U.S. patent application number 11/068985 was filed with the patent office on 2005-10-06 for separator and fuel cell using thereof.
Invention is credited to Takahashi, Ko, Yamaga, Kenji, Yamauchi, Hiroshi.
Application Number | 20050221158 11/068985 |
Document ID | / |
Family ID | 35054716 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050221158 |
Kind Code |
A1 |
Yamauchi, Hiroshi ; et
al. |
October 6, 2005 |
Separator and fuel cell using thereof
Abstract
A fuel cell is provided therein with a metal separator for
aiming at preventing corrosion and at reducing a contact
resistance. The separator is compose of conductive passage board
formed therein with passages, and a metal planar panel, the passage
boards and the metal planar panel being superposed with one
another. The metal planar panel is formed therein with a plurality
of manifolds for passing reactive gas or cooling medium through an
adjacent cell while the passage boards are formed therein with a
plurality of meandering through channels for distributing the
reactive gas or the cooling medium from the manifolds. Further, a
part of the meandering through channels is superposed with a part
or all parts of the manifolds, and a covering layer for preventing
the metal planar panel from being corroded, and for restraining a
growth of a nonconductive film is formed over an entire part of the
metal planar panel or over at least a part thereof which makes
contact with the meandering through channels.
Inventors: |
Yamauchi, Hiroshi; (Hitachi,
JP) ; Yamaga, Kenji; (Hitachi, JP) ;
Takahashi, Ko; (Hitachi, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
35054716 |
Appl. No.: |
11/068985 |
Filed: |
March 2, 2005 |
Current U.S.
Class: |
429/437 ;
429/458; 429/483; 429/514 |
Current CPC
Class: |
H01M 8/0263 20130101;
H01M 8/0204 20130101; H01M 8/0206 20130101; H01M 8/0239 20130101;
H01M 8/1011 20130101; H01M 2008/1095 20130101; H01M 8/0273
20130101; H01M 8/04074 20130101; H01M 8/0234 20130101; H01M 8/0267
20130101; H01M 8/0243 20130101; H01M 8/021 20130101; H01M 8/04029
20130101; Y02E 60/523 20130101; H01M 8/242 20130101; Y02E 60/50
20130101 |
Class at
Publication: |
429/038 ;
429/026; 429/025 |
International
Class: |
H01M 008/02; H01M
002/08; H01M 008/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 2, 2004 |
JP |
2004-110050 |
Claims
1. A separator for a fuel cell, comprising a metal planar panel and
conductive passage boards which are superposed with each other,
intervening therebetween the metal planar panel, the metal planar
panel being formed therein with a plurality of manifolds for
passing reactive fluid or cooling medium through an adjacent cell
while the passage board is formed therein with a plurality of
meandering through channels for distributing the reactive gas or
the cooling medium from the manifolds, wherein a part of the
meandering through channels is arranged so as to be superposed with
a part or all parts of the manifolds.
2. A separator for a fuel cell as set forth in claim 1, wherein a
covering layer for preventing the metal planar panel from being
corroded, and for restraining a growth of a nonconductive film is
formed over an entire part of the metal planar panel or over at
least a part thereof which makes contact with the meandering
through channels.
3. A separator for a fuel cell, comprising a metal planar panel and
conductive and porous passage boards which are superposed with each
other, interposing therebetween the metal planar panel, the metal
planar panel being formed therein with a plurality of manifolds for
passing reactive fluid or cooling medium through an adjacent cell
while the passage board is formed therein with a plurality of
meandering through channels for distributing the reactive gas or
the cooling medium from the manifolds, wherein a part of the
meandering through channels is arranged so as to be superposed with
a part or all parts of the manifolds.
4. A separator as set forth in claim 3, wherein gaskets are
arranged so as to surround the passage boards.
5. A separator for a fuel cell as set forth in claim 3, wherein a
covering layer for preventing the metal planar panel from being
corroded, and for restraining a growth of a nonconductive film is
formed over an entire part of the metal planar panel or over at
least a part thereof which makes contact with the meandering
through channels.
6. A separator for a fuel cell, comprising a planar panel formed
therein with a plurality of manifolds for passing reactive fluid or
cooling medium through adjacent cell, and a pair of conductive
passage boards superposed with one another, interposing
therebetween the planar panel, the passage boards being formed
therein with a plurality of meandering through channels for
distributing the reactive fluid or the cooling medium from the
manifolds, wherein the planar panel is formed therein with slits in
a part in which the two passage boards are superposed with each
other when the passage boards which make contact with the planar
panel are projected.
7. A separator for fuel cell as set forth in claim 6, wherein the
planar panel is made of metal, and a covering layer for preventing
the planar panel from being corroded, and for restraining a growth
of a nonconductive film is formed over an entire part of the metal
planar panel or over at least a part thereof which makes contact
with the meandering through channels.
8. A separator for a fuel cell as set forth in claim 6, wherein the
conductive passage boards are made of a porous conductive
material.
9. A separator for a fuel cell as set forth in any one of claims 1,
3 and 6, wherein the metal planar panel is formed thereon with an
outermost layer made of a material selected from a group consisting
of stainless steel, nickel, nickel base alloy, titanium, titanium
base alloy, niobium, niobium base alloy, tantalum, tantalum base
ally, tungsten, tungsten base alloy, zirconium, zirconium base
alloy, aluminum and aluminum alloy.
10. A separator for a fuel cell as set forth in any one of claims
2, 5 and 7, wherein the covering layer is composed of a-binder
selected from a group consisting of a fluorine group binder, phenol
group binder, an epoxy group binder, a styrene group binder, a
butadiene group binder, a polycarbonate group binder, a
ponlyphenylene sulfide group binder, a mixture thereof and a
copolymer thereof, and a conductive material containing therein not
less than one kind of carbon.
11. A separator for a fuel cell as set forth in any one of claims
2, 5 and 7, wherein the covering layer is conductive and
anticorrosive, and in integrally incorporated with the passage
board.
12. A fuel cell comprising a fuel cell stack of power generation
units each composed of an integrated electrolyte membrane electrode
structure, and a pair of separator each including, a metal planar
panel, and conductive passage boards superposed with each other,
interposing therebetewen the metal planar panel, the metal planar
panel being formed therein with a plurality of manifolds for
passing reactive fluid or cooling medium through an adjacent cell
while the passage boards are formed therein with a plurality of
meandering through channels for distributing the reactive fluid or
the cooling medium from the manifolds, a part of the meandering
through passage is superposed with a part or all parts of the
manifolds, power collector panels arranged outside of the fuel cell
stack and end plates arranged further outside thereof.
13. A fuel cell as set forth in claim 12, wherein among the power
generation units, the passage boards which are provided at every
other power generation unit are for cooling water.
14. A separator for a fuel cell as set forth in claim 12, wherein a
covering layer for preventing the metal planar panel from being
corroded, and for restraining a growth of a nonconductive film is
formed over an entire part of the metal planar panel or over at
least a part thereof which makes contact with the meandering
through channels.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a separator which is one of
components in a fuel cell, and also relates to a fuel cell using
thereof.
[0002] There have been several kinds of fuel cells which are sorted
in view of kinds of electrolytes used therein. For example, a
phosphate acid fuel cell (PAFC) has a carrier impregnated therein
with phosphate, and is adapted to be operated at a temperature in a
range from 150 to 220 deg.C. A molten carbonate fuel cell (MCFC)
includes a molded electrolyte carrier made of a mixture of lithium
carbonate and potassium carbonate, and is adapted to be operated at
a temperature in a range from 600 to 700 deg.C. Further, a solid
oxide fuel cell uses, as electrolyte, stabilized zirconium having
oxygen ion conductivity, and is adapted to be operated at a
temperature from 700 to 1,000 deg.C. Any of the above-mentioned
fuel cells utilizes hydrogen, reformed gas, hydrocarbon or the like
as a fuel, and air or the like as oxidizer gas.
[0003] Among several kinds of fuel cells, a proten exchange
membrane fuel cell (PEMFC) or a direct methanol fuel cell (DMFC)
mainly has such a feature that a membrane-like solid electrolyte
made of polymer is jointed thereto at its opposite surfaces with
carbon electrodes carrying catalyst such as platinum. This will be
referred to a membrane electrode assembly (an electrolytic
membrane/electrode integral structure) which is abbreviated to
"MEA". The solid polymer electrolyte fuel cell has such a
configuration that the MEA is interposed between a pair of panels
called as separators and formed therein with passages for fuel gas
(containing hydrogen) and oxidizer gas (oxygen or air).
[0004] It is noted that the fluid such as gas as fuel and the fluid
such as gas as an oxidizer will be inclusively referred to as
reaction gas or reaction fluid. In general, a porous carbon sheet
is interposed between the MEA and the separator. This constitutes a
gas diffusion layer which can enhance such a function that the
reaction gas is efficiently and uniformly fed to electrodes. The
above-mentioned components are bundled into a set which is called
as a unit cell, and a fuel cell stack is composed of a plurality of
unit cells stacked one upon another. The separator has such a roll
that the reaction gas is efficiently fed to electrodes, and
therefore, when the reaction gas is fed to a fuel cell while an
suitable load is applied, an electric power can be produced. In
association, heat such as heat of reaction and Joule's heat is also
generated. In order to remove the heat, the fuel cell incorporates,
in general, a separator for feeding cooling water which passes
through a part of the above-mentioned separator.
[0005] A separator also has a roll of transferring electric power
between adjacent cells with less energy loss, and accordingly, it
is, in general, made of carbon group conductive materials and is
formed therein with passage channels for ventilating reaction gas
and passing cooling medium. It has been considered that a metal
sheet or the like is used as a material of the separator as a
separator material, in addition to the carbon group material. Since
a metal has a low material cost, and can be simply fabricated by
stamping, and since a thin sheet metal can be used, it can offer
such a merit that the separator can be compact and lightweight, and
such a feature that the costs thereof are reduced.
[0006] However, in the case of a separator made of metal, should a
thin sheet metal be formed therein with passage channels by
pressing, it would be difficult to obtain fluid passages having
desired depths and widths due to a limitation of workability caused
by a process limit to a metal material. Thus, there would be caused
such hindrances as non-uniformity of reaction gas streams, and less
area of contact with an electrode. As a result, there would be
caused such a problem that a desired power generating performance
cannot be obtained. Even though a desired channel can be formed,
the separator after fabrication would be warped or deformed, or
could not have a required degree of finishing accuracy, resulting
in leakage of reaction gas or increase in contact resistance.
[0007] As another disadvantage caused by the press-formed metal
separator, apex tops of channels after fabrication have curvatures,
and accordingly, an area of contact with the gas diffusion layer or
the like becomes less. As a result, there would be caused such a
problem that the resistance is increased.
[0008] In the case of making conventional metal separators in
contact with one another, there would be caused such a problem that
their contact area cannot be obtained sufficiently. That is, since
the apices of channels for passage of reaction gas, which are
defined by spaces between two separators mated with one another,
are not flat, the separators are made into line or point contact
with one another, and accordingly, the resistance of contact
becomes higher, resulting in difficulty in obtaining a satisfactory
performance of power generation. In order to eliminate the
above-mentioned problem, JP-A-2003-173791 discloses such a
configuration that parts of apices having curvatures are removed so
as to be flattened. Further, JP-A-2003-123801 discloses such a
configuration that a conductive sheet gasket is interposed between
contact surfaces of separators in order to prevent occurrence of
voltage drop caused by a resistance of contact at surfaces of
cooling water between the separators.
[0009] As one of conventional inventions which can effectively
solve the above-mentioned problems, there is a separator as
disclosed in JP-A-2000-123850 or JP-A-2000-294257. This separator
is composed of a metal thin sheet and a carbon paper which is cut
so as to form passages in order to serve as a gas passage member.
Thus, a single separator can be obtained without press-forming, and
accordingly, it can reduce the costs. Further, since the passage
part is formed by cutting the carbon paper, the degree of finishing
accuracy is high, and further, it has a flat surface making contact
with a gas diffusion layer, thereby it is possible to eliminate the
above-mentioned problems.
[0010] The separator composed of the thin metal sheet and the
carbon paper which is cut so as to form passages in order to serve
as the gas passage member, as disclosed in JP-A-2000-123850 or
JP-A-2003-123801 have several advantages. However, the carbon paper
forming the passage part is split into several members, the larger
the number of passages, the larger the number of subdivided passage
members. As a result, there have been such problems that the number
of components constituting a cell is increased, and that the number
of manufacturing steps is increased since the components are
fastened to one another by conductive materials. Further, in the
inventions stated in the above-mentioned patent documents, no
countermeasures are considered against corrosion on the metal side
which is caused at contact surfaces of the metal separator and the
passage part. Thus, there would be caused increase in contact
resistance caused by corrosion on the metal side, contamination to
electrodes and electrolytic membranes caused by corrosion products,
and the like, resulting in deterioration of the fuel cell.
BRIEF SUMMARY OF THE INVENTION
[0011] A first object of the present invention is to provide a
separator for a fuel cell, comprising a planar panel, conductive
passage boards which are joined to each other and between which the
planer panel is held, the planar panel being formed therein with a
plurality of manifolds while the passage boards are formed therein
with a plurality of meandering through-channels a part of which is
superposed with a part or all parts of the above-mentioned
manifolds.
[0012] Further, a second object of the present invention is to
provide a fuel cell using the above-mentioned separator.
[0013] The separator according to the present invention is the
so-called stack type separator composed of a planar panel such as a
planar metal panel, and a pair of conductive passage boards which
are stacked one upon another.
[0014] According to the present invention, there is provided a
separator which can be easily fabricated and assembled with a lower
internal voltage drop and less performance deterioration, and there
is provided a fuel cell using this separator. Further, since the
above-mentioned components can be simply prepared by mere drilling,
and are planar as they are, a contact area therebetween and a
contact area thereof with another component can be larger.
[0015] There may be provided a covering layer for preventing
corrosion of the planar metal panel and restraining growth of a
film over the entire surface of the planar metal panel or at least
a part thereof which makes contact with the meandering
through-channels.
[0016] According to the present invention, there is provided a
separator for a fuel cell, comprising a planar metal panel, passage
boards made of porous conductive materials, which are superposed
with the planar metal panel, the planar metal panel being formed
therein with a plurality of manifolds for passing reactive fluid or
cooling medium through adjacent cells while the passage boards are
formed therein with a plurality of meandering through-channels for
passing therethrough the reactive fluid or the cooling medium from
the manifold, wherein a part of the meandering through-channels is
superposed with a part or all parts of the manifolds.
[0017] In the above-mentioned separator, a gasket may be arranged
so as to surround the passage boards. Further, a covering layer for
preventing corrosion of the planar metal panel, or restraining
growth of a nonconductive film may be provided over the entire
surface of the outer surface of the planar metal panel or at least
part thereof which make contact with the meandering
through-channels.
[0018] Further, according to the present invention, there is
provided a separator for a fuel cell, comprising a planar panel
formed therein with a plurality of manifolds for passing reactive
fluid or cooling medium through a cell adjacent to the separator,
and a pair of passage boards superposed with each other and
interposing therebetween the planar panel, the passage boards being
formed therein with a plurality of meandering through-channels for
distributing the reactive fluid or the cooling medium from the
manifolds, and a slit being formed in a part of the planar panel
where the pair of passage boards are superposed with each other
when the passage boards which make contact with opposite surfaces
of the planar panel are projected.
[0019] As sated above, in the case of the planar panel which is
made of metal, a covering layer for preventing the planar metal
panel from being corroded or for restraining a growth of a
nonconductive film, may be provided over each of the entire surface
of the planar panel, or over at least a part thereof which makes
contact with the meandering through-channels.
[0020] Further, the passage boards may be made of conductive porous
materials.
[0021] In the above-mentioned separator, it is desirable that the
metal planar panel is formed thereon with an outermost layer made
of a material selected from a group consisting of stainless steel,
nickel, nickel base alloy, titanium, titanium base alloy, niobium,
niobium base alloy, tantalum, tantalum base alloy, tungsten,
tungsten base alloy, zirconium, zirconium base alloy aluminum and
aluminum base alloy,
[0022] The above-mentioned covering layer is composedd of a resin
binder made of a material selected from a group consisting of
fluororesin, phenolic resin, epoxy resin, styrenic resin, butadiene
resin, polycarbonate resin, polyphenylene-sulphido resin, a mixture
thereof or a copolymer thereof, and a conductive material
containing not less than one kind of carbon. By integrally
incorporating the passage board and the covering layer with each
other, the handling ability of the separator can be enhanced.
[0023] Further, according to the present invention, there is
provided a fuel cell comprising a fuel cell stack which comprises a
plurality of power generating units each composed of an integrated
membrane electrode structure, a pair of gas diffusion layers mated
with opposite surfaces of the integral membrane electrode
structure, a pair of separators arranged outside the gas diffusion
layers, and each having a metal planar panel, conductive passage
boards superposed with each other and interposing therebetween the
metal planar panel, the metal planar panel being formed therein
with a plurality of manifolds for passing reactive fluid or cooling
medium through an adjacent cell, and the passage boards being
formed therein with a plurality of meandering through-channels for
distributing the reactive fluid or cooling medium from the
manifolds, a part of the meandering through-channels being arranged
so as to be superposed with a part of or all parts of the
manifolds, power collector panels arrange outside of the fuel cell
stack, and end plates arranged further outside thereof.
[0024] In this fuel cell, it is desirable that those of the
above-mentioned passage boards which are arranged every other power
unit, are for cooling water.
[0025] It is noted that the present invention should not be
specifically limited to the above-mentioned fuel cell including the
above-mentioned separators, but can involve various modifications
thereof.
[0026] According to one aspect of the present invention, with the
combination of the planar metal panel provided with the covering
layers for prevention of corrosion, and the conductive passage
boards, it is possible to provide a separator which has low costs
and a long use life. Further, a single separator can be composed of
a passage board which is conductive and which is formed therein a
plurality of punched-out meandering channels for distributing
reactive gas, and a planar covered metal panel. With this
configuration, by superposing a part of the passage board with the
manifolds of the covered metal panel, a separator having meandering
passage channels can be constituted of at least a single passage
board and a single metal panel.
[0027] Thus, since the separator can be formed merely by punching
process steps, it is possible to reduce the costs, and to ensure a
sufficient contact area. Further, with the results of various tests
as to the use life of the separator, it has been found that
corrosion of metal is remarkable in a part where a current runs
through, and accordingly, the covering layers for restraining
corrosion of the metal panel or the like are formed on the surfaces
of the metal panel. With this configuration, it is possible to
greatly prolong the use lift of the separator.
[0028] Further, the covered metal is formed therein with a slit
which allows the passage boards which are located on opposite sides
of the cover metal panel, to make electrical contact with one
another while no metal is present in the running path of a current.
Thus, it is possible to eliminate such a serious problem that the
contact resistance is increased due to the growth of a
nonconductive film and corrosion which are caused in use of metal
as a material of the separator (Embodiment 1). Further, since no
adhesion is required, the manufacturing process can be simplified.
In the separator formed of a metal planar panel and conductive
passage boards, the metal planar panel is formed therein with a
plurality of manifolds for passing reactive fluid or cooling medium
through an adjacent cell.
[0029] The passage boards are formed therein with a plurality of
meandering through-channels for distributing the active fluid or
cooling medium from the manifold, and are arranged so that a part
of the meandering through-channels is superposed with a part or all
parts of the manifolds. Further, the surfaces of the metal planar
panel are formed thereon with covering layers for restraining
corrosion or a growth of a nonconductive film, in its entirety or
over at least a part thereof which makes contact with the
meandering through channels.
[0030] Other objects, features and advantages of the invention will
become apparent from the following description of the embodiments
of the invention taken in conjunction with the accompanying
drawings.
BRIEF SUMMARY OF THE SEVERAL VIEWS OF THE DRAWING
[0031] FIG. 1 is an exploded perspective view illustrating a basic
configuration of an embodiment 1 of a separator according to the
present invention;
[0032] FIG. 2A is a plan view illustrating the separator shown in
FIG. 1, in which a covered panel is superposed over its opposite
surfaces with passage boards;
[0033] FIG. 2B is a sectional view illustrating the separator shown
in FIG. 2A;
[0034] FIG. 3A is a sectional view illustrating the covered metal
panel 12, in an example of the separator;
[0035] FIG. 3B is a sectional view illustrating another example of
the covered metal panel;
[0036] FIG. 4 is an exploded perspective illustrating a
configuration of a fuel cell in which the separator is used;
[0037] FIG. 5 is an exploded perspective view illustrating an
embodiment 2 of a separator in which porous passage boards are
used;
[0038] FIG. 6A is a plan view illustrating a separator in which a
covered metal panel is superposed over its opposite surface with
passage boards;
[0039] FIG. 6B is a sectional view illustrating the separator shown
in FIG. 6A;
[0040] FIG. 7 is an exploded perspective view illustrating an
embodiment 3 of a separator in which a covered metal panel formed
therein with slits is used;
[0041] FIG. 8 is a perspective view for explaining a positional
relationship between the slits in the covered metal plane and the
passage boards;
[0042] FIG. 9A is a sectional view illustrating the separator in
the embodiment 3;
[0043] FIG. 9B is an enlarged sectional view illustrating a part of
the separator surrounded by a chain line c;
[0044] FIG. 9A is an enlarged sectional view illustrating a part of
the separator surrounded by a chain line c;
[0045] FIG. 10 is an exploded view for explaining the order of
superposition of a fuel cell in an embodiment 4;
[0046] FIG. 11A is a sectional view illustrating a separator in
which passage boards are bonded to a covered metal panel with a
conductive paint;
[0047] FIG. 11B is an enlarged sectional view illustrating a part
surrounded by a dotted line in FIG. 11A; and
[0048] FIG. 12 is a sectional view illustrating an integral
MEA.
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1
[0049] Explanation will be made of a power generation cell in an
embodiment 1 of the present invention with reference to the
drawings. Referring to FIG. 1 which shows a basic configuration of
a separator according to the present invention, the single
separator 1 is composed of covered metal panel 3 formed therein
with manifolds 301, and passage boards 2A, 2B superposed over
opposite surfaces of the covered metal panel 3 and formed therein
with meandering through-channels for distributing reactive gas and
cooling medium from the manifolds 301. The passage boards 2A, 2B
are formed therein with meandering channels 202 which pierce
therethrough and are also formed therein with a plurality of
manifolds 201A, 201B as required.
[0050] Referring to FIGS. 2A and 2B which show the covered metal
panel 3 and the passage boards 2A, 2B which are superposed with
each other, one upon another, interposing therebetween the covered
metal panel 3, that is, FIG. 2A is a top plan view and FIG. 2B is a
schematic sectional view, the covered metal panel 3 and the passage
board 2A, 2B are arranged so that the manifolds 201A, 201B in the
passage boards 2A, 2B can be aligned with the manifolds 301 in the
covered metal panel 3 so as to allow the reactive gas and the
cooling water to flow therethgouh.
[0051] With this arrangement, a part or all parts of the channels
202 in the passage boards 2A, 2B is superposed with manifolds 301.
The size of the manifolds 301 is greater than that in the passage
boards 2A, 2B so as to allow the reactive gas to flow through the
manifolds 301 with less resistance, thereby it is possible to
reduce pressure loss in the stream of the reactive gas in order to
enhance the efficiency of the cell.
[0052] The reactive gas exhibits, for example, a steam as shown in
FIG. 1. The reaction gas flows through the manifolds 201B and the
manifolds 301 and comes into the manifold 201A. Since the channels
202 piercing through the passage board 2A are located in the
manifold 201A, a part of the reactive gas branches out in the
in-surface direction of the separator 1, and the remainder thereof
advances straightforward as it is. The reactive gas which flows in
the in-surface direction travels along the channels 202A, and flows
in to the manifolds on opposite sides so as to merges together.
[0053] With this configuration, the passage board 2 can be formed
with a passage part from a single plate. Further, the covered metal
panel 32 and the passage board 2 can be both fabricated by
stamping, thereby it is possible to reduce the fabricating
costs.
[0054] Referring to FIGS. 3A and 3B which are sectional views
illustrating the covered metal panel 3, in which FIG. 3A shows such
a case that a base panel 304 is coated over its entire surface with
a covering layer 3, there is obtained such a technical effect that
corrosion of the base panel 304 and a growth of a nonconductive
film can be restrained with the provision of the covering
layer.
[0055] With the provision of the above-mentioned configuration, it
is possible to provide a separator having a low cost and a long use
life can be obtained.
[0056] After several basic power generation tests were conduced,
there have been found that a metal separator is corroded
particularly in a zone where current runs. That is, the interfaces
through which the passage channels 202A, 202B of the passage boards
2A, 2B make contact with the covered metal panel 3, as shown in
FIG. 3A, are seriously corroded. Since no corrosion was found in
the remaining zone, the covering layer 303 may be formed only in a
zone where the metal panel 3 makes contact with the passage
channels 202, as shown in FIG. 3B.
[0057] Next, referring to FIG. 4 which shows an example of a fuel
cell including two cells with the use of the above-mentioned
separators, a separator 1A is the same as that shown in FIG. 1.
Separators 1B and 1C have such a configuration that a cooling water
passage boards 6 is provided, instead of the above-mentioned
passage board 2 in order to pass cooling water through one side
surface thereof. An integral MEA 5 is composed of an MEA, a gas
diffusion layer and a seal member (gasket) provided along the outer
peripheral side of the gas diffusion layer. With the combination of
the separators 1A, 1B and with the combination of the separators
1A, 1C, the integral MEA (Membrane Electrode Assembly) 5 is held
therebetween so as to constitute a single power generation cell
(power generation unit). The cooling water passage boards 6 are
interposed between the separator 1B and a power collection panel 8
and between the separator 1C and a power collection panel 8 on
opposite sides of the two power generation cells so as to
constitute cooling cells.
[0058] Since no MEA and the like are required in the cooling water
cells, the covered metal panel 3, the cooling water passage panel 6
and the collector panel 8 are stacked one upon another in the
mentioned order in the cooling cell. Further, the insulation panel
9 and an end plate 10 are arranged on each of opposite sides
thereof, and by fastening the end plates 10 with the use of
fastening bolts or the like, the fuel cell having two cells is
completed.
[0059] Referring to FIG. 12 is a sectional view illustrating the
integral MEA 5 which is used in this embodiment and as well in
other embodiments which will be explained hereinbelow, gas
diffusion layers 7 are arranged at opposite surfaces of an MEA 502,
and further, gaskets 503 are joined to the outer peripheral parts
of the gas diffusion layers so as to cover manifolds 501. Thus, the
MEA 502, the gaskets 503 and the gas diffusion layers 7 which have
conventionally been separated from each other, can be integrally
incorporated with one another, thereby it is possible to enhance
the workability of assembling the fuel cell. It should be noted
that an MEA whose components are separated from one another as in
the conventional one may also be used with no problem even though
the integral MEA 5 is used in each of the several embodiments of
the present invention.
[0060] Since the passage channels are rectangular in the separator
according to the present invention, not only the contact resistance
between components in the separator but also the contact resistance
between the separator and the gas diffusion layer are never
increased. On the contrary, in the case of press-forming the
separator from a metal sheet, apex parts of the channels through
which current runs possibly have curvatures, and as a result, the
contact area of the separator and the gas diffusion layer is
decreased. However, according to the present invention, the contact
area between the separator and the passage channels 202 can be
increased, thereby it is possible to decrease the contact
resistance.
Embodiment 2
[0061] Explanation will be hereinbelow made of an embodiment 2 of
the present invention with reference to FIG. 5. In this embodiment,
the passage boards 2 are made of conductive porous materials. If
the passage boards 2 are made of porous material, the quantity of
gas fed to the electrode by way of the passage board can be
increased, and accordingly, there can be offered such an advantaged
that the power generation voltage and the diffusion limit current
can be enhanced. Referring to FIG. 5 which shows the separator 1
using the porous passage boards 2, since the passage boards 2 are
made of porous materials, the reactive gas can flow though the
porous materials, smoothly. Thus, the single passage board 2 as
stated in the embodiment 1 cannot be used.
[0062] In this embodiment, by arranging the gaskets 4 around the
passage boards 2, it is possible to restrain occurrence of
cross-leakage of reaction gas from the anode to the cathode or from
the cathode to the anode, leakage between the cooling cell and the
power generation cell and leakage outside of the fuel cell
body.
[0063] The passage boards 2A, 2B are arranged at opposite surfaces
of the covered metal panel 3 shown in FIG. 5. The covered metal
panel 3 is formed thereon a layer which is conductive and
anti-corrosive, and is formed therein with manifolds 301 through
which reactive gas and cooling medium flow. Similar to the passage
boards 2 stated in the embodiment 1, each of the passage boards 2A,
2B is formed therein with a plurality of meandering
through-channels for passing the reactive gas and cooling medium
therethrough. The passage boards 2A, 2B are in part superposed with
the manifolds 301 in the covered metal panel 3. Further, the
gaskets 4A, 4B are arranged, having cutouts so as to prevent the
passage boards 2 from being superposed therewith, and accordingly,
a set of the separators is obtained.
[0064] Referring to FIGS. 6A and 6B which show such a configuration
that the gaskets 4 and the passage boards 2 are superposed one upon
another, interposing therebetween the covered metal panel 3, FIG.
6a being a top plane view while FIG. 6b is a schematic sectional
view, the metal panel 3 has the same configuration as that
explained in the embodiment 1, as shown in FIG. 3A. Instead of the
separator 1 in the embodiment 1 as shown in FIG. 4, the fuel cell
may also use therein the separator 1 explained in this
embodiment.
Embodiment 3
[0065] Explanation will be hereinbelow made of an embodiment 3 with
reference the accompanying drawings. In this embodiment, the
covered metal panel 3 as used in the embodiment 1 or 2 is formed
therein with slits 310 in a part corresponding to an electrode (the
passage channels part of the passage board 2). Referring to FIG. 7
which shows a separator 1 having the covered metal panel 3 formed
therein with the slits 310, the basic configuration of the
separator in this embodiment is the same as that in the embodiment
1 shown in FIG. 1, except the covered metal panel 3. The part of
the covered metal panel 3 in which the slits 310 are formed is a
zone where the passage channels 202 corresponding to the electrode
in the passage boards 2A, 2B which are mated with each another are
superposed with each other. This configuration is shown in FIG.
8.
[0066] The two passage boards 2A, 2B which are superposed with each
other are shown in the upper right part of the figure while the
covered metal panel 3 formed therein with the slit 310 is shown in
the lower left part thereof. FIG. 8 is prepared for the sake of
convenience for an explanation purpose while FIG. 7 shows the
actual configuration so as to exhibit the positional relationship.
In the upper right part of FIG. 8 in which the two passage boards
2A, 2B are superposed with each other, the passage board 2A is
depicted with the solid line while the passage board 2B is depicted
by hatching. The parts in which the passage boards 2A, 2B are
superposed with each other through the passage channels is
exhibited by dark hatching. The part of the covered metal panel 3
in which the slits 310 are formed is those corresponding to the
dark hatching. Some of the corresponding parts are exhibited by the
broken lines. The size of the slits 310 formed in the covered metal
panel 3 is smaller than that of the dark hating parts so as to
prevent the passage channels 202 of the passage boards 2 from being
depressed into the slit 310 when these components are stacked one
upon another. Referring to FIGS. 9A, 9B and 9c are sectional views
illustrating this situation, frankly speaking, the area where
current runs is very small in this situation, resulting in voltage
drop of the cell. However, by selecting a material having low
elastic modulus, such as carbon sheet or carbon paper for the
passage boards 2, the passage channels 202 are collapsed, as shown
in an enlarged view illustrating the slit 310 part, when the
components are stacked so as to form a cell, the electrical
conduction can be obtained between the passage channels 202A, 202B.
Thereby it is possible to exhibit such technical effects that no
covered metal panel 3 is present in the running direction of
current, and accordingly, the covering layer 301 for corrosion
control is not always necessary for the covered metal panel 3.
Should a poor anticorrosion metal such as aluminum be selected as
the material of the covered metal panel 3 while carbon is selected
as the material of the passage boards 2, a growth of a film of
aluminum oxide or hydroxoide would be possibly caused during power
generation for a long time even with provision of the covering
layers in the separator explained in the embodiment 1 or 2,
resulting in higher cell resistance. Thus, the performance of power
generation would be deteriorated. However, with the provision of
the measures explained in this embodiment, no covered metal panel 3
is present in the running path of current, and accordingly, less
affection upon the performance of the cell is caused even though
the aluminum is oxidized.
[0067] In the case of the covered metal panel 3 made of stiff
materials such as metal, the passage boards 2A, 2B are sometime not
deformed so that no electric conduction cannot be obtained. In this
case, by filling a conductive filler 11 such as conductive paint in
the slits 310, the electrical conduction can be obtained.
[0068] By using the covered metal panel 3 with the slits 310 stated
in this embodiment, instead of the coated metal panel 3 in the
separator stated in the embodiment 1 or the embodiment 2, a similar
fuel cell can be constituted.
[0069] In addition, it is not always necessary that the covered
metal panel 3 is made of metal. Resin or ceramics having a
strength, heat-resistance, water-proof and the like which are
sufficient may be used since the passage boards which confront each
other with the covered metal panel 3 being held therebetween are
electrically connected with each other, direct to each other.
Embodiment 4
[0070] In this embodiment, comparison of performances of five types
of fuel cells is exemplified in table 1. The first to third fuel
cells correspond to those explained in the embodiments 1 to 3 while
the fourth fuel cell is of such a type that the embodiments 2 and 3
are combined. The fifth fuel cell is for comparison, in which a
separator formed by press-forming a metal sheet is used. The
separator 1 in the first fuel cell in the embodiment 1 is composed
of the covered metal panel 3 and the two passage boards 2 while the
separator 1 in the second fuel cell is composed of the covered
metal panel 3 and the two porous passage boards 2 and the two
gaskets, and the separator 1 in the third fuel cell is composed of
the covered metal panel 3 formed therein with the slits 310. The
separator 1 in the forth fuel cell is in the combination of the
embodiment 1 and the embodiment 2, and in the passage boards 2 are
made of porous materials while the covered metal panel 3 is formed
therein with the slits 310.
[0071] Any of the fuel cells mentioned above, had an electrode area
of 10 cm.sup.2, 2 mm pitches of passage channels and ribs in the
cathode and the anode, and a depth of channels of 0.4 mm. The
thickness and the material of the metal part of the separator 1
were 0.1 mm and stainless steel (JIS Standard SUS304),
respectively. Barr or the like which was caused when the base board
304 was fabricated, were removed by polishing.
[0072] The covering layer 303 was formed over the entire surface of
this metal. The covering layer 303 was formed in such a way that a
conductive material which was a mixture of graphite and carbon
black was coated thereover with conductive paint having PVDF (poly
vinylidene di-fluroride) as a binder and NPM
(N-methyl-2-pyrrolidene) as a solvent by dipping, and was then
vacuum-dried at a temperature of about 150 deg.C. for 30 minutes.
The concentration of the solvent was adjusted so that the thickness
of the film of the conductive paint after finishing was 20 .mu.m.
The same kinds of MEAs were used for all fuel cells, having the gas
diffusion layer 7 and the gasket 4 which were commercially
available and which were integrally incorporated with each
other.
[0073] In the fifth fuel cell, the separator was press-formed so
that its peripheral part was flat while the passage channel parts
facing the electrode surfaces were rectilinear so that the reactive
gas was distributed over the opposite surface of the singe
separator 1. A frame made of PPS (poly Phenylene Sulfide) was
applied so as to fill a gap formed between the integral MEA 5 and
the periphery of the separator 1 when the separator 1 and the
integral MEA 5 were superposed with each other.
[0074] The passage boards 2 in the first and third fuel cells was
formed of an expanded graphite sheet having a thickness of 0.4 mm,
which was punched out by a Thomson type punching machine so as to
form passage channels 202 and the manifolds 201. In the second and
forth fuel cells, carbon paper having a thickness of about 0.4 mm
and subjected to a water repellant process was punched out by the
Thompson type punching machine so as to form the passage channels
202 and the manifolds 201, thus, the passage boards 2 was prepared.
The covered metal panels 3 used in the second and fourth fuel cells
were formed therein with slits 310 having a size which was smaller
than a size of an overlap obtained by stacking the two passage
boards 2 facing the covered metal panel 3, by 0.4 mm in both
horizontal and vertical directions.
[0075] The above-mentioned components were stacked one upon another
so as to obtain a fuel cell having four power generation cells and
three cooling cells. The stacking order thereof is schematically
shown in FIG. 10. For reference, the streams of reactive gas and
cooling water, as an example, are schematically shown by the broken
lines.
[0076] Power generation tests were carried out under the following
conditions: the temperature of cooling water was controlled so as
to set the temperature of the cell to an about 70 deg.C. Pure
hydrogen was used as fuel gas (AN gas) and the air was used as
oxidant gas (CA gas). Humidification was made so as to set the due
point at each of inlet ports of the fuel cell to 70 deg.C. The flow
rate of gas was controlled so as to set the utilization factors of
hydrogen and oxygen respectively to 80% and 40% with respect to a
current density.
[0077] Averaged cell voltages of the fuel cells at a current
density of 0.25 A/cm.sup.2 were measured after 50 hour and 1,000
hours of power generation. Further, diffusion limit current values
were measured after 50 hours of power generation. The results
thereof are shown in Table 1 in which averaged cell voltages (at
2.5 A/cm.sup.2) and diffusion limit currents are shown.
1 TABLE 1 Voltage (V) Diffusion Voltage (V) After Limit Current
Fuel Cell After 50 h 1,000 h (50 h) A/cm.sup.2 First Fuel 0.73 0.68
1.5 Cell Second Fuel 0.75 0.71 1.8 Cell Third Fuel 0.74 0.72 1.5
Cell Fourth Fuel 0.75 0.73 1.7 Cell Fifth Fuel 0.74 0.65 0.8
Cell
[0078] With reference to Table 1, the first and fourth fuel cells
exhibit high averaged voltage after 50 hours of power generation
(initial stage). The fourth fuel cell exhibits a highest averaged
voltage after 1,000 hours of power generation. The fifth fuel cell
exhibits a highest degree of deterioration after 1,000 hours of
power generation while the third and fourth fuel cells exhibits a
lowest degree of deterioration
[0079] The averaged cell voltage after 50 hours of power generation
have a correlation with respect to an A. C resistance of the cell,
and the second and fourth fuel cells using carbon paper as the
material of the passage boards 2 exhibits a lowest value while the
first fuel cell using an expanded graphite sheet as the material of
the passage boards 2 exhibits a low averaged cell voltage. The
third fuel cell although using the passage boards 2 formed of an
expanded graphite sheet exhibits a low resistance of the covered
metal panel 3 due to such a configuration the covered metal panel 3
is formed therein with the slits 310 so as to allow the opposed two
passage boards to make direct contact with each other. As a result,
it can be understood that the averaged cell voltage of the third
fuel cell is higher than that of the first fuel cell.
[0080] Further, the fourth fuel cell exhibits a highest averaged
cell voltage after 1,000 hours of power generation, but exhibits a
lowest degree of deterioration. It is considered, due to similar
reasons, that the degree of corrosion of the covered metal panel 3
made of SUS304 steel is lowered at maximum since no metal is
present in the running path of current. Further, the third fuel
cell exhibits less drop in the averaged cell voltage after 1,000
hours of power generation. Thus, the fuel cell (third and fourth
fuel cells) in which the slits 340 are formed in the covered metal
panel 3 exhibits such a technical effect that deterioration thereof
can be minimized.
[0081] Meanwhile, the fifth fuel cell (comparison example) exhibits
a less averaged cell voltage after 50 hours of power generation,
and further exhibits a highest degree of deterioration after 1,000
hours of power generation. Since the separator in the fifth fuel
cell was press-formed so that the contact part thereof with the
integral MEA 5 has curvature, it may be estimated that it has a
higher contact resistance. Although the precise reason why the
averaged cell voltage after 1,000 hours of power generation is low
has not yet been clarified, it may be considered that the current
density is locally increased in the contact part of the separator
with the integral MEA 5 since the contact area is small, and
accordingly, the progress of corrosion is promoted.
[0082] The second or fourth fuel cell using the passage boards 2
made of porous materials exhibits a highest diffusion limit
current. Since the passage boards 2 are porous, it is considered
that the reactive gas can be fed to the electrodes through the
intermediary of the passage boards 2.
[0083] However, it is-noted that one and the same technical effect
cannot be always obtained by any of various measures which are used
for the covering layer 303 of the covered metal panel 3. There may
be several measures, that is, a PVD process, plating, chemical
conversion process and the like, which can be selected in
accordance with a material of the base board 304. However, the
measures which can exhibit a high degree of conductivity and
affective corrosion control are limited. In order to evaluate
effective anti-corrosion control, a polarizing curve was measured
within a 0.05 M sulfuric aqueous solution at a temperature of 30
deg. C. in order to evaluate the corrosion preventing performance,
and as a result, it was found that a highest effective covering
layer was the one which was coated thereover with conductive
paint.
[0084] Pin holes or cracks would possibly be caused in the covering
layer 303 formed by other measures, and there would not be obtained
a sufficient corrosion preventing effect unless a sound covering
layer with no pin holes is formed. Among various kinds of
conductive paint, the one using a binder selected from a group
consisting a fluorine group binder, a phenol group binder, an epoxy
group binder, a styrene group binder, a butadiene group binder, a
polycarbonate group binder, a polyphenylene sulfide group binder, a
mixture thereof and a copolymer thereof exhibits a corrosion
preventing effect, and among others, a fluorine group PVDE exhibits
a most remarkable corrosion preventing effect.
[0085] It is required to select an appropriate material as the
conductive material. Paint with ceramic such as tungsten carbide as
the conductive material possibly causes a risk of detrimental
affection upon the fuel cell, since the covering layer 303 is
oxidized during power-generation and is accordingly tuned into
tungstic acid. On the contrary, paint using a carbon material such
as graphite as the conductive material, is electrochemically
stable, and has sufficient durability even in a fuel cell
environment. The mixture of the carbon black and graphite exhibits
such an effect that the electrical conductive can be highly
enhanced.
[0086] There has been used the base board 304 of the covered metal
panel which is made of stainless steel as an example in the
embodiments stated thereinabove. The material of the base board 304
should not be limited to stainless steel, but there may be used any
material if it has a certain degree of corrosion resistance. As to
various metal materials, polarizing curves and degrees of corrosion
by a dipping test were measured within a 0.05 M sulphuric aqueous
solution or a 0.05 M sodium sulfate aqueous solution at a
temperature of 30 deg.C., and as a result, in addition to the
stainless steel, it has been found that nickel, nickel base alloy,
titanium, titanium base alloy, niobium, niobium base alloy,
tantalum, tantalum base alloy, zirconium, zirconium base alloy
exhibit in particular, an excellent corrosion resistance.
[0087] Almost all above-mentioned metals exhibit less emission of
corrosion products, and the degree of affection upon an electrolyte
or an electrode is very small. Accordingly, it is preferable to
constitute the base board 304 with the above-mentioned metals.
[0088] However, it is not always required that the base board 304
is monolithic, but at least outer surface of the base board 304 may
be formed of the above-mentioned metal. For example, the base board
304 having an electrode layer, in which the above-mentioned metal
is formed by measures such as cladding, may be used.
[0089] Meanwhile, it has been found that aluminum or aluminum alloy
is anticorrosive in a neutral solution even though it is corroded
in sulfuric acid. Thus, in a fuel cell using the covered metal
panel formed therein with the slits 310, even though the covered
metal panel 3 made of aluminum was used, since less current runs
through the aluminum, the degree of corrosion was low. This is
because no aluminum is present in the running path of current.
Thus, the resistance of the fuel cell is not increased even though
the aluminum is corroded. A film similar to almite grows on
aluminum in the fuel cell environment, and accordingly, it may be
considered as a factor that the film can restrain corrosion. For
example, even though the corrosion product of the aluminum is
discharged from the base board 304, the affection upon the
electrodes and the electrolyte film is less, and in view of this
point, it has been found that aluminum is effective. It has been
found that iron, low alloy steel or copper are inappropriate since
a stable nonconductive film cannot be formed under the fuel cell
environment.
[0090] The covered metal panel 3 and the passage boards 2 can
constitute a fuel cell without such a measure as adhesive in any of
the embodiments 1 to 4 as stated above. However, if the machining
accuracy or the assembling accuracy of any of the components is
insufficient, reactive gas would cause cross-over between the
opposite electrodes. In particular, the separator in which the
covered metal panel 3 is formed therein with slits 310 (for
example, in the third or fourth fuel cell) causes formation of a
gap if the position of the passage boards 2 is shifted from the
slits, and accordingly, cross-over of the reactive gas would
possibly occur.
[0091] As countermeasures, it is preferable to bond the covered
metal layer 3 and the passage boards 3 with each other beforehand.
This method can reduce the number of components during assembly,
and accordingly, it is possible to exhibit such an additional
effect that the process for assembling a fuel cell can be
simplified.
[0092] In order to bond the covered metal panel 3 and the passage
boards 2 with each other, conductive adhesive or conductive paint
may be used. A one side surface of the passage board 2 on which the
covered metal board 3 is to be bonded, is coated thereover with the
conductive adhesive or the conductive paint by a general purpose
coating means such as spraying, screen printing, roll coater or the
like. The thus coated surface of the passage board 2 is applied to
the covered metal panel 3, and then under the condition with a
predetermined pushing pressure and a drying condition, they are
dried so as to complete the separator 1.
[0093] Referring to FIG. 11 which is a sectional view illustrating
the covered metal panel 3 and the passage boards 2 which are bonded
together with conductive paint as an example, the covered metal
panel 3 and the passage boards 2 are joined by the conductive
adhesive (conductive paint) 120 so as to be integrally incorporated
with each other, and further, the paint 120 can fill gaps which are
present in the interface between the covered metal panel 3 and the
passage board 2. Thus, it is possible to enhance the sealing
ability, and as well to restrain occurrence of cross-leakage of the
reactive gas. In the case of the separator using the covered metal
panel 3 with no slits 310, the paint can exhibits such an effect
that the passage boards 2 can be secured.
[0094] The conductive adhesive (conductive paint) composed of the
resin binder and the carbon conductive material as stated above is
used, the corrosion preventing function can also be obtained. Thus,
it is effective. With this configuration, the base board.304 of the
covered metal panel 3 with no covering layer 303 may be bonded
thereto with the passage boards 2.
[0095] It should be further understood by those skilled in the art
that although the foregoing description has been made on
embodiments of the invention, the invention is not limited thereto
and various changes and modifications may be made without departing
from the spirit of the invention and the scope of the appended
claims.
* * * * *