Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2003-03-26
2004-09-28
Le, Hoa Van (Department: 1752)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000, C427S115000, C427S122000, C254S109000
Reexamination Certificate
active
06797424
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a Continuation Application of PCT Application No. PCT/JP01/08593, filed Sep. 28, 2001, which was not published under PCT Article 21(2) in English.
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-301469, filed Sep. 29, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a separator for a fuel cell (stack) which is used in a fuel cell, a production process thereof, and a solid polymer fuel cell using the separator for a fuel cell (stack) and comprising a solid polymer with ionic conductivity as an electrolyte.
2. Description of the Related Art
Hereinafter, prior art regarding a solid polymer fuel cell will be described with reference to
FIGS. 12 and 13
.
FIG. 12
is a cross-sectional diagram showing a unit cell of a conventional solid polymer fuel cell, and
FIG. 13
is a cross-sectional diagram showing a conventional solid polymer fuel cell stack.
In the fuel cell stack, a number of unit cells
26
shown in a schematic diagram
2
are laminated vertically. Each unit cell
26
comprises a film electrode composite
23
comprising a flat solid polymer film
21
and a flat fuel electrode
22
a
and an oxidant electrode
22
b
which are disposed on the opposing surfaces of the solid polymer film
21
so as to form a gas diffusion electrode
22
; two separators
24
which are in direct contact with the fuel electrode
22
a
and the oxidant electrode
22
b,
respectively; and packing materials
25
.
To extract an electric current from the film electrode composite
23
, a fuel gas and an oxidant gas which are reaction gases must be fed to the electrodes
22
a
and
22
b,
respectively. Further, at the same time, components having a function of a current collector must be present in contact the electrodes
22
a
and
22
b.
These components which feed these reaction gases to the respective electrodes
22
a
and
22
b
without mixing the reaction gases together and have a function of a current collector are referred to as separators
24
.
As the solid polymer film
21
, a perfluorocarbonsulfonic acid film or the like is used. Since the solid polymer film
21
also serves to prevent mixing of the reaction gases to be fed to the fuel electrode
22
a
and the oxidant electrode
22
b,
its area is generally larger than the area of the electrode.
The separator
24
is preferably made of a material which hardly allows the two types of reaction gases to pass therethrough so as to prevent mixing of the reaction gases. Further, since conductivity is required, a material such as metal or carbon is used. A separator
24
on the fuel electrode
22
a
constitutes a front surface of a unit fuel and another separator
24
on the oxidant electrode
22
b
constitutes a rear surface of the unit fuel. The separators
24
and packing materials
25
for sealing the reaction gases are disposed so as to form a unit cell
26
. The packing material
25
is also provided so as to prevent mixing of the two types of reaction gases and leakage of the reaction gases to the outside. When such a phenomenon as mixing of the two types of reaction gases and leakage of the reaction gases to the outside occurs, stable electric power generation with high efficiency cannot be achieved.
The unit cell
26
comprises the film electrode composite
23
, the two separators
24
which are in contact with the fuel electrode
22
a
and the oxidant electrode
22
b,
and the packing materials
25
.
In the separator
24
, a plurality of breakthroughs each referred to as a manifold
27
for feeding the reaction gases to each unit cell and a number of fuel gas channels
28
a
and oxidant gas channels
28
b
which connect the breakthroughs with one another are formed. Thereby, gas channels
28
for feeding the fuel gas and the oxidant gas which are required for a cell reaction to the fuel electrode
22
a
and the oxidant electrode
22
b
are formed.
Since an electromotive force obtained in the unit cell
26
is as small as 1 V or less, a plurality of unit cells
26
are laminated together and electrically connected to each other in series so as to constitute a fuel cell stack
29
, thereby increasing the electro-motive force. In the stack
29
, a cooling plate for cooling the cell is generally provided for each unit cell
26
or each group of unit cells
26
. The cooling plates are not shown in the drawings.
After a required number of unit cells
26
are laminated to form the stack
29
, they are clamped in the lamination direction by means of such a clamping mechanism as clamping plates, clamping rods, springs, nuts or the like. This is done to secure electrical and thermal contacts and sealability in between the unit cells
26
.
Meanwhile, to cause the solid polymer fuel cell to generate electric power, water must also be fed to the solid polymer film
21
, in addition to feeding of the reaction gases to the electrodes
22
a
and
22
b
. This is because the ion conductivity of the solid polymer film
21
is significantly improved when it absorbs water. Conversely, if water is not fed to the solid polymer film
21
, stable electric power generation cannot be achieved.
In a conventional solid polymer fuel cell, the ionic conductivity of a solid polymer film, i.e., the performance of the cell is very sensitive to changes in the flow rates, temperatures and humidities of reaction gasses. Hence, for example, when an abrupt load change occurs, a time lag is produced until the reaction gases settle at a temperature and humidity corresponding to the load, so that the performance of the fuel cell is liable to change and unstable during the time lag. Consequently, to keep the performance of the fuel cell constantly stable, a function to cause the fuel cell to adapt to such an environmental change must be provided in the fuel cell or in a system to cause the fuel cell to generate electric power.
As a method of providing such a function in particular into the body of the solid polymer fuel cell, an invention that separators are made of an expansion graphite having high water absorbability is disclosed in U.S. Pat. No. 5,300,370.
However, the invention has the following problems. That is, on one hand, the separator made of the expansion graphite is water-absorbable and hydrophilic, so that it has such advantages as having excellent dischargeability of water remaining in channels, being capable of conforming to an environmental change such as an abrupt load change, and having low gas permeability. On the other hand, since the expansion graphite is a relatively soft material, compression creep may occur when the solid polymer fuel cell is clamped in the lamination direction by a clamping mechanism and kept in that condition as described above, thereby causing an increase in the pressure losses of the reaction gases with time. In addition, since the film electrode composite
23
and the separator
24
are laminated repeatedly in the solid polymer fuel cell as described above, a large contact resistance between the two types of components lowers the voltage of the cell, resulting in low power generation efficiency.
To overcome the problems of the first known example described above, the following separator is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 9-274926 (second known example). The second known example is a separator in which projections that constitute gas channels formed on the surfaces of the separator are composed of a conductive elastic member.
However, when the separator of the second known example is applied to the foregoing solid polymer fuel cell of the prior art, the separator cannot conform stably to an environmental change such as an abrupt load change, since the ionic conductivity of the solid polymer film, i.e., the performance of the cell is very sensitive to changes in the flow rates, temperatures and humidities of the reaction gasses.
The present invention has been conceived to solve such problems.
Hori Michio
Kobayashi Masanori
Ogami Yasuji
Ooma Atsushi
Ootani You
Kabushiki Kaisha Toshiba
Le Hoa Van
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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