Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2002-11-04
2004-12-21
Maples, John S. (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000
Reexamination Certificate
active
06833210
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 forming fuel cell stacks, there is one type that is formed in a plate shape by sandwiching between a pair of separators a membrane 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 constructed in this way.
In each fuel cell unit there are provided a flow passage for fuel gas (for example, hydrogen) on one surface of the anode side separator that is positioned facing the anode electrode, and a flow passage 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 flow passage 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 there and moves to the cathode electrode via the solid polymer electrolyte membrane. Electrons generated during this process 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 must flow through a separate flow passage. Therefore, sealing technology that keeps each flow passage sealed in a fluidtight or airtight condition is essential.
Examples of portions that must 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 the cooling medium that are discharged from each fuel cell unit; the outer peripheries of the membrane electrode assemblies; and the outer peripheries between the separators of adjacent fuel cell units. A material that is soft yet also has 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 practical vehicles.
Methods that have been considered for reducing the size of fuel cells 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 flow passage formed inside each fuel cell unit; and also making the separators thinner.
However, there is a limit to how thin the separators can be made due to 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 must be sufficient for the sealing members to be able to be pressed down enough to ensure that 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 space 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 must be made as small as possible.
FIG. 24
is a plan view showing a conventional fuel cell stack. In
FIG. 24
the reference numeral
70
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 stack in the direction in which separators
71
are stacked. The reference numeral
72
indicates an area in which a plurality of fuel gas flow passages, oxidizing gas flow passages, and cooling medium flow passages running along the separators
71
are formed.
FIG. 25
is a longitudinal cross-sectional view of a conventional fuel cell stack
73
taken along the line X—X in FIG.
24
. As can be seen in plan view, in order to make the space occupied by the sealing member, that does not contribute to power generation, as small as possible, conventionally, by locating gas sealing members
76
and
77
, which respectively seal a fuel gas flow passage
74
and an oxidizing gas flow passage
75
, together with a cooling surface sealing member
78
, which seals a cooling medium flow passage, aligned in a row in the stacking direction of the fuel cell units
79
, the outer dimensions in the stacking direction of the fuel cell stack
73
are restrained to the minimum.
However, the drawback with the fuel cell stack
73
that is constructed in this manner is that if the gas sealing members
76
and
77
that seal the flow passages
74
and
75
as well as the cooling surface sealing member
78
are all placed in a row in the stacking direction of the fuel cell unit
79
, then the thickness of the fuel cell stack
73
cannot be made less than a value obtained by adding the height of the cooling surface sealing member
78
to the thickness of each fuel cell unit
79
, and multiplying this result by the number of fuel cell units stacked in the fuel cell stack.
In order to explain this more specifically, the discussion will return to FIG.
25
. According to
FIG. 25
, the fuel gas supply port
70
and the fuel gas flow passage
74
that are isolated in a sealed state by the gas sealing members
76
and
77
are connected by a communication path
80
. The communication path
80
is provided in the separator
81
in the vicinity of the fuel gas supply port
70
so as to detour around, in the thickness direction of the separator
81
, the gas sealing member
77
that seals the entire periphery of the fuel gas flow passage
74
. Moreover, the separator
82
also has a similar communication path (not shown) in the vicinity of the oxidizing gas supply port (not shown).
Accordingly, each of the separators
81
and
82
are formed relatively thickly in order to form the communication path
80
; however, as is seen in the cross section in
FIG. 25
, at the position of the seal line where each of the sealing members
76
to
78
are placed, the separators
81
and
82
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
76
to
78
is formed with the minimum height needed to secure the sealing performance, it is not possible to reduce the height of the sealing members
76
to
78
any further.
As a result, although the thickness of the fuel cell stack
73
is found by multiplying the number of stacks by the sum of the minimum thickness of the two separators
81
and
82
, the thickness needed to form the communication path
80
, the height of the two gas sealing members
76
and
77
, the thickness of the solid polymer electrolyte membrane
83
, and the height of the cooling surface sealing member
78
, because these are all indispensable, it is extremely difficult to achieve any further reduction in thickness.
As a countermeasure for reducing the overall thickness of such a fuel cell stack
73
, it is proposed that the gas sealing members
76
and
77
and the cooling surface sealing member
78
be disposed so as to
Andou Keisuke
Kikuchi Hideaki
Sugita Narutoshi
Sugiura Seiji
Tanaka Hiroyuki
Honda Giken Kogyo Kabushiki Kaisha
Lahive & Cockfield LLP
Laurentano, Esq. Anthony A.
Maples John S.
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