Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2001-03-12
2004-06-15
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000, C427S115000
Reexamination Certificate
active
06749959
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application Nos. 2000-068553 filed on Mar. 13, 2000 and 2000-169897 filed on Jun. 7, 2000 including the specification, drawings and abstract are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a fuel cell gas separator, a manufacturing method thereof, and a fuel cell. More particularly, the invention relates to a fuel cell gas separator provided between adjacent single cells in a fuel cell having a plurality of single cells stacked on each other, for forming a fuel gas flow path or an oxidized gas flow path together with an adjacent member and for separating the fuel gas and the oxidized gas from each other, a manufacturing method thereof, and the fuel cell.
2. Description of Related Art
A fuel cell gas separator is a member that forms a fuel cell stack having a plurality of single cells stacked on each other. The fuel cell gas separator has sufficient gas non-permeability in order to prevent the fuel gas and oxidized gas supplied to each of adjacent single cells from mixing together. Conventionally, such a fuel cell gas separator has been manufactured by using a carbon material or metal material. In general, a metal material exhibits higher strength, and therefore makes it possible to manufacture a thinner gas separator as compared to the case using the carbon material. Such a reduced thickness of the gas separator enables reduction in overall size of the fuel cell. Moreover, a metal gas separator can be manufactured by a simple method of pressing a metal sheet. As a result, the manufacturing process can be conducted in a quick, simplified manner, resulting in improved productivity. Thus, increase in manufacturing cost can be prevented.
A metal used for manufacturing the metal gas separator can be selected as appropriate from the metals having sufficient conductivity, strength and formability. In particular, by using a metal that is mass distributed as a metal material like stainless steel and aluminum, significant reduction in manufacturing cost can be achieved. The use of such a metal material normally requires the structure for ensuring sufficient corrosion resistance in the operation environment of the fuel cell. As the structure for improving corrosion resistance of the gas separator, the structure of coating the surface of the gas separator with silver has been proposed (e.g., Japanese Patent Laid-Open Publication No. SHO 60-115173). By coating the surface with silver, corrosion resistance of the metal gas separator can be significantly improved.
However, the internal environment of the operating fuel cell becomes highly acidic, thereby possibly making the corrosion resistance of the gas separator insufficient even in the case of the silver-coated metal gas separator. The internal environment of the fuel cell is considered to be acidified mainly by the following two factors: in the fuel cell (e.g., polymer electrolyte fuel cell), a catalyst layer including platinum, a platinum alloy or the like is provided on the surface of the electrolyte membrane. This catalyst layer normally contains a residual sulfate or the like of platinum that is used as a material for forming the catalyst layer. Accordingly, when the fuel cell is started, the residual platinum salt is eluted into the water produced in the gas flow path in the fuel cell, thereby acidifying the internal environment of the fuel cell. Moreover, the solid polymer electrolyte membrane provided in the polymer electrolyte fuel cell includes sulfonates as a functional group for realizing the proton conductivity. This solid polymer electrolyte membrane is gradually decomposed little by little at the portions of the sulfonates during power-generating operation of the fuel cell, thereby producing sulfuric acid. Thus, the internal environment of the fuel cell is acidified.
It is known that such platinum-salt elution and sulfonate decomposition as described above acidify the internal environment of the fuel cell to about pH 2. Under such strongly acidic conditions, the corrosion resistance of the gas separator may possibly become insufficient over the long-time operation of the fuel cell, even if the gas separator is coated with silver having a low ionization tendency. As the surface of the gas separator corrodes, the metal forming the gas separator is eluted as metal ions. Thus, if the metal ions (silver ions, or ions of a metal forming the substrate portion of the silver-coated separator) are eluted from the gas separator into the solid polymer electrolyte membrane even in a slight amount, such metal ions are attracted to the ion exchange groups (sulfonates) included in the electrolyte membrane, thereby degrading the proton conductivity of the solid polymer electrolyte membrane. This is not desirable for maintaining the performance of the fuel cell. Accordingly, a fuel cell gas separator with improved corrosion resistance has been desired.
SUMMARY OF THE INVENTION
The invention is made in view of the foregoing problems, and it is an object of the invention to provide a fuel cell gas separator for realizing sufficient corrosion resistance in a metal gas separator, a manufacturing method thereof, and a fuel cell.
In order to achieve the aforementioned object, a fuel cell gas separator according to one aspect of the invention includes a separator base material formed from a metal, a noble metal coating layer formed at least on a part of the separator base material, and a carbon coating layer formed on the noble metal coating layer. The noble metal coating layer is formed at least on the separator base material surface in a region of the gas separator that contacts an adjacent member of the fuel cell when the gas separator is integrated into the fuel cell, in other words, a region associated with a contact resistance corresponding to a contact surface that is in contact with the adjacent member.
A method for manufacturing a fuel cell gas separator according to another aspect of the invention includes the steps of (a) forming a separator base material having a predetermined shape from a metal, (b) forming a noble metal coating layer from a noble metal at least on a part of the separator base material formed in the step (b), i.e., at least on a region associated with a contact resistance with an adjacent member on a separator base material surface corresponding to a contact surface that is in contact with the adjacent member when the gas separator is integrated into the fuel cell, and (c) forming a carbon coating layer from a carbon material on the noble metal coating layer formed in the step (b).
A method for manufacturing a fuel cell gas separator according to still another aspect of the invention includes the steps of (a) forming a noble metal coating layer from a noble metal at least on a region of a surface of a metal member serving as a base material of the gas separator, (b) forming a carbon coating layer from a carbon material on the noble metal coating layer formed in the step (a), and (c) forming the metal member having both the noble metal coating layer and the carbon coating layer being formed on the surface thereof into a predetermined shape.
The fuel cell gas separator according to the aforementioned aspect of the invention as well as the fuel cell gas separators manufactured by the respective manufacturing methods according to the aforementioned aspects of the invention includes a noble metal coating layer formed from a noble metal. This noble metal coating layer is formed at least on a region associated with a contact resistance with an adjacent member on a separator base material surface corresponding to a contact surface that is in contact with the adjacent member when the gas separator is integrated into the fuel cell. Accordingly, in the metal forming such a separator, the region coated with the noble metal coating layer, i.e., the region associated with the conductivity of the fuel cell gas separator, is not oxidized to form a passive state film. As a result, increas
Aihara Hideo
Kaji Yoshifumi
Murate Masashi
Nakata Hiromichi
Onishi Masazumi
Dove Tracy
Kenyon & Kenyon
Ryan Patrick
Toyota Jidosha & Kabushiki Kaisha
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