JPH10284087A - Electrode and membrane-electrode joining body for solid polymer fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance water exhausting performance within a catalyst layer, remove influence of water on the diffusion into the catalyst layer of reaction gas, and obtain stable cell voltage even in high current density region by containing at least two kinds of different EWs of proton conducting polymers in the catalyst layer. SOLUTION: A proton conducting polymer is a perfluorocarbon polymer having a sulfonic acid group, a solid polymer membrane having EW of 700-1500, and a catalyst layer containing at least two kinds of different EWs of proton conducting polymers is preferably arranged. EW of a solid polymer electrolyte membrane is selected so that the difference to EW of the proton conducting polymer being dispersed in the catalyst layer coming in contact with both surfaces of the membrane is 800 or less, preferably within 600. The content of the proton conducting polymer being dispersed in the catalyst layer is in the range of a weight ratio of 0.1-10 based on the weight of carried catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer electrolyte fuel cell, and more particularly to an electrode and a membrane / electrode assembly.

[0002]

2. Description of the Related Art Fuel cells convert fuel chemical energy directly into electric energy by electrochemically oxidizing hydrogen, methanol, etc. in the cell, and take it out as a clean electric energy supply source. Attention has been paid. In particular, polymer electrolyte fuel cells are expected to be used as alternative power sources for vehicles because they operate at lower temperatures than others.

In such a polymer electrolyte fuel cell, a pair of gas diffusion electrodes is joined to both sides of a polymer electrolyte membrane. That is, the solid polymer electrolyte membrane has a structure in which an anode catalyst layer is provided on one surface and a cathode catalyst layer is provided on the other surface, and a pair of gas diffusion layers is adjacent to the outside of both surfaces. Conventionally, the anode and cathode catalyst layers are formed by sheeting a mixture of a carbon black powder supporting an electrode catalyst, a polymer having proton conductivity, and a polymer having water repellency,
The solid polymer electrolyte membrane is joined by hot pressing.

A fuel (eg, hydrogen) is supplied to the gas diffusion electrode as an anode, and an oxidant (eg, oxygen or air gas) is supplied to the gas diffusion electrode as a cathode, and the two electrodes are connected by an external circuit. This operates as a fuel cell. That is, in the anode, protons and electrons are generated by oxidation of the fuel, and the protons pass through the solid electrolyte and move to the cathode side. On the other hand, electrons reach the cathode through an external circuit. At the cathode, water is generated by such protons and electrons and oxygen in the oxidant, and at this time, electric energy can be extracted.

[0005]

In order for protons to move smoothly in the solid polymer electrolyte membrane, water is required, and the fuel is humidified and supplied to the anode together with the water. Water generated at the cathode and excess water that has migrated in the membrane are released to the outside of the electrode together with the oxidizing agent. In order to obtain a high catalyst utilization rate in the catalyst layer, see JP-A-6-3335.
As described in Japanese Patent Publication No. 74, a proton conductive polymer having a high water content, such as “Nafion (5% by weight solution)” commercially available from Aldrich, USA, is uniformly dispersed. Therefore, even when a water-repellent polymer is included, it is difficult for water to be smoothly discharged from the inside of the catalyst layer to the outside of the catalyst layer. During the operation of the fuel cell, water gradually accumulates in the catalyst layer and the gas diffusion layer. The higher the current density, the more water accumulates and the more oxidant is supplied to the catalyst layer. Is greatly hindered. As a result, the resistance of the electrochemical reaction becomes extremely large, causing a problem that the battery voltage that can be taken out is greatly reduced, and the voltage variation between cells in a stack is increased.

[0006] When the fuel cell and the oxidizing agent are pressurized and the fuel cell is operated at a high operating pressure, the reaction efficiency of the electrode increases, but the discharge capability of generated water and the like decreases due to a decrease in the gas flow rate. Therefore, improvement in battery characteristics cannot be expected. Increasing the amount of the water-repellent polymer dispersed in the catalyst layer conversely causes a significant reduction in catalyst utilization and a decrease in output voltage, and thus has a limit. Therefore, a significant improvement in water repellency cannot be expected. In addition, since a proton-conductive polymer is contained, a high-temperature treatment as described in, for example, Japanese Patent Publication No. 5-20868 is performed after a water-repellent polymer such as PTFE is dispersed in the catalyst layer. Is impossible, so that an effective matrix of the water-repellent polymer cannot be formed. The present invention has been made in view of such problems of the prior art, and has been made to improve the water discharging ability in the catalyst layer, to eliminate the influence of water on the diffusion of the reaction gas in the catalyst layer, An object of the present invention is to provide an electrode and a membrane / electrode assembly for a polymer electrolyte fuel cell which exhibit a stable cell voltage even in a current density region.

[0007]

In order to achieve the above object, the present invention provides a gas diffusion electrode for a polymer electrolyte fuel cell, wherein the catalyst layer comprises at least two types of proton conductive polymers having different EWs. There is provided an electrode characterized by including: In the membrane / electrode assembly for a polymer electrolyte fuel cell, the membrane / electrode assembly has an EW of 700 to 1500 and an electrode having a catalyst layer containing at least two types of proton conductive polymers having different EWs. A membrane / electrode assembly is provided. It has been found that a stable battery voltage can be obtained by producing these electrodes and the membrane / electrode assembly, and the present invention has been accomplished.

[0008] The operation of dispersing the proton conductive polymer in the catalyst layer is intended to greatly improve the utilization of the catalyst, but in order to exert its effect more, it is necessary to use a polymer having a high proton conductivity. Ie, a polymer with a lower EW is preferably used. As the proton conductive polymer, a perfluorosulfonic acid polymer represented by Nafion described above is widely used. For example, in this perfluorosulfonic acid polymer, a polymer having lower EW and high proton conductivity shows relatively high hydrophilicity and has a high water content. In the battery reaction, the protons oxidized on the anode catalyst reach the membrane through the polymer having high proton conductivity, pass through the membrane having the same conductivity, and move to the cathode side. It reaches the cathode catalyst through high proton conductive polymer dispersed in the catalyst layer. With this as a three-phase interface, water reacts with oxygen gas as an oxidant reaction gas and electrons that have passed through an external circuit to produce water. Here, the generated water is dispersed in the catalyst layer from above the catalyst active point, and has a higher EW.
Quickly move to a polymer having a lower water content, and is discharged from the catalyst layer to the outside of the gas diffusion layer and the electrode using this passage. In this way, at the active point of the battery reaction catalyst, an electrode having a high reaction rate and a high ability to discharge generated water can be obtained.

Here, the above-mentioned EW represents the equivalent weight of an exchange group having proton conductivity. The equivalent weight is a dry weight of the ion exchange membrane per equivalent of the ion exchange group, and is expressed in units of “g / ew”. The difference between the highest EW and the lowest EW of the proton conductive polymer according to the present invention is preferably 20 or more, which can show the effect of the present invention, and 50 or more is more preferable.
It is particularly preferable if the number is 100 or more. In addition, when three or more types of proton conductive polymers are included, the closest numerical values of E
If the difference of W is 20 or more, the effect of the present invention can be enjoyed. The upper limit of the difference in EW is preferably 800 or less, more preferably 600 or less, and particularly preferably 400 or less.

[0010] The EW of the proton conductive polymer may be at least 700 or more, more preferably 800 or more. And it is preferable that it is 1500 or less, and it is more preferable that it is 1300 or less. If it is less than 700, the hydrophilicity is too high, and smooth movement of water cannot be performed. If it is more than 1500, the proton conductivity is too low.
The effect of the present invention cannot be exhibited. The proton conductive polymer may be any polymer that conducts protons, and preferably has at least one of a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, and a phosphoric acid group with a fluorinated polymer as a skeleton. Things. Further, those having a skeleton of a hydrocarbon such as polyolefin can also be used.

As the fluorine-containing polymer, for example, tetrafluoroethylene, trifluoromonochloroethylene,
Trifluoroethylene, vinylidene fluoride, 1,1-difluoro-2,2-dichloroethylene, 1,1-difluoro-2-chloroethylene, hexafluoropropylene, 1,1,1,3,3-pentafluoropropylene,
Octafluoroisobutylene, ethylene, vinyl chloride,
And a first group of monomers such as alkyl vinyl esters;
Following general formula _{(1), Y- (CF 2} ) a - (CFR f) b - (CFR' f) c -O- - _{[CF (CF 2 X) -CF 2} -O ] _n -CF = CF ₂ (1) (wherein, Y is _{-SO 2 F, -SO 3 NH,} -COOH,
-CN, -COF, -COOR (R is an alkyl group having 1 to 10 carbon atoms), - PO ₃ H _2, a -PO ₃ H, a is Less than six, b is an integer of Less than six, c is 0 or 1, provided that a + b + c is not equal to 0. X is Cl, Br, F or a mixture thereof when n> 1, and n is 0-6. R _f and R ′ _f are independently F, Cl, about 1
It is selected from the group consisting of perfluoroalkyl groups having 10 to 10 carbon atoms and fluorochloroalkyl groups having 1 to 10 carbon atoms. 2) essential from the second group of monomers selected from the second group of monomers represented by
Copolymers of one or more species or three or more monomers, and one or more polymers of the second group. In particular, a perfluorocarbon polymer having a sulfonic acid group is preferable.

The polymer may have two or more monomers bonded to each other. From the viewpoint of durability, the molecular weight is preferably 5,000 or more. Further, by mixing and using a polymer and a low molecular weight compound, EW can be appropriately adjusted. Proton conducting polymers as described above include, for example, methanol, ethanol, propanol,
Alcohols such as butanol, polar solvents such as N, N'-dimethylacetamide, N, N'-dimethylformamide, dimethylsulfoxide and sulfolane, cyclic ethers such as tetrahydrofuran, and two or more kinds selected from the above solvent group It can be used by dissolving it in a mixture, or a mixture of the above solvent group and water. In particular, a lower alcohol alone such as ethanol, 1-propanol and 2-propanol, or a mixture of two or more solvents and water is preferable. Further, at least one of the above solvent groups
A mixed solvent of a seed and a fluorine-containing compound such as a fluorocarbon or a fluorine-containing alcohol can also be used.

[0013] The concentration of the dissolved proton conductive polymer solution is 3 to 20% by weight, which is suitable for forming an appropriate proton conductive polymer coating on the catalyst surface when dispersed in the catalyst layer of the gas diffusion electrode. A range is preferred. If this concentration is too high, the dispersibility of the polymer in the catalyst layer will be poor, and the thickness of the coating will be too large, and the three-phase interface will be non-uniform and the catalyst utilization will be reduced. May not be able to demonstrate. On the other hand, if the concentration is too low, it is not possible to obtain a uniform and sufficient thickness of the proton conductive polymer coating on the catalyst surface, or the proton conductive polymer solution is applied to the surface of the porous catalyst layer sheet so that the inside of the catalyst layer is not coated. In the case of dispersing the polymer in water, the viscosity of the liquid is too low and the polymer locally concentrates, which is not preferable.

The electrode catalyst material used for the anode and cathode catalyst layers may be any material that has a catalytic action on the oxidation reaction of hydrogen and the reduction reaction of oxygen. , Lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum and the like or alloys thereof.

The particle size of the catalyst is preferably from 10 to 300 °, more preferably from 15 to 100 °. If it is less than 10 °, it is practically difficult to manufacture it. If it is more than 300 °, the catalyst utilization is reduced, and a high battery voltage cannot be obtained. These catalyst particles may be supported on a conductive material such as carbon black. The supported amount of the catalyst is 0.01 to 5 mg / cm ² in a state where the catalyst layer sheet is formed,
More preferably, it is 0.1 to 1 mg / cm ² . 0.0
If it is less than 1 mg / cm ² , the performance of the catalyst cannot be effectively exhibited, and if it is 5 mg / cm ² or more, the cost becomes extremely large, and the effect corresponding to the amount of the performance cannot be seen.

The catalyst layer referred to in the present invention is composed of the above-mentioned catalyst material, a conductive material such as a proton conductive polymer and carbon black. If necessary, a water repellent material such as PTFE or a binder is used. May be included. As a method of dispersing the proton conductive polymer in the catalyst layer,
The catalyst layer constituent material may be mixed and molded to form a catalyst layer, or a constituent material other than the proton conductive polymer may be mixed and molded in advance to form a catalyst layer, and then impregnated with a proton conductive polymer. Any conductive material may be used as long as it is an electron conductive material. Examples of the carbon material include carbon black such as furnace black, channel black, and acetylene black, as well as activated carbon, graphite, and various metals. .

The proton conductive polymer such as perfluorosulfonic acid has a function as a binder in the polymer itself, and forms a sufficiently stable matrix with catalyst particles and conductive particles in the catalyst layer. It is possible to form. Further, for the purpose of imparting water repellency in addition to the function as a binder, for example, various resins containing fluorine can be used. The fluorine resin preferably has a melting point of 400 ° C. or lower, and examples thereof include polytetrafluoroethylene (PTFE) and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer.

When a layer of a proton conductive polymer in the catalyst layer or an EW proton conductive polymer different from that of the solid polymer membrane is formed at the interface where the catalyst layer and the solid polymer membrane are in contact with each other, particularly on the cathode side Has higher E than solid polymer membrane
W, by making the EW lower than that of the solid polymer membrane on the anode side, utilizing the difference in hydrophilicity or hydrophobicity, when the humidification of the fuel or oxidizing agent is insufficient or the operating current density of the battery is low Alternatively, even when the operation is stopped, it is also possible to retain water in the membrane and maintain high proton conductivity. The thickness of this layer is 0.05 to 30 μm, more preferably 0.1 to 10 μm. At 0.05 μm or less,
The effect of the above-mentioned sufficient function cannot be obtained. on the other hand,
If it is 30 μm or more, the resistance becomes large, which is not suitable. The EW of the proton conducting polymer layer should be at least 7
It is sufficient if it is 00 or more, and more preferably 800 or more. And it is preferably 1500 or less, and 13
More preferably, it is not more than 00. If it is less than 700, the hydrophilicity is too high and the smooth movement of water cannot be achieved.
If it is more than 00, the proton conductivity is too low, so that the effect of the present invention cannot be exhibited. The difference in EW between the proton conductive polymer layer and the solid polymer membrane at the interface is preferably 2
If the value is 0 or more, the effect of the present invention can be exhibited.
It is more preferable if it is at least 100, and particularly preferable if it is at least 100. In addition, the effect of the present invention can be enjoyed if the difference between the closest numerical values of the EWs when three or more proton conductive polymers are included is 20 or more. The upper limit of the difference in EW is preferably 800 or less, more preferably 600 or less, and particularly preferably 400 or less.

For the membrane used as the solid polymer electrolyte in the present invention, the same material as the above-mentioned proton conductive polymer can be used. That is, at least a sulfonic acid group, a carboxylic acid group, and a fluorinated polymer as a skeleton,
Those having one of a phosphonic acid group and a phosphoric acid group are preferred. Further, a membrane obtained by introducing a monomer having a sulfonic acid group or a carboxylic acid group into a polyolefin membrane such as polyethylene by a graft polymerization reaction or the like can also be used. The fluorinated film is, for example, a copolymer of two or more, usually two to three, essential from the second group of monomers selected from the first group of monomers and the second group of monomers. In addition to the method of reinforcing mechanical strength by laminating these films with a higher EW film, fibrils, woven fabrics, non-woven fabrics, reinforcement with a perfluorocarbon polymer of a porous sheet, It can also be reinforced by coating the film surface with an inorganic oxide or metal. The EW of these films may be 700 or more, more preferably 800 or more. And it is preferable that it is 1500 or less, and it is more preferable that it is 1300 or less. When the molecular weight is less than 700, the proton conductivity is improved, but the mechanical strength of the membrane is reduced, so that it is not practical. If it is more than 1500, the mechanical strength is further improved, but the proton conductivity is lowered and the battery voltage is lowered, which is not preferable.

The EW of the solid polymer electrolyte membrane is the proton conductive polymer dispersed in the catalyst layer in contact with both sides of the membrane.
The difference from W may be 800 or less, and more preferably 600 or less. If it is more than 800, the adhesion between the film and the catalyst layer becomes insufficient, which is not preferable. The catalyst layer can be prepared by various generally known methods, such as a spray method, a transfer method, a screen printing method, and a rolling method.
Proton conductive polymer, catalyst, conductive material, dissolved in a solvent mainly composed of lower alcohol such as ethanol,
After sufficiently stirring the catalyst dispersion comprising the water-repellent polymer and / or, for example, in a transfer method, the catalyst dispersion is applied to a smooth sheet such as PTFE over a certain shape area, and dried to form a catalyst layer. Let it form. At this time, at least two or more types of proton conductive polymers are sequentially or simultaneously added to the catalyst dispersion in advance to form a catalyst layer in which the proton conductive polymers are uniformly dispersed. In another embodiment, the catalyst layer may be formed by stacking a plurality of catalyst layers in which one or more types of different proton conductive polymers are dispersed by repeatedly forming the catalyst layers. In addition, the present invention can take various forms such as a method of directly applying a catalyst dispersion to a membrane, or a combination thereof, and is not limited to the above range.

The amount of the proton conductive polymer dispersed in the catalyst layer is 0.1 to 10 by weight based on the amount of the catalyst carried.
Range. If the weight ratio to the catalyst is 0.1 or less, a sufficient catalyst utilization cannot be obtained due to a decrease in the reaction active point. On the other hand, when the weight ratio is 10 or more, the effect of the hydrophilic property of the proton conductive polymer becomes large, and the effect of the present invention cannot be obtained. Next, on both sides of the solid polymer electrolyte membrane,
The sheets on which the catalyst layers are formed are overlapped with the catalyst layer side facing the membrane side, and the catalyst layers are joined to the solid polymer electrolyte membrane under heating and heating. The pressure and temperature at the time of such bonding are selected from the conditions under which the solid polymer electrolyte membrane, the proton conductive polymer, the catalyst, and the conductive material have sufficient adhesion to each other. In particular, when a perfluorosulfonic acid polymer is used as the solid polymer electrolyte membrane, the temperature should be equal to or higher than the glass transition point, and the preferable bonding temperature is 120 to 200.
° C.

The proton conductive polymer cannot obtain sufficient conductivity unless it is finally a proton type. However, in order to improve the heat resistance of the solid polymer membrane and the proton conductive polymer at the time of joining, It is also an effective method to substitute a monovalent metal ion such as sodium or potassium, or a divalent or trivalent metal, perform a heat treatment, and finally obtain a proton type.

After the catalyst layer is bonded to the solid polymer membrane, it is further bonded or superposed to an electrically conductive porous woven or nonwoven fabric such as carbon paper or carbon cloth as a support for the catalyst layer to form a membrane / electrode bonding. It can be incorporated into a fuel cell unit as a body. As in the case of the diffusion layer, carbon paper or carbon cloth can be provided with water repellency as necessary by impregnating with a polytetrafluoroethylene resin. If the porosity of the electrically conductive porous woven fabric or nonwoven fabric is 50% or more, it has a sufficient material exchange function.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the examples.

【Example】

Example 1 A 5% by weight solution of a proton-type perfluorosulfonic acid polymer resin in 40% by weight of a platinum catalyst-supporting carbon (manufactured by E-TEK, USA) (Asahi Kasei Corporation)
EW = 910, solvent composition ethanol / water = 50 /
50) was added so that the weight ratio of the platinum catalyst to the polymer was 4: 1, and the mixture was uniformly dispersed to form a paste. Then, 5% by weight of a proton-type perfluorosulfonic acid polymer resin having the same EW of 1030 was used. A solution (manufactured by Asahi Kasei Kogyo Co., Ltd., solvent composition was the same as above) was added in the same amount as the polymer weight, and the mixture was dispersed uniformly again to prepare a paste.
This paste was applied on a polytetrafluoroethylene sheet using a 200-mesh screen, and then dried and fixed at 100 ° C. in an air atmosphere, and the platinum carrying amount was 0.2 m.
g / cm ² of the catalyst sheet was obtained.

The two catalyst layer sheets thus obtained are faced to each other, and a perfluorosulfonic acid membrane (manufactured by Asahi Kasei Kogyo Co., Ltd.) having an EW of 950 and a thickness of 100 μm is sandwiched between the catalyst layer sheets at 150 ° C. and a pressure of 50 kg / cm ^2. After hot-pressing, the polytetrafluoroethylene sheets on both sides were peeled off to produce a membrane-electrode assembly. As a catalyst layer support,
Approximately 400 μm thick carbon cloth (manufactured by E-TEK)
After immersion in a tetrafluoroethylene dispersion (60% by weight), sintering was performed at 340 ° C. to impregnate the carbon cloth with 40% by weight. The porosity is 50
%Met.

The membrane / electrode assembly and the catalyst layer support are
Incorporated into a fuel cell single-cell evaluation device, hydrogen gas,
Using an air gas as the oxidizing agent, a single cell characteristic test was performed at normal pressure and a cell temperature of 70 ° C. Hydrogen gas was humidified at 80 ° C., and air gas was supplied to the cell without humidification.
At a current density of 0.5, 1.0 A / cm ² , 0.66
V and 0.51 V were obtained. The following Examples and Comparative Examples were also tested under the same membrane / electrode bonding method, diffusion layer, and single cell operating conditions.

Example 2 A 40% by weight platinum catalyst-supported carbon (manufactured by E-TEK, USA) and a 5% by weight solution of a proton-type perfluorosulfonic acid polymer resin (manufactured by Asahi Kasei Corporation, EW = 950) , A solvent composition of ethanol / water = 50/50) was mixed and stirred at a weight ratio of the platinum catalyst to the polymer of 4: 1, and dried at 100 ° C. in vacuum to prepare a polymer-coated platinum catalyst in advance. Further, the polymer-coated platinum catalyst and 5% by weight of a proton-type perfluorosulfonic acid polymer resin having an EW of 1030 were used.
The solution (manufactured by Asahi Chemical Industry Co., Ltd., solvent composition was the same as above) was mixed at a weight ratio of the platinum catalyst to the polymer of 4: 1 and uniformly dispersed to prepare a paste. Thereafter, a catalyst sheet was formed in the same manner as in Example 1 to obtain a platinum carrying amount of 0.2 mg / cm ² . Further, the anode catalyst layer was manufactured in the same procedure as in Example 1. At a current density of 0.5, 1.0 A / cm ² ,
0.66 V and 0.51 V were obtained, respectively.

Example 3 On the cathode catalyst sheet of Example 1, only a 5% by weight solution of the proton-type perfluorosulfonic acid polymer resin having the EW = 1030 (same as above) was applied using the same screen, and air was applied. Atmosphere 10
After drying at 0 ° C., a polymer layer of 0.20 mg / cm ² was formed. On the other hand, a 5% by weight solution of a proton-type perfluorosulfonic acid polymer resin having EW = 910 (same as above) was applied onto the anode catalyst sheet of Example 1, dried at 100 ° C. in an air atmosphere, and dried. 20mg / c
An m ² polymer layer was formed. The following procedures and methods after production of the membrane / electrode assembly were the same as in Examples 1 and 2.
At a current density of 0.5, 1.0 A / cm ² , 0.67
V and 0.53 V, respectively. FIG. 1 shows a schematic diagram of the cell structure of the third embodiment.

Comparative Example 1 A 5% by weight solution of a proton type perfluorosulfonic acid polymer resin (manufactured by Asahi Kasei Corporation, EW = 910) in 40% by weight of a platinum catalyst-supported carbon (manufactured by E-TEK, USA) And a solvent composition of ethanol / water = 50/50) was added so that the weight ratio of the platinum catalyst to the polymer was 2: 1, and the mixture was uniformly dispersed to prepare a paste. The paste was applied on a polytetrafluoroethylene sheet using a 200-mesh screen, and then dried and fixed at 100 ° C. in an air atmosphere to obtain a catalyst sheet having a platinum loading of 0.2 mg / cm ² . 0.
5, at a current density of 1.0 A / cm ² , 0.53 V,
0.25 V was obtained in each case.

[0030]

As described above, by forming a catalyst layer containing at least two types of proton-conductive polymers having different EWs, a low proton-conductive low EW near the catalytically active point is obtained.
The polymer has the effect of promoting the battery reaction smoothly, while the polymer having a high EW shows that the generated water in the catalyst layer is quickly discharged out of the layer and the gas supply to the catalyst is maintained. As a result, a stable battery voltage can be obtained from a low current density to a high current density. In particular, even when the electrode area becomes large and the gas humidification conditions fluctuate in the cell, the electrode and the membrane of the present invention can be used.
The use of an electrode assembly is a significant improvement.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a cell structure of a polymer electrolyte fuel cell to which the membrane / electrode assembly of the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid polymer membrane 2 Anode 3 Cathode 4 Membrane electrode assembly 5 Catalyst layer support 6 Separator 7 Catalyst layer 8 Proton conductive polymer layer

Claims (5)

[Claims] 1. A gas diffusion electrode for a polymer electrolyte fuel cell, wherein the catalyst layer contains at least two types of proton conductive polymers having different EWs. 2. The electrode according to claim 1, wherein the proton conductive polymer is a perfluorocarbon polymer having a sulfonic acid group. 3. An electrode comprising a solid polymer membrane having an EW of 700 to 1500 and a catalyst layer containing at least two types of proton conductive polymers having different EWs, in a membrane / electrode assembly for a polymer electrolyte fuel cell. A membrane / electrode assembly comprising: 4. The membrane / electrode assembly according to claim 3, wherein the proton conductive polymer is a perfluorocarbon polymer having a sulfonic acid group. 5. An interface where the solid polymer membrane and the catalyst layer are in contact with each other,
5. The membrane-electrode assembly according to claim 3, further comprising a layer of a proton conductive polymer having an EW different from that of the solid polymer membrane.