JP2002343368A - Polymer electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-output fuel cell by lowering resistance caused by a contact part of a separator plate and a gas diffusion layer. SOLUTION: A conductive body layer is formed at the side in contact with a separator plate of a gas diffusion layer. This conductive body layer, preferably, is to be made of aluminum, nickel or stainless steel formed by a thermal spraying method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a portable power supply,
The present invention relates to a polymer electrolyte fuel cell used for a power source for an electric vehicle, a home cogeneration system, and the like.

[0002]

2. Description of the Related Art A fuel cell using a polymer electrolyte generates electric power and heat simultaneously by electrochemically reacting a fuel gas containing hydrogen with an oxidizing gas containing oxygen such as air. Things. This fuel cell basically includes a polymer electrolyte membrane for selectively transporting hydrogen ions, and a pair of electrodes formed on both sides of the polymer electrolyte membrane, that is, an anode and a cathode. The electrode is usually composed mainly of carbon powder carrying a platinum group metal catalyst, and has a catalyst layer formed on the surface of the polymer electrolyte membrane, and gas permeability and electron conduction formed on the outer surface of the catalyst layer. It consists of a gas diffusion layer having both properties. Fuel gas and oxidant gas supplied to the electrode leak out,
A gas sealing material or a gasket is arranged around the electrodes with a polymer electrolyte membrane interposed therebetween so that the two types of gases do not mix with each other. These sealing materials and gaskets are assembled in advance with the electrodes and the polymer electrolyte membrane. This is called an electrolyte membrane-electrode assembly (MEA). M
Outside the EA there is arranged a conductive separator plate for mechanically fixing it and connecting adjacent MEAs electrically in series with each other and possibly in parallel. A gas flow path for supplying a reaction gas to the electrode surface and carrying away generated gas and surplus gas is formed in a portion of the separator plate that contacts the MEA. Although the gas flow path can be provided separately from the separator plate, a method in which a groove is provided on the surface of the separator plate to form a gas flow path is generally used.

In order to supply the fuel gas and the oxidizing gas to these grooves, pipes for supplying the fuel gas and the oxidizing gas are branched into the number of separator plates to be used, and the branch destination is directly connected to the separator plate. A piping jig that connects to the groove is required. This jig is referred to as a manifold, and the type directly connected from the fuel gas and oxidizing gas supply pipes as described above is referred to as an external manifold. This manifold is of a type referred to as an internal manifold which has a simpler structure. The internal manifold is one in which a through hole is provided in a separator plate having a gas flow path formed therein, an inlet / outlet of the gas flow path is passed to this hole, and a fuel gas and an oxidizing gas are directly supplied from this hole. Since the fuel cell generates heat during operation, it is necessary to cool the fuel cell with cooling water or the like in order to maintain the cell in a favorable temperature state. Usually, a cooling unit for flowing cooling water is provided for every 1 to 3 cells. There are a type in which a cooling unit is inserted between separator plates, and a type in which a cooling water flow path is provided on the back surface of the separator plate to form a cooling unit, and the latter is often used. The MEA, the separator plate and the cooling section are alternately stacked and 10 to 200
The general structure of a stacked battery is that cells are stacked, the stacked body is sandwiched between end plates via a current collector plate and an insulating plate, and fixed from both ends with fastening bolts.

In such a polymer electrolyte fuel cell,
The separator plate needs to have high conductivity, high airtightness against fuel gas and oxidizing gas, and high corrosion resistance against the reaction when redoxing hydrogen / oxygen. For this reason, the conventional separator plate is usually made of a carbon material such as glassy carbon or expanded graphite, and the gas flow path is also manufactured by cutting its surface or, in the case of expanded graphite, by molding with a mold. . In the conventional method of cutting a carbon plate, it has been difficult to reduce not only the material cost of the carbon plate but also the cost for cutting the carbon plate. Also, the method using expanded graphite has a high material cost, and this is considered to be an obstacle for practical use. In recent years, instead of conventionally used carbon materials,
Attempts have been made to use metal plates such as stainless steel.

[0005]

However, in the above-mentioned method using a metal plate, the contact resistance with the gas diffusion layer is high, the internal resistance and the impedance of the polymer electrolyte fuel cell are high, and good power generation efficiency is not obtained. There is a problem that it cannot be obtained. An object of the present invention is to provide a fuel cell having a high output by reducing the resistance caused by a contact portion between a separator plate and a gas diffusion layer.

[0006]

According to the present invention, in order to solve the above-mentioned problems, a conductor layer is formed on a surface of a gas diffusion layer in contact with a separator plate. That is, the polymer electrolyte fuel cell of the present invention has a pair of electrodes having a catalyst layer and a gas diffusion layer, a polymer electrolyte membrane sandwiched between the pair of electrodes, and an electrode disposed outside the electrodes. An anode-side separator plate having a flow path for supplying a fuel gas to the anode and a cathode-side separator plate having a flow path for supplying an oxidizing gas to the other electrode, and a conductive surface is provided on a surface of the gas diffusion layer in contact with the separator plate. It has a body layer.
With the above configuration, it is possible to realize a polymer electrolyte fuel cell having a low contact resistance with a separator plate, particularly a metal separator plate, a low internal resistance and impedance, and a high power generation efficiency.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The polymer electrolyte fuel cell of the present invention has a conductor layer on at least a part of a surface of a diffusion layer in contact with a separator plate. This conductor layer reduces the contact resistance between the separator plate and the gas diffusion layer. In a preferred aspect of the present invention, the conductor layer is made of aluminum, nickel, or stainless steel formed by a thermal spraying method. Hereinafter, embodiments of the present invention will be described with reference to the drawings. The structural diagrams used here are for easy understanding, and the relative sizes and positional relationships of the respective elements are not always accurate.

FIG. 1 is a longitudinal sectional view showing a unit cell of a polymer electrolyte fuel cell according to the present invention. 10 is an electrolyte membrane
Represents an electrode assembly (MEA). This MEA is a polymer electrolyte membrane 1
1, an anode 12 and a cathode 13 sandwiching this. Outside the MEA, the anode-side conductive separator plate 2
1 and a cathode-side conductive separator plate 31 are arranged, and current collector plates 22 and 32 are further arranged outside thereof. This is used as a unit cell, and a plurality of units are connected in series to form a battery stack. The separator plate 21 has a groove 41 that forms a fuel gas flow path on a surface in contact with the anode 12. Similarly, the cathode-side conductive separator plate 31 has a groove 42 that forms a flow path for the oxidizing gas on the surface that is in contact with the cathode 13. Here, the anode-side conductive separator plate and the cathode-side conductive separator plate were formed independently, but the anode-side conductive separator plate and the cathode-side conductive separator plate were formed of a single separator plate. Can be used as the anode-side conductive separator plate, and the other surface can be used as the cathode-side conductive separator.

[0009]

Embodiments of the present invention will be described below. << Example 1 >> Acetylene black was added with an average particle size of about 30Å.
Was supported at a weight ratio of 50:50 to prepare a catalyst for an electrode. An isopropanol dispersion of the catalyst powder is
An ethanol dispersion of perfluorosulfonic acid powder (Flemion from Asahi Glass Co., Ltd.) was mixed to form a paste.
Using this paste as a raw material, a catalyst layer was formed on one surface of a carbon nonwoven fabric having a thickness of 250 μm by screen printing. A conductive layer of SUS316 was formed on the other surface of the carbon nonwoven fabric by using a plasma spraying method. At the time of this plasma spraying, a portion corresponding to a groove portion serving as a gas flow path of the separator plate is not masked to form a conductor layer. Amount of platinum contained in the catalyst layer of the obtained electrode thus 0.5 mg / cm ^2, the amount of perfluorocarbon sulfonic acid was adjusted to be 1.2 mg / cm ^2.

These electrodes have the same structure for both the anode and the cathode, and the catalyst layers printed on both sides of the center of the proton conductive polymer electrolyte membrane having an area slightly larger than the electrodes are in contact with the electrolyte membrane side. To form MEA. Here, perfluorocarbon sulfonic acid (Nafion membrane, manufactured by Dupont, USA) was used as the proton conductive polymer electrolyte membrane.
A cell was formed by disposing a predetermined sealing material and a SUS316 separator plate on both sides of the obtained MEA. Then, the battery was set in a unit cell test apparatus, and the battery characteristics were examined. A hydrogen gas heated and humidified so that the dew point is 75 ° C. is supplied to the anode of the cell, and a heated and humidified air is supplied so that the dew point is 60 ° C. to the cathode. ,
The fuel utilization was set at 80% and the air utilization was set at 40%.

FIG. 2 shows a comparison of the current-voltage characteristics of the cells. FIG. 2 shows that the characteristics (curve a) of the unit cell of the embodiment in which the conductor layer was formed on one surface of the gas diffusion layer were superior to the characteristics (curve b) of the unit cell of the comparative example in which the conductor layer was not formed. It indicates that This difference is considered to be due to a difference in contact resistance between the metal separator plate and the gas diffusion layer. As described above, according to the present invention, as a result of forming the conductor layer on one surface of the gas diffusion layer, a metal material such as stainless steel can be used without cutting instead of the conventional carbon plate cutting method, Significant cost reduction can be achieved during mass production. Further, the thickness of the separator plate can be further reduced, which contributes to making the laminated battery compact.

[0012]

As described above, according to the present invention, an excellent polymer electrolyte fuel cell can be provided by forming a conductor layer on one surface of a gas diffusion layer.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a unit cell in an embodiment of the present invention.

FIG. 2 is a diagram showing characteristics of a unit cell of an example of the present invention and a unit cell of a comparative example.

[Explanation of symbols]

 Reference Signs List 10 MEA 11 Polymer electrolyte membrane 12 Anode 13 Cathode 21, 31 Separator plate 22, 32 Current collector plate 41, 42 Groove

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masato Hosaka 1006 Kazuma Kadoma, Kazuma-shi, Osaka Matsushita Electric Industrial Co., Ltd. F-term (reference) 5H018 AA06 AS02 AS03 BB07 CC06 DD06 DD08 EE02 EE04 EE10 5H026 AA06 BB00 BB04 CC03 CX04 EE02 EE08

Claims (2)

[Claims] 1. A pair of electrodes having a catalyst layer and a gas diffusion layer, a polymer electrolyte membrane sandwiched between the pair of electrodes, and a flow path disposed outside the electrodes and supplying a fuel gas to one of the electrodes. Comprising a cathode-side separator plate having a flow path for supplying an oxidizing gas to the anode-side separator plate and the other electrode, and having a conductor layer on the surface of the gas diffusion layer in contact with the separator plate. Polymer electrolyte fuel cell. 2. The polymer electrolyte fuel cell according to claim 1, wherein the conductor layer is made of aluminum, nickel or stainless steel formed by a thermal spraying method.