JP2006140087A - Membrane electrode assembly and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane electrode assembly and a fuel cell, in particular, which prevent a decrease in power generation performance when the load of the fuel cell is fluctuated or started and stopped.
SOLUTION: An electrolyte membrane (solid polymer electrolyte membrane 2), a fuel electrode 5 and an oxidizer electrode 4 disposed on both sides of the electrolyte membrane (solid polymer electrolyte membrane 2), a fuel electrode 5 and an oxidizer electrode. 4 is disposed between the gas diffusion layers 7 and 9 disposed on both sides of the electrode 4 and the electrolyte membrane 2 and at least one of the fuel electrode 5 and the oxidant electrode 4 to prevent diffusion of catalyst metal ions. And catalytic metal ion diffusion preventing means 3 for reducing catalytic metal ions.
[Selection] Figure 1

Description

  The present invention particularly relates to a membrane electrode assembly and a fuel cell applied to a polymer electrolyte fuel cell.

  BACKGROUND ART A fuel cell is a device that generates power by reacting hydrogen gas with an oxidant gas using a fuel gas such as hydrogen gas, and has recently attracted particular attention because of its low pollution and high power generation efficiency. In the automobile industry, there is a rapid increase in the use of fuel cells as a power source for motors that operate in place of internal combustion engines. Since fuel cells for use in automobiles are required to be smaller and have higher output, research and development of solid polymer fuel cells are being promoted among various types of fuel cells.

  A polymer electrolyte fuel cell is composed of a fuel cell stack in which a plurality of unit cells (single cells) serving as a minimum unit of power generation are stacked. In the single cell, a fuel electrode and an oxidant electrode are arranged on both sides of a solid polymer electrolyte membrane to form a membrane electrode assembly (MEA), and separators are formed on both sides of the membrane electrode assembly. . The fuel electrode and the oxidant electrode have a two-layer structure of a catalyst layer and a gas diffusion layer, and the catalyst layer is in contact with the solid polymer electrolyte membrane.

  In the polymer electrolyte fuel cell, when the fuel gas and the oxidant gas are introduced from the gas flow path formed in the separator, the reactions shown in Chemical Formula 1 and Chemical Formula 2 proceed in the fuel electrode and the oxidant electrode. To do.

Fuel electrode ^{_{side] H 2 → 2H + + 2e}} - ... Formula 1
[Oxidant electrode side] 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O + Q (heat of reaction)… chemical formula 2
As the entire battery, the reaction shown in Chemical Formula 3 proceeds to generate an electromotive force, and electrical work is performed on an external load.

[Whole battery] H ₂ + 1 / 2O ₂ → H ₂ O + Q (heat of reaction) ... Chemical formula 3
The reactions shown in Chemical Formula 1 and Chemical Formula 2 proceed at the three-phase interface of the catalytic metal (platinum (Pt)), the generated protons, and the electron conducting material present in the catalyst layer of each electrode. When the fuel cell is operated, a part of the catalyst metal (for example, Pt) in the oxidant electrode catalyst layer is oxidized and ionized (Pt ²⁺ ), and the catalyst metal (Pt, A part of Ru or an alloy of Pt and Ru is oxidized and similarly ionized (Pt ²⁺ , Ru ²⁺ ). In particular, when the load of the fuel cell changes or when the fuel cell is started and stopped, dissolution of the catalyst metal proceeds to facilitate ionization. Since the ionized catalytic metal ions (Pt ²⁺ , Ru ²⁺ ) move to the solid polymer electrolyte membrane side by concentration diffusion, when the fuel cell is operated for a long period of time, the oxidant electrode catalyst layer and the fuel electrode catalyst layer A large amount of catalytic metal ions are eluted, and the eluted catalytic metal ions diffuse to the solid polymer electrolyte membrane side. As a result, the rate at which a three-phase interface was formed decreased.

Conventionally, a solid polymer electrolyte membrane in which a solid polymer electrolyte resin is contained in a void of stretched porous polytetrafluoroethylene (PTFE) is formed on the electrode (fuel electrode, oxidant electrode) surface, and the electrode and the composite polymer A membrane electrode assembly in which a solid electrolyte membrane is integrated is disclosed (see Patent Document 1). According to this membrane electrode assembly, catalytic metal ions (Pt ²⁺ , Ru ²⁺ ) eluted from each electrode of the fuel electrode or the oxidant electrode are reduced at the position where PTFE in the solid polymer electrolyte exists. Had a trend.
JP-A-8-329962 (page 4)

However, in the membrane electrode assembly described above, PTFE exists at an arbitrary position in the film thickness direction in the solid polymer membrane, so that the catalyst metal ions (Pt ²⁺ , Ru ²⁺ ) eluted from each electrode are It was mainly reduced in the solid polymer film and not in the vicinity of the electrode. For this reason, after reducing catalytic metal ions (Pt ²⁺ , Ru ²⁺ ) eluted from each electrode of the fuel electrode and oxidant electrode, again form a three-phase interface with the catalytic metal (Pt, Ru). Was difficult. As a result, when the fuel cell is operated for a long period of time, the power generation performance of the fuel cell may be lowered with the decrease of the metal catalyst in the electrode. In particular, when the load of the fuel cell fluctuates or starts and stops, melting of the catalyst metal easily proceeds, so that the power generation performance of the fuel cell may be significantly reduced.

  The present invention has been made to solve the above-described problems. That is, the membrane electrode assembly of the present invention includes an electrolyte membrane, a fuel electrode and an oxidizer electrode disposed on both sides of the electrolyte membrane, and a fuel. Gas diffusion layers disposed on both sides of the electrode and the oxidant electrode, and between the electrolyte membrane and at least one electrode of the fuel electrode or the oxidant electrode, prevent diffusion of catalyst metal ions And a catalyst metal ion diffusion preventing means for reducing the catalyst metal ion.

  In the fuel cell of the present invention, the fuel electrode and the oxidant electrode are disposed on both sides of the electrolyte membrane, the gas diffusion layers are disposed on both sides of the fuel electrode and the oxidant electrode, respectively, and the electrolyte membrane and at least the fuel electrode or the oxidant are disposed. A membrane electrode assembly that is disposed between any one of the electrodes to prevent elution of the catalyst metal ions and has a catalyst metal ion diffusion preventing means for reducing the catalyst metal ions; The gist is to include a fuel electrode side separator disposed on one surface side and an oxidant electrode side separator disposed on the other surface side of the membrane electrode assembly.

  According to the membrane electrode assembly of the present invention, by reducing catalytic metal ions eluted from the electrode in the vicinity of the electrode, a part of the reduced catalytic metal is used for a power generation reaction, thereby preventing a decrease in power generation performance. Can do.

  According to the fuel cell of the present invention, it is possible to prevent a decrease in power generation performance by reusing the catalyst metal for a power generation reaction.

  Hereinafter, the membrane electrode assembly according to the embodiment of the present invention will be described with reference to an example applied to a solid polymer electrolyte fuel cell.

1st Embodiment (FIGS. 1-5)
In the first embodiment, a membrane in which catalytic metal ion diffusion preventing means is provided both between the solid polymer electrolyte membrane and the oxidant gas diffusion electrode and between the solid polymer electrolyte membrane and the fuel gas diffusion electrode. The electrode assembly will be described.

  FIG. 1 is a cross-sectional view showing a configuration of a membrane electrode assembly of a solid polymer electrolyte fuel cell according to an embodiment of the present invention. As shown in FIG. 1, the membrane electrode assembly 1 includes an oxidizer electrode 4 disposed on one surface side of a solid polymer electrolyte membrane 2 via a catalyst metal ion diffusion preventing means 3, and a solid polymer electrolyte membrane. Similarly, the fuel gas electrode 5 is arranged on the other surface side of 2 via the catalyst metal ion diffusion preventing means 3. The oxidant electrode 4 is formed by laminating the oxidant electrode catalyst layer 6 and the gas diffusion layer 7 from the solid polymer electrolyte membrane 2 side, and the fuel gas electrode 5 is formed from the fuel electrode catalyst layer 8 from the solid polymer electrolyte membrane 2 side. A gas diffusion layer 9 is laminated.

  FIG. 2 shows an enlarged view of the vicinity of the oxidant electrode catalyst layer 6 of the membrane electrode assembly 1 shown in FIG. As shown in FIG. 2, the catalyst metal ion diffusion preventing means 3 is a PTFE (Poly tetra-fluoro Ethylene) fiber 10 knitted into a mesh as a base material and a reducing agent coated on the surface of the PTFE fiber 10. And a surfactant 11. In the cross-sectional view shown in FIG. 2, the PTFE fibers 10 seem to exist individually and independently, but the actual PTFE fibers 10 are knitted into a mesh shape and connected in a surface state. In the vicinity of the catalyst metal ion diffusion preventing means 3, there is an electrolyte component 12, which is substantially the same component as the solid polymer electrolyte membrane 2 and has a material having a sulfonic acid group, and is contained in the oxidant electrode catalyst layer 8. A proton path that connects the electrolyte component and the solid polymer electrolyte membrane 2 is formed.

  The catalyst metal ion diffusion preventing means 3 on the oxidant electrode 4 side is preferably arranged such that the distance to the oxidant electrode catalyst layer 6 is 1 μm or less. As will be described in detail later, the catalyst metal ions eluted from the oxidant electrode catalyst layer 6 are reduced by hydrogen and then become a catalyst metal again, but the reduced catalyst metal becomes a lump of metal crystals and several tens of times. Often the size is from nm to several hundred nm. Therefore, in order to reuse the reduced catalyst metal in the oxidant electrode catalyst layer 6, the distance between the catalyst metal ion diffusion preventing means 3 and the oxidant electrode catalyst layer 6 is reduced to 1 μm or less and recrystallized by reduction. This makes it easier to effectively use the catalyst metal.

  An enlarged view of the vicinity of the fuel electrode catalyst layer 8 of the membrane electrode assembly 1 shown in FIG. 1 is shown in FIG. Similar to the catalytic metal ion diffusion preventing means 3 shown in FIG. 2, the catalytic metal ion diffusion preventing means 3 shown in FIG. 3 covers the PTFE fiber 10 knitted in a mesh shape as a base material and the surface of the PTFE fiber 10. And a surfactant 11 which is a reducing agent.

  As the base material, in addition to PTFE (Poly tetra-fluoro Ethylene) fiber, PVDF (Polyvinylidene Fluoride), etc., conductive materials such as carbon fiber described later can be used.

  As the reducing agent, a surfactant or the like can be mainly used. As the surfactant, any of cationic, nonionic and anionic can be used, but the kind thereof is not limited.

  The electrolyte component 12 is substantially the same component as the solid polymer electrolyte membrane 2, and is formed from a material having a sulfonic acid group.

  The solid polymer electrolyte membrane 2 is formed from Nafion (registered trademark) manufactured by DuPont.

  The oxidant electrode catalyst layer 6 is formed of a material containing platinum (Pt) as a catalyst metal on a carbon fiber and containing an electrolyte component.

The fuel electrode catalyst layer 8 is formed of a material containing an electrolyte component by supporting an alloy of platinum (Pt) and ruthenium (Ru) as a catalytic metal on a carbon fiber. The reason for including Ru as a catalyst metal in addition to Pt is to prevent Pt poisoning by carbon monoxide (CO). For example, as in the case of the oxidant electrode catalyst layer 6, when only Pt is used as the catalyst metal of the fuel electrode catalyst layer 8, a fuel mainly composed of H ₂ obtained by reforming a hydrocarbon fuel. When the gas is supplied to the fuel gas electrode 5, CO contained in the fuel gas is adsorbed by Pt, the hydrogen oxidation reaction is inhibited, and the power generation performance is degraded. On the other hand, by using an alloy of Pt and Ru containing Ru as a catalyst metal, it is possible to suppress the adsorption of CO 2 to Pt and to prevent CO poisoning of Pt.

[Production method of membrane electrode assembly]
A method for manufacturing a membrane electrode assembly according to the present embodiment will be described. First, an existing solid polymer electrolyte membrane is prepared. Next, an oxidant electrode catalyst material is applied on a resin sheet (not shown), and then dried to produce the oxidant electrode catalyst layer 6. Similarly, a fuel electrode catalyst material is applied on a resin sheet (not shown) and then dried to produce the fuel electrode catalyst layer 8. Further, the surface of the PTFE fiber 10 formed in a mesh shape is coated with the surfactant 11 to form the catalyst metal ion diffusion preventing means 3, and then the electrolyte solution is applied. Thereafter, the oxidant electrode catalyst layer 6 and the fuel electrode catalyst layer 8 are sandwiched between both sides of the catalytic metal ion diffusion preventing means 3 coated with the electrolyte solution, and hot pressed to form a membrane electrode assembly. The processing conditions of the hot press were a press pressure of 2 MPa, a temperature of 130 ° C. to 150 ° C., and a time of about 5 to 10 minutes.

  Thus, when the surface of the PTFE fiber 10 is coated with the surfactant 11 in advance, when the solid polymer electrolyte membrane 2 is integrated with the oxidizer electrode 4 and the fuel gas electrode 5, the catalyst metal ion diffusion prevention is performed. It can be easily formed integrally with the means 3 interposed therebetween. As a result, the membrane electrode assembly can be manufactured simply and with high accuracy, and a fuel cell stack in which a plurality of membrane electrode assemblies are stacked can be easily manufactured. Depending on the conditions of hot pressing, etc., there may be a structure in which a part of the PTFE fiber 10 as the catalyst metal ion diffusion preventing means 3 bites into the oxidant electrode catalyst layer 6 or the fuel electrode catalyst layer 8. The same effect can be obtained even when the metal oxide bites into the oxidation electrode catalyst layer 6 or the fuel electrode catalyst layer 8.

  Next, the state of the membrane electrode assembly after the fuel cell has been operated for a predetermined time will be described with reference to FIGS. 4 is an image diagram on the oxidant electrode catalyst layer 6 side, and FIG. 5 is an image diagram on the fuel electrode catalyst layer 8 side.

Due to the operation of the fuel cell, a part of Pt existing in the oxidant electrode catalyst layer 6 is oxidized and becomes a metal ionized state (Pt ²⁺ ), and Pt ²⁺ is moved to the solid polymer electrolyte membrane 2 side by concentration diffusion. Moving. However, since the catalytic metal ion diffusion preventing means 3 is sandwiched between the oxidant electrode catalyst layer 6 and the solid polymer electrolyte membrane 2, the path is physically narrowed, and the oxidant electrode is more than the catalytic metal ion diffusion preventing means 3. The concentration of Pt ²⁺ at the position on the catalyst layer 6 side increases. Note that the dissolution rate of the catalyst represented by Pt and the like varies depending on the environmental conditions such as the potential or temperature of the oxidizer electrode, but the dissolution progresses especially when the fuel cell load fluctuates or starts and stops. And the reaction described above easily occurs. In particular, since the oxidizer electrode 4 is exposed to an air atmosphere and is always in a high potential environment of about 0.5 V to 1.2 V, catalyst metal ions are likely to elute, but when the fuel cell is stopped, the fuel gas When air enters the electrode side, the potential on the fuel electrode side also rises.

On the other hand, an alloy of Pt and Ru existing in the fuel electrode catalyst layer 8 is also partially oxidized and metalized (Pt ²⁺ , Ru ²⁺ ) by the operation of the fuel cell, and Pt ²⁺ and Ru ²⁺ moves to the solid polymer electrolyte membrane 2 side by concentration diffusion. When an alloy of Pt and Ru is used as a catalyst, Ru is more easily oxidized than Pt, and Pt is less likely to be oxidized. However, if air enters the anode catalyst layer 8 side when the fuel cell is stopped and stored, Part is oxidized and metal ionized (Pt ²⁺ ). Similarly to the oxidant electrode 4 side, the catalyst metal ion diffusion preventing means 3 is sandwiched between the solid polymer electrolyte membrane 2 on the fuel electrode catalyst layer 8 side and the fuel electrode side catalyst layer 8. Thus, the passage is narrowed, and the concentrations of Pt ²⁺ and Ru ²⁺ on the fuel electrode catalyst layer 8 side of the catalyst metal ion diffusion preventing means 3 are increased.

Further, in the membrane electrode assembly 1, a crossover phenomenon occurs although not shown. The crossover is a phenomenon in which hydrogen existing on the fuel gas electrode 5 side dissolves and diffuses in the solid polymer electrolyte membrane 2 and moves to the oxidant electrode 4 side. The hydrogen dissolved in the solid polymer electrolyte membrane 2 reacts with a part of metal ions (Pt ²⁺ or Pt ²⁺ and Ru ²⁺ ), as described below, to produce protons and reduced metal ( Pt is generated on the oxidant electrode 4 side, and Pt and Ru) are generated on the fuel gas electrode 5 side.

As shown in FIG. 4, catalytic metal A (Pt) and catalytic metal B (Pt) reduced by hydrogen exist in the vicinity of the catalytic metal ion diffusion preventing means 3 on the oxidant electrode 4 side. Metal ions (Pt ²⁺ ) are also reduced in other regions of the solid polymer electrolyte membrane 2, but since the surfactant 11 is present on the surface of the PTFE fiber 10, in particular, catalytic metal ion diffusion preventing means. In the vicinity of 3, metal ions (Pt ²⁺ ) are easily reduced by hydrogen. The reduced catalyst metal B (Pt) is present in the electrolyte component and the solid polymer electrolyte membrane 2 and is not in contact with the oxidant electrode catalyst layer 6, and no electron transfer path is formed. For this reason, oxygen is not supplied to the reduced catalyst metal B, and the oxygen reduction reaction does not proceed. On the other hand, the catalytic metal A reduced in the vicinity of the oxidant electrode catalyst layer 6 is in contact with the oxidant electrode catalyst layer 6 to form an electron transfer path. For this reason, oxygen is supplied to the reduced catalyst metal B (Pt), and the oxygen reduction reaction proceeds to contribute to power generation.

On the other hand, also on the fuel gas electrode 5 side, hydrogen and a part of metal ions (Pt ²⁺ , Ru ²⁺ ) react to produce protons (H ⁺ ) and reduced metals (Pt, Ru). . Since the surfactant 11 is present on the surface of the PTFE fiber 10 in the vicinity of the catalyst metal ion diffusion preventing means 3, the catalyst metal ions (Pt ²⁺ , Ru ²⁺ ) are particularly easily reduced by hydrogen. Therefore, as shown in FIG. 5, reduced metal catalyst E (Pt, Ru) and metal catalyst F (Pt, Ru) exist in the vicinity of the catalyst metal ion diffusion preventing means 3 on the fuel gas electrode 5 side. . The reduced metal catalyst F (Pt, Ru) is present in the electrolyte component and in the solid polymer electrolyte membrane 2, and an electron transfer path is not formed with the fuel electrode catalyst layer 8. For this reason, it cannot function as redox like the fuel electrode catalyst layer 8 during power generation. On the other hand, the reduced metal catalyst E (Pt, Ru) exists in the vicinity of the fuel electrode catalyst layer 8, and an electron transfer path is formed by contact with the fuel electrode catalyst layer 8. For this reason, if hydrogen spreads, a hydrogen oxidation reaction will progress and it can contribute to electric power generation. Furthermore, even when CO other than hydrogen is distributed over the reduced catalytic metals E and F, Ru is present, so that Pt adsorption to CO can be prevented, and a hydrogen oxidation reaction occurs, which can contribute to power generation. . Note that the metal catalysts E and F may not be an alloy of Pt and Ru.

  According to this embodiment, since the catalyst metal ion diffusion preventing means is provided between the solid polymer electrolyte membrane and the oxidant electrode catalyst layer, it is possible to suppress performance degradation due to the dissolution of the oxidant electrode catalyst. Further, according to the present embodiment, since the catalytic metal ion diffusion preventing means is provided between the solid polymer electrolyte membrane and the fuel gas diffusion electrode, the influence of CO poisoning that is likely to occur due to catalyst dissolution of the fuel electrode. It is possible to suppress the performance deterioration due to. As a result, since the ion conductivity is good and the contact resistance is low, it is possible to provide a fuel cell having high performance and excellent durability.

  In the present embodiment, catalytic metal ion diffusion preventing means is provided both between the solid polymer electrolyte membrane and the oxidant gas diffusion electrode and between the solid polymer electrolyte membrane and the fuel gas diffusion electrode. Although the provided membrane electrode assembly is illustrated, the present invention is not limited to this configuration, and the membrane electrode assembly may be configured by providing a catalyst metal ion diffusion preventing means in one of them. For example, in a polymer electrolyte fuel cell using a membrane electrode assembly in which catalytic metal ion diffusion prevention means is provided between a polymer electrolyte membrane and an oxidant gas diffusion electrode, hydrogen using pure hydrogen as a fuel is used. By applying as a fuel cell system, the maximum effect can be achieved.

  A polymer electrolyte fuel cell using a membrane electrode assembly provided with a catalyst metal ion diffusion preventing means between a polymer electrolyte membrane and an oxidant gas diffusion electrode is a fuel cell system having a reforming system. It is preferable to apply as.

Second Embodiment (FIGS. 6 and 7)
In 2nd Embodiment, the catalyst metal ion diffusion prevention means 3 was improved and the membrane electrode assembly was comprised. In addition, since it is the same as that of the membrane electrode assembly demonstrated in 1st Embodiment except having changed the material of a catalyst metal ion diffusion prevention means, description of the same location is abbreviate | omitted.

  The catalytic metal ion diffusion preventing means 3 according to the present embodiment is composed of a carbon fiber serving as a substrate and a surfactant as a reducing agent coated on the surface of the carbon fiber. The manufacturing method of the membrane / electrode assembly is the same as that of the first embodiment except that a carbon fiber coated with a reducing agent is used as a catalyst metal ion diffusion preventing means.

  FIG. 6 is an enlarged cross-sectional view showing the vicinity of the oxidant electrode catalyst layer 6 of the membrane electrode assembly according to the present embodiment. As shown in FIG. 6, the catalyst metal ion diffusion preventing means 3 has the surface of the carbon fiber 13 coated with a surfactant 11. 6 is a cross-sectional view, the carbon fibers 13 seem to exist independently, but actually, the carbon fibers 13 are entangled in a plane and a part of the carbon fibers are in contact with the oxidant electrode catalyst layer 6. Touching.

When the operation of the fuel cell is continued, a part of the catalyst (Pt) existing in the oxidant electrode catalyst layer 6 is oxidized and becomes a metal ionized state (Pt ²⁺ ), and the solid polymer electrolyte membrane 2 side by concentration diffusion Move to. However, here, since the carbon fiber 13 exists between the solid polymer electrolyte membrane 2 and the oxidant electrode catalyst layer 6, the path is physically narrowed, and the metal ions closer to the oxidant electrode 4 than the carbon fiber 13 are. (Pt ²⁺ ) concentration increases.

In addition, due to the above-described crossover phenomenon, hydrogen dissolved in the solid polymer electrolyte membrane 2 reacts with a part of metal ions (Pt ²⁺ ) to generate protons and reduced metal (Pt). . In particular, since a reduction accelerator (surfactant) is present in the vicinity of the carbon fiber 13, the metal ions (Pt ²⁺ ) are easily reduced with hydrogen, and as shown in FIG. , Z is generated. The reduced catalytic metal Z (Pt) is present in the electrolyte component 12 or the solid polymer electrolyte membrane 2, and no oxidant electrode catalyst layer 6 forms an electron transfer path. The redox reaction that occurs in layer 6 does not proceed. On the other hand, the catalytic metal X reduced in the vicinity of the oxidant electrode catalyst layer 6 and the reduced catalyst metal Y present on the carbon fiber 13 both come into contact with the oxidant electrode catalyst layer 6 and have an electron transfer path. Is formed. For this reason, oxygen is dissolved and diffused in the electrolyte component 12, and an oxygen reduction reaction occurs in the catalyst metal in which the oxygen spreads, and thus the reduced catalyst metal contributes effectively by the power generation reaction.

  According to the present embodiment, even the catalytic metal B reduced on the carbon fiber can contribute to the power generation reaction by spreading oxygen, so the number of catalysts that can be useful is increased compared to the membrane electrode assembly described in the first embodiment. The performance deterioration due to the dissolution of the catalyst can be suppressed. In addition, heat is generated by the oxygen reduction reaction in the oxidant electrode catalyst layer and the catalyst metals A and B. However, since the carbon fiber substrate having excellent thermal conductivity is disposed on the oxidant electrode catalyst layer side, the generated heat is flat. It becomes easy to conduct in the direction and heat dispersibility is improved, and the acceleration of deterioration of the electrolyte component and catalyst deterioration due to hot spots can be suppressed. As a result, not only the same effects as those of the first embodiment can be obtained, but also the high-performance and high-durability fuel cell can be obtained by suppressing the deterioration of the electrolyte for promoting the dispersibility of heat.

  In this embodiment, the example in which the catalyst metal ion diffusion preventing means is arranged on the oxidant electrode catalyst layer side is given, but the same applies to the case where the catalyst metal ion diffusion preventing means is arranged on the fuel electrode catalyst layer side. An effect can be obtained.

It is sectional drawing which shows the structure of the membrane electrode assembly of the polymer electrolyte fuel cell which concerns on 1st Embodiment of this invention. It is an enlarged view of the X section of the membrane electrode assembly shown in FIG. It is an enlarged view of the Y part of the membrane electrode assembly shown in FIG. It is a figure explaining the mode of deterioration of a membrane electrode assembly after a fuel cell operation, and is a sectional view by the side of an oxidant electrode catalyst layer. It is a figure explaining the mode of deterioration of a membrane electrode assembly after fuel cell operation, and is a sectional view by the side of a fuel electrode catalyst layer. It is a figure explaining the structure of the membrane electrode assembly of the polymer electrolyte fuel cell which concerns on 1st Embodiment of this invention, and is sectional drawing which expanded a part by the side of an oxidant electrode catalyst layer. It is a figure explaining the mode of deterioration of a membrane electrode assembly after a fuel cell operation, and is a sectional view by the side of an oxidant electrode catalyst layer.

Explanation of symbols

1 ... Membrane electrode assembly,
2 ... Solid polymer electrolyte membrane,
3 ... Catalyst metal ion diffusion prevention means,
4 ... oxidant electrode,
5 ... Fuel gas electrode,
6 ... oxidant electrode catalyst layer,
7 ... Gas diffusion layer,
8 ... Fuel electrode catalyst layer,
9 ... Gas diffusion layer,
10 ... PTFE fiber (base material),
11 ... surfactant,
12 ... electrolyte component,

Claims (7)

An electrolyte membrane;
A fuel electrode and an oxidant electrode disposed on both sides of the electrolyte membrane;
A gas diffusion layer disposed on both sides of the fuel electrode and the oxidant electrode;
A catalyst metal ion diffusion preventing means disposed between the electrolyte membrane and at least one of the fuel electrode and the oxidant electrode to prevent the diffusion of the catalyst metal ions and to reduce the catalyst metal ions; A membrane electrode assembly comprising:   The membrane electrode assembly according to claim 1, wherein the catalytic metal ion diffusion preventing means includes a porous substrate and a reduction promoting portion formed in the vicinity of the substrate surface.   The membrane electrode assembly according to claim 1, wherein a porous substrate is disposed between the electrolyte membrane and the oxidant electrode, and a reduction promoting portion is provided in the vicinity of the substrate surface.   The membrane electrode assembly according to any one of claims 1 to 3, wherein the porous substrate has a surface coated with a reduction accelerator.   5. The membrane electrode assembly according to claim 1, wherein the distance between the electrode-side surface of the porous substrate and the surface of the electrode on the porous substrate side is 1 μm or less. .   The membrane electrode assembly according to claim 1, wherein the porous substrate is made of a conductive material. A fuel electrode and an oxidant electrode are disposed on both sides of the electrolyte membrane, and gas diffusion layers are respectively disposed on both sides of the fuel electrode and the oxidant electrode. The electrolyte membrane and at least one of the fuel electrode and the oxidant electrode A membrane electrode assembly that is disposed between one electrode and prevents catalyst metal ions from eluting and has catalyst metal ion diffusion preventing means for reducing catalyst metal ions;
A fuel electrode side separator disposed on one surface side of the membrane electrode assembly;
An oxidant electrode side separator disposed on the other surface side of the membrane electrode assembly;
A fuel cell comprising:

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