U.S. patent application number 10/492798 was filed with the patent office on 2004-12-02 for fuel cell-use carbon fiber woven fabric, electrode element, fuel cell mobile unit, and production method for fuel cell-use carbon fiber woven fabric.
Invention is credited to Chida, Takashi, Igakura, Shuichi, Inoue, Mikio.
Application Number | 20040241078 10/492798 |
Document ID | / |
Family ID | 19135624 |
Filed Date | 2004-12-02 |
United States Patent
Application |
20040241078 |
Kind Code |
A1 |
Inoue, Mikio ; et
al. |
December 2, 2004 |
Fuel cell-use carbon fiber woven fabric, electrode element, fuel
cell mobile unit, and production method for fuel cell-use carbon
fiber woven fabric
Abstract
A fuel cell-use carbon fiber woven fabric, especially a carbon
fiber woven fabric preferably used for the electrode diffusion
layer of an electrode element in a fuel cell. The electrode
diffusion layer of an electrode element in a fuel cell, requiring
conductivity, gas diffusing/permeating features, and strength that
withstands handling, is formed from carbon fiber woven fabrics as
is widely known. The conventional carbon fiber woven fabric poses
such problems that deformation by compression is large, the
dimension of a fuel cell is significantly changed by pressurizing,
irregularities by weave texture are large, and contact resistance
is large. A carbon fiber woven fabric used for a fuel cell-use
carbon fiber woven fabric has an average size of warps and wefts
constituting the woven fabric of 0.005-0.028 g/m, and a woven
density of the warps and/or wefts of 20 pieces/cm.
Inventors: |
Inoue, Mikio; (Otsu-shi,
JP) ; Chida, Takashi; (Otsu-shi, JP) ;
Igakura, Shuichi; (Kusatsu-shi, JP) |
Correspondence
Address: |
RATNERPRESTIA
P O BOX 980
VALLEY FORGE
PA
19482-0980
US
|
Family ID: |
19135624 |
Appl. No.: |
10/492798 |
Filed: |
April 15, 2004 |
PCT Filed: |
October 11, 2002 |
PCT NO: |
PCT/JP02/10579 |
Current U.S.
Class: |
423/447.1 |
Current CPC
Class: |
H01M 4/8817 20130101;
D03D 15/275 20210101; H01M 8/0234 20130101; D10B 2101/12 20130101;
Y02E 60/50 20130101; D10B 2321/10 20130101; D10B 2321/042 20130101;
H01M 4/96 20130101; H01M 4/8605 20130101; D10B 2401/022 20130101;
H01M 2250/20 20130101; D10B 2201/24 20130101; Y02T 90/40 20130101;
Y02P 70/50 20151101 |
Class at
Publication: |
423/447.1 |
International
Class: |
D01F 009/12 |
Claims
1. A carbon fiber woven fabric for a fuel cell, characterized in
that the average fineness of the warp yarns and the weft yarns
constituting the woven fabric is in the range of 0.005 to 0.028
g/m, and that the weave density of the warp yarns and/or the weft
yarns is not less than 20 yarns/cm.
2. A carbon fiber woven fabric for a fuel cell, according to claim
1, wherein the unit weight of the woven fabric is in the range of
50 to 150 g/m.sup.2.
3. A carbon fiber woven fabric for a fuel cell, according to claim
1 wherein the thickness of the woven fabric is in the range of 0.1
to 0.3 mm.
4. A carbon fiber woven fabric for a fuel cell, according to claim
1, wherein the value of N.times.W is not less than 0.6 where N
(yarns/cm) is the weave density of the warp yarns and/or the weft
yarns and W (cm/yarn) is the yarn width.
5. A carbon fiber woven fabric for a fuel cell, according to claim
1, wherein the crush value of the woven fabric under compression is
not more than 0.15 mm.
6 A carbon fiber woven fabric for a fuel cell, according to claim
1, wherein the warp yarns and/or the weft yarns are spun yarns.
7 A carbon fiber woven fabric for a fuel cell, according to claim
1, wherein the electric resistance of the woven fabric is not more
than 30 m.OMEGA.cm.sup.2, and the differential pressure caused when
14 cm.sup.3/cm.sup.2/sec of air is passed through the woven fabric
in the thickness direction is not more than 5 mm Aq.
8. A carbon fiber woven fabric for a fuel cell, according to claim
1, wherein the ratio of the number of oxygen atoms to the number of
carbon atoms on the carbon fiber surfaces of the woven fabric is
not less than 0.06 and less than 0.17.
9. A carbon fiber woven fabric for a fuel cell, according to claim
1, wherein the woven fabric contains carbon black on its surfaces
and/or inside.
10. A carbon fiber woven fabric for a fuel cell, according to claim
1, wherein the woven fabric contains a water-repellent
substance.
11. An electrode element for a fuel cell, formed of the carbon
fiber woven fabric as set forth in any one of claims 1 through
10.
12. An electrode element for a fuel cell, comprising an electrode
diffusion layer formed of the carbon fiber woven fabric as set
forth in any one of claims 1 through 10.
13. An electrode element for a fuel cell, according to claim 12,
wherein the electrode diffusion layer has a catalyst layer disposed
thereon in layer.
14. An electrode element for a fuel cell, according to claim 12,
wherein the electrode diffusion layer has a catalyst layer and a
polymer electrolyte membrane disposed thereon in layers.
15. A fuel cell comprising the electrode element as set forth in
claim 11.
16. A fuel cell, according to claim 15, wherein a grooved separator
is provided on the electrode element.
17. A mobile unit mounted with the fuel cell as set forth in claim
15.
18. A method for producing a carbon fiber woven fabric for a fuel
cell, comprising a pressurization step of pressurizing a precursor
fiber woven fabric composed of carbon precursor fibers in the
thickness direction, and a step of carbonizing the precursor fiber
woven fabric.
19. A method for producing a carbon fiber woven fabric for a fuel
cell, according to claim 18, wherein the pressurization step is
carried out at a heating temperature of not more than 300.degree.
C. at a pressure of 5 to 500 kg/cm.
20. A method for producing a carbon fiber woven fabric for a fuel
cell, according to claim 18 or 19, wherein the carbon precursor
fibers are oxidized acrylic fibers.
Description
TECHNICAL FIELD
[0001] The present invention relates to a carbon fiber woven fabric
to be used in a fuel cell, an electrode element using the carbon
fiber woven fabric, a fuel cell using the electrode element, a
mobile unit using the fuel cell, and a method for producing a
carbon fiber woven fabric to be used in the fuel cell. The
invention especially relates to a dense and thin carbon fiber woven
fabric to be used in a fuel cell, which can be preferably used as
the electrode diffusion layer of an electrode element in a solid
polymer electrolyte fuel cell.
BACKGROUND ART
[0002] An electrode diffusion layer of a fuel cell is required to
allow diffusion and permeation of substances participating in
current collecting function and electrode reaction. Furthermore, a
material constituting the electrode diffusion layer is required to
have electric conductivity, gas diffusibility, gas permeability,
strength to endure handling, etc.
[0003] As the material used to form the electrode diffusion layer
of a fuel cell, a porous carbon plate comprising short carbon
fibers bound with carbon, described in JP-06-20710-A,
JP-07-326362-A or JP-07-220735-A, is known. However, the porous
carbon plate has such problems that it is difficult to produce the
plate in a continuous longer form and that the carbon used as a
binder is likely to be destroyed under the pressure acting when the
electrode is produced or when the carbon plate is assembled into a
cell.
[0004] As a material capable of being formed as a continuously long
material to be used for forming an electrode diffusion layer, a
carbon fiber woven fabric is known. Examples of the carbon fiber
woven fabric include "PANEX PWB-3" produced by Stackpole Fibers
Company which is described in U.S. Pat. No. 4,293,396 and "AVCARB"
produced by Textron Specialty Materials which is described in
JP-10-261421-A.
[0005] The "PANEX PWB-3" can provide a continuously long material,
but if the carbon fiber woven fabric is used as an electrode
diffusion layer, it has such problems that a dimension of fuel cell
is greatly changed under pressurization, and that separator grooves
are filled with the woven fabric, since the woven fabric is greatly
deformed under compression. Furthermore, it has a problem that
since it is difficult to apply a catalyst layer because of the
large undulation attributable to its weave texture, the contact
resistance becomes large. Moreover, it has a problem that a woven
fabric formed of thick weaving yarns but having a low unit weight
causes the catalyst layer to come off, since the gaps between
fibers are large.
[0006] The invention has been completed in view of the
above-mentioned problems of the prior art. An object of the
invention is to provide a thin carbon fiber woven fabric slightly
deformable under compression, small in electric resistance and
suitable for use as an electrode diffusion layer in a fuel cell.
Another object of the invention is to provide an electrode element
using a carbon fiber woven fabric to be used in a fuel cell of the
invention, a fuel cell using the electrode element, and a mobile
unit using the fuel cell. A further object of the invention is to
provide a method for producing a carbon fiber woven fabric to be
used in a fuel cell of the invention.
DISCLOSURE OF THE INVENTION
[0007] A carbon fiber woven fabric for a fuel cell of the invention
is characterized in that the average fineness of the warp yarns and
the weft yarns constituting the woven fabric is in the range of
0.005 to 0.028 g/m, and that the weave density of the warp yarns
and/or the weft yarns is not less than 20 yarns/cm.
[0008] It is preferred that the unit weight of the woven fabric is
in the range of 50 to 150 g/m.sup.2.
[0009] It is preferred that the thickness of the woven fabric is in
the range of 0.1 to 0.3 mm.
[0010] It is preferred that the value of N.times.W is not less than
0.6 where N (yarns/cm) is the weave density of the warp yarns
and/or weft yarns and W (cm/yarn) is the yarn width.
[0011] It is preferred that the crush value the woven fabric under
compression is not more than 0.15 mm.
[0012] It is preferred that the warp yarns and/or the weft yarns
are spun yarns.
[0013] It is preferred that the electric resistance of the woven
fabric is not more than 30 m.OMEGA.cm.sup.2, and that the
differential pressure caused when 14 cm.sup.3/cm.sup.2/sec of air
is passed through the woven fabric in the thickness direction is
not more than 5 mm Aq.
[0014] It is preferred that the ratio of the number of oxygen atoms
to the number of carbon atoms on the carbon fiber surfaces of the
woven fabric is not less than 0.06 and less than 0.17.
[0015] It is preferred that the woven fabric contains carbon black
on its surfaces and/or inside.
[0016] It is preferred that the woven fabric contains a
water-repellent substance.
[0017] An electrode element for a fuel cell of the invention is
formed of the above-mentioned carbon fiber woven fabric for a fuel
cell of the invention.
[0018] It is preferred that the electrode element comprises an
electrode diffusion layer formed of the above-mentioned carbon
fiber woven fabric for a fuel cell of the invention.
[0019] It is preferred that the electrode diffusion layer has a
catalyst layer disposed thereon in layer.
[0020] It is preferred that the electrode diffusion layer has a
catalyst layer and a polymer electrolyte film deposited thereon in
layers.
[0021] A fuel cell of the invention comprises the above-mentioned
electrode element of the invention.
[0022] It is preferred that the fuel cell has a grooved separator
provided on the electrode element.
[0023] A mobile unit of the invention is mounted with the
above-mentioned fuel cell.
[0024] A method for producing a carbon fiber woven fabric for a
fuel cell of the invention comprises a pressurization step of
pressurizing a precursor fiber woven fabric composed of carbon
precursor fibers in the thickness direction and a step of
carbonizing the precursor fiber woven fabric.
[0025] In the method for producing a carbon fiber woven fabric for
a fuel cell, it is preferred that the pressurization step is
carried out at a heating temperature of not more than 300.degree.
C. at a pressure of 5 to 500 kg/cm.
[0026] In the method for producing a carbon fiber woven fabric for
a fuel cell, it is preferred that the carbon precursor fibers are
oxidized acrylic fibers.
THE BEST MODES FOR CARRYING OUT THE INVENTION
[0027] In the carbon fiber woven fabric for a fuel cell of the
invention, it is necessary that the average fineness of the warp
yarns and the weft yarns constituting the woven fabric is in the
range of 0.005 to 0.028 g/m. It is preferable that the average
fineness is in the range of 0.01 to 0.026 g/m, and more preferably
in the range of 0.013 to 0.022 g/m. An average fineness of more
than 0.028 g/m is not preferred, since the woven fabric becomes
thick or a space between weaving yarns becomes large.
[0028] If the unit weight of a woven fabric is A (g/m.sup.2), the
density of warp yarns is Nw (yarns/cm), and the density of weft
yarns is Nf (yarns/cm), then the average fineness can be obtained
from the following equation (I).
Average fineness (g/m)=A/(Nw+Nf)/100 (I)
[0029] In the carbon fiber woven fabric for a fuel cell of the
invention, it is necessary that the weave density of the warp yarns
and/or the weft yarns is not less than 20 yarns/cm.
[0030] It is preferable that the weave density is not less than 22
yarns/cm. If the weave density is too low, the spaces between
weaving yarns become large, and such problems are likely to occur
that the catalyst layer is likely to come off, and that since the
electrolytic membrane is likely to dry, high cell characteristics
is cannot be obtained. It is especially preferable that both the
warp yarns and the weft yarns have the weave density mentioned
above. If the weave density increases, the weaving speed declines
to raise the cost. It is, therefore, preferable that the weave
density is not more than 35 yarns/cm, and more preferably not more
than 30 yarns/cm.
[0031] In the measurements of the average fineness and the weave
density, in the case where the warp yarns and the weft yarns cannot
be identified which is which in the woven fabric, the yarns in a
given direction should be considered as warp yarns, and the yarns
in the other direction, as weft yarns.
[0032] It is preferred that the unit weight of the carbon fiber
woven fabric for a fuel cell of the invention is in the range of 50
to 150 g/m.sup.2. A more preferred range is from 70 to 120
g/m.sup.2, and a further more preferred range is from 80 to 98
g/m.sup.2.
[0033] In the case where the unit weight is too low, the spaces
between the weaving yarns constituting the woven fabric are so
large that there occur such problems that the catalyst layer comes
off and that since the electrolytic membrane is likely to dry, high
cell characteristics cannot be obtained. In the case where the unit
weight is too high, it is difficult to produce the woven fabric,
and the woven fabric tends to be thick. As a result, such problems
are likely to occur that the fuel cell is dimensionally greatly
changed under pressurization, and that the separator grooves are
likely to be filled with the woven fabric. In the case where the
woven fabric has carbon black, resin and the like deposited, the
weight excluding these deposits should be the weight of the carbon
fiber woven fabric.
[0034] It is preferred that the thickness of the carbon fiber woven
fabric for a fuel cell of the invention is in the range of 0.1 to
0.3 mm. A more preferred range is from 0.13 to 0.25 mm, and a
further more preferred range is from 0.15 to 0.20. The thickness
refers to the thickness measured when a pressure of 0.15 MPa is
applied to the carbon fiber woven fabric.
[0035] In the case where the thickness is too small, such a problem
occurs that since the electrolytic membrane is likely to dry, high
cell characteristics cannot be obtained. Furthermore, in the case
where the thickness is too large, such problems are likely to occur
that the fuel cell is dimensionally greatly changed under
pressurization, and that the separator grooves are likely to be
filled with the woven fabric.
[0036] If the weave density of the warp yarns and/or the weft yarns
of the carbon fiber woven fabric for a fuel cell of the invention
is N (yarns/cm) and the yarn width is W (cm/yarn), then it is
preferred that the value of product N.times.W is not less than 0.6.
More preferred is not less than 0.65, and further more preferred is
not less than 0.7.
[0037] The yarn width W refers to the width viewed in the direction
perpendicular to the face of the woven fabric. The yarn width W can
also be measured with the woven fabric magnified as an SEM
photograph, etc. It is preferred that the N.times.W values of both
the warp yarns and the weft yarns are not less than 0.6
respectively.
[0038] In the case where the warp yarns cannot be distinguished
from the weft yarns on the woven fabric as explained in the above,
the yarns in a given direction should be warp yarns, and the yarns
in the other direction, weft yarns.
[0039] In the case where the value of N.times.W is too small, there
occur such problems that since the spaces between weave yarns are
large, the catalyst layer comes off, that since the surface is
rough, the contact between the catalyst layer and the separator is
not sufficient, and that since the electrolytic membrane is likely
to dry, high cell characteristics cannot be obtained. It is
preferred that the value of N.times.W is not more than 0.96. More
preferred is not more than 0.90, and further more preferred is not
more than 0.85. If the value of N.times.W is too high, weaving is
so difficult as to lower the weaving speed, hence increasing the
cost.
[0040] It is preferred that the crush value of the carbon fiber
woven fabric for a fuel cell of the invention under compression is
not more than 0.15 mm. More preferred is not more than 0.12 mm, and
further more preferred is not more than 0.10 mm.
[0041] The crush value under compression refers to the difference
between the thickness measured at a pressure of 0.15 MPa and the
thickness measured at a pressure of 1.5 MPa. In the case where the
crush value under compression is too large, there occur such
problems that stack clamping is difficult, that it is difficult to
achieve a uniform height, and that the woven fabric fills the
separator grooves.
[0042] It is preferred that the warp yarns and/or the weft yarns
constituting the carbon fiber woven fabric of the invention are
spun yarns. Since spun yarns have many voids in them, higher air
permeability and higher water permeability can be obtained.
[0043] It is preferred that the electric resistance of the carbon
fiber woven fabric for a fuel cell of the invention is not more
than 30 m.OMEGA.cm.sup.2. More preferred is not more than 25
m.OMEGA.cm.sup.2, and further more preferred is not more than 20
m.OMEGA.cm.sup.2. If the electric resistance is too high, the woven
fabric used in an electrode of a fuel cell increases the voltage
loss.
[0044] The method for measuring electric resistance is as follows.
Two plates each of which is a vitreous carbon plate overlaid with a
copper foil, wherein the vitreous carbon plate has the width of 50
mm, length of 200 mm, thickness of 1.5 mm and a smooth surface, and
the copper foil has the width of 50 mm, length of 200 mm and
thickness of 0.1 mm are prepared. The plates are called test
electrodes. The two test electrodes are overlaid on each other with
the vitreous carbon sheets facing each other, to cross each other
at their central portions. The carbon fiber woven fabrics are cut
to have area S (cm.sup.2), and the cut carbon fiber woven fabrics
are pressurized to apply a pressure of 0.98 MPa for the area of the
fabrics. At the ends on one side of the two test electrodes,
current terminals are installed, and at the ends on the other side,
voltage terminals are installed. Using the current terminals, a
current of 1 A is made to flow between the two test electrodes. The
voltage V (V) across the voltage terminals is measured, to
calculate resistance R (m.OMEGA.cm.sup.2) from the following
equation (II).
R=1,000V.times.S (II)
[0045] It is preferred that the differential pressure is not more
than 5 mm Aq, when 14 cm.sup.3/cm.sup.2/sec of air is passed in the
thickness direction of the carbon fiber woven fabric for a fuel
cell of the invention. A more preferred range is from 0.2 to 2 mm
Aq, and a further more preferred range is from 0.4 to 1.5 mm Aq. In
the case where the differential pressure is too large, the air
permeability, hydrogen permeability and water permeability are low,
and the cell voltage tends to be low. In the case where the
differential pressure is too small, the water is likely to
evaporate, and the resistance of the membrane tends to be higher.
In the case where carbon black, resin and the like are deposited on
the woven fabric, these deposits should be removed before measuring
the differential pressure.
[0046] It is preferred that the ratio of the number of oxygen atoms
to the number of carbon atoms on the surfaces of the carbon fibers
constituting the carbon fiber woven fabric for a fuel cell of the
invention is not less than 0.06 and less than 0.17. A more
preferred range is not less than 0.10 and not more than 0.16, and a
further more preferred range is not less than 0.11 and not more
than 0.15.
[0047] The ratio (O/C) of the number of oxygen atoms to the number
of carbon atoms on the surfaces of the carbon fibers constituting
the carbon fiber woven fabric is defined by the following
equation.
O/C=(Rate of oxygen atoms on fiber surfaces)/(Rate of carbon fibers
on fiber surfaces)
[0048] If the ratio O/C on the surfaces of carbon fibers is less
than 0.06, the fiber surfaces are low in hydrophilicity, and the
migration of water in the yarns owing to the capillary tubes formed
by plural carbon fibers tends to decrease. As a result, the extra
water in the system cannot be efficiently discharged, and the water
produced due to the power generation reaction is accumulated to
clog the cathode electrode with water with a tendency of lowering
the gas diffusibility.
[0049] If the ratio O/C on the surfaces of carbon fibers is not
less than 0.17, the fiber surfaces become too high in
hydrophilicity. Therefore, even in the case where the quantity of
produced water is small, the cathode electrode can be clogged with
water with a tendency of lowering the gas diffusibility. If the
ratio O/C is in the range mentioned above, the surfaces of the
fibers constituting the carbon fiber woven fabric for a fuel cell
of the invention are moderately hydrophilic. Therefore, the water
can highly migrate in the woven fabric owing to the capillary tubes
formed by plural carbon fibers, to give a feature that the cathode
electrode is unlikely to be clogged with water. For this reason,
the extra water in the system can be efficiently discharged, to
allow excellent water control.
[0050] The ratio of the number of oxygen atoms to the number of
carbon atoms on the surfaces of carbon fibers can be measured by
X-ray photoelectron spectroscopy.
[0051] It is preferred that the carbon fiber woven fabric for a
fuel cell of the invention contains carbon black on its surfaces
and/or inside for the purposes of increasing electric conductivity,
smoothening the surfaces and controlling the water permeability.
The method for adding carbon black is not especially limited, but
it is preferred that carbon black is bound to the woven fabric
using a resin or the like as an adhesive.
[0052] It is preferred that the carbon fiber woven fabric for a
fuel cell of the invention contains a water-repellent substance for
the purpose of preventing clogging with water when it is used in a
fuel cell. Furthermore, a water-repellent substance can also be
used as an adhesive for the carbon black. The water-repellent
substance is not especially limited, and for example, a
fluorine-containing compound, silicon-containing compound or the
like can be preferably used.
[0053] The method for producing the carbon fiber woven fabric for a
fuel cell of the invention is not especially limited. For example,
yarns consisting of carbon fibers can be woven to produce a carbon
fiber woven fabric, or carbon precursor fibers can also be woven to
produce a precursor fiber woven fabric that is then carbonized into
a carbon fiber woven fabric. As another method, a commercially
available precursor fiber woven fabric can also be carbonized to
produce a carbon fiber woven fabric. In the case where yarns
consisting of carbon fibers are woven, it is likely to occur that
the carbon fibers are broken or folded. Furthermore, the warp yarns
and the weft yarns are likely to be shifted to deform the meshes of
the produced carbon fiber woven fabric, and the warp yarns and the
weft yarns at the edges of the woven fabric are likely to come off.
Therefore, the latter method of carbonizing a carbon precursor
fiber woven fabric is preferred.
[0054] The carbon fibers or precursor fibers of carbon fibers used
for producing the carbon fiber woven fabric for a fuel cell of the
invention are not especially limited. Examples of them include
polyacrylonitrile-based carbon fibers, rayon-based carbon fibers,
phenol-based carbon fibers, pitch-based carbon fibers, oxidized
acrylic fibers, rayon fibers, phenol fibers, infusible pitch
fibers, etc. An especially preferred method is to carbonize the
woven fabric produced by weaving oxidized acrylic fibers.
[0055] In the process for producing the carbon fiber woven fabric
for a fuel cell of the invention, it is preferred to include a step
of pressurizing in the thickness direction, the woven fabric
produced by weaving carbon precursor fibers, since the crush value
under compression can be kept small, for example, when plural
electrode diffusion layers formed of carbon fiber woven fabrics are
laminated for producing a fuel cell.
[0056] It is preferred that the pressurization in the thickness
direction is carried out before or during carbonization. The
pressurization before or during carbonization is more effective in
lessening the crush value under compression than the pressurization
after carbonization.
[0057] The method of pressurizing before carbonization can be a
continuous pressurization method using a roll press or belt press
or a surface load pressurization method using a batch press or
load. In view of the efficiency of the pressurization step, it is
preferred to use a roll press or belt press that allows continuous
pressurization.
[0058] It is preferred that the temperature during pressurization
is not more than 300.degree. C. A more preferred range is from 150
to 250.degree. C., and a further more preferred range is from 170
to 230.degree. C. In the case where the temperature is too low, the
deformation under compression is too small, and the effect of
reducing the thickness cannot be sufficiently obtained. In the case
where oxidized acrylic fibers are used, a remarkable pressurization
effect can be observed at 150.degree. C. or higher. In the case
where the temperature is too high, since the oxidation of carbon
precursor fibers in air takes place, the pressurization must be
carried out in an inactive atmosphere. Furthermore, because of high
temperature, equipment maintenance and process control become
difficult. In the case of oxidized acrylic fibers, the problems of
oxidation and deterioration do not occur at 250.degree. C. or
lower, since the fibers underwent flame-retarding treatment.
[0059] In the case where the pressurization is carried out using
rolls, it is preferred that the surface of at least one of the two
rolls used for pressurization is made of a soft material such as
rubber, resin, paper or nonwoven fabric for preventing the breaking
of carbon precursor fibers and the decline of tensile strength. It
is preferred that the line load of pressurization is in the range
of 10 to 500 kg/cm. A more preferred range is from 50 to 300 kg/cm,
and a further more preferred range is from 150 to 200 kg/cm.
[0060] In the case where hard rolls made of a metal or the like are
used for pressurization, it is preferred that a clearance of 50
.mu.m or more is established or that the line load is kept in the
range of 5 to 200 kg/cm, for preventing the destruction of the
woven fabric, the breaking of the fibers of the woven fabric, and
the decline of tensile strength. A more preferred range of line
load is from 10 to 100 kg/cm, and a further more preferred range is
from 20 to 70 kg/cm.
[0061] In the case where a surface load is used for pressurization,
it is preferred that the pressure is 5 MPa or more.
[0062] In the case where a woven fabric of carbon precursor fibers
is pressurized while being carbonized, it is only required that the
pressurization is carried out at least at any moment in the
carbonization step. In the case where preliminary carbonization at
the highest temperature of about 500 to 1,000.degree. C. is
followed by regular carbonization at the highest temperature of
higher than 1,000.degree. C. for carrying out carbonization twice,
it is preferred that the woven fabric is pressurized during at
least either preliminary carbonization or regular carbonization.
The method of pressurization can be a continuous pressurization
using rolls or belt, or a surface load pressurization, or a method
of carbonizing a rolled woven fabric for pressurization using the
tension of rolling and the tension caused by the shrinkage during
carbonization, though the method is not limited to these
methods.
[0063] In the case where a rolled woven fabric of carbon precursor
fibers is carbonized, it is preferred that the outermost layer of
the roll is covered with paper, film or woven fabric with a surface
smoother than the woven fabric, since the woven fabric can be
carbonized without wrinkling even at the outermost layer. More
particularly it is preferred to cover the woven fabric of carbon
precursor fibers with paper, film or woven fabric made of carbon or
any other material capable of being carbonized and incapable of
molten when carbonized, such as a polyimide, cellophane or
cellulose.
[0064] In the case where a woven fabric of carbon precursor fibers
is carbonized and subsequently pressurized, it is preferred to
pressurize with the woven fabric wetted with a liquid substance
such as water or organic solvent, or to pressurize the woven fabric
having a resin such as a fluorine resin deposited. It is more
preferred that a carbonized woven fabric having a resin deposited
is pressurized at higher than its melting point or thermal
deformation temperature.
[0065] In the carbon fiber woven fabric for a fuel cell of the
invention, the carbon produced when an organic material deposited
on the carbon fibers or carbon precursor fibers is carbonized, can
also remain deposited. The deposited carbon has an effect of
inhibiting the deformation under the pressurization of the carbon
fiber woven fabric, but on the other hand, has a problem of
lowering the gas permeability and the flexibility of the woven
fabric. Therefore, it is preferred that the amount of the carbon is
20 wt % or less. More preferred is 5 wt % or less, and further more
preferred is 2 wt % or less.
[0066] The carbon fiber woven fabric for a fuel cell of the
invention can be preferably used as an electrode component such as
a gas diffusion electrode for a fuel cell, since it has electric
conductivity and fluid permeability.
[0067] Furthermore, the carbon fiber woven fabric for a fuel cell
of the invention can be preferably used as a conductive sheet to be
used in a fuel cell, especially as an electrode diffusion layer of
a fuel cell. It can be especially suitably used as an electrode
diffusion layer of a fuel cell having a grooved separator. In the
case where a grooved separator is used as passages for feeding
oxygen and a fuel to a fuel cell electrode, if the crush value of
the carbon fiber woven fabric under compression is large, the
portions of the woven fabric facing the grooves and hence not
subjected to compression go into the grooves, to inhibit the
function as the passages of oxygen and fuel. The carbon fiber woven
fabric for a fuel cell of the invention, that is thin in thickness
and small in the crush value under compression, can effectively
avoid inhibiting the passage function. As a result, the grooves can
have a smaller depth and the device can be made more compact.
[0068] Moreover, the carbon fiber woven fabric for a fuel cell of
the invention can be preferably used as an electrode diffusion
layer having a catalyst layer disposed thereon as a layer or having
a catalyst layer and a polymer electrolyte membrane disposed
thereon as layers to form a unit. Still furthermore, the electrode
diffusion layer or the unit can be preferably used as a component
of a fuel cell. The fuel cell containing the carbon fiber woven
fabric for a fuel cell of the invention, which is flexible and
small in the crush value under compression, is strong against
vibration and impact, is compact, and is suitable as a fuel cell
for a mobile unit. It is especially suitable as a fuel cell for a
mobile unit requiring a compact fuel cell, above all, for a motor
vehicle or two-wheeled car.
[0069] Examples are described below. The properties described in
the examples were measured according to the following methods.
[0070] Crush Value Under Compression:
[0071] A carbon fiber woven fabric was placed on a smooth table,
and a micrometer indenter having a diameter of 5 mm was allowed to
descend from above. With a load applied to the indenter, the
thickness was measured at a pressure of 0.15 MPa, and with the load
further increased, the thickness was measured at a pressure of 1.5
MPa. The difference between the thickness measured at a pressure of
0.15 MP and the thickness measured at a pressure of 1.5 MPa was
identified as the crush value. A smaller crush value is more
desirable.
[0072] Electric Resistance:
[0073] The method described before was used to obtain the electric
resistance from the following equation. A lower electric resistance
is more desirable.
R=1,000V.times.S
[0074] where R: Resistance (m.OMEGA.cm.sup.2)
[0075] V: Voltage across voltage terminals (V)
[0076] S: Area of carbon fiber woven fabric (cm.sup.2)
[0077] Voltage at 0.7 A/cm.sup.2:
[0078] A carbon fiber woven fabric was coated with a mixture
consisting of carbon black and polytetrafluoroethylene, and the
coated fabric was heat-treated at 380.degree. C., to produce a
woven fabric having a carbon layer. The deposited amount of the
mixture consisting of carbon black and polytetrafluoroethylene was
about 2 mg/cm.sup.2.
[0079] On the other hand, a mixture consisting of platinum-loaded
carbon as a catalyst and Nafion was deposited on both sides of
Nafion 112 (produced by E. I. du Pont de Nemours and Company), to
prepare a membrane-catalyst sheet. The amount of platinum as a
catalyst was about 0.5 mg/cm.sup.2.
[0080] The membrane-catalyst sheet was held between two
carbon-layered woven fabrics having the carbon layers turned
inside, and the laminate was heated at 130.degree. C. and
pressurized at 3 MPa for integration, to obtain a
membrane-electrode assembly (MEA).
[0081] The MEA was held between grooved separators, and the cell
characteristics were measured according to a conventional method.
The cell temperature was 70.degree. C., and the temperature at
which hydrogen gas was applied was 80.degree. C., while the
temperature at which air was applied was 60.degree. C. The gas
pressure was atmospheric pressure. At 0.7 A/cm.sup.2, the hydrogen
availability was 70% and the air availability was 40%. A higher
voltage is more desirable. At 0.7 A/cm.sup.2, 0.5 V or higher is
acceptable.
[0082] Tensile Strength:
[0083] A woven fabric was cut to have a dimension of 5 to 7 cm in
the warp direction and a dimension of 1.5 to 1.7 cm in the weft
direction. Several warp yarns at both the edges in the weft
direction were removed, to ensure that there were no broken warp
yarns in the sample having a length of 5 to 7 cm. The width across
the remaining warp yarns of the sample was measured as a sample
width, and a tensile test was carried out at a span of 3 cm and
tensile speed of 1 mm/min. The value obtained by dividing the
maximum load (kg) by the sample width (cm) was identified as the
tensile strength.
EXAMPLES 1, 2, 3, 4 and 5
[0084] Spun yarns of oxidized acrylic fibers ("Lastan" produced by
Asahi Kasei Corp., 1/34 Nm=0.029 g/m) were woven into a plain
weave. The woven fabric was carbonized in two steps at the highest
temperatures of 650.degree. C. and 1,950.degree. C. in an inactive
atmosphere, to obtain a carbon fiber woven fabric. The unit weight
and weave densities of each oxidized acrylic fiber woven fabric,
and the unit weight, weave densities, average weave density N,
fineness, thickness, weaving yarn width W and the value of
N.times.W of each carbon fiber woven fabric are shown in Table
1.
EXAMPLE 6
[0085] Spun yarns of oxidized acrylic fibers (produced by Asahi
Kasei Corp., 1/34 Nm=0.029 g/m) were used as warp yarns and spun
yarns of oxidized acrylic fibers (produced by Asahi Kasei Corp.,
2/34 Nm=0.059 Nm) were used as weft yarns to produce a plain weave.
The woven fabric was carbonized in two steps at the highest
temperatures of 650.degree. C. and 1,950.degree. C. in an inactive
atmosphere, to obtain a carbon fiber woven fabric. The unit weight
and weave densities of the oxidized acrylic fiber woven fabric, and
the unit weight, weave densities, average weave density N,
fineness, thickness, weaving yarn width W and the value of
N.times.W of the carbon fiber woven fabric are shown in Table
1.
EXAMPLE 7
[0086] Oxidized acrylic fibers (produced by Toray Industries, Inc.)
were spun into yarns by a draft zone system spinning. The fineness
of the spun yarns was 1/40 Nm=0.025 g/m. The spun yarns were woven
into a plain weave. The woven fabric was carbonized in two steps at
the highest temperatures of 650.degree. C. and 1,950.degree. C. in
an inactive atmosphere, to obtain a carbon fiber woven fabric. The
unit weight and weave densities of the oxidized acrylic fiber woven
fabric, and the unit weight, weave densities, average weave density
N, fineness, thickness, weaving yarn width W and the value of
N.times.W of the carbon fiber woven fabric are shown in Table
1.
EXAMPLE 8
[0087] The oxidized acrylic fiber woven fabric of Example 1 was
held between carbon sheets, carbonized at the highest temperature
of 800.degree. C. in an inactive atmosphere with a pressure of 2.8
g/cm.sup.2 applied to the woven fabric, depressurized and
carbonized at 1,950.degree. C., to obtain a carbon fiber woven
fabric. The unit weight and weave densities of the oxidized acrylic
fiber woven fabric, and the unit weight, weave densities, average
weave density N, fineness, thickness, weaving yarn width W and the
value of N.times.W of the carbon fiber woven fabric are shown in
Table 1.
EXAMPLE 9
[0088] The oxidized acrylic fiber woven fabric of Example 1 was fed
through a roll press consisting of one iron roll and one rubber
roll (iron roll 200.degree. C., rubber roll 120.degree. C.), to be
pressurized at 200 kg/cm. The woven fabric was carbonized in two
steps at the highest temperatures of 650.degree. C. and
1,950.degree. C. in an inactive atmosphere, to obtain a carbon
fiber woven fabric. The unit weight and weave densities of the
oxidized acrylic fiber woven fabric, and the unit weight, weave
densities, average weave density N, fineness, thickness, weaving
yarn width W and the value of N.times.W of the carbon fiber woven
fabric are shown in Table 1.
EXAMPLES 10, 11, 12, 13 and 14
[0089] The oxidized acrylic fiber woven fabric of Example 5 was fed
through a roll press consisting of two iron rolls (roll temperature
60, 100, 125, 150 or 200.degree. C.), to be pressurized at 50
kg/cm. The woven fabric was carbonized at the highest temperature
of 1,950.degree. C. in vacuum, to obtain a carbon fiber woven
fabric. The unit weight and weave densities of the oxidized acrylic
fiber woven fabric, and the unit weight, weave densities, average
weave density N, fineness and thickness of each carbon fiber woven
fabric are shown in Table 1.
EXAMPLES 15, 16, 17 and 18
[0090] The oxidized acrylic fiber woven fabric of Example 5 was fed
through a roll press consisting of two iron rolls (roll temperature
200.degree. C.), to be pressurized at 11, 100, 150 or 250 kg/cm.
The woven fabric was carbonized at the highest temperature of
1,950.degree. C. in vacuum, to obtain a carbon fiber woven fabric.
The unit weight and weave densities of the oxidized acrylic fiber
woven fabric, and the unit weight, weave densities, average weave
density N, fineness and thickness of each carbon fiber woven fabric
are shown in Table 1.
EXAMPLE 19
[0091] The oxidized acrylic fiber woven fabric of Example 5 was fed
through a roll press consisting of two iron rolls (roll temperature
200.degree. C.) having a clearance of 150 .mu.m, to be pressurized
at 250 kg/cm. The woven fabric was carbonized at the highest
temperature of 1,950.degree. C. in vacuum, to obtain a carbon fiber
woven fabric. The unit weight and weave densities of the oxidized
acrylic fiber woven fabric, and the unit weight, weave densities,
average weave density N, fineness and thickness of the carbon fiber
woven fabric are shown in Table 1.
EXAMPLE 20
[0092] In a beaker containing 500 ml of 0.1 N sulfuric acid, a
carbon sheet was used as the cathode, and the carbon fiber woven
fabric of Example 4 cut into a size of 8 cm.times.8 cm was used as
the anode, for carrying out electrolytic treatment with a current
of 48 mA kept flowing for 125 seconds. After completion of
electrolytic treatment, the carbon fiber woven fabric was washed
with purified water, and dried in a 100.degree. C. oven for 10
minutes, to obtain a carbon fiber woven fabric treated to be
hydrophilic.
EXAMPLE 21
[0093] In a beaker containing 500 ml of 0.1 N sulfuric acid, a
carbon sheet was used as the cathode, and the carbon fiber woven
fabric of Example 4 cut into a size of 8 cm.times.8 cm was used as
the anode, for carrying out electrolytic treatment with a current
of 48 mA kept flowing for 250 seconds. After completion of
electrolytic treatment, the carbon fiber woven fabric was washed
with purified water, and dried in a 100.degree. C. oven for 10
minutes, to obtain a carbon fiber woven fabric treated to be
hydrophilic.
COMPARATIVE EXAMPLE 1
[0094] Spun yarns of oxidized acrylic fibers (produced by Asahi
Kasei Corp., 2/34 Nm=0.059 g/m) were woven into a plain weave. The
woven fabric was carbonized in two steps at the highest
temperatures of 650.degree. C. and 1,950.degree. C. in an inactive
atmosphere, to obtain a carbon fiber woven fabric. The unit weight
and weave densities of the oxidized acrylic fiber woven fabric, and
the unit weight, weave densities, average weave density N,
fineness, thickness, weaving yarn width W and the value of
N.times.W of the carbon fiber woven fabric are shown in Table
1.
COMPARATIVE EXAMPLE 2
[0095] Torayca Cloth (produced by Toray Industries, Inc.) "CO6349B"
was heated at 1,400.degree. C. in an inactive atmosphere, to is
remove the sizing agent. The unit weight, weave densities, average
weave density N, fineness, thickness, weaving yarn width W and the
value of N.times.W of the carbon fiber woven fabric are shown in
Table 1.
COMPARATIVE EXAMPLE 3
[0096] In a beaker containing 500 ml of 0.1 N sulfuric acid, a
carbon sheet was used as the cathode, and the carbon fiber woven
fabric of Example 4 cut into a size of 8 cm.times.8 cm was used as
the anode, for carrying out electrolytic treatment with a current
of 48 mA kept flowing for 500 seconds. After completion of
electrolytic treatment, the carbon fiber woven fabric was washed
with purified water, and dried in a 100.degree. C. oven for 10
minutes, to obtain a carbon fiber woven fabric treated to be
hydrophilic.
[0097] For the carbon fiber woven fabrics obtained in Examples 1 to
21 and Comparative Examples 1 to 3, the respective values of the
crush value under compression, electric resistance, and
differential pressure in air permeation are shown in Table 2,
together with the values of the voltage measured with a current of
0.7 A/cm.sup.2 in the solid polymer electrolyte fuel cells produced
using the respective woven fabrics. In the woven fabric of
Comparative Example 1, the applied carbon black and
polytetrafluoroethylene were separated from the woven fabric, not
allow the cell characteristics to be measured.
[0098] As can be seen from Tables 1 and 2, the carbon fiber woven
fabrics for a fuel cell of the invention were thin and small in the
crush value under compression, showing good cell characteristics.
On the other hand, the woven fabrics of Comparative Examples 1 and
2 having an average fineness of more than 0.03 g/m were inferior in
cell characteristics. That is, the woven fabric of Comparative
Example 1 was relatively thick and large in the crush value under
compression. The woven fabric of Comparative Example 2 was as low
as 0.44 V in voltage.
[0099] From the comparison of Examples 5 and 10 to 14, it can be
seen that pressing can reduce the thickness, to make the crush
value under compression small, and that the effect of thinning at
150.degree. C. or higher is remarkable.
[0100] From the comparison of Examples 5 and 14 through 19, it can
be seen that if the pressure of a roll press consisting of two
metallic rolls is raised, the thickness is reduced to make the
crush value under compression small. On the other hand, as shown in
Table 3, if the pressure is raised especially to 100 kg/cm or
higher, it is necessary to establish a clearance between the rolls
and to select an adequate pressure, since otherwise the tensile
strength of the woven fabric declines.
[0101] As shown in Table 4, since the woven fabrics of Examples 15
and 16 are adequately hydrophilic on the fiber surfaces, their
voltages were 0.61 V and 0.62 V respectively, being higher than
0.60 V of Example 4. On the other hand, in Comparative Example 3,
since the ratio O/C was 0.17, the hydrophilicity on the fiber
surfaces was so high that the voltage was as low as 0.41 V.
1 TABLE 1 Oxidized fiber woven fabric Carbon fiber woven fabric
Weave density Weave density Warp Weft Unit Unit Warp Weft Average
yarns yarns weight weight yarns yarns Average weave fineness
Thickness Width W (yarns/cm) (yarns/cm) (g/m.sup.2) (g/m.sup.2)
(yarns/cm) (yarns/cm) density (yarns/cm) (g/m) (mm) (cm) N .times.
W Example 1 17.0 17.5 104 72 20.0 20.0 20.0 0.018 0.19 0.028 0.56
Example 2 24.0 23.0 157 99 28.0 26.0 27.0 0.018 0.22 0.028 0.76
Example 3 24.0 17.5 140 88 27.0 20.5 24.0 0.019 0.22 0.028 0.67
Example 4 22.0 22.0 150 93 25.5 25.5 25.5 0.018 0.24 0.030 0.77
Example 5 22.5 20.0 146 91 25.0 22.5 24.0 0.019 0.22 0.028 0.67
Example 6 14.0 18.0 164 102 16.5 20.0 18.0 0.028 0.25 0.040 0.72
Example 7 23.0 20.0 126 86 27.0 25.0 26.0 0.017 0.23 0.026 0.68
Example 8 17.0 17.5 104 66 20.0 19.0 19.5 0.017 0.18 0.025 0.49
Example 9 22.0 22.0 150 92 25.0 25.5 25.5 0.018 0.20 0.037 0.94
Example 10 22.5 20.0 146 91 25.0 22.5 24.0 0.019 0.21 -- -- Example
11 22.5 20.0 146 91 25.0 22.5 24.0 0.019 0.20 -- -- Example 12 22.5
20.0 146 91 25.0 22.5 24.0 0.019 0.20 -- -- Example 13 22.5 20.0
146 89 25.0 22.5 24.0 0.019 0.18 -- -- Example 14 22.5 20.0 146 89
25.0 22.5 24.0 0.019 0.17 -- -- Example 15 22.5 20.0 146 90 25.0
22.5 24.0 0.019 0.18 -- -- Example 16 22.5 20.0 146 88 25.0 22.5
24.0 0.019 0.16 -- -- Example 17 22.5 20.0 146 88 25.0 22.5 24.0
0.019 0.15 -- -- Example 18 22.5 20.0 146 87 25.0 22.5 24.0 0.018
0.14 -- -- Example 19 22.5 20.0 146 89 24.5 22.5 24.0 0.019 0.19 --
-- Example 20 22.0 22.0 150 93 25.5 25.5 25.5 0.018 0.24 0.030 0.77
Example 21 22.0 22.0 150 93 25.5 25.5 25.5 0.018 0.24 0.030 0.77
Oxidized fiber woven fabric Carbon fiber woven fabric Weave density
Unit weight Warp Weft Unit Weave Warp Weft Average yarns yarns
weight density yarns yarns Average weave fineness Thickness Width W
(yarns/cm) (yarns/cm) (g/m.sup.2) (g/m.sup.2) (yarns/cm) (yarns/cm)
density (yarns/cm) (g/m) (mm) (cm) N .times. W Comparative 17.0
15.5 213 133 19.0 17.0 18.0 0.037 0.31 0.050 0.90 Example 1
Comparative -- -- -- 120 9.0 9.0 9.0 0.066 0.14 0.104 0.94 Example
2 Comparative 22.0 22.0 150 93 25.5 25.5 25.5 0.018 0.24 0.030 0.77
Example 3
[0102] (Note: In the carbon fiber woven fabrics of Examples 9 and
10 of Table 1, the warp yarns could not be distinguished from weft
yarns.)
2 TABLE 2 Carbon fiber woven fabric Crush value Differential under
Electric pressure in air compression resistance permeation Voltage
at (mm) (m.OMEGA.cm) (mmAq) 0.7 A/cm.sup.2 (V) Example 1 0.09 9 0.2
0.51 Example 2 0.10 11 1.8 0.57 Example 3 0.10 11 0.6 0.60 Example
4 0.11 10 1.1 0.60 Example 5 0.11 10 1.1 0.60 Example 6 0.11 11 1.0
0.55 Example 7 0.12 11 0.7 0.58 Example 8 0.07 12 0.2 0.52 Example
9 0.09 10 1.4 0.58 Example 10 0.08 10 1.3 -- Example 11 0.07 10 1.4
-- Example 12 0.07 10 1.5 -- Example 13 0.06 10 1.7 -- Example 14
0.05 10 1.9 -- Example 15 0.07 10 -- -- Example 16 0.05 10 -- --
Example 17 0.05 10 -- -- Example 18 0.05 10 -- -- Example 19 0.07
10 -- -- Example 20 0.11 10 1.1 0.61 Example 21 0.11 10 1.1 0.62
Comparative 0.16 10 2.4 -- Example 1 Comparative 0.03 8 1.6 0.44
Example 2 Comparative 0.11 10 1.1 0.41 Example 3
[0103]
3 TABLE 3 Press pressure Clearance Tensile strength (kg/cm) (.mu.m)
(kg/cm) Example 5 -- -- 2.5 Example 14 50 0 2.6 Example 15 11 0 2.7
Example 16 100 0 2.1 Example 17 150 0 1.7 Example 18 250 0 1.1
Example 19 250 150 2.7
[0104]
4 TABLE 4 Number of oxygen atoms/ Number of carbon atoms (O/C)
Example 4 0.01 Example 20 0.11 Example 21 0.15 Comparative 0.17
Example 3
Industrial Applicability
[0105] Since the carbon fiber woven fabric for a fuel cell of the
invention is a thin and dense woven fabric having a small fineness,
it can be slightly deformed under compression and is small in the
spaces between the fibers and in undulation. Therefore, it can be
suitably used as an electrode diffusion layer to be used in a fuel
cell.
* * * * *