Fuel cell stack with fastening means including support...

Details Fuel cell stack with fastening means including support... Fuel cell stack with fastening means including support...

2000-04-14

2002-03-26

Brouillette, Gabrielle (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S006000, C429S006000, C429S010000, C429S157000, C429S183000

Reexamination Certificate

active

06361895

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-109186, filed Apr. 16, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell stack prepared by making integral a fuel cell laminate body consisting of a plurality of solid polymer type fuel cells each having a solid polymer membrane by a fastening means.
In recent years, the number of motor cars using gasoline engines has rapidly increased such that about two motor cars are owned nowadays by each family. Naturally, the exhaust gas discharged from the motor car attracts social attentions in relation to the air pollution problem. Under the circumstances, vigorous studies are being made in an attempt to use a fuel cell as a power source of a motor that is used in place of the internal combustion engine. The air pollution problem need not be worried about in the motor car using the fuel cell, which does not use a fossil fuel. In addition, noise is scarcely generated from the motor using the fuel cell. Also, the motor using the fuel cell is advantageous over the internal combustion engine in the energy recovery rate.
In using the fuel cell in a motor car, it is desirable for the fuel cell and the auxiliary facilities to be as small as possible, though an unduly large output is not required. Such being the situation, PEFC (polymer electrolyte fuel cell), in which a solid polymer membrane is sandwiched between two kinds of electrodes and these electrodes are wrapped in a separator, attracts attentions among various fuel cells.
FIG. 7
shows the basic construction of a solid polymer type fuel cell. As shown in the drawing, a cell body
1
comprises a solid polymer membrane
2
. An oxygen electrode
3
and a hydrogen electrode
4
are attached to both surfaces of the solid polymer membrane
2
to form an integral structure. The integral structure is prepared by attaching the oxygen electrode
3
and the hydrogen electrode
4
to both surfaces of the solid polymer membrane
2
, followed by applying a hot press to the resultant structure. A reaction membrane
5
a
and a gas diffusion membrane
6
a
are attached to both surfaces of the oxygen electrode
3
such that the reaction membrane
5
a
is in contact with the solid polymer membrane
2
. Likewise, a reaction membrane
5
b
and a gas diffusion membrane
6
b
are attached to both surfaces of the hydrogen electrode
4
such that the reaction membrane
5
b
is in contact with the solid polymer membrane
2
. The cell reaction takes place mainly between the solid polymer membrane
2
and the reaction membranes
5
a,
5
b.
A separator
7
having oxygen supply grooves
7
a
is attached to the surface of the oxygen electrode
3
. Likewise, a separator
8
having hydrogen supply grooves
8
a
is attached to the surface of the hydrogen electrode
4
.
In the fuel cell of the particular construction, oxygen and hydrogen introduced through the oxygen supply grooves
7
a
and the hydrogen supply grooves
8
a
are supplied through the gas diffusion membranes
6
a,
6
b
into the reaction membranes
5
a,
5
b,
respectively. As a result, reactions given below take place at the interface A between the solid polymer membrane
2
and the reaction membrane
5
a
and at the interface B between the solid polymer membrane
2
and the reaction membrane
5
b:
Reaction at interface A: (1/2)O
2
+2H
+
→H
2
O
Reaction at interface B: H
2
→2H
+
→2e
−
The hydrogen ions (2H
+
) generated at the interface B flow from the hydrogen electrode
4
into the oxygen electrode
3
through the solid polymer membrane
2
. On the other hand, the electrons (2e
−
) generated at the interface B flow from the hydrogen electrode
4
into the oxygen electrode
3
through a load
9
so as to obtain an electric energy.
In the fuel cell of the construction described above, it is necessary for the separators
7
and
8
to supply an oxidizing gas and a fuel gas to the back surfaces of the oxygen electrode
3
and the hydrogen electrode
4
, respectively, uniformly and in a completely separated manner. Also, it is necessary for the fuel cell to collect efficiently the electivity generated by the reaction. Further, since heat is generated by the cell reaction, it is necessary to release the reaction heat through the gas separators in order to stabilize the power generating operation. Various separators are proposed for meeting these requirements.
FIG. 8
exemplifies the PEFC structure (fuel cell laminate body) using a plurality of separators S. In the fuel cell stack of the construction shown in the drawing, a fuel gas supply plate
19
is attached to an oxidizing gas supply plate
20
such that a fluid passageway
21
is defined between these supply plates
19
and
20
. A cooling water is circulated through the fluid passageway
21
to suppress the temperature elevation caused by the reaction heat generated at the boundaries between the oxygen electrode and the solid polymer electrolyte plate and between the hydrogen electrode and the solid polymer electrolyte plate.
It was customary in the past to assemble the fuel cell stack
11
as shown in, for example,
FIGS. 9 and 11
. Incidentally,
FIG. 11
is a plan view showing the fuel cell stack
11
shown in FIG.
9
. The fuel cell stack
11
comprises a plurality of unit cells
10
stacked one upon the other in the vertical direction and upper and lower flanges
12
,
13
somewhat larger than the unit cell
10
and positioned on the upper and lower surfaces, respectively, of the stack of the unit cells
10
. Each of these upper and lower flanges
12
,
13
is provided with a plurality of bolt holes positioned outside the stack of the unit cells
10
. Fastening bolts
14
are inserted into the bolt holes to permit these bolts
14
to extend through the upper and lower flanges
12
,
13
, and nuts (not shown) are engaged at the end portions of the fastening bolts
14
so as to fasten the stack of the unit cells
10
held between the upper and lower flanges
12
and
13
. Reference numerals
15
and
16
shown in
FIG. 11
represent a cooling water supply hole and a cooling water discharge hole, respectively, which extend through the flanges
12
,
13
and the fuel cell stack
11
. Also, reference numerals
17
and
18
represent a reactant gas supply hole and a reaction gas discharge hole, respectively, which extend through the flanges
12
,
13
and the fuel cell stack
11
.
The conventional fuel cell laminate body is assembled as shown in, for example,
FIG. 10
to constitute the fuel cell stack
11
. The stack shown in
FIG. 10
is equal to the stack shown in
FIG. 9
, except that, in
FIG. 10
, the flanges
12
,
13
are equal in size to the unit cell
10
.
The conventional fuel cell stack is defective in that, since a large number of fastening bolts
14
are used for fastening the fuel cell laminate body, the effective area ratio of the fuel cell stack is low. For example, where the fuel cell stack shown in
FIG. 9
including the region of the fastening bolts
14
has a length Y
1
of, for example, 140 mm, and a width T
1
of, for example 120 mm, the region of the unit cell
10
, which is shaded in
FIG. 11
, has a length Y
2
of, for example, 130 mm, and a width T
2
of, for example, 100 mm. It follows that the effective area ratio is: T
2
·Y
2
/T
1
·Y
1
={(100×130)/(120×140)}×100≈77%. Also, the conventional fuel cell stack is rendered heavier and more bulky.
Fuel cells are also disclosed in Japanese Patent Disclosure (Kokai) No. 10-189025 and Japanese Patent Disclosure No. 9-92324. JP '025 is directed to a fuel cell in which the direction of the pressurizing force applied to the fuel cell stack housed in a case is kept parallel to the stacking direction of the unit cells so as to prevent the gas sealing properties from being deteriorated and to prevent the contact resistance from being increased. On

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