JPH09265992A - Electrode structure for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the electrode structure for a fuel cell, which can make a power generation efficiency effective, and is costwise favorable in a solid polymer type fuel cell. SOLUTION: As for a second catalyst layer 432, PTFE dispersion solution of 80mg with a weight ratio of 55% is adjusted to the same solution of 79mg by coordinating carbon black carrying platinum with a weight ratio of 20% so as to be mixed with pure water of 40ml and isopropanol of 40ml, so that the mixture is dispersed by the use of an ultrasonic cleaner. As for a first catalyst layer 431, carbon black of 40mg, carrying plattinum with a weight ratio of 40%, is mixed with the PTFE dispersion solution of 29mg so as to allow dispersion solution to be regulated. After an anode side pole joining body and a cathode side pole joining body have been formed, let the cathode side pole joining body and the anode side pole joining body be faced to each other in such a way that respective catalyst layer sides are faced to each other, and a solid polymer electrolytic film is interposed between the aforesaid layers so as to be jointed together. They are then fixed using a press jig so as to be formed into a solid polymer electrolytic film pole joining body by hot pressing them using pressure of roughly 25kgf/cm<2> per unit area of the pole joining body at the temperature of around 155 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode structure of an electrolyte membrane fuel cell.

[0002]

2. Description of the Related Art A fuel cell intends to utilize electric power based on a redox reaction via an electrolyte for various purposes. For this purpose, electrodes are arranged on both sides of the electrolyte to supply a reaction gas. , Is configured to be able to recover electric power. A polymer electrolyte fuel cell is known as one form of the fuel cell. BACKGROUND ART A solid polymer fuel cell generally supplies a power generating element, that is, a solid polymer-electrode assembly and a reaction gas, which is formed by sandwiching a hydrogen ion conductive solid polymer between carbon electrodes carrying a platinum catalyst. A gas passage groove is provided for this purpose, and has a structure in which a gas separation member that supports the power generation element from both sides is laminated. Then, the fuel gas is supplied to one electrode, the oxidant gas is supplied to the other electrode, and the electrical energy is extracted by directly converting the chemical energy of the fuel gas and oxygen into electrical energy. . In the polymer electrolyte fuel cell, when an electrochemical reaction between hydrogen and oxygen occurs, a current is generated between the electrodes and water is generated on the cathode side. Since the polymer electrolyte fuel cell has a relatively low operating temperature of about 80 ° C. as compared with other fuel cells, it is suitable for a portable power source, particularly a power source for electric vehicles. .

However, when used for automobiles,
Hydrogen gas, which is a fuel, must be secured in a vehicle by a portable tank or a portable reformer. On the other hand, as the oxidant gas, air is used for reasons such as weight reduction of the system and cost. In this case, the oxygen partial pressure is reduced to about ⅕ as compared with pure oxygen, which causes problems of oxygen reduction reaction rate and mass transfer in the reaction of the fuel cell. To solve this problem, a method of compressing air and supplying the compressed air to the fuel cell is generally adopted. However, in this case, in order to consume the energy to drive the air compressor,
It should be noted that the energy efficiency of the entire fuel cell is correspondingly reduced. In view of such circumstances, various methods have been proposed to achieve high energy efficiency even under low oxygen partial pressure. For example, the catalytic material (80
It is proposed to improve the catalytic activity by atomizing (a platinum catalyst is the one that has activity at a low temperature of about ℃), increase the density of the catalyst substance, increase the carbon supported on the catalyst, etc. ing. By increasing the catalytic activity, the oxygen reduction reaction rate can be improved and therefore the performance of the fuel cell can be improved.

However, although the improvement of the catalytic activity by the above-mentioned method contributes to the increase of the oxygen reduction reaction rate, there is a problem that it results in the increase of the mass transfer resistance. Another problem is that platinum-based catalysts, which have catalytic activity in a relatively low temperature state, are expensive, so it is desirable from the viewpoint of cost to be able to improve the performance of the fuel cell while suppressing the amount used. Japanese Unexamined Patent Publication No. 7-134993 discloses a technique for improving the performance of a fuel cell by efficiently removing the generated water generated on the cathode electrode side. The fuel cell disclosed in the above publication includes an electrolyte membrane made of a solid polymer, and a fuel electrode and an air electrode arranged on both sides of the electrolyte membrane. The fuel electrode and the air electrode have a catalyst layer disposed in contact with the electrolyte membrane surface and a gas diffusion layer disposed on the opposite side, and the gas diffusion layer of the air electrode includes a catalyst layer. The hydrophobic gradient is provided so that the hydrophobicity becomes higher toward the side, and the gas diffusion layer of the fuel electrode is provided with the hydrophobic gradient such that the hydrophobicity becomes lower toward the catalyst layer side.
In the disclosed fuel cell, with the above configuration, on the fuel electrode side, water that moves with hydrogen ions in the fuel electrode side electrolyte and decreases can be replenished, and a decrease in the water content of the electrolyte can be suppressed, and the air electrode can be suppressed. On the side, it is described that gas diffusion alienation due to flooding of water in the catalyst layer is less likely to occur, and battery performance can be improved.

[0005]

[Problems to be Solved] Japanese Patent Application Laid-Open No. 7-134993
The fuel cell disclosed in U.S. Pat. No. 6,096,981 provides a structure for effectively controlling the supply and removal of water on the anode side or the cathode side of an electrode, and seeks to improve cell performance in terms of mass transfer. It is a thing. In this configuration, 1
Although it is possible to achieve a certain effect in terms of dimensions, it does not take into consideration factors such as the above-mentioned problems of both catalytic activity and mass transfer comprehensively, and it has a certain limit in improving battery performance. It is a thing. The present invention is constructed in view of the above circumstances, and is described in the above-mentioned Japanese Patent Laid-Open No.
An object of the present invention is to provide an electrode structure of a fuel cell, which can improve performance and is advantageous in terms of cost by a method different from the known one disclosed in Japanese Patent Publication No. 34993 / etc.

[0006]

To achieve the above object, the present invention is configured as follows. That is, the present invention provides an electrode structure of a fuel cell having an electrolyte membrane and catalyst electrodes arranged on both sides of the electrolyte membrane, wherein the density of the catalyst substance in the catalyst electrode is near the interface with the electrolyte membrane. It is an electrode structure of a fuel cell having a maximum value. In a preferred embodiment, the catalyst electrode is formed by stacking a plurality of catalyst electrode layers having different catalyst substance densities. In this case, it is preferable that the catalyst electrode layer that is farther from the interface with the electrolyte membrane be thicker. Further, it is preferable that the density of the ionic conductor in the three-phase reaction region consisting of the ionic conductor of the catalytic electrode, the catalytic substance and the reaction gas has a maximum value in the vicinity of the interface with the electrolytic chamber membrane. The catalyst material is platinum or a platinum alloy, and the density of the catalyst material is 10 to 6 with respect to the catalyst carrier.
It is preferably in the range of 0% by weight. If the content of the catalytic substance is too low, it becomes difficult to obtain the desired catalytic activity,
If the weight ratio is too large, the activity corresponding to the amount of platinum cannot be obtained, which is disadvantageous in cost. According to the experience of the inventors, when the content of the catalyst substance exceeds about 60% by weight with respect to the support, a good catalyst dispersed state cannot be obtained, and improvement in performance cannot be expected. Further, the electrolyte membrane is preferably a solid polymer electrolyte membrane.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The electrode reaction of a fuel cell occurs inside the catalyst layers on both sides of the electrolyte membrane, and the more vigorous the reaction, the more energy that can be extracted from the fuel cell. That is, the performance of the fuel cell is improved. But,
The current generated by the electrode reaction is not uniform in the thickness direction of the catalyst layer and is more active at a position closer to the interface of the electrolyte membrane, and the reaction activity decreases as the distance from the interface increases. The present invention has been made by paying attention to the actual state of the electrode reaction phenomenon in such a fuel cell, and is configured to promote a more active reaction in the catalyst layer region near the electrolyte membrane interface where the electrode reaction most actively occurs. To do. That is, in the vicinity of the electrolyte membrane of the catalyst layer, the density of the catalyst substance is increased in order to create an environment in which the electrode reaction is promoted, and the ion conductor density is correspondingly increased to enhance the high reaction activity in this region. The mass transfer resistance in the catalyst layer is reduced as much as possible by maintaining the density and decreasing the density of both materials as the distance from the electrolyte membrane interface increases. That is, the mass transfer resistance can be lowered by decreasing the catalyst material density and the ion conductor density as the distance from the electrolyte membrane increases.
Further, from another viewpoint, the diffusibility of water generated by the electrode reaction on the cathode side can be improved by reducing the density of the ionic conductor.

According to the above-mentioned structure of the present invention, the protons, that is, H ⁺ that have moved from the anode side through the electrolyte membrane, are collected at the anode electrode, perform external work, and are supplied to the cathode electrode through the external circuit. This makes it possible to most efficiently perform the coupling on the cathode side. That is, according to the present invention, the oxidation-reduction reaction rate can be maintained high, and the mass transfer resistance through the electrolyte membrane of the fuel cell, the catalyst layers and diffusion layers arranged on both sides of the electrolyte membrane can be suppressed as low as possible. The catalytic material is typically platinum or a platinum alloy (Pt / C
r, Pt / Co, Pt / Rh, Pt / Ni) and the like, and those carrying the above-mentioned catalyst substance as a carrier of carbon black having conductivity and corrosion resistance by a salt reduction method or the like are used. The catalyst material density is adjusted by changing the weight ratio of catalyst material to support. Further, examples of the above-mentioned ion conductor include fluororesin having a sulfonic acid group.

[0009]

Embodiments of the present invention will be described below. (Solid Polymer Electrolyte Membrane Electrode Assembly According to an Embodiment of the Present Invention) Overall Structure FIG. 1 shows a cross section of a fuel cell including a single solid polymer electrolyte membrane electrode assembly according to an embodiment of the present invention. A schematic is shown. The fuel cell 1 of this example has a solid polymer electrolyte membrane 2 in the center, and an oxidation electrode or anode electrode 3 to which hydrogen as a fuel is supplied on one side, and air as an oxygen source for a reduction reaction on the other side. Has a basic structure including a reduction electrode, that is, a cathode electrode 4. The anode electrode 3 is configured by laminating and bonding a carbon cloth 31, a diffusion layer 32 inside thereof, and a catalyst layer 33 inside thereof. A grooved gas separation plate 30 having a gas separation function and a power collection function for the generated power is provided outside the anode electrode 3. Then, the anode electrode 3 and the grooved gas separation plate 30 constitute an anode electrode side bonded body.

The grooved gas separation plate 30 is provided with a groove for defining an anode gas passage 34 through which hydrogen gas, which is a fuel gas, flows while supplying protons H ⁺ to the electrolyte membrane side. The surface contact portion of the carbon cloth 31 with the diffusion layer 32 constitutes a current collecting portion that collects electrons generated from hydrogen molecules. The cathode electrode side has the same structure, and has a laminated bonding structure of the carbon cloth 41, the diffusion layer 42, and the catalyst layer 43. A grooved gas separation plate 40 is provided on the outer side of the carbon cloth 41 to separate the oxygen gas from leaking to the outside and to prevent the gas from short-passing the groove extending while bending the surface of the carbon cloth. Have a role to play. The grooved gas separation plate 40 has a groove having a depth of about 1 mm that defines a cathode gas passage 44 that allows oxygen to flow in contact with the proton H ⁺ from the electrolyte membrane side to generate water. ing. The cathode electrode 4 and the grooved gas separation plate 40 form a cathode-side electrode assembly.

With the above construction, as conceptually shown in FIG. 1, the protons, that is, H ⁺ , which have moved from the anode side through the electrolyte membrane 2 and the anode electrode 3 are collected to perform external work and pass through an external circuit. The electrons supplied to the cathode electrode 4 are combined on the cathode electrode side. That is, on the anode electrode side, hydrogen molecules are deprived of electrons to generate protons H ⁺ , and on the cathode electrode side,
Protons H ⁺ conducted through the electrolyte membrane 2 react with electrons from an external circuit having an external load and oxygen molecules supplied from the cathode gas passage to generate water molecules. The details of the laminated state from the electrolyte membrane 2 in the middle of the cathode electrode 4 to the electrodes 3 and 4 are shown in FIG. 2, and a catalyst layer is provided outside the electrolyte membrane 2 with a first catalyst layer 431 and a second catalyst layer. Two layers 432 are provided in an adjacently joined state. Then, a diffusion layer 42 is provided on the outer side thereof, and a carbon cloth 41 is further joined on the outer side thereof to form an electrode. The grooved gas separation plate 40 is joined to the outer side thereof as described above to form the entire joined body. Carbon cloth The carbon cloth 31, 41 is a portion which forms a base layer of an electrode portion which is arranged immediately inside the grooved gas separation plates 30, 40 in the solid polymer electrolyte membrane electrode assembly, and is basically the above-mentioned portion. It has a role as a current collecting member responsible for the movement of electrons involved in the anode electrode reaction and the cathode electrode reaction. Further, it is possible to effectively supply the mass transfer in each of the electrodes 3 and 4, particularly the anode gas and the cathode gas to the three-phase reaction region composed of the ion conductor, the catalyst material and the reaction gas. In addition, it is desirable that the water generated in the cathode electrode 4 can be effectively discharged.

In this example, the anode side carbon cloth 31 and the cathode side carbon cloth 41 are both carbon cloths woven from carbon fibers. The carbon cloth used as an electrode in this example is a product name: "A" Cloth manufactured by E-TEK, USA,
The weight is 116 g / m ² and the thickness is 0.35 mm. In constructing the electrode of this example, a fluororesin (polytetrafluoroethylene (hereinafter referred to as PTFE)) dispersion solution (PTFE having a particle size of about 0.2 μm was 54 to 55).
It is contained in a weight percentage and is stably dispersed together with a specified amount of a surfactant (provided by Mitsui DuPont Fluorochemicals Co., Ltd. under the trade name TEFLON FEP120-J) to treat the surface of the carbon cloth. Added water repellency. The water repellent treatment of this carbon cloth is PT
The above carbon cloth was dipped in a solution prepared by diluting 49% by weight of a solution in which FE was dispersed with a surfactant, and then the excess solution was wiped off with a filter paper. The PTFE was sintered for a period of time. Diffusion layer The diffusion layer is provided inside the carbon cloth so as to be in contact with the catalyst layer, and functions to effectively perform mass transfer to and from the catalyst layer similarly to the electrode. In addition to the above, it must be one that effectively exhibits a current collecting function as a medium interposed between the catalyst layer and the electrode.

In this example, the diffusion layer is formed as a sintered body of carbon black and PTFE. The weight ratio of the both is 6: 4, and the densities per unit area thereof are 2.4 mg and 1.6 mg, respectively. As the carbon black, the trade name Vulcan XC-72 (surface area 250 m ² / g) provided by Cabot Corporation was used. Production of Diffusion Layer 315 mg of carbon black and 389 mg of the commercially available PTFE dispersion solution were mixed with 40 ml of pure water and 40 ml of isopropanol and dispersed using an ultrasonic cleaner. This dispersion-prepared liquid was sprayed onto the water repellent carbon cloth as the above-mentioned electrode while being dried using a sprayer and a dryer. The rate at which the dispersion solution adheres to the carbon cloth is 5 to 30%. After the completion of spraying, the carbon cloth having the diffusion layer formed thereon was compressed by a roller of about 50 kg to a thickness of about 0.2 to 0.5 mm. Next, in an electric furnace in the above-mentioned nitrogen atmosphere, about 300 ° C
A diffusion layer was formed on the carbon cloth by sintering PTFE at ~ 350 ° C for about 1 hour.

Catalyst layer (cathode electrode side) In this example, the catalyst layer on the cathode electrode side is composed of two layers, and the first catalyst layer on the electrolyte membrane side is approximately 10 μm in this example, and the outside thereof. The second catalyst layer adjacent to the diffusion layer is finished to a thickness of 20 μm. As the catalyst, the above carbon black (Vu
lcan XC-72) supported with platinum was used. However, the density of platinum, which is the catalytic metal, is higher in the first catalyst layer and the platinum / carbon ratio is 40% Pt /
C (weight percent), the second catalyst layer is 20 percent P
t / C (percent by weight). The average particle size of platinum is about 2.5 nm. The composition of each catalyst layer is as shown in FIG. In FIG. 3, Nafion is a trade name polymer-containing liquid of an electrolyte membrane provided by DuPont, and the structure of the polymer is Aciplex-S (100
It is similar to 4). This polymer-containing liquid Nafion
Is a dispersion of a predetermined amount of polymer in a solution obtained by mixing equal amounts of water and ethanol. In this example, a polymer concentration of 5 wt% is used. The production of the catalyst layer on the cathode electrode side will be described. In forming the catalyst layer, first, a dispersion solution containing a predetermined amount of raw materials is prepared. The weight ratio of the second catalyst layer 432 is 20
160% carbon black carrying platinum
mg, 55% by weight of PTFE dispersion solution (TEFLON FEP12
158 mg of 0-J) was prepared, and this was mixed with 40 ml of pure water and 40 ml of isopropanol and dispersed using an ultrasonic cleaner. For the first catalyst layer 431, 40
% Platinum-supported carbon black 40 mg and PTFE dispersion solution (TEFLON FEP120-J) 29 mg are mixed to prepare a dispersion solution. In the PTFE dispersion solution, PTFE having a particle diameter of about 0.2 μm is 54 to 55.
It is contained in a weight percentage and is stably dispersed together with a predetermined amount of surfactant.

Next, of the two types of dispersion solutions for the catalyst layer prepared above, first, the dispersion solution for the second catalyst layer is sprayed to the surface of the diffusion layer of the semi-finished product on which the diffusion layer is formed. The second catalyst layer 432 was formed by spraying on the surface. Then, as in the case of forming the diffusion layer, in the electric furnace in a nitrogen atmosphere, the glass transition temperature of PTFE is around (about 300 to 35).
The sintering treatment of PTFE was performed at 0 ° C. for about 1 hour.
Then, in a similar manner, the dispersion solution for the first catalyst layer having a slightly high platinum density was sprayed onto the surface of the second catalyst layer 431 formed above by using a spray to apply the dispersion solution for the back catalyst layer. Next, sintering treatment is performed in the same manner as the diffusion layer and the second catalyst layer, and the first catalyst layer 4 is formed on the second catalyst layer 432.
31 was formed. Next, the carbon cloth 41 formed as described above and the diffusion layer 4 on the carbon cloth 41
2. The above-mentioned polymer electrolyte solution Nafion is applied onto the surface of the first catalyst layer 431 of the solid polymer electrolyte membrane electrode assembly semi-finished product consisting of the second and first catalyst layers 432 and 431 on the diffusion layer. In this example, Nafion is dipped in a suitable brush to remove Na
Fion was included and applied on the surface of the first catalyst layer 431. The coating amount was about 0.6 mg / cm ² . (Anode electrode side) The catalyst layer on the anode electrode side in this example is composed of a single layer having a uniform catalyst density. And the above carbon black (Vulcan XC-72) carrying platinum (20% Pt / C, average platinum particle size 2.5n
The m) the catalyst layer so that 0.4 mg / cm ² in the same manner as the method of forming the catalyst layer of the cathode side, the sintering process of spraying and subsequent PTFE to diffusion layer surface of the dispersion Formed by doing. In this case, the amount of carbon black in the catalyst layer and the diffusion layer is about 4.0.
It was prepared to be about mg / cm ² . Then, the entire anode-side electrode assembly excluding the grooved gas separation plate 30 was set to about 0.35 mm.

Electrolyte Membrane A solid polymer electrolyte membrane is a non-porous polymer material,
Fluorine resin (polytetrafluoroethylene (hereinafter PTF
E))). The electrolyte membrane of this example is a product name provided by Asahi Kasei Corporation: Aciplex-S
It is (1004). Its thickness is about 2-6 mils (about 50
About 150 μm). The chemical structure is as shown in FIG. As described above, according to the basic operation of the polymer electrolyte fuel cell, a reaction occurs in which electrons are deprived from hydrogen, which is the fuel gas, at the anode electrode, which generates electrons and hydrogen ions (protons H ⁺ ). , The electrons pass through the load, while the proton H ⁺ conducts in the electrolyte membrane and reaches the cathode electrode. At the cathode electrode, the proton H ⁺ produces reaction water by reacting with oxygen. That is, the electrolyte membrane has a role of conducting the proton H ⁺ to the cathode side, as well as a role of preventing unreacted hydrogen gas from entering the cathode side in a molecular state, as is clear from the above basic operation. is there. When the proton H ⁺ moves in the electrolyte membrane toward the cathode side, it moves along with water molecules. Therefore, the electrolyte membrane must also have a water molecule holding function for holding water molecules for this purpose. I won't. Further, in the electrolyte membrane having an ionic conductor group (a sulfonic acid group in this example), the ratio of the weight of the sulfonic acid group per unit weight, that is, the sulfonic acid group equivalent is preferably about 500 to 1500 (g / eq). . The electrolyte membrane has (1) a proton H ⁺ conduction function,
(2) As long as this condition is satisfied, which has a separation function for separating hydrogen gas in the anode gas passage and oxygen gas (air) in the cathode gas passage, and (3) a predetermined water retention function, Any one can be used. An anode catalyst layer is formed on the anode side and a cathode catalyst layer is formed on the cathode side of the electrolyte membrane.

Formation of Electrode Bonded Body After the anode side electrode bonded body and the cathode side electrode bonded body are constructed as described above, the cathode side electrode bonded body and the anode side electrode bonded body are respectively faced with the catalyst layers facing each other. Then, the solid polymer electrolyte membrane was sandwiched between them and bonded. Then, fix it with a press jig to about 1
Approximately 25 kg per unit area of electrode assembly at a temperature of 55 ° C
A solid polymer electrolyte membrane electrode assembly was manufactured by hot pressing at a pressure of f / cm ² .

(Solid Polymer Electrolyte Membrane Electrode Assembly According to Comparative Example) In the structure of the comparative example, the cathode side electrode was also composed of a single catalyst layer, like the anode side electrode. A dispersion solution was prepared in the same manner as in the example to form the catalyst layer. In this case, platinum-supporting carbon black (Vulcan XC-72) is 160 mg Pt / C 20% platinum weight ratio, PTF
A dispersion was prepared in the same manner as above using 158 mg of the E dispersion solution (FEP120-J), and the catalyst layer was formed by spraying. In addition, the deposition rate of the dispersion liquid by spraying is 15 to 20% of the spraying amount. After that, the same sintering treatment was performed. Other configurations are the same as those in the embodiment. An experiment of power generation by a fuel cell including the solid polymer electrolyte membrane electrode assemblies according to the examples and comparative examples thus formed was conducted. The result is shown in FIG. As is clear from the results shown in FIG. 5, the fuel cell according to the example of the present invention relates to the generated voltage as compared with the fuel cell according to the comparative example.
It was found that the value was increased by about 25 mV at 00 mA / cm ² . This means that the power generation efficiency of the fuel cell is about 60.
% To 62%. According to the results of this experiment in the fuel cell structure including a single solid polymer electrolyte membrane electrode assembly, the power generation efficiency is remarkably improved in the fuel cell including a large number of laminated structures.

In this embodiment, the catalyst layer on the cathode electrode side is composed of two layers having different catalyst densities, but it is also possible to stack more layers having different densities.
In this case, the layers are stacked so that the catalyst density on the electrolyte membrane side is high. Further, in this example, the anode electrode was formed by a single catalyst layer having a uniform catalyst density, but it is not always necessary to do so, and a plurality of layers having different catalyst densities may be laminated in the same manner as the cathode electrode. It can also be configured. Further, in the present example, the catalyst layer was configured by laminating layers having different catalyst densities, but if the configuration is such that the catalyst density gradient decreases from the electrolyte membrane side toward the diffusion layer side, a single catalyst layer is formed. It may be a layer. Further, in the production of the catalyst layer, if it is a method that can obtain the catalyst gradient as described above, it is possible to obtain a thin film thickness of 10 to 10 regardless of spraying and brush coating.
Any known means can be used to form a thin layer of about 100 μm.

[0020]

As described above, in the present invention, in the solid polymer electrolyte membrane fuel cell, it is possible to improve the power generation efficiency with a simple structure and without increasing the manufacturing cost.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an electrode assembly of a polymer electrolyte fuel cell according to one embodiment of the present invention,

FIG. 2 is a cross-sectional view showing a stacked state of each layer of the fuel cell of FIG.

FIG. 3 is a graph showing the composition of the cathode side catalyst layer,

FIG. 4 is a diagram showing an example of the structure of PTFE constituting an ionic conductor,

FIG. 5 is a graph showing a relationship between voltage and current density for showing characteristics of a fuel cell.

[Explanation of symbols]

 1 Fuel Cell 2 Solid Polymer Electrolyte Membrane 3 Anode Electrode 4 Cathode Electrode 43, 33 Catalyst Layer

Claims (6)

[Claims] 1. An electrode structure for a fuel cell, comprising an electrolyte membrane and catalyst electrodes arranged on both sides of the electrolyte membrane, wherein the density of the catalyst substance in the catalyst electrode is near an interface with the electrolyte membrane. A fuel cell electrode structure having a maximum value. 2. The electrode structure for a fuel cell according to claim 1, wherein the catalyst electrode is formed by stacking a plurality of catalyst electrode layers having different catalyst substance densities. 3. The electrode structure of a fuel cell according to claim 2, wherein the catalyst electrode layer farther from the interface with the electrolyte membrane is thicker. 4. The density of an ionic conductor in a three-phase reaction region comprising an ionic conductor of a catalyst electrode, a catalytic substance and a reaction gas according to claim 1 or 2, is maximized near an interface with an electrolytic chamber membrane. An electrode structure for a fuel cell, comprising: 5. The catalyst according to claim 1, wherein the catalyst substance is platinum.
An electrode structure for a fuel cell, which is a platinum alloy and has a density of the catalyst material in the range of 10 to 60% by weight based on the catalyst carrier. 6. The fuel cell electrode structure according to claim 1, wherein the electrolyte membrane is a solid polymer electrolyte membrane.