U.S. patent application number 10/713146 was filed with the patent office on 2004-05-20 for electrode structure for polymer electrolyte fuel cell and method for manufacturing the same.
This patent application is currently assigned to HONDA MOTOR CO., LTD. Invention is credited to Hama, Yuichiro, Iguchi, Masaru, Kanaoka, Nagayuki, Mitsuta, Naoki, Yano, Junichi.
Application Number | 20040096731 10/713146 |
Document ID | / |
Family ID | 32303630 |
Filed Date | 2004-05-20 |
United States Patent
Application |
20040096731 |
Kind Code |
A1 |
Hama, Yuichiro ; et
al. |
May 20, 2004 |
Electrode structure for polymer electrolyte fuel cell and method
for manufacturing the same
Abstract
There is provided an electrode structure for a polymer
electrolyte fuel cell having excellent power generation performance
and excellent durability and a method for manufacturing the same.
Also provided is a polymer electrolyte fuel cell including the
electrode structure and an electrical apparatus and a transport
apparatus using the polymer electrolyte fuel cell. The electrode
structure includes a polymer electrolyte membrane 2 sandwiched
between a pair of electrode catalyst layers 1, 1 containing carbon
particles supporting catalyst particles. The polymer electrolyte
membrane 2 is made of a sulfonated polyarylene-based polymer. The
sulfonated polyarylene-based polymer has an ion exchange capacity
in the range of 1.7 to 2.3 meq/g, and the polymer contains a
component insoluble in N-methylpyrrolidone in an amount of 70% or
less relative to the total amount of the polymer, after the polymer
is subjected to heat treatment for exposing it under a constant
temperature atmosphere of 120.degree. C. for 200 hours. A catalyst
paste containing catalyst particles and a polymer electrolyte is
coated on a sheet--like support 6 and dried to form an electrode
catalyst layer 1 containing a solvent in an amount in the range of
0.5% or less by weight of the total membrane. The electrode
catalyst layers 3, 3 are thermally transferred and joined on both
sides of the polymer electrolyte membrane 1.
Inventors: |
Hama, Yuichiro; (Wako-shi,
JP) ; Iguchi, Masaru; (Wako-shi, JP) ; Yano,
Junichi; (Wako-shi, JP) ; Kanaoka, Nagayuki;
(Wako-shi, JP) ; Mitsuta, Naoki; (Wako-shi,
JP) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN
1050 CONNECTICUT AVENUE, N.W.
SUITE 400
WASHINGTON
DC
20036
US
|
Assignee: |
HONDA MOTOR CO., LTD
|
Family ID: |
32303630 |
Appl. No.: |
10/713146 |
Filed: |
November 17, 2003 |
Current U.S.
Class: |
429/482 ;
427/115; 429/493; 429/524; 429/532; 429/535; 502/101 |
Current CPC
Class: |
H01M 4/926 20130101;
H01M 8/1039 20130101; H01M 4/8807 20130101; H01M 8/1025 20130101;
H01M 8/1004 20130101; H01M 4/8882 20130101; H01M 4/8828 20130101;
Y02E 60/50 20130101; H01M 4/92 20130101; Y02P 70/50 20151101 |
Class at
Publication: |
429/044 ;
429/033; 427/115; 502/101 |
International
Class: |
H01M 004/96; H01M
008/10; H01M 004/88; B05D 005/12 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 18, 2002 |
JP |
2002-333566 |
Nov 18, 2002 |
JP |
2002-334302 |
Oct 31, 2003 |
JP |
2003-371834 |
Oct 31, 2003 |
JP |
2003-371835 |
Claims
What is claimed is:
1. An electrode structure for a polymer electrolyte fuel cell
comprising a pair of electrode catalyst layers containing carbon
particles supporting platinum particles as a catalyst and a polymer
electrolyte membrane sandwiched between the electrode catalyst
layers, wherein said polymer electrolyte membrane is made of a
sulfonated polyarylene-based polymer; said sulfonated
polyarylene-based polymer has an ion exchange capacity in the range
of 1.7 to 2.3 meq/g; and said polymer contains a component
insoluble in N-methylpyrrolidone in an amount of 70% or less
relative to the total amount of the polymer, after said polymer is
subjected to heat treatment for exposing the same under a constant
temperature atmosphere of 120.degree. C. for 200 hours.
2. The electrode structure for a polymer electrolyte fuel cell
according to claim 1, wherein said sulfonated polyarylene-based
polymer is a sulfonated product of a copolymer represented by
formula (1): 9
3. The electrode structure for a polymer electrolyte fuel cell
according to claim 1, wherein said sulfonated polyarylene-based
polymer is a copolymer represented by formula (2): 10
4. A method for manufacturing an electrode structure for a polymer
electrolyte fuel cell comprising a pair of electrode catalyst
layers containing carbon particles supporting platinum particles as
a catalyst and a polymer electrolyte membrane sandwiched between
the electrode catalyst layers, wherein said polymer electrolyte
membrane is made of a sulfonated polyarylene-based polymer,
comprising the steps of: forming a polymer electrolyte membrane
from a solution of a sulfonated polyarylene-based polymer; coating
a catalyst paste containing catalyst particles in which platinum
particles are supported on carbon particles and a polymer
electrolyte on a sheet-like support and drying the same to form an
electrode catalyst layer; and thermally transferring to join said
electrode catalyst layer to both sides of the polymer electrolyte
membrane containing a solvent in the range of 0.5% or less by
weight of the total membrane.
5. The method for manufacturing an electrode structure for a
polymer electrolyte fuel cell according to claim 4, wherein said
sulfonated polyarylene-based polymer is a sulfonated product of a
copolymer represented by formula (1): 11
6. The method for manufacturing an electrode structure for a
polymer electrolyte fuel cell according to claim 4, wherein said
sulfonated polyarylene-based polymer is a copolymer represented by
formula (2): 12
7. A polymer electrolyte fuel cell comprising an electrode
structure for a polymer electrolyte fuel cell comprising a pair of
electrode catalyst layers containing carbon particles supporting
platinum particles as a catalyst and a polymer electrolyte membrane
sandwiched between the electrode catalyst layers, wherein said
polymer electrolyte membrane is made of a sulfonated
polyarylene-based polymer; said sulfonated polyarylene-based
polymer has an ion exchange capacity in the range of 1.7 to 2.3
meq/g; and said polymer contains a component insoluble in
N-methylpyrrolidone in an amount of 70% or less relative to the
total amount of the polymer, after said polymer is subjected to
heat treatment for exposing the same under a constant temperature
atmosphere of 120.degree. C. for 200 hours.
8. An electrical apparatus using a polymer electrolyte fuel cell
comprising an electrode structure for a polymer electrolyte fuel
cell comprising a pair of electrode catalyst layers containing
carbon particles supporting platinum particles as a catalyst and a
polymer electrolyte membrane sandwiched by the electrode catalyst
layers, wherein said polymer electrolyte membrane is made of a
sulfonated polyarylene-based polymer; said sulfonated
polyarylene-based polymer has an ion exchange capacity in the range
of 1.7 to 2.3 meq/g; and said polymer contains a component
insoluble in N-methylpyrrolidone in an amount of 70% or less
relative to the total amount of the polymer, after said polymer is
subjected to heat treatment for exposing the same under a constant
temperature atmosphere of 120.degree. C. for 200 hours.
9. A transport apparatus using a polymer electrolyte fuel cell
comprising an electrode structure for a polymer electrolyte fuel
cell comprising a pair of electrode catalyst layers containing
carbon particles supporting platinum particles as a catalyst and a
polymer electrolyte membrane sandwiched by the electrode catalyst
layers, wherein said polymer electrolyte membrane is made of a
sulfonated polyarylene-based polymer; said sulfonated
polyarylene-based polymer has an ion exchange capacity in the range
of 1.7 to 2.3 meq/g; and said polymer contains a component
insoluble in N-methylpyrrolidone in an amount of 70% or less
relative to the total amount of the polymer, after said polymer is
subjected to heat treatment for exposing the same under a constant
temperature atmosphere of 120.degree. C. for 200 hours.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electrode structure for
a polymer electrolyte fuel cell and a method for manufacturing the
same.
[0003] 2. Description of the Related Art
[0004] Petroleum resources are going to be exhausted, and at the
same time environmental issues such as global warming due to the
consumption of fossil fuels are becoming more critical. Thus, as a
clean power source for an electric motor that is not associated
with the generation of carbon dioxide, a fuel cell has attracted
attention, has been developed extensively, and has become
commercially practical in some applications. When the fuel cell is
mounted on a vehicle and the like, a polymer electrolyte fuel cell
using a polymer electrolyte membrane is suitably used because high
voltage and a large current are readily obtained.
[0005] There is known an electrode structure for use in the polymer
electrolyte fuel cell comprising a pair of electrode catalyst
layers which is formed by supporting a catalyst such as platinum on
a catalyst carrier such as carbon black and being integrated by an
ion conducting polymer binder, wherein an ion-conducting polymer
electrolyte membrane is sandwiched between the both electrode
catalyst layers and a diffusion layer is laminated on each of the
electrode catalyst layers (Refer to, for example, Japanese Patent
Laid-Open No. 2000-223136). The electrode structure can compose a
polymer electrolyte fuel cell by further laminating a separator,
which also serves as a gas channel, on each diffusion layer.
[0006] In the polymer electrolyte fuel cell, one of the electrode
catalyst layers is used as a fuel electrode, into which a reducing
gas such as hydrogen or methanol is introduced through the
diffusion layer, and the other electrode catalyst layer is used as
an oxygen electrode, into which an oxidizing gas such as air or
oxygen is introduced through the diffusion layer. In this way, at
the fuel electrode side, the catalyst contained in the electrode
catalyst layer acts to produce protons from the reducing gas, and
the protons move through the polymer electrolyte membrane to the
electrode catalyst layer at the oxygen electrode side. Further, the
protons react with the oxidizing gas introduced into the oxygen
electrode side to produce water in the electrode catalyst layer at
the oxygen electrode by the action of the catalyst contained in the
electrode catalyst layer. Consequently, the polymer electrolyte
fuel cell can provide current by connecting the fuel electrode to
the oxygen electrode with a lead wire.
[0007] Conventionally, in the electrode structure,
perfluoroalkylenesulfon- ic acid polymer compound(e.g., Nafion
(trade name) made by E.I. du Pont de Nemours and Company) has been
widely utilized as the polymer electrolyte membrane. The
perfluoroalkylenesulfonic acid polymer compound has excellent
proton conducting properties as it is sulfonated and also has
chemical resistance as a fluoropolymer, but has a problem that it
is very expensive.
[0008] Therefore, it has been studied to compose an electrode
structure for a polymer electrolyte fuel cell using a less
expensive ion-conducting material as an alternative to
perfluoroalkylenesulfonic acid polymer compound. For example, a
sulfonated polyarylene-based polymer is known as the less expensive
ion-conducting material.
[0009] However, the electrode structure using the polymer
electrolyte membrane made of the sulfonated polyarylene-based
polymer has the problem of degradation of the polymer electrolyte
membrane by the heat during operation, when composing a fuel cell,
causing to mix the gases introduced into the fuel electrode and
oxygen electrode sides and to develop cross-leak in which the poles
are short-circuited.
[0010] Conventionally, the electrode structure has been produced,
for example, as described below. First, a polymer electrolyte
membrane is formed by a casting method from a solution prepared by
dissolving the sulfonated polyarylene-based polymer in a solvent
such as N-methylpyrrolidone.
[0011] Catalyst particles in which platinum particles are supported
on carbon particles are dispersed in the polymer electrolyte
solution to prepare a catalyst paste containing the catalyst
particles and the polymer electrolyte. The catalyst paste is coated
on a she t-like support such as a polyethylene terephthalate film
and dried to form an electrode catalyst layer.
[0012] Then, the both sides of the polymer electrolyte membrane are
sandwiched between the electrode catalyst layers and maintained at
the temperature ranging from 80 to 160.degree. C. After the polymer
electrolyte membrane and the polymer electrolyte contained in the
electrode catalyst layers are softened, they are maintained under a
pressure in the range of 1 to 10 MPa for 1 to 60 minutes. As a
result, the electrode catalyst layers are transferred to the
polymer electrolyte membrane from the polyethylene terephthalate
film to be joined to the polymer electrolyte membrane by
thermocompression bonding.
[0013] Then, the electrode catalyst layers at the both sides are
sandwiched between diffusion layers and subjected to hot press.
Thereby, the diffusion layers are joined to each of the electrode
catalyst layers to form an electrode structure.
[0014] However, the electrode structure produced by the
conventional production method has a problem that it has large
change in dimensions.
SUMMARY OF THE INVENTION
[0015] It is an object of the present invention to provide an
electrode structure for a polymer electrolyte fuel cell having
excellent power generation performance and excellent durability to
the heat during the operation of a fuel cell.
[0016] Another object of the present invention is to provide a
method for producing the electrode structure for a polymer
electrolyte fuel cell.
[0017] A further object of the present invention is to provide a
method in which the electrode structure for a polymer electrolyte
fuel cell having excellent dimensional stability can be
produced.
[0018] A polyarylene-based polymer can be provided with an ion
exchange function by sulfonation. A greater number of sulfonic acid
groups to be introduced into the polymer provides larger ion
exchange capacity. On the other hand, the greater number of
sulfonic acid groups causes the polymer to be more easily degraded
by heat.
[0019] The inventors have studied the sulfonated polyarylene-based
polymer, and have found that when the number of the introduced
sulfonic acid groups is large, an intermolecular crosslinking
reaction occurs by the sulfonic acid groups upon heating, resulting
in the formation of a component insoluble in a solvent such as
N-methylpyrrolidone. The inventors have further studied based upon
the above knowledge, and have attained the present invention by
finding that the amount of the component insoluble in the solvent
affects the toughness of the polymer electrolyte membrane made of
the sulfonated polyarylene-based polymer, and that the reduction of
toughness is related to the power generation performance of a fuel
cell and the durability to the heat during the operation of the
fuel cell.
[0020] Thus, for achieving these objects, an electrode structure
for a polymer electrolyte fuel cell of the present invention
comprises a pair of electrode catalyst layers containing carbon
particles supporting platinum particles as a catalyst and a polymer
electrolyte membrane sandwiched between the electrode catalyst
layers, wherein the polymer electrolyte membrane is made of a
sulfonated polyarylene-based polymer; the sulfonated
polyarylene-based polymer has an ion exchange capacity in the range
of 1.7 to 2.3 meq/g; and the polymer contains a component insoluble
in N-methylpyrrolidone in an amount of 70% or less relative to the
total amount of the polymer, after the polymer is subjected to heat
treatment for exposing the same under a constant temperature
atmosphere of 120.degree. C. for 200 hours.
[0021] The content of the insoluble component can be calculated by
determining elution curves from gel permeation chromatographs for
an untreated polymer electrolyte membrane and the polymer
electrolyte membrane after subjected to the treatment for exposing
it under a constant temperature atmosphere of 120.degree. C. for
200 hours and by determining the ratio of the areas of these
elution curves (the area of the elution curve for the untreated
polymer electrolyte membrane is defined as 100).
[0022] The electrode structure for a polymer electrolyte fuel cell
of the present invention can provide excellent power generation
performance and excellent durability to the heat during the
operation of the fuel cell, when the sulfonated polyarylene-based
polymer has the ion exchange capacity in the above-described range,
and the polymer contains a component insoluble in
N-methylpyrrolidone in an amount in the range described above after
the polymer is subjected to the above-described heat treatment.
[0023] In the present specification, a "sulfonated
polyarylene-based polymer" refers to a sulfonated product of a
polymer having the structure of the formula: 1
[0024] (wherein --X-- denotes a single bond or a divalent organic
group; --W-- denotes a divalent electron attractive group; --I--
denotes a divalent organic group; R.sup.1 to R.sup.8 each denotes a
fluorine atom, a hydrogen atom, an alkyl group, an aryl group or an
allyl group, and each independently may be the same or different; p
is 0.5 to 100; q is 99.5 to 0; r is an integer of 0 to 10; and s is
an integer of 1 to 100)
[0025] The divalent organic groups may include electron attractive
groups such as --CO--, --CONH--, --(CF.sub.2).sub.p--(pis an
integer of 1 to 10), --C(CF.sub.3).sub.2 --, --COO--, --SO--, and
--SO.sub.2--; groups such as --O--, --S--, --CH.dbd.CH--, and
--C.ident.C--; and electron donative groups represented by the
formula: 2
[0026] The divalent electron attractive groups may include groups
such as --CO--, --CONH--, --(CF.sub.2).sub.p-- (p is an integer of
1 to 10), --C(CF.sub.3).sub.2--, --COO--, --SO--, and
--SO.sub.2--.
[0027] The electrode structure for a polymer electrolyte fuel cell
of the present invention cannot provide sufficient power generation
performance, if the ion exchange capacity of the sulfonated
polyarylene-based polymer is less than 1.7 meq/g. In addition, it
cannot provide sufficient durability to the heat during the
operation of the fuel cell, if the ion exchange capacity of the
sulfonated polyarylene-based polymer is more than 2.3 meq/g, and
the polymer contains a component insoluble in N-methylpyrrolidone
in an amount of more than 70% relative to the total amount of the
polymer, after the polymer is subjected to the above-described heat
treatment.
[0028] In the electrode structure for a polymer electrolyte fuel
cell of the present invention, when the ion exchange capacity is in
the above-described range, the sulfonated polyarylene-based polymer
is preferably, for example, a sulfonated product of a copolymer
represented by formula (1) or a copolymer represented by formula
(2), in order to bring the content of the insoluble component after
the heat treatment into the above-described range: 3
[0029] Moreover, the inventors have diligently studied the reason
why the change of dimensions is increased when a polymer
electrolyte fuel cell is formed from the electrode structure
produced by the conventional production method. As a result, it has
been found that, in the conventional production method, the
solvent, which is contained in a polymer electrolyte membrane, in
order to facilitate the thermocompression bonding with electrode
catalyst layers, is evaporated by the heat for thermally
transferring the electrode catalyst layers, causing shrinkage of
the polymer electrolyte membrane.
[0030] The polymer electrolyte membrane contains the solvent in an
amount from about 1 to 30% by weight of the total membrane, and so
the membrane swells and is easily softened by heating, facilitating
the thermocompression bonding with electrode catalyst layers.
Therefore, the polymer electrolyte membrane, after formed by a
casting method, is dried in an oven or the like to contain the
solvent in an amount within the above-described range.
Alternatively, the polymer electrolyte membrane, after dried in the
oven or the like, is immersed in a solvent such as ethanol or
methanol, or is sprayed with the solvent to contain the solvent in
an amount within the above-described range.
[0031] The inventors have further continued investigation based
upon the above-described knowledge. As a result, it has been found
that excellent dimensional stability can be provided by reducing
the amount of the solvent contained in the polymer electrolyte
membrane below the predetermined range, to suppress the shrinkage
of the polymer electrolyte membrane when the electrode catalyst
layers are thermally transferred.
[0032] Thus, the method for manufacturing an electrode structure of
the present invention comprises a method for manufacturing an
electrode structure for a polymer electrolyte fuel cell comprising
a pair of electrode catalyst layers containing carbon particles
supporting platinum particles as a catalyst and a polymer
electrolyte membrane sandwiched between the electrode catalyst
layers, wherein the polymer electrolyte membrane is made of a
sulfonated polyarylene-based polymer, comprising the steps of:
forming a polymer electrolytemembrane from a solution of a
sulfonated polyarylene-based polymer; coating a catalyst paste
containing catalyst particles in which platinum particles are
supported on carbon particles and a polymer electrolyte on a
sheet-like support and drying the same to form an electrode
catalyst layer; and thermally transferring to join said electrode
catalyst layer to both sides of the polymer electrolyte membrane
containing a solvent in the range of 0.5% or less by weight of the
total membrane.
[0033] According to the manufacturing method of the present
invention, in the step of thermally transferring the electrode
catalyst layer, the polymer electrolyte membrane contains a solvent
in an amount in the range of 0.5% or less by weight of the total
membrane. Consequently, as for the electrode structure obtained in
the manufacturing method of the present invention, the amount of
the solvent that evaporates from the polymer electrolyte membrane
when the electrode catalyst layer is thermally transferred is
extremely small, so that the shrinkage of the polymer
electrolytemembrane can be suppressed to obtain excellent
dimensional stability.
[0034] In the step of thermally transferring the electrode catalyst
layer, when the polymer electrolyte membrane contains a solvent in
an amount more than 0.5% by weight of the total membrane, the
shrinkage of the polymer electrolyte membrane due to the
evaporation of the solvent from the polymer electrolyte membrane
cannot be suppressed.
[0035] Moreover, the polymer electrolyte fuel cell needs to be
subjected to the treatment (aging) for stabilizing the potential by
actually operating the cell to discharge the solvent contained in
the polymer electrolyte membrane, after forming the polymer
electrolyte fuel cell from the electrode structure. The electrode
structure obtained by the manufacturing method of the present
invention contains extremely reduced amount of the solvent
contained in the polymer electrolyte membrane to 0.5% or less by
weight of the total membrane as described above, so that the time
required for the aging can be extremely reduced when the polymer
electrolyte fuel cell is formed.
[0036] Moreover, the present invention also resides in a polymer
electrolyte fuel cell comprising the electrode structure for a
polymer electrolyte fuel cell. The polymer electrolyte fuel cell of
the present invention can be used, for example, as a power source,
a backup power source and the like for an electrical apparatus such
as a personal computer and a cellular phone. In addition, the
polymer electrolyte fuel cell of the present invention can also be
used, for example, as a power for a transport apparatus such as a
vehicle and a ship such as a submarine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is an illustrative sectional view showing one example
of an electrode structure for a polymer electrolyte fuel cell of
the present invention;
[0038] FIGS. 2(a) to 2(f) are manufacturing process views
schematically showing a method for manufacturing an electrode
structure for a polymer electrolyte fuel cell of the present
invention;
[0039] FIG. 3 is a graphical representation showing the relation of
the solvent content in a polymer electrolyte membrane to the
dimensional change ratio; and
[0040] FIG. 4 is a graphical representation showing the change of
voltage with time when a polymer electrolyte fuel cell composed
using an electrode structure for a polymer electrolyte fuel cell
obtained by a manufacturing method of the present invention is
subjected to aging.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0041] The embodiments of the present invention will now be
described further in detail with reference to the attached
drawings.
[0042] The electrode structure of the present embodiment consists
of a pair of electrode catalyst layers 1, 1, a polymer electrolyte
membrane 2 sandwiched by the electrode catalyst layers 1, 1 and
diffusion layers 3, 3 laminated on each of the electrode catalyst
layers 1, 1. The diffusion layer 3 consists of a carbon paper 4 and
a primary coat 5 formed on one side of the carbon paper 4, and is
laminated on the electrode catalyst layer 1 through the primary
coat 5.
[0043] The electrode catalyst layer 1 consists of catalyst
particles in which platinum particles are supported on carbon
particles and an ion conducting binder. As the ion conducting
binder, polymer electrolytes such as the above-described
perfluoroalkylenesulfonic acid polymer compound (e.g., Nafion
(trade name) made by E.I. du Pont de Nemours and Company) and a
sulfonated polyarylene-based polymer are used.
[0044] The polymer electrolyte membrane 2 is made of a sulfonated
polyarylene-based polymer, which has an ion exchange capacity in
the range of 1.7 to 2.3 meq/g. In addition, the sulfonated
polyarylene-based polymer to be used contains a component insoluble
in N-methylpyrrolidone in an amount of 70% or less relative to the
total amount of the polymer, after the polymer is subjected to heat
treatment for exposing it under a constant temperature atmosphere
of 120.degree. C. for 200 hours.
[0045] The sulfonated polyarylene-based polymers in which, when the
ion exchange capacity is in the above-described range, the content
of the insoluble component after the heat treatment is brought into
the above-described range, may include, for example, a sulfonated
product of a copolymer represented by formula (1) or a copolymer
represented by formula (2): 4
[0046] The copolymer represented by formula (1) can be obtained by
copolymerizing a monomer represented by formula (3) with an
oligomer represented by formula (4): 5
[0047] The copolymer represented by formula (1) can be sulfonated
by reacting with concentrated sulfuric acid to introduce a sulfonic
acid group to a benzene ring that is not adjacent to an electron
attracting group.
[0048] Further, the copolymer represented by formula (2) can be
obtained by copolymerizing a monomer represented by formula (5)
with the oligomer represented by formula (4), and then by
hydrolyzing a sulfonate ester group
(--SO.sub.3CH(CH.sub.3)C.sub.2H.sub.5) to form a sulfonic acid
group (--SO.sub.3H). 6
[0049] The diffusion layer 3 consists of, for example, a carbon
paper 4 and a primary coat 5 formed on the carbon paper 4. The
primary coat 5 to be used includes a mixture prepared by mixing,
for example, carbon black with polytetrafluoroethylene (PTFE)
particles in a weight ratio of carbon black:PTFE=4:6.
[0050] The method for manufacturing an electrode structure of the
present embodiment will now be described with reference to FIGS.
2(a) to 2(f).
[0051] In the method for manufacturing the electrode structure of
present invention, as the sulfonated polyarylene-based polymer, the
sulfonated product of the copolymer represented by formula (1) or
the copolymer represented by formula (2) is first dissolved in
N-methylpyrrolidone to prepare a polymer electrolyte solution.
Next, a membrane is cast from the polymer electrolyte solution by a
casting method and dried in an oven to form a polymer electrolyte
membrane 2 shown in FIG. 2(a). The polymer electrolyte membrane 2
has a dry thickness of 40 .mu.m and contains 0.5% or less by weight
of a solvent relative to the total weight of the membrane.
[0052] Next, platinum particles are supported on carbon black
(furnace black), for example, in a weight ratio of carbon black:
platinum particles=1:1 to prepare catalyst particles. Then, the
catalyst particles are uniformly dispersed in a
perfluoroalkylenesulfonic acid polymer compound(e.g., Nafion (trade
name) made by E.I. du Pont de Nemours and Company) solution as an
ion conducting polymer binder solution, for example, in a weight
ratio of catalyst particles:ion conducting polymer binder=2:1 to
prepare a catalyst paste.
[0053] Next, the catalyst paste is screen-printed on a polyethylene
terephthalate film 6 shown in FIG. 2(b) and then dried to form an
electrode catalyst layer 1. Then, as shown in FIG. 2(c), the
polymer electrolyte membrane 2 is sandwiched by a pair of electrode
catalyst layers 1, 1, and hot-pressed from above the polyethylene
terephthalate films 6.
[0054] The hot-pressing is performed, for example, at a temperature
in the range of 80 to 160.degree. C. under application of a surface
pressure in the range of 1 to 10 MPa for 1 to 60 minutes. As a
result, the electrode catalyst layer 1 is transferred to the
polymer electrolyte membrane 2 to be joined with the polymer
electrolyte membrane 2. Then, removal of the polyethylene
terephthalate film 6 provides a structure 7 in which the polymer
electrolyte membrane 2 is sandwiched by a pair of electrode
catalyst layers 1, 1, as shown in FIG. 2(d).
[0055] Next, a slurry, in which a mixture obtained by mixing carbon
black with polytetrafluoroethylene (PTFE) particles, for example,
in a weight ratio of 1:1 is uniformly dispersed in ethylene glycol,
is coated on one of the surfaces of the carbon paper 4 shown in
FIG. 2(e) and then dried to form a primary coat 5, forming a
diffusion layer 3 consisting of the carbon paper 4 and the primary
coat 5.
[0056] Next, as shown in FIG. 2(f), the structure 7 is sandwiched
by a pair of the diffusion layers 3,3 on the sides with the primary
coats 5, 5 and hot-pressed from above the carbon papers 4. The
hot-pressing is performed, for example, at a temperature in the
range of 100 to 180.degree. C. under application of a surface
pressure in the range of 10 to 100 MPa for 1 to 60 minutes. As a
result, the diffusion layer 3 is joined to the electrode catalyst
layer 1 through the primary coat 5 to provide the electrode
structure 8 comprising the structure in which the structure 7 is
sandwiched between the diffusion layers 3, 3.
[0057] In the electrode structure 8, a reducing gas such as
hydrogen and methanol is introduced into the electrode catalyst
layer 1 through the diffusion layer 3 for the fuel electrode
(anode) side, and an oxidizing gas such as air and oxygen is
introduced into the electrode catalyst layer 1 through the
diffusion layer 3 for the oxygen electrode (cathode) side. On the
fuel electrode side, protons and electrons are produced from the
reducing gas by the action of the catalyst contained in the
electrode catalyst layer 1. The protons move to the electrode
catalyst layer 1 on the oxygen electrode side through the polymer
electrolyte membrane 2, and react with the oxidizing gas and
electrons introduced into the catalyst layer 1, to form water by
the action of the catalyst contained in the electrode catalyst
layer 1. Therefore, a circuit for sending the electrons produced in
the fuel electrode to the oxygen electrode is formed by connecting
the fuel electrode to the oxygen electrode through a lead wire, and
current can be taken out. Thus, the electrode structure 8 can be
used as a fuel cell.
[0058] The examples and comparative examples of the present
invention will now be shown.
EXAMPLE 1
[0059] In the present example, firstly, into a 1 liter,
three-necked flask equipped with a stirrer, a thermometer, a
condenser, a Dean-Stark tube, and a three-way cock for introducing
nitrogen, 67.3 g (0.20 mole) of
2,2-bis(4-hydroxypheny)-1,1,1,3,3,3-hexafluoropropane (bisphenol
AF), 53.5 g (0.214 mole) of 4,4'-dichlorobenzophenone, 34.6 g
(0.251 mole) of potassium carbonate, 300 ml of
N,N-dimethylacetamide and 150 ml of toluene were charged, heated
under nitrogen atmosphere in an oil bath and reacted at 130.degree.
C. while stirring. The reaction was carried out while the water
produced by the reaction was azeotropically distilled with toluene
and removed to the outside of the system through the Dean-Stark
tube. Production of water almost stopped in about 3 hours, and then
most of the toluene was removed by increasing the reaction
temperature slowly from 130.degree. C. to 150.degree. C. After
continued the reaction for 10 hours at 150.degree. C., 3.3 g
(0.0133 mole) of 4,4'-dichlorobenzophenone was added and further
reacted for 5 hours.
[0060] After the resultant reaction solution was cooled in air, a
by-product that is a precipitate of an inorganic compound was
removed by filtration and the filtrate was added into 4 liter of m
thanol. A precipitated product was filtered, recovered, dried, and
then dissolved in 300 ml of tetrahydrofuran. The resultant solution
was reprecipitated with 4 liter of methanol, obtaining 98 g of an
oligomer (yield 93%) represented by formula (4): 7
[0061] Next, 28.4 g (2.87 mmol) of the oligomer represented by
formula (4), 29.2 g (67.1 mmol) of
2,5-dichloro-4'-(4-phenoxy)phenoxybenzophenone- , 1.37 g (2.1 mmol)
of bis(triphenylphosphine)nickel dichloride, 1.36 g (9.07 mmol) of
sodium iodide, 7.34 g (28.0 mmol) of triphenylphosphine, and 11.0
parts by weight (168 mmol) of zinc powder were charged into a flask
and substituted with dry nitrogen. Then, the mixture was added with
130 ml of N-methyl-2-pyrrolidone, heated to 80.degree. C. and
subjected to polymerization for 4 hours while stirring. A polymer
solution was diluted with tetrahydrofuran, and a polymer was
recovered by coagulating with hydrochloric acid/methanol. The
recovered product was repeatedly washed with methanol and dissolved
in tetrahydrofuran. It was purified by reprecipitation with
methanol, and the polymer that was obtained by filtration was
vacuum-dried, to obtain 5.07 g of a polyarylene-based polymer
(yield 96%) represented by formula (1): 8
[0062] Next, the polyarylene-based polymer represented by formula
(1) was added with concentrated sulfuric acid to be sulfonated so
as to have an ion exchange capacity of 1.7 meq/g, preparing a
sulfonated polyarylene-based polymer.
[0063] Next, the sulfonated polyarylene-based polymer was dissolved
in N-methylpyrrolidone to prepare a polymer electrolyte solution,
from which the polymer electrolyte membrane 2 having a dry
thickness of 35 .mu.m shown in FIG. 2(a) was prepared by a casting
method. The polymer electrolyte membrane 2 was found to contain
0.5% or less by weight of a solvent relative to the total weight of
the membrane.
[0064] Next, platinum particles were supported on carbon black
(furnace black) in a weight ratio of platinum particles: carbon
black particles=1:1 to prepare catalyst particles. Then, the
catalyst particles were uniformly dispersed in a
perfluoroalkylenesulfonic acid polymer compound(e.g., Nafion (trade
name) made by E.I. du Pont de Nemours and Company) solution as an
ion conducting polymer binder solution, in a weight ratio of
catalyst particles:ion conducting polymer binder=5:7, to prepare a
catalyst paste.
[0065] Next, the catalyst paste was screen-printed on a
polyethylene terephthalate film 6, as shown in FIG. 2(b), and then
dried to form an electrode catalyst layer 1. Then, as shown in FIG.
2(c), the polymer electrolyte membrane 2 was sandwiched between a
pair of electrode catalyst layers 1, 1, and hot-pressed from above
the polyethylene terephthalate film 6 at 160.degree. C. and 4 MPa
for 10 minutes, transferring the electrode catalyst layer 1 to the
polymer electrolyte membrane 2. After the hot-pressing, removal of
the polyethylene terephthalate film 6 provided a structure 7 in
which both sides of the polymer electrolyte membrane 2 were joined
with the electrode catalyst layers 1, 1, as shown in FIG. 2(d).
[0066] Next, a slurry, in which a mixture obtained by mixing carbon
black with polytetrafluoroethylene (PTFE) particles in a weight
ratio of 4:6 is uniformly dispersed in ethylene glycol, was coated
on one of the surfaces of the carbon paper 4 and dried to form a
primary coat 5, forming a diffusion layer 3 consisting of the
carbon paper 4 and the primary coat 5, as shown in FIG. 2(e).
[0067] Next, as shown in FIG. 2(f), the structure 7 was sandwiched
by a pair of the diffusion layers 3,3 on the sides with the primary
coats 5,5 and hot-pressed from above the carbon papers 4 at
140.degree. C. and 3 MPa for 5 minutes. As a result, the diffusion
layer 3 was joined to the electrode catalyst layer 1 through the
primary coat 5 to provide the electrode structure 8 comprising the
structure in which the structure 7 is sandwiched between the
diffusion layers 3, 3.
[0068] Next, the content of the insoluble component in the
polyarylene-based polymer in the polymer electrolyte membrane 2
obtained in the pr sent example was determined, and the power
generation performance of the electrode structure 8 obtained in the
present example was evaluated.
[0069] As for the determination of the content of the insoluble
component in the polyarylene-based polymer, the polymer electrolyte
membrane 2 was subjected to the heat treatment for exposing it
under a constant temperature atmosphere of 120.degree. C. for 200
hours, and then the elution curves from gel permeation
chromatographs were determined for an untreated polymer electrolyte
membrane 2 and for the polymer electrolyte membrane 2 after
subjected to the above-described heat treatment. Then, the content
of the insoluble component in the polyarylene-based polymer was
calculated from the ratio of the areas for the above-described
elution curves, wherein the area of the elution curve for the
untreated polymer electrolyte membrane 2 was defined as 100.
[0070] The gel permeation chromatographs were determined by the
HLC-8020 (trade name) made by Tosoh Corporation using a refractive
index detector. As columns, two pieces of ShodexKD-806M (trade
name) made by Showa Denko K. K. were used, and one piece of
ShodexKD-G (trade name) made by Showa Denko K. K. was used as a
pre-column. N-methylpyrrolidone(1st grade reagent, containing 50
mmol/l of lithium chloride and 50 mmol/l of phosphoric acid) was
used as a solvent, with a flow rate of 1.0 ml/minute. The
temperatures were set at 40.degree. C. for all of the column part,
the inlet part and the detection part. Samples were filtered with a
0.5 .mu.m polytetrafluoroethylene filter; the concentration was set
at 0.3% by weight; and the feed volume was set at 0.3 ml.
[0071] As a result, for the polymer electrolyte membrane 2 obtained
in the present example, the content of the insoluble component in
the polyarylene-based polymer was 15% by weight.
[0072] Next, the electrode structure 8 obtained in the present
example was used to evaluate power generation performance, under
the power generation conditions of a temperature of 95.degree. C.,
a relative humidity for the fuel electrode side of 35% and a
relative humidity for the oxygen electrode side of 65%. The results
are shown in Table 1. Cell potentials at a current density of 0.5
A/cm.sup.2 were measured. When the cell potential was 0.4 V or
higher, the power generation performance was defined as good and
indicated as [Good] in Table 1, and it was defined as poor when the
cell potential was lower than 0.4 V and indicated as [Poor] in
Table 1.
[0073] Further, the service life was measured until the cross-leak
occurred between the fuel electrode side and the oxygen electrode
side when the power was generated under the above-described
conditions. The results are also shown in Table 1.
EXAMPLE 2
[0074] In the present example, the electrode structure 8 was
manufactured exactly the same way as in Example 1 except that the
polyarylene-based polymer represented by formula (1) was sulfonated
so as to have an ion exchange capacity of 2.0 meq/g to prepare a
sulfonated polyarylene-based polymer.
[0075] Next, the content of a component insoluble in
N-methylpyrrolidone in the polyarylene-based polymer in the polymer
electrolyte membrane 2 obtained in the present example was
determined exactly the same way as in Example 1. For the polymer
electrolyte membrane 2 obtained in the present example, the content
of the insoluble component in the polyarylene-based polymer was 35%
by weight.
[0076] Next, power generation performance was evaluated and the
above-described service life was measured, exactly the same way as
in Example 1, using the electrode structure 8 obtained in the
present example. The results are shown in Table 1.
EXAMPLE 3
[0077] In the present example, the electrode structure 8 was
manufactured exactly the same way as Example 1 except that the
polyarylene-based polymer represented by formula (1) was sulfonated
so as to have an ion exchange capacity of 2.3 meq/g to prepare a
sulfonated polyarylene-based polymer.
[0078] Next, the content of a component insoluble in
N-methylpyrrolidone in the polyarylene-based polymer in the polymer
electrolyte membrane 2 obtained in the present example was
determined exactly the same way as in Example 1. For the polymer
electrolyte membrane 2 obtained in the present example, the content
of the insoluble component in the polyarylene-based polymer was 56%
by weight.
[0079] Next, power generation performance was evaluated and the
above-described service life was measured, exactly the same way as
in Example 1, using the electrode structure 8 obtained in the
present example. The results are shown in Table 1.
COMPARATIVE EXAMPLE 1
[0080] In the present comparative exampl , the electrode structur 8
was manufactured exactly the same way as in Example 1 except that
the polyarylene-based polymer represented by formula (1) was
sulfonated so as to have an ion exchange capacity of 1.5 meq/g to
prepare a sulfonatedpolyarylene-based polymer.
[0081] Next, the content of a component insoluble in
N-methylpyrrolidone in the polyarylene-based polymer in the polymer
electrolyte membrane 2 obtained in the present comparative example
was determined exactly the same way as in Example 1. For the
polymer electrolyte membrane 2 obtained in the present comparative
example, the content of the insoluble component in the
polyarylene-based polymer was zero.
[0082] Next, power generation performance was evaluated, exactly
the same way as in Example 1, using the electrode structure 8
obtained in the present example. As the power generation
performance was poor, the above-described service life was not
measured. The results are shown in Table 1.
COMPARATIVE EXAMPLE 2
[0083] In the present comparative example, the electrode structure
8 was manufactured exactly the same way as in Example 1 except that
the polyarylene-based polymer represented by formula (1) was
sulfonated so as to have an ion exchange capacity of 2.4 meq/g to
prepare a sulfonated polyarylene-based polymer.
[0084] Next, the content of a component insoluble in
N-methylpyrrolidone in the polyarylene-based polymer in the polymer
electrolyte membrane 2 obtained in the present comparative example
was determined exactly the same way as in Example 1. For the
polymer electrolyte membrane 2 obtained in the present comparative
example, the content of the insoluble component in the
polyarylene-based polymer was 75% by weight.
[0085] Next, power generation performance was evaluated and the
above-described service life was measured, exactly the same way as
in Example 1, using the electrode structure 8 obtained in the
present example. The results are shown in Table 1.
COMPARATIVE EXAMPLE 3
[0086] In the present comparative example, the electrode structure
8 was manufactured exactly the same way as in Example 1 except that
the polyarylene-based polymer represented by formula (1) was
sulfonated so as to have an ion exchange capacity of 2.5 meq/g to
prepare a sulfonated polyarylene-based polymer.
[0087] Next, the content of a component insoluble in
N-methylpyrrolidone in the polyarylene-based polymer in the polymer
electrolyte membrane 2 obtained in the present comparative example
was determined exactly the same way as in Example 1. For the
polymer electrolyte membrane 2 obtained in the present comparative
example, the content of the insoluble component in the
polyarylene-based polymer was 78% by weight.
[0088] Next, power generation performance was evaluated and service
life was measured, exactly the same way as Example 1, using the
electrode structure 8 obtained in the present example. The results
are shown in Table 1.
1 TABLE 1 Content Ion exchange of insoluble Power capacity
component generation Service life (meq/g) (wt %) performance (hr)
Comparative 1.5 0 Poor -- Example 1 Example 1 1.7 15 Good 1100
Example 2 2.0 35 Good 950 Example 3 2.3 56 Good 800 Comparative 2.4
75 Good 400 Example 2 Comparative 2.5 78 Good 200 Example 3
[0089] It is apparent from Table 1 that an ion exchange capacity of
less than 1.7 meq/g (Comparative Example 1) cannot provide
sufficient power generation performance. On the other hand, it is
apparent that an ion exchange capacity of 1.7 meq/g or more can
provide excellent power generation performance.
[0090] Moreover, it is apparent that, when the ion exchange
capacity is in the range of 1.7 to 2.3 meq/g and the content of an
insoluble component in the polyarylene-based polymer is 70% by
weight or less (Examples 1 to 3), the service life is much longer
and has excellent durability to the heat during the operation of
the fuel cell in addition to the excellent power generation
performance, compared with the case where the ion exchange capacity
is more than 2.3 meq/g and the content of an insoluble component in
the polyarylene-based polymer is more than 70% by weight
(Comparative Examples 2 and 3).
EXAMPLE 4 AND COMPARATIVE EXAMPLE 4
[0091] Next, the above-described structures 7 were manufactured so
that the content of the solvent in the polymer electrolyte membrane
2 relative to the total membrane is each 0.1%, 0.3%, 0.5%, 1.0% and
5.0%, by weight, when the electrode catalyst layer 1 is thermally
transferred to the side of the polymer electrolyte membrane 2.
Then, the dimensional change ratio when the electrode structure 8
was composed from each structure 7 was determined. The results are
shown in FIG. 3.
[0092] It is apparent from FIG. 3 that, when the content of the
solvent in the polymer electrolyte membrane 2 relative to the total
membrane is in the range of 0.1 to 0.5% by weight (Example 4), no
change in dimensions of the electrode structure 8 was observed. On
the other hand, it is apparent that, when the content of the
solvent is 1.0% and 5.0% by weight (Comparative Example 4), that
is, higher than 0.5% by weight, the dimensional change ratio is
large and it increases as the increase of the solvent content.
[0093] Next, the polymer electrolyte fuel cell composed of the
electrode structures 8 manufactured so that the content of the
solvent in the polymer electrolyte membrane 2 relative to the total
membrane is 0.5% by weight when the electrode catalyst layer 1 is
thermally transferred to the side of the polymer electrolyte
membrane 2 (Example 4), and the polymer electrolyte fuel cell
composed of the electrode structure 8 manufactured so that the
solvent content is 5.0% by weight (Comparative Example 4) were
operated, and the time until the potential becomes constant (time
required for aging) was measured. Th results are shown in FIG.
4.
[0094] It is apparent from FIG. 4 that, although it takes about 30
hours until the potential becomes constant for the polymer
electrolyte fuel cell of Comparative Example 4, it takes only
eleven hour for the polymer electrolyte fuel cell of Example 4, so
that the time required for aging was extremely reduced.
* * * * *