JP2008269847A - INK FOR FUEL CELL CATALYST LAYER AND PROCESS FOR PRODUCING THE SAME - Google Patents

Abstract

In a polymer electrolyte fuel cell, the surface area of a catalyst layer is increased, the supply rate of oxygen to a reaction site is improved, and a catalyst layer having a small activation overvoltage can be produced. An ink and a production method thereof, and a membrane electrode assembly for a fuel cell formed using the ink and the production method are provided.
An ink for a fuel cell catalyst layer containing a catalyst metal, carbon particles, a polymer electrolyte, and a water-alcohol mixed solvent, wherein an alcohol ratio in the mixed solvent is 20 to 30% by mass.
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Description

  The present invention relates to a fuel cell catalyst layer ink, a method for producing the same, and a fuel cell membrane electrode assembly including a catalyst layer formed using the catalyst layer ink.

  A fuel cell directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to be oxidized electrochemically. Unlike thermal power generation, fuel cells are not subject to the Carnot cycle and thus exhibit high energy conversion efficiency. Fuel cells are particularly portable because solid polymer electrolyte fuel cells using solid polymer electrolyte membranes as electrolyte membranes have advantages such as being easy to miniaturize and operating at low temperatures. It is attracting attention as a power source for mobile objects.

As an example, in solid polymer electrolyte fuel cells that use proton-conducting solid electrolyte membranes such as Nafion (trade name, manufactured by DuPont) that require entrainment of water for proton conduction, hydrogen is the fuel. The reaction of the formula (1) proceeds at the anode (fuel electrode).
H ₂ → 2H ⁺ + 2e ⁻ (1)
The electrons generated by the equation (1) reach the cathode (oxidant electrode) after working with an external load via an external circuit. Then, the proton generated in the formula (1) moves in the solid polymer electrolyte membrane from the anode side to the cathode side by electroosmosis while being hydrated with water.
On the other hand, when oxygen is used as the oxidizing agent, the reaction of formula (2) proceeds at the cathode.
4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O (2)
The water produced at the cathode mainly passes through the gas diffusion layer and is discharged to the outside.
As described above, the fuel cell is a clean power generation device that has no emissions other than water.

A laminate of electrodes on both sides of the electrolyte membrane is called a membrane electrode assembly (MEA). In general, a pair of electrodes (that is, a fuel electrode and an oxidant electrode) provided on both surfaces of the electrolyte membrane generally have a structure in which a catalyst layer and a gas diffusion layer are laminated in order from the electrolyte membrane side.
The catalyst layer usually includes a catalyst component that promotes a reaction in each electrode (anode, cathode), a polymer electrolyte that forms a proton conduction path, and a conductive material that forms an electron conduction path. It is a part. As the polymer electrolyte contained in the catalyst layer, the same polymer electrolyte as that for forming the electrolyte membrane is often used.
On the other hand, the gas diffusion layer is made of a conductive porous body and is provided for the purpose of improving the diffusion of the reaction gas into the catalyst layer and the electronic conductivity.

The fuel cell includes a plurality of single cells including such a membrane electrode assembly. However, the fuel cell is required to have a high output density and high energy efficiency, and conventionally, in particular, the utilization efficiency of the catalyst layer which is an electrode is increased. Various catalyst inks and methods for producing catalyst inks have been considered.
For example, platinum or a platinum alloy is used as an electrode catalyst. However, since these noble metals are expensive, Patent Document 1 discloses a solid polymer using carbon nanotubes having an external surface area of 100 m ² / g or more. A coating solution for forming a catalyst electrode layer used in an electrolyte fuel cell is disclosed. In Patent Document 1, since the carbon nanotube has an external surface area in the above range, it is possible to carry a highly dispersed noble metal. Therefore, the noble metal is efficiently used, and the total amount and cost of the noble metal are reduced. It is described that it can.

Further, as a method for producing a catalyst ink in a highly dispersed, stable and efficient manner, Patent Document 2 discloses that a catalyst-supporting carbon black, an ion exchange resin, and a solvent are mixed and externally sheared with an external shearing machine. A fuel cell catalyst paste is disclosed in which internal shearing is performed with a shearing machine, and external shearing is performed again with the external shearing machine or another type of external shearing machine.
Moreover, in patent document 3, after disperse | distributing the liquid mixture containing a catalyst metal carrying | support carbon black, a 1st ion exchange resin solution, and a solvent with a medialess high-speed mixer, the 2nd ion exchange resin solution is added and stirred. comprising a catalyst paste for manufacturing an electrode of a polymer electrolyte fuel cell, the specific surface area of the catalyst metal supported carbon black is 50cm 2 ^/ g~1000m 2 ^{/ g,} said first ion exchange resin solution EW (ion exchange equivalent) value of 500 to less than 1000, and the amount of ion exchange resin in the first ion exchange resin solution is 30% to 80% by weight with respect to the carbon content of the catalyst metal-supported carbon black. The solvent is a mixed solution of water and ethanol, and the mixing ratio is water / ethanol = 50/50 to 80/20, and the second ion exchange resin solution The fuel cell electrode is characterized in that the EW value of the catalyst paste is 1000 or more and less than 1200, and the total amount of ion exchange resin in the catalyst paste is 80% to 220% by weight with respect to the carbon content of the catalyst metal-supported carbon black. A catalyst paste is disclosed. Patent Document 3 describes that the catalyst paste can be stored with good stability, and an electrode of a fuel cell exhibiting good discharge performance can be prepared with good yield in a short time.

In increasing the power density, it is important to reduce the overvoltage of the oxygen reduction of the cathode, which involves a large energy loss. For this purpose, in particular, increase the reaction site of the cathode (where the catalyst and the ion-exchange resin (polymer electrolyte) that contacts the catalyst are in contact with each other, and supply protons, electrons, and oxygen), and increase oxygen to the reaction site. It is effective to expedite the diffusion and supply of the contained gas.
In Patent Document 4, an anode and a cathode composed of a gas diffusion electrode having a catalyst layer containing a fluorinated ion exchange resin having a sulfonic acid group and a catalyst, and a solid polymer disposed between the anode and the cathode A solid polymer fuel cell comprising an electrolyte membrane, wherein the fluorine ion exchange resin contained in the catalyst layer of the cathode has a specific surface area of 3 m ² / g or more. Disclosure. In Patent Document 4, since a cathode resin having a large specific surface area is used as the cathode resin contained in the cathode catalyst layer, the supply rate of the reaction gas to the catalyst in the coating resin layer in the catalyst layer is increased, and the overvoltage is small. It is stated that a cathode is obtained.
However, in these techniques, a solvent is not defined considering the surface area of the polymer electrolyte in the electrode catalyst layer.

JP 2005-322446 A JP 2005-216661 A JP 2006-302644 A JP 2002-208406 A

  The present invention has been made in view of the above circumstances, and its purpose is to increase the specific surface area of the catalyst layer in the polymer electrolyte fuel cell and to increase the supply rate of the reaction gas to the reaction site in the catalyst layer. An object of the present invention is to provide a fuel cell catalyst layer ink capable of improving and producing a catalyst layer having a high output density, a method for producing the same, and a fuel cell membrane electrode assembly formed using the ink.

  The ink for a fuel cell catalyst layer of the present invention contains a catalyst metal, carbon particles, a polymer electrolyte, and a water-alcohol mixed solvent, and an alcohol ratio in the mixed solvent is 20 to 30% by mass. And

  The alcohol is preferably ethanol.

  The catalyst metal and the carbon particles are preferably contained in the form of catalyst-supported carbon particles.

  The method for producing an ink for a fuel cell catalyst layer according to the present invention comprises mixing catalyst-supported carbon particles, alcohol, water, or a polymer electrolyte solution in which a polymer electrolyte is dissolved in a water-alcohol mixture, and a predetermined amount of water or alcohol. The mixture is adjusted to a final composition containing a water-alcohol mixed solvent having an alcohol ratio of 20 to 30% by mass and then stirred.

  The fuel cell membrane electrode assembly of the present invention was formed on at least one surface side of the solid polymer electrolyte membrane using the fuel cell catalyst layer ink or the fuel cell catalyst layer ink produced by the method. A catalyst layer is provided.

According to the fuel cell catalyst layer ink of the present invention and the production method thereof, and the fuel cell membrane electrode assembly formed using the ink and the ink obtained by the production method, in the polymer electrolyte fuel cell, By increasing the specific surface area of the catalyst layer, the supply rate of the reaction gas to the reaction site in the catalyst layer can be improved, and a catalyst layer having a large output density can be created.
In addition, by increasing the specific surface area of the catalyst layer, water transpiration of the catalyst layer is improved, flooding can be suppressed, and battery performance can be improved.

  The fuel cell membrane electrode assembly of the present invention uses a fuel cell catalyst layer ink described later or a fuel cell catalyst layer ink produced by a method described later on at least one side of the solid polymer electrolyte membrane. The formed catalyst layer is provided.

Hereinafter, the fuel cell catalyst layer ink according to the present invention, a method for producing the same, and a fuel cell membrane electrode assembly including a catalyst layer formed using the ink will be described in detail with reference to FIG. The present invention is not limited to the embodiment shown in FIG.
FIG. 1 is a schematic cross-sectional view showing an embodiment of a membrane electrode assembly obtained by the present invention. As shown in FIG. 1, the electrolyte membrane 2 is provided with a cathode (oxidant electrode) 5 a on one surface and an anode (fuel electrode) 5 b on the other surface to form a membrane electrode assembly 1. In this example, the cathode 5a has a structure in which a cathode side catalyst layer 3a and a cathode side gas diffusion layer 4a are laminated in order from the electrolyte membrane side, and the anode 5b has an anode side catalyst layer in order from the electrolyte membrane side. 3b and the anode side gas diffusion layer 4b are laminated.

  As a method of forming a membrane electrode assembly (MEA) of a fuel cell, particularly a method of forming a catalyst layer on the surface of an electrolyte membrane, a catalyst component, a polymer electrolyte, and a conductive material are dissolved and dispersed in a solvent. Generally, a method using a catalyst ink is used. Specifically, for example, after applying a catalyst ink to a conductive porous body to be a gas diffusion layer and drying, the conductive porous body is thermocompression-bonded to the electrolyte membrane with the application surface of the catalyst ink facing the electrolyte membrane. There is a way to do it. In addition, the catalyst ink is applied onto a substrate such as polytetrafluoroethylene, and the dried product is transferred to a conductive porous body. Further, the conductive porous body on which the catalyst layer is formed and the electrolyte membrane are thermocompression bonded. There is a way to do it. Alternatively, there is a method in which a catalyst ink is applied to the surface of the electrolyte membrane and dried, and then the electrolyte membrane is thermocompression bonded to the conductive porous body with the application surface of the catalyst ink facing the conductive porous body.

(Catalyst layer)
The ink for a fuel cell catalyst layer of the present invention contains a catalyst metal, carbon particles, a polymer electrolyte, and a water-alcohol mixed solvent, and an alcohol ratio in the mixed solvent is 20 to 30% by mass. And Furthermore, other components or materials such as a water repellent polymer and a binder may be included as necessary.
The catalyst metal is not particularly limited as long as it has a catalytic action for hydrogen oxidation reaction at the anode and oxygen reduction reaction at the cathode. For example, platinum, ruthenium, iridium, rhodium, palladium, osnium, tungsten, It can be selected from metals such as lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, or alloys thereof. Pt and an alloy made of Pt and another metal such as Ru are preferable.
Examples of the carbon particles include conductive materials such as carbon materials such as carbon particles and carbon fibers.
The catalyst metal and the carbon particles are preferably contained in the form of catalyst-supported carbon particles.

The polymer electrolyte for an electrode is not particularly limited as long as it is a polymer electrolyte for an electrode having a water-repellent main skeleton (water repellent part) and a hydrophilic side chain (hydrophilic part), and is used as an electrolyte membrane described later. The material can be appropriately selected from the materials, and specific examples include fluorine electrolyte resins represented by Nafion (trade name) perfluorocarbon sulfonic acid resin. The polymer electrolyte for electrodes and the polymer electrolyte for electrolyte membrane may be different, but usually the same one is preferably used.
The polymer electrolyte for electrodes can be dissolved in alcohol, water or a water-alcohol mixture to prepare a polymer electrolyte solution, which can be used for the preparation of a catalyst ink. There are no particular limitations on the mixing ratio or the like at the time of dissolution.

  Other materials such as a water repellent polymer and a binder may be added to the catalyst ink as necessary. Further, the concentration of each component in the catalyst ink, the mixing procedure and method when preparing the catalyst ink are not particularly limited.

  The catalyst ink is obtained by dissolving or dispersing the above catalyst metal, carbon particles, and electrode polymer electrolyte in a solvent. The solvent of the catalyst ink in the present invention is a water-alcohol mixed solvent, and is adjusted so that the alcohol ratio is 20 to 30% by mass in the final composition stage. The alcohol may be appropriately selected according to the polymer electrolyte for electrodes. For example, methanol, ethanol, propanol, propylene glycol, or the like can be used. In particular, in the present invention, the alcohol is preferably ethanol.

The method for producing an ink for a fuel cell catalyst layer according to the present invention comprises, in particular, catalyst-supporting carbon particles, a polymer electrolyte solution in which a polymer electrolyte is dissolved in alcohol, water, or a water-alcohol mixture, and a predetermined amount of water or alcohol. After mixing and adjusting to a final composition containing a water-alcohol mixed solvent having an alcohol ratio of 20 to 30% by mass, the water-repellent main skeleton (water-repellent part) and the hydrophilic side chain (hydrophilic) are mixed by stirring. Part of the polymer electrolyte for an electrode having a large amount of water agglomerates with the hydrophilic part facing outside (solvent side) and the water repellent part facing inside (side relatively not in contact with the solvent). Side chains having a relatively large specific surface area than the main skeleton are present on the surface of the aggregated polymer electrolyte for electrodes. Therefore, the specific surface area of the polymer electrolyte for electrodes is relatively large, and when the catalyst layer is formed using the catalyst ink containing such a polymer electrolyte for electrodes, the specific surface area of the catalyst layer is considered to be large. It is done. The specific surface area of the catalyst layer can be controlled by such a simple adjustment process.
In particular, in the cathode catalyst layer, by increasing the specific surface area of the catalyst layer, the cathode reaction site (catalyst and ion exchange resin (polymer electrolyte) covering the catalyst are in contact with each other, and protons, electrons, and oxygen are supplied. Field) increases, and the diffusion and supply of oxygen-containing gas to the reaction site can be accelerated, and a catalyst layer with a small activation overvoltage can be realized.
Further, by increasing the surface area of the catalyst layer, water transpiration of the catalyst layer is improved, flooding can be suppressed, and battery performance can be improved.

A method for applying the catalyst ink to the electrolyte membrane 1 is not particularly limited, and examples thereof include a spray method, a screen printing method, a doctor blade method, a gravure printing method, and a die coating method. After the application, the catalyst layer is formed by natural drying or heat drying such as a hot plate, an oven, or warm air.
The amount of catalyst ink applied varies depending on the composition of the catalyst ink and the catalyst performance of the catalyst metal used for the electrode catalyst, but the amount of catalyst component per unit area is about 0.1 to 1.0 mg / cm ^2. What should I do? Moreover, the film thickness of the catalyst layer 2 is not particularly limited, but may be about 5 to 50 μm.

(Electrolyte membrane)
As the electrolyte membrane 1 in the present invention, a polymer electrolyte for an electrolyte membrane conventionally used in a solid polymer electrolyte fuel cell, for example, an electrolyte membrane containing a fluorine-based polymer electrolyte and a hydrocarbon-based polymer electrolyte is used. be able to.
Examples of the fluorine-based polymer electrolyte include fluorine-based ion exchange resins such as perfluorocarbon sulfonic acid. Examples of the perfluorocarbon sulfonic acid membrane include commercially available products such as Nafion manufactured by DuPont of the United States and Flemion manufactured by Asahi Glass.

On the other hand, a hydrocarbon-based polymer electrolyte has a polymer main chain composed of carbon and hydrogen and an ion exchange group, and typically has a proton dissociable polar group as an ion exchange group. A proton-conducting hydrocarbon polymer electrolyte is used. Examples of proton dissociative polar groups include sulfonic acid groups, carboxylic acid groups, boronic acid groups, phosphonic acid groups, phosphoric acid groups, and hydroxyl groups.
An electrolyte membrane made of a hydrocarbon-based polymer electrolyte is economically advantageous because it is cheaper than that made of a fluorine-based polymer electrolyte, and is also advantageous in terms of durability because of its high heat resistance.

  The hydrocarbon polymer electrolyte is a fluorine polymer electrolyte in which the main chain and side chain hydrogen represented by perfluorocarbon sulfonic acid resin membranes such as Nafion (trade name, manufactured by DuPont) are all substituted with fluorine. Not included. The hydrocarbon-based polymer electrolyte typically does not contain any fluorine. However, when a polymer electrolyte having a relatively high glass transition temperature is used, the effect according to the present invention can be sufficiently obtained, and therefore, partially substituted with fluorine or contains hetero atoms other than fluorine. Even if the glass transition temperature is high to some extent, it is included in the hydrocarbon polymer electrolyte.

  The hydrocarbon polymer electrolyte having a proton-dissociating polar group (hereinafter sometimes simply referred to as a hydrocarbon polymer electrolyte) includes an aromatic ring in the main chain and / or side chain, and proton dissociation. A high molecular resin containing a polar group can be used. Specifically, the proton-dissociating properties described above are applied to engineering plastics such as polyether ether ketone, polyether ketone, polyether sulfone, polyphenylene sulfide, and polyphenylene ether, and general-purpose plastics such as polystyrene, ABS resin, and AS resin. Examples thereof include a polar group introduced and covalently bonded. Further, it is composed of a complex of a basic polymer and a strong acid, such as polybenzimidazole, polypyrimidine, and polybenzoxazole, which are disclosed in JP-A-11-503262. Examples also include polymer electrolytes such as solid polymer electrolytes.

  Since it is excellent in heat resistance and can be suitably used for a fuel cell operated under high temperature conditions, the hydrocarbon polymer electrolyte has a Tg (glass transition temperature) of 110 ° C. or higher, particularly 130 ° C. or higher. Furthermore, it is preferable that it is 160 degreeC or more. Hydrocarbon polymer electrolytes having an aromatic ring structure in the main chain skeleton of the polymer are excellent in heat resistance and many have a Tg in the above range, and can be suitably used.

The electrolyte membrane 1 is obtained by dissolving or dispersing the above polymer electrolyte in a solvent appropriately combined with alcohols such as methanol, ethanol, propanol, or water, or in a polar organic solvent such as dimethyl sulfoxide or dimethylformamide. The electrolyte solution can be prepared by casting and drying the obtained solution on the surface or mold of a substrate or the like. It can also be produced by a method of extruding a polymer electrolyte at a temperature above the glass transition point.
The electrolyte membrane 1 may contain only one type of polymer electrolyte as described above, or may contain two or more types. Moreover, the proton dissociative polar group to be introduced may be one type or two or more types. Moreover, the other component may be included as needed.

The film thickness of the electrolyte membrane 1 may usually be about 10 to 100 μm. The electrolyte membrane 1 is preferably thin from the viewpoint of improving proton conductivity. However, if it is too thin, the function of isolating gas is reduced, the permeation amount of non-proton hydrogen is increased, and cross leakage occurs in a severe case. To do.
The electrolyte membrane 1 can be reinforced with a perfluorocarbon polymer in the form of a fibril, a fabric, a non-fabric, or a porous sheet, or by coating the membrane surface with an inorganic oxide or a metal.

(Gas diffusion layer)
A gas diffusion layer 3 is further laminated on the catalyst layer 2. The gas diffusion layer 3 has gas diffusibility and conductivity that can efficiently supply gas to the catalyst layer 2, and strength required as a material constituting the gas diffusion layer.
Examples of the gas diffusion layer 3 include carbonaceous porous bodies such as carbon paper, carbon cloth, and carbon felt, titanium, aluminum, copper, nickel, nickel-chromium alloy, copper and its alloys, silver, aluminum alloys, Conductive porous materials such as metal meshes or metal porous materials composed of metals such as zinc alloy, lead alloy, titanium, niobium, tantalum, iron, stainless steel, gold, platinum, etc. Can be formed.

The gas diffusion layer 3 may be composed of a single layer of the conductive porous body as described above, but a water repellent layer may be provided on the side facing the catalyst layer. The water repellent layer may be a layer impregnated in the conductive porous body.
The water-repellent layer usually has a porous structure containing conductive particles such as carbon particles and carbon fibers, a water-repellent resin such as polytetrafluoroethylene, and the like. The water-repellent layer is not always necessary, but it can improve the drainage of the gas diffusion layer while maintaining an appropriate amount of water in the catalyst layer and the electrolyte membrane. There is an advantage that electrical contact can be improved.
The gas diffusion layer 3 can be bonded by thermocompression bonding a gas diffusion layer sheet provided with a water-repellent layer as necessary to the surface of the catalyst layer by a technique such as hot pressing.
The thickness of the gas diffusion layer 3 is preferably about 15 to 100 μm.

  In the catalyst ink application step, for example, when the catalyst ink is applied to the surface of the electrolyte membrane, the catalyst layer is formed on the surface of the electrolyte membrane by drying the catalyst ink. The electrolyte membrane having the catalyst layer formed on the surface in this manner is obtained by joining the catalyst layer and the gas diffusion layer sheet so as to sandwich the catalyst layer between the gas diffusion layer sheet and the electrolyte membrane. A membrane / electrode assembly including an electrode composed of a gas diffusion layer can be produced.

  Further, when the catalyst ink is applied to the surface of the gas diffusion layer sheet on the catalyst layer side, the catalyst layer is formed on the surface of the gas diffusion layer sheet by drying the catalyst ink. In this way, the gas diffusion layer sheet having the catalyst layer formed on the surface is obtained by joining the catalyst layer and the electrolyte membrane so that the catalyst layer is sandwiched between the electrolyte membrane and the gas diffusion layer sheet. Can be produced.

Further, when the catalyst ink is applied onto a transfer substrate such as polytetrafluoroethylene, the catalyst layer sheet obtained by drying the catalyst ink on the surface of the transfer substrate is joined to the electrolyte membrane or the gas diffusion layer sheet, After the substrate is peeled off, the membrane / electrode assembly can be produced by joining the gas diffusion layer sheet or the electrolyte membrane so that the catalyst layer is sandwiched between the electrolyte membrane and the gas diffusion layer.
Bonding between the electrolyte membrane and each layer in the membrane / electrode assembly can be performed, for example, by hot pressing.

The membrane / electrode assembly 1 is further sandwiched between separators 22a and 22b to form a single cell 21, as shown in FIG. The separator 22 is formed with an oxidant gas passage 23 or a fuel gas passage 24. As the separator 22, for example, a carbon separator containing a high concentration of carbon fiber and made of a composite material with a resin, a metal A metal separator using a material can be used. Examples of the metal separator include those made of a metal material excellent in corrosion resistance, and those coated with a coating that enhances the corrosion resistance by coating the surface with carbon or a metal material excellent in corrosion resistance. .
The unit cells 21 having such a configuration are electrically assembled to form a stack and accommodated in a container to form a fuel cell.

As described above, according to the fuel cell catalyst layer ink of the present invention, the method for producing the same, and the fuel cell membrane electrode assembly formed using the ink, the surface area of the catalyst layer in the solid polymer fuel cell Can be increased, the oxygen supply rate to the reaction site can be improved, and a catalyst layer having a large output density can be produced.
In addition, by increasing the surface area of the catalyst layer, water transpiration of the catalyst layer is improved, flooding can be suppressed, and battery performance can be improved.

Example 1
Each material is weighed so that the value obtained by dividing the weight of Nafion Solution DE1020 (trade name, manufactured by DuPont) by the weight of carbon black is 0.8, and pure water is mixed so that the alcohol ratio is 25% by mass. To obtain a mixed solution. The Nafion Solution DE1020 contained alcohol.
The above mixed solution was centrifuged and stirred for 5 minutes with a mixer (trade name: Awatori Nertaro, manufactured by Shinky Co., Ltd.), and then stirred with a homogenizer (trade name: ultrasonic disperser GSD600CVP, manufactured by Ginsen Co., Ltd.). Obtained.
The obtained catalyst ink was applied onto a PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) sheet with a doctor blade, dried at 120 ° C. for 1 hour in a vacuum dryer, and then the ratio of the catalyst layer was measured by a nitrogen adsorption method. The surface area was measured.

(Comparative Example 1)
A catalyst ink was prepared in the same manner as in Example 1 except that the alcohol ratio was 0% by mass, and the specific surface area of the catalyst layer was measured.

(Comparative Example 2)
A catalyst ink was prepared in the same manner as in Example 1 except that the alcohol ratio was 50% by mass, and the specific surface area of the catalyst layer was measured.

(Comparative Example 3)
A catalyst ink was prepared in the same manner as in Example 1 except that the alcohol ratio was 70% by mass, and the specific surface area of the catalyst layer was measured.

(Comparative Example 4)
A catalyst ink was prepared in the same manner as in Example 1 except that the alcohol ratio was 85% by mass, and the specific surface area of the catalyst layer was measured.

(Measurement result)
The measurement results of Example 1 and Comparative Examples 1 to 4 are shown in FIG.
From the measurement results, it was found that the specific surface area of the catalyst layer in Example 1 was larger than the specific surface area of the catalyst layers in Comparative Examples 1 to 4.

It is sectional drawing which shows typically one Embodiment of the membrane electrode assembly provided by the manufacturing method which concerns on this invention. It is sectional drawing which shows typically one Embodiment of the single cell provided with the membrane electrode assembly provided by the manufacturing method which concerns on this invention. It is a graph which shows the measurement result obtained by the Example and the comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Membrane electrode assembly 2 ... Electrolyte membrane 3a ... Cathode side catalyst layer 3b ... Anode side catalyst layer 4a ... Cathode side gas diffusion layer 4b ... Anode side gas diffusion layer 5a ... Cathode 5b ... Anode 21 ... Single cell 22a, 22b ... Separator 23 ... Oxidant gas passage 24 ... Fuel gas passage

Claims (5)

  A fuel cell catalyst layer ink comprising a catalyst metal, carbon particles, a polymer electrolyte, and a water-alcohol mixed solvent, wherein an alcohol ratio in the mixed solvent is 20 to 30% by mass.   The fuel cell catalyst layer ink according to claim 1, wherein the alcohol is ethanol.   The fuel cell catalyst layer ink according to claim 1, wherein the catalyst metal and the carbon particles are contained in the form of catalyst-supported carbon particles.   Catalyst-supported carbon particles, alcohol, water or a polymer electrolyte solution in which a polymer electrolyte is dissolved in a water-alcohol mixture, and a predetermined amount of water or alcohol are mixed, and a water-alcohol having an alcohol ratio of 20 to 30% by mass. A method for producing an ink for a fuel cell catalyst layer, comprising adjusting the final composition containing a mixed solvent and then stirring.   5. The fuel cell catalyst layer produced by the fuel cell catalyst layer ink according to any one of claims 1 to 3 or the fuel cell catalyst layer produced by the method according to claim 4 on at least one surface side of the solid polymer electrolyte membrane. A membrane electrode assembly for a fuel cell, comprising a catalyst layer formed using an ink for fuel.

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