Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2002-03-11
2004-08-10
Le, Hoa Van (Department: 1752)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000, C429S006000, C429S006000
Reexamination Certificate
active
06773843
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a portable fuel cell stack which can be used in various applications, such as a power source for outdoor activities and picnics and a household generator, and which uses light, silent and pollution-free solid polymer cells.
Fuel cell stacks generally use hydrogen as a main fuel and take out the energy generated during the chemical reaction of this hydrogen with oxygen. There are several types of fuel cell stack and one type is a solid polymer electrolyte fuel cell stack. This solid polymer electrolyte fuel cell stack has features such as low operating temperature and high output density.
An example of fuel cell stack in which such conventional solid polymer electrolyte fuel cell stack is disclosed in U.S. Pat. No. 5,595,834. As shown in
FIG. 5
, a unit cell
10
comprises a solid polymer electrolyte membrane
12
, an anode (fuel electrode)
13
a
and a cathode (oxygen electrode)
13
b
, which are provided on both sides of the solid polymer electrolyte membrane
12
, a fuel flow field plate
14
and an oxygen flow field plate
18
, which are provided on sides of these electrodes
13
a
and
13
b
, and separator plates
34
, which are provided on sides of these flow field plates
14
and
18
, to form the unit cell
10
by making them integral with each other. A plurality of unit cells
10
are stacked, and the stacked unit cells
10
are formed as a whole construction by inserting a fuel distribution manifold, which comprises a hydrophilic sleeve
32
connected to the fuel flow field plate
14
, into a center hole of the unit cell
10
, by further providing end plates
24
on both ends of a bolt
26
, which is passed through the center of the sleeve
32
, so as to sandwich them between the two ends of the bolt
26
, and by fastening and fixing the whole by means of nuts via washers
38
a
to
38
d
and an O-rings
36
. Because such fuel cell stacks are suitable for low power fuel cells, they can be designed as small-sized and lightweight fuel cell stacks.
Furthermore, in this polymer electrolyte fuel cell stack, a fuel feed flow field plate
29
is provided between one end plate
24
and the separator plate
34
adjacent to the unit cell
10
to provide communication with the hydrophilic sleeve
32
, which constitutes the fuel distribution manifold for supplying fuel to the fuel flow field plate
14
, and a port
28
is provided in the outer peripheral portion of the end plate
24
so that fuel is introduced into the port
28
and supplied to the fuel flow field plate
14
.
However, in the above conventional electrolyte fuel cell stack, because the two electrodes of anode (fuel electrode)
13
a
and cathode (oxygen electrode)
13
b
are provided on both surfaces of the solid polymer electrolyte membrane
12
and the fuel flow field plate
14
and oxygen flow field plate
18
are provided on sides of these electrodes
13
a
and
13
b
, there are many contact portions, with the result that internal resistance is large and that the performance of the whole cell stack decreases.
Moreover, the above conventional electrolyte fuel cell stack not only has a large number of components, such as the fuel flow field plate
14
and fuel feed flow field plate
29
on the fuel supply side and the port
28
of the end plate
24
for fuel supply, but also is of a construction that fuel is fed from the side of the end plate
24
toward the center via the fuel feed flow field plate
29
, resulting in an increase both in the flow resistance of the fuel supply passage and in the concentration fluctuation of fuel, thus having an influence on stable energy supply. Using a large number of components causes burdensome maintenance, complex shape and large size.
The present invention was made in view of the foregoing problems. Accordingly, an object of the invention is to provide a portable fuel cell stack in which the number of components is reduced by reducing the number of flow field plates, cell stack performance is improved by reducing the number of contact portions to thereby lower internal resistance, fuel is fed and supplied from the center of an end plate directly to a fuel distribution manifold.
Another object of the invention is to provide a portable fuel cell stack which is capable of being further reduced in size and weight by reducing the number of components.
SUMMARY OF THE INVENTION
In the first concept of the invention for achieving the above objects, a unit cell is provided in an electrolytic fuel cell stack, which includes a polymer electrolyte membrane, an oxygen electrode and a fuel electrode provided on both sides of the polymer electrolyte membrane, a flow field plate installed on the oxygen electrode side, a separator plate installed on the outside of the flow field plate on the oxygen electrode side so as to be in contact therewith, and another separator plate installed on the outside of the fuel electrode so as to be in contact therewith.
According to this first concept, the following advantageous effects are obtained:
(1) Because the flow field plate installed on the fuel electrode side in the conventional electrolyte fuel cell stack is not provided, the number of contact surfaces decreases by two surfaces and the electric resistance in the contact portions decreases so as to lead to a decrease in internal resistance and make it possible to perform the energy generation of the cell stack efficiently.
(2) Because the number of parts of a unit cell decreases, it is possible to make an inexpensive product as a whole and the assembling of unit cells becomes easy, making it possible to increase the production efficiency.
The second concept of the invention is characterized in that one of the fixing nuts has a fuel supply port which provide communication with the fuel distribution manifold for fuel supply from the center of the end plate.
By this second concept, the following effects are obtained:
(3) Because the fuel is directly supplied to the fuel distribution manifold without flowing through the fuel flow field, the flow resistance decreases and fuel supply can be smoothly performed. In addition, the concentration fluctuation in fuel supply can be reduced. Therefore, stable power generation can be carried out.
(4) Because the fuel flow field in the cell stack was eliminated, the number of components of the cell stack can be reduced and besides the cell stack can be reduced in size and weight.
Furthermore, by the third concept of the invention, the fuel distribution manifold is formed by arranging hydrophilic synthetic fiber threads on a tie bolt in the axial direction of the tie bolt.
(5) Because this fuel distribution manifold by the third concept uses hydrophilic synthetic fibers, it is possible to select a material for the fuel distribution manifold from easily obtainable ones and the fuel distribution manifold can be easily formed because of low cost and easy handling.
In addition, according to the fourth concept of the invention, the other fixing nut is provided with a bleeder valve capable of supplying fuel to the flow field plate, etc. by one-touch operation at the end of the bolt.
(6) Because the other fixing nut according to the fourth concept is provided with a bleeder valve, during the startup of the fuel cell stack, fuel can be supplied in a sufficient amount by one-touch operation to the fuel electrode side of the polymer electrolyte membrane, whereby the power generation action during startup can be smoothly started.
REFERENCES:
patent: 5514486 (1996-05-01), Wilson
patent: 5595834 (1997-01-01), Wilson et al.
patent: 0 823 743 (1998-02-01), None
Ido Yasuo
Inaba Takashi
Kato Eiji
Kitagawa Koji
Naruse Yukio
Browdy and Neimark PLLC
Daido Metal Company Ltd.
Le Hoa Van
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