sulfonate, alkanoyl methyl tauride, lauryl sulfate sodium salt, cetyl sulfate Sulfonic acid type surfactants such as sodium salt, stearyl sulfate sodium salt, oleyl sulfate sodium salt, lauryl ether sulfate ester salt, sodium alkylbenzene sulfonate, oil-soluble alkylbenzene sulfonate, α-olefin sulfonate, alkyl sulfate Sulfates such as ester salts, alkyl sulfates, alkyl sulfates, alkyl ether sulfates, polyoxyethylene alkyl ether sulfates, alkyl polyethoxysulfates, polyglycol ether sulfates, alkyl polyoxyethylene sulfates, sulfated oils, highly sulfated oils, etc. Ester-type surfactant, phosphate (mono or di) alkyl salt, (mono or di) alkyl phosphate, (mono or di) alkyl phosphate ester salt, alkyl phosphate polyoxyethylene salt, alkyl ether phosphate, alkyl polyethoxy・ Re Phosphate, polyoxyethylene alkyl ether, alkylphenyl polyoxyethylene phosphate, alkylphenyl ether phosphate, alkylphenyl polyethoxy phosphate, polyoxyethylene alkylphenyl ether phosphate, higher alcohol phosphate mono Examples thereof include phosphoric acid ester-type surfactants such as ester disodium salt, higher alcohol phosphoric acid diester disodium salt, and zinc dialkyldithiophosphate.

Examples of cationic surfactants are benzyldimethyl {2- [2- (P-1,1,3,3-tetramethylbutylphenoxy) ethoxy] ethyl} ammonium chloride, octadecylamine acetate, tetradecylamine acetate. , Octadecyltrimethylammonium chloride, beef trimethylammonium chloride, dodecyltrimethylammonium chloride, coconut trimethylammonium chloride, hexadecyltrimethylammonium chloride, behenyltrimethylammonium chloride, coconut dimethylbenzylammonium chloride, tetradecyldimethylbenzylammonium chloride, octadecyldimethylbenzylammonium chloride , Dioleyl dimethylammonium chloride, 1-hydroxyethyl-2-beef imidazoline quaternary salt, 2-heptadecenyl-hydroxyethyl imidazoline, stearamide ethyl diethylamine acetate, stearamide ethyl diethylamine hydrochloride, triethanolamine monostearate Examples thereof include formates, alkylpyridium salts, higher alkylamine ethylene oxide adducts, polyacrylamideamine salts, modified polyacrylamideamine salts, and perfluoroalkyl quaternary ammonium iodide.

Examples of amphoteric surfactants include dimethyl coconut betaine, dimethyl lauryl betaine, sodium lauryl aminoethylglycine, sodium lauryl aminopropionate, stearyl dimethyl betaine, lauryl dihydroxyethyl betaine, amide betaine, imidazolinium betaine, lecithin, 3-[ Examples thereof include ω-fluoroalkanoyl-N-ethylamino] -1-propanesulfonate sodium, N- [3- (perfluorooctanesulfonamide) propyl] -N, N-dimethyl-N-carboxymethylene ammonium betaine and the like.

Examples of nonionic surfactants are 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), oleate diethanolamide (1: 1 type), hydroxyethyl laurylamine, polyethylene glycol laurylamine, polyethylene glycol palmamine, polyethylene glycol stearylamine, polyethylene glycol beef amine, polyethylene glycol beef propylenediamine, polyethylene glycol dioleylamine, Dimethyllaurylamine oxide, dimethylstearylamine oxide, dihydroxyethyllaurylamine oxide, perfluoroalkylamine oxide, polyvinylpyrrolidone, higher alcohol ethylene oxide adduct, alkylphenol ethylene oxide adduct, fatty acid ethylene oxide adduct, polypropylene glycol ethylene oxide adduct , Glycerin fatty acid ester, pentaerythlit fatty acid ester, sorbit fatty acid ester, sorbitan fatty acid ester, sugar fatty acid ester and the like.

Among the above-mentioned surfactants, sulfonic acid type surfactants such as alkylbenzene sulfonic acid, oil-soluble alkylbenzene sulfonic acid, α-olefin sulfonic acid, sodium alkylbenzene sulfonate, oil-soluble alkylbenzene sulfonate, α-olefin sulfonic acid salt, etc. The agent can be suitably used as a dispersant in consideration of the dispersion effect of carbon, the change in catalytic performance due to the residual dispersant, and the like.
Increasing the amount of polymer electrolyte in the catalyst ink generally reduces the pore volume. On the other hand, when the amount of carbon particles in the catalyst ink is increased, the pore volume becomes large. Also, when a dispersant is used, the pore volume becomes smaller.

Further, the catalyst ink is subjected to a dispersion treatment 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 treatment of the catalyst ink. The distributed processing can be performed by adopting various devices. In particular, the method of distributed processing is not limited. For example, examples of the dispersion treatment include treatment with a ball mill or roll mill, treatment with a shear mill, treatment with a wet mill, ultrasonic dispersion treatment, and the like. Further, a homogenizer or the like that agitates by centrifugal force may be adopted. The pore volume becomes smaller as the dispersion time becomes longer, because the agglomerates of the catalyst-supported particles are destroyed.

If the solid content in the catalyst ink is too large, the viscosity of the catalyst ink becomes high, so that cracks are likely to occur on the surfaces of the electrode catalyst layers 2 and 3. On the other hand, if the solid content in the catalyst ink is too small, the film formation 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-supported particles and a polymer electrolyte. If the content of the catalyst-supported particles is increased among the solid content, the viscosity increases even with the same solid content. On the other hand, if the content of the catalyst-supported particles in the solid content is reduced, the viscosity becomes low even with the same solid content. Therefore, the ratio of the catalyst-supported particles to the solid content is preferably 10% by mass or more and 80% by mass or less.

The viscosity of the catalyst ink is preferably about 0.1 cP or more and 500 cP or less (0.0001 Pa · s or more and 0.5 Pa · s or less), and 5 cP or more and 100 cP or less (0.005 Pa · s or more and 0.1 Pa · s or less). Is more preferable. Further, the viscosity can be controlled by adding a dispersant at the time of dispersing the catalyst ink.
Further, the catalyst ink may contain a pore-forming agent. The pore-forming agent can form pores by removing the pore-forming agent after forming the electrode catalyst layer. Examples thereof include acids, alkalis, substances that dissolve in water, sublimating substances such as camphor, and substances that thermally decompose. If the pore-forming agent is a substance that dissolves in warm water, it may be removed with water generated during power generation.

Acid-soluble inorganic salts such as calcium carbonate, barium carbonate, magnesium carbonate, magnesium sulfate and magnesium oxide, inorganic salts soluble in alkaline aqueous solutions such as alumina, silica gel and silica sol, and aluminum as pore-forming agents that are soluble in acids, alkalis and water. , Zinc, tin, nickel, iron and other acids and alkali-soluble metals, sodium chloride, potassium chloride, ammonium chloride, sodium carbonate, sodium sulfate, monosodium phosphate and other water-soluble inorganic salts, polyvinyl alcohol, polyethylene glycol Such as water-soluble organic compounds and the like can be mentioned. Further, the above-mentioned pore-forming agent may be used alone or in combination of two or more, but it is preferable to use two or more in combination.
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 and the like can be adopted.

A transfer sheet can be used as the base material used for producing the electrode catalyst layers 2 and 3.
The transfer sheet used as the base material may be any material having good transferability, for example, ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroper. Fluorine-based resins such as fluoroalkyl vinyl ether copolymer (PFA) and polytetrafluoroethylene (PTFE) can be used. In addition, polymer sheets and films such as polyimide, polyethylene terephthalate, polyamide (nylon), polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyetherimide, polyarylate, and polyethylene naphthalate are transferred. It can be used as a sheet.
When a transfer sheet is used as the base material, the transfer sheet is peeled off after the electrode film, which is the coating film after removing the solvent, is bonded to the polymer electrolyte membrane 1, and the electrode catalysts are applied to both surfaces of the polymer electrolyte membrane 1. The membrane electrode assembly 11 including the layers 2 and 3 can be obtained.

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, a porous carbon material such as carbon cloth, carbon paper, or non-woven fabric can be used.
As the separators 10a and 10b, carbon type or metal type separators can be used. The gas diffusion layers 4 and 5 and the separators 10a and 10b may have an integral structure, respectively. Further, when the separators 10a and 10b or the electrode catalyst layers 2 and 3 perform the functions of the gas diffusion layers 4 and 5, the gas diffusion layers 4 and 5 may be omitted. The polymer electrolyte fuel cell 12 can be manufactured by assembling a gas supply device, a cooling device, and other accompanying devices.
Hereinafter, the method for producing the electrode catalyst layer 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's not something.

<Example>
First, the first ink was produced by the following method.
A 20% by mass polymer electrolyte solution (first polymer) containing platinum-supported carbon particles (catalyst-supported particles) having a carrying density of 50% by mass and a first polymer electrolyte having an ion exchange capacity of 1.2 meq / g. Electrolyte solution) was mixed in a solvent and dispersed in a planetary ball mill for 10 minutes.
The platinum-supported carbon particles were those in which a platinum catalyst was supported on the carbon particles, and the compounding ratio of the carbon particles and the first polymer electrolyte was set to 1: 1 by mass ratio. The solvent was a mixed solvent of ultrapure water and 1-propanol, and the mixing ratio of both was 1: 1. The solid content in the ink was adjusted to be 10% by mass.

Next, the second ink was produced by the following method.
Carbon particles and a 20 mass% polymer electrolyte solution (second polymer electrolyte solution) containing a second polymer electrolyte having an ion exchange capacity of 1.0 meq / g are mixed in a solvent to form a planetary type. The dispersion treatment was performed for 10 minutes with a ball mill.
The compounding ratio of the carbon particles and the second polymer electrolyte was 1: 1 in terms of mass ratio. The solvent was a mixed solvent of ultrapure water and 1-propanol, and the mixing ratio of both was 1: 1. The solid content in the ink was adjusted to be 10% by mass.
Next, the first ink and the second ink were mixed so that the mass ratio of the first ink: the second ink was 2: 1 and the dispersion treatment was performed for 20 minutes with a planetary ball mill. As a result, a catalytic ink was obtained.

The obtained catalyst ink was applied on a base material of a polytetrafluoroethylene (PTFE) sheet by a doctor blade method, and dried in an air atmosphere at 80 ° C. ^{The amount of catalyst ink applied is 0.1 mg / cm 2} for the electrode catalyst layer that serves as the fuel electrode (anode) and ^{0.3 mg / cm 2} for the electrode catalyst layer that serves as the air electrode (cathode). Each was adjusted so as to be. The base material on which the electrode catalyst layer as the anode and the base material on which the electrode catalyst layer as the cathode was formed were punched to 5 cm × 5 cm, respectively, and the transfer temperature was 130 ° C. and the transfer pressure was 5.0 × on both sides of the polymer electrolyte membrane. A membrane electrode assembly was prepared by transferring under the condition of ^{10 6 Pa.}

<Comparison example>
[Adjustment of catalyst ink]
A 20% by mass polymer electrolyte solution (first polymer) containing platinum-supported carbon particles (catalyst-supported particles) having a carrying density of 50% by mass and a first polymer electrolyte having an ion exchange capacity of 1.2 meq / g. Electrolyte solution), carbon particles, and a 20 mass% polymer electrolyte solution (second polymer electrolyte solution) containing a second polymer electrolyte having an ion exchange capacity of 1.0 meq / g in a solvent. The mixture was mixed and dispersed in a planetary ball mill for 30 minutes.
The compounding ratio of the carbon particles (carrier) of the platinum-supported carbon particles, the carbon particles, the first polymer electrolyte, and the second polymer electrolyte is calculated by the mass ratio, and the carrier: carbon particles: the first polymer electrolyte. : Second polymer electrolyte = 2: 1: 2: 1. The solvent was a mixed solvent of ultrapure water and 1-propanol, and the mixing ratio of both was 1: 1. The solid content in the ink was adjusted to be 10% by mass.
As a result, a catalytic ink was obtained. This catalyst ink has the same composition as in the examples, but unlike the examples, it is obtained by mixing and dispersing all the components at once.
The obtained catalyst ink was applied onto a substrate and then dried to prepare a membrane electrode assembly. The membrane electrode assembly was prepared in the same manner as in the examples.

<Evaluation>
[Power generation characteristics]
Carbon paper is laminated as a gas diffusion layer so as to sandwich each membrane electrode assembly obtained in Examples and Comparative Examples, installed in a power generation evaluation cell, and current / voltage measurement is performed 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 as shown below. In addition, hydrogen was used as the fuel gas and air was used as the oxidant gas, and the flow rate was controlled 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 humidification): Relative humidity Anode 30% RH, Cathode 30% RH

〔Measurement result〕
The membrane electrode assembly prepared in the example showed superior power generation performance under low humidification operating conditions as compared with the membrane electrode assembly prepared in the comparative example. In addition, the membrane electrode assembly produced in the examples had the same level of power generation performance as the operating conditions of full humidification even under the operating conditions of low humidification. In particular, the power generation performance at a current density of around 0.5 A / cm ^{2 was improved.} The cell voltage at a current density of 0.5A / cm ² of the membrane electrode assembly produced in Example, as compared with the cell voltage at a current density of 0.5A / cm ² of the membrane electrode assembly fabricated in Comparative Example 0.23V It showed high power generation characteristics.
From the results of the power generation characteristics of the membrane electrode assembly prepared in the example and the membrane electrode assembly prepared in the comparative example, the membrane electrode assembly of the example has increased water retention, and the power generation characteristics under low humidification operating conditions are improved. It was confirmed that the power generation characteristics were equivalent to those under the operating conditions of full humidification.
Further, under the operating conditions of full humidification, ^{the cell voltage at the current density of 0.5 A / cm 2} of the membrane electrode assembly produced in the example was 0.5 A / cm in the current density of the membrane electrode assembly produced in the comparative example. ^It showed a power generation characteristic 0.18V higher than the cell voltage in 2.
From the results of the power generation characteristics of the membrane electrode assembly prepared in the example and the membrane electrode assembly prepared in the comparative example, the membrane electrode assembly prepared in the example has high diffusibility of the reaction gas and is generated by the electrode reaction. It was confirmed that the removal of the water was not hindered.

<Summary>
In this embodiment, a membrane electrode assembly 11 exhibiting high power generation characteristics under low humidification conditions, a manufacturing method thereof, and a polymer electrolyte fuel cell 12 including the membrane electrode assembly are described.
In the electrode catalyst layers 2 and 3 of the membrane electrode assembly 11 of the present embodiment, the ion exchange capacity of the polymer electrolyte close to the catalyst-supporting particles is larger than the ion exchange capacity of the polymer electrolyte close to the carbon particles.

The membrane electrode assembly produced by the method for producing an electrode catalyst layer according to the present embodiment enhances water retention without inhibiting removal of water generated by the electrode reaction, and exhibits high power generation characteristics even under low humidification conditions. .. Further, the method for producing the electrode catalyst layer according to the present embodiment can efficiently and economically easily produce the membrane electrode assembly as described above.
That is, a first catalyst ink in which catalyst-supporting particles and a first polymer electrolyte solution are dispersed in a solvent, and a second catalyst ink in which carbon particles and a second polymer electrolyte solution are dispersed in a solvent are used. The above-mentioned film electrode junction can be produced only by mixing each of them and forming an electrode catalyst layer using this catalyst ink.
Therefore, it can be manufactured without complicated manufacturing steps, and both water retention and diffusibility of the reaction gas can be improved by using the electrode catalyst layer prepared in the above procedure. Therefore, for example, a humidifier. It can be operated without providing special means such as, and cost reduction can be achieved.

In addition, only one of the electrode catalyst layers 2 and 3 formed on both sides of the polymer electrolyte membrane 1 may be used as an electrode catalyst layer using the catalyst ink produced in the first step. In that case, it is preferable that the electrode catalyst layer using the catalyst ink produced in the first step is arranged on the air electrode (cathode) side where water is generated by the electrode reaction. However, from the viewpoint of retaining water in the polymer electrolyte under low humidification conditions, it is more preferable that the polymer electrolyte membrane 1 is formed on both sides.
Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and even if there are changes within the scope of the present invention, the present invention includes the embodiments.

1 ... Polymer electrolyte membrane 2 ... Electrode catalyst layer 3 ... Electrode catalyst layer 4 ... Gas diffusion layer 5 ... Gas diffusion layer 6 ... Air electrode (cathode)
7 ... Fuel electrode (anode)
8a, 8b ... Gas flow path 9a, 9b ... Cooling water flow path 10a, 10b ... Separator 11 ... Membrane electrode assembly 12 ... Solid polymer fuel cell

Claims (3)

A catalyst-supported particle composed of a carrier on which a catalyst is supported, carbon particles, and a first polymer electrolyte and a second polymer electrolyte having different ion exchange capacities are contained in a mixed state.
The ion exchange capacity of the first polymer electrolyte is larger than the ion exchange capacity of the second polymer electrolyte.
The first polymer electrolyte is present at a position close to the catalyst-supporting particles, and the second polymer electrolyte is located at a position away from the catalyst-supporting particles. The ion exchange capacity of the first polymer electrolyte is 0.9 meq / g or more and 3.0 meq / g or less, and the ion exchange capacity of the second polymer electrolyte is 0.8 meq / g or more and 2.8 meq / g. The electrode catalyst layer for a fuel cell according to claim 1, which is as follows. The first step of producing a catalyst ink containing catalyst-supported particles, carbon particles, a polymer electrolyte, and a solvent composed of a catalyst-supported carrier, and applying the catalyst ink onto a substrate to dry the solvent. Including the second step of forming the electrode catalyst layer in
As the polymer electrolyte, a first polymer electrolyte and a second polymer electrolyte having different ion exchange capacities are used, and the ion exchange capacity of the first polymer electrolyte is the ion exchange capacity of the second polymer electrolyte. Larger
The first step is
A step of mixing the first polymer electrolyte solution containing the first polymer electrolyte and the catalyst-supporting particles in the solvent and dispersing the catalyst-supporting particles to prepare a first ink.
A step of mixing the second polymer electrolyte solution containing the second polymer electrolyte and the carbon particles in the solvent and dispersing the carbon particles to prepare a second ink.
A step of mixing the first ink and the second ink to disperse the catalyst-supporting particles and the carbon particles.
A method for manufacturing an electrode catalyst layer for a fuel cell.

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