JP2003109606A - High molecular electrolyte fuel cell and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple electrode of high performance without using a foaming material as an electrode for a high molecular electrolyte fuel cell, and to provide a compact electrode of high performance by smoothing the movement of materials in the electrode. SOLUTION: The electrode having a porous catalyst layer is manufactured by atomizing and spraying ink to a porous conductive electrode base. By spraying a coating material from plural spray nozzles, the electrode wherein the quantity of high molecular electrolyte is gradually reduced from a side abutted on the high molecular electrode film to a gas diffusion electrode side is manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell as a power generator for consumer cogeneration and mobiles, and more particularly to a polymer electrolyte fuel cell using a polymer electrolyte.

[0002]

2. Description of the Related Art A fuel cell electrochemically reacts a fuel such as hydrogen and an oxidant gas such as air at an electrode containing a catalyst to simultaneously generate electricity and heat. There are several types of fuel cells depending on the type of electrolyte used. A polymer electrolyte fuel cell uses a polymer electrolyte having hydrogen ion conductivity as an electrolyte. As a hydrogen-ion conductive polymer electrolyte used in a polymer electrolyte fuel cell, a polymer in which -CF2- is used as a skeleton and a sulfonic acid is introduced at the end of a side chain is generally used at present. The battery structure consists of a polymer electrolyte membrane, both sides of which a catalyst layer mainly composed of carbon powder carrying a platinum-based noble metal is adhered, and a gas diffusion layer having both gas permeability and conductivity is arranged on this outer surface. To do. In the above structure, the portion where the gas diffusion layer is joined to the catalyst layer is called an electrode, and the portion where the electrodes are joined to both sides of the polymer electrolyte membrane is called an MEA (electrolyte membrane electrode assembly).

On the outside of the MEA, a conductive separator plate for mechanically fixing a bonded body of an electrode and an electrolyte and for electrically connecting adjacent bonded bodies in series with each other is arranged. The separator plate is provided with a gas flow path for supplying a fuel gas containing hydrogen to one electrode and an oxidant gas containing oxygen to the other electrode. Here, the electrode that supplies the fuel gas is called the fuel electrode, and the electrode that supplies the oxidant gas is called the air electrode. The gas flow path has not only a function of supplying gas to the electrodes, but also a function of discharging water and surplus gas generated by the reaction of hydrogen and oxygen. A seal member such as a gasket or a sealant is arranged around the gas flow path and the electrode to prevent the reaction gas from directly mixing and leaking to the outside.

When this is actually used as a power generator, it is customary to stack a plurality of unit cells each composed of an MEA and a separator plate in order to increase the output voltage. A fuel gas such as hydrogen gas and air are supplied from the outside through a manifold to the inlet of the gas passage of each unit cell.

In the above-mentioned electrode, the fuel electrode constantly supplies water and fuel gas for smoothly diffusing hydrogen ions generated in the electrode into the polymer electrolyte membrane, and the air electrode generates water generated by the electrode reaction. It is necessary to have a function of smoothly removing and supplying air as an oxidant gas. In particular, the above-mentioned function is required in the catalyst layer having poor gas diffusivity.

Heretofore, a method of mixing a water-repellent resin such as PTFE into the catalyst layer has been generally used as a method for enhancing the gas diffusivity in the catalyst layer. Other than this, a method of positively forming pores for gas diffusion in the catalyst layer has been devised.

As a method for manufacturing such an electrode, a powder of a metal or an oxide thereof as a pore-forming agent is mixed in advance in the catalyst layer, and after forming the electrode, it is immersed in an acidic solution so that it is placed inside the catalyst layer. A method for producing an electrode having pores is disclosed in JP-A-6-36771. Further, in Japanese Patent Application Laid-Open No. 8-138715, when forming a catalyst layer on a polymer electrolyte membrane, an electrode catalyst salt and polymer particles are both adsorbed by a chemical plating method, and then the polymer particles are treated with an acidic solution. A method for producing a polymer electrolyte fuel cell has been proposed in which the porous catalyst layer is removed to form a polymer electrolyte fuel cell. Furthermore, JP-A-9
-199138, carbon fine powder carrying a noble metal,
A polymer electrolyte solution and an alcohol solvent are mixed with a sublimable pore-forming agent such as camphor to form an ink, and this ink is screen-printed to form a catalyst layer on the polymer electrolyte membrane. A method of manufacturing an electrode has been proposed in which a catalyst layer having a plurality of pores is formed by sublimation.

[0008]

Generally, the gas diffusivity in a normal catalyst layer is high on the gas diffusion layer side where the gas flowing through the separator plate diffuses first, and small on the polymer electrolyte membrane side. It is considered to be. That is, the gas diffusivity on the polymer electrolyte membrane side in the catalyst layer becomes poor. However,
As described above, when the pores are formed in the catalyst layer without defining the size of the pore-forming agent, the pores are almost evenly distributed in the catalyst layer. For this reason, the number of pores on the side of the polymer electrolyte membrane where gas diffusivity is most needed is actually reduced, and the effect of introducing a pore-forming agent to form pores is not sufficiently exhibited. Further, although it depends on the shape of the pore-forming agent, the shape of the pores is formed in the catalyst layer in a shape close to a sphere, so the flow of gas diffusion from the gas diffusion layer side to the polymer electrolyte membrane side becomes small. . Furthermore, when a sublimable pore-forming agent is used, the pore size changes randomly depending on the temperature distribution during sublimation, resulting in non-uniform gas diffusivity. When the pore size becomes random, there is a problem that the space in the catalyst layer where large pores exist becomes large, and the conductivity of the catalyst layer becomes insufficient in this part, and the catalyst layer itself becomes brittle. It was

[0009]

In order to solve the above problems, the polymer electrolyte fuel cell of the present invention comprises a pair of electrodes arranged with a polymer electrolyte membrane sandwiched therebetween, wherein one of the electrodes contains hydrogen. In a polymer electrolyte fuel cell in which a fuel gas is sandwiched by a pair of separator plates having a gas flow path for supplying an oxidant gas containing oxygen to the other of the electrodes, the electrode is the polymer electrolyte membrane. A catalyst layer in contact with
A gas diffusion layer in contact with the separator plate, the catalyst layer has at least carbon particles carrying a polymer electrolyte and a catalyst, the size of the pores in the catalyst layer is the polymer electrolyte membrane side From the above to the gas diffusion layer side in the thickness direction.

At this time, it is effective that the size of the pores in the catalyst layer is increased in the thickness direction from the side in contact with the polymer electrolyte membrane toward the gas diffusion layer side.

Furthermore, a pair of electrodes arranged with a polymer electrolyte membrane sandwiched therebetween is used to supply a fuel gas containing hydrogen to one of the electrodes and an oxidant gas containing oxygen to the other of the electrodes. In a polymer electrolyte fuel cell sandwiched by a pair of separator plates having a path, the electrode has a catalyst layer in contact with the polymer electrolyte membrane, and a gas diffusion layer in contact with the separator plate, the catalyst layer It is characterized in that it has at least carbon particles supporting a polymer electrolyte and a catalyst, and that the pores in the catalyst layer have an anisotropic shape with an aspect ratio of 2 to 10.

At this time, it is effective that the pores in the catalyst layer are oriented in the thickness direction of the catalyst layer.

Further, it is effective that the fractal dimension of the pore structure in the catalyst layer is 2 to 3.

The pores in these catalyst layers are effectively formed by using a pore-forming agent.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The polymer electrolyte fuel cell of the present invention has a structure in which a catalyst layer and a gas diffusion layer are arranged from the surface in contact with the polymer electrolyte membrane, and the size of pores in the catalyst layer is large. However, it changes from the side in contact with the polymer electrolyte membrane to the gas diffusion layer side. Here, the size of the pores in the catalyst layer is preferably larger from the side in contact with the polymer membrane toward the gas diffusion layer side. As means for realizing such a constitution, when forming the catalyst layer, pore-forming agents having different particle diameters are mixed in the catalyst ink and once the catalyst layer is formed on a base material sheet such as PET (polyethylene terephthalate). Form. At this time, since particles having a large particle size have high sedimentability, they move to the base material sheet side,
Since the small pore-forming agent has a low sedimentation property, it stays in the upper layer of the catalyst layer. By thermally transferring this to a polymer electrolyte membrane and removing the pore-forming agent, a polymer electrolyte fuel with large pores from the side in contact with the polymer electrolyte membrane to the gas diffusion layer side as shown in FIG. Batteries can be made. Also, this catalyst ink is directly applied onto a gas diffusion layer base material such as carbon paper to form a catalyst layer, which is bonded to a polymer electrolyte membrane and the pore-forming agent is removed to obtain the same structure. The polymer electrolyte fuel cell can be produced.

In addition to the above, a plurality of catalyst inks using pore-forming agents having different particle diameters were prepared, and these were coated on a base material sheet in order of decreasing particle diameter, and transferred in the same manner as above. The polymer electrolyte fuel cell having the constitution of the present invention can also be produced by removing the pore-forming agent. In this case, the same structure can be produced by forming the catalyst layer on the gas diffusion layer. It is also possible to coat the polymer electrolyte membrane in order from a catalyst ink using a pore former having a small particle size. As a method of applying the above-mentioned catalyst ink, a screen printing method, a doctor blade method, a gravure printing method, a die coater coating method, or the like can be used.

By thus increasing the size of the pores in the catalyst layer from the side in contact with the polymer membrane to the gas diffusion layer side, the gas diffusibility in the thickness direction of the catalyst layer can be improved. I can. By reducing the pore size from the side closer to the gas diffusion layer toward the polymer electrolyte membrane, the supply gas can be easily diffused to a portion closer to the polymer electrolyte membrane. Further, with this configuration, the water produced by the reaction can be discharged smoothly. In this case, the pores have a shape similar to the tree branch structure, so that gas diffusion in the thickness direction of the catalyst layer is smooth, and as a result, there is no flooding due to water, high performance and long life. A molecular electrolyte fuel cell is obtained. Further, the constitution of the polymer electrolyte fuel cell of the present invention is such that the catalyst layer and the gas diffusion layer are arranged from the surface in contact with the polymer electrolyte membrane, and the pores in the catalyst layer have an aspect ratio of 2 to 10. It has an anisotropic shape. Here, the pores in the catalyst layer are preferably oriented in the thickness direction of the catalyst layer.

As means for realizing such a structure,
When forming the catalyst layer, fine metal powder or oxide powder having a shape with an aspect ratio of 2 to 10 is mixed in the catalyst ink and coated on the substrate sheet. When the coated substrate sheet is dried, a magnetic field perpendicular to the coated surface is applied to orient it in the thickness direction of the catalyst layer. By thermally transferring this to a polymer electrolyte membrane and removing the pore-forming agent, a polymer electrolyte fuel cell having pores oriented in the thickness direction of the catalyst layer as shown in FIG. 2 can be produced. In this case, the catalyst layer can be formed on the gas diffusion layer such as the polymer electrolyte membrane or carbon paper.

In the thus constituted catalyst layer, pores oriented in the thickness direction of the catalyst layer are formed as shown in FIG. 2, so that the gas supplied from the gas diffusion layer is directed to the polymer electrolyte membrane side. We can supply enough. In the catalyst layer having the conventional structure, the gas diffusion from the gas diffusion layer side to the polymer electrolyte side is complicated as shown in FIG. 3, and the diffusion path becomes long. As shown, since the diffusion path is shortened and the pore occupying area in the catalyst layer cross section is reduced, the gas flow density (flux) is increased.
Further, with this configuration, the catalyst layer does not become brittle, high conductivity can be maintained, and a polymer electrolyte fuel cell with high performance and durability can be obtained.

Here, when the aspect ratio of the pore-forming agent is smaller than 2, the shape is similar to that of FIG. 3, so that the gas diffusivity is almost the same as the conventional one, and the effect peculiar to the present invention cannot be obtained. Also, when the aspect ratio becomes larger than 10,
Since the pore-forming agent aggregates in the catalyst ink and cannot be uniformly dispersed and entangled with each other, the gas diffusivity decreases. Therefore, sufficient gas diffusivity cannot be obtained unless a pore-forming agent having an aspect ratio of 2 to 10 is used.

Further, in the constitution of the polymer electrolyte fuel cell of the present invention, the fractal dimension of the pore structure of the catalyst layer is 2 to 3. When examining the structure of the pores of the present invention,
All parts of the catalyst layer are formed in the same shape, and the pore structure is a fractal structure, which is completely different from the conventional pore structure. Regarding this pore structure,
The fractal analysis was performed to obtain the fractal dimension, which was between 2 and 3. The fractal analysis was performed by a conventional method that changes the degree (pattern) of coarse graining. That is, a pattern obtained by image-processing a transmission electron micrograph is subdivided into a large number of squares, and the extent to which the number of squares completely contained in a pore portion changes when the side length of the square changes is determined. The fractal dimension was calculated using a numerical method. The larger the fractal dimension, the more multidimensional it is,
Since the fractal dimension of the present invention is between 2 and 3,
It was clarified that pores were distributed and formed even inside the catalyst layer.

The fuel cell electrode of the present invention will be described below with reference to the drawings.

Example 1 First, a pore-forming agent A was prepared by mixing nickel powders having an average particle diameter of 0.1 μm, 0.5 μm and 1.0 μm in an equal ratio. Carbon powder supporting 25% by weight of platinum, pore-forming agent A, 5% by weight of polymer electrolyte solution (Nafion manufactured by Aldrich), and 2-propanol (IPA) as a solvent were mixed at 3: 3: 50. : 4
The catalyst ink A was prepared by mixing in a weight ratio of 4 and ultrasonically dispersing.

The catalyst ink A was coated on a carbon paper (TGP-H-90 manufactured by Toray) serving as a gas diffusion layer by a doctor blade type coating device. 60 this
After the two electrodes were prepared by drying at a temperature of ° C, they were sandwiched with a polymer electrolyte membrane (Nafion 112, manufactured by DuPont), joined by a hot press machine set at 120 ° C, and MEA-A. did.

This MEA-A was immersed in 1N dilute sulfuric acid and boiled to remove the pore-forming agent from the catalyst layer of MEA-A. After repeating this treatment with dilute sulfuric acid 3 times, boiling washing with ion-exchanged water 5 times is performed, and thus MEA-
The pore-forming agent was completely eluted and removed from A.

The MEA-A thus obtained was sandwiched together with a gasket between a pair of separator plates having a gas flow path processed. The separator plate was sandwiched on both sides of the separator plate by stainless steel end plates to prepare a unit cell A.

Next, for comparison, a catalyst ink B was prepared by using only nickel powder having an average particle size of 0.5 μm as a pore-forming agent, electrodes were prepared in the same manner, and then MEA-B was prepared.
This was subjected to the same steps as described above to fabricate a single battery B.

Here, when the cross sections of the electrode portions of MEA-A and MEA-B were examined, the structures as shown in FIGS. 1 and 3 were obtained. Thus, it was found that the pores were enlarged from the polymer electrolyte membrane side to the gas diffusion layer.

Next, in the produced unit cell, hydrogen gas was supplied to the fuel electrode and air was supplied to the air electrode, the cell temperature was 80 ° C., the fuel utilization rate was 90%, the air utilization rate was 40%, and the gas humidification was hydrogen gas. Was adjusted to 75 ° C. and air was adjusted to 70 ° C. and 50 ° C. to examine the battery characteristics.

A comparison of the current-voltage characteristics of the batteries at this time is shown in FIG. The unit cell A of the present invention is the unit cell B more than this.
It has been found that the battery characteristics are higher than the above. In particular, in the case where the humidification temperature of air was high at 70 ° C. and in the high current density range, the cell voltage of the unit cell B was lowered due to flooding due to the lowered gas diffusibility.

Further, instead of the above catalyst ink A, catalyst inks C and D using nickel powder having an average particle diameter of 0.1 μm and 1.0 μm as a pore forming agent were prepared, and the catalyst ink was placed on carbon paper. Ink D, catalyst ink B described above, catalyst ink C
In this order, coating was sequentially performed with a doctor blade type coating apparatus so that the size of the pore-forming agent was gradually reduced. An MEA was produced using the electrode thus produced, and a unit cell C was produced through the same steps as described above. When the battery characteristics of this single cell were examined, it was found that the same characteristics as those of the single cell A were exhibited.

From these results, the polymer electrolyte fuel cell using the electrode in which the pores are enlarged from the side of the polymer electrolyte membrane to the side of the gas diffusion electrode, which is adopted in the present example, has a conventional uniform pore forming agent. It was found that the gas diffusivity was improved as compared with the battery produced by using the battery, and the battery voltage was stable even under high humidification. In this example, nickel powder was used as the pore-forming agent, but metals and salts that are soluble in acids such as zinc, iron, and aluminum, as well as proteins such as water-soluble alcohol and gelatin, starch, and the like according to the present invention. The present invention is not limited to this embodiment as long as it can form Also regarding the particle size, 0.05 μm, 0.1 μm, 0.3 μm
However, the combination is not limited to the present embodiment. As a method for forming the catalyst layer, another coating method such as a screen printing method may be used, or a method in which the catalyst layer is once formed on the PET film and then transferred to the polymer electrolyte membrane may be used. Although carbon paper is used for the gas diffusion layer, a material such as carbon cloth or carbon felt can also be used. Other components and composition of catalyst ink,
As long as the present invention is applicable, such as the type of polymer electrolyte membrane, any one may be used.

Example 2 First, as a pore-forming agent, iron powder having a diameter of 0.2 μm and a length of 1.6 μm and an aspect ratio of 8 was prepared, and 25 wt% of platinum-supported carbon powder was prepared. By mixing a 5 wt% polyelectrolyte solution (Aldrich, Nafion) and 2-propanol (IPA) as a solvent in a weight ratio of 3: 3: 50: 44, and ultrasonically dispersing the mixture. A catalyst ink E was prepared.

This catalyst ink A was coated on a carbon paper (TGP-H-90 manufactured by Toray) serving as a gas diffusion layer by a doctor blade type coating device. 60 this
A magnetic field perpendicular to the electrode surface at a temperature of ℃ 10 per unit area
It was dried while operating at 0 A / m. Two electrodes prepared in this manner were prepared, sandwiched between polymer electrolyte membranes (Nafion 112 manufactured by DuPont), and joined by a hot press machine set at 120 ° C. to obtain MEA-E. The pore-forming agent was removed from this MEA-E by the method shown in Example 1 to fabricate a unit cell D.

When the cross section of the electrode portion of MEA-E was examined, it was found that it had pores oriented in the thickness direction of the catalyst layer as shown in FIG.

Next, in the prepared unit cell, hydrogen gas was passed through the fuel electrode and air was passed through the air electrode, the cell temperature was 80 ° C., the fuel utilization rate was 90%, the air utilization rate was 40%, and the gas humidification was hydrogen. The gas characteristics were adjusted by adjusting the gas to 75 ° C. and the air to 70 ° C. and 50 ° C. to examine the battery characteristics.

The current-voltage characteristics of the battery at this time are shown in Example 1.
6 shows a comparison with the single battery B of FIG. From this, it was found that the unit cell D of the present invention has higher battery characteristics than the unit cell B. Also, as in Example 1, the difference between the unit cell B and the case where the air humidification temperature was high at 70 ° C. and the high current density range was large.

Further, iron components having various aspect ratios were prepared as a pore-forming agent, a single cell was constructed as described above, and the cell characteristics under high humidification were examined. Table 1 shows that the cell temperature is 80 ° C, the fuel utilization rate is 90%, the air utilization rate is 40%,
Gas humidification shows the battery voltage when the current density is 0.7 A / cm 2 with hydrogen gas at 75 ° C. and air at 50 ° C. From this, it was found that the battery characteristics deteriorate both when the aspect ratio is smaller than 2 and when the aspect ratio is larger than 10. This is because when the aspect ratio of the pore-forming agent is smaller than 2, the shape is close to that of the conventional example, so that the gas diffusivity is almost the same as that of the conventional example, and when the aspect ratio is larger than 10, the pore-forming agent is different. The agent agglomerates in the catalyst ink and cannot be uniformly dispersed, resulting in entanglement.
It was considered that the orientation could not be sufficiently performed and the gas diffusibility was lowered.

[0039]

[Table 1]

From these results, the polymer electrolyte fuel cell using the electrode having the pores with the aspect ratio of 2 to 10 oriented in the thickness direction of the catalyst layer adopted in this example is the same as the conventional uniform pore forming. It was found that the gas diffusivity was improved and a stable battery voltage was exhibited even under high humidification as compared with the battery manufactured using the agent.

Further, the fractal dimension of the catalyst layer of MEA-E was measured by the above method. The measured fractal dimensions were all values between 2-3. From this, it was considered that the pores were distributed and formed even in the inside of the catalyst layer, and exhibited the stable characteristics as described above.

In this embodiment, iron powder was used as the pore-forming agent, but it is not limited to this embodiment as long as it is a ferromagnetic substance that is soluble in an acid, such as cobalt, nickel, or an alloy thereof. Further, as for the method of orienting the pore-forming agent, the present invention may be realized by installing it in an electric field or a gravitational field other than the method using a magnetic field. It can also be formed by erecting metal fibers on a substrate using a flocking technique or the like. Further, the present invention can be realized by forming the catalyst layer without adding the pore-forming agent to the catalyst ink and then inserting the pore-forming agent into the catalyst layer by a method such as a spray method. In such a case, the pore-forming agent need not be an acid-soluble ferromagnetic material,
Metals or salts thereof, proteins such as water-soluble alcohol or gelatin, and starch may be used as long as they can be removed with an aspect ratio of 2 to 10. Further, as a method for forming the catalyst layer, another coating method such as a screen printing method may be used, or a method in which the catalyst layer is once formed on the PET film and then transferred to the polymer electrolyte membrane may be used. Although carbon paper is used for the gas diffusion layer, a material such as carbon cloth or carbon felt can also be used. In addition, any material may be used as long as the present invention can be applied, such as the components and composition of the catalyst ink and the type of polymer electrolyte membrane.

[0043]

As described above, according to the present invention, the size of the pores in the catalyst layer is increased from the side in contact with the polymer membrane to the gas diffusion layer side, so that the gas in the thickness direction of the catalyst layer is increased. The diffusivity can be improved, and the supply gas can be easily diffused to a portion closer to the polymer electrolyte membrane. Further, in the present invention, since the pores oriented in the thickness direction of the catalyst layer are formed, the gas supplied from the gas diffusion layer can be sufficiently supplied to the polymer electrolyte membrane side. With this configuration, gas diffusion in the thickness direction of the catalyst layer can be smoothly performed, and as a result, a polymer electrolyte fuel cell with high performance and long life can be obtained without filling due to water.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a fuel cell according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing the configuration of a fuel cell according to a second embodiment of the present invention.

FIG. 3 is a schematic diagram showing the configuration and gas flow of a conventional fuel cell.

FIG. 4 is a schematic diagram showing the configuration and gas flow of a fuel cell according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between current and voltage of the polymer electrolyte fuel cell single cell according to the first embodiment of the present invention.

FIG. 6 is a diagram showing a relationship between current and voltage of a polymer electrolyte fuel cell single cell according to a second embodiment of the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Junji Morita             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Makoto Uchida             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Yasuo Takebe             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Kuro Gyoten             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 5H018 AA06 AS01 BB01 BB03 BB05                       BB08 BB12 BB13 DD01 DD06                       EE03 EE05 EE18 HH00 HH05                 5H026 AA06 CC01 CX05 EE05 HH00                       HH05

Claims (6)

[Claims] 1. A gas for supplying a fuel gas containing hydrogen to one of the electrodes and a oxidant gas containing oxygen to the other of a pair of electrodes arranged with a polymer electrolyte membrane sandwiched therebetween. In a polymer electrolyte fuel cell sandwiched by a pair of separator plates having a flow path, the electrode has a catalyst layer in contact with the polymer electrolyte membrane, and a gas diffusion layer in contact with the separator plate, the catalyst The layer has carbon particles supporting a polymer electrolyte and a catalyst, and the size of the pores in the catalyst layer was changed in the thickness direction from the polymer electrolyte membrane side toward the gas diffusion layer side. A polymer electrolyte fuel cell characterized by the above. 2. The polymer electrolyte fuel cell according to claim 1, wherein the size of the pores in the catalyst layer is increased from the side in contact with the polymer electrolyte membrane toward the gas diffusion layer side. . 3. A pair of electrodes arranged with a polymer electrolyte membrane sandwiched therebetween, for supplying a fuel gas containing hydrogen to one of the electrodes and supplying an oxidant gas containing oxygen to the other of the electrodes. In the polymer electrolyte fuel cell sandwiched by a pair of separator plates having a gas flow path, the electrode has a catalyst layer in contact with the polymer electrolyte membrane, and a gas diffusion layer in contact with the separator plate, The catalyst layer has carbon particles supporting a polymer electrolyte and a catalyst, the aspect ratio of the pores in the catalyst layer is 2 or more and 10 or less, and the shape of the pores in the catalyst layer is anisotropic. And a polymer electrolyte fuel cell. 4. The polymer electrolyte fuel cell according to claim 3, wherein the pores in the catalyst layer are oriented in the thickness direction of the catalyst layer. 5. The polymer electrolyte fuel cell according to claim 1, wherein the fractal dimension of the pore structure in the catalyst layer is 2-3. 6. The method for producing a polymer electrolyte fuel cell according to claim 1, wherein the pores in the catalyst layer are formed by using a pore-forming agent.