Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2001-05-02
2004-03-02
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S047000
Reexamination Certificate
active
06699613
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel cell comprising a membrane electrode assembly having a solid polymer electrolyte membrane, an anode side gas diffusion electrode disposed at one side of the solid polymer electrolyte membrane, and a cathode side gas diffusion electrode disposed at the other side of the solid polymer electrolyte membrane, and a pair of separators holding the membrane electrode assembly; and to a method for producing the same: In particular, the present invention relates to a fuel cell in which the membrane electrode assembly can be reliably sealed between the separators, and to a method for producing the same.
Further, the present invention relates to a fuel cell in which the peripheries of openings for fuel gas, oxidant gas, and coolant is reliably sealed, and to a method for producing the same.
Further, the present invention relates to a fuel cell stack whose fuel cell units can be easily replaced.
2. Description of the Related Art
In conventional fuel cells, the membrane electrode assembly comprises a solid polymer electrolyte membrane, and an anode side diffusion electrode and a cathode side diffusion electrode which are disposed at both sides of the membrane. The membrane electrode assembly is held by a pair of separators. By supplying fuel gas (for example, hydrogen gas) onto a reaction surface of the anode side diffusion electrode, the hydrogen gas becomes ionized, and moves toward the cathode side diffusion electrode through the solid polymer electrolyte membrane. The electrons produced in this process are extracted to an external circuit, and are utilized as electric energy of a direct current. Since oxidant gas (for example, air which contains oxygen) is supplied to the cathode electrode, water is generated by the reaction of the hydrogen ions, the electrons, and the oxygen.
An example is explained with reference to FIG.
17
. In
FIG. 17
, reference numeral
1
denotes the solid polymer electrolyte membrane. A fuel cell
4
is assembled such that the solid polymer electrolyte membrane
1
is held between gas diffusion electrodes (an anode side diffusion electrode and a cathode side diffusion electrode)
2
and
3
. Sheet-type gaskets
5
which have openings corresponding to the reaction faces of the fuel cell
4
are provided at both sides of the fuel cell
4
. While the gaskets
5
cover the edges of the fuel cell
4
and press the edges of the fuel cell
4
using outer pressers, the fuel cell
4
is held between separators
7
(disclosed in Japanese Unexamined Patent Application. First Publication No. Hei 6-325777).
In the above conventional fuel cell, the gaskets
5
separate the spaces between the separators
7
and the gas diffusion electrodes
2
and
3
from the outside. Therefore, this fuel cell advantageously prevents the leakage of the fuel gas and the oxidant gas, and prevents the mixing of those gases, to thereby achieve efficient electric power generation. Variations in the thickness of the separators
7
and
8
and the gas diffusion electrodes
2
and
3
are unavoidable. Therefore, when the gaskets
5
which have varying thicknesses are combined with the separators
7
and the gas diffusion electrodes
2
and
3
, the reaction force produced by the gaskets is not uniform. Thus, there is the problem that the sealing between the separators
7
and the gas diffusion electrodes
2
and
3
is not uniform.
Further, the fuel cell has an internal manifold for supplying fuel gas, oxidant gas, and coolant to the anode side diffusion electrode and the cathode side diffusion electrode. The internal manifold has a number of openings through the separators.
An example of the conventional technique will be explained with reference to FIG.
32
. Reference numeral
201
denotes a solid polymer electrolyte membrane. The fuel cell
204
is assembled such that the solid polymer electrolyte membrane
201
is held by gas diffusion electrodes (an anode side diffusion electrode and a cathode side diffusion electrode)
202
and
203
. The fuel cell
204
is held between separators
205
and
205
.
Openings
206
which constitute the internal manifold are formed in the peripheries of the separators
205
holding the fuel cell
204
. The oxidant gas, or the fuel gas supplied from the openings
206
reaches the reaction surfaces of the respective fuel cells
204
.
To seal the peripheries of the openings
206
, a gasket
207
is inserted between the separators
205
and makes contact with the peripheries of the openings
206
(disclosed in Japanese Unexamined Patent Application. First Publication No. Hei 6-96783, and U.S. Pat. No. 4,510,213).
The above-mentioned fuel cell has problems in that the surface pressure of the gasket
207
varies in the peripheries of the openings of the separators
205
, and in that a partial bending stress acts in the peripheries of the openings.
Another conventional fuel cell will be explained with reference to FIG.
47
. In
FIG. 47
, reference numeral
301
denotes a solid polymer electrolyte membrane
301
. The fuel cell
304
is assembled such that the solid polymer electrolyte membrane
301
is held by gas diffusion electrodes (an anode side diffusion electrode and a cathode diffusion electrode)
302
and
303
. The fuel cells
304
are held via carbon plates
305
, which are disposed in the peripheries thereof, by separators
306
and
306
. The fuel cell units are assembled such that the separators
306
are attached to the fuel cells
304
by two-side adhesive agent sheet
307
, and the fuel cell units are stacked to produce the fuel cell stack (disclosed in Japanese Unexamined Patent Application. First Publication No. Hei 9-289029).
That is, the fuel cells
304
and the separators
306
are bound by the two-side adhesive agent sheet
307
, and the fuel cell units are thus assembled. Then, the fuel cell units are stacked. However, there is the problem in that, when replacing either the solid polymer electrolyte membrane
301
or the separators
306
, the two-sided adhesive agent sheet
307
must be separated, and this takes much labor.
Further, when the two-sided adhesive agent sheet
307
is separated, components other than the replaced component may be deformed.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a fuel cell which can improve the seal between the membrane electrode assembly and the separators, and a method for producing the same.
In the first aspect of the present invention, the fuel cell comprises: a membrane electrode assembly (
12
) having a solid polymer electrolyte membrane (
18
), an anode side gas diffusion electrode (an anode electrode
22
, and a second gas diffusion layer
26
) disposed at one side of the solid polymer electrolyte membrane, and a cathode side gas diffusion electrode (a cathode electrode
20
, and a first gas diffusion layer
24
) disposed at the other side of the solid polymer electrolyte membrane; a pair of separators (
14
and
16
) which hold the membrane electrode assembly; a projecting portion (
18
a
) which extends from the solid polymer electrolyte membrane and which projects from the peripheries of the anode side diffusion electrode and the cathode side diffusion electrode; and a seal, provided onto the separators, which was a liquid sealant (S) at the time of application. The sealant makes contact with the projecting portion while the membrane electrode assembly is disposed between the separators.
In the second aspect of the present invention, the seal is provided in grooves (
28
) formed in the separator.
According to the first and second aspects of the present invention, the liquid sealant (which means liquid or gel sealant) is directly in contact with the projecting portion provided at the periphery of the solid polymer electrolyte membrane, is pressed between the solid polymer electrolyte membrane and the separators, fitting the varying sizes of the seal sections, and maintains gas-tightness between the solid polymer electrolyte membrane and the separators. Therefore
Hatano Harumi
Inoue Masajiro
Kimura Nobuaki
Suenaga Toshihiko
Alejandro Raymond
Honda Giken Kogyo Kabushiki Kaisha
Kalafut Stephen
Lahive & Cockfield LLP
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