JP2000235859A - Gas diffusing electrode and fuel cell provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the active over-voltage, resistant over-voltage and concentration over-voltage of an electrode by providing the porous electrolyte having three-dimensional communication holes, and providing catalyst and electrolyte in the described holes, and setting the ion exchange capacity of the porous electrolyte larger than the ion exchange capacity of the electrolyte in the holes. SOLUTION: In a first gas diffusing electrode 5, a first gas diffusing layer 4 is bonded to a first catalyst layer 1. A fine porous aggregate 3 including the catalyst and the electrolyte B is included in the holes of the porous electrolyte A having three-dimensional communication holes. The porous electrolyte A is formed with a route for proton conduction, and the catalyst and the electrolyte B included in the holes form a three-phase interface. Since the porous electrolyte A2 has high proton conductivity, proton conductivity of the first catalyst layer 1 is improved. Since the electrolyte B coating the catalyst in the first catalyst layer 1 and forming the three-phase interface has a relatively large solubility of the reactive material, supplying property of the reactive material such as oxygen and hydrogen to the reaction site is improved.

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 of a solid polymer electrolyte fuel cell and a fuel cell having the same.

[0002]

2. Description of the Related Art A solid polymer electrolyte fuel cell is an electrochemical device which supplies hydrogen, for example, as a fuel to an anode and oxygen, for example, as an oxidant to a cathode and electrochemically reacts to obtain electric power. . The anode and the cathode are gas diffusion electrodes, and the anode is joined to one surface of the electrolyte membrane and the cathode is joined to the other surface to form a gas diffusion electrode.
Construct an electrolyte membrane assembly.

The gas diffusion electrode is composed of a gas diffusion layer and a catalyst layer. The catalyst layers of the anode and the cathode are provided with metal particles of platinum group metals or carbon particles carrying these particles as catalysts. For example, porous carbon paper having water repellency is used. This gas diffusion electrode-electrolyte membrane assembly is sandwiched between a pair of gas-impermeable separators in which gas supply channels are formed to form a unit cell as a basic unit. A plurality of such unit cells are stacked to form a solid polymer electrolyte fuel cell.

When a solid polymer electrolyte fuel cell is operated, the following electrochemical reaction proceeds.

Anode: 2H ₂ → 4H ⁺ + 4e ⁻ Cathode: O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O Generally, in a fuel cell for reacting oxygen and hydrogen,
A large activation overpotential of the oxygen reduction reaction is one of the causes of the voltage drop at a high current density. Therefore, a catalyst such as a platinum group metal is applied to the electrode to reduce the activation overpotential.

In a solid polymer electrolyte fuel cell having a solid polymer electrolyte membrane, an electrochemical reaction between a cathode and an anode is formed at a so-called three-phase interface formed by a catalyst, an electrolyte, and a reactant contained in the cathode and the anode. proceed. Therefore, in order to increase the output of these fuel cells, it is required to increase the contact area between the catalyst and the electrolyte.

[0007] In order to increase the output of a solid polymer electrolyte fuel cell, there is a method of increasing the contact area between an electrode containing a catalyst, particularly a catalyst layer in the electrode and the electrolyte membrane, by providing irregularities on the surface of the electrolyte membrane. Invented. One method is to increase the surface area of the solid polymer electrolyte membrane to increase the contact surface with the electrode. For example, JP-A-3-158486 discloses a method using a roll having irregularities, and JP-A-4-1690069.
Discloses a method using sputtering, see JP-A-4-220
No. 957 proposes a method using plasma etching, and Japanese Unexamined Patent Publication No. Hei 6-279600 proposes a method of providing unevenness on the surface of a solid polymer electrolyte membrane by a method of embedding a cloth and then peeling it off.

Alternatively, there is a method in which holes are provided in the surface of the solid polymer electrolyte membrane to increase the contact surface between the electrolyte membrane and the catalyst layer. For example, JP-A-58-7432 discloses a method of crystallizing a dispersion medium for dissolving an electrolyte into small droplets and removing the droplets. JP-A-62-146926 discloses a method of removing particles after embedding the particles, or JP-A-5-1
No. 94764 proposes a method of mixing and removing low-molecular-weight organic materials.

Another method is to carry a platinum group metal on the surface of the electrolyte membrane to increase the contact interface between the electrolyte and the catalyst. For example, Japanese Patent Publication No. 59-42078 and Japanese Patent Publication No. 2-43830 propose a method of performing electroless plating on the surface of an electrolyte.

Further, there is a method of increasing the contact surface between the catalyst and the electrolyte by adding an electrolyte to the catalyst layer. For example, in Japanese Patent Publication No. 2-7398, a solution of a catalyst and an electrolyte and PTFE
Such as a method of producing an electrode from a mixture of fluororesins,
Japanese Patent Publication No. 2-7399 states that catalyst coated with electrolyte and PTF
A method for producing an electrode from a fluororesin such as E has been proposed. Further, US Pat. No. 5,221,1984 proposes a method for producing an electrode from a mixture of a catalyst and an electrolyte solution.

[0011]

As described above, in the method using a roll, the method using sputtering, the method using plasma etching, or the method using cloth,
There is a problem that the process of providing the unevenness is complicated, resulting in inferior productivity, and that the formed unevenness is coarse 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. Residues hinder contact between the electrolyte membrane and the electrode and cause a decrease in electrode activity. Alternatively, these residues hinder ionic conduction between the electrolyte membrane and the electrode. 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 the above reasons, there is a problem that the performance of a fuel cell using these electrolyte membranes is reduced.

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, and the improvement of the catalyst activity by this method is insufficient.

With respect to a catalyst layer comprising a catalyst and an electrolyte,
That the proton conductivity is low and the resistance of proton transfer is large, or that the part where the influence of the decrease in voltage due to the resistance of proton transfer is small is near the electrolyte membrane,
J. Electrochem. Soc. , 140 , 35
13 (1993). In such a catalyst layer, as the amount of the catalyst increases, the thickness of the catalyst layer also increases. Therefore, at a high current density, the effect of the voltage drop due to the resistance of the catalyst layer to proton transfer increases.

That is, the effect of reducing the activation overvoltage due to the increase in the amount of catalyst and the effect of increasing the resistance overvoltage due to the increase in the thickness of the catalyst layer have a trade-off relationship. For this reason, there is a problem that the improvement of the characteristics is not so large as to the increase in the amount of the catalyst.

[0016]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to increase the amount of a catalyst in a catalyst layer to form a large number of so-called three-phase interfaces in which an electrode reaction proceeds. Reducing the activation overpotential, and improving the proton conductivity of the catalyst layer to suppress the voltage drop caused by the resistance of proton transfer, and further forming an appropriate hole in the catalyst layer, and By increasing the solubility of the reactants in the electrolyte forming the three-phase interface in the layer,
An object of the present invention is to provide a high-output fuel cell by reducing concentration overvoltage.

As the electrolyte of the solid polymer electrolyte fuel cell, an ion exchange resin having proton conductivity such as perfluorosulfonic acid resin is used. In the catalyst layer, the catalyst is coated with the ion exchange resin as the electrolyte. The reactants are supplied by dissolving and diffusing into the electrolyte, forming a so-called three-phase interface where the catalyst, the electrolyte and the reactants come into contact.

Generally, an ion exchange resin as an electrolyte has a property that the proton conductivity is high when the ion exchange capacity is large, and the solubility of the reactant is high when the ion exchange capacity is small. By using this characteristic to improve the proton conductivity of the electrolyte contained in the catalyst layer and the supply property of the reactant for each function, it is possible to achieve both the proton conductivity and the supply property of the reactant as the whole catalyst layer. .

That is, a porous electrolyte having three-dimensionally communicating pores is formed of a resin having a relatively large ion exchange capacity and a high proton conductivity in the catalyst layer to improve the proton conductivity. By providing a catalyst coated with a resin having a relatively small ion exchange capacity and a high solubility of the reactant in the pores, the supply of the reactant to the so-called three-phase interface is improved.

According to a first aspect of the present invention, in a gas diffusion electrode having a catalyst layer and a gas diffusion layer, the catalyst layer includes a porous electrolyte A having three-dimensionally communicating pores, and a catalyst and an electrolyte B in the pores. A gas diffusion electrode having a structure including a microporous aggregate, wherein the ion exchange capacity of the porous electrolyte A is larger than the ion exchange capacity of the electrolyte B in the pores.

The second invention is characterized in that, in the first invention, both the porous electrolyte A and the electrolyte B in the pores thereof are perfluorosulfonic acid resins.

A third invention is a solid polymer electrolyte fuel cell including the gas diffusion electrode according to the first invention or the second invention.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION In the catalyst layer of the gas diffusion layer according to the present invention, the porous electrolyte A having three-dimensionally communicating pores forms a proton conduction path, and the catalyst contained in the pores and the electrolyte are contained. B forms a so-called three-phase interface. Since the porous electrolyte A forming the proton conduction path in the catalyst layer has high proton conductivity, the proton conductivity of the catalyst layer is improved. Further, since the electrolyte B in the catalyst layer, which covers the catalyst and forms a three-phase interface, has a relatively high solubility of the reactant, the supply of the reactant such as oxygen and hydrogen to the reaction site is improved.

Porous electrolyte A having three-dimensionally communicating pores
In, the electrolyte A forms a three-dimensional network-like skeleton structure, and at the same time, three-dimensionally communicating holes are formed in the thickness direction and the plane direction. The surface area of the porous electrolyte A is extremely large because micropores are formed three-dimensionally. For this reason, the contact area in which protons are exchanged between the porous electrolyte A and the electrolyte B that covers the catalyst provided in the pores increases. Therefore, the protons involved in the reaction are produced by the porous electrolyte A having high proton conductivity.
And the electrolyte B having low proton conductivity
Is minimized, so that a voltage drop due to the movement of protons can be prevented.

In the catalyst layer of the gas diffusion electrode according to the present invention, the microporous aggregate containing the catalyst and the electrolyte B provided in the pores of the porous electrolyte A having three-dimensionally communicating pores is, for example, PTFE or the like. Or a conductive particle such as carbon or metal. In short, the microporous aggregate containing at least the catalyst and the electrolyte B may be provided in the pores. As the catalyst, a platinum group metal, an alloy thereof, or an oxide thereof, or a catalyst in which a platinum group metal, an alloy thereof, or an oxide thereof is supported on a conductive carrier such as carbon can be used.

FIG. 2 shows an example of the manufacturing process of the gas diffusion electrode according to the present invention. The manufacturing process can be divided into five steps. In the first step, a porous electrolyte A having three-dimensionally communicating pores is formed using an ion exchange resin having high proton conductivity, that is, a large ion exchange capacity. In the second step, a catalyst dispersion is prepared by dispersing a catalyst such as a platinum-supported carbon catalyst in a solution containing an electrolyte B made of an ion exchange resin having a high solubility of a reactant, that is, a small ion exchange capacity. In the third step, the catalyst dispersion is applied to the porous electrolyte A having three-dimensionally communicating pores. In the fourth step, the catalyst dispersion is filled into the pores of the porous electrolyte A having three-dimensionally communicating pores by a method such as pressing, and the catalyst and the electrolyte B are filled in the pores. Comprising a microporous assembly. In the fifth step, a gas diffusion electrode is prepared by bonding water-repellent carbon paper as a gas diffusion layer.

Next, an example of a specific method for manufacturing the gas diffusion electrode according to the present invention will be described.

In the first step, a solution in which the electrolyte A is dissolved in a solvent containing alcohols is applied to at least one surface of the electrolyte membrane C of the fuel cell, and then the organic solvent having a polar group other than the alcoholic hydroxyl group is applied. To produce a porous electrolyte A having three-dimensionally communicating pores.

The solution obtained by dissolving the electrolyte A in a solvent containing alcohols is obtained by dissolving a perfluorosulfonic acid resin in a mixed solvent of water and alcohol. As the alcohol used in the mixed solvent, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol or a mixture thereof having 4 or less carbon atoms can be used. As a method of applying the solution in which the electrolyte A is dissolved to the electrolyte membrane C of the fuel cell, a method such as application or impregnation using a conventionally known method such as spraying, doctor blade method, screen printing method, or the like can be used.

As the electrolyte membrane C of the fuel cell, a polymer membrane having proton conductivity can be used, and for example, a perfluorosulfonic acid resin membrane can be used.

Examples of the organic solvent having a polar group other than the alcoholic hydroxyl group include organic solvents having an alkoxycarbonyl group in the molecule and having 1 to 7 carbon atoms, such as propyl formate, butyl formate, and formic acid. Isobutyl, ethyl acetate, propyl acetate, isopropyl acetate, allyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, isopentyl acetate, methyl propionate, ethyl propionate, 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, 2- (2-ethoxyethoxy) ethyl acetate, etc., alone or in mixture, or in the molecule Carbon of carbon chain with ether bond Is an organic solvent having 3 to 5, for example, dipropyl ether, dibutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, tripropylene glycol monomethyl ether, alone or a mixture of tetrahydrofuran, or a carbon chain having a carbonyl group in the molecule. 4-8 carbon atoms
Organic solvents, for example, methyl butyl ketone, methyl isobutyl ketone, methyl hexyl ketone, alone or a mixture of dipropyl ketone, or an organic solvent having 1 to 5 carbon atoms in the carbon chain having an amino group in the molecule, for example, Isopropylamine, isobutylamine, tert-butylamine, isopentylamine, a single or mixture of diethylamine, or an organic solvent having 1 to 6 carbon atoms in the carbon chain having a carboxyl group in the molecule, for example, propionic acid, valeric acid, Caproic acid, heptanoic acid, etc., alone or in combination, or a combination thereof can be used. However, the organic solvent having a polar group other than the alcoholic hydroxyl group used for forming the porous electrolyte A having three-dimensionally communicating pores preferably has an alkoxycarbonyl group.

In the second step, the catalyst is dispersed in a dispersion medium, and a solution in which the electrolyte B is dissolved is added thereto and mixed well to prepare a catalyst dispersion. As the dispersion medium, water or an alcohol having 4 or less carbon atoms, such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, or a mixture thereof can be used.

The solution in which the electrolyte B is dissolved is obtained by dissolving a perfluorosulfonic acid resin in a mixed solvent of water and alcohol. As the alcohol of the mixed solvent, methanol, ethanol, 1-propanol having 4 or less carbon atoms,
2-propanol, 1-butanol, 2-butanol or a mixture can be used.

The ion exchange capacity of the perfluorosulfonic acid resin used as the electrolyte B is smaller than the ion exchange capacity of the porous electrolyte A having three-dimensionally communicating pores prepared in the first step.

In the third step, the catalyst dispersion prepared in the second step is applied to the surface of the porous electrolyte A having three-dimensionally communicating pores prepared in the first step. In this step, for example, a coating method such as spraying, a doctor blade method, a screen printing method, or a conventionally known method such as a precipitation method or an impregnation method can be used.

In the fourth step, the pores of the porous electrolyte A having the three-dimensionally communicating pores are pressed by, for example, applying pressure to the porous electrolyte A having the three-dimensionally communicating pores provided with the catalyst dispersion. A catalyst dispersion is filled therein, and a catalyst layer having a microporous aggregate containing a catalyst and an electrolyte B in its pores is formed. The compression can be applied by a method such as a flat press or a roll press. At this time, moderate pores may be formed in the pores of the porous electrolyte A without being completely filled with the microporous aggregate containing the catalyst and the electrolyte B.

In the fifth step, the gas diffusion layer is joined to produce the gas diffusion electrode of the present invention. As the gas diffusion layer, for example, a sheet formed by using a water-repellent carbon paper or carbon powder as a binder with a water-repellent fluorine-based resin such as PTFE can be used.

As an example of the present invention, a schematic diagram of a cross section of a gas diffusion electrode / electrolyte membrane assembly having a gas diffusion electrode according to the present invention provided on one surface of an electrolyte membrane C of a fuel cell is shown in FIG. FIG.
, 1 is a first catalyst layer, 2 is a porous electrolyte A having three-dimensionally communicating pores, and 3 is a microporous aggregate containing a catalyst and an electrolyte B. The microporous aggregate 3 containing the catalyst and the electrolyte B is contained in the pores of the porous electrolyte A having three-dimensionally communicating pores. The ion-exchange capacity of the ion-exchange resin constituting the porous electrolyte A having the two-dimensionally communicating pores is the electrolyte B of the porous assembly containing the catalyst 3 and the electrolyte B.
Is larger than the ion exchange capacity of the ion exchange resin constituting the above. Reference numeral 4 denotes a first gas diffusion layer, and reference numeral 5 denotes a first gas diffusion electrode. As the first gas diffusion layer 4, for example, carbon paper having water repellency can be used. The first gas diffusion electrode 5 is obtained by joining the first gas diffusion layer 4 to the first catalyst layer 1.

Reference numeral 6 denotes an electrolyte membrane C of the fuel cell, which is provided with a first gas diffusion electrode 5 of the present invention on one side and a second gas diffusion electrode 9 on the other side. The second gas diffusion electrode 9 is formed by joining the second gas diffusion layer 8 to the second catalyst layer 7. Second
The catalyst layer 7 is composed of, for example, a catalyst dispersion composed of a catalyst and an electrolyte, and the second gas diffusion layer 8 is composed of, for example, the same material as the first gas diffusion layer 4.

The first surfaces of both sides of the electrolyte membrane C (6) of the fuel cell
Provided with the gas diffusion electrode 5 or the second gas diffusion electrode 9, or provided with the first gas diffusion electrode 5 on one side of the electrolyte membrane C (6) and the second gas diffusion electrode 9 on the other side. This is the gas diffusion electrode electrolyte membrane contact 10.

FIG. 3 is an enlarged schematic view of a microporous assembly comprising a catalyst and an electrolyte B contained in the pores of a porous electrolyte A having three-dimensionally communicating pores. In FIG. 3, 1
1 is a carbon carrier, 12 is a catalyst, and 13 is an electrolyte B. As the carbon carrier 11, for example, carbon black or the like is used. As the catalyst 12, for example, fine powder of a platinum group metal such as platinum or an alloy thereof, platinum black powder or the like can be used. The platinum supported on the carbon carrier 11 as a catalyst is a so-called platinum-supported carbon catalyst. The electrolytic electrolyte B (13) covers the catalyst, and is formed in a film form on and near the surface of the catalyst, has a function of a binder, and forms a so-called three-phase interface in which an electrochemical reaction proceeds. I do. As the electrolyte B (13), an ion exchange resin having a smaller ion exchange capacity and a higher gas permeability than the porous electrolyte A having three-dimensionally communicating pores is used.

Example 1 A method for manufacturing a gas diffusion electrode according to the present invention will be described based on an example.

First step: a step of forming a layer of a porous electrolyte A having three-dimensionally connected pores on one side of an electrolyte membrane C of a fuel cell.

The ion exchange capacity is 1.11 (m · eq / g)
・ Dry resin) perfluorosulfonic acid resin 2
0 g, a mixed solvent of ethanol and water (ethanol: water =
(9: 1, weight ratio), 100 g was mixed, placed in a metal closed container, heated to 240 ° C., and perfluorosulfonic acid resin was dissolved in the mixed solvent to prepare a solution E.

Next, the Nafion 115 membrane as the electrolyte membrane C of the fuel cell was washed three times with purified water, then boiled with 3% hydrogen peroxide for 1 hour, degreased, and washed several times with purified water. The mixture was further boiled with 0.5 M sulfuric acid for 1 hour, protonated, washed several times with purified water, and stored in purified water. Thereafter, the Nafion 115 film was immersed in ethanol for 10 minutes to perform an ethanol treatment to sufficiently swell. The Nafion 115 membrane was removed from ethanol, and excess ethanol present on the surface of the swollen Nafion 115 membrane was wiped off using a filter paper.

Next, the solution E was applied to one side of the Nafion 115 membrane.
Was sprayed to form a coating layer of the solution E. The Nafion 115 membrane was immersed in butyl acetate for 10 minutes, taken out and dried at room temperature to obtain a Nafion 115 membrane having a layer of porous electrolyte A having three-dimensionally connected pores on one side, and this was purified water. Was stored. The portion of the porous electrolyte A layer having three-dimensionally connected pores was 3.5 cm in diameter and about 6 μm in thickness.

Second step: Step of preparing catalyst dispersion M.

The ion exchange capacity is 0.91 (m · eq / g)
・ Dry resin) perfluorosulfonic acid resin 5
g, ethanol and water mixed solvent (ethanol: water = 9:
1, weight ratio) 95g mixed, put in a metal closed container,
The solution was heated to 240 ° C., and the perfluorosulfonic acid resin was dissolved in the mixed solvent to prepare a solution F.

Next, 13 ml of the solution F was gradually added to 1.5 g of a platinum-supported carbon catalyst supporting 30 wt% of platinum while stirring, followed by stirring for 30 minutes. The mixture is further heated to 60 ° C. with stirring, and concentrated until the weight of the solid content of the perfluorosulfonic acid resin with respect to the dispersion medium (a mixed solvent of ethanol and water) becomes 15 wt%. A catalyst dispersion M was prepared in which a perfluorosulfonic acid resin and a platinum-supported carbon catalyst were dispersed.

Third step: a step of applying the catalyst dispersion M to the pores of the porous electrolyte A having three-dimensionally communicating pores.

The Nafion 115 membrane formed with the porous electrolyte A layer having three-dimensionally connected pores on one side was prepared in the first step, so that the surface on which the porous electrolyte A layer was formed was the upper surface. It was placed on a glass plate. The catalyst dispersion M prepared in the second step was applied to the layer of the porous electrolyte A using a doctor blade having a gap adjusted to 15 μm. Next, the portion of the catalyst dispersion M applied to the layer of the porous electrolyte A is left in a circular shape with a diameter of 3 cm, and the unnecessary catalyst dispersion M is removed.
Was removed to form an electrolyte membrane catalyst dispersion applied body.

On the other hand, a release-paper-catalyst-dispersed-coated body having a catalyst layer formed on release paper was prepared. 1.11 ion exchange capacity
5 g of (m · eq / g · dry resin) perfluorosulfonic acid resin and 95 g of a mixed solvent of ethanol and water (ethanol: water = 9: 1, weight ratio) were mixed, and the mixture was placed in a metal closed container. The solution was heated to 240 ° C., and the perfluorosulfonic acid resin was dissolved in the mixed solvent to prepare a solution G. Next, 13 ml of solution G was gradually added to 1.5 g of a platinum-supported carbon catalyst supporting 30 wt% of platinum while stirring, and the mixture was stirred for 30 minutes. 60 ° C with further stirring
And the weight of the solid content of the perfluorosulfonic acid resin with respect to the dispersion medium (a mixed solvent of ethanol and water) is 18 wt.
%, To prepare a catalyst dispersion N in which a perfluorosulfonic acid resin and a platinum-supported carbon catalyst were dispersed in a mixed solvent of ethanol and water. By screen coating, a catalyst dispersion N is applied to a tetrafluoroethylene-hexafluoropropylene copolymer sheet as a release paper,
A release paper catalyst dispersion applied body was prepared and cut into a circular shape having a diameter of 3 cm.

Fourth step: a step of filling the catalyst dispersion M into the pores of the porous electrolyte A having three-dimensionally communicating pores.

The coated electrolyte membrane catalyst dispersion and the release paper catalyst dispersion prepared in the third step were mixed with the surface of Nafion 115 to which the catalyst dispersion M of the electrolyte membrane catalyst dispersion was not coated and the release paper catalyst dispersion. The layers were laminated so that the surfaces of the coated bodies to which the catalyst dispersion N was applied faced each other. In this state, 250k
g / cm ² at 135 ° C. for 5 minutes while applying pressure. Then, the catalyst layer of the release paper catalyst layer dispersion applied body was transferred from the release paper to the Nafion 115 film. Further, on the surface of the electrolyte membrane catalyst dispersion coated body coated with the catalyst dispersion M,
The catalyst dispersion M is filled in the pores of the porous electrolyte A having three-dimensionally communicating pores by heating and pressing, and the catalyst layer provided with the microporous aggregate containing the catalyst and the electrolyte B in the pores is formed. Been formed. In this way, the catalyst layer including the porous electrolyte A having the three-dimensionally connected pores of the present invention on one surface of the Nafion 115 membrane and the microporous aggregate containing the catalyst and the electrolyte B in the pores, and the like. A catalyst layer / electrolyte membrane assembly having a catalyst layer made of the catalyst dispersion N on the surface was prepared.

In this catalyst layer electrolyte membrane assembly, the ion exchange capacity of the porous electrolyte A having three-dimensionally communicating pores is 1.11 (m · eq / g · dry resin), The ion exchange capacity of the electrolyte B in the microporous aggregate contained in the pores of the porous electrolyte A having pores was 0.91 (m · eq / g · dry resin). That is, the ion exchange capacity of the porous electrolyte A having three-dimensionally communicating pores was larger than the ion exchange capacity of the electrolyte B in the microporous aggregate provided in the pores. This catalyst layer electrolyte membrane assembly was designated as catalyst layer electrolyte membrane assembly S of the present invention.

Fifth step: joining of gas diffusion layers.

After impregnated with a dispersion liquid of polytetrafluoroethylene as a gas diffusion layer and dried, calcined at 400 ° C. to give water repellency, thickness 0.2 mm, diameter 3 cm
Are placed on both sides of the catalyst layer-electrolyte membrane assembly S, and heated and pressed (120 kg / cm ² ,
(135 ° C., 5 minutes) to form a gas diffusion electrode / electrolyte membrane assembly T.

The gas diffusion electrode / electrolyte membrane assembly T is sandwiched by a metal separator having a gas supply passage formed thereon, and the catalyst layer of the present invention is disposed on the cathode side to obtain a solid polymer electrolyte fuel cell X. Configured.

[Comparative Example] As a comparative example, the catalyst layer had a structure in which a porous electrolyte A having three-dimensionally communicating pores and a microporous aggregate including a catalyst and an electrolyte B in the pores were used. A gas diffusion electrode having a catalyst layer and a gas diffusion layer in which the ion exchange capacity of the porous electrolyte A is the same as the ion exchange capacity of the electrolyte B in the microporous aggregate is produced by the following five steps. did.

In the first step, using the solution E of the perfluorosulfonic acid resin used in the first step of Example 1, the same degreasing treatment, protonation treatment, and ethanol treatment as in the first step of Example 1 were performed. On one surface of the applied Nafion 115 membrane, a layer of porous electrolyte A having three-dimensionally connected pores was formed. The portion of the porous electrolyte A layer had a diameter of 3.5 cm and a thickness of about 6 μm.

In the second step, in the same manner as in the third step of Example 1, a catalyst dispersion N in which a perfluorosulfonic acid resin and a platinum-supported carbon catalyst were dispersed in a mixed solvent of ethanol and water was prepared.

In the third step, similarly to the third step of the first embodiment, Nafion 115 formed with a layer of porous electrolyte A having three-dimensionally communicating pores on one side formed in the first step.
The catalyst dispersion prepared in the second step was applied to the porous electrolyte A layer of the membrane. Next, leaving a coated portion of the catalyst dispersion N applied to the layer of the porous electrolyte A in a circular shape having a diameter of 3 cm,
Unnecessary catalyst dispersion N was removed to form an electrolyte membrane catalyst dispersion coated body.

On the other hand, in the same manner as in the third step of Example 1,
The catalyst dispersion N was applied to a tetrafluoroethylene-hexafluoropropylene copolymer sheet as release paper to prepare a release paper catalyst dispersion applied product, which was cut into a circular shape having a diameter of 3 cm.

In the fourth step, the coated electrolyte membrane catalyst dispersion and the release paper catalyst dispersion prepared in the third step are combined with the surface of Nafion 115 on which the catalyst dispersion N of the coated electrolyte membrane catalyst is not coated. The release paper catalyst dispersion coated body was laminated so that the surfaces on which the catalyst dispersion N was applied faced each other. In this state, pressure was applied by heating and pressing at 250 kg / cm ² at 135 ° C. for 5 minutes. Then, the catalyst layer was transferred from the release paper to the electrolyte membrane on the surface where the release paper catalyst layer dispersion applied body was laminated. Further, on the surface of the electrolyte membrane catalyst dispersion applied body on which the catalyst dispersion N is applied, the catalyst dispersion M is filled in the pores of the porous electrolyte A having three-dimensionally communicating pores by heating and pressing, and the pores are filled. A catalyst layer provided with a microporous aggregate containing the catalyst and the electrolyte B therein was formed. In this way,
A catalyst layer including a porous electrolyte A having three-dimensionally communicating pores on one surface of a Nafion 115 membrane and a microporous aggregate containing a catalyst and an electrolyte B in the pores, and a catalyst dispersion N on the other surface. A catalyst layer electrolyte membrane assembly V having a catalyst layer was produced. In the catalyst layer electrolyte membrane assembly V, the ion exchange capacities of the porous electrolyte A and the electrolyte B were the same.

In the fifth step, the carbon paper having water repellency is cut into a diameter of 3 cm, and the catalyst layer electrolyte membrane assembly V
On both sides by heating pressure welding (120 kg / cm ² , 135 ° C,
(5 minutes) to form a gas diffusion electrode / electrolyte membrane assembly W.

The gas diffusion electrode / electrolyte membrane assembly W is sandwiched between metal separators having gas supply passages, and a catalyst layer having a porous electrolyte is disposed on the cathode side to provide a solid polymer electrolyte for comparison. A fuel cell Y was constructed.

Pure hydrogen is supplied to the anode and air is supplied to the cathode at a pressure of ² kg / cm ² G, and air and hydrogen are supplied by humidification using a bubbler humidifier set at 60 ° C.
Solid polymer electrolyte fuel cell X with a battery temperature of 65 ° C.
The current-voltage characteristics of the solid polymer electrolyte fuel cell Y were measured. FIG. 4 shows the results.

FIG. 4 shows that the solid polymer electrolyte fuel cell X in which the gas diffusion electrode according to the present invention is disposed at the cathode has a lower cell voltage at a higher current density than the comparative solid polymer electrolyte fuel cell Y. Was small and had a high output.

Thus, in the gas diffusion electrode provided with the catalyst layer and the gas diffusion layer, the microporous assembly containing the porous electrolyte A having the three-dimensionally communicating pores and the catalyst and the electrolyte B in the pores. In the catalyst layer provided with the body, the fact that the ion exchange capacity of the porous electrolyte A is larger than the ion exchange capacity of the electrolyte B in the microporous assembly is effective for increasing the output of the solid polymer electrolyte fuel cell. Was shown.

That is, from FIGS. 2 and 3, the gas diffusion electrode electrolyte membrane assembly T and the gas diffusion electrode electrolyte membrane assembly W
Porous electrolyte A having three-dimensionally communicating pores in its catalyst layer
Due to the formation of (2), the proton conductivity is improved. Further, the gas diffusion electrode electrolyte membrane assembly T
By increasing the solubility of the reactants by using perfluorosulfonic acid resin having a small ion exchange capacity for the electrolyte B (13) covering the catalyst of the catalyst layer, the supply of the reactant gas to the three-phase interface is improved. In addition, even when the current density is high, the decrease in the battery voltage due to the concentration overvoltage is reduced.

[0071]

According to the gas diffusion electrode of the present invention, a porous electrolyte having three-dimensionally communicating pores as a proton conduction path is formed using a resin having a large ion exchange capacity and a high proton conductivity. By using a resin having a small ion exchange capacity and a high solubility of the reactant than a porous electrolyte having porous pores, and covering the catalyst in the pores of the porous electrolyte to form a three-phase interface, An improvement in proton conductivity, an increase in the three-phase interface, and an improvement in the supply of reactants are achieved. For this reason, the activation overvoltage, the resistance overvoltage, and the concentration overvoltage of the electrode can be reduced, and a solid polymer electrolyte fuel cell having a high output density can be provided.

[0072]

[Brief description of the drawings]

FIG. 1 is a schematic view of a cross section of a gas diffusion electrode / electrolyte membrane assembly according to the present invention.

FIG. 2 is a float view showing a manufacturing process of gas diffusion according to the present invention.

FIG. 3 is an enlarged schematic view of a microporous aggregate including a catalyst and an electrolyte B provided in pores of a porous electrolyte A having three-dimensionally communicating pores.

FIG. 4 is a diagram showing current-voltage characteristics of a solid polymer electrolyte fuel cell X in which a gas diffusion electrode according to the present invention is disposed on a cathode and a solid polymer electrolyte fuel cell Y for comparison.

[Explanation of symbols]

 1 First catalyst layer. 2 Porous electrolyte A having three-dimensionally communicating pores. 3 Microporous assembly containing catalyst and electrolyte B 4 First gas diffusion layer 5 First gas diffusion electrode 6 Electrolyte membrane C for fuel cell 7 Second catalyst layer 8 Second gas diffusion layer 9 Second Gas diffusion electrode 10 Gas diffusion electrode electrolyte membrane assembly 11 Carbon carrier 12 Catalyst 13 Electrolyte B

Claims (3)

[Claims] 1. A gas diffusion electrode comprising a catalyst layer and a gas diffusion layer, wherein the catalyst layer has a porous electrolyte A having three-dimensionally communicating pores and a microporous electrolyte containing a catalyst and an electrolyte B in the pores. A gas diffusion electrode having a structure including an aggregate, wherein the ion exchange capacity of the porous electrolyte A is larger than the ion exchange capacity of the electrolyte B in the pores. 2. The gas diffusion electrode according to claim 1, wherein both the porous electrolyte A and the electrolyte B in the pores thereof are perfluorosulfonic acid resins. 3. A solid polymer electrolyte fuel cell comprising the gas diffusion electrode according to claim 1 or 2.