Fuel cell having a gasket with an adhesive layer

Details Fuel cell having a gasket with an adhesive layer Fuel cell having a gasket with an adhesive layer

1999-01-28

2001-11-13

Kalafut, Stephen (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

Reexamination Certificate

active

06316139

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel cell which uses as a fuel such a reducing agent as pure hydrogen or reform hydrogen obtained from methanol or a fossil fuel and uses air, oxygen or the like as an oxidizing agent. In more particular, it relates to a gasket used for a polymer electrolyte fuel cell.
2. Description of Related Art
It is known that in a polymer electrolyte fuel cell, in cases where for example the cell uses a cation exchange membrane, which is a proton conductor, as the polymer electrolyte and hydrogen and oxygen are introduced thereinto respectively as the fuel and the oxidizing agent, reactions represented by the following formulas (1) and (2) take place.
H
2
→2H
+
+2
e
−
  (1)
1/2O
2
+2H
+
+2
e
−
→H
2
O  (2)
In the negative electrode, hydrogen dissociates into protons and electrons. The proton moves through the cation exchange membrane toward the positive electrode. The electron moves through electroconductive separator plates, cells stacked therewith in series and further an external circuit and reaches the positive electrode, whereby electricity is generated. In the positive electrode, on the other hand, proton which have moved and reached through the cation exchange membrane, electrons which have moved and reached through the external circuit and oxygen introduced from outside react with one another to form water. Since the reaction is accompanied by heat generation, electricity, water and heat are generated from hydrogen and oxygen, as a whole.
A polymer electrolyte fuel cell differs greatly from other fuel cells in that its electrolyte is composed of an ion exchange membrane, which is a solid polymer. The ion exchange membrane used includes, for example, a perfluorocarbonsulfonic acid membrane (such as that sold under the trade name NAFION, mfd. by Du Pont de Nemours, E. I. Co., USA). In order to show a sufficient proton conductivity, the membrane needs to be in a sufficiently hydrated condition. The hydration of the ion exchange membrane may be effected, as described for example in J. Electrochem. Soc., 135 (1988), p. 2209, by passing the reaction gas through a humidifier to introduce water vapor into the cell and thereby to prevent the drying of the ion exchange membrane. Sealing of each cell may be effected, as described for example in J. Power Sources, 29 (1990), p. 367, by a method wherein the area of the ion exchange membrane is made larger than the electrode area and the circumferential part of the ion exchange membrane which is not bonded to the electrode is held by the upper and the lower gaskets between them.
The materials generally used for the gasket include glass fiber fabric coated with polytetrafluoro-ethylene (such as that sold trade name TEFLON, mfd. by Du Pont de Nemours, E. I. Co., USA) and fluororubber. U.S. Pat. No. 4,826,741 discloses the use of silicone rubber and fluororubber.
FIG. 2
shows an exterior view of a common stack-type polymer electrolyte fuel cell. Separator plates
2
formed of a conductive material, such as glassy carbon, and internal cells (not shown in the Figure) whose circumferential parts are held between insulating gaskets
1
are stacked alternately. A copper-made current collecting plate
3
is closely affixed to the outermost separator plate to form a stack as a whole. The stack is put between stainless steel end plates
5
via insulating plates
4
and the two end plates are bound fast with bolts and nuts. In the Figure, numeral
6
indicates a hydrogen inlet,
7
a hydrogen outlet,
8
an oxygen inlet,
9
an oxygen outlet and
10
a water discharge drain.
FIG. 3
shows a sectional view of an internal cell of a common stack-type cell. Electrodes
12
are bonded to both sides of an ion exchange membrane
11
of the center to form an assembly. Grooved separator plates
2
are positioned at the upper and lower sides of the assembly. The ion exchange membrane
11
has a larger area than the electrode
12
, and the circumferential part of the membrane is held by gaskets
1
between them to seal each cell and insulate the separator plates from each other. When, as shown in the Figure, a gas path
13
is provided inside the stack according to necessity (that is, in the case of internal manifold type), the gasket serves also to seal the gas path. The separator plate
2
provided with grooves may have various structures; for example, a porous grooved plate is fixed into the groove, or a wire mesh is used in the groove.
BRIEF SUMMARY OF THE INVENTION
However, the above-mentioned prior methods have various problems. When the respective cells are stacked, in the operation of placing the gasket accurately on the separator plate and holding the assembly of the ion exchange membrane
11
and the electrode
12
by the gaskets between them, the gasket, which is soft and in the form of sheet, can be difficulty to position and hence gives a poor operation efficiency, or it is apt to a give rise to defective seal due to mispositioning.
Further, when a high pressure gas is used, the gasket tends to get away to the outside of the stack.
To solve the above-mentioned problems, the gasket used in the present invention is given a structure comprising an elastomer layer which is inexpensive and highly resistant to chemicals, particularly to acids, and exhibits a high sealability and an adhesive layer. By virtue of the structure, a polymer electrolyte fuel cell having a large economical advantage which uses the gasket that is easy to position and easy to assemble is provided.
Thus, the fuel cell of the present invention is a fuel cell which comprises unit cells each comprising a solid polymer ion exchange membrane and a positive and a negative electrodes formed on the both sides of the membrane and gaskets each arranged at the circumferential part of the unit cell alternately stacked with each other via a separator placed therebetween, wherein the gasket comprises an elastomer layer and an adhesive layer, said elastomer layer being adhered to at least one side of the separator via said adhesive layer. Accordingly, at the time of assembling a cell stack, since the gasket can be adhered to the separator, mispositioning of the gasket is prevented from occurring.


REFERENCES:
patent: 4826741 (1989-05-01), Aldhart et al.
patent: 5206293 (1993-04-01), Sakai et al.
patent: 5284718 (1994-02-01), Chow et al.
patent: 5942091 (1997-11-01), Romine
patent: 2719946 (1995-11-01), None
patent: 09-097619-A (1997-04-01), None
3 M Laminating Adhesives/Data Page, Jul. 12, 1993.*
Journal of Power Sources, Supramaniam Srinivasan, et al., “Recent Advances in Solid Polymer Electrolyte Fuel Cell Technology with Low Platinum Loading Electrodes”, 1990, pp. 367-387 (No month availabe).
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Chemical Abstracts, vol. 128, No. 18, May 4, 1998, Columbus, Ohio, US; abstract No. 219471, Kurita, Takeshi, et al.: “Assembled Structure of Thin Fuel Cells with Good Gas-Shielding Properties,” XP002104994, & JP 10-055813A (Aisin Seiki Co., Ltd., Japan), & Patent Abstracts of Japan, vol. 98, No. 6, April 30, 1998, & JP 10-055813A (Aisin Seiki Co., Ltd., Japan), Feb. 24, 1998, & Database WPI, Derwent Publications Ltd., London, GB; AN 98-203398, XP002104995.
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Patent Abstracts of Japan, vol. 9, No. 251

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