Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2002-09-17
2004-11-02
Maples, John S. (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S429000, C429S006000
Reexamination Certificate
active
06811909
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel cell formed by stacking a plurality of fuel cell units that are formed by sandwiching an electrode assembly between separators.
2. Description of the Related Art
Among fuel cell units, there is one type that is formed in a plate shape by sandwiching between a pair of separators an electrode assembly that is formed by placing an anode electrode and a cathode electrode respectively on either side of a solid polymer electrolyte membrane. A fuel cell is formed by stacking in the thickness direction of the fuel cell units a plurality of fuel cell units that are structured in this way.
In each fuel cell unit there are provided a communication path for fuel gas (for example, hydrogen) on one surface of the anode side separator that is positioned facing the anode electrode, and a communication path for oxidizing gas (for example, air that contains oxygen) on one surface of the cathode side separator that is positioned facing the cathode electrode. In addition, a communication path for a cooling medium (for example, pure water) is provided between adjacent separators of adjacent fuel cell units.
When fuel gas is supplied to the electrode reaction surface of the anode electrode, hydrogen is ionized here and moves to the cathode electrode via the solid polymer electrolyte membrane. Electrons generated between these two are extracted to an external circuit and used as direct current electrical energy. Because oxidizing gas is supplied to the cathode electrode, hydrogen ions, electrons, and oxygen react to generate water. Because heat is generated when water is created at the electrode reaction surface, the electrode reaction surface is cooled by a cooling medium made to flow between the separators.
The fuel gas, oxidizing gas (generically known as reaction gas), and the cooling medium each need to flow through a separate communication path. Therefore, sealing technology that keeps each communication path sealed in a fluid-tight or airtight condition is essential.
Examples of portions that need to be sealed are: the peripheries of penetrating supply ports formed in order to supply and distribute reaction gas and cooling medium to each fuel cell unit of the fuel cell; the peripheries of discharge ports that collect and discharge the reaction gas and cooling medium that are discharged from each fuel cell unit; the outer peripheries of the electrode assemblies; and the outer peripheries between the separators of adjacent fuel cell units. A material that is soft yet also has the appropriate resiliency such as organic rubber is employed for the sealing member.
In recent years, however, size and weight reduction, as well as a reduction in the cost of fuel cells, have become the main barriers in progress towards the more widespread application of fuel cells through their being mounted in actual vehicles.
Methods that have been considered for reducing the size of a fuel cell include making each fuel cell unit forming the fuel cell thinner, more specifically, reducing the size of the space between separators while maintaining a maximum size for the reaction gas communication path formed inside each fuel cell unit; and also making the separators thinner.
However, a limit is imposed on how thin the separators can be made by the strength requirements for each separator and by the rigidity requirements for the fuel cell. Reducing the height of the sealing members is effective in reducing the size of the spacing between separators, however, the height of the sealing members needs to be sufficient for the sealing members to be able to be pressed down enough to ensure the required sealing performance is obtained. Therefore, there is also a limit to how much the height of the sealing members can be reduced.
Furthermore, in a fuel cell unit, although the volume occupied by the sealing members is indispensable in order for the reaction gas and cooling medium to be sealed in, because this space contributes substantially nothing to power generation it needs to be made as small as possible.
FIG. 23
is a plan view showing a conventional fuel cell. In
FIG. 23
the symbol
107
indicates a communication port such as a fuel gas supply port and discharge port, an oxidizing gas supply port and discharge port, and a cooling medium supply port and discharge port that each penetrate the fuel cell
106
in the direction in which separators
109
and
110
are stacked. The symbol
112
indicates an area formed by a plurality of fuel gas communication paths, oxidizing gas communication paths, and cooling medium communication paths running along the separators
109
and
110
.
FIG. 24
is a longitudinal cross-sectional view of a conventional fuel cell
106
taken along the line X—X in FIG.
23
. As can be seen in plan view, in order to make the volume occupied by the sealing member (which doesn't contribute to power generation) as small as possible, conventionally, by locating gas sealing members
102
and
103
, which respectively seal a fuel gas communication path
100
and an oxidizing gas communication path
101
, together with a cooling surface sealing member
104
, which seals a cooling medium communication path, aligned in a row in the stacking direction of the fuel cell units
105
, the outer dimensions in the stacking direction of the fuel cell
106
are kept to the minimum.
However, the drawback with the fuel cell
106
that is structured in this manner is that if the gas sealing members
102
and
103
that seal the communication paths
100
and
101
as well as the cooling surface sealing member
104
are all placed in a row in the stacking direction of the fuel cell unit
105
, then the thickness of the fuel cell
106
cannot be made less than a value obtained by adding the height of the cooling surface sealing member
104
to the minimum thickness of each fuel cell unit
105
, and multiplying this result by the number of fuel cell units stacked in the fuel cell.
In order to explain this more specifically, the description will return to FIG.
24
.
FIG. 24
is a longitudinal cross-sectional view showing a cross section of the fuel cell
106
in the vicinity of the fuel gas supply port
107
in the stacking direction of the fuel cell units
105
. According to
FIG. 24
, the fuel gas supply port
107
and the fuel gas communication path
100
that are isolated in a sealed state by the gas sealing members
102
and
103
are connected by a communication path
108
. The communication path
108
is provided in the separator
109
so as to detour around, in the thickness direction of the separator
109
, the gas sealing member
102
that seals the entire periphery of the fuel gas communication path
100
. Moreover, the separator
110
also has a similar communication path (not shown) in the oxidizing gas supply port (not shown).
Accordingly, each of the separators
109
and
110
are formed comparatively thickly in order to form the communication path
108
, however, as is seen in the cross section in
FIG. 24
, at the position of the seal line where each of the sealing members
102
to
104
are placed, the separators
109
and
110
are formed with the minimum thickness needed to ensure the required strength, and it is not possible to make them any thinner.
Moreover, because each of the sealing members
102
to
104
is formed with the minimum height needed to secure the sealing performance, it is not possible to reduce the height of the sealing members
102
to
104
any further.
As a result, although the thickness of the fuel cell
106
is found by multiplying the number of stacks by the sum of the minimum thickness of the two separators
109
and
110
, the thickness needed to form the communication path
108
, the height of the two gas sealing members
102
and
103
, the thickness of the solid polymer electrolyte membrane
111
, and the height of the cooling surface sealing member
104
, because these are all indispensable it is extremely difficult to achieve any further reduction in thickness.
The present inv
Sugita Narutoshi
Sugiura Seiji
Honda Giken Kogyo Kabushiki Kaisha
Lahive & Cockfield LLP
Laurentano, Esq. Anthony A.
Maples John S.
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