JP2002329504A - Polyelectrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To resolve concentration of loads such as differential pressures of fuel and oxidizer gas and vibration to a cell in a polyelectrolyte film portion between a gasket and an electrode and easy fracture of the polyelectrolyte film in an edge part of the electrode or a gasket end face. SOLUTION: An angle α comprised of an end part face of at least one electrode and a contact surface of the polyelectrolyte film and the electrode is >90 deg. and <180 deg.. An angle β comprised of the end face of the gasket in at least one electrode side and a contact surface of the polyelectrolyte film and the gasket is >90 deg. and <180 deg.. By this, the loads to the polyelectrolyte film are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a polymer electrolyte fuel cell. More specifically, the present invention relates to an improvement in an electrode sandwiching a polymer electrolyte membrane and an opposed end face portion of a gasket disposed on a peripheral portion thereof.

[0002]

2. Description of the Related Art In a polymer electrolyte fuel cell, a fuel gas such as hydrogen and an oxidizing gas such as air are electrochemically reacted by a gas diffusion electrode to simultaneously generate electricity and heat. FIG. 1 shows a general configuration of such a polymer electrolyte fuel cell. In FIG. 1, a catalyst layer 12 mainly composed of a carbon powder carrying a platinum group metal catalyst is disposed in close contact with both sides of a polymer electrolyte membrane 11 that selectively transports hydrogen ions. A pair of diffusion layers 13 having both gas permeability and conductivity are provided on the outer surface of the catalyst layer 12.
Are arranged in close contact with this. The diffusion layer 13 and the catalyst layer 12 form an electrode 14. Outside the electrode 14, a conductive separator plate 16 is arranged. The conductive separator plate 16 includes the electrode 14 and the polymer electrolyte membrane 11.
And the membrane-electrode assembly (MEA) formed by the above is mechanically fixed, the adjacent MEAs are electrically connected to each other in series, a reaction gas is supplied to the electrodes, and a gas generated by the reaction is supplied. A gas passage 17 for carrying away excess gas is provided on one surface.

The gas flow path can be provided separately from the separator plate 16, but a gas flow path is generally provided by providing a groove on the surface of the separator plate. On the other surface of the separator plate 16, a cooling channel 18 for circulating cooling water for keeping the battery temperature constant is provided. By circulating the cooling water in this way, the heat energy generated by the reaction can be used in the form of hot water or the like. In such a stacked battery, a so-called internal manifold type in which a gas supply hole and a discharge hole, and further, a cooling water supply hole and a discharge hole are secured inside the stacked battery is generally used.

A gasket 15 having a sealing function for preventing gas leakage to the counter electrode or gas leakage to the outside is provided at the peripheral portion of the electrode 14. As the gasket, an O-ring, a rubber-like sheet, a composite sheet of an elastic resin and a rigid resin, or the like is used. From the viewpoint of the handleability of the MEA, a composite gasket having some rigidity is often integrated with the MEA. In the polymer electrolyte fuel cell stack as described above, it is necessary to constantly tighten the entire cell in order to reduce the electrical contact resistance of components such as a bipolar plate. To this end, it is effective to stack a number of unit cells in one direction, arrange end plates at both ends thereof, and fix the two end plates using a fastening member. As a tightening method, it is desirable to tighten the cells as uniformly as possible within the plane. From the viewpoint of mechanical strength, metal materials such as stainless steel are usually used for fastening members such as end plates.

[0005]

However, in a polymer electrolyte fuel cell using a rigid gasket as described above, the fuel gas and the oxidized gas are deposited on the polymer electrolyte membrane between the gasket and the electrode. There is a problem that loads such as a differential pressure of the agent gas and vibrations to the battery are concentrated, and the polymer electrolyte membrane is likely to be damaged at an edge of the electrode or the end face of the gasket.

[0006]

In order to solve the above problems, a polymer electrolyte fuel cell according to the present invention has an end face of at least one electrode and a contact surface between the polymer electrolyte membrane and the electrode. The angle α is 90 ° <α <180 °. Further, an angle β formed between an electrode-side end surface of at least one gasket and a contact surface between the polymer electrolyte membrane and the gasket is 90 ° <β <180 °. At least one of the gasket and the electrode is formed into a predetermined size by a punching die, and a cut surface thereof is formed at an obtuse angle with a contact surface between the gasket and / or the electrode having the cut surface and the polymer electrolyte membrane. , And the electrolyte membrane.

[0007]

As described above, in the polymer electrolyte fuel cell of the present invention, the angle between the cut surface of the electrode end and the contact surface between the polymer electrolyte membrane and the electrode becomes an obtuse angle. ing. Therefore, the polymer electrolyte membrane is less likely to be damaged at the edge of the electrode. Further, the angle formed by the cut surface at the end of the gasket and the contact surface between the polymer electrolyte membrane and the gasket is obtuse. Therefore, the polymer electrolyte membrane is less likely to be damaged at the edge of the gasket end. Further, when the cut surfaces of the gasket and the electrode end are both obtuse, damage of the polymer electrolyte membrane between the gasket and the electrode is further reduced. The electrode substrate of the electrode used in the present invention is preferably a nonwoven fabric made of carbon fibers such as carbon paper. The gasket is preferably made of a non-conductive elastic resin and a non-conductive rigid resin.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 shows an MEA including a polymer electrolyte membrane 21, a pair of electrodes 23 sandwiching the polymer electrolyte membrane 21, and a pair of gaskets 25 arranged on the periphery of the electrodes. Since the diffusion layer is in direct contact with the polymer electrolyte membrane at the periphery of the electrode where damage to the polymer electrolyte membrane is a problem, the catalyst layer is not shown in FIG. FIG. 3 is an enlarged cross-sectional view of a main part of the MEA at the periphery of the electrode. In the present invention, the outer peripheral end face of at least one electrode 23 and the polymer electrolyte membrane 21
And the contact surface between the electrode 23 and the electrode 23 is 90 ° <α <
180 °. Alternatively, the angle β between the end surface of the gasket 25 on at least one electrode side and the contact surface between the polymer electrolyte membrane 21 and the gasket 25 is set to 90 ° <β <180.
°. In FIG. 3A, the end faces of the electrode and the gasket are straight, but it goes without saying that the end faces of the electrode and the gasket may be rounded as shown in FIGS. 3B and 3C. Absent. FIG. 3 shows a most preferable embodiment in which both the pair of electrodes and the pair of gaskets satisfy the above conditions.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail with reference to the drawings. Example 1 A carbon powder having a particle diameter of several microns or less was immersed in an aqueous solution of chloroplatinic acid, and a platinum catalyst was supported on the surface of the carbon powder by a reduction treatment. The weight ratio of carbon to the supported platinum was 1: 1. Next, the carbon powder carrying platinum was dispersed in an alcohol solution of a polymer electrolyte to form a slurry. On the other hand, the thickness of the electrode 40
After impregnating a 0 μm carbon paper with an aqueous dispersion of fluororesin (manufactured by Daikin Industries, Ltd., trade name: Neoflon ND1), this is dried and dried at 400 ° C. for 30 minutes.
A minute heat treatment was applied to impart water repellency. Next, the above-mentioned slurry containing carbon powder was uniformly applied to one surface of the water-repellent carbon paper to form a catalyst layer. This was punched out by a punching die having an electrode size to obtain an electrode.

At this time, by adjusting the angle and direction of the blade of the punching die, the end face of the electrode 23 and the contact surface between the electrode 23 and the polymer electrolyte membrane 21 are formed as shown in FIG. The angle α was set to 135 °. The two electrodes 23 produced in this manner were placed on both sides of the polymer electrolyte membrane 21 having a size slightly larger than the electrodes, with the surfaces having the catalyst layers facing the polymer electrolyte membrane, respectively. They were overlapped so as to be located at the center of the electrolyte membrane. A composite material gasket laminated in three layers of silicon rubber / polyethylene terephthalate / silicone rubber was positioned on the outer periphery of the electrodes, and hot-pressed at 100 ° C. for 5 minutes to obtain an MEA. In the gasket 25 used here, as shown in FIG. 5A, the punching die was adjusted so that the angle β formed between the cut surface of the inner edge and the contact surface of the polymer electrolyte membrane was 90 °. A cell formed using this MEA is referred to as a battery A.

<< Embodiment 2 >> As shown in FIG. 5 (b), the angle α between the contact surface of the electrode and the polymer electrolyte membrane and the end surface of the electrode is 90 °, and the contact angle between the gasket and the polymer electrolyte membrane is 90 °. An MEA was obtained in the same manner as in Example 1 except that the angle β formed by the end face of the gasket was 135 °. This ME
A single cell constituted by using A is referred to as a battery B.

<< Embodiment 3 >> As shown in FIG. 5 (c), the angle α between the contact surface of the electrode and the polymer electrolyte membrane and the end surface of the electrode is 135 °, and the contact surface of the gasket and the polymer electrolyte membrane is An MEA was obtained in the same manner as in Example 1 except that the angle β formed by the end face of the gasket was 135 °. This M
A cell formed using EA is referred to as a battery C.

Comparative Example 1 As shown in FIG. 5D, the angle α between the contact surface of the electrode and the polymer electrolyte membrane and the end surface of the electrode is 90 °, and the contact angle between the gasket and the polymer electrolyte membrane is 90 °. An MEA was obtained in the same manner as in Example 1 except that the angle β formed by the end face of the gasket was 90 °. This MEA
A cell constituted using the above is referred to as a battery D.

At the cell temperature of 75 ° C., at the battery temperature of 75 ° C., humidified hydrogen was supplied to the anode at a pressure of 85 ° C. at 1 atm, and humidified air was supplied to the cathode at a pressure of 75 ° C. Supply at atmospheric pressure, hydrogen utilization rate 70
%, Oxygen utilization 20%, current density 0.7 A / cm ² at 6
Activated for hours. Thereafter, the current density was set to 0 A / cm ² , the hydrogen side was replaced with nitrogen, the cell temperature was lowered to room temperature (about 25 ° C.), and both the anode and the cathode were allowed to stand at normal pressure in a sealed state for 6 hours. This operating condition was defined as one cycle, and the cycle was repeated. 0.7 for the number of cycles at that time
The voltage at A / cm ² is shown in FIG. FIG. 6 shows that the batteries A, B, and C according to Examples 1, 2, and 3 each have a longer life than the battery D of the comparative example. When the MEA was observed by disassembling the battery with a reduced voltage, all were due to breakage of the polymer electrolyte membrane and pinholes at the boundary between the electrode and the gasket. That is, according to the configuration of the example, it is understood that the load on the electrolyte membrane at the boundary between the electrode and the gasket can be reduced.

Next, each battery was operated under the same conditions as described above, and a test was conducted in which a single cell was subjected to an acceleration of 3 G and a frequency of 20 Hz while extracting power at a current density of 0.7 A / cm ² . 0.7 A / c for test time
The change in voltage at m ² is shown in FIG. From FIG. 7, it can be seen that the batteries A, B and C of the examples have a longer cycle life than the battery D of the comparative example. When the MEA was observed by disassembling the battery with a reduced voltage, all were due to breakage of the polymer electrolyte membrane and pinholes at the boundary between the electrode and the gasket.

As is clear from the above, it can be understood that the structure of the present invention can suppress the deterioration of the performance of the polymer fuel cell due to start / stop and vibration. In the example,
Although the angle of the cut surface is adjusted by the punching die, the same effect can be obtained when the angle of the cut surface is adjusted by another molding technique, for example, cutting or thermoforming. Further, in the embodiment, the cut surface of the electrode and the gasket is flat, but if the angle formed between the tangential direction of the cut surface and the contact surface of the polymer electrolyte membrane is adjusted in the same manner as in the embodiment, the cut surface may be a curved surface. Similar effects can be obtained.

[0017]

As described above, according to the present invention, the difference between the electrode and the gasket due to the differential pressure between the fuel gas and the oxidizing gas generated during the operation of the polymer electrolyte fuel cell and the stress caused by external vibrations. A decrease in performance due to breakage of the polymer electrolyte membrane can be suppressed.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a configuration of a polymer electrolyte fuel cell.

FIG. 2 is a schematic longitudinal sectional view of an MEA of the battery.

FIG. 3 is a sectional view of a main part showing an embodiment of a MEA of a polymer electrolyte fuel cell according to the present invention.

FIG. 4 is a cross-sectional view of a main part of a MEA of a conventional polymer electrolyte fuel cell.

FIG. 5 is a cross-sectional view of a main part of a MEA of a polymer electrolyte fuel cell of an example and a comparative example.

FIG. 6 is a diagram showing the number of start / stop cycles and the voltage change at a constant current density of the polymer electrolyte fuel cells of the examples and comparative examples.

FIG. 7 is a diagram showing the number of cycles in a vibration test of a polymer electrolyte fuel cell of an example and a comparative example and a voltage change at a constant current density.

[Explanation of symbols]

 11, 21 polymer electrolyte membrane 12 catalyst layer 13 diffusion layer 14, 23 electrode 15, 25 gasket 16 separator plate 17 gas flow path 18 cooling water flow path

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroki Kusakabe 1006 Kazuma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. F-term (reference) 5H026 AA06 CC03 CX03 CX05 EE05 EE18 HH03

Claims (5)

[Claims] 1. An anode-side conductive separator plate having a polymer electrolyte membrane, a pair of electrodes having a catalyst layer sandwiching the polymer electrolyte membrane, a gas flow path for supplying a fuel gas to one of the electrodes, On the other side, a cathode-side conductive separator plate having a gas flow path for supplying an oxidizing gas, and a gasket disposed on a peripheral portion of each of the electrodes, an end surface of at least one of the electrodes, the polymer electrolyte membrane, A polymer electrolyte fuel cell, wherein an angle α formed by a contact surface with an electrode satisfies 90 ° <α <180 °. 2. The polymer electrolyte fuel cell according to claim 1, wherein the electrode substrate of the electrode is a nonwoven fabric made of carbon fiber. 3. An anode-side conductive separator plate having a polymer electrolyte membrane, a pair of electrodes having a catalyst layer sandwiching the polymer electrolyte membrane, a gas flow path for supplying a fuel gas to one of the electrodes, On the other side, a cathode-side conductive separator plate having a gas flow path for supplying an oxidizing gas, and a gasket disposed on a peripheral portion of each of the electrodes, an electrode-side end surface of at least one of the gaskets, and the polymer electrolyte The angle β between the membrane and the contact surface with the gasket is 90
° <β <180 °, wherein the polymer electrolyte fuel cell is characterized in that: 4. The polymer electrolyte fuel cell according to claim 3, wherein the gasket is made of a non-conductive elastic resin and a non-conductive rigid resin. 5. The polymer electrolyte fuel cell according to claim 1, wherein at least one of the electrode and the gasket is cut into a predetermined size by a punching die.