Solid polymer electrolyte fuel cell and method for producing...

Details Solid polymer electrolyte fuel cell and method for producing... Solid polymer electrolyte fuel cell and method for producing...

1999-04-16

2002-04-16

Huff, Mark F. (Department: 1756)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S006000, C429S006000, C429S006000, C429S006000

Reexamination Certificate

active

06372373

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to fuel cells which operates at room temperature used in portable power sources, power sources for electric vehicles, household cogeneration systems and the like. Further, the present invention relates to a solid polymer electrolyte fuel cell and a method for producing the same, in particular.
The solid polymer electrolyte (hereinafter, referred to simply as “polymer electrolyte”) fuel cells allow a fuel gas such as hydrogen to electrochemically react with an oxidization agent gas such as air at their gas-diffusion electrode, thereby to simultaneously generates electricity as well as heat.
An example of this kind of the polymer electrolyte fuel cells is illustrated in FIG.
2
.
On both surfaces of a polymer electrolyte film (hereinafter, referred to simply as “electrolyte film”)
3
, which selectively transports hydrogen ions, catalytic reaction layers
2
consisting mainly of carbon powder carrying a platinum group metal catalyst are arranged in close contact with the film. On the surfaces of the catalytic reaction layers
2
, a pair of diffusion layers
1
having both of gas-permeability and electrical conductivity are additionally arranged while being in close contact. An electrode
23
is configured with this diffusion layer
1
and the catalytic reaction layer
2
.
On the surfaces of the electrode
23
, there are arranged electrically conductive separator
4
in the form of plate for mechanically fixing an electrode-electrolyte assembly
22
composed of these electrodes
23
and electrolyte film
3
(hereinafter, referred to as “MEA”) and electrically connecting the adjacent MEAs
22
with each other in series. On the surfaces of the separators
4
in contact with the electrode
23
, there are formed gas-flow paths
5
for supplying the reactive gases to the electrodes and exhausting gases generated by the reaction or residual gases. The gas-flow paths
5
may be provided independent of the separator
4
, but it is general to provide grooves on the surfaces of separator
4
as the gas-flow paths.
In order to supply the fuel gas to the grooves, it is required to branch a pipeline for supplying the fuel gas into the separators in their numbers and to connect the ends of the branched pipelines directly to the grooves of the separators by means of a piping jig. This jig is referred to as “manifold”, and one of the type that connects the pipelines of the fuel gas directly to the grooves is referred to as “outer manifold”.
On the other hand, there is also the other type called “inner manifold” whose structure is simple. The inner manifold is configured by providing ports on the separator already having the gas-flow paths and allowing the inlets and outlets of the gas-flow paths to reach to the ports. The fuel gas is supplied through the ports.
On the other surfaces of the separators
4
which are placed in every two cells and not in contact with the MEAs, there are provided coolant-flow paths
24
for distributing cooling water employed for maintaining the cell temperature constant. By distributing the cooling water, thermal energy generated by the reaction may be recovered and utilized in the form of hot or warmed water.
In addition, in order to prevent hydrogen and/or air from leaking outside of the cell or mixing with each other, and in order to prevent the cooling water from leaking outside of the cell, sealants
17
that put the electrolyte film
3
therebetween or O-rings
18
are arranged around the circumference of the electrodes
23
. There is also such a case wherein these sealants
17
and O-rings
18
have previously been assembled by combining them with the electrodes
23
and electrolyte films
3
in an integral body.
As another method for the sealing, there is such a structure as shown in
FIG. 3
, wherein a gasket
19
of a resin or a metal having a thickness of substantially the same as that of the electrode is arranged around the circumference of the electrode and the gaps between the gasket
19
and the separators
4
are sealed with the sealant
17
such as grease or an adhesive.
In recent years, there is proposed an alternative method as shown in
FIG. 4
, wherein the MEAs configured with the electrodes
23
of the same size as that of the electrolyte film
3
are used. And, a resin
21
which has a sealing effect has previously been impregnated into the portions where the gas-tight sealing are required, thereby to allow the resin to solidify therein. That is, the method of securing the gas-sealing property between the separators
4
by impregnating the resin
21
is devised.
As previously described, many of the fuel cells employ a laminated structure configured by stacking a number of unit cells. In order to exhaust heat generated by the electric power during the fuel cell operation to the outside of the cells, cooling plates are arranged in every 1 to 3 unit cells of the laminated cell. As the cooling plates, one that has such a structure wherein a thermal medium such as cooling water is distributed through a space surrounded by metallic plates is generally employed. As shown in
FIG.2
to
FIG.4
, the coolant-flow paths
24
are formed on the rear face of the separator
4
, i.e. the surface where the cooling water flows through, thereby to allow the separator
4
itself to function as the cooling plate. In this structure, the O-rings or the gaskets are required for sealing the thermal medium such as cooling water, but in this sealing method, it is necessary to secure a satisfactory electrical conductivity between the top and bottom surfaces of the cooling plates by, for instance, completely pressurizing and deforming the O-rings.
Then, as regards the previously-described manifold, the inner manifold type is generally used that have the gas-supply ports and the gas-exhaust ports for the respective unit cells as well as the supply/exhaust ports for the cooling water inside of the laminated cell. Herein, as an example of the polymer electrolyte fuel cells of the inner manifold type, a partly cut-out perspective view thereof is illustrated in FIG.
5
.
As the same as the structure shown in
FIG. 2
, the diffusion layers
1
, the catalytic reaction layers
2
, the electrolyte films
3
and separators
4
are laminated, and the gas-flow paths
5
are formed. And, the gas manifolds
8
for supplying/exhausting the gas to/from the cells as well as the cooling water manifolds
8
′ for supplying/exhausting the water for cooling the cell are also formed in the laminated structure.
In the case of operating the cell of such inner manifold-type by the use of a reformed gas, however, the electrode is poisoned to decrease the temperature of the cell as the result of increase in the concentration of carbon monoxide at the down streams of the fuel gas-flow paths in the respective unit cells. And the decrease in the temperature further facilitates the electrodes to be poisoned.
In order to suppress such decrease in the cell performance, the outer manifold-type is now also attracting attention again whose structure capable of securing a width of the gas supplying and exhausting portions from the manifold to the respective unit cells as largely as possible.
In the case of the fuel cells of the inner manifold type, the reliability on the gas-sealing property is high in general because a squeezing or tightening (binding) pressure is constantly added onto the whole cell structure. In contrast, in the case of the fuel cells of the outer manifold type, it is relatively hard to obtain an even and flat sealing face because the flanks (side faces) of the laminated unit cells that are in contact with the flange of the manifold are a laminated body composed of the thin sheets such as MEAs and separators. That is, the outer manifold type in general has a lower reliability as compared with the inner manifold type.
In the case of the inner manifold type, however, when the lamination number and the output power of the fuel cell are increased, a large quantity of fluid must be supplied and exhausted through the ports of the i

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