U.S. patent application number 11/984907 was filed with the patent office on 2008-04-10 for polymer electrolyte fuel cell and production method of the same.
This patent application is currently assigned to MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.. Invention is credited to Teruhisa Kanbara, Junji Morita, Yasushi Sugawara, Makoto Uchida, Eiichi Yasumoto, Akihiko Yoshida.
Application Number | 20080085440 11/984907 |
Document ID | / |
Family ID | 27346183 |
Filed Date | 2008-04-10 |
United States Patent
Application |
20080085440 |
Kind Code |
A1 |
Yasumoto; Eiichi ; et
al. |
April 10, 2008 |
Polymer electrolyte fuel cell and production method of the same
Abstract
A polymer electrolyte fuel cell comprising: a hydrogen
ion-conductive polymer electrolyte membrane; an anode and a cathode
with the electrolyte membrane interposed therebetween; an
anode-side conductive separator having a gas flow channel for
supply of a fuel gas to the anode; and a cathode-side conductive
separator having a gas flow channel for supply of an oxidant gas to
the cathode, wherein each of the anode and the cathode comprises at
least a catalyst layer in contact with the electrolyte membrane and
a gas diffusion layer in contact with the catalyst layer and the
separator, and at least one of the anode and the cathode contains a
compound represented by the formula (I):
R.sub.1--O--{(C.sub.2H.sub.4O).sub.n--(C.sub.3H.sub.6O).sub.m}--R.sub.2
(I) where R.sub.1 and R.sub.2 are independent of each other and
each represents a hydrogen atom or an alkyl group having not less
than 5 and not more than 15 carbon atoms, n and m are integers
which satisfy 0.ltoreq.n.ltoreq.5, 0.ltoreq.m.ltoreq.5 and
1.ltoreq.n+m.ltoreq.5, and when neither n nor m is 0, at least one
of the ethylene oxide group and at least one of the propylene oxide
group are arranged in a random fashion.
Inventors: |
Yasumoto; Eiichi;
(Soraku-gun, JP) ; Yoshida; Akihiko; (Osaka,
JP) ; Uchida; Makoto; (Osaka, JP) ; Morita;
Junji; (Osaka, JP) ; Sugawara; Yasushi;
(Osaka, JP) ; Kanbara; Teruhisa; (Osaka,
JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, NW
WASHINGTON
DC
20005-3096
US
|
Assignee: |
MATSUSHITA ELECTRIC INDUSTRIAL CO.,
LTD.
Osaka
JP
|
Family ID: |
27346183 |
Appl. No.: |
11/984907 |
Filed: |
November 26, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10372945 |
Feb 26, 2003 |
7316860 |
|
|
11984907 |
Nov 26, 2007 |
|
|
|
PCT/JP02/02044 |
Mar 5, 2002 |
|
|
|
10372945 |
Feb 26, 2003 |
|
|
|
Current U.S.
Class: |
429/492 ;
429/514; 429/528; 429/532 |
Current CPC
Class: |
H01M 4/92 20130101; H01M
4/8828 20130101; H01M 4/926 20130101; H01M 2300/0082 20130101; H01M
4/8807 20130101; H01M 4/8821 20130101; H01M 8/1004 20130101; Y02E
60/50 20130101; H01M 4/8605 20130101; Y02P 70/50 20151101 |
Class at
Publication: |
429/030 ;
429/039 |
International
Class: |
H01M 8/10 20060101
H01M008/10; H01M 8/04 20060101 H01M008/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 7, 2001 |
JP |
JP2001-063057 |
Mar 15, 2001 |
JP |
JP2001-073730 |
Mar 23, 2001 |
JP |
JP2001-084770 |
Claims
1-6. (canceled)
7. A polymer electrolyte fuel cell comprising: a hydrogen
ion-conductive polymer electrolyte membrane; an anode and a cathode
with said electrolyte membrane interposed therebetween; an
anode-side conductive separator having a gas flow channel for
supply of a fuel gas to said anode; and a cathode-side conductive
separator having a gas flow channel for supply of an oxidant gas to
said cathode, wherein each of said anode and said cathode comprises
at least a catalyst layer in contact with said electrolyte membrane
and a gas diffusion layer in contact with said catalyst layer and
said separator, and at least one of said catalyst layers of said
anode or cathode comprises at least one oxide containing at least
one metal selected from the group consisting of silicon, titanium,
aluminum, zirconium, magnesium and chromium in an amount of 1 to
10,000 ppm with respect to a total solid particulate material
remaining in said catalyst layer of said anode or said cathode,
wherein said total solid particulate material comprises carbon
particles carrying catalyst particles thereon and a hydrogen ion
conductive polymer electrolyte.
Description
FIELD OF INVENTION
[0001] The present invention relates to a polymer electrolyte fuel
cell which directly uses a gaseous fuel such as a hydrogen gas or a
liquid fuel such as methanol, ethanol or dimethyl ether and an
oxidant such as air or oxygen, and particularly relates to the
electrode thereof.
BACKGROUND OF THE INVENTION
[0002] A typical structure of a conventional polymer electrolyte
fuel cell will be described:
[0003] A fuel cell using a polymer electrolyte generates electric
power and heat simultaneously by electrochemical reaction of a fuel
gas containing hydrogen with an oxidant gas containing oxygen such
as air.
[0004] FIG. 1 shows a schematic sectional view of an electrolyte
membrane-electrode assembly (MEA) 15 of the polymer electrolyte
fuel cell. The MEA comprises a hydrogen ion-conductive polymer
electrolyte membrane 11 and a pair of electrodes 14 arranged on
both sides of the electrolyte membrane 11. Each of the electrodes
comprises a catalyst layer 12 in contact with the electrolyte
membrane 11 and a gas diffusion layer 13 in contact with the
catalyst layer 12. The catalyst layer 12 is formed from a mixture
of the hydrogen ion-conductive polymer electrolyte and carbon
particles carrying platinum-group metal catalyst particles
thereon.
[0005] The electrolyte membrane 11 used in the present invention is
a copolymer of perfluorocarbon sulfonic acid and
polytetrafluoroethylene (hereinafter referred to as perfluorocarbon
sulfonic acid), for example, a Nafion film produced by Du Pont in
the US, and the like having the following formula: ##STR1## wherein
5.ltoreq.x.ltoreq.13.5, y=1000, m=1 and n=2.
[0006] The gas diffusion layer 13 used is a conductive porous
substrate such as carbon paper having gas permeability. The
conductive porous substrate may be made water-repellent.
[0007] A sealing member such as a gasket is arranged around the
electrode 14 with the electrolyte membrane 11. The sealing member
is intended to prevent the fuel gas and the oxidant gas for supply
to the electrodes from being leaked to the outside or mixed with
each other. The sealing member is integrated with the MEA.
[0008] FIG. 2 shows a schematic sectional view of a unit cell 23 of
the polymer electrolyte fuel cell. The unit cell 23 comprises the
MEA 15 and a pair of conductive separators 21 arranged on both
sides of the MEA. The conductive separator 21 serves to
mechanically fix the MEA. On the face of the separator 21 in
contact with the MEA 15 formed is a gas flow channel 22 for
supplying the fuel gas or the oxidant gas to the electrode and
carrying away redundant gas and water produced through an electrode
reaction. Although the gas flow channel 22 can be provided
independently of the separator 21, a typical process is to arrange
a groove in the surface of the separator so as to form the gas flow
channel 22. By supplying the fuel gas to one gas flow channel and
supplying the oxidant gas to the other gas flow channel,
electromotive force of about 0.8 V can be generated out of one unit
cell 23.
[0009] Normally, plural unit cells 23 are connected in series to
obtain a voltage of several volts to several hundreds volts.
Therefore, the gas flow channels 22 are formed on both faces of the
separator 21, and then the unit cells are connected in series in
order: separator/MEA/separator/MEA.
[0010] The gas is supplied to the gas flow channel through a
manifold. There are two types of manifolds: a manifold connecting
several branches of a gas supply pipe directly to the gas flow
channel (called an external manifold) and manifold in the form of
trough holes, arranged through the separator with the gas flow
channel and communicating with the inlet and outlet of the gas flow
channel (called an internal manifold).
[0011] Next, three functions of the gas diffusion layer will be
described:
[0012] First, the gas diffusion layer has the function of diffusing
the gas in order to supply the fuel gas or the oxidant gas
uniformly to the catalyst particles in the catalyst layer.
[0013] Secondly, the gas diffusion layer has the function of
promptly carrying away water produced in the catalyst layer into
the gas flow channel.
[0014] Thirdly, the gas diffusion layer has the function of
conducting electrons involved in the reaction.
[0015] The gas diffusion layer is required to have excellent gas
permeability, steam permeability and conductivity. Conventionally,
therefore, the gas diffusion layer has been made from a conductive
porous substrate with pores developed therein such as carbon paper,
carbon cloth or carbon felt in order to secure the gas
permeability. The steam permeability is secured by dispersing
water-repellent polymers in the gas diffusion layer. Further, the
conductivity is secured by using a conductive material such as
carbon fiber, metal fiber or a carbon fine powder for the gas
diffusion layer.
[0016] Next, four functions of the catalyst layer will be
described:
[0017] Firsts the catalyst layer has the function of supplying the
fuel gas or the oxidant gas supplied from the gas diffusion layer
to a reaction site.
[0018] Secondly, the catalyst layer has the function of promptly
conducting hydrogen ions involved in the reaction to the
electrolyte membrane.
[0019] Thirdly, the catalyst layer has the function of conducting
electrons involved in the reaction.
[0020] Fourthly, the catalyst layer has the function of promptly
advancing a redox reaction by providing a large reaction area and a
highly-active catalyst.
[0021] The catalyst layer is required to have excellent gas
permeability, hydrogen ion permeability and conductivity, but also
to provide an excellent reaction site for the reaction.
Conventionally, therefore, the gas permeability is secured by
forming a catalyst layer precursor from a mixture of a
pore-producing agent and carbon particles with pores developed
therein, and removing the pore-producing agent. The hydrogen ion
permeability is secured by dispersing the polymer electrolyte in
the vicinity of the catalyst particles to form a hydrogen
ion-conductive network. Further, the conductivity is secured by
forming a catalyst carrier from a conductive material such as
carbon particles or carbon fiber. Moreover, by making
several-nm-size fine catalyst particles comprising a platinum-group
metal on a carrier, the dispersibility of the catalyst particles in
the catalyst layer are enhanced, enabling provision of a favorable
reaction site.
[0022] The following problems exist concerning the electrode of the
conventional fuel cell:
[0023] First, there is a problem that the gas permeability, steam
permeability and conductivity of the electrode are properties
mutually contradictory. For example, when the gas diffusion layer
is made of carbon fiber with a small diameter or the porosity of
the gas diffusion layer is increased in order to enhance the gas
permeability of the electrode, the conductivity of the gas
diffusion layer decreases. When the water-repellent polymers are
added to the gas diffusion layer in order to enhance the steam
permeability, the gas permeability and conductivity of the gas
diffusion layer decrease. Thus, there is a need to make the
mutually contradictory properties compatible by forming the gas
diffusion layer, not from a single material, but from a combination
of a layer comprising the carbon fiber and a layer comprising the
carbon particles and the water-repellent polymers. Also it has been
proposed to use of a surfactant to obtain a favorable dispersed
state of the carbon particles and the water-repellent polymers. For
example, the conventional process for producing the gas diffusion
layer comprises the steps of preparing a water-repellent ink which
includes carbon particles, water-repellent polymers, a surfactant
and a dispersion medium and applying the water-repellent ink to the
conductive porous substrate has been studied. There are, however,
few examples of detailed studies regarding the effect of the
surfactant.
[0024] Japanese Laid-Open Patent Publication No. Hei 11-335886,
Japanese Laid-Open Patent Publication No. Hei 11-269689, Japanese
Laid-Open Patent Publication No. Hei 11-50290, Japanese Laid-Open
Patent Publication No. Hei 10-092439 and Japanese Laid-Open Patent
Publication No. Hei 6-116774 disclose octyl phenol ethoxylate
belonging to alkylphenol group as the surfactant for dispersing the
water-repellent polymers in the water-repellent ink. Further,
Japanese Laid-Open Patent Publication No. Hei 64036771 discloses:
anionic surfactants such as fatty acid soap, alkylbenzene
sulfonate, alkylaryl sulfonate and alkylnaphthalene sulfonate;
cationic surfactants such as alkylamine salt, amide-bonded amide
salt, ester-bonded amine salt, alkylammonium salt, aide-bonded
ammonium salt, ester-bonded ammonium salt, ether-bonded ammonium
salt, alkylpyridinium salt and ester-bonded pyridinium salt;
amphoteric surfactants such as a long-chain alkylamino acid; and
nonionic surfactants such as alkyl aryl ether, alkyl ether,
alkylamine fatty acid glyceric ester, anhydro sorbitol fatty acid
ester, polyethylene imine and fatty acid alkylolamide. In the
examples of the above documents, however, only octyl phenol
ethoxylate belonging to alkylphenol was studied. Therefore, the
above documents simply introduce a variety of common surfactants
extensively, and effects of these surfactants when used for an
electrode of a fuel cell are unclear.
[0025] Surfactants of alkylphenol group are environmental hormones
suspected of having the endocrine-disrupting function. For this
reason, such surfactants raise a safety issue, safety of the
production of the electrode and the MEA, safety of a final product
in a case where a trace quantity of alkylphenol is left, and safety
in waste disposal of the final product. In order to reduce these
safety hazard, extraction of the surfactant by solvent is
necessary. However, this extraction requires liquid waste disposal,
a scrubber and the like, thereby raising a problem of increased
cost.
[0026] Meanwhile, when no surfactant is used, the following problem
may arise. First, the water-repellent polymers do not sufficiently
disperse and are unevenly distributed in the electrode, making it
impossible to control the water content of the electrode and to
secure sufficient electrode strength. Second, since stability of
the water-repellent ink decreases, the solid matter concentration
thereof does not become uniform and a pipe or a pump of an applying
apparatus is clogged with the water-repellent ink in the production
process of the gas diffusion layer. As a result, variation or
defect of a coating of the water-repellent ink occurs, causing the
discharge performance of the electrode to deteriorate.
[0027] Next, there is a problem with the electrode of the
conventional fuel cell that the water content increases with the
passage of time. This is because water is produced through the
electrode reaction, and further, the reaction gas contains water
for humidification. When the water content of the catalyst layer
and the gas diffusion layer increase, micropores as gas channels
become clogged, which causes insufficient supply of the gases to
the electrodes, leading to deterioration in cell performance. On
the other hand, when the humidity of the gas is decreased or
humidification is suspended for a long time, the water content of
the polymer electrolyte and the electrolyte membrane in the MEA
decrease to cause the hydrogen ion-conductive network to
deteriorate, leading to deterioration in cell performance. The
cause of such a phenomenon lies in the difficulty of controlling
the water content of the electrode due to insufficient moisture
retention of the conventionally-used electrode.
[0028] For this reason, Japanese Laid-Open Patent Publication No.
Hei 10-334922 proposes making a moisture retentive agent comprising
sulfuric acid or phosphoric acid contained in the catalyst layer.
Since sulfuric acid and phosphoric acid are apt to vaporize,
control of the water content is difficult. Further, the use of
sulfuric acid or phosphoric acid may raise a further problem,
corrosion of the structural members of the fuel cell system.
Moreover, Japanese Laid-Open Patent Publication No. 2000-251910,
Japanese Laid-Open Patent Publication No. 2001-15137, Japanese
Examined Patent Publication No. Hei 10-52242 and Japanese Laid-Open
Patent Publication No. 2000-340247 disclose a means of controlling
the water content of the catalyst layer and the gas diffusion layer
from the outside of the electrode or the catalyst layer by the use
of a polymer water-absorptive sheet. However, it is not possible to
control local water content of the catalyst layer and the gas
diffusion layer in the method for controlling the water content of
the catalyst layer and the gas diffusion layer from the
outside.
[0029] Next, there is another problem with the electrode of the
conventional fuel cell and that is it is difficult to produce a
catalyst layer with catalyst particles evenly distributed therein.
The catalyst layer is required to simultaneously have high gas
diffusibility, conductivity, catalyst activity and hydrogen ion
permeability. To satisfy this requirement, it is necessary to
evenly distribute the catalyst particles along the plane of the
catalyst layer.
[0030] A typical catalyst layer is formed by applying the catalyst
ink. Examples of the applying method may include a screen-printing
method, a spraying method, a gravure-printing method and a coater
method. The catalyst ink is prepared by mixing carbon particles
carrying catalyst particles thereon, a hydrogen ion-conductive
polymer electrolyte and a dispersion medium such as water or
alcohol. It is common that the catalyst ink is further mixed with a
thickener for facilitating the application.
[0031] Generally, the viscosity of the catalyst ink is measured by
a single shear rate, and in the field of the catalyst ink of the
fuel cell. There have been few detailed studies on thixotropy
conducted by changing the shear rate.
[0032] In Japanese Laid-Open Patent Publication No. Hei 8-235122,
thickeners with a high viscosity such as fluorine-atom-containing
alcohols are used to control the catalyst ink's viscosity. Further,
there also is a method in which a thickener with a high viscosity
such as glycerol is used. Since the thickener needs to be removed
from the catalyst layer, the use of the thickener necessitates
heating of the catalyst layer at high temperature after the
formation thereof. Problems may hence arise in that the hydrogen
ion-conductive polymer electrolyte in the catalyst ink deteriorates
and that the production cost of the electrode increases due to a
high heating temperature of 100.degree. C. or higher.
[0033] As indicated in Japanese Laid-Open Patent Publication No.
Hei 11-16586, there is another method in which catalyst ink is
prepared with no thickener added thereto and the viscosity of the
obtained catalyst ink is adjusted by heating. In this method,
however, it is difficult to control the amount of evaporating
dispersion medium, and thus it is not easy to adjust the viscosity.
Moreover, a problem may arise that the hydrogen ion-conductive
polymer electrolyte in the catalyst ink denatures or agglomerates
in heating.
SUMMARY OF THE INVENTION
[0034] It is an object of the present invention to enhance safety
of a product and a production process of a fuel cell and also to
decrease variation and defect of a coating of water-repellent ink
in the production process by optimizing a surfactant for improving
dispersibility of water-repellent polymers in a gas diffusion layer
of an electrode of a fuel cell.
[0035] It is another object of the present invention to further
enhance cell performance by optimizing the water content of the
electrode of the fuel cell.
[0036] It is still another object of the present invention to
obtain a fuel cell having a catalyst layer with catalyst particles
evenly distributed along the plane thereof by controlling viscosity
of the catalyst ink by means of a solid matter concentration,
without using a thickener nor heating.
[0037] The present invention relates to a polymer electrolyte fuel
cell comprising: a hydrogen ion-conductive polymer electrolyte
membrane; an anode and a cathode with the electrolyte membrane
interposed therebetween; an anode-side conductive separator having
a gas flow channel for supply of a fuel gas to the anode; and a
cathode-side conductive separator having a gas flow channel for
supply of an oxidant gas to the cathode, wherein each of the anode
and the cathode comprises at least a catalyst layer in contact with
the electrolyte membrane and a gas diffusion layer in contact with
the catalyst layer and the separator, and at least one of the anode
and the cathode contains a compound represented by the formula (I):
R.sub.1--O--{(C.sub.2H.sub.4O).sub.n--(C.sub.3H.sub.6O).sub.m}--R.sub.2
(I) where R.sub.1 and R.sub.2 are independent of each other and
each represent a hydrogen atom or an alkyl group having not less
than S and not more than 15 carbon atoms, n and m are integers
which satisfy 0.ltoreq.n.ltoreq.5, 0.ltoreq.m.ltoreq.5 and
1.ltoreq.n+m.ltoreq.5, and when neither n nor m is 0, at least one
of the ethylene oxide group and at least one of the propylene oxide
group are arranged in a random fashion.
[0038] It is preferable that at least one of the anode and the
cathode further comprises at least one oxide containing at least
one metal selected from the group consisting of silicon, titanium,
aluminum, zirconium, magnesium and chromium.
[0039] It is preferable that at least one of the anode and the
cathode contains the metal oxide in an amount of 1 to 10,000
ppm.
[0040] The present invention also relates to a production method of
a polymer electrolyte fuel cell comprising: (a) preparing a
water-repellent ink including carbon particles, carbon fiber or
mixtures thereof; a water-repellent polymer, a surfactant; and a
dispersion medium; (b) preparing a catalyst ink including carbon
particles carrying catalyst particles thereon, a hydrogen
ion-conductive polymer electrolyte and a dispersion medium; (c)
applying the water-repellent ink onto a conductive porous substrate
and evaporating the dispersion medium in the water-repellent ink to
form a gas diffusion layer; (d) forming a catalyst layer with the
catalyst ink; and (e) assembling a unit cell by assembling the gas
diffusion layer, the catalyst layer and a hydrogen ion-conductive
polymer electrolyte membrane, wherein the surfactant used in step
(a) comprises a compound represented by the formula (I):
R.sub.1--O--{(C.sub.2H.sub.4O).sub.n--(C.sub.3H.sub.6O).sub.m}--R.sub.2
(I) where R.sub.1 and R.sub.2 are independent of each other and
each represent a hydrogen atom or an alkyl group having not less
than 5 and not more than 15 carbon atom, n and m are integers which
satisfy 0.ltoreq.n.ltoreq.5, 0.ltoreq.m.ltoreq.5 and
1.ltoreq.n+m.ltoreq.5, and when neither n nor m is 0, at least one
of the ethylene oxide group and at least one of the propylene oxide
group are arranged in a random fashion; wherein the catalyst ink is
a Non-Newtonian liquid having a viscosity of not less than 10 Pas
at a shear rate of 0.1 (1/sec) and a viscosity of not more than 1
Pas at a shear rate of 100 (1/sec).
[0041] It is preferable that step (d) of the process comprises a
step of evaporating the dispersion medium out of a coating formed
with the catalyst ink at a temperature of not lower than 40.degree.
C. and not higher than 100.degree. C.
[0042] It is preferable that the weight ratio of the catalyst
particles, the carbon particles and the polymer electrolyte
contained in the catalyst ink is substantially 1:1:1.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIG. 1 is a schematic sectional view of an MEA of a polymer
electrolyte fuel cell.
[0044] FIG. 2 is a schematic sectional view of a unit cell of the
polymer electrolyte fuel cell.
[0045] FIG. 3 is a pattern view of an applying apparatus for use in
the present invention.
[0046] FIG. 4 is a voltage-operation time characteristic diagram of
a hydrogen-air type fuel cell with the electrode thereof added with
a metal oxide.
[0047] FIG. 5 is a voltage-operation time characteristic diagram of
a direct type methanol fuel cell with the electrode thereof added
with a metal oxide.
[0048] FIG. 6 is a diagram representing the relationship between
the cell voltage and the metal oxide content of the electrode of a
hydrogen-air type fuel cell.
[0049] FIG. 7 is a diagram representing the relationship between
the cell voltage and the metal oxide content of the direct type
methanol fuel cell.
[0050] FIG. 8 is a diagram representing relationship between
viscosities and shear rates of catalyst ink.
[0051] FIG. 9 is a current-voltage characteristic diagram of unit
cells A to E.
[0052] FIG. 10 is a view representing the appearance (a) and the
cross section (b) of the catalyst layers C1 to C5.
[0053] FIG. 11 is a current-voltage characteristic diagram of unit
cells C1 to C5.
DETAILED DESCRIPTION OF THE INVENTION
[0054] A polymer electrolyte fuel cell of the present invention
comprises: a hydrogen ion-conductive polymer electrolyte membrane;
an anode and a cathode with the electrolyte membrane interposed
therebetween; an anode-side conductive separator having a gas flow
channel for supply of a fuel gas to the anode; and a cathode-side
conductive separator having a gas flow channel for supply of an
oxidant gas to the cathode.
[0055] Each of the anode and the cathode comprises a catalyst layer
in contact with the electrolyte membrane and a gas diffusion layer
in contact with the catalyst layer and the separator.
[0056] At least one of the anode and the cathode contains an
alkylene oxide compound represented by the formula (I):
R.sub.1--O--{(C.sub.2H.sub.4O).sub.n--C.sub.3H.sub.6O).sub.m}--R.sub.2
(I) where R.sub.1 and R.sub.2 are independent of each other and
each represent a hydrogen atom or an alkyl group having not less
than 5 and not more than 15 carbon atoms, where n and m are
integers which satisfy 0.ltoreq.n.ltoreq.5, 0.ltoreq.m.ltoreq.5 and
1.ltoreq.n+m.ltoreq.5, and when neither n nor m is 0, at least one
ethylene oxide group and at least one propylene oxide group are
arranged in a random fashion.
[0057] The alkylene oxide compound contributes to the dispersion of
a water-repellent polymer contained in the gas diffusion layer of
at least one of the electrodes. The alkylene oxide compound also
contributes to the dispersion of a binder which may be included in
at least one of the electrodes. The alkylene oxide compound does
not have the disrupting endocrine function. Moreover, an electrode
using this compound has excellent current-voltage characteristics
for the following reasons:
[0058] The gas diffusion layer is produced by applying a
water-repellent ink containing a water-repellent polymer and carbon
particles and/or carbon fibers onto a conductive porous substrate
such as carbon paper or carbon felt. When the alkylene oxide
compound as a surfactant is contained in the water-repellent ink,
the water-repellent polymer and the carbon particles sufficiently
disperse in the ink and are thus not unevenly distributed therein,
thereby implementing advanced control of the water content of the
electrode and also to securing sufficient electrode strength.
Further, since the water-repellent polymer is not unevenly
distributed in the ink, the stability of the water-repellent ink is
increased. As a result, there are fewer instances where a pipe, a
pump or the like is clogged with the solid matter of the ink in
such processes as applying and printing and where the physical
properties of the ink change, resulting in a decrease in variation
or defect of the coating.
[0059] It is preferable that the water-repellent polymer be
contained in the water-repellent ink in an amount of 5 to 40 parts
by weight per 100 parts by weight of carbon material such as carbon
particles, carbon fiber or mixtures thereof. The water-repellent
polymer preferably used is a fluorocarbon resin such as
polytetrafluoroethylene (hereinafter referred to as PTFE) or a
tetrafluoroethylene-hexafluoropropylene copolymer.
[0060] It is preferable that the alkylene oxide compound be
contained in the water-repellent ink in an amount of 1 to 20 parts
by weight per 100 parts by weight of the carbon material.
[0061] It is preferable that the water-repellent ink be applied
onto the conductive porous substrate at a rate of 5 to 40
g/m.sup.2.
[0062] Among the surfactants conventionally in wide use are
substances suspected as having the endocrine-disrupting function
such as alkylphenols. These substances have a phenol group in the
molecule. On the other hand, the alkylene oxide compound used in
the present invention includes neither the phenol group nor has the
endocrine-disrupting function. According to the present invention,
therefore, the water-repellent ink is safer and the gas diffusion
layer is improved. Further, in the case of using a surfactant that
is likely to have an endocrine-disrupting function, an extraction
treatment of the surfactant by solvent, liquid waste disposal, a
scrubber and the like are required for the purpose of securing
safety, as opposed to this, according to the present invention,
such treatments and an apparatus are unnecessary. It is thereby
possible to reduce production cost. Moreover, since there is no
fear of a trace quantity of residual environmental hormone in a
final product, safety of the product can be secured and hence
special waste disposal becomes unnecessary.
[0063] It is preferable for optimization of the wet condition of
the electrode that the anode and/or cathode further comprises an
oxide containing at least one metal selected from the group
consisting of silicon, titanium, aluminum, zirconium, magnesium and
chromium. The oxide may be a composite oxide containing plural
metals. Further, one oxide may be used singly or plural oxides may
be used in combination.
[0064] It is preferable that the anode and/or cathode contain the
metal oxide in an amount of 1 to 10,000 ppm.
[0065] Since the oxide has water retentivity, the wet condition of
the electrode can be controlled by dispersing the particles of the
oxide within micropores in the catalyst layer and the gas diffusion
layer. Namely, because the oxide absorbs redundant water, such a
phenomenon is inhibited as the pores serving as the gas flow
channels in the catalyst layer and the gas diffusion layer are
clogged with a steam added to a reaction gas or water produced
through the electrode reaction. Meanwhile, even when the water
content of the reaction gas is lowered or humidification of the gas
is suspended for a long time, a decrease in hydrogen
ion-conductivity is inhibited due to supply of water from the metal
oxide to the polymer electrolyte and the electrolyte membrane in
the electrode. Thus, the fuel cell is capable of exerting high
performance for a long time.
[0066] Furthermore, differently from the conventional method for
controlling the wet condition of the electrode by the use of the
conventional sheet comprising water-absorbing polymers, the
aforesaid oxide enables control of the wet condition in the local
area of the electrode. Accordingly, partial dryness of the
electrode, or the like, can be prevented, which thus allows a high
gas diffusibility and hydrogen ion-conductivity of the electrode to
be kept over a long period of time.
[0067] The metal oxide can be made of finer particles than those of
conventionally-used polymers such as polyamide, cotton,
polyester/regenerated cellulose, polyester/acrylate, regenerated
cellulose/polychlal and sodium polyacrylate. It is therefore
possible to effectively disperse the oxide particles within the
micropores in the catalyst layer and the gas diffusion layer. For
example, the oxide particles can be arranged in the vicinity of the
polymer electrolyte requiring humidification in contact with the
catalyst particles. Further, since the oxide particles can also be
arranged in the vicinity of the pores inside the electrode which
functions as flow channels of the reaction gas, redundant water is
absorbed into the oxide particles. Thereby, the clogging of the gas
flow channel can be prevented.
[0068] Because oxides such as silica, titania, alumina, zirconia,
magnesia and chromia are chemically very stable. They do not
dissolve in the dispersion medium like the polymer particles and
are resistant to the dispersion medium used in production of the
electrode. Further, in a heat treatment for removing the dispersion
medium and the surfactant, when the oxide is used, a treatment can
be at high temperature of 300.degree. C. or higher. On the other
hand, when the polymer particles are used, a treatment can be at
low temperatures thereby preventing the polymers from being neither
altered nor decomposed.
[0069] It should be noted that, when the oxide is added to the
catalyst layer, a predetermined amount of oxide may be added to the
catalyst ink in advance. When the oxide is added to the gas
diffusion layer, a predetermined amount of oxide may be added to
the water-repellent ink in advance.
[0070] As thus described, an oxide having water retentivity is most
suitable for controlling the wet condition of the electrode at the
microlevel, and furthermore, the use of the oxide widens a range of
conditions in the production process.
[0071] A production method of a fuel cell of the present invention
is described below:
[0072] First, a description will be given to viscosities of liquids
by reference to "Rheology Guide", written and edited by Shoten Oka.
A typical liquid has a constant viscosity regardless of the shear
rate thereof, as long as the temperature thereof is kept at
constant. Such a liquid is called a Newtonian fluid. As opposed to
this, a liquid whose viscosity changes as the shear rate thereof
changes even with the temperature thereof kept at constant is
called a Non-Newtonian fluid.
[0073] Next, a description will be given to the viscosity of the
catalyst ink by taking as an example the case of applying a
catalyst ink 36 onto a substrate 34 with the use of an applying
apparatus 31 as shown in FIG. 3. The catalyst ink 36 is put into a
tank 32 and is applied through nozzle 37 and applying roll 35 onto
the substrate 34 of the gas diffusion layer or the polymer
electrolyte membrane. The substrate 34 is supplied from a wind-off
part 33. The coating formed on the substrate 34 passes through a
drying room 38 and a guide roll 39 to be taken up by a wind-up part
30.
[0074] In a case where the catalyst ink 36 is the Newtonian fluid,
when the viscosity of the ink is excessively low, the ink drips in
applying or the coating extends too much in the width direction
thereof, making it difficult to form an even catalyst layer. On the
other hand, when the viscosity of the catalyst ink 36 is
excessively high, the tip of the nozzle 37 is clogged with the ink
or the coating obtained is uneven or streaks, making it difficult
to form an even catalyst layer.
[0075] However, when the catalyst layer is the Non-Newtonian fluid,
because the catalyst ink 36 passes through a very narrow clearance
near the tip of the nozzle 37, the shear rate becomes higher and
the viscosity of the ink becomes lower, whereby the ink flows
easier. Further, because the shear rate of the ink after the
application thereof onto the substrate 34 is very small, the
viscosity of the ink increases. Thus, a stable coating is formed on
the substrate 34 without the coating dripping or extending in the
width direction thereof.
[0076] Accordingly, by using the catalyst ink of the thixotropic
Non-Newtonian fluid whose viscosity is low at a high shear rate and
high at a low shear rate, instead of using the Newtonian fluid, a
stable catalyst layer can be formed.
[0077] From the aforesaid viewpoint, in the present invention, a
catalyst ink of a Non-Newtonian liquid is prepared having a
viscosity of not less than 10 Pas at a shear rate of 0.1 (1/sec)
and a viscosity of not more than 1 Pas at a shear rate of 100
(1/sec). The Non-Newtonian liquid catalyst ink comprises carbon
particles carrying catalyst particles thereon, a hydrogen
ion-conductive polymer electrolyte and a dispersion medium.
[0078] When the catalyst ink satisfies the above condition, the
shear rate at the tip of the nozzle 37 is high. The viscosity of
the catalyst ink 36 decreases and a coating having an even
thickness is thus formed. Moreover, the coating of the ink after
the application thereof onto the substrate 34 where shear is not
applied, the viscosity increases, and the coating neither drips nor
extends in the width direction thereof.
[0079] It is preferable that the catalyst ink be produced from a
mixture comprising a carbon particles carrying catalyst particles
thereon, a hydrogen ion-conductive polymer electrolyte and a
dispersion medium with the use of a stirring or mixing machine
having grinding/dispersing means such as a bead mill or a ball
mill.
[0080] The shear rate of the catalyst ink can be controlled, for
example, by changing the rate of the solid matter content of the
catalyst ink to the dispersion medium. The shear rate can also be
controlled by changing the composition of the solid matter. For
example, it is preferable that the catalyst ink contains 1 to 10 wt
% of the catalyst particles (e.g., platinum-group metal), 1 to 10
wt % of carbon particles as a carrier of the catalyst particles,
and 1 to 10 wt % of the polymer electrolyte. It is most preferable
that the weight ratio of the catalyst particles, the carbon
particles and the polymer electrolyte in the catalyst ink be
substantially 1:1:1.
[0081] The catalyst ink is applied onto a substrate such as a
hydrogen ion-conductive polymer electrolyte membrane or the gas
diffusion layer, and then the dispersion medium in the catalyst ink
is evaporated to form a catalyst layer. It is preferable that the
step for evaporating the dispersion medium is conducted at a
temperature of not lower than 40.degree. C. and not higher than
100.degree. C., from the viewpoint of preventing the hydrogen
ion-conductive polymer in the catalyst layer from degenerating and
the coating from cracking.
EXAMPLE 1
(i) Production of Gas Diffusion Layer
[0082] 100 parts by weight of acetylene black as conductive carbon
particles (Denka black with a particle size of 35 nm, produced by
DENKI KAGAKU KOGYO KABUSHIKI KAISHA), 10 parts by weight of
alkylene oxide type surfactant represented by the following
formula:
R.sub.1--O--{(C.sub.2H.sub.4O).sub.n--(C.sub.3H.sub.6O.sub.m}--R.sub.2,
and a PTFE aqueous dispersion (D-1E, produced by DAIKIN INDUSTRIES,
LTD.) containing 20 parts by weight of PTFE were mixed to prepare a
water-repellent ink. R.sub.1, R.sub.2, n and m in the formula are
set forth in Tables 1-13 below.
[0083] Next, the water-repellent ink was applied onto the surface
of carbon paper (TGPH060H with a porosity of 75% and a thickness of
180 .mu.m, produced by Toray Industries, Inc.) as a substrate of a
gas diffusion layer at a rate of 30 g/m.sup.2 so that the
water-repellent ink was impregnated in the carbon paper. The carbon
paper with the water-repellent ink impregnated therein was then
placed in an air atmosphere, which was heat-treated at 350.degree.
C. with a hot air dryer to produce a gas diffusion layer.
(ii) Formation of Catalyst Layer
(ii-1) Cathode Side
[0084] 50 parts by weight of platinum particles having a mean
particle size of about 30 angstroms are carried on 100 parts by
weight of conductive carbon particles (Ketjen black EC, produced by
AKZO Chemie in Holland) having a mean primary particle size of 30
nm. The carbon particles carrying the platinum particles thereon
were then mixed with an alcohol dispersion containing 9 wt % of
hydrogen ion-conductive polymer electrolyte to prepare a catalyst
ink for the cathode side. Herein, the carbon particles carrying the
platinum particles thereon were mixed with the dispersion of the
hydrogen ion-conductive polymer electrolyte in a weight ratio of
4:96. The hydrogen ion-conductive polymer electrolyte used was
perfluorocarbon sulfonic acid (Flemion, produced by Asahi Glass
Co., Ltd).
[0085] Subsequently, the catalyst ink for the cathode side was
printed on one face of the gas diffusion layer and on one face of a
hydrogen ion-conductive polymer electrolyte membrane (Nafion 112,
produced by Du Pont in the US) which was a size larger than the gas
diffusion layer, and then dried at 70.degree. C. to each form a
cathode-side catalyst layer with a thickness of 10 .mu.m.
(ii-2) Anode Side
[0086] 25 parts by weight each of platinum particles and ruthenium
particles, both having a mean particle size of about 30 angstroms
were carried on on 100 parts by weight of Ketjen black EC carbon
particles. The carbon particles carrying the platinum particles and
ruthenium particles thereon were then mixed with an alcohol
dispersion containing 9 wt % of hydrogen ion-conductive polymer
electrolyte to prepare a catalyst ink for the anode side. The
carbon particles carrying the platinum particles and the ruthenium
particles thereon were mixed with the dispersion of the hydrogen
ion-conductive polymer electrolyte in a weight ratio of 4:96. The
hydrogen ion-conductive polymer electrolyte used was
perfluorocarbon sulfonic acid (Flemion, produced by Asahi Glass
Co., Ltd).
[0087] The catalyst ink for the anode side was then printed on the
other face of the gas diffusion layer and on the other face of the
hydrogen ion-conductive polymer electrolyte membrane, and then
dried at 70.degree. C. to each form an anode-side catalyst layer
with a thickness of 15 .mu.m.
(iii) Production of MEA
[0088] The cathode-side catalyst layers and the anode-side catalyst
layers were mutually opposed. The hydrogen ion-conductive polymer
electrolyte membrane having the catalyst layers on both sides
thereof was interposed between the gas diffusion layers, each layer
having the catalyst layer on one side thereof, and then hot pressed
to produce an MEA. This is referred to as MEA-1.
(iv) Assembly of Fuel Cell
[0089] A rubber gasket was bonded to the periphery of the
electrolyte membrane of MEA-1 and manifold holes for passage of
cooling water, a fuel gas and an oxidant gas were formed
therethrough.
[0090] Meanwhile, a variety of separators made of phenol
resin-impregnated graphite plate with an external size of 20
cm.times.32 cm, a thickness of 1.3 mm and a depth of the gas flow
channel or cooling water channel thereon of 0.5 mm were
prepared.
[0091] The gas flow channel side of a separator with an oxidant gas
flow channel was on the cathode side of MEA-1, while the gas flow
channel side of a separator with a fuel gas flow channel was on the
anode side of MEA-1, so that the whole was integrated into
constitute a unit cell.
[0092] Subsequently, two unit cells were stacked and then
interposed between a pair of separators with cooling water flow
channels formed thereon such that the cooling water flow channel
sides of the separators were directed inwardly. This pattern was
repeated to produce a cell stack of 100 cells. A current collector
plate made of stainless steel and an insulating plate made of an
electrically-insulating material were arranged on both ends of the
cell stack, and further, with the use of end plates and tie rods,
the whole was fixed. The clamping pressure per area of the
separator was 15 kgf/cm.sup.2. The cell thus produced was referred
to as Cell 1.
(v) Evaluation Test
[0093] A pure hydrogen gas and air were supplied to the anode and
the cathode of Cell 1, respectively, and at a cell temperature of
75.degree. C. and under conditions of a fuel gas utilization rate
(Uf) of 70% and an air utilization rate (Uo) of 40%, a discharge
test was conducted on the cell. The gases were humidified by
passage of the pure hydrogen gas through a bubbler at 60.degree. to
70.degree. C. and by passage of the air through a bubbler at
45.degree. to 70.degree. C.
[0094] The relationship between the parameters R.sup.1, R.sup.2, m
and n in the formula of the surfactant used for Cell 1 and the cell
voltages of Cell 1 at a current density of 0.2 mA/cm.sup.2 are
shown in the following Tables 1 to 13: TABLE-US-00001 TABLE 1
R.sub.1* or H R.sub.2** n m E*** 4 4 1 0 430 5 450 15 320 16 110 5
4 500 5 761 15 783 16 451 15 4 452 5 772 15 789 16 432 16 4 320 5
411 15 489 16 310 H 4 110 5 775 15 792 16 325 4 4 2 0 431 5 455 15
310 16 150 5 4 502 5 741 15 783 16 458 15 4 412 5 782 15 779 16 482
16 4 330 5 401 15 479 16 300 H 4 170 5 785 15 742 16 305 R.sub.1*
Number of carbon atoms in R.sub.1 R.sub.2** Number of carbon atoms
in R.sub.2 E*** Cell voltage
[0095] TABLE-US-00002 TABLE 2 R.sub.1* or H R.sub.2** n m E*** 4 4
3 0 320 5 321 15 110 16 115 5 4 450 5 772 15 755 16 320 15 4 210 5
786 15 750 16 455 16 4 325 5 321 15 441 16 120 H 4 150 5 758 15 786
16 450 4 4 4 0 401 5 321 15 220 16 149 5 4 420 5 765 15 772 16 325
15 4 402 5 758 15 754 16 452 16 4 369 5 485 15 481 16 210 H 4 189 5
756 15 774 16 298 R.sub.1* Number of carbon atoms in R.sub.1
R.sub.2** Number of carbon atoms in R.sub.2 E*** Cell voltage
[0096] TABLE-US-00003 TABLE 3 R.sub.1* or H R.sub.2** n m E*** 4 4
5 0 325 5 441 15 241 16 251 5 4 450 5 784 15 774 16 362 15 4 421 5
756 15 781 16 402 16 4 311 5 328 15 441 16 325 H 4 140 5 781 15 756
16 362 4 4 6 0 251 5 455 15 120 16 100 5 4 150 5 150 15 240 16 320
15 4 381 5 254 15 268 16 247 16 4 147 5 351 15 257 16 361 H 4 189 5
258 15 159 16 357 R.sub.1* Number of carbon atoms in R.sub.1
R.sub.2** Number of carbon atoms in R.sub.2 E*** Cell voltage
[0097] TABLE-US-00004 TABLE 4 R.sub.1* or H R.sub.2** n m E*** 4 4
1 1 358 5 145 15 352 16 234 5 4 481 5 751 15 756 16 458 15 4 551 5
735 15 728 16 458 16 4 368 5 325 15 451 16 321 H 4 325 5 745 15 776
16 451 4 4 2 1 325 5 410 15 352 16 251 5 4 254 5 768 15 751 16 451
15 4 440 5 754 15 752 16 251 16 4 352 5 245 15 256 16 100 H 4 152 5
754 15 745 16 362 R.sub.1* Number of carbon atoms in R.sub.1
R.sub.2** Number of carbon atoms in R.sub.2 E*** Cell voltage
[0098] TABLE-US-00005 TABLE 5 R.sub.1* or H R.sub.2** n m E*** 4 4
3 1 321 5 321 15 351 16 365 5 4 352 5 775 15 742 16 254 15 4 365 5
726 15 746 16 325 16 4 214 5 256 15 352 16 254 H 4 265 5 749 15 784
16 231 4 4 4 1 362 5 254 15 214 16 251 5 4 254 5 724 15 754 16 254
15 4 256 5 785 15 745 16 235 16 4 214 5 236 15 254 16 365 H 4 254 5
766 15 754 16 251 R.sub.1* Number of carbon atoms in R.sub.1
R.sub.2** Number of carbon atoms in R.sub.2 E*** Cell voltage
[0099] TABLE-US-00006 TABLE 6 R.sub.1* or H R.sub.2** n m E*** 4 4
5 1 321 5 325 15 321 16 251 5 4 324 5 225 15 321 16 352 15 4 324 5
325 15 321 16 352 16 4 325 5 412 15 215 16 251 H 4 325 5 214 15 251
16 325 4 4 1 2 326 5 325 15 321 16 352 5 4 324 5 756 15 784 16 125
15 4 235 5 746 15 754 16 325 16 4 265 5 341 15 254 16 321 H 4 210 5
765 15 785 16 365 R.sub.1* Number of carbon atoms in R.sub.1
R.sub.2** Number of carbon atoms in R.sub.2 E*** Cell voltage
[0100] TABLE-US-00007 TABLE 7 R.sub.1* or H R.sub.2** n m E*** 4 4
2 2 100 5 254 15 241 16 256 5 4 254 5 745 15 724 16 321 15 4 325 5
745 15 746 16 256 16 4 452 5 235 15 256 16 120 H 4 251 5 774 15 754
16 231 4 4 3 2 362 5 325 15 214 16 265 5 4 251 5 745 15 756 16 254
15 4 236 5 785 15 745 16 213 16 4 265 5 250 15 23 16 251 H 4 25 5
784 15 722 16 123 R.sub.1* Number of carbon atoms in R.sub.1
R.sub.2** Number of carbon atoms in R.sub.2 E*** Cell voltage
[0101] TABLE-US-00008 TABLE 8 R.sub.1* or H R.sub.2** n m E*** 4 4
4 2 235 5 124 15 23 16 251 5 4 235 5 114 15 123 16 156 15 4 231 5
251 15 325 16 214 16 4 214 5 25 15 321 16 20 H 4 325 5 36 15 251 16
20 4 4 1 3 251 5 254 15 23 16 214 5 4 251 5 754 15 745 16 251 15 4
236 5 774 15 745 16 231 16 4 10 5 25 15 325 16 241 H 4 365 5 745 15
785 16 245 R.sub.1* Number of carbon atoms in R.sub.1 R.sub.2**
Number of carbon atoms in R.sub.2 E*** Cell voltage
[0102] TABLE-US-00009 TABLE 9 R.sub.1* or H R.sub.2** n m E*** 4 4
2 3 365 5 251 15 458 16 25 5 4 241 5 745 15 786 16 252 15 4 457 5
784 15 733 16 251 16 4 325 5 254 15 12 16 25 H 4 265 5 788 15 754
16 521 4 4 3 3 251 5 25 15 145 16 21 5 4 35 5 265 15 25 16 214 15 4
2 5 254 15 325 16 25 16 4 25 5 11 15 25 16 2 H 4 244 5 214 15 2 16
35 R.sub.1* Number of carbon atoms in R.sub.1 R.sub.2** Number of
carbon atoms in R.sub.2 E*** Cell voltage
[0103] TABLE-US-00010 TABLE 10 R.sub.1* or H R.sub.2** n m E*** 4 4
1 4 2 5 25 15 56 16 23 5 4 25 5 745 15 748 16 65 15 4 244 5 754 15
712 16 251 16 4 212 5 25 15 15 16 356 H 4 32 5 754 15 774 16 25 4 4
2 4 32 5 542 15 25 16 21 5 4 35 5 325 15 21 16 25 15 4 2 5 26 15 2
16 251 16 4 25 5 251 15 11 16 235 H 4 21 5 114 15 253 16 21
R.sub.1* Number of carbon atoms in R.sub.1 R.sub.2** Number of
carbon atoms in R.sub.2 E*** Cell voltage
[0104] TABLE-US-00011 TABLE 11 R.sub.1* or H R.sub.2** n m E*** 4 4
0 1 412 5 410 15 120 16 254 5 4 257 5 751 15 762 16 421 15 4 451 5
774 15 775 16 215 16 4 451 5 251 15 254 16 62 H 4 110 5 774 15 784
16 362 4 4 0 2 25 5 254 15 213 16 25 5 4 544 5 751 15 757 16 451 15
4 415 5 778 15 754 16 75 16 4 362 5 25 15 14 16 158 H 4 455 5 774
15 795 16 333 R.sub.1* Number of carbon atoms in R.sub.1 R.sub.2**
Number of carbon atoms in R.sub.2 E*** Cell voltage
[0105] TABLE-US-00012 TABLE 12 R.sub.1* or H R.sub.2** n m E*** 4 4
0 3 325 5 315 15 152 16 14 5 4 455 5 778 15 754 16 320 15 4 215 5
777 15 769 16 451 16 4 325 5 322 15 41 16 45 H 4 455 5 755 15 751
16 444 4 4 0 4 451 5 251 15 25 16 45 5 4 255 5 774 15 771 16 485 15
4 444 5 754 15 758 16 458 16 4 362 5 451 15 211 16 251 H 4 154 5
712 15 722 16 296 R.sub.1* Number of carbon atoms in R.sub.1
R.sub.2** Number of carbon atoms in R.sub.2 E*** Cell voltage
[0106] TABLE-US-00013 TABLE 13 R.sub.1* or H R.sub.2** n m E*** 4 4
0 5 25 5 21 15 214 16 21 5 4 215 5 744 15 754 16 321 15 4 25 5 711
15 721 16 482 16 4 330 5 401 15 479 16 25 H 4 170 5 755 15 741 16
25 4 4 1 5 236 5 251 15 41 16 251 5 4 325 5 25 15 215 16 21 15 4
255 5 211 15 23 16 255 16 4 214 5 233 15 25 16 21 H 4 25 5 362 15
25 16 211 R.sub.1* Number of carbon atoms in R.sub.1 R.sub.2**
Number of carbon atoms in R.sub.2 E*** Cell voltage
[0107] The above results show that, when R.sup.1 and R.sup.2 are
independently hydrogen or an alkyl group having not less than 5 and
not more than 15 carbon atoms, and n and m satisfied
0.ltoreq.n.ltoreq.5, 0.ltoreq.m.ltoreq.5 and 1.ltoreq.n+m.ltoreq.5,
the discharge performance was high and a cell voltage of not less
than 700 mV was obtained. When each parameter was out of the above
range, on the other hand, the cell voltage was not more than 500
mV.
COMPARATIVE EXAMPLE 1
[0108] An MEA was produced in the same manner as in Example 1,
except that, in the production process of the gas diffusion layer,
a surfactant of octyl phenol ethoxylate (Triton X-100, produced by
NAGASE & CO., LTD.) was used in place of the alkylene oxide
type surfactant and D-1 produced by DAIKIN INDUSTRIES, LTD. was
used as a dispersion of PTFE in place of D-1E produced by DAIKIN
INDUSTRIES, LTD. This MEA is referred to as MEA-2. Further, Cell 2
comprising a cell stack of 100 cells was produced in the same
manner as in Example 1, except that MEA-2 was used in place of
MEA-1.
[0109] The same discharge test as in Example 1 was conducted on
Cell 2 and a cell voltage of 735 mV was obtained.
EXAMPLE 2
[0110] By carrying out the same operation as in Example 1 except
that 2 mol/l of a methanol aqueous solution at a temperature of
60.degree. C. was supplied to the anode of Cell 1, a discharge test
was conducted on the cell as a direct type methanol fuel cell. Also
here, humidification was conducted by passage of the air through a
bubbler at 45.degree. to 70.degree. C., and the cell temperature
was set at 75.degree. C. and the air utilization rate (Uo) was set
at 40%.
[0111] The relationship between the parameters R.sup.1, R.sup.2, m
and n in the formula of the surfactant used for Cell 1 and the cell
voltages of Cell 1 at a current density of 0.05 mA/cm.sup.2 are
shown in the following Tables 14 to 26: TABLE-US-00014 TABLE 14
R.sub.1* or H R.sub.2** n m E*** 4 4 1 0 12 5 123 15 12 16 15 5 4 1
5 445 15 415 16 45 15 4 25 5 475 15 412 16 20 16 4 14 5 25 15 0 16
21 H 4 25 5 457 15 458 16 21 4 4 2 0 25 5 12 15 47 16 5 5 4 256 5
485 15 510 16 25 15 4 21 5 447 15 458 16 25 16 4 2 5 36 15 2 16 4 H
4 25 5 456 15 541 16 21 R.sub.1* Number of carbon atoms in R.sub.1
R.sub.2** Number of carbon atoms in R.sub.2 E*** Cell voltage
[0112] TABLE-US-00015 TABLE 15 R.sub.1* or H R.sub.2** n m E*** 4 4
3 0 25 5 1 15 2 16 14 5 4 25 5 485 15 445 16 52 15 4 25 5 455 15
521 16 52 16 4 54 5 52 15 3 16 54 H 4 25 5 458 15 574 16 25 4 4 4 0
21 5 52 15 32 16 4 5 4 25 5 456 15 512 16 47 15 4 251 5 458 15 455
16 25 16 4 52 5 14 15 3 16 25 H 4 25 5 455 15 566 16 25 R.sub.1*
Number of carbon atoms in R.sub.1 R.sub.2** Number of carbon atoms
in R.sub.2 E*** Cell voltage
[0113] TABLE-US-00016 TABLE 16 R.sub.1* or H R.sub.2** n m E*** 4 4
5 0 25 5 21 15 23 16 6 5 4 25 5 455 15 424 16 52 15 4 14 5 510 15
512 16 25 16 4 47 5 32 15 0 16 2 H 4 53 5 451 15 412 16 25 4 4 6 0
21 5 25 15 3 16 52 5 4 256 5 458 15 500 16 321 15 4 52 5 21 15 52
16 3 16 4 25 5 12 15 25 16 1 H 4 25 5 25 15 2 16 0 R.sub.1* Number
of carbon atoms in R.sub.1 R.sub.2** Number of carbon atoms in
R.sub.2 E*** Cell voltage
[0114] TABLE-US-00017 TABLE 17 R.sub.1* or H R.sub.2** n m E*** 4 4
1 1 25 5 12 15 25 16 2 5 4 152 5 451 15 410 16 25 15 4 14 5 421 15
411 16 25 16 4 321 5 25 15 21 16 25 H 4 24 5 451 15 410 16 25 4 4 2
1 25 5 32 15 25 16 25 5 4 1 5 455 15 410 16 25 15 4 325 5 451 15
456 16 25 16 4 214 5 2 15 1 16 0 H 4 255 5 458 15 475 16 254
R.sub.1* Number of carbon atoms in R.sub.1 R.sub.2** Number of
carbon atoms in R.sub.2 E*** Cell voltage
[0115] TABLE-US-00018 TABLE 18 R.sub.1* or H R.sub.2** n m E*** 4 4
3 1 25 5 3 15 25 16 2 5 4 1 5 455 15 475 16 25 15 4 24 5 455 15 465
16 252 16 4 252 5 5 15 23 16 25 H 4 25 5 458 15 471 16 5 4 4 4 1 62
5 58 15 2 16 1 5 4 456 5 512 15 2 16 58 15 4 2 5 412 15 441 16 25
16 4 321 5 25 15 32 16 0 H 4 41 5 412 15 452 16 2 R.sub.1* Number
of carbon atoms in R.sub.1 R.sub.2** Number of carbon atoms in
R.sub.2 E*** Cell voltage
[0116] TABLE-US-00019 TABLE 19 R.sub.1* or H R.sub.2** n m E*** 4 4
5 1 6 5 2 15 0 16 0 5 4 0 5 25 15 2 16 3 15 4 0 5 0 15 0 16 25 16 4
0 5 0 15 35 16 0 H 4 0 5 47 15 2 16 5 4 4 1 2 25 5 21 15 2 16 47 5
4 261 5 455 15 421 16 41 15 4 25 5 412 15 432 16 25 16 4 0 5 2 15 1
16 0 H 4 0 5 485 15 547 16 20 R.sub.1* Number of carbon atoms in
R.sub.1 R.sub.2** Number of carbon atoms in R.sub.2 E*** Cell
voltage
[0117] TABLE-US-00020 TABLE 20 R.sub.1* or H R.sub.2** n m E*** 4 4
2 2 25 5 2 15 0 16 0 5 4 23 5 410 15 410 16 2 15 4 56 5 475 15 466
16 5 16 4 2 5 0 15 0 16 0 H 4 236 5 452 15 496 16 23 4 4 3 2 0 5 0
15 3 16 2 5 4 251 5 462 15 561 16 23 15 4 2 5 455 15 412 16 362 16
4 23 5 0 15 0 16 0 H 4 25 5 452 15 468 16 49 R.sub.1* Number of
carbon atoms in R.sub.1 R.sub.2** Number of carbon atoms in R.sub.2
E*** Cell voltage
[0118] TABLE-US-00021 TABLE 21 R.sub.1* or H R.sub.2** n m E*** 4 4
4 2 23 5 0 15 0 16 0 5 4 15 5 0 15 0 16 0 15 4 25 5 0 15 0 16 25 16
4 0 5 0 15 0 16 25 H 4 0 5 0 15 0 16 0 4 4 1 3 235 5 2 15 52 16 2 5
4 254 5 456 15 510 16 25 15 4 251 5 561 15 521 16 25 16 4 25 5 1 15
0 16 0 H 4 362 5 458 15 517 16 331 R.sub.1* Number of carbon atoms
in R.sub.1 R.sub.2** Number of carbon atoms in R.sub.2 E*** Cell
voltage
[0119] TABLE-US-00022 TABLE 22 R.sub.1* or H R.sub.2** n m E*** 4 4
2 3 21 5 0 15 0 16 25 5 4 2 5 451 15 482 16 213 15 4 25 5 469 15
458 16 214 16 4 23 5 25 15 0 16 0 H 4 256 5 475 15 496 16 51 4 4 3
3 23 5 0 15 0 16 0 5 4 41 5 0 15 0 16 25 15 4 0 5 0 15 251 16 0 16
4 0 5 25 15 0 16 0 H 4 0 5 32 15 0 16 0 R.sub.1* Number of carbon
atoms in R.sub.1 R.sub.2** Number of carbon atoms in R.sub.2 E***
Cell voltage
[0120] TABLE-US-00023 TABLE 23 R.sub.1* or H R.sub.2** n m E*** 4 4
1 4 0 5 25 15 123 16 251 5 4 25 5 451 15 412 16 25 15 4 125 5 451
15 462 16 25 16 4 251 5 2 15 0 16 0 H 4 25 5 451 15 423 16 25 4 4 2
4 32 5 0 15 1 16 2 5 4 0 5 0 15 0 16 0 15 4 0 5 25 15 0 16 0 16 4 0
5 2 15 0 16 0 H 4 0 5 52 15 0 16 0 R.sub.1* Number of carbon atoms
in R.sub.1 R.sub.2** Number of carbon atoms in R.sub.2 E*** Cell
voltage
[0121] TABLE-US-00024 TABLE 24 R.sub.1* or H R.sub.2** n m E*** 4 4
0 1 11 5 13 15 20 16 0 5 4 48 5 441 15 410 16 25 15 4 23 5 410 15
421 16 36 16 4 32 5 25 15 15 16 32 H 4 25 5 455 15 412 16 36 4 4 0
2 36 5 56 15 121 16 56 5 4 254 5 455 15 500 16 25 15 4 62 5 410 15
485 16 26 16 4 69 5 3 15 0 16 0 H 4 25 5 440 15 444 16 21 R.sub.1*
Number of carbon atoms in R.sub.1 R.sub.2** Number of carbon atoms
in R.sub.2 E*** Cell voltage
[0122] TABLE-US-00025 TABLE 25 R.sub.1* or H R.sub.2** n m E*** 4 4
0 3 25 5 21 15 2 16 0 5 4 36 5 455 15 451 16 25 15 4 62 5 441 15
456 16 25 16 4 0 5 25 15 0 16 0 H 4 25 5 410 15 441 16 25 4 4 0 4
21 5 0 15 0 16 20 5 4 0 5 441 15 510 16 210 15 4 32 5 440 15 411 16
25 16 4 1 5 0 15 0 16 0 H 4 255 5 441 15 551 16 25 R.sub.1* Number
of carbon atoms in R.sub.1 R.sub.2** Number of carbon atoms in
R.sub.2 E*** Cell voltage
[0123] TABLE-US-00026 TABLE 26 R.sub.1* or H R.sub.2** n m E*** 4 4
0 5 25 5 21 15 21 16 25 5 4 25 5 410 15 412 16 2 15 4 14 5 413 15
412 16 251 16 4 25 5 25 15 2 16 25 H 4 254 5 456 15 411 16 25 4 4 1
5 23 5 0 15 1 16 0 5 4 0 5 0 15 0 16 14 15 4 0 5 0 15 0 16 0 16 4
25 5 0 15 0 16 0 H 4 0 5 0 15 0 16 2 R.sub.1* Number of carbon
atoms in R.sub.1 R.sub.2** Number of carbon atoms in R.sub.2 E***
Cell voltage
[0124] The above results show that, when R.sup.1 and R.sup.2 are
independently hydrogen or an alkyl group having not less than 5 and
not more than 15 carbon atoms, and n and m satisfied
0.ltoreq.n.ltoreq.5, 0.ltoreq.m.ltoreq.5 and 1.ltoreq.n+m.ltoreq.5,
the discharge performance was high and a cell voltage of not less
than 400 mV was obtained. When each parameter was out of the above
range, on the other hand, the cell voltage was not more than 500
mV.
[0125] Further, when the same discharge test was conducted on Cell
2 using a conventional surfactant, a cell voltage of 415 mV was
obtained.
[0126] It is understood from the above that the use of the
surfactant of the present invention secures cell characteristics
better than or equivalent to the characteristics of a cell using
the conventional surfactant having the endocrine-disrupting
function, without impairing dispersibility of the water-repellent
polymer.
TEST EXAMPLE 1
[0127] An alkylene oxide type surfactant represented by the
formula:
H--O--{(C.sub.2H.sub.4O).sub.2--(C.sub.3H.sub.6O).sub.3}--C.sub.5H.sub.11-
, and octyl phenol ethoxylate (Triton X-100, produced by NAGASE
& CO., LTD.) were subjected to a thermal decomposition behavior
analysis (TG-MS). They were each heated in the air to raise the
temperate thereof from room temperature to 300.degree. C., retained
at 300.degree. C. for 120 minutes, and then heated to 400.degree.
C. they were then cooled down and the residues thereof subjected to
an infrared spectroscopic analysis (FT-IR).
[0128] The respective amounts of the residues of the alkylene oxide
type surfactant and the octyl phenol ethoxylate were about 0.09 wt
% and about 1.1 wt %.
[0129] While the residue of the alkylene oxide type surfactant was
a simple hydrocarbon component, a component having benzene-ring
structure was detected from the residue of octyl phenol ethoxylate.
It was concluded from this result that a phenol group was from the
octyl phenol ethoxylate.
[0130] This result further indicates that the conventional
surfactant (octyl phenol ethoxylate) may be incompletely decomposed
by a normal thermal treatment at 290.degree. to 380.degree. C. with
a hot air dryer, and hence the problematic phenol group was left
therein. Accordingly, even when the normal thermal treatment as
above described was conducted on an MEA and an electrode using the
conventional surfactant, the environmental hormone component cannot
be completely removed therefrom. As a result, the environmental
hormone component may be left in the product, which requires a
special treatment for safely treating the environmental hormone
component at the time of waste disposal of the product.
[0131] On the other hand, in an MEA and an electrode using the
alkylene oxide type surfactant of the present invention, the
surfactant is removed by a simple thermal treatment and no
problematic component remains, ensuring safety of the product.
Therefore, the special treatment is unnecessary at the time of
waste disposal of the product, and hence reduction in total cost
while considering the life cycle of the product is possible.
[0132] It is to be noted that, although the pure hydrogen gas was
used as the fuel in Example 1, similar results were obtained by
using reformed hydrogen containing impurities such as carbon
dioxide, nitrogen and carbon monoxide. Further, although the
methanol aqueous solution was used as the fuel in Example 2,
similar results were obtained by using liquid fuels such as ethanol
and dimethyl ether, and a mixture thereof. The liquid fuel may be
evaporated in advance and then supplied as a vapor. In Examples 1
and 2, the gas diffusion layer was produced with the use of
acetylene black and carbon paper; however, the materials are not
limited to these. Similar effects were obtained by using carbon
black, carbon cloth and the like. Further, the constitution of the
present invention is not limited by the catalyst layer, the
electrolyte membrane and the like used in Examples. A variety of
catalyst layers, electrolyte membranes and the like can be used.
Moreover, the MEA in accordance with the present invention is
applicable to a generator of such gas as oxygen, ozone and
hydrogen, a purifier, and a variety of gas sensors such as an
oxygen sensor and an alcohol sensor.
REFERENCE EXAMPLE 1
(i) Production of Gas Diffusion Layer
[0133] Acetylene black as conductive carbon particles (Denka black
with a particle size of 35 nm, produced by DENKI KAGAKU KOGYO
KABUSHIKI KAISHA) was mixed with a PTFE aqueous dispersion (D-1,
produced by DAIKIN INDUSTRIES, LTD.) to prepare a water-repellent
ink. The content of PTFE in the water-repellent ink was 20 parts by
weight per 100 parts by weight of acetylene black.
[0134] Next, the water-repellent ink was applied onto the surface
of carbon paper (TGPH060H, produced by Toray Industries, Inc.) as a
substrate of a gas diffusion layer at a rate of 30 g/m.sup.2 so
that the water-repellent ink was impregnated in the carbon paper.
The carbon paper with the water-repellent ink impregnated therein
was then placed in air atmosphere and heat-treated at 300.degree.
C. with a hot air dryer to produce a gas diffusion layer.
(ii) Formation of Catalyst Layer
[0135] 50 parts by weight of platinum particles having a mean
particle size of about 30 angstroms were carried on 100 parts by
weight of conductive carbon particles (Ketjen Black EC, produced by
Ketjen Black International Company) having a mean particle size of
30 nm. The carbon particles carrying the platinum particles
thereon, an alcohol dispersion of a hydrogen ion-conductive polymer
electrolyte and a metal oxide powder were then mixed to prepare a
catalyst ink. The weight ratio of the carbon particles carrying the
platinum particles thereon to the hydrogen ion-conductive polymer
electrolyte was 66:33. The hydrogen ion-conductive polymer
electrolyte used was perfluorocarbon sulfonic acid ionomer (5 wt %
Nafion dispersion, produced by Aldrich in the US). The metal oxide
powder used was silica (SiO.sub.2), titania (TiO.sub.2), alumina
(Al.sub.2O.sub.3), zirconia (ZrO.sub.2), magnesia (MgO) or chromia
(Cr.sub.2O.sub.3) each having a mean particle size of 0.8 .mu.m.
The content of the oxide powder in the catalyst ink was 1 to 10,000
ppm with respect to the solid matter.
[0136] Subsequently, the catalyst ink was printed on one face of
the gas diffusion layer and then dried at 70.degree. C. to form a
catalyst layer with a thickness of 10 .mu.m. As thus described, an
electrode comprising the catalyst layer and the gas diffusion layer
was produced.
(iii) Production of MEA-a
[0137] A hydrogen ion-onductive polymer electrolyte membrane
(Nafion 112, produced by Du Pont in the US) was interposed between
a pair of electrodes such that the catalyst layer sides were
directed inwardly, and then hot pressed to produce MEA-a.
(iv) Assembly of Fuel Cell
[0138] A rubber gasket was bonded to the periphery of the
electrolyte membrane of MEA-a and manifold holes for passage of
cooling water, a fuel gas and an oxidant gas were formed
therethrough.
[0139] Meanwhile, a variety of separators made of phenol
resin-impregnated graphite plate with an external size of 20
cm.times.32 cm, a thickness of 1.3 mm and a depth of the gas flow
channel or cooling water channel thereon of 0.5 mm were
prepared.
[0140] The gas flow channel side of the separator with an oxidant
gas flow channel was attached to the cathode side of MEA-a, while
the gas flow channel side of the separator with a fuel gas flow
channel was attached to the anode side of MEA-a, to constitute a
unit cell.
[0141] Subsequently, two unit cells were stacked and then
interposed between a pair of separators with cooling water flow
channels formed thereon such that the cooling water flow channel
sides of the separators were directed inwardly. This pattern was
repeated to produce a cell stack of 100 cells. A current collector
plate made of stainless steel and an insulating plate made of an
electrically-insulating material were arranged on both ends of the
cell stack, and further, with the use of end plates and tie rods,
the whole was assembled. The clamping pressure per area of the
separator was 15 kgf/cm.sup.2. The cell thus produced was referred
to as Cell A.
(v) Evaluation Test
[0142] A pure hydrogen gas and air were supplied to the anode and
the cathode of Cell A, respectively, at a cell temperature of
75.degree. C. and at a fuel gas utilization rate (Uf) of 70% and an
air utilization rate (Uo) of 40%. A discharge test was conducted on
the cell. The gases were humidified by passage of the pure hydrogen
gas through a bubbler at 70.degree. C. and by passage of the air
through a bubbler at 50.degree. C.
[0143] Next, 2 mol/l of methanol aqueous solution at a temperature
of 60.degree. C. was supplied to the anode of Cell A at a cell
temperature of 75.degree. C. and under an air utilization rate (Uo)
of 40%. The gas was humidified by passage of the air through a
bubbler at 50.degree. C. A discharge test was conducted on the
cell.
REFERENCE EXAMPLE 2
(i) Production of Gas Diffusion Layer
[0144] Acetylene black as conductive carbon particles (Denka black
with a particle size of 35 nm, produced by DENKI KAGAKU KOGYO
KABUSHIKI KAISHA), a PTFE aqueous dispersion (D-1, produced by
DAIKIN INDUSTRIES, LTD.) and a metal oxide powder were mixed to
prepare a water-repellent ink. The content of PTFE in the
water-repellent ink was 20 parts by weight per 100 parts by weight
of acetylene black. The metal oxide powder used was silica
(SiO.sub.2), titania (TiO.sub.2), alumina (Al.sub.2O.sub.3),
zirconia (ZrO.sub.2), magnesia (MgO) or chromia (Cr.sub.2O.sub.3),
each having a mean particle size of 0.8 .mu.m. The content of the
oxide powder in the water-repellent ink was 1 to 10,000 ppm with
respect to the solid matter.
[0145] Next, the water-repellent ink was applied onto the surface
of carbon paper (TGPH060H, produced by Toray Industries, Inc.) as a
substrate of a gas diffusion layer at a rate of 30 g/m.sup.2 so
that the water-repellent ink was impregnated in the carbon paper.
The carbon paper with the water-repellent ink impregnated therein
was then placed in air atmosphere and heat-treated at 300.degree.
C. with a hot air dryer to produce a gas diffusion layer.
(ii) Formation of Catalyst Layer
[0146] 50 parts by weight of platinum particles having a mean
particle size of about 30 angstroms were carried on 100 parts by
weight of conductive carbon particles (Ketjen Black EC, produced by
Ketjen Black International Company) having a mean particle size of
30 nm. The carbon particles carrying the platinum particles thereon
was then mixed with an alcohol dispersion of a hydrogen
ion-conductive polymer electrolyte to prepare a catalyst ink. The
mixing ratio of the carbon particles carrying the platinum
particles thereon to the hydrogen ion-conductive polymer
electrolyte was 66:33. The hydrogen ion-conductive polymer
electrolyte used was perfluorocarbon sulfonic acid ionomer (5 wt %
Nafion dispersion, produced by Aldrich in the US). Subsequently,
the catalyst ink was printed on one face of the gas diffusion layer
and then dried at 70.degree. C. to form a catalyst layer with a
thickness of 10 .mu.m. As thus described, an electrode comprising
the catalyst layer and the gas diffusion layer was produced.
(iii) Production of MEA-b
[0147] A hydrogen ion-conductive polymer electrolyte membrane
(Nafion 112, produced by Du Pont in the US) was interposed between
a pair of electrodes such that the catalyst layer sides were
directed inwardly, and then hot pressed to produce MEA-b.
(iv) Assembly of Fuel Cell
[0148] Cell B comprising a cell stack of 100 cells was produced in
the same manner as in Reference Example 1.
(v) Evaluation Test
[0149] The same discharge test as in Reference Example 1 was
conducted on Cell B.
REFERENCE EXAMPLE 3
(i) Production of MEA-c
[0150] MEA-c was produced in the same manner as in Reference
Example 1 except that the water-repellent ink prepared in Reference
Example 2 was used in place of the water-repellent ink prepared in
Reference Example 1. In MEA-c, both a gas diffusion layer and a
catalyst layer comprise a metal oxide powder. It should be noted
that the same metal oxide powder was used for each MEA-c. Further,
the gas diffusion layer and the catalyst layer contain the same
amount of metal oxide powder.
(ii) Assembly of Fuel Cell
[0151] Cell C comprising a cell stack of 100 cells was produced in
the same manner as in Reference Example 1.
(iii) Evaluation Test
[0152] The same discharge test as in Reference Example 1 was
conducted on Cell C.
COMPARATIVE EXAMPLE 2
(i) Production of MEA-x
[0153] MEA-x was produced in the same manner as in Reference
Example 1 except that the catalyst ink prepared in Reference
Example 2 was used in place of the catalyst ink prepared in
Reference Example 1. In MEA-x, neither the gas diffusion layer nor
the catalyst layer comprises the metal oxide powder.
(ii) Assembly of Fuel Cell
[0154] Cell X comprising a cell stack of 100 cells was produced in
the same manner as in Reference Example 1.
(iii) Evaluation Test
[0155] The same discharge test as in Reference Example 1 was
conducted on Cell X.
RESULTS OF EVALUATION TESTS IN REFERENCE EXAMPLES 1 TO 3
(i) Hydrogen-Air Type Fuel Cell
[0156] FIG. 4 shows a comparison of the life characteristics of
hydrogen-air type fuel Cells A to C in Reference Examples to
hydrogen-air type fuel Cell X in the Comparative Example. The fuel
cells A to C used silica as the metal oxide powder, 10 ppm of metal
oxide powder was contained in the catalyst layer and 10 ppm of
metal oxide powder was contained in the gas diffusion layer.
[0157] FIG. 4 shows the relationship between the operation time of
the cell in hours and the cell voltage at a current density of 300
mA/cm.sup.2. As shown in FIG. 4, in the initial stage, the
respective average voltages of Cells A, B, C and X are 759 mV, 747
mV, 768 mV and 726 mV, respectively. After 2,700 hours, they are
718 mV, 706 mV, 747 mV and 528 mV, respectively. The cell voltage
of Cell X in the Comparative Example 2 declined by as much as 198
mV, while the voltages of Cells A, B and C in the Reference
Examples decline only by 41 mV, 41 mV and 21 mV, respectively.
[0158] Accordingly, the inhibitory effect on deterioration was
larger in the case of adding the metal oxide powder to the catalyst
layer than in the case of adding the same to the gas diffusion
layer. Further, in Cell C, where the metal oxide powder was added
to both the catalyst layer and the gas diffusion layer, the least
decline in voltage was observed. This is presumably a consequence
of maintained hydrogen ion-conductivity, gas diffusibility and
discharge ability of the water produced over a long period of time
due to inhibition of deterioration in the water content of the
polymer electrolyte of each layer and of deterioration in water
repellency of the carbon particles.
(ii) Direct Type Methanol Fuel Cell
[0159] FIG. 5 shows one example of life characteristics of Cells A
to C in the Reference Examples and of Cell X in the Comparative
Example. The life characteristics were obtained when silica was
used as the metal oxide powder. The catalyst layer contained 10 ppm
of metal oxide powder while 10 ppm of metal oxide powder was
contained in the gas diffusion layer.
[0160] In an MEA for a direct type methanol fuel cell, an
anode-side catalyst layer was produced using carbon particles
carrying platinum and ruthenium particles thereon in place of the
carbon particles carrying the platinum particles only thereon. The
carbon particles carrying the platinum and ruthenium particles
thereon was prepared by contacting 100 parts by weight of
conductive carbon particles (Ketjen Black EC, produced by Ketjen
Black International Company) having a mean particle size of 30 nm
with 40 parts by weight of platinum particles having a mean
particle size of about 30 angstroms and 20 parts by weight of
ruthenium particles having a mean particle size of about 30
angstroms.
[0161] FIG. 5 shows the relationship between the operation time of
the cells and the voltages per one unit cell at a current density
of 200 mA/cm.sup.2. As shown in FIG. 5, in the initial stage, the
respective average voltages of the unit cells of Cells A, B, C and
X are 621 mV, 597 mV, 635 mV and 583 mV, respectively. After 2,700
hours, the respective average voltages are 589 mV, 568 mV, 618 mV
and 210 mV. While the average voltage of Cell X in Comparative
Example 2 declined by as much as 373 mV, the average voltages of
Cells A, B and C in Reference Examples decline by only 32 mV, 29 mV
and 17 mV, respectively.
[0162] From these results, it is clear that the direct type
methanol fuel cell also exerts the inhibitory effect on
deterioration in characteristics as a result of the inclusion of
the metal oxide to the electrode.
(iii) Content of Metal Oxide in Hydrogen-Air Fuel Cell
[0163] FIG. 6 shows the relationship between the voltage of Cell C
as the hydrogen-air fuel cell and the content of the metal oxide
powder in the electrode. The abscissa of FIG. 6 shows the content
of the metal oxide powder in the whole electrode. The ordinate of
FIG. 6 shows the voltage per one unit cell at a current density of
280 mA/cm.sup.2 after 2,500 hours.
[0164] In FIG. 6, the cell voltage is kept high when the content of
the metal oxide powder is in the range of 1 to 10,000 ppm, because
of the effect of adding the metal oxide powder. The reason for the
decline in cell voltage when the content of the metal oxide powder
was more than 10,000 ppm is believed to be that, with the metal
oxide being insulative, the internal resistance of the electrode
increased.
[0165] The more favorable content of the metal oxide powder in the
electrode in the case of silica (SiO.sub.2), titania (TiO.sub.2),
alumina (Al.sub.2O.sub.3), zirconia (ZrO.sub.2), magnesia (MgO) and
chromia (Cr.sub.2O.sub.3) are 1 to 10,000 ppm, 3 to 4,000 ppm, 1 to
3,000 ppm, 1 to 10,000 ppm, 2 to 2,000 ppm and 1 to 2,000 ppm,
respectively.
(iv) Content of Metal Oxide in Direct Type Methanol Fuel Cell
[0166] FIG. 7 shows the relationship between the voltage of Cell C
as the direct type methanol fuel cell and the content of the metal
oxide powder in the electrode. The abscissa of FIG. 7 shows the
content of the metal oxide powder in the whole electrode. The
ordinate of FIG. 7 shows the voltage per one unit cell at a current
density of 180 mA/cm.sup.2 after 2,500 hours.
[0167] In the MEA for a direct type methanol fuel cell, an
anode-side catalyst layer was produced using carbon particles
carrying platinum and ruthenium particles thereon in place of the
carbon particles carrying the platinum particles only thereon. The
carbon particles carrying the platinum and ruthenium particles
thereon were prepared by contacting 100 parts by weight of
conductive carbon particles Ketjen Black EC, produced by Ketjen
Black International Company) having a mean particle size of 30 nm
with 40 parts by weight of platinum particles having a mean
particle size of about 30 angstroms and 20 parts by weight of
ruthenium particles having a mean particle size of about 30
angstroms.
[0168] In FIG. 7, the cell voltage is kept high when the content of
the metal oxide powder is in the range of 1 to 10,000 ppm because
of the effect of adding the metal oxide powder is confirmed. The
reason for the decline in cell voltage when the content of the
metal oxide powder was more than 10,000 ppm is believed to be that,
with the metal oxide being insulative, the internal resistance of
the electrode increased.
[0169] The more favorable content of the metal oxide powder in the
electrode in the case of silica (SiO.sub.2), titania (TiO.sub.2),
alumina (Al.sub.2O.sub.3), zirconia (ZrO.sub.2), magnesia (MgO) and
chromia (Cr.sub.2O.sub.3) are 1 to 10,000 ppm, 2 to 4,000 ppm, 1 to
10,000 ppm, 1 to 10,000 ppm, 1 to 2,000 ppm and 2 to 10,000 ppm,
respectively.
EXAMPLE 3
(i) Production of Gas Diffusion Layer
[0170] Acetylene black conductive carbon particles (Denka black
having a particle size of 35 nm, produced by DENKI KAGAKU KOGYO
KABUSHIKI KAISHA), an alkylene oxide type surfactant represented by
the following formula:
H--O--{(C.sub.2H.sub.4O).sub.2--(C.sub.3H.sub.6O).sub.3}--C.sub.5H.sub.11
and a aqueous dispersion (D-1E, produced by DAIKIN INDUSTRIES,
LTD.) were mixed to prepare a water-repellent ink A. The respective
contents of the surfactant and the PTFE in the water-repellent ink
A were 10 parts by weight and 20 parts by weight per 100 parts by
weight of acetylene black.
[0171] Next, the water-repellent ink A was applied onto the surface
of carbon paper (TGPH060H, produced by Toray Industries, Inc.) as a
substrate for a gas diffusion layer. The ink was applied at a rate
of 30 g/m.sup.2 so that the water-repellent ink was impregnated in
the carbon paper. The carbon paper with the water-repellent ink
impregnated therein was then placed in air atmosphere and
heat-treated at 350.degree. C. with a hot air dryer to produce a
gas diffusion layer.
(ii) Formation of Catalyst Layer
[0172] 50 parts by weight of platinum particles having a mean
particle size of about 30 angstroms were carried on 100 parts by
weight of conductive carbon particles (Ketjen Black EC, produced by
Ketjen Black International Company) having a mean particle size of
30 nm. The carbon particles carrying the platinum particles, an
alcohol dispersion of a hydrogen ion-conductive polymer electrolyte
and a metal oxide powder were then mixed to prepare a catalyst ink.
The weight ratio of the carbon particles carrying the platinum
particles thereon and the hydrogen ion-conductive polymer
electrolyte was 66:33. The hydrogen ion-conductive polymer
electrolyte used was a perfluorocarbon sulfonic acid ionomer (5 wt
% Nafion dispersion, produced by Aldrich in the US). The metal
oxide powder used was selected from the group consisting of silica
(SiO.sub.2), titania (TiO.sub.2), alumina (Al.sub.2O.sub.3),
zirconia (ZrO.sub.2), magnesia (MgO) and chromia (Cr.sub.2O.sub.3),
each having a mean particle size of 0.8 .mu.m. The content of the
oxide powder in the catalyst ink was 1 to 10,000 ppm with respect
to the solid matter.
[0173] The catalyst ink was printed on one face of the gas
diffusion layer and then dried at 70.degree. C. to form a catalyst
layer having a thickness of 10 .mu.m. As thus described, an
electrode comprising the catalyst layer and a gas diffusion layer
was produced.
(iii) Production of MEA
[0174] A hydrogen ion-conductive polymer electrolyte membrane
(Nafion 112, produced by Du Pont in the US) was interposed between
a pair of electrodes such that the catalyst layer sides were
directed inwardly, and then hot pressed to produce MEA-A.
(iv) Assembly of Fuel Cell
[0175] Except that MEA-A was used in place of MEA-a, Cell A'
comprising a cell stack of 100 cells was produced in the same
manner as in Reference Example 1.
(v) Evaluation Test
[0176] The same discharge test as in Reference Example 1 was
conducted on Cell A'.
EXAMPLE 4
(i) Production of Gas Diffusion Layer
[0177] The water-repellent ink A prepared in Example 3 was further
mixed with a metal oxide powder to prepare a water-repellent ink B.
The metal oxide powder used was selected from the group consisting
of silica (SiO.sub.2), titania (TiO.sub.2), alumina
(Al.sub.2O.sub.3), zirconia (ZrO.sub.2), magnesia (MgO) and chromia
(Cr.sub.2O.sub.3), each having a mean particle size of 0.8 .mu.m.
The content of the oxide powder in the catalyst ink B was 1 to
10,000 ppm with respect to the solid matter.
[0178] Next, the water-repellent ink B was applied onto the surface
of carbon paper (TGPH060H, produced by Toray Industries, Inc.) as a
substrate of a gas diffusion layer. The ink was applied at a rate
of 30 g/m.sup.2 so that the water-repellent ink was impregnated in
the carbon paper. The carbon paper with the water-repellent ink
impregnated therein was then placed in air atmosphere and
heat-treated at 350.degree. C. with a hot air dryer to produce a
gas diffusion layer.
(ii) Formation of Catalyst Layer
[0179] 50 parts by weight of platinum particles having a mean
particle size of about 30 angstroms were carried on 100 parts by
weight of conductive carbon particles (Ketjen Black EC, produced by
Ketjen Black International Company) having a mean particle size of
30 nm. The carbon particles carrying the platinum particles thereon
was then mixed with an alcohol dispersion of a hydrogen
ion-conductive polymer electrolyte to prepare a catalyst ink. The
weight ratio of the carbon particles carrying the platinum
particles and the hydrogen ion-conductive polymer electrolyte was
66:33. As the hydrogen ion-conductive polymer electrolyte used was
perfluorocarbon sulfonic acid ionomer (5 wt % Nafion dispersion,
produced by Aldrich in the US). Subsequently, the catalyst ink was
printed on one face of the gas diffusion layer and then dried at
70.degree. C. to form a catalyst layer having a thickness of 10
.mu.m. As thus described, an electrode comprising the catalyst
layer and the gas diffusion layer was produced.
(iii) Production of MEA
[0180] A hydrogen ion-conductive polymer electrolyte membrane
(Nafion 112, produced by Du Pont in the US) was interposed between
a pair of electrodes such that the catalyst layer sides were
directed inwardly, and then hot pressed to produce MEA-B.
(iv) Assembly of Fuel Cell
[0181] Except that MEA-B was used in place of MEA-A, Cell B'
comprising a cell stack of 100 cells was produced in the same
manner as in Reference Example 1.
(v) Evaluation Test
[0182] The same discharge test as in Reference Example 1 was
conducted on Cell B'.
EXAMPLE 5
(i) Production of MEA
[0183] Except that the water-repellent ink B prepared in Example 4
was used in place of the water-repellent ink A prepared in Example
3, MEA-C was produced in the same manner as in Example 3. In MEA-C,
both a gas diffusion layer and a catalyst layer comprise a metal
oxide powder. It should be noted that the same metal oxide powder
was used for each MEA-C. Further, the gas diffusion layer and the
catalyst layer contain the same amount of metal oxide powder.
(ii) Assembly of Fuel Cell
[0184] Except that MEA-C was used in place of MEA-A, Cell C'
comprising a cell stack of 100 cells was produced in the same
manner as in Reference Example 1.
(iii) Evaluation Test
[0185] The same discharge test as in Reference Example 1 was
conducted on Cell C'.
RESULTS OF EVALUATION TESTS IN EXAMPLES 3 TO 5
(i) Hydrogen-Air Type Fuel Cell
[0186] Life characteristics of Cells A' to C' in Examples as
hydrogen-air type fuel cells were measured. The relationship
between the operation time of the cells and the voltages per one
unit cell were observed at a current density of 300
mA/cm.sup.2.
[0187] When 10 ppm of silica was contained in the catalyst layer
and 10 ppm of metal oxide powder was contained in the gas diffusion
layer, the respective average voltages of the unit cells of Cells
A', B' and C' in the initial stage were 757 mV, 745 mV and 765 mV,
respectively. After 2,700 hours, they were 715 mV, 702 mV and 741
mV, respectively. Hence, the voltages of Cells A', B' and C'
declined only by 42 mV, 43 mV and 24 mV, respectively.
[0188] It is understood from the above that the equivalent
inhibitory effect to the one in Reference Examples on deterioration
in characteristics can also be obtained when the alkylene oxide
type surfactant was used.
(ii) Direct Tape Methanol Fuel Cell
[0189] The life characteristics of Cells A' to C' in Examples as
direct type methanol fuel cell were measured. The relationship
between the operation time of the cells and the voltages per one
unit cell were observed at a current density of 200
mA/cm.sup.2.
[0190] In an MEA for the direct type methanol fuel cell, an
anode-side catalyst layer was produced by the use of carbon
particles carrying platinum and ruthenium particles thereon in
place of the carbon particles carrying the platinum particles only
thereon. The carbon particles carrying the platinum and ruthenium
particles thereon was prepared by contacting 100 parts by weight of
carbon particles (Ketjen Black EC, produced by Ketjen Black
International Company) having a mean particle size of 30 nm with 40
parts by weight of platinum particles having a mean particle size
of about 30 angstroms and 20 parts by weight of ruthenium particles
having a mean particle size of about 30 angstroms.
[0191] When 10 ppm of silica was contained in the catalyst layer
and 10 ppm of silica was contained in the gas diffusion layer, the
respective average voltages of the unit cells of Cells A', B' and
C' in the initial stage were 619 mV, 595 mV and 630 mV,
respectively. After 2,700 hours, the respective average voltages
were 582 mV, 562 mV and 612 mV.
[0192] Hence, the voltages of Cells A', B' and C' declined only by
37 mV, 33 mV and 18 mV, respectively.
[0193] The results above show that also in the direct type methanol
fuel cell, the equivalent inhibitory effect to the one in Reference
Examples on deterioration in characteristics is exhibited when the
alkylene oxide type surfactant is used.
(iii) Content of Metal Oxide in Hydrogen-Air Fuel Cell
[0194] The relationship between the voltage of Cell C' as the
hydrogen-air fuel cell and the amount of metal oxide powder in the
electrode was observed. When the content of the metal oxide powder
was in the range of 1 to 10,000 ppm the voltage per one unit cell
at a current density of 280 mA/cm.sup.2 after 2,500 hours was kept
at the equivalent value to the one in Reference Example 3. Further,
the more preferable amount of the metal oxide powder in the
electrode was in the same range as in Reference Example 3.
(iv) Content of Metal Oxide in Direct Type Methanol Fuel Cell
[0195] The relationship between the voltage of Cell C' as the
direct type methanol fuel cell and the content of the metal oxide
powder in the electrode was observed. When the content of the metal
oxide powder was in the range of 1 to 10,000 ppm, the voltage per
one unit cell at a current density of 180 mA/cm.sup.2 after 2,500
hours was kept at the equivalent value to the one in Reference
Example 3. Further, the more preferable amount of the metal oxide
powder in the electrode was in the same range as in Reference
Example 3.
[0196] It must be noted that, although pure hydrogen or methanol
was used as the fuel in Reference Examples 1 to 3, a similar result
was obtained when using a fuel-reformed hydrogen containing
impurities such as carbon dioxide, nitrogen and carbon monoxide.
Further, similar results were also obtained when using ethanol,
dimethyl ether and the mixture thereof in place of methanol. The
liquid fuel may be evaporated in advance and then supplied to the
cell as a vapor.
REFERENCE EXAMPLE 4
(i) Formation of Catalyst Layer
[0197] 50 parts by weight of platinum particles having a mean
particle size of about 30 angstroms were carried on 50 parts by
weight of conductive carbon particles (Ketjen Black EC, produced by
AKZO Chemie in Holland) having a mean primary particle size of 30
nm. The carbon particles carrying the platinum particles thereon,
an alcohol dispersion of a hydrogen ion-conductive polymer
electrolyte and a predetermined amount of water were then mixed
with the use of a beads mill disperser (Dispermat SL-C12Z, produced
by GETZMANN in Germany), to prepare catalyst inks A, B, C, D and E
which contained different amounts of the solid matter. The weight
ratio of the carbon particles carrying the platinum particles and
the hydrogen ion-conductive polymer electrolyte was 100:50. The
hydrogen ion-conductive polymer electrolyte used was
perfluorocarbon sulfonic acid (5 wt % Nafion dispersion, produced
by Aldrich in the US).
[0198] The content of the solid matter is a percentage value
obtained by dividing the total weight of the conductive carbon
particles, the platinum particles and the hydrogen ion-conductive
polymer electrolyte in the catalyst ink by the weight of the
catalyst ink and then multiplying the obtained value by 100. The
content of the solid matter in the catalyst inks A, B, C, D and E
were 20 wt %, 18 wt %, 15 wt %, 12 wt % and 5 wt %,
respectively.
[0199] These catalyst inks were placed in a viscoelasticity
measuring device (Reo stress RS150, produced by HAAKE in Germany)
to measure the viscosities of the ink. The shear rate was changed
using a corn plate-type measuring head. The relationship between
the shear rates and the viscosities is shown in FIG. 8.
[0200] FIG. 8 shows that catalyst inks A, B, C and D exhibit
behavior of a Non-Newtonian liquid, the viscosity of which
decreased with increase in shear rate. On the other hand, catalyst
ink E exhibited behavior of a Newtonian liquid, the viscosity of
which hardly changed even with changes in shear rate.
[0201] These inks were applied onto a substrate using a coating
apparatus as shown in FIG. 3. The substrate used was a film made of
polyethylene terephthalate (hereinafter referred to as PET)
(thickness: 50 .mu.m, width: 250 mm). After catalyst ink 36 was put
into a coat material tank 32, the PET film 34 was supplied from a
wind-off part 33 of the coating apparatus. The catalyst ink was
applied onto the substrate 34 from a tank 32 through a nozzle 37.
The coating applied onto the substrate was dried as passing though
a drying room 38 at a preset temperature of 60.degree. C. In the
same manner, catalyst layers A, B, C, D and E were each formed on
the substrate 34.
[0202] When catalyst ink A was used, the coating streaked or became
uneven because of the excessively high ink viscosity. When catalyst
ink E was used, the ink dripped from the tip of the nozzle in the
reverse direction of movement of the substrate. Further, the
coating of ink E flowed in the width direction, making the applying
extremely unstable. When catalyst inks B, C and D were used, the
applying can be conducted stably without unevenness of the
coating.
[0203] The relationship among the various catalyst ink
compositions, the viscosities of the ink at shear rate of 0.1
(1/sec) and 100 (1/sec), and the stabilities of the applying are
summarized in Table 27: TABLE-US-00027 TABLE 27 Shear Rate Shear
Rate Catalyst Ink 0.1 (1/s) 100 (1/s) Stability A 250 Pa s 5 Pa s
Deteriorated B 150 Pa s 1 Pa s Good C 80 Pa s 0.9 Pa s Good D 10 Pa
s 0.8 Pa s Good E 1 Pa s 0.7 Pa s Deteriorated
[0204] It is understood from Table 27 that, with catalyst ink E
having a viscosity of less than 10 Pas at a shear rate of 0.1
(1/sec) and with catalyst ink A having a viscosity of more than 1
Pas at a shear rate of 100 (1/sec), an even coating cannot be
formed.
(ii) Production of Unit Cell
[0205] A hydrogen ion-conductive polymer electrolyte membrane
(Nafion 112, produced by Du Pont in the US) was interposed between
a pair of catalyst layers A and then hot pressed. The electrolyte
membrane-catalyst layer A assembly was then interposed between a
pair of carbon paper (TGP-H-120, produced by Toray Industries,
Inc.) to produce unit cell A. In the same manner, unit cells B to E
were produced using the catalyst layers B to E.
(iii) Evaluation of Unit Cell
[0206] Unit cells A to E were set in a test device to study
characteristics of each unit cell. An anode of each unit cell was
supplied with a simulated reformed gas (a hydrogen balanced gas
containing 25% of carbon oxide and 50 ppm of carbon monoxide) and a
cathode was supplied with air, and a discharge test was conducted
on the cells at a cell temperature of 80.degree. C. and under
conditions of a fuel utilization rate of 80% and an air utilization
rate of 40%. Each gas was humidified such that the dew point of the
simulated reformed gas was 75.degree. C. and the dew point of the
air was 60.degree. C.
[0207] FIG. 9 shows the comparison among current-voltage
characteristics of unit cells A to E. FIG. 9 shows that unit cells
A and E, using the uneven catalyst layer A and catalyst layer E
formed from catalyst ink A and E which are unstable in applying,
have lower cell characteristics than the other unit cells.
[0208] It is therefore possible to form an even coating stably by
using a catalyst ink of a Non-Newtonian liquid having a viscosity
of not less than 10 Pas at a shear rate of 0.1 (1/sec) and a
viscosity of not more than 1 Pas at a shear rate of 100 (1/sec).
Further, a fuel cell produced with the use of the catalyst ink of
the Non-Newtonian liquid performs favorably.
REFERENCE EXAMPLE 5
(i) Formation of Catalyst Layer
[0209] Using catalyst ink C prepared in Reference Example 4, the
ink was applied onto a substrate in the same manner as in Reference
Example 4. However, by setting a drying temperature for the coating
at 30.degree. C., 40.degree. C., 60.degree. C., 100.degree. C. and
130.degree. C., catalyst layers C1, C2, C3, C4 or C5 were formed.
The appearances of catalyst layers C1 to C4 were almost the same.
On part of catalyst layer C5, however, a crack was observed. The
appearance (a) and the cross section (b) of catalyst layers C1 to
C5 are shown in FIG. 10.
(ii) Production of Unit Cell
[0210] Using these catalyst layers C1 to C5, unit cells C1 to C5
were produced and then the cell characteristics thereof were
studied in the same manner as in Reference Example 4.
(iii) Evaluation of Unit Cell
[0211] A condition for a test on the unit cells was the same as in
Reference Example 4. The current-voltage characteristics of these
unit cells are shown in FIG. 11.
[0212] FIG. 11 shows that unit cell C1 using catalyst layer C1 and
unit cell C5 using catalyst layer C5 have lower characteristics
than the other unit cells. This is presumably because, in the case
of catalyst layer C1, the dispersion medium of the ink was left in
the catalyst layer due to the low drying temperature of 30.degree.
C. In the case of catalyst layer C5, the lower characteristic is
presumably due to the drying temperature set to be as high as
130.degree. C., causing the hydrogen ion-conductive polymer
electrolyte in the catalyst layer to be altered such that there is
a decrease in hydrogen ion-conductivity thereof and because of a
crack in the catalyst layer, thereby deteriorating the cell
characteristics.
[0213] It is therefore possible to stably produce a
high-performance fuel cell by controlling the drying temperature
for the catalyst ink after application. Although the drying was
conducted at one stage in the present example, it can be conducted
at plural stages by changing the drying temperature.
EXAMPLE 6
(i) Production of Gas Diffusion Layer
[0214] 100 parts by weight of acetylene black as conductive carbon
particles (Denka black with a particle size of 35 nm, produced by
DENKI KAGAKU KOGYO KABUSHIKI KAISHA), 10 parts by weight of
alkylene oxide type surfactant represented by the following
formula:
H--O--{(C.sub.2H.sub.4O).sub.2--(C.sub.3H.sub.6O).sub.3}--C.sub.5H.sub.11
and a PTFE aqueous dispersion (D-1E, produced by DAIKIN INDUSTRIES,
LTD.) containing 20 parts by weight of PTFE were mixed to prepare a
water-repellent ink.
[0215] Next, the water-repellent ink was applied to the surface of
carbon paper (TGP-H-120, produced by Toray Industries, Inc.) as a
substrate of a gas diffusion layer at a rate of 30 g/m.sup.2 so
that the water-repellent ink was impregnated in the carbon paper.
The carbon paper with the water-repellent ink impregnated therein
was then placed in air atmosphere and heat-treated at 350.degree.
C. with a hot air dryer to produce a gas diffusion layer.
(ii) Production of Unit Cell
[0216] Except that the above gas diffusion layer was used in place
of the carbon paper, unit cells C1' to C5' using catalyst layers C1
to C5 were produced in the same manner as in Reference Example
5.
(iii) Evaluation of Unit Cell
[0217] A condition for a test on the unit cells was, the same as in
Reference Example 4. As a result, in unit cells C1' to C5',
current-voltage characteristics almost equivalent to those of unit
cells C1 to C5 were obtained.
[0218] It should be noted that, although the beads mill was used as
a device to grind and disperse the catalyst ink in the above, a
roll mill, a homogenizer, a ball mill and the like can also be
used. Further, although the viscosity of the ink was adjusted by
changing the content of the solid matter of the catalyst ink in the
above, the viscosity of the ink can also be adjusted by changing
the dispersed matter's condition of the catalyst ink while keeping
the content of the solid matter constant. Moreover, the viscosity
of the ink can also be adjusted by using a method such as changing
the composition of the solid matter. In the application method of
the catalyst ink, a screen-printing, a gravure-printing and the
like can also be applied. Furthermore, although the PET film was
used as the substrate onto which the catalyst ink was applied, the
ink can directly be applied onto the polymer electrolyte membrane
and the gas diffusion layer.
INDUSTRIAL APPLICABILITY
[0219] According to the present invention, by optimizing a
surfactant for the purpose of improving dispersibility of a
water-repellent polymer and a binder in a gas diffusion layer of an
electrode of a fuel cell, it is possible to improve safety of the
product and the production process of the fuel cell and also to
reduce the variation and defect of the coating of the
water-repellent ink in the production process. Moreover, according
to the present invention, by optimizing the water content of the
electrode of the fuel cell, it is possible to further enhance the
cell performance. Furthermore, according to the present invention,
by controlling the viscosity of a catalyst ink with the solid
matter content, it is possible to obtain a fuel cell having a
catalyst layer in which catalyst particles are evenly distributed
along the plane thereof without using a thickener or heating.
* * * * *