JP2000106200A - Gas diffused electrode-electrolyte film joint body and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure, capable of preventing lowering of ion conductivity due to the contamination of the electrolyte with the impure material and the deterioration of the electrolyte by making the contact area of an interface between the electrolyte film of the gas diffused electrode-electrolyte film joint body and the catalyst large so as to improve the output of the fuel cell. SOLUTION: At least one surface of a solid high polymer electrolyte film is formed with a porous solid high polymer electrolyte layer having three- dimensional communicating holes, and platinum group metal is carried by the porous solid high polymer electrolyte layer. A gas diffused electrode formed of a layered structure of a catalyst layer and a gas diffused layer is bonded onto the porous solid high polymer electrolyte layer so that the catalyst layer makes contact therewith, and a gas diffused electrode-electrolyte film joint body is thereby structured, and this is used in fuel cell.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas diffusion electrode-electrolyte membrane assembly and a fuel cell using the same.

[0002]

2. Description of the Related Art A fuel cell has a structure in which a cathode is provided on one side of an electrolyte membrane and an anode is provided on the other side. The electrolyte membrane and the cathode or anode are integrated with each other. May not be. There is a gas diffusion electrode-electrolyte membrane assembly as an integrated body. Such a assembly is a solid polymer electrolyte fuel cell using a solid polymer electrolyte represented by an ion exchange membrane as an electrolyte. It is used in direct methanol fuel cells using methanol as a fuel.

For example, in a solid polymer electrolyte fuel cell, a gas diffusion electrode composed of a catalyst layer and a gas diffusion layer is used as a cathode and an anode, and the catalyst layer is joined to the electrolyte membrane so as to be in contact with the electrolyte membrane. Gas diffusion electrode
Electrolyte membrane assemblies have been used. Then, the gas diffusion electrode-electrolyte membrane assembly is sandwiched between a pair of gas-impermeable separators having a gas supply passage formed therein to form a unit cell serving as a basic unit. A polymer electrolyte fuel cell is configured.

The above-mentioned catalyst layer is formed by binding a catalyst such as platinum group metal catalyst particles or carbon powder carrying the platinum group metal catalyst particles with a binder or the like, and an electrolyte is added to the catalyst layer. Sometimes. Generally, a fluorine-based resin such as polytetrafluoroethylene (PTFE) is used as the binder. In this case, the fluorine-based resin is also a water repellent that imparts appropriate water repellency to the catalyst layer. Further, as the gas diffusion layer, carbon paper having water repellency is used.

In such a solid polymer electrolyte fuel cell, for example, oxygen is supplied to the cathode as an oxidizing agent, and hydrogen is supplied to the anode as a fuel, and these are electrochemically reacted to extract electric power. However, the reaction is represented by 2H ₂ → 4H ⁺ + 4e ⁻ at the anode and O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O at the cathode. That is, protons move from the anode to the cathode via the electrolyte, and electrons move to the cathode after being guided from the anode to an external load.

[0006] Since the cathode reaction and the anode reaction proceed at the interface between the catalyst and the electrolyte membrane contained in the cathode or anode, the contact area of the interface between the catalyst and the electrolyte membrane is increased to obtain high output. Is required. Therefore, a method has been proposed in which the surface of the electrolyte membrane is provided with irregularities to increase the contact area with the electrode containing the catalyst, particularly the catalyst layer.

For example, a method has been proposed in which the surface area of the electrolyte membrane is increased by providing irregularities to increase the contact interface with the electrode. Specifically, Japanese Patent Laid-Open No. 15848/1991 has been proposed.
6, a method using a roll having irregularities, a method using a sputtering method described in JP-A-4-169069, a method using plasma etching described in JP-A-4-220957, No. 6,279,600 discloses a method of embedding a cloth and then peeling it off. Further, a method has been proposed in which holes are provided in the surface of the electrolyte membrane to increase the contact area between the electrolyte membrane and the catalyst layer.
No. 7432, a method of crystallizing a dispersion medium in which an electrolyte is dissolved into small droplets and then removing the droplets;
A method described in Japanese Patent Application Laid-Open No. 2-146926, in which certain particles are embedded and then removed, and a method described in Japanese Patent Application Laid-Open No. 5-194766, in which a low molecular organic material is mixed and then removed, have been proposed. Further, a method has been proposed in which a platinum group metal is adhered to the surface of the electrolyte membrane to increase the contact interface between the electrolyte and the catalyst.
JP-A-42078 and JP-B-2-43830 have proposed a method of performing electroless plating on the surface of an electrolyte membrane.

[0008]

As described above, in the method using a roll, the method using sputtering, the method using plasma etching, or the method using cloth,
There are problems in that the process of providing the unevenness is complicated and the productivity is poor, and that the formed unevenness is rough and insufficient to increase the contact area at the interface with the electrode.

In the method of forming pores by removing the crystallized dispersion medium, embedded particles or mixed low molecular weight organic material, it is difficult to completely remove the dispersion medium, particles or low molecular weight organic material. These residues have a problem that they hinder contact between the electrolyte membrane and the electrode and cause a decrease in activity, and that these residues hinder ion conduction between the electrolyte membrane and the electrode.

[0010] In addition, the electrolyte is deteriorated by the heating or solvent treatment performed in the step of removing them, and the ionic conductivity is reduced. For example, in a fuel cell using such an electrolyte membrane, the performance is reduced. There's a problem.

Further, the platinum group metal formed on the surface of the electrolyte membrane by a method such as electroless plating has a small surface area and a low activity as a catalyst. There is a problem that it is insufficient for improvement.

Accordingly, the present invention provides a gas diffusion electrode which has a large contact area at the interface between the electrolyte membrane and the catalyst and can be manufactured without causing a decrease in ionic conductivity due to contamination of impurities or deterioration of the electrolyte. An object of the present invention is to provide an electrolyte membrane assembly and a high-output fuel cell using the same.

[0013]

A porous electrolyte having three-dimensionally communicating pores has a large number of pores per se, and a membrane made of such a porous electrolyte has the following problems.
The holes are three-dimensionally formed in a state communicating with the thickness direction and the plane direction, and the electrolyte is also formed three-dimensionally in a state communicating with the thickness direction and the plane direction. It is significantly increased because micropores are originally formed. That is, by applying a platinum group metal as a catalyst to the surface of the electrolyte portion of the porous electrolyte having three-dimensionally communicating pores, the contact area between the catalyst and the electrolyte is increased, and the site where the electrochemical reaction proceeds is increased. As a result, the output of the fuel cell can be increased.

The invention of the present application has been made by finding the above points. The first invention is to form a porous electrolyte layer having three-dimensionally communicating pores on at least one surface of an electrolyte membrane. A gas diffusion electrode-electrolyte membrane assembly obtained by bonding a gas diffusion electrode on the porous electrolyte layer,
A gas diffusion electrode-electrolyte membrane assembly, wherein a platinum group metal is supported on the porous electrolyte layer.

In the gas diffusion electrode-electrolyte membrane assembly of the present invention, the platinum group metal supported on the porous electrolyte layer is mainly distributed near the surface of the porous electrolyte layer on the gas diffusion electrode side. Is more preferred.

In the fuel cell according to the third aspect of the present invention, a porous solid polymer electrolyte layer having three-dimensionally communicating pores is formed on at least one surface of the solid polymer electrolyte membrane, and the catalyst layer and the gas diffusion layer are formed. A gas diffusion electrode comprising a laminate of the gas diffusion electrode and an electrolyte membrane joined together so that the catalyst layer is in contact with the porous solid polymer electrolyte layer, the porous solid polymer electrolyte layer It is characterized in that a platinum group metal is supported. Also in this case, the platinum group metal supported on the porous solid polymer electrolyte layer is more preferably distributed mainly near the interface with the catalyst layer. Further, the fuel cell of the present invention is particularly suitable for a direct methanol fuel cell.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for producing a gas diffusion electrode-electrolyte membrane assembly according to the present invention will be specifically described. The gas diffusion electrode-electrolyte membrane assembly of the present invention is, for example, a step of forming a porous electrolyte layer having three-dimensionally communicating pores on at least one surface of the electrolyte membrane, a platinum group on the surface of the porous electrolyte layer It can be manufactured through a step of applying a metal, and further a step of forming a gas diffusion electrode and a gas diffusion electrode-electrolyte membrane assembly. Hereinafter, this case will be described.

First, the step of forming a porous electrolyte layer having three-dimensionally connected pores will be described.

The porous electrolyte layer having three-dimensionally connected pores is prepared by dissolving the electrolyte while adjusting the concentration in a solvent containing alcohols to prepare an electrolyte solution having a controlled concentration. This is prepared by applying this solution in layers on the surface and then subjecting the solution to a porous treatment. The porous treatment can be performed by immersing the coating layer of the electrolyte solution in an organic solvent having a polar group other than an alcoholic hydroxyl group, and the dissolved electrolyte is solidified by this treatment to form pores having three-dimensional communication. Is formed.

More specifically, it is formed, for example, as follows. An electrolyte is dissolved in a solvent containing alcohol to prepare an electrolyte solution. As a commercially available solution in the form of a solution of perfluorosulfonic acid resin, there is a 5 wt% Nafion solution (Aldrich, USA), which can be used as it is. In this case, various concentrations of the electrolyte solution are prepared by concentrating or diluting the electrolyte solution.

A coating and a porous treatment are performed using this solution, and a method for simultaneously bonding with the electrolyte membrane will be described. In this case, for example, Nafion 115, which is a commercially available perfluorosulfonic acid resin film, is used as the electrolyte solution coated body.
A membrane (manufactured by DuPont, USA) can be used. The Nafion 115 film is a non-porous film.

First, the Nafion 115 membrane is boiled with purified water for 1 hour and stored in purified water at room temperature. Thereafter, the Nafion 115 film is further swelled by immersion in an alcohol such as ethanol. The swollen Nafion 115 film is taken out of ethanol, excess ethanol on the surface of the film is removed by wiping or the like, and a Nafion solution having a adjusted concentration is applied to the surface on which the porous electrolyte is to be formed by spraying or the like. Thereafter, the coated body is immersed in an organic solvent having a polar group other than an alcoholic hydroxyl group such as butyl acetate, taken out and dried at room temperature. The solution applied by this operation becomes a porous electrolyte having three-dimensionally communicating pores, and the bonding with the electrolyte is completed at the same time. Nafion is a registered trademark of DuPont.

As the solution obtained by dissolving the electrolyte in the alcohol-containing solvent used above, any solution other than the commercially available 5 wt% Nafion solution can be used as long as it is a perfluorosulfonic acid resin solution. A solution of another perfluorosulfonic acid resin such as glass) can be used.

The concentration of the solution can be arbitrarily changed by a method such as dilution or concentration. For example, a method of adding and diluting alcohol, water, or a mixture thereof to the electrolyte solution, or a method of removing a part of the solvent of the electrolyte solution by a method such as heating or the like to concentrate the solution can be used. In this case, the alcohol has 4 carbon atoms.
The following methanol, ethanol, 1-propanol, 2
-Propanol, 1-butanol or 2-butanol can be used.

The electrolyte solution coated body is also made of a proton-containing material such as a perfluorosulfonic acid film other than Nafion 115, a perfluorosulfonic acid film such as a perfluorocarboxylic acid film, or a hydrocarbon-based electrolyte film such as styrene vinylbenzene sulfonic acid. A polymer film exhibiting conductivity can be widely used. When used in a fuel cell, among these polymer membranes, a fluorine-based electrolyte membrane such as a perfluorosulfonic acid membrane or a perfluorocarboxylic acid membrane having excellent heat resistance is particularly preferred.

In addition, as a mere application body, a sheet or plate-like material such as a polymer, ceramics, or metal can be used other than the electrolyte membrane. in this case,
A joined body is formed by, for example, transferring a porous electrolyte having three-dimensionally communicating pores formed on an electrolyte solution coated body to an electrolyte membrane.

The application of the electrolyte solution to the electrolyte membrane can be performed by a method other than spraying, for example, a doctor blade method, a screen printing method, etc., and various methods can be used.

As the alcohol for moistening the electrolyte membrane in a water-containing state, methanol, 1-propanol, 2-propanol, 1-butanol or 2-butanol having 4 or less carbon atoms can be used in addition to ethanol.

Examples of the organic solvent having a polar group other than the alcoholic hydroxyl group include, in addition to the above-mentioned butyl acetate, a carbon chain having an alkoxycarbonyl group in the molecule having 1 carbon atom.
To 7 organic solvents, for example, propyl formate, butyl formate, isobutyl formate, ethyl acetate, propyl acetate, isopropyl acetate, allyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, isopentyl acetate, methyl propionate, propionic acid Ethyl, propyl propionate, methyl acrylate, butyl acrylate, isobutyl acrylate, methyl butyrate, methyl isobutyrate, ethyl butyrate, ethyl isobutyrate, methyl methacrylate, propyl butyrate, isopropyl isobutyrate, 2-ethoxyethyl acetate, acetic acid 2-
(2ethoxyethoxy) ethyl or the like alone or in combination, or an organic solvent having a carbon chain having an ether bond in the molecule and having 3 to 5 carbon atoms, for example, dipropyl ether, dibutyl ether, ethylene glycol dimethyl ether, ethylene glycol Glycol diethyl ether, tripropylene glycol monomethyl ether, tetrahydrofuran or the like alone or as a mixture, or an organic solvent having 4 to 8 carbon atoms in the carbon chain having a carbonyl group in the molecule;
For example, methyl butyl ketone, methyl isobutyl ketone, methylhexyl ketone, dipropyl ketone, etc., alone or in combination, or an organic solvent having 1 to 5 carbon atoms in the carbon chain having an amino group in the molecule, for example, isopropyl Amine, isobutylamine, tertiary butylamine, isopentylamine, diethylamine, etc., alone or as a mixture, or an organic solvent having a carboxyl group in the molecule having 1 to 6 carbon atoms such as propionic acid, It is possible to use varic acid, caproic acid, heptanoic acid, etc., alone or in combination, or those obtained from a combination thereof. And in the porous treatment,
Among these organic solvents, those having an alkoxycarbonyl group are particularly preferred.

Next, the step of applying a platinum group metal to the surface of a porous electrolyte membrane having three-dimensionally communicating pores will be described.

For applying the platinum group metal to the surface of the porous electrolyte having three-dimensionally connected pores, for example, an electroless plating method can be used. A porous electrolyte having three-dimensionally communicating pores is immersed in a solution of a platinum group metal to replace a counter ion of the electrolyte with a platinum group metal ion. The platinum group metal ion type electrolyte is exposed to a reducing atmosphere to reduce the platinum group metal ions and deposit the platinum group metal near the surface of the electrolyte. Thereafter, the substrate is washed with an acidic aqueous solution in order to remove the remaining platinum group metal ions, and further washed with purified water.

Platinum group metals include, for example, platinum complexes such as hexaammineplatinum (〓) salts in the case of platinum, ruthenium complexes such as hexaammineruthenium in the case of ruthenium,
In the case of iridium, an iridium complex or a mixture thereof can be used for a pentaaqua iridium (〓) salt or the like.

For the formation of the reducing atmosphere, a method of immersing the platinum group metal ion type electrolyte in an aqueous solution of sodium borohydride or a method of holding it in a hydrogen gas can be used.

For washing, an acidic aqueous solution such as hydrochloric acid, sulfuric acid or nitric acid can be used.

For the application of the platinum group metal to the surface of the porous electrolyte having three-dimensionally communicating pores, for example, a method of applying a platinum group metal can be used in addition to the electroless plating method. As a method for providing a platinum group metal densely at the interface, an electroless plating method is preferable.

Next, a process for forming a gas diffusion electrode and a gas diffusion electrode-electrolyte membrane assembly will be described.

The gas diffusion electrode-electrolyte membrane assembly is formed, for example, by electroless plating of a platinum group metal on a porous electrolyte having three-dimensionally communicating holes formed on at least one surface of the electrolyte membrane by the method described above. To make this a catalyst layer,
The catalyst layer may be prepared by bonding a water-repellent carbon paper as a gas diffusion layer, for example, by a method such as heating and pressure welding. Preferably, the catalyst layer is further provided on a porous electrolyte layer carrying a platinum group metal. It is preferable to form a catalyst layer and a gas diffusion layer thereon.

In this case, after preparing a catalyst dispersion in advance,
This catalyst dispersion is applied on a porous electrolyte layer having three-dimensionally interconnected pores electrolessly plated with a platinum group metal to form a catalyst layer, on which a gas diffusion layer such as water-repellent carbon is formed. Paper is joined by a method such as heating and pressure welding. In this configuration, the catalyst layer is substantially composed of a porous electrolyte having three-dimensionally interconnected pores electrolessly plated with a platinum group metal and an applied catalyst dispersion.
It becomes a heavy structure.

In this method, the catalyst dispersion is prepared by mixing the catalyst with a dispersion medium and preparing a liquid or a paste. The catalyst may be a carbon carrying a platinum group metal, a platinum group metal. Or an oxide thereof or a mixture thereof. As the dispersion medium, alcohol having 4 or less carbon atoms, water, or a mixture thereof can be used. Further, an electrolyte solution, a fluorine-based powder or a dispersion liquid may be added to the catalyst dispersion. As a coating method, a conventionally known method such as a spray method, a doctor blade method, and a screen method can be used.

The gas diffusion electrode thus produced
The case where the electrolyte membrane assembly is applied to a direct methanol fuel cell will be described below. First, as the anode, a porous electrolyte having three-dimensionally interconnected pores electrolessly plated with a platinum group metal is used as the catalyst layer as it is, without joining a gas diffusion layer such as water-repellent carbon paper. This can be used as an electrode as it is. As the cathode, a gas diffusion electrode having a catalyst layer made of a porous electrolyte having three-dimensionally interconnected pores, which has been subjected to electroless plating of the above-mentioned platinum group metal, may be used. It is preferable to use a gas diffusion electrode-electrolyte membrane assembly in which a gas diffusion electrode is bonded on a plated porous electrolyte layer having three-dimensionally connected pores.

For example, the catalyst layer-electrolyte-gas diffusion electrode assembly obtained by the above-described combination is sandwiched between a pair of gas-impermeable separators having gas supply passages to form a unit cell serving as a basic unit. By stacking a plurality of such cells, a direct methanol fuel cell can be constructed.

In the direct methanol fuel cell thus manufactured, by supplying, for example, oxygen as an oxidizing agent to the cathode and a mixture of methanol and water as the fuel to the anode, the following reaction occurs and power is taken out.

At the anode, an electrochemical reaction of CH ₃ OH + H ₂ O → 6H ⁺ + CO ₂ + 6e ^{− at the} cathode proceeds at 3 / 2O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O, and protons convert the electrolyte. The electrons move from the anode to the cathode through, and the electrons move to the cathode after being guided from the anode to an external load.

[0044]

(Example 1) Gas diffusion in which a porous electrolyte layer having three-dimensionally communicating pores is formed on at least one surface of an electrolyte membrane, and a gas diffusion electrode is joined on the porous electrolyte layer. An electrode-electrolyte membrane assembly, in which a gas diffusion electrode-electrolyte assembly having a structure in which a platinum group metal is supported on the porous electrolyte layer is produced and applied to a fuel cell, for example, The present invention will be specifically described with reference to the drawings.

First, a method for forming a porous electrolyte having three-dimensionally connected pores on both sides of the electrolyte membrane will be described. The method consists of five steps.

In the first step, the concentration of the electrolyte solution is adjusted. A commercially available 5 wt% Nafion solution was placed in a sample bottle, and heated to 60 ° C with stirring to concentrate the solution to 16 wt%.

In the second step, a pretreatment is performed on the electrolyte membrane. After washing the commercially available Nafion 115 membrane three times with purified water, it is boiled with 3% hydrogen peroxide for one hour as a degreasing treatment, washed three times again with purified water, and further boiled with purified water for one hour. To purified water at room temperature. After that, the electrolyte membrane was immersed in ethanol for 10 minutes to make Nafion 115
The membrane was fully swollen.

In the third step, a coating layer of an electrolyte solution is formed on both sides of the Nafion 115 film. The defatted and ethanol-treated Nafion 115 membrane is removed from the ethanol, and the swollen Nafion 115 membrane is removed using a filter paper.
After wiping off excess ethanol on the surface of the membrane,
16w quickly so that the Nafion 115 membrane does not dry
The t% Nafion solution was applied to both sides of the electrolyte membrane by spraying, and a coating layer of the electrolyte solution was formed on both sides of Nafion 115. The applied amount of this Nafion solution was about 15 mg / cm ² on one side.

In the fourth step, a porous electrolyte having three-dimensionally connected pores on both sides of the Nafion 115 membrane is formed. Nafion 1 with coated electrolyte solution on both sides
15 was immersed in butyl acetate for 10 minutes, taken out and dried at room temperature. The 16 wt% Nafion solution applied to both sides of the electrolyte membrane solidifies to form a porous electrolyte having three-dimensionally communicating pores, and the thickness thereof is about 22 μm.
m.

In the fifth step, a pretreatment is performed on the electrolyte membrane. After the produced electrolyte membrane was washed three times with purified water, it was washed with 0.1 mL of water.
The mixture was boiled with 5 M dilute sulfuric acid for 1 hour to replace the counter ion of the electrolyte with the proton type, washed five times with purified water, and stored in purified water. The thus-prepared Nafion 115 having a porous electrolyte having three-dimensionally connected pores on both surfaces is defined as an electrolyte membrane A1. FIG. 2 shows an electron micrograph showing the surface properties of the electrolyte membrane A1.

As shown in the figure, the communicating void portions are formed three-dimensionally, and the continuous electrolyte portion is formed three-dimensionally.

Next, a method for supporting a platinum group metal on both surfaces of the electrolyte membrane A1 will be described. This method consists of three steps.

In the first step, the counter ion of the electrolyte membrane A1 is exchanged for a complex ion of a platinum group metal. Hexammineplatinum (〓) chloride salt was dissolved in purified water to prepare a 0.006 M aqueous solution. The electrolyte membrane A1 was immersed in this aqueous solution for 2 hours, and the counter ion of the electrolyte was exchanged for a platinum ammine complex ion.

In the second step, platinum ammine complex ions are reduced to deposit platinum metal. Sodium borohydride was dissolved in purified water to prepare 0.04% and 1% sodium borohydride aqueous solutions. First, the electrolyte membrane A1 ion-exchanged in a 0.04% sodium borohydride aqueous solution was immersed for 30 minutes, and then washed three times with purified water. This operation was repeated three times. Next, after immersing the electrolyte membrane A1 in a 1% aqueous solution of sodium borohydride for 1 hour,
Washed three times with purified water. When the reduction treatment with the aqueous sodium borohydride solution was performed, the platinum ammine complex ion was reduced to platinum metal, and the platinum metal was deposited on the surface of the porous electrolyte having three-dimensionally conductive pores.

In the third step, washing is performed with an acidic aqueous solution. An electrolyte membrane A1 on which platinum metal is deposited to remove residues and impurities of hexaammineplatinum (〓) chloride salt
Is boiled with 0.5 M diluted sulfuric acid for 1 hour, and then washed five times with purified water. At this time, the deposited platinum metal was about 1 mg / cm ² on one surface. An electrolyte membrane A2 is obtained by subjecting a surface of a porous electrolyte having pores of three-dimensional communication formed on both sides of the thus-prepared Nafion 115 membrane to electroless plating of platinum metal. FIG. 1 shows an electron micrograph showing the surface properties of the electrolyte membrane A2.

As shown in the figure, the shape of the electrolyte membrane A1 is taken over, the communicating holes are formed three-dimensionally, and the continuous electrolyte part is formed three-dimensionally. FIG. 3 is a schematic diagram showing the basic configuration of the surface of the porous electrolyte having three-dimensionally communicating pores. 1 is an electrolyte part of a porous electrolyte having three-dimensionally communicating pores, 2 is a pore part of a porous electrolyte having three-dimensionally communicating pores, and 3 is a porous electrolyte having three-dimensionally communicating pores. Represents the opening diameter of the pore portion, and 4 represents the diameter of the electrolyte portion of the porous electrolyte having three-dimensionally communicating pores.

In FIG. 1, the pore diameter of the pore portion of the porous electrolyte having three-dimensionally communicating pores is 0.3 to 5.0 μm.
m, the diameter of the electrolyte portion of the porous electrolyte having pores having three-dimensional communication is 0.2 to 1.0 μm, and the porosity is 70%.
In addition, depending on the concentration of the Nafion solution applied to the electrolyte membrane, the opening diameter of the mesh portion of the network skeleton structure of the porous electrolyte having three-dimensionally communicating pores is in the range of 0.1 to 10 μm. A diameter in the range of 0.1 to 30 μm,
Porosity can be adjusted in the range of 10-90%.
The thickness of the porous electrolyte having pores with three-dimensional communication formed on the surface of the electrolyte membrane can be adjusted in the range of 1 to 50 μm depending on the amount of the Nafion solution to be applied.

Next, the step of forming a gas diffusion electrode-electrolyte membrane assembly using the electrolyte membrane A2 will be described.
The method consists of five steps.

In the first step, a catalyst dispersion is prepared.
45 ml of purified water was added to 2.6 g of a carbon catalyst supporting 30 wt% of platinum, and then 45 ml of 2-propanol was added while gradually diffusing the platinum-supported carbon catalyst into water / 2-.
Disperse in a propanol mixed solvent, and further mix for 30 minutes using a stirrer. 0.5 ml of a PTFE dispersion solution (manufactured by Du Pont-Mitsui Fluorochemicals, PTFE solid component: 60%) is gradually added to this mixture with stirring, and after addition, the mixture is stirred for 30 minutes, and then a 5 wt% Nafion solution (Aldrich, USA) 17.5 ml) was gradually added with stirring, and further stirred for 30 minutes to prepare a catalyst dispersion.

In the second step, the catalyst dispersion is added to the electrolyte membrane A
2 to form a catalyst layer. The prepared catalyst dispersion was applied to both sides of the electrolyte membrane A2 in a square shape of 5 cm × 5 cm by a spray method, and then dried to form catalyst layers on both sides of the electrolyte membrane A2. The catalyst dispersion was applied such that the content of the platinum catalyst in this catalyst layer was about 0.3 mg / cm ² .

In the third step, a gas diffusion layer is formed.
A water-repellent carbon paper cut into a square of 5 cm × 5 cm as a gas diffusion layer is disposed on both sides of an electrolyte membrane A2 having a catalyst layer formed on both sides, and 120 kg / c.
Bonding was performed by heating and pressing under a condition of m ² at 135 ° C. for 5 minutes to produce a gas diffusion electrode-electrolyte membrane assembly according to the present invention. This is referred to as a gas diffusion electrode-electrolyte membrane assembly A.

The gas diffusion electrode-electrolyte membrane assembly A manufactured as described above is sandwiched between metal separators having gas supply passages formed therein to manufacture a solid polymer electrolyte type fuel cell A according to the present invention. did.

Comparative Example 1 A gas diffusion electrode-electrolyte membrane assembly in which a catalyst layer was formed on a Nafion 115 membrane having a porous electrolyte having three-dimensionally communicating pores on both surfaces and a gas diffusion layer was bonded. did. That is, the catalyst dispersion prepared in Example 1 was applied to both surfaces of the electrolyte membrane A1 prepared in Example 1 in a square shape of 5 cm × 5 cm by a spray method, and dried to form a catalyst layer. The content of the platinum catalyst in this catalyst layer was about 0.3 mg / cm ² .

Next, a water-repellent carbon paper cut into a square of 5 cm × 5 cm as a gas diffusion layer was placed on both sides of the electrolyte membrane A 1 having a catalyst layer formed on both sides, and 120 kg / cm ² at 135 ° C. The gas diffusion electrode of the comparative example was joined by heating and pressure welding under the condition of 5 minutes.
An electrolyte membrane assembly was produced. This is referred to as a gas diffusion electrode-electrolyte membrane assembly B.

The solid polymer electrolyte fuel cell B of the present invention was constructed by sandwiching the gas diffusion electrode-electrolyte membrane assembly B thus produced by a metal separator having a gas supply passage formed therein.

(Comparative Example 2) A Nafion 115 membrane was boiled with a 3% concentration of hydrogen peroxide for 1 hour, washed with purified water five times, and then boiled with 0.5M diluted sulfuric acid for 1 hour to form a proton. After replacing with a mold, the resultant was washed five times with purified water. The normal surface electrolyte membrane thus obtained was used as the electrolyte membrane C1. A platinum metal deposition layer was formed on both sides of a 5 cm × 5 cm portion of the electrolyte membrane C1 by electroless plating using the same platinum ammine complex as in Example 1. This is used as the electrolyte membrane C2.
And The amount of platinum metal deposited at this time is about 1 mg / c
m ² .

Next, the catalyst dispersion prepared in Example 1 was applied to both sides of a 5 cm × 5 cm portion of the electrolyte membrane C2 by a spray method, and dried to form a catalyst layer.

Further, a water-repellent carbon paper cut into a square of 5 cm × 5 cm as a gas diffusion layer was placed on both sides of an electrolyte membrane C 2 having a catalyst layer formed on both sides, and was placed at 120 kg / cm ² at 135 ° C. By bonding by heating and pressing under the condition of minutes, a gas diffusion electrode-electrolyte membrane assembly was produced. This is referred to as a gas diffusion electrode-electrolyte membrane assembly C.

The gas diffusion electrode-electrolyte membrane assembly C produced in this manner was sandwiched between metal separators having gas supply passages formed therein to form a solid polymer electrolyte fuel cell C of the present invention.

The solid polymer electrolyte fuel cells A, B and C were operated under the following conditions, and the current-voltage characteristics were measured. After humidifying with a bubbler humidifier set at 60 ° C using pure hydrogen as the fuel gas,
The battery was supplied at a flow rate at which the utilization factor became 70%. After humidifying with a bubbler humidifier set to 60 ° C. using pure oxygen as the oxidizing gas, the gas was supplied to the battery at a flow rate at which the utilization factor became 50%. The reaction gases were each supplied at atmospheric pressure. Coolant at 65 ° C. was circulated through the battery to keep the battery temperature constant.

FIG. 4 shows current-voltage characteristics of the solid polymer electrolyte fuel cells A, B and C. As is apparent from FIG. 4, the solid polymer electrolyte fuel cell A including the gas diffusion electrode-electrolyte membrane assembly of the present invention has a high output with little decrease in voltage due to an increase in current, and has a three-dimensional structure on both surfaces. A solid polymer electrolyte fuel cell B provided with a gas diffusion electrode-electrolyte membrane assembly using an electrolyte membrane formed with a porous electrolyte having communicating pores has a high output. The solid polymer electrolyte fuel cell C provided with a conventional gas diffusion electrode-electrolyte membrane assembly using an electrolyte membrane in which platinum metal was deposited on the surface of the membrane had the lowest output.

In the gas diffusion electrode-electrolyte membrane assembly of the present invention, a porous electrolyte having three-dimensionally communicating pores is formed on the surface of the electrolyte membrane, and the surface area of the porous electrolyte is large, and the porous electrolyte has a large surface area. The interface was significantly increased, and the platinum at the interface between the electrolyte and the catalyst layer was increased, whereby a highly active catalyst layer could be formed.

(Example 2) Nafion 11 provided with a porous electrolyte having pores of three-dimensional communication produced in Example 1
A direct methanol fuel cell including an electrolyte membrane A2 in which five films were subjected to electroless plating of platinum metal was manufactured. First, after dispersing 3 g of platinum black in 50 ml of purified water, 5 w
5.3 ml of a t% Nafion solution was added and stirred for 30 minutes to prepare an ink-like catalyst dispersion. This is designated as catalyst dispersion P. Next, Pt-RuOx was added to 50 ml of purified water.
(Pt: Ru = 1: 1) After dispersing 3 g, 5 wt%
12.5 ml of Nafion solution was added and stirred for 30 minutes to prepare an ink-like catalyst dispersion. This is called Catalyst Dispersion R
And On one surface of the electrolyte membrane A2, a catalyst dispersion P was applied in a circular shape having a diameter of 3 cm by spraying and dried to form a cathode catalyst layer. Platinum amount is about 2.5mg
/ Cm ² . On the other surface of the electrolyte membrane A2, a catalyst dispersion R having a diameter of 3 cm was formed by spraying.
Was applied and dried to form an anode catalyst layer. The amount of platinum was about 2.0 mg / cm ² . Carbon paper is disposed on both sides of the electrolyte membrane A on which the cathode and the anode are formed, and heated and pressed (120 kg / cm 2, 13 kg).
(5 ° C, 5 minutes) to form a gas diffusion electrode
An electrolyte membrane assembly D was produced.

The gas diffusion electrode-electrolyte membrane assembly D thus produced was sandwiched between metal separators in which gas supply passages were formed, whereby a direct methanol fuel cell D according to the present invention was constructed.

(Comparative Example 3) A direct methanol fuel cell provided with the electrolyte membrane A1, which is a Nafion 115 provided with a porous electrolyte having pores having three-dimensional communication on both sides prepared in Example 1 was manufactured. On one surface of the electrolyte membrane A1, the catalyst dispersion P prepared in Example 2 was applied in a circular shape having a diameter of 3 cm by spraying and dried to form a cathode catalyst layer. The amount of platinum was about 2.5 mg / cm ² . The other surface of the electrolyte membrane A1 is sprayed with a diameter of 3
The catalyst dispersion R prepared in Example 2 was applied in a circular shape having a diameter of 10 cm and dried to form an anode catalyst layer. The amount of platinum is
It was about 2.0 mg / cm ² . Carbon paper is placed on both sides of the electrolyte membrane A1 on which the cathode and the anode are formed, and heated and pressed (120 kg / cm ² , 135 kg).
(C, 5 minutes) to form a gas diffusion electrode-electrolyte membrane assembly E.

This gas diffusion electrode-electrolyte membrane assembly E was
A direct methanol fuel cell E having a conventional structure was manufactured by sandwiching the metal separator having a gas supply passage formed therein.

The direct methanol fuel cells D and E were operated under the following conditions, and the current-voltage characteristics were measured. Oxygen pressurized to 3 atm is supplied to the cathode, and 2
1M methanol / water pressurized to atmospheric pressure was supplied. A coolant at 110 ° C. was circulated through the battery to keep the battery temperature constant.

FIG. 5 shows the current-voltage characteristics of the direct methanol fuel cells D and E. As is clear from FIG. 5, the direct methanol fuel cell D provided with the gas diffusion electrode-electrolyte membrane assembly D of the present invention has a porous electrolyte having three-dimensionally connected pores on both surfaces, but the surface thereof has The output is higher than that of the direct methanol fuel cell E including the gas diffusion electrode-electrolyte membrane assembly E using an electrolyte membrane in which platinum metal is not electrolessly plated. Even in a direct methanol fuel cell, the method of forming platinum metal at the interface between the electrolyte and the catalyst layer was effective in increasing the output.

[0079]

According to the gas diffusion electrode-electrolyte membrane assembly of the present invention, the contact area of the interface between the electrolyte membrane and the catalyst can be increased, and the ionic conductivity is reduced due to the contamination of impurities and the deterioration of the electrolyte. Therefore, it is possible to effectively form a region having a high catalytic activity at the interface between the electrolyte and the catalyst layer, and by using such a gas diffusion electrode-electrolyte membrane assembly, a high-output fuel cell Can be manufactured.

Further, according to the fuel cell of the present invention, it is possible to manufacture a high-output solid polymer electrolyte fuel cell.

[Brief description of the drawings]

FIG. 1 is a view (electron micrograph) showing the surface properties of an electrolyte membrane A2.

FIG. 2 is a view (electron micrograph) showing a surface property of an electrolyte membrane A1.

FIG. 3 is a schematic diagram showing a basic configuration of a surface of a porous electrolyte having three-dimensionally communicating pores.

FIG. 4 is a diagram showing current-voltage characteristics of solid polymer electrolyte fuel cells A, B, and C.

FIG. 5 is a diagram showing current-voltage characteristics of direct methanol fuel cells D and E.

[Explanation of symbols]

1: electrolyte part 2: hole part 3: opening diameter of hole part 4: diameter of electrolyte part

Claims (3)

[Claims] 1. A gas diffusion electrode-electrolyte membrane comprising: a porous electrolyte layer having three-dimensionally connected pores formed on at least one surface of an electrolyte membrane; and a gas diffusion electrode joined to the porous electrolyte layer. A gas diffusion electrode-electrolyte membrane assembly, wherein a platinum group metal is supported on the porous electrolyte layer. 2. The gas diffusion electrode-electrolyte membrane bonding according to claim 1, wherein the platinum group metal carried on the porous electrolyte layer is mainly distributed near the surface of the porous electrolyte layer. body. 3. A gas diffusion electrode comprising a porous solid polymer electrolyte layer having three-dimensionally communicating pores formed on at least one surface of the solid polymer electrolyte membrane, and a laminate of a catalyst layer and a gas diffusion layer. Is provided with a gas diffusion electrode-electrolyte membrane assembly joined so that the catalyst layer is in contact with the porous solid polymer electrolyte layer, and a platinum group metal is supported on the porous solid polymer electrolyte layer A fuel cell, characterized in that: