JP2020173935A - Membrane electrode assembly for fuel cell and solid polymer fuel cell - Google Patents

Abstract

To provide a membrane electrode assembly for a fuel cell and a solid polymer fuel cell in which drainage performance in a high current region where a large amount of generated water is generated is improved without impairing water retention under a low humidification condition, and high power generation performance and durability are exhibited even under a high humidification condition, and the manufacturing cost of an electrode catalyst layer is reduced.SOLUTION: A membrane electrode assembly for a fuel cell includes a polymer electrolyte membrane 1, and a pair of electrode catalyst layers 2 and 3 pinching the polymer electrolyte membrane 1 therebetween. At least one of the pair of electrode catalyst layers 2 and 3 contains catalyst-carrying particles, water-retaining fiber, and a polymer electrolyte.SELECTED DRAWING: Figure 1

Description

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

A fuel cell is a power generation system that uses a fuel gas containing hydrogen and an oxidant gas containing oxygen to 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 of fuel cells depending on the type of ionic conductor used, and a fuel cell 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, and are expected to be used as in-vehicle power supplies and household stationary power supplies. In recent years, various research and development have been carried out. ing. In the 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 arranged on both sides of a polymer electrolyte membrane is sandwiched between a pair of separators. It is a battery.
One separator has a gas flow path for supplying a fuel gas containing hydrogen to one of the electrodes, and the other separator has an oxidizing agent gas containing oxygen to the other of the electrodes. Gas flow path is formed.

Here, the above-mentioned one electrode to which the fuel gas is supplied is referred to as a fuel electrode, and the above-mentioned other electrode to which the oxidant gas is supplied is referred to as an air electrode. These electrodes include an electrode catalyst layer having carbon particles (catalyst-supported particles) carrying a catalyst such as a polymer electrolyte and a platinum-based noble metal, and a gas diffusion layer having both gas permeability and electron conductivity. There is. The gas diffusion layer constituting these electrodes is arranged so as to face the separator, that is, between the electrode catalyst layer and 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. One of them relates to the pores in the electrode catalyst layer. The pores in the electrode catalyst layer are located ahead of the separator through the gas diffusion layer and serve as a passage for transporting a plurality of substances. At the fuel electrode, the pores not only smoothly supply the fuel gas to the three-phase interface, which is the reaction field for redox, but also supply water for smoothly conducting the generated protons in the polymer electrolyte membrane. Fulfill function. At the air electrode, the pores serve to smoothly remove water generated by the electrode reaction as well as supply the oxidant gas.

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 water content close to the saturated water vapor pressure atmosphere, and currently, water is supplied from the outside by a humidifier.
On the other hand, in order to reduce power consumption and simplify the system, the development of a polymer electrolyte membrane that exhibits sufficient proton conductivity even under low humidification conditions that does not require a humidifier has been promoted. ing.

For example, as described in Patent Document 1, in order to improve the water retention 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 proposed. .. Patent Document 1 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.
Further, Patent Document 2 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.

Here, in the electrode catalyst layer with improved water retention, in the high current region where a large amount of generated water is generated, the power generation reaction is stopped or lowered due to the hindrance of substance transport in the fuel electrode and the air electrode, which is called "flooding". There is a problem that the phenomenon occurs. In order to prevent this, a configuration for improving drainage has been studied (see, for example, Patent Document 3, Patent Document 4, Patent Document 5, and Patent Document 6).

JP-A-2006-252948 JP-A-2007-141588 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

However, the fuel cell using the electrode catalyst layer obtained by these methods has room for improvement in terms of power generation performance and durability. Further, these methods are complicated, and there is also a problem that the manufacturing cost of the electrode catalyst layer is high.
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 and durability under low humidification conditions. Further, these methods are complicated, and there is room for improvement in reducing the manufacturing cost of the electrode catalyst layer.
The present invention has been made by paying attention to 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 the water retention under low humidification conditions is improved. However, it is an object of the present invention to provide a membrane electrode assembly for a fuel cell and a polymer electrolyte fuel cell, which exhibit high power generation performance and durability and reduce the manufacturing cost of an electrode catalyst layer.

In order to solve the problem, one aspect of the membrane electrode assembly of the present invention comprises a polymer electrolyte membrane and a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane, and the pair of electrode catalyst layers. At least one of the above contains catalyst-supporting particles, a polymer electrolyte, and water-retaining fibers having an average fiber length of 3 μm or more and 600 μm or less, and the mass of the water-retaining fibers is 0, which is the mass of the carrier in the catalyst-supporting particles. The gist is that it is 05 times or more and 1.0 times or less.
Further, one aspect of the polymer electrolyte fuel cell of the present invention is a fuel cell membrane electrode assembly, a pair of gas diffusion layers sandwiching the fuel cell membrane electrode assembly, and the fuel cell membrane electrode assembly. The gist is to include a body and a pair of separators facing each other with the pair of gas diffusion layers interposed therebetween.

According to one aspect of the membrane electrode assembly of the present invention, water retention under low humidification conditions is improved without inhibiting the removal of water generated by the electrode reaction, and high power generation performance even under low humidification conditions. It shows durability and can reduce the manufacturing cost of the electrode catalyst layer.
Further, according to one aspect of the polymer electrolyte fuel cell of the present invention, water retention under low humidification conditions is improved without inhibiting the removal of water generated by the electrode reaction, and under low humidification conditions. However, it exhibits high power generation performance and durability, and can reduce the manufacturing cost of the electrode catalyst layer.

It is an exploded perspective view which shows typically the membrane electrode assembly which has the electrode catalyst layer for a fuel cell which concerns on one 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.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
Here, the drawings are schematic, and the relationship between the thickness and the plane dimension, the ratio of the thickness of each layer, and the like are different from the actual ones. Further, the embodiments shown below exemplify a configuration for embodying the technical idea of the present invention, and the technical idea of the present invention describes the materials, shapes, structures, etc. of the constituent parts as follows. It is not specific to anything. The technical idea of the present invention may be modified in various ways within the technical scope specified by the claims stated in the claims.

[Membrane electrode assembly]
As shown in FIG. 1, the membrane electrode assembly 11 of the present embodiment includes a polymer electrolyte membrane 1 and a pair of electrode catalyst layers 2 and 3 that sandwich the polymer electrolyte membrane 1 from above and below.
Further, each electrode catalyst layer 2 and 3 includes catalyst-supporting particles and a polymer electrolyte. At least one of the pair of electrode catalyst layers 2 and 3 has an electrolyte fiber. Hereinafter, the electrode catalyst layer having an electrolyte fiber may be referred to as an “improved electrode catalyst layer”. It is preferable that both of the pair of electrode catalyst layers 2 and 3 are improved electrode catalyst layers.

The average fiber length of the water-retaining fibers contained in the improved electrode catalyst layer is 3 μm or more and 600 μm or less.
The average fiber diameter of the water-retaining fibers contained in the improved electrode catalyst layer is preferably 0.1 μm or more and 2.5 μm or less.
The average fiber diameter and average fiber length of the hydrophobic polymer fibers were calculated from five arbitrarily selected hydrophobic polymer fibers from the cross section imaged by a scanning electron microscope (SEM).
Further, the mass of the water-retaining fiber contained in the improved electrode catalyst layer is 0.05 times or more and 1.0 times or less the mass of the carrier in the catalyst-supporting particles.
The present invention has confirmed that the improved electrode catalyst layer having the following structure has drainage property, but the detailed mechanism having the drainage property is unknown. However, it is presumed as follows. The present invention is not bound by the following mechanism.

The improved electrode catalyst layer having the above configuration can obtain high durability and mechanical properties, such as suppressing the occurrence of cracks in the electrode catalyst layer, which causes a decrease in durability due to the entanglement of water-retaining fibers. Further, pores are formed in the electrode catalyst layer by the entanglement of the catalyst-supporting particles and the water-retaining fibers. It is presumed that the formed pores allow the water generated by the electrode reaction to be discharged in the high current region even in the electrode catalyst layer having enhanced water retention, and the diffusibility of the reaction gas can be enhanced. Further, the diffusibility of the reaction gas can be maintained by temporarily holding the excess generated water generated when the load fluctuates with the water retention fiber. On the other hand, when non-fibrous water-retaining particles are used, pores are less likely to be formed in the electrode catalyst layer because there is no entanglement with the catalyst-supporting particles, and in the electrode catalyst layer with improved water retention, water generated by the electrode reaction It is presumed that it is difficult to discharge and the diffusibility of the reaction gas cannot be increased in the high current range.

If the average fiber length of the water-retaining fibers is less than 3 μm, it is estimated that the mechanical properties may deteriorate due to the weak entanglement of the water-retaining fibers. Further, when the average fiber length of the water-retaining fibers exceeds 600 μm, it is presumed that the entanglement of the water-retaining fibers is strongly affected and the ink may not be dispersed as ink.
When the mass of the water-retaining fiber is less than 0.05 times the mass of the carrier in the catalyst-supporting particles, the water generated by the electrode reaction is sufficiently used in the high current region due to the influence of the small number of pores formed in the electrode catalyst layer. It is presumed that it may not be possible to drain water and increase the diffusivity of the reaction gas. Further, when the mass of the water-retaining fiber exceeds 1.0 times the mass of the carrier in the catalyst-supporting particles, the water-retaining property can be enhanced under low humidification conditions due to the influence of many pores formed in the electrode catalyst layer. It is estimated that it may be difficult.

When the average fiber diameter of the water-retaining fibers is less than 0.1 μm, it is presumed that pores may not be easily formed in the electrode catalyst layer due to the strong influence of the flexibility of the water-retaining fibers. Further, when the average fiber diameter of the water-retaining fiber exceeds 2.5 μm, it is estimated that the water-retaining fiber may not be dispersed as an ink due to the strong influence of the straightness.
According to the membrane electrode assembly 11 of the present embodiment, unlike the case where the drainage property is improved by changing the configuration of the electrode catalyst layer as in the conventional case, the power generation characteristic is 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, in the high current region where a large amount of generated water is generated, as compared with the conventional polymer electrolyte fuel cell provided with the membrane electrode assembly. The power generation characteristics of the

[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. An air electrode (cathode) 6 is formed by the electrode catalyst layer 2 and the gas diffusion layer 4. A fuel electrode (anode) 7 is formed by the electrode catalyst layer 3 and the gas diffusion layer 5.
Further, a set of separators 10a and 10b are arranged outside the gas diffusion layers 4 and 5, respectively. Each separator 10a and 10b is made of a conductive and impermeable material having gas flow paths 8a and 8b for gas flow and cooling water flow paths 9a and 9b for cooling water flow.

For example, hydrogen gas is supplied as the fuel gas to 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 to the gas flow path 8a of the separator 10a on the air electrode 6 side. An electromotive force can be generated between the fuel electrode 7 and the air electrode 6 by causing an electrode reaction between hydrogen as a fuel gas and oxygen as an oxidant gas in the presence of a catalyst.
In the polymer electrolyte fuel cell 12, the pair of separators 10a and 10b sandwich the polymer electrolyte membrane 1, the pair of electrode catalyst layers 2 and 3, and the pair of gas diffusion layers 4 and 5. The polymer electrolyte fuel cell 12 shown in FIG. 2 is an example of a fuel cell having a single cell structure, but is a polymer electrolyte fuel cell configured by stacking a plurality of cells via a separator 10a or a separator 10b. Even if there is, the present invention can be applied.

[Manufacturing method of electrode catalyst layer]
Next, an example of a method for manufacturing the improved electrode catalyst layer having the above configuration will be described.
The improved electrode catalyst layer is 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, water-retaining fibers, a polymer electrolyte, and a solvent.
The second step is a step of forming an improved electrode catalyst layer by applying the catalyst ink obtained in the first step onto a substrate and drying the solvent.
An electrode catalyst layer other than the improved electrode catalyst layer may be manufactured in the same process.
Then, the membrane electrode assembly 11 is obtained by attaching the produced pair of electrode catalyst layers 2 and 3 to the upper and lower surfaces of the polymer electrolyte membrane 1.

[Details]
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 any one having proton conductivity, and for example, a fluorine-based polymer electrolyte membrane or a hydrocarbon-based polymer electrolyte membrane can be used. Examples of fluorine-based polymer electrolyte membranes include Nafion (registered trademark) manufactured by DuPont, Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., AGClex (registered trademark) manufactured by Asahi Kasei Corporation, and Gore Select (registered trademark) manufactured by Gore. Etc. can be used.
Further, as the hydrocarbon-based polymer electrolyte membrane, for example, 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. Further, the catalyst ink for the improved electrode catalyst layer includes catalyst-supporting particles having a water-repellent coating, electrolyte fibers, a polymer electrolyte, and a solvent.
The polymer electrolyte contained in the catalyst ink may be any one having proton conductivity, and the same material as the polymer electrolyte membrane 1 can be used. For example, a fluorine-based polymer electrolyte and a hydrocarbon-based polymer can be used. Electrolytes 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, for example, 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.

As the catalyst used in the present embodiment (hereinafter, may be referred to as catalyst particles or catalyst), for example, a metal or an alloy thereof, an oxide, a double oxide, or the like can be used. Examples of the metal include platinum, palladium, ruthenium, iridium, rhodium, osmium, and other platinum group elements, as well as gold, iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. 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 particle size obtained by the X-ray diffractometry in the case of measurement with a catalyst supported on a carrier such as carbon particles. Further, in the case of measurement with a catalyst not supported on a carrier, it is the arithmetic mean particle size 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. As the carbon particles, for example, carbon black, graphite, graphite, activated carbon, carbon fiber, carbon nanotubes, and fullerenes can be used.
The average particle size of the carbon particles is preferably 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 particle size 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.

The catalyst-supporting particles described above may have a hydrophobic coating, and in this case, the film thickness is preferably such that the reaction gas can be sufficiently permeated. Specifically, the film thickness of the hydrophobic film is preferably 40 nm or less. If it is thicker than this, the supply of the reaction gas to the active site may be hindered. On the other hand, if the hydrophobic coating is 40 nm or less, the reaction gas is sufficiently permeated, so that the catalyst-supported particles can be imparted with hydrophobicity.
Further, the film thickness of the hydrophobic film provided on the catalyst-supporting particles is preferably a film thickness that sufficiently repels the generated water. Specifically, the film thickness of the hydrophobic film is preferably 2 nm or more. If it becomes thinner than this, the produced water may stay and the supply of the reaction gas to the active site may be hindered.

The hydrophobic film provided on the catalyst-supported particles is composed of a fluorine-based compound having at least one polar group. Examples of the polar group include a hydroxyl group, an alkoxy group, a carboxyl group, an ester group, an ether group, a carbonate group and an amide group. Due to the presence of polar groups, the fluorine-based compound can be immobilized on the outermost surface of the catalyst layer. The portion of the fluorine-based compound other than the polar group preferably has a structure composed of fluorine and carbon because of its high hydrophobicity and chemical stability. However, it is not limited to such a structure as long as it has sufficient hydrophobicity and chemical stability.

As the water-retaining fiber, fibers such as hydrophilic carbon, a water-absorbing polymer, a metal oxide, and a water-absorbing fiber having water retention as a single substance can be used. Further, as described above, a composite containing at least one single substance having water retention can also be used as the water retention fiber. By using these substances having high water retention as the water retention fiber, a high water retention effect can be obtained. Examples of the hydrophilized carbon include carbon fibers having a hydrophilic group introduced on the surface. As the water-absorbent polymer, silica gel, polyacrylic acid and the like can be used. Further, as the metal oxide, TiO2, SiO2 and the like can be used.
As the water retention fiber, only one of the above-mentioned fibers may be used, or two or more of them may be used.

The solvent used as the dispersion medium for the catalyst ink is particularly limited as long as it does not erode the catalyst substance-carrying 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 something. 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 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 substance-supporting 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-methyl taurine, potassium oleate / diethanolamine salt, alkyl ether sulfate tri. Ethanolamine salt, polyoxyethylene alkyl ether sulfate triethanolamine salt, amine salt of special modified polyether ester acid, amine salt of higher fatty acid derivative, amine salt of special modified polyester acid, amine salt of high molecular weight polyether ester acid , Special modified phosphoric acid ester 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 polyoxyethylene phosphate 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 surface activity such as alkylbenzene sulfonic acid, oil-soluble alkylbenzene sulfonic acid, α-olefin sulfonic acid, sodium alkylbenzene sulfonate, oil-soluble alkylbenzene sulfonate, α-olefin sulfonate, 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. As the dispersion time increases, the pore volume becomes smaller due to the destruction of aggregates of catalyst-supported particles.
If the solid content in the catalyst ink is too high, the viscosity of the catalyst ink becomes high, so that the surfaces of the electrode catalyst layers 2 and 3 are likely to be cracked. 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 consists of catalyst-supporting particles and a polymer electrolyte. When the content of the catalyst substance-supporting particles is increased in the solid content, the viscosity increases even with the same solid content. On the other hand, if the content of the catalyst substance-supporting particles in the solid content is reduced, the viscosity becomes low even with the same solid content. Therefore, the ratio of the catalyst substance-supporting 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 when dispersing the catalyst ink.
Further, the catalyst ink may contain a pore-forming agent. The pore-forming agent can form pores by removing it after the electrode catalyst layer is formed. Examples 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.

Examples of pore-forming agents that are soluble in acids, alkalis, and water include acid-soluble inorganic salts, inorganic salts that are soluble in alkaline aqueous solutions, metals that are soluble in acids or alkalis, water-soluble inorganic salts, and water-soluble organic compounds. Be done. Examples of acid-soluble inorganic salts include calcium carbonate, barium carbonate, magnesium carbonate, magnesium sulfate, magnesium oxide and the like. Examples of inorganic salts soluble in an alkaline aqueous solution include alumina, silica gel, and silica sol. Examples of metals soluble in acid or alkali include aluminum, zinc, tin, nickel and iron. Examples of the water-soluble inorganic salts include sodium chloride, potassium chloride, ammonium chloride, sodium carbonate, sodium sulfate, monosodium phosphate and the like. Examples of the water-soluble organic compounds include polyvinyl alcohol and polyethylene glycol.
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, for example, 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 such as polyimide, polyethylene terephthalate, polyamide (nylon (registered trademark)), polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyetherimide, polyarylate, polyethylene naphthalate, etc. The molecular film can be used as a transfer 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 separator 10 (10a, 10b), a carbon type, a metal type, or the like can be used. The gas diffusion layers 4 and 5 and the separators 10 (10a, 10b) may have an integral structure, respectively. Further, when the separators 10 (10a, 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.

<Action and others>
In this embodiment, a membrane electrode assembly 11 exhibiting high power generation characteristics under high humidification conditions, a method for manufacturing the membrane electrode assembly 11, and a polymer electrolyte fuel cell 12 including the membrane electrode assembly 11 are described. In the electrode catalyst layers 2 and 3 of the membrane electrode assembly 11 of the present embodiment, high durability and mechanical properties are obtained, such as suppressing cracking of the electrode catalyst layer which causes a decrease in durability due to entanglement of water-retaining fibers. Be done. Further, pores are formed in the electrode catalyst layer by the entanglement of the catalyst-supporting particles and the water-retaining fibers. Due to the formed pores, even in the electrode catalyst layer having enhanced water retention, water generated by the electrode reaction can be discharged in a high current region, and the diffusibility of the reaction gas can be enhanced. Further, the diffusibility of the reaction gas can be maintained by temporarily holding the excess generated water generated when the load fluctuates with the water retention fiber.
The membrane electrode assembly produced by the method for producing an electrode catalyst layer according to the present embodiment has improved drainage in a high current region where a large amount of generated water is generated without impairing water retention under low humidification conditions. In addition, it exhibits high power generation performance and durability even under high 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, the above-mentioned membrane electrode assembly is manufactured only by forming an electrode catalyst layer using a catalyst ink in which a platinum-supported carbon catalyst (catalyst-supported particles), a polymer electrolyte, and a water-retaining fiber are dispersed in a solvent. be able to.
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 by the above procedure. Therefore, for example, a humidifier. It can be operated without providing special means such as, and cost reduction can be achieved.

Only one of the electrode catalyst layers 2 and 3 formed on both sides of the polymer electrolyte membrane 1 may be used as the improved electrode catalyst layer. In that case, the improved electrode catalyst layer is preferably arranged on the air electrode (cathode) side where water is generated by the electrode reaction. However, from the viewpoint of drainage in a high current region, it is more preferable that the polymer electrolyte membrane 1 is formed on both surfaces.
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 is included in the present invention even if there are changes within a range that does not deviate from the gist of the present invention.

Hereinafter, a method for producing an improved electrode catalyst layer and a membrane electrode assembly for 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. However, this embodiment is not limited by the following examples and comparative examples.
In each of the following examples, the case where the pair of electrode catalyst layers are both used as the improved electrode catalyst layer is illustrated. Only one of the pair of electrode catalyst layers may be used as the improved electrode catalyst layer.

<Example 1>
[Preparation of catalyst ink]
A platinum-supported carbon catalyst (catalyst-supported particles) having a loading density of 50% by mass, a 25% by mass polymer electrolyte solution, and polyacrylic acid fibers (water-retaining fibers) having an average fiber length of 200 μm and an average fiber diameter of 1 μm. , Was mixed in a solvent and dispersed in a planetary ball mill. At this time, the dispersion time was set to 30 minutes, and the catalyst ink was prepared. The composition ratio of the starting material of the prepared catalyst ink was 0.2: 1: 0.6 in terms of mass ratio of polyacrylic acid fiber: carbon carrier: polymer electrolyte. The solvent of the catalyst ink was ultrapure water and 1-propanol in a volume ratio of 1: 1. Further, the solid content in the catalyst ink was adjusted to be 15% by mass.

〔Base material〕
A polytetrafluoroethylene (PTFE) sheet was used as a base material constituting the transfer sheet.
[Method of forming an electrode catalyst layer on a substrate]
The catalyst ink prepared above was applied onto a substrate by the doctor blade method and dried at 80 ° C. in an air atmosphere. The coating amount of the catalyst ink is 0.05 mg / cm ² for the electrode catalyst layer serving as the fuel electrode (anode) and 0.2 mg / cm ² for the electrode catalyst layer serving as the air electrode (cathode). Each was adjusted so as to be.

[Preparation of membrane electrode assembly]
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 120 ° C. and the transfer pressure was 5.0 × on both sides of the polymer electrolyte membrane. The membrane electrode assembly of the example was prepared by transfer under the condition of 10 ⁶ Pa.

<Comparative example 1>
[Preparation of catalyst ink]
The catalyst ink of Comparative Example 1 was prepared in the same manner as in Example 1 except that the polyacrylic acid fibers (water-retaining fibers) in Example 1 were replaced with polyacrylic acid particles having an average particle size of 0.3 μm. The composition ratio of the starting material of the prepared catalyst ink was 0.2: 1: 0.6 in terms of mass ratio of polyacrylic acid particles: carbon carrier: polymer electrolyte. The solvent of the catalyst ink was ultrapure water and 1-propanol in a volume ratio of 1: 1. Further, the solid content in the catalyst ink was adjusted to be 15% by mass.

〔Base material〕
A polytetrafluoroethylene (PTFE) sheet was used as a base material constituting the transfer sheet.
[Method of forming an electrode catalyst layer on a substrate]
The catalyst ink prepared above was applied onto a substrate by the doctor blade method and dried at 80 ° C. in an air atmosphere. The coating amount of the catalyst ink is 0.05 mg / cm ² for the electrode catalyst layer serving as the fuel electrode (anode) and 0.2 mg / cm ² for the electrode catalyst layer serving as the air electrode (cathode). Each was adjusted so as to be.

[Preparation of membrane electrode assembly]
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 120 ° C. and the transfer pressure was 5.0 × on both sides of the polymer electrolyte membrane. The membrane electrode assembly of Comparative Example 1 was prepared by transfer under the condition of 10 ⁶ Pa.

<Comparative example 2>
[Preparation of catalyst ink]
The catalyst ink of Comparative Example 2 was prepared in the same manner as in Example 1 except that it did not contain polyacrylic acid fibers (water-retaining fibers). The composition ratio of the starting material of the prepared catalyst ink was 1: 0.6 by mass ratio of carbon carrier: polymer electrolyte. The solvent of the catalyst ink was ultrapure water and 1-propanol in a volume ratio of 1: 1. Further, the solid content in the catalyst ink was adjusted to be 15% by mass.

〔Base material〕
A polytetrafluoroethylene (PTFE) sheet was used as a base material constituting the transfer sheet.
[Method of forming an electrode catalyst layer on a substrate]
The catalyst ink prepared as described above was applied onto the substrate by the doctor blade method and dried at 80 ° C. in an air atmosphere. The coating amount of the catalyst ink is 0.05 mg / cm ² for the electrode catalyst layer serving as the fuel electrode (anode) and 0.2 mg / cm ² for the electrode catalyst layer serving as the air electrode (cathode). Each was adjusted so as to be.

[Preparation of membrane electrode assembly]
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. It was transferred under the condition of 10 6 ^Pa, to prepare a membrane electrode assembly of Comparative example 2.

<Evaluation>
[Power generation characteristics]
A sample was prepared by laminating carbon paper as a gas diffusion layer so as to sandwich each membrane electrode assembly obtained in Examples and Comparative Examples 1 and 2. Then, each sample was installed in the power generation evaluation cell, and the current and voltage were measured using the fuel cell measuring device. The cell temperature at the time of measurement was 65 ° C., and the operating conditions were high humidification and low humidification as shown below. Further, hydrogen was flowed as a fuel gas at a flow rate at which the hydrogen utilization rate was 90%, and air was used as the oxidant gas at a flow rate at which the oxygen utilization rate was 40%. The back pressure was 50 kPa.

[Operating conditions]
Condition 1 (high humidification): Relative humidity Anode 90% RH, Cathode 80% RH
Condition 2 (low humidification): Relative humidity Anode 90% RH, Cathode 30% RH

〔Measurement result〕
The membrane electrode assembly produced in Example 1 showed superior power generation performance under highly humidified operating conditions as compared with the membrane electrode assembly produced in Comparative Examples 1 and 2. Further, the membrane electrode assembly produced in Example 1 had the same level of power generation performance as under the operating conditions of low humidification even under the operating conditions of high humidification. In particular, the power generation performance at a current density of around 1.5 A / cm ² was improved. The cell voltage at the current density of 1.5 A / cm ² of the membrane electrode assembly produced in Example 1 is 0 as compared with the cell voltage at the current density of 1.5 A / cm ² of the membrane electrode assembly produced in Comparative Example 1. It was .25V higher. Further, the membrane electrode assembly produced in Example 1 exhibited a power generation characteristic 0.27 V higher than the cell voltage at a current density of 1.5 A / cm ² of the membrane electrode assembly produced in Comparative Example 2.

From the results of the power generation characteristics of the membrane electrode assembly produced in Example 1 and the membrane electrode assembly prepared in Comparative Examples 1 and 2, the membrane electrode assembly of Example 1 has improved drainage and is under highly humidified operating conditions. It was confirmed that the power generation characteristics below show the same power generation characteristics as the operating conditions of low humidification.
Further, under low humidification operating conditions, the cell voltage at the current density of 1.5 A / cm ² of the membrane electrode assembly produced in Example 1 is the current density of 1.5 A of the membrane electrode assembly produced in Comparative Example 1. It was 0.28 V higher than the cell voltage at / cm ² . Further, the membrane electrode assembly produced in Example 1 exhibited a power generation characteristic 0.29 V higher than the cell voltage at a current density of 1.5 A / cm ² of the membrane electrode assembly produced in Comparative Example 2.
From the results of the power generation characteristics of the membrane electrode assembly prepared in Example 1 and the membrane electrode assembly prepared in Comparative Examples 1 and 2, in the membrane electrode assembly prepared in Example 1, the water produced by the electrode reaction It was confirmed that the drainage property was high and the water retention under low humidification conditions was not hindered.

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 (5)

A polymer electrolyte membrane and a pair of electrode catalyst layers that sandwich the polymer electrolyte membrane are provided.
A membrane electrode assembly for a fuel cell, wherein at least one of the pair of electrode catalyst layers contains catalyst-supporting particles, a polymer electrolyte, and a water-retaining fiber capable of holding water. The membrane electrode assembly for a fuel cell according to claim 1, wherein the mass of the water-retaining fiber is 0.05 times or more and 1.0 times or less the mass of the carrier in the catalyst-supporting particles. The membrane electrode assembly for a fuel cell according to claim 1 or 2, wherein the water-retaining fiber contains at least one of a hydrophilic carbon, a water-absorbent polymer, a metal oxide, and a water-absorbent fiber. The water-retaining fiber has an average fiber diameter of 0.1 μm or more and 2.5 μm or less.
The membrane electrode assembly for a fuel cell according to any one of claims 1 to 3, wherein the average fiber length is 3 μm or more and 600 μm or less. The membrane electrode assembly for a fuel cell according to any one of claims 1 to 4.
A pair of gas diffusion layers that sandwich the membrane electrode assembly for a fuel cell,
The membrane electrode assembly for a fuel cell and the pair of separators facing each other with the pair of gas diffusion layers interposed therebetween.
A solid polymer fuel cell characterized by being provided with.