JP7131274B2 - Membrane electrode assembly for fuel cell and polymer electrolyte fuel cell - Google Patents

Description

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

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

Among fuel cells, polymer electrolyte fuel cells are expected to be used as power sources for automobiles and homes because they can be used at around room temperature. ing. A polymer electrolyte fuel cell has 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, sandwiched between a pair of separators. Battery.
One separator is formed with a gas flow path for supplying a hydrogen-containing fuel gas to one of the electrodes, and the other separator is formed for supplying an oxygen-containing oxidant gas to the other electrode. of gas flow paths are formed.

Here, the one electrode to which the fuel gas is supplied is the fuel electrode, and the other electrode to which the oxidant gas is supplied is the air electrode. These electrodes comprise a polymer electrolyte, an electrode catalyst layer having carbon particles (catalyst-carrying particles) supporting a catalyst such as a platinum-based noble metal, and a gas diffusion layer having both gas permeability and electronic conductivity. there is The gas diffusion layers that make up these electrodes are arranged so as to face the separator, that is, between the electrode catalyst layer and the separator.

Efforts have been made to improve the gas diffusibility of the electrode catalyst layer in order to improve the power density of the fuel cell. One of them relates to pores in the electrode catalyst layer. Pores in the electrode catalyst layer are located beyond the separator through the gas diffusion layer and serve as passageways for transporting multiple substances. In the fuel electrode, the pores not only smoothly supply the fuel gas to the three-phase interface, which is the redox reaction field, but also supply water to smoothly conduct the generated protons in the polymer electrolyte membrane. fulfill a function. In the air electrode, the pores fulfill the function of smoothly removing the water produced by the electrode reaction as well as the supply of the oxidant gas.

In addition, while the challenges for commercialization of polymer electrolyte fuel cells include improvements in output density and durability, the biggest challenge is cost reduction (cost reduction).
One of the means for this cost reduction is the reduction of humidifiers. Perfluorosulfonic acid membranes and hydrocarbon-based membranes are widely used for the polymer electrolyte membrane positioned at the center of the membrane electrode assembly. In order to obtain excellent proton conductivity, it is necessary to manage moisture close to the saturated water vapor pressure atmosphere, and at present, moisture is supplied from the outside using a humidifier.
On the other hand, in order to reduce power consumption and simplify the system, development of a polymer electrolyte membrane that exhibits sufficient proton conductivity even under low humidification conditions, such as not requiring a humidifier, has been promoted. ing.

For example, as described in Patent Document 1, a method of sandwiching a humidity control film between an electrode catalyst layer and a gas diffusion layer has been proposed in order to improve the water retentivity of a fuel cell under low humidity conditions. . Patent Literature 1 describes a method for preventing dry-up by exhibiting a humidity control function with a humidity control film composed of conductive carbonaceous powder and polytetrafluoroethylene.
Further, Patent Document 2 describes a method of forming grooves on the surface of a catalyst electrode layer that contacts a 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, thereby suppressing deterioration in power generation performance under low humidity conditions.

However, in an electrode catalyst layer with enhanced water retention, in a high current region where a large amount of water is generated, the power generation reaction is stopped or reduced due to obstruction of material transport at the fuel electrode and the air electrode, a phenomenon called "flooding". There is a problem that occurs. In order to prevent this, constructions that improve drainage have been studied (see, for example, Patent Documents 3, 4, 5, and 6).
However, fuel cells using electrode catalyst layers obtained by these methods have room for improvement in terms of power generation performance and durability. Moreover, these methods are complicated, and there is also the problem that the manufacturing cost of the electrode catalyst layer is high.

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

The present invention has been made with a focus on the above points, and improves drainage in a high current region where a lot of water is generated without impeding water retention under low humidification conditions, and An object of the present invention is to provide a fuel cell membrane electrode assembly and a polymer electrolyte fuel cell that exhibit high power generation performance and durability even under highly humidified conditions.

In order to solve the problem, a fuel cell membrane electrode assembly according to one aspect of the present invention includes a polymer electrolyte membrane and a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane. At least one of the catalyst layers contains catalyst-carrying particles with a hydrophobic coating, a polymer electrolyte, and a fibrous material having an average fiber diameter of 10 nm or more and 300 nm or less, and the mass of the fibrous material is the catalyst The gist is that it is 0.2 to 1.0 times the mass of the carrier in the carrier particles.

According to the membrane electrode assembly of one aspect of the present invention, the membrane electrode includes an electrode catalyst layer that increases water retention without hindering the removal of water generated by an electrode reaction and exhibits high power generation properties even under low humidity conditions. It is possible to form a bonded body and provide a polymer electrolyte fuel cell having high power generation characteristics.

1 is an exploded perspective view schematically showing a membrane electrode assembly having a fuel cell electrode catalyst layer according to an embodiment of the present invention; FIG. FIG. 2 is an exploded perspective view schematically showing the structure of a polymer electrolyte fuel cell provided with the membrane electrode assembly of FIG. 1;

Embodiments of the present invention will be described below with reference to the accompanying drawings.
Here, the drawings are schematic, and the relationship between the thickness and the planar dimension, the ratio of the thickness of each layer, and the like are different from the actual ones. Further, the embodiments shown below are examples of configurations for embodying the technical idea of the present invention. It is not specific to a thing. Various modifications can be made to the technical idea of the present invention within the technical scope defined by the claims.

[Membrane electrode assembly]
As shown in FIG. 1, a membrane electrode assembly 11 of this embodiment includes a polymer electrolyte membrane 1 and a pair of electrode catalyst layers 2 and 3 sandwiching the polymer electrolyte membrane 1 from above and below.
Further, each of the electrode catalyst layers 2, 3 comprises catalyst-carrying particles and a polymer electrolyte. At least one electrode catalyst layer (hereinafter also referred to as an improved electrode catalyst layer) of the pair of electrode catalyst layers 2 and 3 has a fibrous substance. Both of the pair of electrode catalyst layers 2 and 3 are preferably improved electrode catalyst layers.

In the improved electrocatalyst layer, the catalyst-supporting particles are provided with a hydrophobic coating.
The fibrous substance contained in the improved electrode catalyst layer has an average fiber diameter of 10 nm or more and 300 nm or less. The average fiber diameter of the fibrous substance is preferably 100 nm or more and 200 nm or less. The average fiber length of the fibrous substance is preferably 0.7 μm or more and 20 μm or less.
Further, in the improved electrode catalyst layer, the mass of the fibrous material is 0.2 times or more and 1.0 times or less the mass of the carrier in the catalyst-carrying particles provided with the hydrophobic coating. The mass of the fibrous substance is preferably 0.4 to 0.8 times the mass of the carrier in the catalyst-carrying particles provided with a hydrophobic coating.
The inventors have confirmed that the improved electrode catalyst layer having the above structure has drainage properties, but the detailed mechanism of the drainage properties is unknown. However, it is estimated as follows. The present invention is in no way bound by the mechanism presumed below.

The improved electrode catalyst layer having the above structure can obtain high durability and mechanical properties such as suppression of cracking of the electrode catalyst layer, which causes deterioration of durability, due to the entanglement of fibrous substances. In addition, since the catalyst-supporting particles provided with a hydrophobic coating have an affinity for hydrophobic fibrous substances, pores are formed in the electrode catalyst layer due to the entanglement of the catalyst-supporting particles and the fibrous substances. It is presumed that the formed pores enable the water generated by the electrode reaction to be discharged in a high current region even in an electrode catalyst layer with enhanced water retention, and the diffusivity of the reaction gas can be enhanced. On the other hand, when catalyst-supporting particles not provided with a hydrophobic coating are used, the catalyst-supporting particles become hydrophilic and have no affinity with fibrous substances that exhibit hydrophobicity. , the catalyst-supporting particles are filled. Therefore, it is difficult to form pores in the electrode catalyst layer, and in the electrode catalyst layer with enhanced water retention, it is difficult to discharge the water generated by the electrode reaction, and it is difficult to increase the diffusivity of the reaction gas in the high current region. Presumed.

If the average fiber diameter of the fibrous material is less than 10 nm, it is presumed that pores are difficult to form in the electrode catalyst layer due to the strong bendability of the fibrous material. In addition, when the average fiber diameter of the fibrous substance exceeds 300 nm, it is presumed that the fibrous substance may not be dispersed as an ink due to the strong influence of the linearity of the fibrous substance.
If the mass of the fibrous material is less than 0.4 times the mass of the support in the catalyst-supporting particles provided with a hydrophobic coating, the electrode reaction does not occur in the high-current region due to the effect of fewer pores formed in the electrode catalyst layer. It is presumed that there are cases where the water produced in 1 cannot be sufficiently drained and the diffusivity of the reaction gas cannot be enhanced. In addition, when the mass of the fibrous substance exceeds 0.8 times the mass of the carrier in the catalyst-carrying particles with a hydrophobic coating, many pores are formed in the electrode catalyst layer. It is presumed that there are cases where it is difficult to increase water retention.

If the average fiber length of the fibrous material is less than 0.7 μm, it is presumed that the mechanical properties may deteriorate due to weak entanglement of the fibrous material. Further, when the average fiber length of the fibrous substance exceeds 20 μm, it is presumed that the entanglement of the fibrous substance is strongly influenced, and it may not be possible to disperse the ink as an ink.
According to the membrane electrode assembly 11 of the present embodiment, unlike the conventional case where the drainability is improved by changing the configuration of the electrode catalyst layers, deterioration in power generation characteristics due to an increase in interfacial resistance is not observed. As a result, according to the polymer electrolyte fuel cell including the membrane electrode assembly 11, in a high current region in which a large amount of water is generated, compared to a conventional polymer electrolyte fuel cell including a membrane electrode assembly. power generation characteristics are enhanced.

[Polymer electrolyte fuel cell]
Next, a polymer electrolyte fuel cell provided with the membrane electrode assembly 11 of the embodiment will be described with reference to FIG.
The polymer electrolyte fuel cell 12 shown in FIG. and a gas diffusion layer 5 disposed on the fuel electrode side. 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 .
A set of separators 10a, 10b are also arranged outside the gas diffusion layers 4 and 5, respectively. Each of the separators 10a, 10b is made of an electrically conductive and impermeable material having gas passages 8a, 8b for gas circulation and cooling water passages 9a, 9b for cooling water circulation.

For example, hydrogen gas is supplied as a fuel gas to the gas flow path 8b of the separator 10b on the fuel electrode 7 side. On the other hand, oxygen gas, for example, is supplied as an oxidant 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 the hydrogen of the fuel gas and the oxygen of the oxidizing gas in the presence of a catalyst.
In the polymer electrolyte fuel cell 12, a pair of separators 10a and 10b sandwich a polymer electrolyte membrane 1, a pair of electrode catalyst layers 2 and 3, and a pair of gas diffusion layers 4 and 5. FIG. The polymer electrolyte fuel cell 12 shown in FIG. 2 is an example of a fuel cell with a single cell structure. Even if there is, the present invention can be applied.

[Method for producing electrode catalyst layer]
Next, an example of a method for manufacturing the improved electrode catalyst layer having the above structure 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 to prepare a catalyst ink comprising catalyst-carrying particles with a hydrophobic coating, a fibrous material, a polyelectrolyte, 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 also be manufactured in the same process.
Then, the pair of electrode catalyst layers 2 and 3 thus produced are attached to the upper and lower surfaces of the polymer electrolyte membrane 1 to obtain the membrane electrode assembly 11 .

〔detail〕
The membrane electrode assembly 11 and polymer electrolyte fuel cell 12 will be described in more detail below.
As the polymer electrolyte membrane 1, any one having proton conductivity may be used, and for example, a fluorine-based polymer electrolyte membrane or a hydrocarbon-based polymer electrolyte membrane may 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., Aciplex (registered trademark) manufactured by Asahi Kasei Corporation, and Gore Select (registered trademark) manufactured by Gore. etc. can be used.
As the hydrocarbon-based polymer electrolyte membrane, for example, electrolyte membranes such as sulfonated polyetherketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used. In particular, Nafion (registered trademark)-based materials manufactured by DuPont can be preferably used as the polymer electrolyte membrane 1 .

The electrode catalyst layers 2 and 3 are formed on both sides of the polymer electrolyte membrane 1 using catalyst ink. The catalyst ink for the electrode catalyst layers 2 and 3 contains catalyst-carrying particles, a polymer electrolyte and a solvent. Also, the catalyst ink for the improved electrocatalyst layer includes catalyst-carrying particles with a water-repellent coating, a fibrous material, a polymer electrolyte, and a solvent.
As the polymer electrolyte contained in the catalyst ink, any material having proton conductivity can be used, and the same material as the polymer electrolyte membrane 1 can be used. Electrolytes can be used. As an example of the fluorine-based polymer electrolyte, a Nafion (registered trademark)-based material manufactured by DuPont can be used. As the hydrocarbon polymer electrolyte, for example, electrolytes such as sulfonated polyetherketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used. In particular, a Nafion (registered trademark)-based material manufactured by DuPont can be preferably used as the fluorine-based polymer electrolyte.

As the catalyst (hereinafter sometimes referred to as catalyst particles or catalyst) used in the present embodiment, for example, metals, alloys thereof, oxides or multiple oxides can be used. Examples of metals include platinum group elements such as platinum, palladium, ruthenium, iridium, rhodium, and osmium, as well as gold, iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. Note that the composite oxide referred to here means an oxide composed of two kinds of metals.
When the catalyst particles are one or more metals selected from platinum, gold, palladium, rhodium, ruthenium, and iridium, the electrode reactivity is excellent and the electrode reaction can be efficiently and stably performed. can. When the catalyst particles are one or more metals selected from platinum, gold, palladium, rhodium, ruthenium, and iridium, the polymer electrolyte fuel cell 12 provided with the electrode catalyst layers 2 and 3 is It is preferable because it exhibits high power generation characteristics.

Further, the average particle diameter of the catalyst particles described above is preferably 0.5 nm or more and 20 nm or less, more preferably 1 nm or more and 5 nm or less. Here, the average particle size is the average particle size determined by the X-ray diffraction method in the case of measurement of a catalyst supported on a carrier such as carbon particles. In the case of measurement with a catalyst that is not supported on a carrier, it is the arithmetic mean particle size obtained from 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 electronically conductive powder (carrier) that supports the above-mentioned catalyst. The type of carbon particles is not limited as long as they are fine particles, have electrical conductivity, and are not attacked by a catalyst. Examples of carbon particles that can be used include carbon black, graphite, graphite, activated carbon, carbon fiber, carbon nanotubes, and fullerene.
The average particle diameter of the carbon particles is preferably 10 nm or more and 1000 nm or less, more preferably 10 nm or more and 100 nm or less. Here, the average particle size is the average particle size determined 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, it is preferable because the activity and stability of the catalyst are improved. This is preferable because it facilitates the formation of electron conduction paths and improves the gas diffusibility and catalyst utilization of the two electrode catalyst layers 2 and 3 .

The hydrophobic coating provided on the catalyst-carrying particles preferably has a film thickness sufficient to allow reaction gas to permeate. Specifically, the film thickness of the hydrophobic coating is preferably 40 nm or less. If it is thicker than this, the supply of reaction gas to the active points may be hindered. On the other hand, if the hydrophobic coating has a thickness of 40 nm or less, the reactant gas is sufficiently permeable, so that the catalyst-carrying particles can be made hydrophobic.
Moreover, the film thickness of the hydrophobic coating provided on the catalyst-carrying particles is preferably a film thickness sufficient to repel generated water. Specifically, the film thickness of the hydrophobic coating is preferably 2 nm or more. If the thickness is thinner than this, the generated water may stay and the supply of reaction gas to the active sites may be hindered.

The hydrophobic coating provided on the catalyst-supporting particles is composed of a fluorine-based compound having at least one polar group. Polar groups include, for example, hydroxyl groups, alkoxy groups, carboxyl groups, ester groups, ether groups, carbonate groups, amide groups and the like. Due to the presence of the polar group, the fluorine-based compound can be immobilized on the outermost surface of the catalyst layer. The portion other than the polar group in the fluorine-based compound 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 fibrous substances, for example, electron-conducting fibers and proton-conducting fibers can be used. Examples of electronically conductive fibers include carbon fibers, carbon nanotubes, carbon nanohorns, and conductive polymer nanofibers. From the viewpoint of conductivity and dispersibility, it is preferable to use carbon nanofibers as the fibrous substance.

Electron-conducting fibers having catalytic ability are more preferable in that they can reduce the amount of catalysts formed from noble metals. When the electrode catalyst layer is used as the electrode catalyst layer that constitutes the oxygen electrode, examples of the electron conductive fibers having catalytic ability include carbon alloy catalysts made from carbon nanofibers. The electron conductive fiber having catalytic ability may be a fiber obtained by processing an electrode active material for a fuel electrode into a fibrous form. A material containing at least one transition metal element selected from the group consisting of Ta, Nb, Ti, and Zr can be used as the electrode active material. Substances containing fiber metal elements may include partial oxides of carbonitrides of transition metal elements, or conductive oxides of transition metal elements, and conductive oxynitrides of transition metal elements.

The proton-conducting fiber may be a fiber obtained by processing a polyelectrolyte having proton-conducting properties into a fibrous form. Fluoropolymer electrolytes, hydrocarbon-based polymer electrolytes, and the like can be used as materials for forming the proton cell-resistant fibers. Examples of fluorine-based polymer electrolytes include Nafion (registered trademark) manufactured by DuPont, Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., Aciplex (registered trademark) manufactured by Asahi Kasei Corporation, and Gore's Gore Select (registered trademark) or the like can be used. Electrolytes such as sulfonated polyetherketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used as the hydrocarbon polymer electrolyte. Among these, Nafion (registered trademark) manufactured by DuPont is preferably used as the polymer electrolyte.
For the fibrous substance, only one type of the fibers described above may be used, or two or more types may be used. As the fibrous substance, electron-conducting fibers and proton-conducting fibers may be used in combination. The fibrous substance preferably contains at least one selected from the group consisting of carbon nanofibers, carbon nanotubes, and electrolyte fibers among the fibrous substances described above.

The solvent used as the dispersion medium for the catalyst ink is not particularly limited as long as it does not corrode the catalyst substance-supporting particles or the polymer electrolyte and can dissolve or disperse the polymer electrolyte as a fine gel in a highly fluid state. not something. However, the solvent desirably contains at least a volatile organic solvent. Examples of solvents used as dispersion media for catalyst ink include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, and pentanol, and acetone. , methyl ethyl ketone, pentanone, methyl isobutyl ketone, heptanone, cyclohexanone, methyl cyclohexanone, acetonylacetone, diisobutyl ketone 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 and 1-methoxy-2-propanol can be used. A mixed solvent in which two or more of the above materials are mixed may be used as the solvent.

In addition, when a lower alcohol is used as a dispersion medium for the catalyst ink, it is preferable to use a mixed solvent with water because the solvent using a lower alcohol has a high risk of ignition. Furthermore, water that is well compatible with the polymer electrolyte (water with high affinity) may be included. The amount of water to be added is not particularly limited as long as the polyelectrolyte is not separated to cause white turbidity or gelation.
The catalyst ink may contain a dispersant in order to disperse the catalyst substance-carrying particles. Examples of dispersants include anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, and the like.

Examples of anionic surfactants include alkyl ether carboxylate, ether carboxylate, alkanoyl sarcosine, 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 , amine salt of special modified phosphoric acid ester, amide amine salt of high molecular weight polyester acid, amide amine salt of special fatty acid derivative, alkylamine salt of higher fatty acid, amide amine salt of high molecular weight polycarboxylic acid, sodium laurate, sodium stearate, oleic acid Carboxylic acid surfactants such as sodium, dialkylsulfosuccinates, dialkyl sulfosuccinates, 1,2-bis(alkoxycarbonyl)-1-ethanesulfonates, alkylsulfonates, alkylsulfonates, paraffinsulfonates, α-Olefin sulfonate, linear alkylbenzene sulfonate, alkylbenzene sulfonate, polynaphthyl methanesulfonate, polynaphthyl methanesulfonate, naphthalene sulfonate-formalin condensate, alkylnaphthalene sulfonate, alkanoyl methyl tauride, sodium lauryl sulfate, cetyl sulfate Sulfonic acid surfactants such as sodium salts, stearyl sulfate sodium salts, oleyl sulfate sodium salts, lauryl ether sulfates, sodium alkylbenzene sulfonates, oil-soluble alkylbenzene sulfonates, α-olefin sulfonates, etc., alkyl sulfates Sulfuric acid such as ester salts, alkyl sulfates, alkyl sulfates, alkyl ether sulfates, polyoxyethylene alkyl ether sulfates, alkyl polyethoxy sulfates, polyglycol ether sulfates, alkyl polyoxyethylene sulfates, sulfated oils, and highly sulfated oils Ester-type surfactants, (mono- or di)alkyl phosphates, (mono- or di)alkyl phosphates, (mono- or di)alkyl phosphate ester salts, alkyl polyoxyethylene phosphate salts, alkyl ether phosphates, alkyl polyethoxy・Li phosphate, polyoxyethylene alkyl ether, alkylphenyl phosphate/polyoxyethylene salt, alkylphenyl ether/phosphate, alkylphenyl polyethoxy phosphate, polyoxyethylene/alkylphenyl ether phosphate, higher alcohol monophosphate Phosphate ester type surfactants such as ester disodium salt, higher alcohol phosphate diester disodium salt, zinc dialkyldithiophosphate, and the like are included.

Examples of cationic surfactants include benzyldimethyl{2-[2-(P-1,1,3,3-tetramethylbutylphenoxy)ethoxy]ethyl}ammonium chloride, octadecylamine acetate, tetradecylamine acetate , octadecyltrimethylammonium chloride, beef tallow trimethylammonium chloride, dodecyltrimethylammonium chloride, palm trimethylammonium chloride, hexadecyltrimethylammonium chloride, behenyltrimethylammonium chloride, palmdimethylbenzylammonium chloride, tetradecyldimethylbenzylammonium chloride, octadecyldimethylbenzylammonium chloride , dioleyldimethylammonium chloride, 1-hydroxyethyl-2-tallow imidazoline quaternary salt, 2-heptadecenyl-hydroxyethylimidazoline, stearamidoethyldiethylamine acetate, stearamidoethyldiethylamine hydrochloride, triethanolamine monostearate Examples include formates, alkylpyridium salts, higher alkylamine ethylene oxide adducts, polyacrylamideamine salts, modified polyacrylamideamine salts, perfluoroalkyl quaternary ammonium iodides, and the like.

Examples of amphoteric surfactants include dimethyl coconut betaine, dimethyl lauryl betaine, sodium laurylaminoethylglycinate, sodium laurylaminopropionate, stearyldimethylbetaine, lauryldihydroxyethyl betaine, amidobetaine, imidazolinium betaine, lecithin, 3-[ ω-fluoroalkanoyl-N-ethylamino]-1-sodium propanesulfonate, N-[3-(perfluorooctanesulfonamido)propyl]-N,N-dimethyl-N-carboxymethylene ammonium betaine and the like.

Examples of nonionic surfactants include coconut fatty acid diethanolamide (1:2 type), coconut fatty acid diethanolamide (1:1 type), bovine fatty acid diethanolamide (1:2 type), bovine fatty acid diethanolamide (1:1 type), oleic acid diethanolamide (1:1 type), hydroxyethyllaurylamine, polyethylene glycol laurylamine, polyethylene glycol coconut amine, polyethylene glycol stearylamine, polyethylene glycol beef tallow amine, polyethylene glycol beef tallow propylene diamine, 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, pentaerythrityl fatty acid ester, sorbitol fatty acid ester, sorbitan fatty acid ester, sugar fatty acid ester, and the like.

Among the above surfactants, sulfonic acid-type interfaces such as alkylbenzenesulfonic acid, oil-soluble alkylbenzenesulfonic acid, α-olefinsulfonic acid, sodium alkylbenzenesulfonate, oil-soluble alkylbenzenesulfonate, and α-olefinsulfonate The activator can be suitably used as a dispersant in consideration of the dispersing effect of carbon, changes in catalyst performance due to residual dispersant, and the like.
Increasing the amount of polyelectrolyte in the catalyst ink generally reduces the pore volume. On the other hand, increasing the amount of carbon particles in the catalyst ink increases the pore volume. Also, the use of dispersants reduces the pore volume.

Further, the catalyst ink is subjected to dispersion processing as necessary. The viscosity of the catalyst ink and the size of the particles contained in the catalyst ink can be controlled by the conditions of the catalyst ink dispersion treatment. Distributed processing can be performed using a variety of devices. In particular, the distributed processing method is not limited. 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. Also, a homogenizer or the like that agitates by centrifugal force may be employed. The pore volume becomes smaller as the dispersion time becomes longer, as aggregates of the catalyst-carrying particles are destroyed.

If the solid content in the catalyst ink is too high, the viscosity of the catalyst ink increases, and cracks tend to occur on the surfaces of the electrode catalyst layers 2 and 3 . On the other hand, if the solids content in the catalyst ink is too low, the film formation rate will be very slow, resulting in low productivity. 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 substance-carrying particles and a polymer electrolyte. When the content of the catalyst substance-supporting particles is increased in the solid content, the viscosity increases even if the solid content is the same. On the other hand, if the content of the catalyst substance-supporting particles is reduced in the solid content, the viscosity will be lowered even if the solid content is the same. 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. Further, 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 preferred. Also, the viscosity can be controlled by adding a dispersant when dispersing the catalyst ink.

Moreover, the catalyst ink may contain a pore-forming agent. Pores can be formed by removing the pore-forming agent after forming the electrode catalyst layer. Acids, alkalis, substances that dissolve in water, substances that sublimate such as camphor, substances that thermally decompose, and the like can be mentioned. 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 soluble in acids, alkalis, and water include acid-soluble inorganic salts, inorganic salts soluble in alkaline aqueous solutions, metals 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, and magnesium oxide. Examples of inorganic salts soluble in alkaline aqueous solution include alumina, silica gel and silica sol. Examples of acid- or alkali-soluble metals include aluminum, zinc, tin, nickel, and iron. Examples of water-soluble inorganic salts include sodium chloride, potassium chloride, ammonium chloride, sodium carbonate, sodium sulfate, monosodium phosphate and the like. Examples of water-soluble organic compounds include polyvinyl alcohol and polyethylene glycol.
The above-mentioned pore-forming agents may be used singly or in combination of two or more kinds, but it is preferable to use them in combination of two or more kinds.
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, or the like can be employed.

A transfer sheet can be used as a base material for manufacturing the electrode catalyst layers 2 and 3 .
The transfer sheet used as the base material may be any material that has good transferability. Fluorinated resins such as fluoroalkyl vinyl ether copolymer (PFA) and polytetrafluoroethylene (PTFE) can be used. Polymer sheets such as polyimide, polyethylene terephthalate, polyamide (nylon (registered trademark)), polysulfone, polyether sulfone, polyphenylene sulfide, polyether ether ketone, polyether imide, polyarylate, polyethylene naphthalate, etc. A molecular film can be used as a transfer sheet. Further, when a transfer sheet is used as the base material, the transfer sheet is peeled off after bonding the electrode film, which is the coating film after removing the solvent, to the polymer electrolyte membrane 1 , and the electrode catalyst is applied to both surfaces of the polymer electrolyte membrane 1 . A membrane electrode assembly 11 comprising layers 2 and 3 can be provided.

As the gas diffusion layers 4 and 5, a material having gas diffusion properties and electrical 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 or a metal type can be used. Incidentally, the gas diffusion layers 4 and 5 and the separators 10 (10a and 10b) may each have an integral structure. Further, when the separators 10 (10a, 10b) or the electrode catalyst layers 2, 3 function as the gas diffusion layers 4, 5, the gas diffusion layers 4, 5 may be omitted. The polymer electrolyte fuel cell 12 can be manufactured by assembling a gas supply device, a cooling device, and other accompanying devices.

<Other effects>
In this embodiment, a membrane electrode assembly 11 that exhibits high power generation characteristics under highly humidified conditions, a method for manufacturing the same, and a polymer electrolyte fuel cell 12 comprising 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, the entanglement of the highly crystalline fibrous material suppresses the occurrence of cracks in the electrode catalyst layers that cause a decrease in durability. and mechanical properties are obtained. In addition, since the catalyst-supporting particles provided with a hydrophobic coating have affinity with fibrous substances exhibiting hydrophobicity, pores are formed in the electrode catalyst layer due to the entanglement of the fibrous substances. Due to the formed pores, even in an electrode catalyst layer with 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.
The membrane electrode assembly produced by the method for producing an electrode catalyst layer according to the present embodiment does not impair water retention under low humidification conditions, and has improved drainage properties in a high current region where a large amount of water is produced. In addition, it exhibits high power generation performance and durability even under highly humidified conditions. In addition, the method for producing the electrode catalyst layer according to the present embodiment can efficiently and economically produce the membrane electrode assembly as described above.

In other words, the above-described electrode catalyst layer is formed by simply using a catalyst ink in which a platinum-supported carbon catalyst (catalyst-supporting particles) having a hydrophobic coating, a polymer electrolyte, and a fibrous substance are dispersed in a solvent. A membrane electrode assembly can be manufactured.
Therefore, it can be manufactured without a complicated manufacturing process, and by using the electrode catalyst layer produced by the above procedure, both water retention and reaction gas diffusivity can be improved. It is possible to operate without providing special means such as, and to reduce costs.

Only one of the electrode catalyst layers 2 and 3 formed on both surfaces of the polymer electrolyte membrane 1 may be the improved electrode catalyst layer. In that case, the improved electrode catalyst layer is preferably arranged on the side of the air electrode (cathode) where water is generated by the electrode reaction. However, it is more preferable to be formed on both surfaces of the polymer electrolyte membrane 1 from the viewpoint of drainage in a high current region.
Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and the present invention includes any modifications that do not depart from the gist of the present invention.

The method for manufacturing the improved electrode catalyst layer and the membrane electrode assembly for polymer electrolyte fuel cells according to the present embodiment will be described below with reference to specific examples and comparative examples. However, this embodiment is not limited to the following examples and comparative examples.
In each of the following examples, a case where both a pair of electrode catalyst layers are used as improved electrode catalyst layers is exemplified. Only one of the pair of electrode catalyst layers may be the improved electrode catalyst layer.

<Example>
[Adjustment of catalyst ink]
A platinum-supported carbon catalyst (catalyst-supporting particles) with a hydrophobic coating of 20 nm and a support density of 50% by mass, a 25% by mass polymer electrolyte solution with an ion exchange capacity of 0.7 meq/g, and an average fiber diameter of 150 nm. and a fibrous material having an average fiber length of 6 μm were mixed in a solvent and dispersed by a planetary ball mill. At this time, the dispersion time was set to 30 minutes, and the catalyst ink was adjusted.
The composition ratio of the starting materials of the adjusted catalyst ink was fibrous substance: carbon carrier: polymer electrolyte at a mass ratio of 0.5:1:0.6. The solvent for the catalyst ink was ultrapure water and 1-propanol at a volume ratio of 1:1. Also, the solid content in the catalyst ink was adjusted to 12% by mass.

〔Base material〕
A polytetrafluoroethylene (PTFE) sheet was used as a base material constituting the transfer sheet.
[Method for Forming Electrode Catalyst Layer on Substrate]
The catalyst ink prepared above was applied onto a substrate by a doctor blade method, and dried at 80° C. in an air atmosphere. The amount of catalyst ink to be applied was 0.1 mg/cm ² of platinum supported on the electrode catalyst layer serving as the fuel electrode (anode), and 0.3 mg/cm ² of platinum supported on the electrode catalyst layer serving as the air electrode (cathode). adjusted for each.
[Production of membrane electrode assembly]
A base material on which an electrode catalyst layer serving as an anode and a base material on which an electrode catalyst layer serving as a cathode were formed were punched out into pieces of 5 cm×5 cm, respectively, and a transfer temperature of 130° C. and a transfer pressure of 5.0× were applied to both sides of the polymer electrolyte membrane. The transfer was performed under the condition of 10 ⁶ Pa to produce the membrane electrode assembly of the example.

<Comparative Example 1>
[Adjustment of catalyst ink]
A platinum-supported carbon catalyst (catalyst-supporting particles) with a support density of 50% by mass, a 25% by mass polymer electrolyte solution with an ion exchange capacity of 0.7 meq/g, and an average fiber diameter of 150 nm and an average fiber length of 6 μm. A certain fibrous substance was mixed in a solvent and subjected to a dispersion treatment using a planetary ball mill. At this time, the dispersion time was set to 30 minutes, and the catalyst ink was adjusted.
The composition ratio of the starting materials of the adjusted catalyst ink was fibrous substance: carbon carrier: polymer electrolyte at a mass ratio of 0.5:1:0.6. The solvent for the catalyst ink was ultrapure water and 1-propanol at a volume ratio of 1:1. Also, the solid content in the catalyst ink was adjusted to 12% by mass.

〔Base material〕
A polytetrafluoroethylene (PTFE) sheet was used as a base material constituting the transfer sheet.
[Method for Forming Electrode Catalyst Layer on Substrate]
The catalyst ink prepared above was applied onto a substrate by a doctor blade method, and dried at 80° C. in an air atmosphere. The amount of catalyst ink to be applied was 0.1 mg/cm ² of platinum supported on the electrode catalyst layer serving as the fuel electrode (anode), and 0.3 mg/cm ² of platinum supported on the electrode catalyst layer serving as the air electrode (cathode). adjusted for each.
[Production of membrane electrode assembly]
A base material on which an electrode catalyst layer serving as an anode and a base material on which an electrode catalyst layer serving as a cathode were formed were punched out into pieces of 5 cm×5 cm, respectively, and a transfer temperature of 130° C. and a transfer pressure of 5.0× were applied to both sides of the polymer electrolyte membrane. Transfer was carried out under the condition of 10 ⁶ Pa, and a membrane electrode assembly of Comparative Example 1 was produced.

<Comparative Example 2>
[Adjustment of catalyst ink]
A platinum-supported carbon catalyst (catalyst-supporting particles) with a support density of 50% by mass and a 25% by mass polymer electrolyte solution with an ion exchange capacity of 0.7 meq/g are mixed in a solvent and dispersed in a planetary ball mill. processed. At this time, the dispersion time was set to 30 minutes, and the catalyst ink was adjusted.
The composition ratio of the starting materials of the prepared catalyst ink was 1:0.6 (mass ratio of carbon carrier:polymer electrolyte). The solvent for the catalyst ink was ultrapure water and 1-propanol at a volume ratio of 1:1. Also, the solid content in the catalyst ink was adjusted to 12% by mass.

〔Base material〕
A polytetrafluoroethylene (PTFE) sheet was used as a base material constituting the transfer sheet.
[Method for Forming Electrode Catalyst Layer on Substrate]
The catalyst ink prepared above was applied onto a substrate by a doctor blade method, and dried at 80° C. in an air atmosphere. The amount of catalyst ink to be applied was 0.1 mg/cm ² of platinum supported on the electrode catalyst layer serving as the fuel electrode (anode), and 0.3 mg/cm ² of platinum supported on the electrode catalyst layer serving as the air electrode (cathode). adjusted for each.
[Production of membrane electrode assembly]
A base material on which an electrode catalyst layer serving as an anode and a base material on which an electrode catalyst layer serving as a cathode were formed were punched out into pieces of 5 cm×5 cm, respectively, and a transfer temperature of 130° C. and a transfer pressure of 5.0× were applied to both sides of the polymer electrolyte membrane. Transfer was carried out under the condition of 10 ⁶ Pa, and a membrane electrode assembly of Comparative Example 2 was produced.

<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 Example and Comparative Examples 1 and 2. Then, each sample was placed in a power generation evaluation cell, and current-voltage measurement was performed using a fuel cell measuring device.
The cell temperature at the time of measurement was 60° C., and the following operating conditions were adopted: high humidification and low humidification. Further, hydrogen was flowed as the fuel gas at a flow rate at which the hydrogen utilization rate was 90%, and air was flowed at a flow rate at which the oxygen utilization rate was 50% as the oxidant gas. In addition, the back pressure was set to 50 kPa.
[Operating conditions]
Condition 1 (high humidity): relative humidity anode 90% RH, cathode 90% RH
Condition 2 (low humidity): relative humidity anode 90% RH, cathode 40% RH

〔Measurement result〕
The membrane electrode assemblies produced in Examples exhibited better power generation performance than the membrane electrode assemblies produced in Comparative Examples 1 and 2 under highly humidified operating conditions.
In addition, the membrane electrode assembly produced in the example had the same level of power generation performance even under high humidification operating conditions as that under low humidification operating conditions. In particular, the power generation performance was improved at a current density of around 1.2 A/cm ² .
The cell voltage at a current density of 1.2 A/cm ² of the membrane electrode assembly produced in Example 1 was 0.2 A/cm 2 compared to the cell voltage at a current density of 1.2 A/cm ² for the membrane electrode assembly produced in Comparative Example 1. The cell voltage was 17 V higher, and compared with the cell voltage of the membrane electrode assembly produced in Comparative Example 2 at a current density of 1.2 A/cm ² , the power generation characteristics were 0.24 V higher.

From the results of the power generation characteristics of the membrane electrode assemblies produced in Examples and the membrane electrode assemblies produced in Comparative Examples 1 and 2, it was found that the membrane electrode assemblies of Examples had improved drainage properties and under highly humidified operating conditions. It was confirmed that power generation characteristics are equivalent to those under low humidity operating conditions.
In addition, under the operating condition of low humidity, the cell voltage at the current density of 1.2 A/cm ² of the membrane electrode assembly produced in Example 1 was lower than that of the membrane electrode assembly produced in Comparative Example 1 at the current density of 1.2 A/cm 2 . cm ² , and 0.26 V higher than the cell voltage of the membrane electrode assembly produced in Comparative Example 2 at a current density of 1.2 A/cm ² .
From the results of the power generation characteristics of the membrane electrode assemblies produced in Examples and the membrane electrode assemblies produced in Comparative Examples 1 and 2, it was found that the membrane electrode assemblies produced in Examples had excellent drainage properties for the water generated by the electrode reaction. was high, and it was confirmed that it did not inhibit water retention under low humidity conditions.

DESCRIPTION OF SYMBOLS 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 channels 9a, 9b... Cooling water channels 10a, 10b... Separator 11... Membrane electrode assembly 12... Polymer electrolyte fuel cell

Claims (4)

A polymer electrolyte membrane and a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane,
At least one of the pair of electrode catalyst layers contains catalyst-supporting particles provided with a hydrophobic coating, a polymer electrolyte, and a fibrous substance having an average fiber diameter of 10 nm or more and 300 nm or less,
A membrane electrode assembly for a fuel cell, wherein the mass of the fibrous substance is 0.2 to 1.0 times the mass of the carrier in the catalyst-carrying particles. The fibrous substance has an average fiber diameter of 100 nm or more and 200 nm or less,
2. The membrane electrode assembly for a fuel cell according to claim 1, wherein the mass of said fibrous material is 0.4 times or more and 0.8 times or less of the mass of the support in said catalyst-carrying particles. 3. The fuel cell membrane electrode assembly according to claim 1, wherein the fibrous material has an average fiber length of 0.7 [mu]m to 20 [mu]m. a membrane electrode assembly according to any one of claims 1 to 3;
a pair of gas diffusion layers sandwiching the membrane electrode assembly;
a pair of separators facing each other with the membrane electrode assembly and the pair of gas diffusion layers interposed therebetween;
A polymer electrolyte fuel cell comprising:

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