Chemistry: electrical current producing apparatus – product – and – Having earth feature
Reexamination Certificate
1999-12-10
2001-08-28
Bell, Bruce F. (Department: 1741)
Chemistry: electrical current producing apparatus, product, and
Having earth feature
C429S047000, C429S047000, C029S623100, C029S623500
Reexamination Certificate
active
06280872
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electrode for an electrochemical fuel cell and a method for producing the electrode. An electrode comprising a catalyst layer and a gas diffusion layer contacts an electrolyte membrane and a separator on each side of the electrode.
BACKGROUND OF THE INVENTION
An electrode adopted in an electrochemical fuel cell comprises a catalyst layer and a gas diffusion layer. Two of the electrodes contact an electrolyte membrane on each side of the electrolyte membrane. The catalyst layer functions as an anode or a cathode on each surface of the electrolyte membrane. The gas diffusion layer, which diffuses and supplies gas to the catalyst layer, is deposited on the outer side of the catalyst layer.
The gas diffusion layer functions not only as diffusing a gas as mentioned above, but also as removing moisture which comes out on the surface of the catalyst layer, or etc. Accordingly, a good gas diffusion ability, a good electric conductivity, and a good water repellency are required for the gas diffusion layer.
In order to improve the electric conductivity of the gas diffusion layer, in usual case a carbon-based material such as carbon fiber cloths, a carbon fiber paper, or etc. is used for the gas diffusion layer. By making polytetrafluoethylene (PTFE) permeate into the carbon-based material, the water repellency is added to the characteristics of the gas diffusion layer. Furthermore, by the process of coating a carbon compound (or paste) which is mixed and kneaded with PTFE and carbon powder such as carbon black, the gas diffusion layer is produced. For example, such an electrode in an electrochemical fuel cell is proposed in Japanese Laid-Open Patent Application No. 5-283082.
In the conventional electrode for an electrochemical fuel cell such as the above-mentioned electrode, a carbon-based material such as carbon fiber cloths or a carbon fiber paper is used in order to improve the electric conductivity of the electrode. However, such a conventional electrode is problematic, because the cost of the electrode is high, since such a carbon-based material is expensive.
SUMMARY OF THE INVENTION
It is thus one object of the present invention to solve the aforementioned problems. Another object of the invention is to provide an electrode which has a high performance and a low cost. Another object of the invention is to provide a method for producing such an electrode for an electrochemical fuel cell.
An electrochemical fuel cell comprises an electrolyte membrane, an electrode, and a separator. Two of the electrodes contact the electrolyte membrane on each side of the electrolyte membrane, and the separator contacts on the other side of each electrode. According to one aspect of the invention, as the embodiment of an electrode for an electrochemical fuel cell, the electrode comprises a catalyst layer, and a gas diffusion layer contacting the catalyst layer. The gas diffusion layer comprises carbon powder and a high polymer having a water repellency. The gas diffusion layer may also consist essentially of carbon powder and the high polymer.
For example, the gas diffusion layer comprises an inner layer and an outer layer, and the inner layer is closer-grained than the outer layer. Furthermore, it is also effective that the gas diffusion layer comprises carbon black and that the carbon black in the inner layer is smaller in structure than the carbon black in the outer layer.
A method for producing the electrode comprises coating a catalyst layer on the electrolyte membrane, coating a compound of carbon powder and a high polymer having a water repellency on the catalyst layer, and baking the carbon compound on the catalyst layer.
As mentioned above, according to this invention, a porous carbon-based material is not used for producing the gas diffusion layer in the electrode. Consequently, the cost of the electrode is low.
REFERENCES:
patent: 6017650 (2000-01-01), Rammuni et al.
patent: 6054228 (2000-04-01), Cisar et al.
patent: 63-24563 (1988-02-01), None
patent: 5-283082 (1993-10-01), None
Kawahara Tatsuya
Ozaki Toshiaki
Bell Bruce F.
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
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