JP2005190749A - Membrane electrode assembly for fuel cell and solid polymer fuel cell using the same - Google Patents

Abstract

A fuel capable of mitigating attack by a gas diffusion electrode on a proton ion conductive solid polymer membrane and stress concentration on the polymer membrane and preventing deterioration in performance of the polymer electrolyte membrane. Provided are a membrane electrode assembly for a battery and a high-performance polymer electrolyte fuel cell using such a membrane electrode assembly.
An intermediate layer (5) between the electrode catalyst layer (3) and the polymer electrolyte membrane (2) in a membrane electrode assembly (1) comprising a proton ion conductive solid polymer electrolyte membrane (2), an electrode catalyst layer (3) and a gas diffusion layer (4). As a material of the intermediate layer 5, a mixed material of the same proton ion conductive solid polymer material as that of the polymer electrolyte membrane 2 and a carbon material which is the main component of the electrode catalyst layer 3 is used.
[Selection] Figure 1

Description

  The present invention relates to a polymer electrolyte fuel cell (PEFC) using, as an electrolyte, a proton ion conductive solid polymer membrane such as a fluororesin polymer, and more particularly, a proton ion conductive solid polymer. Membrane Electrode Assembly (MEA) comprising a membrane, a pair of electrode catalyst layers sandwiching the solid polymer membrane, and a pair of gas diffusion layers sandwiching them from the outside And a polymer electrolyte fuel cell using such a membrane electrode assembly.

Solid polymer fuel cells using proton ion conducting solid polymer membranes operate at lower temperatures than other types of fuel cells, and are expected to be used as power sources for mobile vehicles such as automobiles. Is also progressing.
In such a polymer electrolyte fuel cell, a fuel gas containing hydrogen and an oxidizing gas containing oxygen are placed on a pair of electrodes (oxygen electrode and fuel electrode) with a proton ion conductive solid polymer membrane sandwiched therebetween. By supplying each, the reaction shown by the following formula occurs, and electric energy is taken out.
Cathode reaction (oxygen electrode): 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O
Anode reaction (fuel electrode): H ₂ → 2H ⁺ + 2e ⁻

The gas diffusion electrode used in the polymer electrolyte fuel cell is a catalyst-supported carbon fine particle coated with an ion exchange resin (polymer electrolyte) of the same type or different from the polymer electrolyte membrane (proton ion conductive solid polymer membrane). And a gas diffusion layer that supplies a reaction gas to the catalyst layer and collects charges generated in the catalyst layer, and the electrode catalyst layer side of the gas diffusion layer is a polymer electrolyte membrane. In the state of being opposed to each other, the membrane electrode assembly is formed by bonding by hot pressing. The gas diffusion layer is generally made of carbon paper, woven fabric, or non-woven fabric made using carbon fibers.
And a fuel cell is comprised by laminating | stacking many such membrane electrode assemblies through the separator (gas flow path formation member) provided with the gas flow path.

As an example of the structure of such a polymer electrolyte fuel cell, for example, in Patent Document 1, a water retention layer is installed between the gas diffusion layer and the electrode catalyst layer, and further between the water retention layer and the gas diffusion layer. Or providing a water repellent layer.
JP 2002-289230 A

However, conventional polymer electrolyte fuel cells have a membrane electrode assembly having a laminated structure in which a polymer electrolyte membrane is sandwiched between a gas diffusion electrode comprising an electrode catalyst layer and a gas diffusion layer. When assembling a membrane electrode assembly into a cell, there is a problem that the tip portion of the carbon fiber of the gas diffusion layer in the gas diffusion electrode may mechanically attack the membrane and cause a deterioration in the performance of the membrane. There is a problem that the mechanical stress caused by the gas diffusion layer or electrode catalyst layer coming into contact with a soft polymer electrolyte membrane cannot be relieved, and it is a conventional membrane electrode assembly for fuel cells that can eliminate such problems It was a problem in.
In the fuel cell disclosed in Patent Document 1, the membrane / electrode assembly includes a water retention layer and a water repellent layer, but these water retention layers and water repellent tanks control the humidified state of the polymer electrolyte membrane. The stress applied to the polymer electrolyte membrane by the water-retaining layer is not alleviated by the water-retaining layer, since it is interposed between the gas diffusion layer and the electrode catalyst layer. Contact of the electrolyte membrane with the electrode catalyst layer cannot be avoided and has essentially the same problem.

  The present invention has been made paying attention to the above-mentioned problems in conventional membrane electrode assemblies for fuel cells, and the object of the present invention is to attack proton ion conductive solid polymer membranes by gas diffusion electrodes, The concentration of stress on the polymer membrane can be alleviated, and the membrane electrode assembly for fuel cells that can prevent the performance degradation of the polymer electrolyte membrane, and the membrane electrode assembly using such a membrane electrode assembly The object is to provide a polymer electrolyte fuel cell having high performance.

  As a result of intensive studies on the material and structure of the gas diffusion electrode with the aim of solving the above-mentioned problems, the present inventor has found that between the proton ion conductive solid polymer membrane and the gas diffusion electrode, that is, the polymer electrolyte membrane. The above object is achieved by providing an intermediate layer between the electrode catalyst layer and the electrode catalyst layer to prevent direct contact between the polymer electrolyte membrane and the gas diffusion electrode, and to function as a stress relaxation layer. As a result, the present invention has been completed.

  That is, the membrane electrode assembly for fuel cells of the present invention has the same proton ion conductivity as the proton ion conductive solid polymer membrane between the proton ion conductive solid polymer membrane and the electrode catalyst layer in the membrane electrode assembly. An intermediate layer containing a solid polymer material and a carbon material constituting the electrode catalyst layer is provided.

  The polymer electrolyte fuel cell of the present invention is characterized in that a plurality of the membrane electrode assemblies of the present invention are laminated via a gas flow path forming member.

According to the present invention, since the intermediate layer is arranged between the electrode catalyst layer and the proton ion conductive polymer electrolyte membrane in the membrane electrode assembly, the polymer electrolyte membrane and the gas diffusion electrode are separated from each other. Even if pressure is applied when assembling the membrane electrode assembly or stacking the fuel cell stack, the polymer electrolyte membrane and the gas diffusion layer or electrode catalyst layer of the gas diffusion electrode, which is a rigid body, are not in direct contact. The problem that the polymer electrolyte membrane is damaged by the carbon fiber tip of the gas diffusion layer or the edge-like portion of the end face of the electrode catalyst layer, or gas cross-lease is thereby eliminated, can be solved.
In addition, since this intermediate layer uses the same proton ion conductive solid polymer material as the electrolyte membrane and a carbon material that is the main component of the electrode catalyst layer, the mechanical strength of the electrolyte membrane and the electrode catalyst is high. Since it functions as a stress relaxation layer applied to the film in an intermediate state with respect to the layer, the polymer electrolyte membrane can be effectively prevented from being broken by mechanical stress.

  In the polymer electrolyte fuel cell of the present invention, a plurality of the membrane electrode assemblies of the present invention are used and laminated together with a gas flow path forming member that functions as a separator. It has excellent durability against stress and can exhibit excellent battery performance over a long period of time.

  Hereinafter, the fuel cell membrane electrode contact assembly of the present invention will be described in more detail.

1A and 1B are a schematic cross-sectional view and a plan view, respectively, showing the structure of a fuel cell membrane electrode assembly of the present invention. The fuel cell membrane electrode assembly 1 shown in FIG. The proton ion conductive solid polymer membrane 2 is sandwiched by a gas diffusion electrode comprising an electrode catalyst layer 3 and a gas diffusion layer 4, and the electrode catalyst layer 3 of the gas diffusion electrode and the polymer electrolyte membrane 2 are An intermediate layer 5 is provided between them.
The intermediate layer 5 is formed of a mixed material containing the same proton ion conductive solid polymer material as that of the polymer electrolyte membrane 2 and a carbon material that is the main component of the electrode catalyst layer 3.

  In addition, a separator made of a conductive material provided with a gas flow path, that is, a gas flow path forming member (not shown) is provided on the outer side of the membrane electrode assembly 1, so that a plurality of the membrane electrode assemblies 1 are formed. By laminating, the solid oxide fuel cell of the present invention is formed.

  In the fuel cell membrane electrode assembly 1 having such a structure, as is apparent from FIG. 1, the electrode catalyst layer 3 and the gas diffusion layer 4 of the gas diffusion electrode are formed of the polymer electrolyte membrane by the intermediate layer 5. 2, even when pressure is applied to the membrane electrode assembly 1, the polymer electrolyte membrane 2 is not damaged by the carbon fibers of the gas diffusion 4. In addition, the pressure is applied to the polymer electrolyte membrane 2 through the gas diffusion layer 4 and the electrode catalyst layer 3, but is relaxed by the intermediate layer 5, and stress concentration at the end face edge portion of the electrode catalyst layer 3 is reduced. It is avoided and damage to the polymer electrolyte membrane 2 is prevented.

At this time, the intermediate layer 5 contains both the proton ion conductive solid polymer material and the carbon material as described above, but the carbon concentration of the electrode catalyst layer 3 is increased from the polymer electrolyte membrane 2 side. It is desirable to have a multistage concentration layer structure or a gradient concentration structure that increases stepwise or continuously as it goes to the side, whereby the bonding property between the polymer electrolyte membrane 2 and the electrode catalyst layer 3 is improved. improves.
Furthermore, it is desirable that the intermediate layer 5 be larger than the electrode catalyst layer 3 and the gas diffusion layer 4, whereby the stress applied to the end edge portion of the electrode catalyst layer 3 is directly applied to the polymer electrolyte membrane 2. Therefore, the stress concentration on the polymer electrolyte membrane 2 is more reliably suppressed.

  Hereinafter, the present invention will be specifically described based on examples. Needless to say, the present invention is not limited to these examples. In this example, “%” means mass percentage unless otherwise specified.

(Example 1)
First, a slurry for obtaining an intermediate layer disposed on both sides of the proton ion conductive solid polymer membrane was prepared.
That is, carbon black (Vulcan XC72) having a particle size of several microns or less is used as a carbon material, and 5% of this carbon black powder and a proton ion conductive solid polymer solution (Nafion (registered trademark: manufactured by DuPont)). Solution A), an alcohol solution, and water were used to prepare slurry A in which the mass ratio of the carbon black powder after drying and the polymer material was 2 to 8. Further, a slurry B was prepared by the same material and method so that the mass ratio of the carbon black powder after drying and the polymer material was 8: 2.

  Next, the slurry A was applied to the surface of a Nafion 112 manufactured by DuPont as a proton ion conductive solid polymer membrane and dried. Further, by further applying and drying the slurry B, the carbon black powder concentration on the polymer electrolyte membrane side is 20%, and the carbon black powder concentration on the outside (electrode catalyst side) is 80%. An intermediate layer of structure was formed on both sides of the polymer electrolyte membrane.

Next, on the further outer side of the polymer electrolyte membrane provided with an intermediate layer on both sides, a carbon paper as a gas diffusion layer and an electrode catalyst layer mainly composed of the carbon black (Vulcan XC72) was placed. The membrane electrode assembly was obtained by pressing for 90 seconds at a temperature of 140 ° C. and a pressure of 100 kgf / cm ² .

  The membrane electrode assembly thus obtained was sandwiched between separators (gas flow path forming members) having gas diffusion channels from both sides to form a single cell of a fuel cell. The tightening pressure at this time was 1 MPa. Using this single cell, voltage measurement at the open end was performed in order to confirm the cross leak characteristics of the polymer electrolyte membrane.

(Example 2)
Using the same materials and methods as in Example 1 above, together with the slurry C such that the mass ratio of the carbon black powder after drying and the polymer material is 4 to 6, the mass ratio is 6: 4. Slurry D was prepared.

Next, the slurry C is coated and dried on the surface of the same polymer electrolyte membrane, and then the slurry D is coated and dried, so that the carbon black powder concentration on the polymer electrolyte membrane side is 40%, and the outside (electrode catalyst) The intermediate layer having a two-layer structure having a carbon black powder concentration of 60% was formed on both sides of the polymer electrolyte membrane.
And while obtaining the membrane electrode assembly using the same method and material, the voltage measurement in an open end was similarly performed about the fuel cell single cell using this.

(Example 3)
Using the same material and method as in Example 1, a slurry E was prepared so that the mass ratio of the carbon black powder after drying and the polymer material was 5: 5.
Next, after applying and drying the slurry A used in Example 1 on the surface of the polymer electrolyte membrane, the slurry E was applied and dried, and further the slurry B of Example 1 was applied and dried. The polymer electrolyte membrane is an intermediate layer having a three-layer structure in which the carbon black powder concentration on the molecular electrolyte membrane side is 20%, the carbon black powder concentration on the outside (electrode catalyst side) is 80%, and the central carbon black powder concentration is 50%. Formed on both sides.

  And the membrane electrode assembly was formed using the same method and material, and the voltage measurement in an open end was similarly performed about the fuel cell single cell using the said membrane electrode assembly.

Example 4
Except for using Denka Black instead of Vulcan XC72 as the carbon black powder, the same operation as in Example 1 was repeated to obtain a membrane electrode assembly of this example, and a fuel cell unit using the same For the cell, voltage measurement at the open end was similarly performed.

(Example 5)
The same operation as in Example 1 was repeated except that Asahi Kasei's Aciplex (registered trademark) was used as the polymer electrolyte membrane, and the Aciplex solution was used as the proton ion conductive solid polymer solution. Thus, a membrane electrode assembly of this example was obtained.
And the fuel cell single cell using the said membrane electrode assembly was formed, and the voltage measurement in an open end was similarly performed.

(Comparative example)
Without forming an intermediate layer, the surface of Nafion 112, which is a proton ion conductive solid polymer membrane, was hot-pressed with a carbon paper adhered to carbon paper in the same manner as in Example 1 above. A membrane electrode assembly of a comparative example was obtained.
And the fuel cell single cell using the said membrane electrode assembly was formed, and the voltage measurement in an open end was similarly performed.

〔Measurement result〕
Table 1 shows the voltage measurement results at the open end of the single fuel cell using the membrane electrode assemblies according to the above examples and comparative examples.

(A) And (b) is sectional drawing and a top view which respectively show the structure of the membrane electrode assembly for fuel cells of this invention.

Explanation of symbols

1 Fuel Cell Membrane / Electrode Assembly 2 Proton Ion Conductive Solid Polymer Membrane (Polymer Electrolyte Membrane)
3 Electrocatalyst layer 4 Gas diffusion layer
5 middle class

Claims (4)

  In a membrane / electrode assembly for a fuel cell comprising a proton ion conductive solid polymer membrane, an electrode catalyst layer, and a gas diffusion layer, the proton ion conductive solid polymer membrane is interposed between the proton ion conductive solid polymer membrane and the electrode catalyst layer. Membrane electrode assembly for a fuel cell comprising an intermediate layer containing the same proton ion conductive solid polymer material as the proton ion conductive solid polymer membrane and a carbon material constituting an electrode catalyst layer .   2. The fuel cell membrane electrode assembly according to claim 1, wherein the composition ratio of the carbon material in the intermediate layer increases from the proton ion conductive solid polymer membrane side toward the electrode catalyst layer side.   The membrane electrode assembly for a fuel cell according to claim 1 or 2, wherein the size of the intermediate layer is at least larger than the sizes of the electrode catalyst layer and the gas diffusion layer.   A polymer electrolyte fuel cell comprising a plurality of fuel cell membrane electrode assemblies according to any one of claims 1 to 3 and a plurality of gas flow path forming members.

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