Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer or spacer insulating structure
Reexamination Certificate
2001-09-18
2003-03-11
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer or spacer insulating structure
C429S143000, C429S147000, C429S006000, C429S010000, C429S010000, C429S006000, C429S006000, C429S006000
Reexamination Certificate
active
06531245
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. HEI 11-39921 filed on Feb. 18, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a gas separator for use in a fuel cell, a fuel cell, and a method for distributing gas in a fuel cell. More particularly, the invention relates to a fuel cell separator which is provided between adjacent unit cells in a fuel cell formed of a stacked plurality of unit cells, and which forms a fuel gas passage and an oxidative gas passage, together with adjacent members and separates a fuel gas and an oxidative gas from each other, a fuel cell incorporating the separator, and a method for distributing gas in the fuel cell.
2. Description of the Related Art
A fuel cell gas separator is a member that constitutes a fuel cell stack formed of a stacked plurality of unit cells, and that has a gas impermeability sufficiently high to prevent mixture of a fuel gas and an oxidative gas that are supplied to adjacent unit cells. A typical fuel cell gas separator has a rib-like surface structure having recessed and protruding portions forming passages for the fuel gas and the oxidative gas (this type of gas separator is often termed a “ribbed inter-connector”). When incorporated in a fuel cell stack, fuel cell separators form fuel gas or oxidative gas passages (in-cell gas passages) between their rib-like surface structures and adjacent members (gas diffusion layers).
In addition to the rib-like surface structure for forming a gas passage, a typical fuel cell separator has a predetermined hole structure. If unit cells provided with such gas separators are stacked to form a fuel cell stack, the hole structures of adjacent gas separators meet so as to form gas manifolds that extend through the fuel cell stack in a stacking direction. The manifolds convey the fuel gas or the oxidative gas supplied into the fuel cell from an external device to distribute the gas to the individual unit cells, and collect a waste fuel gas or a waste oxidative gas resulting from electrochemical reactions that occur in the individual unit cells to discharge the waste gas to the outside of the fuel cell. For these functions, the gas manifolds are connected to a gas passage in each unit cell (that is, the in-cell oxidative gas passage or in-cell fuel gas passage of each unit cell), so that the gas can flow between the gas manifolds and each in-cell gas passage.
FIG. 18
illustrates the construction of a known fuel cell gas separator in a plan view. A separator
930
has a hole structure, that is, four holes
940
,
942
,
950
,
952
formed near the periphery of the separator
930
. When a plurality of unit cells, each including a separator
930
, are stacked to form a fuel cell, corresponding holes of adjacent separators
930
meet so as to form four manifolds extending through the fuel cell. Specifically, these four manifolds are: an oxidative gas supply manifold for distributing the oxidative gas supplied from outside, into each in-cell oxidative gas passage; an oxidative gas discharge passage for collecting the waste oxidative gas from each in-cell oxidative gas passage and conveying the gas to the outside of the fuel cell; a fuel gas supply manifold for distributing the fuel gas supplied from outside, into each in-cell fuel gas passage; and a fuel gas discharge passage for collecting the waste fuel gas from each in-cell fuel gas passage and conveying the gas to the outside of the fuel cell.
A recessed portion
990
connecting the hole
940
and the hole
942
is formed in a surface of the separator
930
as shown in FIG.
18
. The opposite surface of the separator
930
is provided with a recessed portion (not shown) connecting the hole
950
and the hole
952
. Each recessed portion has a serpentine groove structure with two turns. When cell component members including separators
930
are stacked to form a fuel cell, the recessed portions of the separators
930
form, together with the members adjacent to the separators
930
, in-cell gas passages. The recessed portion
990
connecting the holes
940
and
942
of each separator
930
forms an in-cell gas passage for the oxidative gas. The recessed portion connecting the holes
950
and
952
of each separator
930
forms an in-cell gas passage for the fuel gas. Therefore, the oxidative gas supplied into the fuel cell is conveyed through the oxidative gas supply manifold formed by the holes
940
of the separators
930
, and distributed into the oxidative gas passage formed in each unit cell where the gas is used for the electrochemical reaction. After that, the waste gas flows out into the oxidative gas discharge manifold formed by the holes
942
of the separators
930
, whereby the gas is discharged to the outside of the fuel cell. Similarly, the fuel gas supplied into the fuel cell is conveyed through the fuel gas supply manifold formed by the holes
950
of the separators
930
, and distributed into the fuel gas passage formed in each unit cell, where the gas is used for the electrochemical reaction. After that, the waste gas flows out into the fuel gas discharge manifold formed by the holes
952
of the separators
930
, whereby the gas is discharged to the outside of the fuel cell.
Since the recessed portion in each of the opposite surfaces of the separator
930
shown in
FIG. 18
has a serpentine shape having two turns, the in-cell gas passage formed by each recessed portion has a reduced cross-sectional area in comparison with in-cell gas passages having no turns. Therefore, the gas flow velocity at a given location in each in-cell gas passage is increased, so that the gas flowing through the in-cell gas passage becomes well stirred and diffused. In such a well-stirred condition, hydrogen or oxygen in the gas (the fuel gas or the oxidative gas) is more likely to contact a catalyst layer provided on an electrode, so that the gas utilization rate in the electrochemical reactions increases.
A recessed structure formed in a surface of a fuel cell gas separator other than the recessed structure shown in
FIG. 18
is proposed (in, for example, Japanese Patent Application Laid-open No. HEI 7-263003), in which a plurality of recessed portions, each having a serpentine shape with two turns as described above, are formed parallel in a surface of a separator, and gas is supplied to and discharged from the recessed portions via a gas introducing hole and a gas discharging hole that form a gas supply manifold and a gas discharge manifold.
However, in the fuel gas cell separators as illustrated in
FIG. 18
or as described in the aforementioned laid-open patent application, each in-cell gas passage is provided with only one hole for introducing gas thereto (the hole
940
or
950
in
FIG. 18
) and only one hole for discharging gas therefrom (the hole
942
or
952
in FIG.
18
), so that the flow of gas distributed to the individual unit cells of a fuel cell is likely become non-uniform or unequal. For example, water which is present as a result of the electrochemical reactions or the like may condense in a gas passage and may reside in an in-cell gas passage or near a junction between an in-cell gas passage and a gas manifold. If this happens, residing condensed water provides a resistance to gas flow, thereby impeding smooth flow of gas. If the gas supply condition deteriorates in this manner in a unit cell, sufficient progress of the electrochemical reactions in the unit cell is hindered. This may decrease the output voltage of the unit cell. In this manner, the output voltage varies among the unit cells of the entire fuel cell and, therefore, the performance of the fuel cell deteriorates.
Water condensation that may occur in a gas passage will be described. Condensation in the oxidative gas in a passage is attributed to water produced on a cathode side by an electrochemical reaction. The electrochemical reactions that occur in each unit cell of a polymer electr
Mizuno Seiji
Takahashi Tsuyoshi
Wada Mikio
Kenyon & Kenyon
Martin Angela J
Ryan Patrick
Toyota Jidosha & Kabushiki Kaisha
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