U.S. patent application number 11/137514 was filed with the patent office on 2005-09-29 for polymer electrolyte fuel cell and method for prudoucing the same.
This patent application is currently assigned to MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.. Invention is credited to Gyoten, Hisaaki, Kanbara, Teruhisa, Kusakabe, Hiroki, Morita, Junji, Sakai, Osamu, Sugawara, Yasushi, Uchida, Makoto, Yasumoto, Eiichi, Yoshida, Akihiko.
Application Number | 20050214599 11/137514 |
Document ID | / |
Family ID | 27335494 |
Filed Date | 2005-09-29 |
United States Patent
Application |
20050214599 |
Kind Code |
A1 |
Sakai, Osamu ; et
al. |
September 29, 2005 |
Polymer electrolyte fuel cell and method for prudoucing the
same
Abstract
A polymer electrolyte fuel cell is provided comprising: a
hydrogen ion conductive polymer electrolyte membrane; an anode and
a cathode sandwiching the hydrogen ion conductive polymer
electrolyte membrane; an anode side electroconductive separator
having a gas channel for supplying a fuel gas to the anode; a
cathode side electroconductive separator having a gas channel for
supplying an oxidant gas to the cathode; characterized in that the
anode and the cathode comprise a gas diffusion layer and a catalyst
layer formed on the gas diffusion layer at the side in contact with
the hydrogen ion conductive polymer electrolyte membrane, the
catalyst layer has catalyst particles and a hydrogen ion conductive
polymer electrolyte, and at least either of hydrogen ion
conductivity and gas permeability of at least either of the anode
and the cathode varies in a thickness direction of the anode or the
cathode.
Inventors: |
Sakai, Osamu; (Osaka,
JP) ; Gyoten, Hisaaki; (Osaka, JP) ; Kusakabe,
Hiroki; (Osaka, JP) ; Yasumoto, Eiichi;
(Soraku-gun, JP) ; Sugawara, Yasushi; (Osaka,
JP) ; Kanbara, Teruhisa; (Osaka, JP) ;
Yoshida, Akihiko; (Osaka, JP) ; Uchida, Makoto;
(Osaka, JP) ; Morita, Junji; (Osaka, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
MATSUSHITA ELECTRIC INDUSTRIAL CO.,
LTD.
Osaka
JP
|
Family ID: |
27335494 |
Appl. No.: |
11/137514 |
Filed: |
May 26, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11137514 |
May 26, 2005 |
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10088484 |
Mar 20, 2002 |
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10088484 |
Mar 20, 2002 |
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PCT/JP00/06451 |
Sep 20, 2000 |
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Current U.S.
Class: |
429/482 ;
29/623.1; 429/492; 429/532; 429/534 |
Current CPC
Class: |
H01M 8/2415 20130101;
Y02P 70/56 20151101; H01M 8/0234 20130101; H01M 8/241 20130101;
Y02B 90/12 20130101; H01M 2250/20 20130101; H01M 8/2457 20160201;
H01M 2250/402 20130101; Y02B 90/10 20130101; Y02E 60/50 20130101;
Y02T 90/32 20130101; H01M 8/1007 20160201; Y10T 29/49108 20150115;
H01M 2300/0082 20130101; Y02E 60/521 20130101; Y02T 90/40 20130101;
H01M 8/0245 20130101; Y02P 70/50 20151101; Y02P 90/40 20151101;
H01M 4/8657 20130101; H01M 8/1004 20130101; H01M 8/2484 20160201;
H01M 4/8636 20130101 |
Class at
Publication: |
429/012 ;
029/623.1 |
International
Class: |
H01M 006/00; C25B
001/46; H01M 008/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 21, 1999 |
JP |
HEI 11266803 |
Sep 29, 1999 |
JP |
HEI 11275762 |
Oct 27, 1999 |
JP |
HEI 11305990 |
Claims
1-11. (canceled)
12. A polymer electrolyte fuel cell comprising: a hydrogen ion
conductive polymer electrolyte membrane; an anode and a cathode
sandwiching said hydrogen ion conductive polymer electrolyte
membrane; an anode side electroconductive separator having a gas
channel for supplying a fuel gas to said anode; a cathode side
electroconductive separator having a gas channel for supplying an
oxidant gas to said cathode; wherein: said anode and said cathode
comprise a gas diffusion layer and a catalyst layer formed on said
gas diffusion layer at the side in contact with said hydrogen ion
conductive polymer electrolyte membrane, and said catalyst layer
comprises a layer comprising catalyst particles; and a layer, which
is not in contact with said hydrogen ion conductive polymer
electrolyte membrane, comprising a hydrogen ion conductive polymer
electrolyte.
13. The polymer electrolyte fuel cell according to claim 12,
wherein said catalyst layer comprises said layer comprising said
catalyst particles and said layer comprising said hydrogen ion
conductive polymer electrolyte that are alternately laminated.
14. A polymer electrolyte fuel cell according to claim 12, wherein
the amount of catalyst particles contained in the layer comprising
catalyst is from 0.005 to 1.0 mg/cm.sup.2 and the amount of
hydrogen ion conductive polymer electrolyte contained in the layer
comprising a hydrogen ion conductive polymer electrolyte is from
0.01 to 4 mg/cm.sup.2.
15. A polymer electrolyte fuel cell according to claim 12, wherein
the total number of layers comprising catalyst particles and layers
comprising a hydrogen ion conductive polymer electrolyte is from 2
to 10.
16. A polymer electrolyte fuel cell according to claim 12, wherein
the layer comprising catalyst particles contains a carbon powder
which is water repellent.
17. A polymer electrolyte fuel cell according to claim 12, wherein
the porosity of said gas diffusion layer is high at the side of
said electroconductive separator and is low at the side of said
catalyst layer.
18. A polymer electrolyte fuel cell according to claim 12, wherein
said gas diffusion layer comprises a plurality of porous conductive
base materials each having different porosities.
19. A polymer electrolyte fuel cell according to claim 12, wherein
one side of the gas diffusion layer, which is in contact with the
catalyst layer is water repellent.
20. A consumer co-generation system comprising a fuel cell
according to claim 12.
21. A mobile power-generating appliance comprising a fuel cell
according to claim 12.
Description
TECHNICAL FIELD
[0001] The present invention relates to polymer electrolyte fuel
cells useful as consumer co-generation systems and mobile
power-generating appliances.
BACKGROUND ART
[0002] In the electrodes of fuel cells, a fuel gas such as hydrogen
and an oxidant gas such as air react electrochemically to generate
electricity and heat simultaneously. Owing to the variety of
electrolytes with which they are equipped, there are several types
of fuel cells.
[0003] FIG. 1 is a sectional view illustrating a structure of
conventional polymer electrolyte fuel cells. Polymer electrolyte
fuel cells comprise electrolyte membrane-electrode assemblies 5
(MEAs), comprising a hydrogen ion conductive polymer electrolyte
membrane 1 and a pair of electrodes 4 sandwiching the membrane. The
pair of electrodes comprise an anode and a cathode, wherein a fuel
gas is supplied to the anode and an oxidant gas is supplied to the
cathode. The polymer-electrolyte membrane, for example, has a
--CF.sub.2-skeleton and comprises a perfluorocarbon sulfonate
having sulfonic acids on the terminal ends of its side chains.
[0004] The anode and the cathode comprise a catalyst layer 2
contiguous with the hydrogen ion conductive polymer electrolyte
membrane and a gas diffusion layer 3 having gas-permeability and
electroconductivity arranged on the outer face of the catalyst
layer.
[0005] Electroconductive separators 7 for affixing an MEA, and at
the same time electrically interconnecting in series neighboring
MEAs, are arranged on the outer faces of the MEA. The
electroconductive separator has a gas channel 6 for supplying the
fuel gas or the oxidant gas to the anode or the cathode, and for
conveying a surplus gas and water created by the reaction of
hydrogen and oxygen. The gas channels can be provided independently
of the electroconductive separator, but the gas channel is
generally formed by providing ribs or grooves on the surface of the
electroconductive separator.
[0006] A cooling water channel 8 can be formed on some of the
electroconductive separators. For example, electroconductive
separators, each having a gas channel on one side thereof and a
prescribed groove on the other side thereof, are bonded together
with a sealant 10 in such a manner that the side having the gas
channel faces outside, thereby the prescribed grooves form a
cooling water channel as shown in FIG. 1.
[0007] Gaskets 9 are arranged between both peripheries of the
electroconductive separators and the MEA, in order to prevent gases
from mixing with each other and from leaking outside.
[0008] To increase output voltage in procuring power-generating
devices, a plurality of unit cells, comprising an MEA and a pair of
electroconductive separators having gas channels, are laminated. A
fuel gas or an oxidant gas is supplied from the exterior through a
manifold to the inlet of the gas channel within each unit cell.
Electric current generated through the electrode reactions is then
collected to the gas diffusion layers and taken out to the exterior
through the electroconductive separators.
[0009] During the operation of the cell, for example, oxygen moves
from the gas channel to the catalyst layer through the gas
diffusion layer in the cathode while hydrogen moves from the gas
channel to the catalyst layer through the gas diffusion layer in
the anode. Herein, if the contact between the catalyst particles
and the hydrogen ion conductive polymer electrolyte in the catalyst
layer is insufficient, the reaction area becomes small, leading to
deterioration of discharging performance of the cell.
[0010] Conversely, water produced through the cell reaction moves
from the catalyst layer to the gas channel through the gas
diffusion layer to be removed outside of the cell with the surplus
gas. If the gas diffusion layer does not have proper gas
permeability, the polymer electrolyte membrane cannot be kept wet
in a proper degree. If the water content in the polymer electrolyte
membrane is decreased, its hydrogen ion conductivity will be
lowered. On the other hand, if the water content in the polymer
electrolyte membrane is extremely high, condensed water will clog
micropores of the gas diffusion layer or gas channels of the
electroconductive separators, resulting in considerable degradation
of the cell performance. This condition is called "flooding".
[0011] Therefore, the contact condition of the catalyst particles
with the hydrogen ion conductive polymer electrolyte and the gas
permeability in the anode and the cathode considerably affect
discharging performance of the fuel cell.
[0012] In order to enlarge the reaction area of the anode and the
cathode, it is effective that the hydrogen ion conductive polymer
electrolyte is included in the catalyst layer (Japanese Examined
Patent Publication No. Sho 62-61118, U.S. Pat. No. 5,211,984).
Likewise, in order to increase gas permeability of the anode and
the cathode, it is effective that a water-repellent is included in
the catalyst layer (Japanese Laid-Open Patent Publication No. Hei
5-36418, J. Electroanal. Chem. 197, 195(1986)). Therefore, the
catalyst layer generally contains catalyst particles, a hydrogen
ion conductive polymer electrolyte and, if necessary, water
repellent. Further, carbon powders carrying a platinum-group metal
are utilized as the catalyst particles.
[0013] Generally, the anode and the cathode are obtained by forming
a catalyst layer on one side of the gas diffusion layer. The
catalyst layer is usually formed by applying an ink, which
comprises catalyst particles, a dispersion of a hydrogen ion
conductive polymer electrolyte and an organic solvent such as
isopropyl alcohol, onto the gas diffusion layer by using a screen
printing method or a transfer printing method. The above-mentioned
ink normally contains a pore-producing agent, but the
pore-producing agent is to be removed during calcination of the
electrode after forming the catalyst layer; thereby, micropores for
passing a gas through are formed inside of the catalyst layer. The
catalyst layer thus obtained has a constant mixing ratio of the
catalyst particles to the hydrogen ion conductive polymer
electrolyte in its thickness direction.
[0014] Conventional polymer electrolyte fuel cells as mentioned
above have following problems.
[0015] First, it is considered to be effective that the mixing
ratio of catalyst particles to a hydrogen ion conductive polymer
electrolyte in a thickness direction of the catalyst layer varies
in the thickness direction of the catalyst layer in order for
hydrogen ions and electrons in the catalyst layer to move smoothly.
It would be theoretically possible to vary the structure of the
catalyst layer step by step, by preparing a plurality of inks each
having different compositions and applying them over and over using
a screen printing method or a transfer printing method, but it is
practically very difficult and such a catalyst layer is not yet
obtained, let alone seamlessly varying the structure of the
catalyst layer by a screen printing method or a transfer printing
method.
[0016] Conventional production process of anode and cathode has a
problem of becoming complicated because it has a calcination
process or a washing process for removing a pore-forming agent.
[0017] If an ink containing a solvent such as alcohols is
screen-printed on a porous conductive base material, the ink is
permeated inside the base material or passes through the base
material. Accordingly, there is also a problem that a catalyst
layer cannot be formed directly on the surface of a porous
conductive base material. On the other hand, if an ink is
screen-printed on a polymer electrolyte membrane, there are
problems such as the polymer electrolyte membrane is swelled with
the solvent in the ink and the polymer electrolyte membrane is
difficult to be fixed on a device.
[0018] If catalyst particles and a water repellent or a carbon
powder which is made water repellent are mixed with a dispersion of
a polymer electrolyte, a plenty of the polymer electrolyte is
adsorbed on the surface of the water repellent or the carbon powder
which is made water repellent. Therefore, the contact condition of
the polymer electrolyte with the catalyst particles becomes uneven
and sufficient reaction area cannot be retained. Further, if a
water repellent is added to an ink, catalyst particles are
excessively.covered with the water repellent, thereby decreasing a
reaction area.
[0019] Since porous conductive base materials such as carbon paper,
carbon cloth and carbon felt are conventionally used as the gas
diffusion layer, it is difficult to adjust the porosity of the gas
diffusion layer to the appropriate range.
[0020] As constant pressure is applied to the unit cells in
laminating direction in order to decrease the contact resistance of
each part and ensuring the gas sealing property, there is also such
a problem that, if porosity of the gas diffusion layer is too
large, the gas diffusion layer is crushed at the portion where the
electroconductive separator and the gas diffusion layer are in
contact and the gas permeability of the gas diffusion layer turns
out to be uneven in a plane direction.
DISCLOSURE OF INVENTION
[0021] In view of the foregoing problems, it is an object of the
present invention to provide a polymer electrolyte fuel cell having
a large reaction area and proper gas permeability, which
demonstrates high discharging performance even when the cell is
operated at a high current density.
[0022] The present invention relates to a polymer electrolyte fuel
cell comprising: a hydrogen ion conductive polymer electrolyte
membrane; an anode and a cathode sandwiching the hydrogen ion
conductive polymer electrolyte membrane; an anode side
electroconductive separator having a gas channel for supplying a
fuel gas to the anode; a cathode side electroconductive separator
having a gas channel for supplying an oxidant gas to the cathode;
characterized in that the anode and the cathode comprise a gas
diffusion layer and a catalyst layer formed on the gas diffusion
layer at the side in contact with the hydrogen ion conductive
polymer electrolyte membrane, the catalyst layer has catalyst
particles and a hydrogen ion conductive polymer electrolyte, at
least either of hydrogen ion conductivity and gas permeability of
at least either of the anode and the cathode varies in a thickness
direction of the anode or the cathode.
[0023] The amount of the hydrogen ion conductive polymer
electrolyte may be varied in a thickness direction of the catalyst
layer in order that the hydrogen ion conductivity of at least
either of the anode and the cathode is varied in the thickness
direction of the anode or the cathode.
[0024] It is preferable that the amount of the hydrogen ion
conductive polymer electrolyte in the catalyst layer is large at
the hydrogen ion conductive polymer electrolyte membrane side and
is small at the gas diffusion layer side.
[0025] It is also preferable that the catalyst layer comprises a
layer comprising the catalyst particles and a layer, which is not
in contact with the hydrogen ion conductive polymer electrolyte
membrane, comprising the hydrogen ion conductive polymer
electrolyte.
[0026] It is more preferable that the catalyst layer comprises the
layer comprising the catalyst particles and the layer comprising
the hydrogen ion conductive polymer electrolyte that are
alternately laminated.
[0027] It is preferable that the porosity of the gas diffusion
layer is high at the electroconductive separator side and low at
the catalyst layer side.
[0028] It is also preferable that the gas diffusion layer has a
plurality of porous conductive base materials each having different
porosities.
[0029] The present invention also relates to a producing method of
the polymer electrolyte fuel cell comprising a step of preparing a
plurality of catalyst-layer-forming inks having different mixing
ratios of the catalyst particles to the hydrogen ion conductive
polymer electrolyte, by mixing the catalyst particles and the
hydrogen ion conductive polymer electrolyte with a dispersion
medium, and a step of forming a catalyst layer in which hydrogen
ion conductivity varies in a thickness direction, by alternately
applying the plurality of catalyst layer-forming inks on one side
of the gas diffusion layer or at least one side of the hydrogen ion
conductive polymer electrolyte membrane.
[0030] It is preferable that the catalyst-layer-forming inks
contain carbon particles that are made water repellent.
[0031] It is preferable that the producing method of the polymer
electrolyte fuel cell comprises a step of forming a gas diffusion
layer, in which gas permeability varies in a thickness direction,
by laminating a plurality of porous conductive base materials
having different porosities.
[0032] It is also preferable that the producing method of the
polymer electrolyte fuel cell comprises a step of making a surface,
which is supposed to be in contact with the catalyst layer, of the
gas diffusion layer water repellent.
[0033] It should be noted that the electroconductive separator may
have a gas channel for supplying an oxidant gas to the cathode on
one side thereof and a gas channel for supplying a fuel gas to the
anode on the other side thereof.
BRIEF DESCRIPTION OF DRAWINGS
[0034] FIG. 1 is a sectional view illustrating a configuration of a
conventional polymer electrolyte fuel cell.
[0035] FIG. 2 is a sectional view illustrating a configuration of a
unit cell A1 in Example 1 of the present invention.
[0036] FIG. 3 is a graph showing the current-voltage
characteristics of unit cells A1, B1, C1 and X1 in Examples 1 to 3
and Comparative Example 1 of the present invention.
[0037] FIG. 4 is a diagram illustrating a configuration of a spray
application device used in Example 4 of the present invention.
[0038] FIG. 5 is a graph showing the current-voltage
characteristics of unit cells A2, B2 and C2 in Examples 4 and 5 and
Comparative Example 2 of the present invention.
[0039] FIG. 6 is schematic sectional views of electrodes of unit
cells A2, B2 and C2 in Examples 4 and 5 and Comparative Example 2
of the present invention.
[0040] FIG. 7 is a graph showing the current-voltage
characteristics of a unit cell D2 in Example 6 of the present
invention.
[0041] FIG. 8 is a sectional view illustrating a configuration of a
unit cell of a fuel cell A3 in Example 7 of the present
invention.
[0042] FIG. 9 is a partially cross sectional oblique view
illustrating a configuration of fuel cell A3 in Example 7 of the
present invention.
[0043] FIG. 10 is a graph showing the current-voltage
characteristics of fuel cells A3, B3 and C3 in Example 7 and
Comparative Examples 3 and 4 of the present invention.
[0044] FIG. 11 is a graph showing a relation between oxygen
utilization rate and voltage of fuel cells A3, B3 and C3 in Example
7 and Comparative Examples 3 and 4 of the present invention.
[0045] FIG. 12 is a graph showing the current-voltage
characteristics of fuel cells A3 and D3 in Examples 7 and 8 of the
present invention.
[0046] FIG. 13 is a graph showing a relation between oxygen
utilization rate and voltage of fuel cells A3 and D3 in Examples 7
and 8 of the present invention.
[0047] FIG. 14 is a graph showing a relation between oxygen
utilization rate and voltage of fuel cells A3 and E3 in Examples 7
and 9 of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
EMBODIMENT 1
[0048] The catalyst layer in accordance with the present embodiment
comprises a layer comprising catalyst particles facilitating the
reaction of a fuel gas and an oxidant gas, and a layer comprising a
hydrogen ion conductive polymer electrolyte. The layer comprising
catalyst particles may contain a water repellent or a carbon powder
which is made water repellent; in such a case, it is preferable
that the layer does not contain a hydrogen ion conductive polymer
electrolyte. On the other hand, it is preferable that the layer
comprising a hydrogen ion conductive polymer electrolyte does not
contain a water repellent or a carbon powder which is made water
repellent.
[0049] Alternate lamination of the layer comprising catalyst
particles and the layer comprising a hydrogen ion conductive
polymer electrolyte allows sufficient amount of the hydrogen ion
conductive polymer electrolyte to exist on the surface of the
catalyst particles, resulting in an increased reaction area of the
catalyst layer.
[0050] The catalyst particles comprise a metal catalyst and its
carrier. Platinum-group metals such as platinum, nickel and
palladium; ruthenium; iridium; iron; tin and the like are
preferably used as the catalyst metal. A carbon powder is
preferably utilized as the carrier. It is preferable that the mean
particle size of the carrier is from 10 to 50 nm from the viewpoint
of enlarging the reaction area. Likewise, it is preferable that the
mean particle size of the metal carried on the carrier is from 1 to
8 nm. It is preferable that the carried amount of the metal is from
10 to 70 parts by weight per 100 parts by weight the carrier.
[0051] The hydrogen ion conductive polymer electrolyte is
preferably a perfluorocarbonsulfonic acid represented by, for
example, the following structural formula: 1
[0052] wherein:
5.ltoreq.x.ltoreq.13.5
y.apprxeq.1000
1.ltoreq.z
[0053] The above-mentioned catalyst layer can be obtained by
alternately applying an ink containing the catalyst particles and
an ink containing a hydrogen ion conductive polymer electrolyte
onto the surface of the gas diffusion layer or the hydrogen ion
conductive polymer electrolyte membrane. However, in order not to
return to the same result that the hydrogen ion conductive polymer
electrolyte membrane is thickened, it is necessary to design the
catalyst layer in such a manner that the layer comprising a
hydrogen ion conductive polymer electrolyte is not in contact with
the hydrogen ion conductive polymer electrolyte membrane.
[0054] Porous conductive base materials such as carbon paper,
carbon cloth and carbon felt are used as the gas diffusion layer.
Further, as the hydrogen ion conductive polymer electrolyte
membrane, those that have conventionally been utilized may be
used.
[0055] According to the above-mentioned method, if a water
repellent such as a fluorocarbon resin or a carbon powder which is
made water repellent by fluorocarbon resin is mixed in the ink
containing the catalyst particles, a large amount of the hydrogen
ion conductive polymer electrolyte is prevented from adsorbing on
the surface of the water repellent. Therefore, the catalyst
particles can be in contact with the hydrogen ion conductive
polymer electrolyte evenly and sufficiently.
[0056] The total number of layers comprising catalyst particles and
layers comprising a hydrogen ion conductive polymer electrolyte is
preferably as small as 2 from the viewpoint of reducing the
production cost. Likewise, it is preferably from 3 to 10 from the
viewpoint of enlarging the reaction area as well as obtaining a
high performance electrode.
[0057] For the applying method, such method is preferable that an
ink is sprayed on the surface of a gas diffusion layer or a
hydrogen ion conductive polymer electrolyte membrane.
[0058] For the organic solvent serving as the dispersion medium of
the ink, alcohols such as methanol, ethanol, propanol, butanol,
1-propanol, 2-methyl-1-propanol, 2-methyl-2-propanol; butyl
acetate; tetrahydrofuran and the like are preferable. These may be
used singly, or in combination of two or more thereof.
[0059] The preferred conditions for the spray application are
nozzle diameter of 1 mm or less, spraying pressure of from
3.0.times.10.sup.5 to 10.times.10.sup.5 Pa, the distance between
the nozzle tip and the surface of the gas diffusion layer or that
of the hydrogen ion conductive polymer electrolyte membrane of 100
mm or less.
[0060] The thickness of the layer comprising catalyst particles is
preferably from 10 to 10000 nm per layer from the viewpoint of
improving the electrode performance. Likewise, the thickness of the
layer comprising a hydrogen ion conductive polymer electrolyte is
preferably from 10 to 10000 nm per layer. From the same viewpoint,
the amount of the catalyst particles contained in the layer
comprising catalyst particles per layer and per unit area is
preferably from 0.005 to 1.0 mg/cm.sup.2, and the amount of the
hydrogen ion conductive polymer electrolyte contained in the layer
comprising a hydrogen ion conductive polymer electrolyte per layer
and per unit area is preferably from 0.01 to 4 mg/cm.sup.2.
EMBODIMENT 2
[0061] The amount of the hydrogen ion conductive polymer
electrolyte contained in a catalyst layer in accordance with the
present embodiment decreases toward the gas diffusion layer side
from the hydrogen ion conductive polymer electrolyte membrane
side.
[0062] The above-mentioned catalyst layer can be formed by
preparing a plurality of inks having different mixing ratios of
catalyst particles to a hydrogen ion conductive polymer
electrolyte, and alternately applying the plurality of inks onto
the surface of the gas diffusion layer or the hydrogen ion
conductive polymer electrolyte membrane. The components of the inks
are catalyst particles, a hydrogen ion conductive polymer
electrolyte, a water repellent, a carbon powder which is made water
repellent and the like. These may be contained in the inks singly
or in combination of two or more thereof.
[0063] For the applying method, such method is preferable that the
inks are sprayed onto the surface of the gas diffusion layer or the
hydrogen ion conductive polymer electrolyte membrane. Further, it
is preferable that the plurality of inks having different mixing
ratios of catalyst particles to a hydrogen ion conductive polymer
electrolyte are sprayed from different nozzles respectively.
[0064] In the above-mentioned method, inks are atomized and sprayed
onto the surface of the gas diffusion layer or the hydrogen ion
conductive polymer electrolyte membrane; as a result, most of the
solvent in the inks are vaporized before the atomized inks are
adhered onto the surface of the gas diffusion layer or the hydrogen
ion conductive polymer electrolyte membrane. Therefore, the inks do
not spread easily on the surface of the gas diffusion layer or the
hydrogen ion conductive polymer electrolyte membrane, and the
catalyst particles are adhered so that they are sedimented.
[0065] For example, it is preferable that while two kinds of inks
are sprayed simultaneously from different directions (opposite
directions, for example), the gas diffusion layer or the hydrogen
ion conductive polymer electrolyte membrane is moved from one
nozzle side to the other nozzle side. This method allows the amount
of the hydrogen ion conductive polymer electrolyte in the catalyst
layer to seamlessly vary in a thickness direction of the catalyst
layer.
[0066] If the amount of the polymer electrolyte is seamlessly
decreased toward the gas diffusion layer side from the polymer
electrolyte membrane side, the distribution of the polymer
electrolyte turns into a distribution similar to the dendritic
structure extended toward the gas diffusion layer side from the
polymer electrolyte membrane side; therefore, ions and electrons
can move smoothly in the thickness direction of the catalyst
layer.
EMBODIMENT 3
[0067] The porosity of the gas diffusion layer of the present
embodiment is high at the electroconductive separator side and low
at the catalyst layer side. Such a structure allows the hydrogen
ion conductive polymer electrolyte within the catalyst layer to wet
in a proper degree and excessive water within the electrode to be
rapidly delivered to outside, and also permits an excellent fuel
cell to be obtained in which the gas diffusion layer does not
easily lose its shape.
[0068] The aforementioned gas diffusion layer can be obtained by
laminating a plurality of porous conductive base materials each
having different porosities such that a porous conductive base
material having a larger porosity comes to the electroconductive
separator side and a porous conductive base material having a low
porosity comes to the catalyst layer side. Carbon paper, carbon
cloth, carbon felt and the like can be used as the porous
conductive base material. Herein, one side of the gas diffusion
layer, which is in contact with the catalyst layer, is desirably
made water repellent. It is effective to make the porous conductive
base material disposed at the catalyst layer side water repellent
in order to prevent the cathode from drying, when the current
density is small or the dew point of the oxidant gas is low.
[0069] The gas diffusion layer having a small porosity disposed at
the catalyst layer side serves to keep the catalyst layer wet,
whereas the gas diffusion layer having a large porosity disposed at
outer side serves to rapidly pass the excessive water to the gas
channel of the electroconductive separator.
[0070] Carbon paper is generally produced by making a sheet of
paper out of a polyacrylonitrile type fiber and calcining it at a
high temperature of 1000.degree. C. or more. If two sheets of paper
of different kinds each having different porosities are laminated
and calcined, two sheets of carbon paper of different kinds are
obtained that are adhered to each other.
[0071] The present invention is described concretely below based on
examples. It should be noted, however, that the present invention
is not limited to them.
EXAMPLE 1
[0072] A carbon powder (Acetylene black, approx. 50 nm mean primary
particle size) was immersed in an aqueous solution of
chloroplatinic acid, and then was subjected to a reduction
treatment, thereby platinum (30 .ANG. mean particle size) was made
carried on the surface of the carbon powder. The weight ratio of
the carbon powder to the carried platinum was 75:25.
[0073] The obtained carbon powder carrying platinum, a dispersion
containing 60 wt % polytetrafluoroethylene (trade name: DI,
manufactured by DAIKIN INDUSTRIES, Ltd.) and 2-propanol were mixed
in a weight ratio of 5:20:75 to obtain an ink A1.
[0074] Likewise, perfluorocarbonsulfonic acid serving as a hydrogen
ion conductive polymer electrolyte (trade name: Flemion,
manufactured by ASAHI GLASS CO., Ltd.) was dispersed in ethanol to
obtain an ink B1.
[0075] The ink B1 was sprayed on one side of carbon paper having a
thickness of 250 .mu.m, which serves as a gas diffusion layer, to
form a layer comprising a hydrogen ion conductive electrolyte.
Subsequently, the ink A1 was sprayed on the layer comprising a
hydrogen ion conductive electrolyte to form a layer comprising
catalyst particles.
[0076] In the spray, nozzle diameter was set to 0.5 mm, spraying
pressure to 5.times.10.sup.5 Pa, the distance between the nozzle
and the carbon paper to 50 mm.
[0077] The thickness of each layer was 10 to 10000 nm respectively.
Further, the amounts of platinum and the hydrogen ion conductive
polymer electrolyte contained in the catalyst layer having the
layer comprising the catalyst particles and the layer comprising
the hydrogen ion conductive electrolyte were 0.5 mg/cm.sup.2 and
1.2 mg/cm.sup.2 respectively.
[0078] A unit cell as shown in FIG. 2 was assembled as described
below by using the obtained electrode.
[0079] First, a pair of electrodes and a hydrogen ion conductive
polymer electrolyte membrane 20 (trade name: Nafion 112,
manufactured by Du Pont Corp.) were arranged such that the catalyst
layers and the hydrogen ion conductive polymer electrolyte membrane
20 were in contact with each other. Then, the hydrogen ion
conductive polymer electrolyte membrane 20 was sandwiched between
the electrodes and hot-pressed to obtain an electrode-membrane
assembly (MEA). One of the electrodes serves as an anode 18, and
the other serves as a cathode 19. Outsides of the obtained MEA
attached was a hydrogen gas supplying plate 13 having a hydrogen
gas supplying inlet 11 and a hydrogen gas exhausting outlet 12, and
attached was an oxidant gas supplying plate 16 having an oxidant
gas supplying inlet 14 and an oxidant gas exhausting outlet 15.
Lastly, the anode and the cathode of the assembly were connected
with an external circuit 17, thereby to obtain a unit cell A1.
[0080] Discharging test was conducted by respectively supplying a
hydrogen gas and air to the anode and cathode of the unit cell A1.
The cell temperature was set to 75.degree. C., the fuel utilization
rate to 80%, and the air utilization rate to 30%. Furthermore, each
of the gases was humidified so that the dew point of the hydrogen
gas would be 75.degree. C., and the dew point of the air would be
65.degree. C. The current-voltage characteristic of the unit cell
A1 is shown in FIG. 3.
EXAMPLE 2
[0081] The inks A1 and B1 were alternately sprayed twice each on
one side of carbon paper having a thickness of 250 .mu.m to form a
catalyst layer. It should be noted that the amounts of platinum and
the hydrogen ion conductive polymer electrolyte contained in the
catalyst layer were respectively adjusted to 0.5 mg/cm.sup.2 and
1.2 mg/cm.sup.2, which were the same as those in Example 1. Then, a
unit cell B1 shown in FIG. 2 was assembled and discharging test was
conducted in the same manner as in Example 1. The current-voltage
characteristic of the unit cell B1 is shown in FIG. 3.
EXAMPLE 3
[0082] The inks A1 and B1 were alternately sprayed five times each
on one side of carbon paper having a thickness of 250 .mu.m to form
a catalyst layer. It should be noted that the amounts of platinum
and the hydrogen ion conductive polymer electrolyte contained in
the catalyst layer were respectively adjusted to 0.5 mg/cm.sup.2
and 1.2 mg/cm.sup.2, which were the same as those in Example 1.
Then, a unit cell C1 shown in FIG. 2 was assembled and discharging
test was conducted in the same manner as in Example 1. The
current-voltage characteristic of the unit cell C1 is shown in FIG.
3.
Comparative Example 1
[0083] An ink C1 was obtained by previously mixing the inks A1 and
B1. Then, the ink C1 was sprayed on one side of carbon paper having
a thickness of 250 .mu.m to form a catalyst layer. It should be
noted that the amounts of platinum and the hydrogen ion conductive
polymer electrolyte contained in the catalyst layer were
respectively adjusted to 0.5 mg/cm.sup.2 and 1.2 mg/cm.sup.2, which
were the same as those in Example 1. Then, a unit cell X1 shown in
FIG. 2 was assembled and discharging test was conducted in the same
manner as in Example 1. The current-voltage characteristic of the
unit cell X1 is shown in FIG. 3.
[0084] FIG. 3 indicates that the characteristics of the unit cells
A1, B1 and C1 are significantly excellent as compared with the unit
cell X1 despite the amounts of platinum and the hydrogen ion
conductive polymer electrolyte contained in the catalyst layer are
the same. This is considered to be because the catalyst particles
were in contact with the layer comprising a hydrogen ion conductive
polymer electrolyte, thereby the reaction area was enlarged and
hydrogen ions were transferred with high efficiency. Further, the
thickness of the layer comprising a hydrogen ion conductive polymer
electrolyte was about from 10 to 10000 nm; which corresponds to the
thickness of a monomolecular film. Accordingly, it is conceivable
that the hydrogen ion conductive polymer electrolyte permeates into
the inside of the micropores of the carbon powder in the catalyst
layers of the unit cells A1, B1 and C1. This means that the
platinum carried inside of the micropores of the carbon powder was
covered with the hydrogen ion conductive polymer electrolyte,
contributing to the reaction effectively.
[0085] In Examples 1 to 3 and Comparative Example 1, incidentally,
the amount of hydrogen ion conductive polymer electrolyte contained
in the catalyst layer was 1.2 mg/cm.sup.2, but the similar
characteristics were also obtained in the range of 0.1 to 3.0
mg/cm.sup.2.
EXAMPLE 4
[0086] A carbon powder (Acetylene black, approx. 50 nm mean primary
particle size) was immersed in an aqueous solution of
chloroplatinic acid, and then subjected to a reduction treatment,
thereby platinum (30 .ANG. mean particle size) was made carried on
the surface of the carbon powder. The weight ratio of the carbon
powder to the carried platinum was 75:25.
[0087] The obtained carbon powder carrying platinum, an ethanol
dispersion containing 9 wt % hydrogen ion conductive polymer
electrolyte (trade name: Flemion, manufactured by ASAHI GLASS CO.,
Ltd.) and 2-propanol were mixed in a weight ratio of 6:50:44, and
stirred well using a ball mill to obtain an ink A2.
[0088] Likewise, an ethanol dispersion containing 9 wt % hydrogen
ion conductive polymer electrolyte (trade name: Flemion,
manufactured by ASAHI GLASS CO., Ltd.) and 2-propanol were mixed in
a weight ratio of 1:1 to obtain an ink B2.
[0089] Next, the inks A2 and B2 were sprayed on one side of carbon
paper (trade name: TGPH-120, manufactured by TORAY INDUSTRIES,
INC.) as described below by using a spray application device as
shown in FIG. 4 to obtain an electrode.
[0090] First, the ink A2 was poured into a container 1A and
constantly stirred with a stirring blade. Likewise, the ink B2 was
poured into a container 1B and constantly stirred with a stirring
blade. Then, the ink A2 in the container 1A was introduced with
pressure to a nozzle 3A by a pump 2A, and the ink A2 was sprayed
from the nozzle 3A in an oblique downward direction. The remaining
of the ink A2, which was not sprayed from the nozzle 3A, was
circulated to collect in the container 1A. Likewise, the ink B2 in
the container 1B was introduced with pressure by a pump 2B to a
nozzle 3B placed on the opposite side of the nozzle 3A, and the ink
B2 was sprayed from the nozzle 3B in an opposite oblique downward
direction to the spraying direction of the ink A2. The remaining of
the ink B2, which was not sprayed from the nozzle 3B, was
circulated to collect in the container 1B. It should be noted that
the tips of the nozzles 3A and 3B were located in the same height,
and the distance between the nozzle tips was set to 0.8 m.
[0091] Next, carbon paper 21 was placed on a chassis 23, and the
chassis 23 was moved to the nozzle 3B side from directly below the
nozzle 3A. Incidentally, the moving velocity was set to 1.5
cm/sec., and the vertical length between the nozzle tip and the
carbon paper was set to 20 cm. Further, a frame 22 for masking,
which was cut into a 60.times.60 mm square, was disposed on the
carbon paper.
[0092] An MEA was assembled in the same manner as in Example 1 by
using the obtained electrode. The obtained MEA was sandwiched
between a pair of electroconductive separators comprising a carbon
material. A gas channel having a width of 2 mm and a depth of 1 mm
was formed by cutting on the surface, which was supposed to be in
contact with the electrode, of each separator. Each separator has a
thickness of 4 mm.
[0093] Then, a metal end plate (SUS 304) was disposed outside of
each separator and manifolds were attached at a pair of facing
sides of the MEA via an insulator and a gasket, thereby to obtain a
unit cell A2. Then, hydrogen, air and cooling water were supplied
and exhausted through the manifold.
[0094] Discharging test was conducted by respectively supplying a
hydrogen gas and air to the anode and cathode of the unit cell A2.
The cell temperature was set to 80.degree. C., the fuel utilization
rate was set to 90%, and the air utilization rate was set to 40%.
Furthermore, each of the gases was humidified so that the dew point
of the hydrogen gas would be 75.degree. C., and the dew point of
the air would be 60.degree. C. The current-voltage characteristic
of the unit cell A2 is given in FIG. 5.
EXAMPLE 5
[0095] The inks A2' and B2' having the same ingredient compositions
as the inks A2 and B2 and half amount of the dispersion media of
the inks A2 and B2 were prepared. Then, an electrode was produced
as described below using the inks A2' and B2' by means of a common
screen printing method. The reason why the amount of the dispersion
media of the inks was reduced herein was to make the viscosity
suitable for the screen printing.
[0096] First, the ink A' was printed on carbon paper using a
100-mesh screen. After this was dried at 60.degree. C., the ink B'
was screen printed in the same manner as described earlier.
Subsequently, it was sufficiently dried at 60.degree. C. to remove
the solvent therefrom, thereby obtaining an electrode. After that,
a unit cell B2 was obtained in the same manner as in Example 4 by
using the obtained electrode. And discharging test was conducted in
the same manner as in Example 4. The current-voltage characteristic
of the unit cell B2 is shown in FIG. 5.
Comparative Example 2
[0097] Only the ink A' was printed on carbon paper using a 100-mesh
screen. After that, it was sufficiently dried at 60.degree. C. to
remove the solvent therefrom to obtain an electrode. Consequently,
a unit cell C2 was obtained in the same manner as in Example 4
using the obtained electrode. Then, discharging test was conducted
in the same manner as in Example 4. The current-voltage
characteristic of the unit cell C2 is shown in FIG. 5.
[0098] FIG. 5 indicates that the unit cells A2 and B2 are more
excellent in characteristics as compared with the unit cell C2.
[0099] Schematic sectional views of each electrode of the unit
cells A2, B2 and C2 are given in FIG. 6. In FIG. 6, a black dot
represents the hydrogen ion conductive polymer electrolyte. FIG. 6
shows that the hydrogen ion conductive polymer electrolyte is
gradually decreased in a thickness direction of the electrode
toward the carbon paper 25 from the surface of the electrode in the
catalyst layer 24 of the unit cell A2. Such a structure can be
obtained by spraying two kinds of inks onto carbon paper using a
spray application device as shown in FIG. 4. It is considered to be
because the amount of the hydrogen ion conductive polymer
electrolyte applied on the carbon paper was increased as the carbon
paper was moved to the nozzle 3B side.
[0100] On the other hand, the catalyst layer 24 of the unit cell B2
is divided into a layer 26 having a large amount of the ion
conductive polymer electrolyte and a layer 27 having a small amount
of the ion conductive polymer electrolyte. Further, it can be seen
that the hydrogen ion conductive polymer electrolyte is distributed
evenly in the whole catalyst layer 24 of the unit cell C2.
[0101] These results prove that the electrode in which the amount
of a hydrogen ion conductive polymer electrolyte in the catalyst
layer is large at the hydrogen ion conductive polymer electrolyte
membrane side and is small at the gas diffusion layer side has
excellent characteristic as compared with conventional
electrodes.
[0102] It should be noted that a spray application method was used
in Example 4 as a method for making the amount of the hydrogen ion
conductive polymer electrolyte seamlessly varied in the thickness
direction but methods other than this can also be used.
[0103] When the amount of a hydrogen ion conductive polymer
electrolyte in the catalyst layer is made varied in the thickness
direction, for example, the amount of the hydrogen ion conductive
polymer electrolyte may be small at the hydrogen ion conductive
polymer electrolyte membrane side and large at the gas diffusion
layer side contrary to Example 4 from the view point of providing
corrosion resistance against CO.
EXAMPLE 6
[0104] A carbon powder (Acetylene black, approx. 50 nm mean primary
particle size) was immersed in an aqueous solution of
chloroplatinic acid, and then subjected to a reduction treatment,
thereby platinum (30 .ANG. mean particle size) was made carried on
the surface of the carbon powder. The weight ratio of the carbon
powder to the carried platinum was 75:25.
[0105] The obtained carbon powder carrying platinum, a carbon
powder carrying 5 wt % polytetrafluoroethylene, an ethanol
dispersion containing 9 wt % polymer electrolyte (trade name:
Flemion, manufactured by ASAHI GLASS CO., Ltd.) and 2-propanol were
mixed in a weight ratio of 6:3:50:41, and stirred well using a ball
mill to obtain an ink C2.
[0106] Likewise, a carbon powder carrying 5 wt %
polytetrafluoroethylene, an ethanol dispersion containing 9 wt %
polymer electrolyte (trade name: Flemion, manufactured by ASAHI
GLASS CO., Ltd.) and 2-propanol were mixed in a weight ratio of
3:50:47 to obtain an ink D2.
[0107] Next, an electrode was produced in the same manner as in
Example 4 by using the spray application device to obtain a unit
cell D2. Then, the same discharging test as Example 4 was
conducted. The current-voltage characteristic of the unit cell D2
is shown in FIG. 7.
[0108] FIG. 7 indicates that the unit cell D2 is more excellent in
characteristic as compared with the unit cell A2. This is
considered to be because the water generated in the catalyst layer
was efficiently exhausted since the carbon powder which had been
made water repellent with polytetrafluoroethylene was contained in
the catalyst layer.
EXAMPLE 7
[0109] A carbon powder (approx. 50 nm mean primary particle size)
was immersed in an aqueous solution of chloroplatinic acid, and
then subjected to a reduction treatment, thereby platinum was made
carried on the surface of the carbon powder. The weight ratio of
the carbon powder to the carried platinum was 1:1.
[0110] The obtained carbon powder carrying 50 wt % of platinum, an
ethanol dispersion containing 9 wt % polymer electrolyte (trade
name: Flemion, manufactured by ASAHI GLASS CO., Ltd.) and
2-propanol were mixed in a weight ratio of 6:50:44, and stirred
well using a ball mill to obtain a slurry A3.
[0111] Next, a unit cell shown in FIG. 8 was constituted as
described below.
[0112] First, carbon paper having a thickness of 180 .mu.m, a
length of 20 cm, a width of 10 cm and a porosity of 75% was
prepared, and the slurry A3 was applied evenly on one side of the
carbon paper to form a catalyst layer 2; thereby an electrode
precursor was obtained. Then, a hydrogen ion conductive polymer
electrolyte membrane 1 (trade name: Nafion 112, manufactured by Du
Pont Corp.), which was one size larger than the electrode
precursor, was sandwiched between a pair of the electrode
precursors such that the catalyst layer and the hydrogen ion
conductive polymer electrolyte membrane were in contact. Then,
silicon rubber gaskets 9 having a thickness of 250 .mu.m were
disposed on both sides of the protruded portion of the hydrogen ion
conductive polymer electrolyte membrane from the electrode;
subsequently it was hot pressed at 130.degree. C. for 5 minutes to
obtain an MEA precursor. Finally, carbon paper 3" having a
thickness of 180 .mu.m, a length of 20 cm, a width of 10 cm and a
porosity of 90% was placed outside of carbon paper 3' of the MEA
precursor to obtain an MEA 5.
[0113] Next, electroconductive separators 7 were attached outsides
of the carbon paper 3" of the MEA to obtain a unit cell. Then, the
same four unit cells were laminated to form a stack cell. The
electroconductive separators were made of a carbon material, and
had a thickness of 4 mm and gas tightness. Further, a gas channel 6
having a width of 2 mm and a depth of 1 mm was formed by cutting on
the surface, which was supposed to be in contact with the carbon
paper 3", of the electroconductive separators.
[0114] Next, a fuel cell shown in FIG. 9 was assembled. FIG. 9
shows a sectional view close to the front so that the internal
structure of the fuel cell can be seen.
[0115] First, metal end plates 31 (SUS 304) were disposed on the
upper and lower sides of the stack cell, and insulators 32 were
disposed at both sides of the stack cell. Next, fuel gas manifolds
34, cooling water manifolds 35 and oxidant gas manifolds 36 were
placed in parallel outsides of the insulators 32 via gaskets 33.
Then, hydrogen, cooling water and air were respectively supplied
through the fuel gas manifolds 34, the cooling water manifolds 35
and the oxidant gas manifolds 36. The obtained fuel cell is
represented by a cell A3.
[0116] It should be noted that gas channels were formed on both
surfaces of the electroconductive separator which was in contact
with the MEAs 5 at both surfaces thereof. Likewise, a cooling water
channel was formed by cutting on the interface 8 where one
electroconductive separator was in contact with the other
electroconductive separator.
[0117] Discharging test was conducted by respectively supplying a
hydrogen gas and air to the anode and cathode of the unit cell A3.
The cell temperature was set to 75.degree. C., the fuel utilization
rate to 70%, and the air utilization rate to 40%. Furthermore, each
of the gases was humidified so that the dew point of the hydrogen
gas would be 75.degree. C., and the dew point of the air would be
65.degree. C.. The current-voltage characteristic of the fuel cell
A3 is shown in FIG. 10.
[0118] Further, the relation between oxygen utilization rate and
voltage at a current density of 0.7 A/cm.sup.2 was evaluated. The
results are shown in FIG. 11.
Comparative Example 3
[0119] A fuel cell B3 was assembled and the evaluation was made in
the same manner as in Example 7, except that the carbon paper 3"
having a porosity of 90% was used singly. The results are given in
FIGS. 10 and 11.
Comparative Example 4
[0120] A fuel cell C3 was assembled and the evaluation was made in
the same manner as in Example 7, except that the carbon paper 3'
having a porosity of 75% was used singly. The results are shown in
FIGS. 10 and 11.
[0121] FIGS. 10 and 11 indicate that the fuel cell A3 is excellent
in characteristics as compared with B3 and C3. This is considered
to be because the polymer electrolyte of the fuel cell A3 was kept
wet and excessive water due to generated water was rapidly
delivered.
EXAMPLE 8
[0122] A fuel cell D3 was assembled and the evaluation was made in
the same manner as in Example 7, except that carbon paper having a
thickness of 360 .mu.m and a porosity of 90% was used singly as the
gas diffusion layer at the anode side and the same gas diffusion
layer as that in Example 7, which was made by laminating two sheets
of carbon paper of different kinds having different porosities, was
employed as the gas diffusion layer at the cathode side which
serves to exhaust the generated water. The results are given in
[0123] FIGS. 12 and 13 along with that of the fuel cell A3.
[0124] FIGS. 12 and 13 indicate that the fuel cell D3 also has the
similar characteristic as the fuel cell A3.
EXAMPLE 9
[0125] Before the slurry containing the carbon powder carrying
platinum was applied onto the carbon paper having a porosity of
75%, the catalyst layer side of the carbon paper had been made
water repellent. To be specific, carbon paper 3' having a thickness
of 180 .mu.m and a porosity of 75%, which was cut into a length of
20 cm and a width of 10 cm, was immersed in an aqueous dispersion
containing a copolymer of tetrafluoroethylene and
hexafluoropropylene, and then it was heated at 400.degree. C. for
30 minutes to give water repellency to the carbon paper. A fuel
cell E3 was assembled in the same manner as in Example 7 except
those mentioned above.
[0126] Next, the relation between oxygen utilization rate and
voltage at a current density of 0.7 A/cm.sup.2 was evaluated in the
same manner as in Example 7 except that air was humidified so that
the dew point at the cathode side would be 50.degree. C. The result
is shown in FIG. 14 along with that of the fuel cell A3.
[0127] FIG. 14 suggests that the fuel cell E3 also has the similar
characteristic as the fuel cell A3. Further, when the air having a
low dew point is supplied, there is fear that the cathode side
dries; however, it has been confirmed that the water repellent
treatment as mentioned above is effective.
[0128] Industrial Applicability
[0129] In a polymer electrolyte fuel cell in accordance with the
present invention, since at least either of hydrogen ion
conductivity and gas permeability of at least either of an anode
and a cathode varies in a thickness direction of the anode or the
cathode, the reaction area is enlarged and hydrogen ions and
electrons can move smoothly in a thickness direction of the
catalyst layer; as a result, a hydrogen ion conductive polymer
electrolyte membrane in an electrode is kept wet and excessive
water due to the generated water is rapidly delivered. Therefore,
the present invention can realize a polymer electrolyte fuel cell
having excellent characteristics.
* * * * *