Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1999-05-03
2001-09-18
Huff, Mark F. (Department: 1756)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000, C427S115000
Reexamination Certificate
active
06291094
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas separator for use in a fuel cell, and a fuel cell incorporating the gas separator, and a method of production of the gas separator. More particularly, the invention relates to a fuel cell gas separator which is provided between adjacent unit cells in a fuel cell formed by stacking a plurality of unit cells, and which forms a fuel gas passage and an oxidative gas passage, together with adjacent members, and separates a fuel gas and an oxidative gas from each other, and a fuel cell incorporating the gas separator, and a method of production of the gas separator.
2. Description of the Related Art
A fuel cell gas separator is a component member of a fuel cell stack formed by stacking a plurality of unit cells. The gas separator has a sufficiently high gas impermeability so as to prevent mixture of a fuel gas and an oxidative gas that are supplied to adjacent unit cells. A typical fuel cell gas separator is formed by using a carbon material or a metal material. Normally, metal materials have excellent strength, and therefore allow formation of a thinner gas separator than carbon materials. This allows the size of a fuel cell to be reduced. Furthermore, metal-made gas separators can be produced by a simple and easy methods, for example, by pressing a metal sheet, so that the gas separator production process can be simplified and made less time-consuming. Therefore, adoption of a metal-made gas separator improves productivity and controls the production costs.
For production of a metal-made gas separator, a suitable metal may be selected from metals having sufficiently high electric conductivity, strength and formability. Normally, an anticorrosion measure is needed to secure a sufficiently high corrosion resistance of the gas separator under environmental conditions for the operation of a fuel cell. One example of a measure for improving the corrosion resistance of a gas separator is to coat a gas separator with a metal having a good corrosion resistance, for example, platinum, gold, rhodium, iridium and the like (described in, for example, Japanese Patent Application Laid-Open No. HEI 5-182679).
However, these metals are rarely-occurring natural resources, and the use of such a costly noble metal increases the production cost of a fuel cell. Furthermore, if plating or the like method is employed for the metal coating process, the problem of formation of micro-holes in the coating surface is likely to arise. If there are holes in a coating surface, corrosion advances gradually therefrom. Thus, if a gas separator is coated with a noble metal as mentioned above, it is still difficult to secure a sufficiently high corrosion resistance. An attempt may be made to restrict the effect of corrosion starting at holes in a coating surface within an allowable range. However, this attempt necessitates an increase in the coating thickness, thereby increasing the amount of noble metal used. A technology for achieving an improved corrosion resistance of a gas separator by coating it with nickel is known (for example, Japanese Patent Application Laid-Open No. HEI 7-282821). In some cases, however, the nickel coating fails to secure a sufficiently high corrosion resistance under environmental conditions for the operation of a polymer electrolyte fuel cell.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to achieve a sufficiently high corrosion resistance of a metal-made gas separator without using a costly material.
In accordance with one aspect of the invention, a separator for a fuel cell includes a metallic base member, a first coating layer covering at least a portion of a surface of the base member, the first coating layer being formed from a first electrically conductive material, and a second coating layer covering at least a face where the first coating layer is formed, the second coating layer being formed from a second electrically conductive material different from the first electrically conductive material. The first coating layer being formed at least on a face of the separator that contacts another fuel cell component member when the separator is incorporated into the fuel cell.
In the above aspect of the invention, the second electrically conductive material may be a carbon material.
In the gas separator for a fuel cell of the invention, a metal-made gas separator base member is coated with an electrically conductive material other than carbon and with a carbon material, so that a sufficiently high corrosion resistance can be achieved without using a costly material, such as a noble metal. The separator has a carbon material coating on a contact face that contacts an adjacent member (for example, a gas diffusion electrode) when the separator is incorporated into a fuel cell. Since the adjacent member is also formed of a carbon material, the contact resistance between the carbon material coating of the separator and the adjacent member can be reduced. Thus, the provision of the first coating layer of an electrically conductive material and the second coating layer secures a sufficiently high corrosion resistance and a sufficiently high electric conductivity. Therefore, it becomes possible to form a base member of the separator from a metal that has a sufficiently high electric conductivity and that is low cost but which is insufficient in corrosion resistance, for example, stainless steel, aluminum and the like.
Fuel cells into which the separator is incorporated are able to maintain sufficiently high performance over long hours of use since an increase in the internal resistance caused by corrosion of the gas separator does not occur.
In the above aspect of the invention, the carbon material of the second coating layer may be a thermal expansion graphite.
Use of a thermal expansion graphite eliminates the need to add a binder to the carbon material for the second coating layer when the second coating layer is to be formed by press-fitting the carbon material onto the separator base member. Therefore, a reduction in the electric conductivity of the separator surface caused by a binder is eliminated.
The base member may be electrically conductive at least in a region thereof where the first coating layer is formed. If the separator base member forms a substantially non-electrically conductive coating on a surface thereof, the substantially non-electrically conductive coating may be removed from the surface of the separator base member before the first coating layer is formed thereon.
By removing a substantially non-electrically conductive coating from the separator base member, a sufficiently high electric conductivity between the base member and the second coating layer covering the first coating layer can be secured, so that the internal resistance of the separator can be sufficiently reduced. Therefore, if the separator base member is formed from stainless steel, which tends to form a passive state film on its surface, or aluminum, which tends to form an oxide film on its surface, the separator for a fuel cell attains a sufficiently high electric conductivity.
In the separator for a fuel cell of the invention, the first coating layer may have a rough surface.
If the first coating layer ha s a rough surface, it becomes possible to increase the adhesion strength between the first coating layer and the second coating layer and to increase the contact area therebetween and therefore decrease the contact resistance.
REFERENCES:
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patent: 5798188 (1998-08-01), Mukohyama et al.
patent: 6090228 (2000-07-01), Hwang et al.
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patent: 7-282821 (1975-10-01), None
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patent: WO9735349 (1997-09-01), None
(Reese Puckett, Stephen L. Michel, William E. Hughes), Ion Beam Etching, Thin Film Processes II, V2, 749-782, 1991.*
Patent Abs
Nonobe Yasuhiro
Yamane Keiji
Yoshimura Joji
Chacko-Davis Daborah
Huff Mark F.
Kenyon & Kenyon
Toyota Jidosha & Kabushiki Kaisha
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