Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2001-04-27
2004-02-17
Gulakowski, Randy (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000
Reexamination Certificate
active
06692860
ABSTRACT:
RELATED APPLICATIONS
This application claims priority to Japanese Patent Application No. P2000-133863 filed May 2, 2000 in Japan and Japanese Patent Application No. P2001-088555 filed Mar. 26, 2001 in Japan. The contents of the aforementioned applications are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel cell. More specifically, the present invention relates to a fuel cell assembled such that a membrane electrode assembly, which is formed by a solid polymer electrolyte membrane and an anode side gas diffusion electrode and a cathode side gas diffusion electrode, is held by a pair of separators. Especially, the present invention relates to a fuel cell in which the membrane electrode assembly is sealed with certainty between the separators.
2. Description of 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 located 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 flow through an external circuit, and can provide electric energy in the form of a direct current. Since an oxidizing gas (for example, air which contains oxygen) is supplied to the anode electrode, water is generated by the reaction of the hydrogen ions, the electrons, and the oxygen.
One example of a conventional fuel cell is explained with reference to FIG.
20
. In
FIG. 20
, 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
. A pair of separators
5
is provided so as to sandwich the fuel cell, and an O-ring
7
is fit to a groove portion
6
formed on each of the separators
5
. Thus, the solid polymer electrolyte membrane
1
is held by the O-ring
7
and, in that state, the fuel cell
4
is held between the separators
5
(refer to Japanese Unexamined Patent Application, First Publication No. Hei 8-148169).
In the above conventional fuel cell, the O-ring
7
separates the spaces between the separators
5
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. However, even a slight shift in the position of the O-ring
7
may result in an insufficient seal reaction force and deteriorate the sealing property thereof. Also, if the solid polymer electrolyte membrane is pulled in the vertical direction in FIG.
20
and twisted due to the above-mentioned shift in the position of the O-ring
7
, a force separating the solid polymer electrolyte membrane
1
and the gas diffusion electrodes
2
and
3
may be generated and this phenomenon is not preferable.
In order to avoid the above-mentioned problem, it is necessary to strictly control the accuracy of the size of the groove portion
6
. However, this leads to an increase in the manufacturing cost.
Accordingly, an object of the invention is to provide a fuel cell having an improved sealing property between the membrane electrode assembly and the separators, which may be produced readily at a reasonable manufacturing cost.
SUMMARY OF THE INVENTION
Accordingly, one of the objectives of the present invention is to provide a fuel cell including a membrane electrode assembly having a solid polymer electrolyte membrane (for instance, a solid polymer electrolyte membrane
18
in the embodiments), an anode side diffusion electrode (for instance, the combination of an anode electrode
22
and a second gas diffusion layer
26
in the embodiments) and a cathode side diffusion electrode (for instance, the combination of a cathode electrode
20
and a first gas diffusion layer
24
in the embodiments) located at both sides of the solid polymer electrolyte membrane, and a pair of separators (for instance, a first separator
14
and a second separator
16
in the embodiments) which holds the membrane electrode assembly. The fuel cell further includes a first seal (for instance, a first seal S
1
in the embodiments) substantially disposed between one of the separators and a periphery portion of whichever of the anode side diffusion electrode and the cathode side diffusion electrode has the larger surface area, the first seal being disposed so as to surround whichever of the anode side diffusion electrode and the cathode side diffusion electrode has the smaller surface area; and a second seal (for instance, a second seal S
2
in the embodiments) substantially disposed between the separators so as to surround whichever of the anode side diffusion electrode and the cathode side diffusion electrode has the larger surface area.
According to the above fuel cell, the first seal and the second seal may function independently of each other. Thus, problems such as deficiencies in the sealing force caused by a positional shift of the seals may be eliminated and, hence, the seal seals the membrane electrode assembly and the separators with certainty. Also, although it is possible to use only members made of the same kind of material in order to equalize the reaction force for the cases where the seals are disposed so as to oppose each other, such an effect of the reaction force need not be considered according to the present invention and the material to be used may be freely selected.
In accordance with another aspect of the invention, the size of the solid polymer electrolyte membrane is smaller than the size of whichever of the anode side diffusion electrode and the cathode side diffusion electrode has the larger surface area.
According to the above fuel cell, since the size of the solid polymer electrolyte membrane, which is expensive, is decreased, it becomes possible to reduce the cost of the solid polymer electrolyte membrane and the fuel cell per se.
In yet another aspect of the invention, at least one of the first seal and the second seal makes contact with an end face of the anode side diffusion electrode or an end face of the cathode side diffusion electrode.
According to the above fuel cell, since at least one of the first seal and the second seal makes contact with an end face of the anode side diffusion electrode or an end face of the cathode side diffusion electrode, it becomes possible to prevent a reaction gas from leaking out of the end face and from passing through to the outlet side without making contact with the electrically active surface. Accordingly, the seal of the fuel cell may further be improved.
In yet another aspect of the invention, the first seal makes contact with an end face of whichever of the anode side diffusion electrode and the cathode side diffusion electrode has the smaller surface area; and the first seal being extended so as to cover whichever of the anode side diffusion electrode and the cathode side diffusion electrode has the larger surface area.
According to the above fuel cell, the first seal prevents the reaction gas from leaking out of the end face. Also, since no space is present between the first seal and the second seal, it becomes possible to prevent the reaction gas from passing through to the outlet side without making contact with the electrically active surface. Accordingly, the sealing property of fuel cell may further be improved, and unnecessary pressure is not applied to a sealed portion by an expansion/contraction of the space between the end face and the seal due to changes in temperature.
In yet another aspect of the invention, the second seal
Inoue Masajiro
Kikuchi Hideaki
Kimura Nobuaki
Sugita Narutoshi
Gulakowski Randy
Lahive & Cockfield LLP
Wills M.
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