Electrode substrate for fuel cell

Disclosed herein is an electrode substrate for a fuel cell, wherein at least a part of the electrode substrate comprises a flexible carbon material obtained from a composite material comprising carbon fibers of not less than 1 mm in mean length which have been treated at a temperature of not lower than 1000.degree. C. and a binding agent, the electrode substrate being contacted with flow channels of a reactant gas and the flexible carbon material comprising carbon lumps derived from the binding agent which are dispersed in the matrix of the carbon fibers and restrain a plurality of the carbon fibers and the carbon fibers slidably held to one another by the carbon lumps.

BACKGROUND OF THE INVENTION 
The present invention relates to an electrode substrate for a fuel cell, 
and more specifically relates to an electrode substrate in contact with 
flow channels for a reactant gas, and wherein at least a part of the 
electrode substrate comprises a flexible carbon material as a reactant gas 
diffusion part. The term, "electrode substrate for a fuel cell" as used in 
connection with the present invention means all substrates which become an 
electrode for a fuel cell either by applying a catalyst to the substrate 
itself or by stacking on the substrate a porous electrode carrying a 
previously applied catalyst. 
The flexible carbon material according to the present invention is obtained 
by carbonizing a composite material comprised of carbon fibers and a 
binding agent, wherein carbon lumps are derived from the binding agent and 
are dispersed in the matrix of the carbon fibers so as to restrain a 
plurality of the carbon fibers while yet slidably holding the fibers one 
to another by means of the carbon lumps. 
In recent years, carbon materials made of carbon fibers as the basic 
material have been used in various industrial fields. Increasing usage of 
carbon fiber-based materials has, in turn, increased market demands for 
production of, and physical product improvements for, such materials. 
Carbon fiber-based materials are generally recognized as exhibiting 
excellent physical properties, for instance, heat-resistance, 
corrosion-resistance, conductivity, mechanical strength, and the like. 
On the other hand, there have also been high demands for fuel cells for 
generating clean energy which can freely make and break electrical 
circuits, normalize the operation of thermal power generation or water 
power generation, and/or improve efficiencies of systems employing fuel 
cells. 
Previously, a bipolar separator-type fuel cell has been provided with a 
bipolar separator obtained by mechanically ribbing an impermeable thin 
plate of graphite. 
In addition, to the above-mentioned bipolar separator-type fuel cell, 
monopolar-type electrode substrates (i.e., a substrate in which one of the 
sides thereof is ribbed and the other side of which has a flat electrode 
surface so that a reactant gas diffuses from the ribbed side to the flat 
side of the electrode) are known. 
Monopolar-type electrode substrates for a fuel cell have been proposed to 
be fabricated by press-molding short carbon fibers as the base (refer to 
U.S. Pat. No. 4,506,028). The electrode substrate obtained by this 
conventional method of production consists of one layer which has a 
uniform structure as a whole. 
In an electrode substrate having a uniform single layer construction, 
(i.e., where the bulk density of the electrode substrate is large), since 
the gas-diffusion coefficient is small, rapid decrease of electrode 
substrate performance occurs because the limiting current density becomes 
smaller and the retained amount of electrolytic solution is insufficient. 
That is, such an electrode substrate exhibits a short life. On the other 
hand, in the case where the bulk density of the electrode substrate is 
small, the electrode substrate has insufficient mechanical strength, such 
as bending strength. 
The present inventors have offered a composite electrode substrate which 
has been produced by press-molding and heat treatment (rather than by more 
difficult mechanical processing) using short carbon fibers as the basic 
material and providing the flow channels of a reactant gas near the center 
of the thickness of a porous carbonaceous gas-diffusion layer. The 
obtained composite electrode substrate exhibits excellent physical 
properties similar to those separators having a unitary body with a 
carbonized electrode substrate (refer to U.S. Pat. No. 4,522,895). 
According to the invention, it has become possible to use an electrode 
substrate which has a gas-diffusion portion exhibiting a large 
gas-diffusion coefficient (namely, a small bulk density). Furthermore, the 
contact resistance of the electrode substrate is reduced by a large margin 
as compared to conventional monopolar-type and bipolar-type substrates by 
uniting the separator in the body with the carbonized electrode substrate. 
The electrode substrate of this invention obviates conventional ribbing and 
boring steps by using a binding material comprising a thermosetting resin 
of a specified carbonizing yield and a pore-regulator which is thermally 
decomposed at a temperature higher than the molding temperature. The 
porous carbonaceous layer is thus formed so that desirable continuous 
pores are formed in the porous carbonaceous layer but, as will be 
described later, it was impossible to avoid exfoliation of the porous 
carbonaceous layer from the gas-impermeable layer (the compact 
carbonaceous layer) in the steps of carbonization and calcination in the 
process of producing the electrode substrate. Particularly, when a larger 
substrate having a broad surface was produced, exfoliation occurred in 
spite of elevating the temperature to the calcining temperature, resulting 
in low production yields. Accordingly, an improvement of the process for 
producing the electrode substrate was definitely needed. 
It was considered by the present inventors that exfoliation occurred in the 
calcination step (up to the maximum temperature of 3000.degree. C.) of the 
molded substrate due to the thermal expansion rate difference between the 
porous carbonaceous layer and the gas-impermeable layer when the substrate 
was subjected to elevated temperatures or to the thermal shrinkage 
difference between both layers when the calcined substrate was cooled to 
room temperature. Accordingly, methods of reducing or removing the 
expansion and shrinkage differences between the two layers were examined 
using a buffer layer interposed between the two layers, the buffer layer 
thereby compensating for the above-mentioned expansion and shrinkage 
differences. 
As a result, the present inventors have examined a flexible graphite sheet 
which has relatively large expansion and shrinkage rates, improved 
adhesion properties, and is not highly gas permeable. By interposing the 
flexible graphite sheet between the porous carbonaceous layer of the 
above-mentioned electrode substrate and the separator and by joining the 
sheet to the two materials via a carbonizable adhesive, the present 
inventors have found that it is possible to prevent interlayer exfoliation 
which has hitherto been a problem and to produce a large-sized composite 
electrode substrate. 
The flexible graphite sheet is obtained by subjecting naturally occurring 
graphite to acid treatment and further to heating, thereby expanding the 
interlayer of carbon-to-carbon bonding and compression-molding the thus 
form so-called expanded graphite particles. The thus obtained flexible 
graphite sheet can be made to be adhesive because of its scaly surface 
with some gas-permeability which allows impregnation of an adhesive and 
further, such a flexible graphite sheet is most suitable for absorbing 
expansion and shrinkage of the materials for the present invention due to 
the above-mentioned flexiblity properties. 
As a result of further continued studies of the present inventors, it has 
been found surprisingly that the flexible carbon material (which will be 
defined below) is obtained by carbonizing a composite material comprising 
carbon fibers of not less than 1 mm in mean length which have been treated 
at a temperature of not lower than 1000.degree. C. and a binding agent. 
In considering that development of carbon materials has focused upon the 
physical properties thereof, for example, mechanical strength, 
corrosion-resistance, conductivity, etc., it was not expected (nor was it 
intended) that the above-mentioned flexible carbon material could be 
obtained. 
The present inventors have further found that in the cases where the 
above-mentioned flexible carbon material is used as the electrode 
substrate in the composite electrode substrate for a fuel cell, even in 
the case where the above-mentioned flexible graphite sheet is not used 
between the electrode substrate and the separator, the electrode substrate 
can be joined firmly with the separator without cracking, exfoliation, 
warping, etc. at the time the electrode substrate is produced. 
The fundamental object of the present invention lies in the use of a novel 
flexible carbon material having a particularly novel microstructure as the 
electrode layer in the composite electrode substrate which is in contact 
with the flow channels for a reactant gas in a fuel cell. The flexible 
carbon material is obtained from a composite material comprising carbon 
fibers of not less than 1 mm in mean length which have been treated at a 
temperature of not lower tan 1000.degree. C. and a binding agent, wherein 
carbon lumps derived from the binding agent are dispersed in the matrix of 
the carbon fibers so as to restrain a plurality of the carbon fibers 
thereby slidably holding the fibers one to another. 
SUMMARY OF THE INVENTION 
In a first aspect of the present invention, there is provided an electrode 
substrate for a fuel cell, wherein at least a part of the electrode 
substrate comprises a flexible carbon material obtained from a composite 
material comprising carbon fibers of not less than 1 mm in mean length 
which have been treated at a temperature of not lower than 1000.degree. C. 
and a binding agent, the electrode substrate being contacted with flow 
channels of a reactant gas and the flexible carbon material comprising 
carbon lumps derived from the binding agent which are dispersed in the 
matrix of the carbon fibers and restrain a plurality of the carbon fibers 
and the carbon fibers slidably held to one another by the carbon lumps. 
In a second aspect of the present invention, there is provided an electrode 
substrate for a fuel cell, wherein the flexible carbon materials as the 
gas-diffusion part have been respectively stacked on respective top 
surfaces of ribs on both sides of a ribbed separator, ribs on the one of 
the separator sides being perpendicular to those on the other side 
thereof. 
In a third aspect of the present invention, there is provided an electrode 
substrate for a fuel cell, wherein the flexible carbon materials have been 
mechanically ribbed and respectively stacked on both sides of a separator 
so that the respective top surfaces of the ribs are in contact with both 
sides of the separator. 
In a fourth aspect of the present invention, there is provided an electrode 
substrate for a fuel cell, wherein the flexible carbon materials have been 
provided with ribs by molding a rib material on the flexible carbon 
material, the ribs being stacked on both surfaces of a separator so that 
the respective top surfaces of the ribs contact both surfaces of the 
separator. 
In a fifth aspect of the present invention, there is provided an electrode 
substrate for a fuel cell, comprising (1) two flexible carbon materials, 
one side of each having a plurality of mutually parallel flow channels 
(provided by mechanical ribbing) for a reactant gas, the ribbed flexible 
carbon materials being joined to both surfaces of a separator so that the 
respective top surfaces of the ribs contact both surfaces of the separator 
and the flow channels in one of the ribbed flexible carbon materials are 
perpendicular to those in another ribbed flexible carbon material, (2) the 
separator having extended parts which extend beyond a periphery of the 
flexible carbon material, which is parallel to the flow channels of a 
reactant gas therein and (3) peripheral sealers joined to the extended 
parts of the separator. 
In a sixth aspect of the present invention, there is provided an electrode 
substrate for a fuel cell, comprising (1) two ribbed flexible carbon 
materials obtained by integrally molding ribs on the flexible carbon 
material, the ribbed flexible carbon materials being joined to both 
surfaces of a separator so that respective top surfaces of the ribs 
contact both surfaces of the separator such that flow channels of a 
reactant gas formed by the molded ribs in one of the ribbed flexible 
carbon materials are perpendicular to those in the other ribbed flexible 
carbon material, (2) the separator having extended parts which extend 
beyond a periphery of the flexible carbon material, which is parallel to 
the flow channels of a reactant gas therein, and (3) peripheral sealers 
joined to the extended parts of the separator. 
In a seventh aspect of the present invention, there is provided an 
electrode substrate for a fuel cell comprising (1) the two flexible carbon 
materials on one side of each of which a plurality of mutually parallel 
flow channels have been provided by mechanical ribbing, the ribbed 
flexible carbon materials being joined on both surfaces of a separator so 
that the respective top surfaces of the ribs contact with the both 
surfaces of the separator and the flow channels of a reactant gas in one 
of the ribbed flexible carbon materials are perpendicular to those in the 
another ribbed flexible carbon material, (2) the separator having extended 
parts which extend beyond the flexible carbon material and (3) a manifold 
material provided with a flow passage for supplying a reactant gas, joined 
to the extended part of the separator. 
In an eighth aspect of the present invention, there is provided an 
electrode substrate for a fuel cell comprising (1) two ribbed flexible 
carbon materials formed by integrally molding ribs on the flexible carbon 
material, the ribbed flexible carbon materials being joined to both 
surfaces of a separator so that the respective top surfaces of the ribs 
contact both surfaces of the separator such that the flow channels formed 
by the molded ribs in one of the ribbed flexible carbon materials are 
perpendicular to those in the other ribbed flexible carbon material, (2) 
the separator having an extended part which extends beyond the flexible 
carbon material and (3) a manifold material provided with a flow passage 
for supplying a reactant gas, joined to the extended part of the separator 
.

DETAILED DISCRIPTION OF THE INVENTION 
The present invention principally relates to an electrode substrate for a 
fuel cell, wherein at least a part of the electrode substrate comprises a 
flexible carbon material obtained from a composite material comprising 
carbon fibers of not less the 1 mm in mean length which have been treated 
at a temperature of not lower than 1000.degree. C. and a binding agent, 
the electrode substrate being contacted with flow channels of a reactant 
gas, and the flexible carbon material comprising carbon lumps derived from 
the binding agent which are dispersed in the matrix of the carbon fibers 
and restrain a plurality of the carbon fibers, the carbon fibers moreover 
being slidably held one to another by means of the carbon lumps. 
Secondly, the present invention relates to an electrode substrate for a 
fuel cell wherein the flexible carbon materials as the gas-diffusion part 
have been respectively stacked on the respective top surfaces of ribs on 
both surfaces of a ribbed separator, the ribs on the one surface of the 
separator being perpendicular to those on another surface thereof. 
Thirdly, the present invention relates to an electrode substrate for a fuel 
cell wherein the flexible carbon materials have been mechanically ribbed 
and respectively stacked on both surfaces of a separator so that the 
respective top surfaces of the ribs contact with both surfaces of the 
separator. 
Fourthly, the present invention relates to an electrode substrate for a 
fuel cell, wherein the flexible carbon materials have been provided with 
ribs by molding a rib material (hereinafter referred to as the mold rib) 
which has been separately prepared by subjecting a mixture comprising 
short carbon fibers, a binding agent and a pore-regulator to thermal 
press-molding, on the flexible carbon material so as to form it into one 
body with the flexible carbon material and have been stacked on both 
surfaces of the separator so that the respective top surfaces of the mold 
ribs contact with the both surfaces of the separator. 
Fifthly, the present invention relates to an electrode substrate for a fuel 
cell, comprising (1) two flexible carbon materials on one side of each of 
which a plurality of mutually parallel flow channels of a reactant gas 
have been provided by mechanical ribbing, the ribbed flexible carbon 
materials being joined to both surfaces of a separator so that the 
respective top surfaces of the ribs contact the both surfaces of the 
separator and the flow channels in one of the ribbed flexible carbon 
materials are perpendicular to those in the ribbed flexible carbon 
material, (2) the separator having extended parts which extend beyond a 
periphery of the flexible carbon material, which is parallel to the flow 
channels of a reactant gas therein and (3) peripheral sealers each of 
which comprises a gas-impermeable and compact carbon material and has been 
joined to the extended part of the separator. 
Sixthly, the present invention relates to an electrode substrate for a fuel 
cell, comprising (1) two ribbed flexible carbon materials obtained by 
integrally molding ribs on the flexible carbon material so as to form into 
one body with the flexible carbon material, the ribbed flexible carbon 
materials being joined to both surfaces of a separator so that the 
respective top surfaces of the ribs contact with the both surfaces of the 
separator and flow channels of a reactant gas formed by the mold ribs in 
one of the ribbed flexible carbon materials are perpendicular to those in 
the another ribbed flexible carbon material, (2) the separator having 
extended parts which extend beyond a periphery of the flexible carbon 
material, which is parallel to the flow channels of a reactant gas 
therein, and (3) peripheral sealers each of which comprises a 
gas-impermeable and compact carbon material and has been joined to the 
extended part of the separator. 
Concerning the last two mentioned electrode substrates for a fuel cell, as 
has been described as above, since the flexible carbon material has a 
flexibility before and after carbonization and calcination, the flexible 
carbon material exhibits its own buffer action to thermal expansion and 
shrinkage the steps of calcining and cooling. 
Accordingly, the conventionally used flexible graphite sheet may not be 
used in the above-mentioned cases. However, in the case of producing a 
composite electrode substrate of a large size, such a flexible graphite 
sheet may be further interposed between the flexible carbon material or 
the ribbed flexible carbon material and the separator. In such a case, it 
is desirable, after adhesively joining the materials together, to calcine 
the thus joined material under a reduced pressure and/or in an inert 
atmosphere at a temperature not lower than 800.degree. C., thereby 
producing the composite electrode substrate into one body as carbon from 
the view point of obtaining excellent conductivity. In addition, between 
the peripheral sealer and the separator, a flexible graphite sheet or a 
layer of fluorocarbon resin may be interposed. 
In the seventh place, the present invention relates to an electrode 
substrate for a fuel cell comprising (1) the two flexible carbon materials 
on one side of each of which a plurality of mutually parallel flow 
channels have been provided by mechanical ribbing, the ribbed flexible 
carbon materials being joined on both surfaces of a separator so that the 
respective top surfaces of the ribs contact both surfaces of the separator 
and the flow channels of a reactant gas in one of the ribbed flexible 
carbon materials are perpendicular to those in the other ribbed flexible 
carbon material, (2) the separator having an extended part which extends 
beyond the flexible carbon material and (3) a manifold material provided 
with a flow passage for supplying a reactant gas, which comprises a 
gas-impermeable and compact carbon material and has been joined to the 
extended part of the separator. 
In the eighth place, the present invention relates to an electrode 
substrate for a fuel cell comprising (1) two ribbed flexible carbon 
materials formed by molding mold ribs on the flexible carbon material so 
as to form into one body with the flexible carbon material, the ribbed 
flexible carbon materials being joined to both surfaces of a separator so 
that the respective top surfaces of the ribs contact with the both 
surfaces of the separator and the flow channels formed by the mold ribs in 
one of the ribbed flexible carbon materials are perpendicular to those in 
the another ribbed flexible carbon material, (2) the separator having an 
extended part which extends beyond the flexible carbon material and (3) a 
manifold material provided with a flow passage for supplying a reactant 
gas, which comprises a gas-impermeable and compact carbon material and has 
been joined to the extended part of the separator. 
Concerning the electrode substrate for a fuel cell mentioned in the seventh 
and eighth places, a flexible graphite sheet may be interposed between the 
flexible carbon material or the ribbed flexible carbon material and the 
separator, and in such a case, it is desirable to produce the composite 
electrode substrate by joining the materials together while using an 
adhesive and then calcining the thus joined materials into one body as 
carbon, because excellent conductivity is obtained. In addition, a 
flexible graphite sheet or a layer of fluorocarbon resin may be interposed 
between the manifold material and the separator. 
The present invention will be explained more in detail as follows: 
In the present invention, a flexible carbon material which will be 
described in detail as follows is fundamentally used at least partially in 
the electrode substrate for a fuel cell which contacts the flow channels 
of the reactant gas. 
The flexible carbon material used according to the present invention is 
obtained by carbonizing a composite material comprising carbon fibers of 
not less than 1 mm in mean length which have been treated at a temperature 
of not lower than 1000.degree. C. and a binding agent, the carbon lumps 
derived from the binding agent being dispersed in the matrix of the carbon 
fibers and restraining a plurality of the carbon fibers. The carbon fibers 
are moreover slidably held one to another by means of the carbon lumps. 
Although in the flexible carbon material used according to the present 
invention, almost all the carbon lumps derived from the binding agent are 
individually dispersed and restrain the carbon fibers, there are gaps 
between the carbon fibers and the carbon lumps in these restraining 
regions. That is, although almost all the carbon fibers are restrained by 
the carbon lumps, the carbon fibers are not chemically or physically 
joined to the carbon lumps. Accordingly, in the case where an external 
force is applied onto the flexible carbon material, the carbon fibers 
slide in the above-mentioned carbon lumps. This novel microstructure has 
been confirmed by electronmicroscope and polarizing microphotograph (as 
shown in FIGS. 11 to 13). 
In the case where an external force is applied on the carbon material of 
the present invention, the carbon material shows a flexibility which is 
observed by the fact that an amount of displacement remains. The 
above-mentioned flexibility is represented by the ratio of the diameter 
(D) of curvature just before breakage when the flexible carbon is bent 
(referred to as the minimum diameter of curvature) to the thickness (d) of 
the carbon material, and the ratio, namely D/d is preferably not more than 
200. 
Although the flexible carbon material according to the present invention 
has the flexibility shown above, the other physical properties thereof are 
nearly the same as those of the conventional carbon fiber paper sheet (for 
instance, refer to U.S. Pat. No. 3,998,689) or are superior thereto. For 
example, the tensile strength of the flexible carbon material of the 
present invention is not less than 0.05 kgf/mm.sup.2, the electric 
resistance thereof is not more than 900 m.OMEGA..cm and the bulk density 
thereof is from 0.2 to 1.3 g/cm.sup.3. In the flexible carbon material of 
the present invention, not less than 80% (in number) of the micropores 
have the pore diameter of from 10 to 400 .mu.m. On the other hand, the 
conventional carbon fiber paper sheet does not show the flexibility shown 
above. 
It is necessary that the mean length of the carbon fibers in the flexible 
carbon material according to the present invention is not less than 1 mm, 
preferably not less than 3 mm and more preferably not less than 6 mm. 
However, it is preferred that the maximum length of the carbon fibers 
according to the present invention is not more than 50 mm, because the 
thus prepared composite material becomes heterogeneous in the case where 
the mean length thereof is over 50 mm. 
It is preferable that the diameter of the above-mentioned carbon fiber is 
from 4 to 25 .mu.m. 
The above-mentioned carbon fibers may be oriented at random 
two-dimensionally or three-dimensionally, and the ratio of the volume 
occupied by the carbon fibers in the flexible carbon material to the total 
volume of flexible carbon material is from 5 to 50%, preferably from 10 to 
40%. 
Although it is not necessary that the carbon lumps derived from the binding 
agent are in a spherical form, in the case where it is regarded as sphere, 
the diameter of the lumps is 2 to 200 times the diameter of the carbon 
fibers, preferably 3 to 100 times thereof, and the ratio of the volume 
occupied by the carbon lumps in the flexible carbon material to the total 
volume of the carbon material of the present invention is 5 to 70%, 
preferably 10 to 60%. 
In the production of the flexible carbon material according to the present 
invention, a composite material comprising carbon fibers of not less than 
1 mm in mean length and a binding agent is prepared at first. As the 
carbon fibers used according to the present invention, various fibers such 
as those of polyacrylonitriles, of rayons, of phenol resins, of isotropic 
pitches, of anisotropic pitches, etc. may be mentioned, and they are used 
after being treated at a temperature of not lower than 1000.degree. C., 
preferably not lower than 1500.degree. C., and more preferably not lower 
than 2000.degree. C. under a reduced pressure and/or in an inert 
atmosphere. 
The carbon fibers used according to the present invention are not less than 
1 mm, preferably not less than 3 mm and more preferably 6 mm in mean 
length and are 4 to 25 .mu.m in diameter. 
As the binding agent, an organic substance having a carbonizing yield of 
not less than 10%, preferably not less than 20%, for instance, one or more 
kinds of phenol resin, furan resin, pitch of petroleum series or coal 
series, polyvinyl alcohol, polyvinyl chloride, polyacrylonitrile, rayon, 
polymer of siloxane series, etc. are used. 
In order to prepare a composite material comprising the above-mentioned 
carbon fibers and the binding agent, various methods may be used. For 
instance, after impregnating a carbon fiber matrix (for instance 
manufactured by wet process or dry process to be a sheet of paper) with a 
solution prepared by dissolving the binding agent in a solvent, the 
solvent is removed from the sheet of carbon fiber paper, or the binding 
agent is uniformly added to the carbon fiber matrix by pouring the powdery 
form, sheet-form or pellet-form binding agent into the carbon fiber matrix 
while heating. Or, the binding agent may be preliminarily applied on the 
surface of the carbon fibers. For instance, the carbon fiber matrix may be 
prepared from the thus coated carbon fibers and then the binding agent may 
be added to the thus prepared carbon fiber matrix to obtain the composite 
material. In such a case, when the surface of the carbon fibers are coated 
with a high polymeric substance of a low carbonizing yield, a favorable 
result is obtained because of the formation of the space between the 
carbon fibers and the carbon lumps derived from the binding agent during 
the subsequent steps of thermal molding under a pressure and calcining. 
For instance, after mixing the fibrous or granular high polymeric 
substance having the low carbonizing yield with the carbon fibers and 
preparing the carbon fiber matrix therefrom by paper-manufacturing method, 
the binding material is added to the thus prepared carbon fiber matrix, 
thereby preparing the composite material. As such a high polymeric 
substance, polyvinyl alcohol may be mentioned. In addition, one or more 
kinds of carbon black, graphite particles or carbon particles may be used 
as an aggregate together with the carbon fibers. 
Further, in the case where the carbon fibers sheafed by a sheafing agent 
are used as they are, the desired physical property can not be obtained 
even by calcining the material after molding. 
It has been found that, in such a case, a favorable product is available by 
using the carbon fibers from which the sheafing agent has been removed 
preliminarily by washing the carbon fibers with a solvent. 
In addition, since there may be cases where the sheafing agent still 
remains on the carbon fibers after only washing them with a solvent, it is 
preferable to treat the carbon fibers at a high temperature after washing 
them with a solvent and thereby make the surface of the carbon fibers 
inactive. 
The composite material prepared in the above-mentioned manner is thermally 
molded under the conditions of a molding temperature of not lower than 
100.degree. C., a molding pressure of not less than 2 kgf/cm.sup.2 G and a 
pressure holding time of not less than one min. Thereafter, the thus 
molded article is wholly carbonized by calcining under a reduced pressure 
and/or in an inert atmosphere according to the conventional method. The 
temperature of calcination is not lower than 850.degree. C., preferably 
not lower than about 1500.degree. C. and most preferably not lower than 
about 2000.degree. C. 
In addition, in the process for producing the electrode substrate of our 
invention, the raw material before calcination for preparing the flexible 
carbon material may be used directly for the production of the electrode 
substrate. 
In the flexible carbon material thus obtained according to the present 
invention, the carbon lumps derived from the binding agent and the carbon 
fibers are not completely stick to each other and the carbon fibers can 
slide within the carbon lump derived from the binding agent because of the 
presence of a space between the binding part of the two components. 
Consequently, the flexible carbon material according to the present 
invention has a flexibility which has never been considered in the 
conventional carbon fiber paper, etc. Further, the other specific 
properties of the flexible carbon material according to the present 
invention are also not at all inferior to those of the conventional carbon 
fiber paper. The specific properties of the flexible carbon material 
according to the present invention are compared with those of the 
conventional carbon paper (refer to U.S. Pat. No. 3,998,689) in Table 1. 
As is clearly seen in Table 1, the conventional carbon fiber paper scarcely 
shows any flexibility (as that defined above), and on the other hand, the 
flexible carbon material of the present invention is excellent in 
flexibility, and the other specific properties are retained in the same 
level. The reason why the conventional carbon fiber paper does not show 
flexibility is considered to be due to the fact that the carbon lumps 
derived from the binding agent adheres closely to the carbon fibers. 
TABLE 1 
______________________________________ 
Conventional 
Flexible carbon 
carbon fiber 
fiber paper 
paper according 
according to the 
to U.S. Pat. No. 
present invention 
3,998,689 
______________________________________ 
Flexibility (D/d)(cm/cm) 
30-200 500-1000 
Apparent density (g/cc) 
0.3-1.2 0.3-0.8 
Gas-permeability 
.sup. 1-10.sup.5 
10.sup.2 -10.sup.5 
(ml/cm.sup.2 .multidot. hr .multidot. mmAq.) 
Pore diameter (.mu.m) 
10-200 10-200 
Linear thermal expansion 
3.4 .times. 10.sup.-6 
4.5 .times. 10.sup.-6 
coefficient (1/.degree.C.) 
Resistance to hot water 
very large very large 
Electrical resistance 
20-900 20-900 
(m.OMEGA. .multidot. cm) 
Tensile strength (kgf/mm.sup.2) 
0.1-0.3 0.4-0.7 
Tensile elastic modulus 
10-30 60-110 
(kgf/mm.sup.2) 
______________________________________ 
Namely, hitherto the improvement of the mechanical strength and the 
reduction of the electric resistance have been required for the carbon 
fiber paper and accordingly, it has been desired that the carbon lumps and 
the carbon fibers are mutually adhered closely. 
The flexible carbon material according to the present invention has the 
same usefullness in the same usage of the conventional carbon materials 
and in addition, it is particularly useful in the fields wherein 
flexibility is requested together with heat-resistance, 
corrosion-resistance, conductivity and mechanical strength. The respective 
uses for various electrode substrate will be clearly understandable for 
the person skilled in the art. 
The electrode substrate for a fuel cell according to the present invention 
is characterized in that the above-mentioned flexible carbon material is 
used at least as a part of the electrode substrate which contacts with the 
flow channels of a reactant gas. As the actual electrode substrate, there 
are various modes of embodiment, and some of them will be explained while 
referring to the attached drawings as follows: 
A first embodiment of the electrode substrate for a fuel cell of the 
present invention is shown in FIG. 1 of the attached drawings. 
In the electrode substrate for a fuel cell shown in FIG. 1, the flexible 
carbon materials 1 and 1' as the gas-diffusion part have been stacked on 
both surfaces of the separator 2 which is provided with ribs 21. 
The gas-diffusion part 1 (electrode substrate) comprising the flexible 
carbon material is porous and carbonaceous, and it is preferable that the 
gas-diffusion part shows the properties of a mean bulk density of from 0.3 
to 0.9 g/cm.sup.3, a gas-permeability of not less than 200 
ml/cm.sup.2.hour.mmAq and an electric resistance of not more than 200 
m.OMEGA..cm after having been calcined at a temperature of not lower than 
1000.degree. C. under a reduced pressure and/or in an inert atmosphere. 
It is preferable that the separator shows the properties of a mean bulk 
density of not less than 1.4 g/cm.sup.3, a gas-permeability of not more 
than 10.sup.-6 ml/cm.sup.2.hour.mmAq and an electric resistance of not 
more than 10 m.OMEGA..cm and is not more than 2 mm in thickness excluding 
the rib. 
The embodiment of the electrode substrate shown in FIG. 1 is available by 
interposing the ribbed separator between the two flexible carbon materials 
prepared as above and simply stacking the three materials. 
As the material used in the present invention for the separator, a compact 
carbon plate of a calcining shrinkage of not more than 0.2% after 
calcining thereof at 2000.degree. C. under a reduced pressure and/or in an 
inert atmosphere is preferable, and it is used after providing the rib 
thereon by a suitable means in the case of using the ribbed separator. 
In the above-mentioned embodiment according to the present invention, since 
the carbon material of the electrode is flexible, the handling loss is 
small in the case, for instance, wherein the carbon material is subjected 
to water-repellent treatment by TEFLON.RTM. dispersion and the catalyst 
layer is formed thereon up to prepare a fuel cell by stacking the thus 
produced electrode substrate, and since the contact between the flexible 
carbon material and the ribbed separator is closely maintained, there is 
an effect of reducing the contact resistance up to, for instance, 30 
m.OMEGA..cm.sup.2 from 80 m.OMEGA..cm.sup.2 in the case of the 
conventional joining. 
The second embodiment of the electrode substrate for a fuel cell of the 
present invention is shown in FIG. 2. 
In the second embodiment of the electrode substrate shown in FIG. 2, the 
ribs 11 and 11' have been respectively formed by mechanical means onto the 
flexible carbon materials 1 and 1' as the electrode substrate, and the 
stacked electrode substrate is obtained by interposing the plate-form 
separator 2 between the ribs of the two electrode substrates and simply 
stacking the materials. In addition, in the present specification, the 
simple word "separator" designates a separator having a flat plate-form. 
The physical properties of the respective parts in the electrode substrate 
of the second embodiment shown in FIG. 2 are the same as those of the 
first embodiment shown in FIG. 1. 
The method for producing the electrode substrate shown in the embodiment in 
FIG. 2 is a little different from that in the case of the first embodiment 
shown in FIG. 1, and the flexible carbon material is ribbed preliminarily 
before joining by using a suitable mechanical means. 
In the case of using the electrode substrate of the second embodiment shown 
in FIG. 2, the same effect is obtained as that described in the first 
embodiment shown in FIG. 1. 
In the next place, the third embodiment of the electrode substrate for a 
fuel cell of the present invention is shown in FIG. 3. 
Although the construction and shape of the electrode substrate of the third 
embodiment shown in FIG. 3 are nearly the same as those of the second 
embodiment shown in FIG. 2, in the third embodiment shown in FIG. 3, the 
ribbed flexible carbon materials 1 and 1' prepared by molding a ribbed 
material 111 and 111' on the flexible carbon materials 1 and 1' so that 
the former is formed into one body with the flexible carbon materials 1 
and 1' and thus are used as the electrode substrates 1 and 1'. 
The physical properties of the respective parts of the electrode substrate 
of the third embodiment shown in FIG. 3 are the same as those in the 
embodiments shown in FIGS. 1 and 2. 
Further, also the method for production of the electrode substrate of the 
third embodiment shown in FIG. 3 resembles to that of the embodiments 
shown in FIGS. 1 and 2. However, the mold rib in the ribbed flexible 
carbon material shown in FIG. 3 has been produced by (1) scattering a raw 
material for a mold substrate comprising (i) carbon fibers of length of 
0.1 to 1.0 mm obtained by calcining at a temperature of not lower than 
800.degree. C., most preferably at a temperature of not lower than 
2000.degree. C. under a reduced pressure and/or in an inert atmosphere and 
(ii) particles of the binding agent on the flexible carbon materials which 
has not been yet calcined, (2) supplying the thus treated flexible carbon 
material into a metal mold of the prescribed shape and (3) subjecting the 
thus supplied material to thermal press-molding, thereby forming the mold 
rib. 
In the case where the electrode substrate of the third embodiment shown in 
FIG. 3 is used, in addition to the same effect as in the cases of using 
the embodiments shown in FIGS. 1 and 2, there is an additional effect that 
the large deformation does not appear due to the absorption of the 
shrinkage of the mold rib at the time of calcination because of the 
flexibility of the flexible carbon material of the electrode substrate of 
the present invention as compared to the conventional electrode substrate 
provided with the mold rib. 
The fourth embodiment of the electrode substrate for a fuel cell of the 
present invention is shown in FIG. 4. 
The composite electrode substrate for a fuel cell of the present invention 
shown in the embodiment of FIG. 4 has a construction formed by (1) the two 
electrode substrates 1 and 1' comprising the flexible carbon materials 
having a plurality of parallel flow channels of a reactant gas 4 and 4', 
(2) the separator 2 interposed between the two electrode substrates and 
(3) the peripheral sealers 3 and 3' each of which is a gas impermeable and 
compact carbon material and disposed on the extended part of the separator 
which extends beyond the periphery of the electrode substrate, which is 
parallel to the flow channels 4 and 4' of the electrode substrate. 
The separator 2 is larger in surface area than the electrode substrates 1 
and 1' and has been extended, as is shown in FIG. 4, beyond the periphery 
of the electrode substrate along the periphery which is parallel to the 
flow channels 4 and 4' of one of the electrode substrates (the outer edge 
of the extended part coincides with the outer edge of the another 
electrode facing to the electrode substrate while holding the separator), 
and the peripheral sealers 3 and 3' have been joined to the 
above-mentioned extended part. Further, as the electrode substrates 1 and 
1' in the above-mentioned case, the ribbed electrode substrate in the 
above-mentioned embodiment in FIG. 2 or 3 (formed by mechanical ribbing or 
mold ribbing) may be used. 
It is preferable that the peripheral sealer is not less than 1.4 g/cm.sup.3 
in mean bulk density and not more than 10.sup.-4 ml/cm.sup.2.hour.mmAq in 
gas-permeability. 
In order to produce the composite electrode substrate provided with the 
peripheral sealers for a fuel cell of the present invention of the fourth 
embodiment shown in FIG. 4, the ribbed flexible carbon material (before or 
after calcination thereof) and the separator material are joined together 
under the predetermined conditions while using an adhesive in the case 
where the ribbed flexible carbon material has been calcined or while using 
the adhesive optionally in the case where the ribbed carbon material has 
not yet been calcined, and further, (1) after calcinating the thus joined 
materials at a temperature of not lower than about 1000.degree. C. under a 
reduced pressure and/or in an inert atmosphere, the peripheral sealer is 
joined to the thus calcined materials, or (2) except for the case where 
the peripheral sealer is joined to the separator material by a layer of a 
fluorocarbon resin, the joined materials may be calcined after joining the 
peripheral sealer without the calcination before joining the peripheral 
sealer. As the method for joining the peripheral sealer, the peripheral 
sealer is joined to the extended part of the separator which extends 
beyond the periphery of the electrode substrate parallel to the flow 
channels of a reactant gas therein. Thus the electrode substrate of FIG. 4 
is made to be one body together with the separator by calcination, thereby 
forming the composite electrode substrate. 
As the peripheral sealer material, the compact carbon material of a 
calcining shrinkage of not more than 0.2% when calcinated at 2000.degree. 
C. under a reduced pressure and/or in an inert atmosphere is preferable. 
At the above-mentioned time, a flexible graphite sheet may be interposed 
respectively between the ribbed flexible carbon material and the separator 
material and between the peripheral sealer material and the separator 
material thereby joining the each materials together. 
As the adhesive and the joining conditions, those generally used in joining 
the carbon materials together may be utilized. 
In addition, in the case where a particularly large composite electrode 
substrate is produced, as has been described above, a method can be 
adopted wherein the separator material and the flexible carbon material 
are joined together while interposing a flexible graphite sheet between 
them and using an adhesive between the respective materials. 
The flexible graphite sheet prepared by compressing expanded graphite 
particles and used according to the present invention is prepared by 
compressing the expanded graphite particles obtained by subjecting 
graphite particles of not more than 5 mm in diameter to acid-treatment and 
further heating the thus treated graphite particles, and it is preferable 
that the flexible graphite sheet is not more than 1 mm in thickness, 1.0 
to 1.5 g/cm.sup.3 in a bulk density, not more than 0.35.times.10.sup.-2 
cm.sup.2 /kgf in a rate of compression strain (namely, the rate of strain 
under the compression load of 1 kgf/cm.sup.2) and has a flexibility of not 
being broken when being bent to 20 mm in the radius of curvature. As a 
favorable example of the flexible graphite sheet commercialized, 
GRAFOIL.RTM. (made by U.C.C.) may be exemplified. 
As the adhesive used on the joining surfaces when the above-mentioned 
electrode substrate material and the peripheral sealer material are joined 
to the separator material via the flexible graphite sheet, the adhesive 
generally used for joining the ordinary carbon materials together may be 
mentioned, however, particularly it is preferable to use a thermosetting 
resin selected from phenol resins, epoxy resins and furan resins for that 
purpose. 
Although the thickness of the layer of the adhesive is not particularly 
restricted, it is preferable to apply the adhesive uniformly in a 
thickness of not more than 0.5 mm. 
Furthermore, the joining by the above-mentioned adhesive can be carried out 
under the conditions of a pressing temperature of 100.degree. to 
180.degree. C., a pressure of 1.5 to 50 kgf/cm.sup.2 G and a pressure 
holding time of 1 to 120 min. 
After joining the electrode substrate with the separator material as above, 
the thus joined materials are calcined at a temperature of not lower than 
about 800.degree. C. under a reduced pressure and/or in an inert 
atmosphere to obtain the composite electrode substrate of the present 
invention. 
Further, it may be possible to join the peripheral sealer and the separator 
together by interposing a layer of a fluorocarbon resin between them. 
FIG. 8 shows the above-mentioned another example of the composite electrode 
substrate provided with the peripheral sealer in the fourth embodiment of 
the present invention. The electrode substrate shown in FIG. 8 has a 
construction formed by: 
(1) the two flexible carbon materials 1 and 1' on one side of each of which 
a plurality of mutually parallel flow channels of a reactant gas 4 and 4' 
have been provided by mechanical ribbing, the ribbed flexible carbon 
materials 1 and 1' being joined to both surfaces of a separator 2 via 
flexible graphite sheets 7 and 7' so that the respective top surfaces of 
the ribs 11 and 11' contact with the flexible graphite sheets 7 and 7' and 
the flow channels 4 in the ribbed flexible carbon material 1 are 
perpendicular to the flow channels 4' in the ribbed flexible carbon 
material 1', 
(2) the separator 2 having extended parts which extend beyond peripheries 
of the flexible carbon materials 1 and 1', which are parallel to the flow 
channels of a reactant gas 4 and 4' therein and 
(3) peripheral sealers 3 and 3' joined to the extended parts of the 
separator 2 via flexible graphite sheets 8 and 8' or layers of a 
fluorocarbon resin 8 and 8'. 
Further, FIG. 9 shows the above-mentioned one example of the electrode 
substrate provided with the peripheral sealer in the fifth embodiment of 
the present invention. 
The electrode substrate shown in FIG. 9 has a construction formed by (1) 
two ribbed flexible carbon materials 1 and 1' obtained by molding mold 
ribs 111 and 111' on said flexible carbon material 1 and 1' so a to form 
into one body with said flexible carbon material 1 and 1', said ribbed 
flexible carbon materials being joined to both surfaces of a separator 2 
via flexible graphite sheets 7 and 7' so that the respective top surfaces 
of said ribs 111 and 111' contact with the flexible graphite sheets 7 and 
7' and flow channels of a reactant gas 4 formed by said mold ribs 111 in 
the ribbed flexible carbon material 1 are perpendicular to the flow 
channels 4' in the ribbed flexible carbon material 1', (2) the separator 2 
having extended parts which extend beyond peripheries of the flexible 
carbon materials 1 and 1' which are parallel to the flow channels of a 
reactant as 4 and 4' therein, and (3) peripheral sealers 3 and 3' joined 
to the extended parts of the separator 2 via flexible graphite sheets 8 
and 8' or layers of a fluorocarbon resin 8 and 8'. 
The fluorocarbon resin which can be used in the present invention is 
generally a fluorocarbon resin of a melting point of not lower than 
200.degree. C., and although it is not particularly limited, for instance, 
tetrafluoroethylene resin (abbreviated to as PTFE, a melting point of 
327.degree. C. and a thermally deforming temperature of 121.degree. C. 
under a pressure of 4.6 kgf/cm.sup.2 G), the copolymer resin of 
tetrafluoroethylene and hexafluoropropylene (abbreviated to as FEP, a 
melting point of from 250.degree. to 280.degree. C., a thermally deforming 
temperature of 72.degree. C. under a pressure of 4.6 kgf/cm.sup.2 G), 
fluorinated alkoxyethylene resin (abbreviated to as PFA, a melting point 
of from 300.degree. to 310.degree. C. and a thermally deforming 
temperature of 75.degree. C. under a pressure of 4.6 kgf/cm.sup.2 G), 
fluorinated copolymer resin of ethylene and propylene (abbreviated to as 
TFP, a melting point of from 290.degree. to 300.degree. C.), etc. may be 
mentioned, the above-mentioned fluorocarbon resins being commercialized. 
In the above fluorocarbon resins, PTFE resin is most preferable for 
producing the product of the present invention. 
In the case of using the above-mentioned fluorocarbon resin, it is used, 
for instance, as a sheet of about 50 .mu.m in thickness or as an 
dispersion containing about 60% by weight of the resin. A small amount of 
a surfactant may be added to the above-mentioned dispersion. 
In the case of using the above-mentioned fluorocarbon resin, the dispersion 
of the fluorocarbon resin is applied on the joining surfaces of the 
extended part of the separator material and the peripheral sealer material 
which is to be joined to the extended part of the separator material, or 
the sheet of the fluorocarbon resin is interposed between the 
above-mentioned two materials, and then the thus composite materials are 
joined together by melt-adhesion of the resin under a pressure of not less 
than 2 kgf/cm.sup.2 G at a temperature of not lower than the temperature 
of lower by 50.degree. C. than the melting point of the fluorocarbon 
resin. 
In the case of using the above-mentioned composite electrode substrate of 
the fourth embodiment shown respectively in FIGS. 4 and 8 and the fifth 
embodiment shown in FIG. 9 according to the present invention, although 
the above-mentioned effects can be obtained of course, since the 
peripheral sealer has been joined and formed into one body with the 
separator material, it is not necessary to provide a special peripheral 
sealer which is necessitated in the ordinary fuel cell for preventing the 
leakage of the reactant gas to the side of the fuel cell, and the use of 
such a composite electrode substrate exhibits the following effect. 
Namely, since the peripheral sealers have been evenly disposed and joined 
around the thin plate-form electrode substrate while holding the separator 
alternately in both sides, there is a reinforcing effect due to the 
above-mentioned structure, and as a result, the thus formed electrode 
substrate is excellent in the handling property at the time of producing 
the fuel cell. 
In addition, since in the composite electrode substrate of the present 
invention, the electrode substrate has the flexibility in contrast to the 
conventional electrode substrate, the thus composite electrode substrate 
can be obtained without causing cracks, exfoliation and warps of the 
materials by calcining after joining a precursor thereof while not using 
(1) the flexible graphite sheet between the electrode substrate and the 
separator or (2) the flexible graphite sheet or the layer of fluorocarbon 
resin between the peripheral sealer and the separator. As a result, the 
thickness of the thus produced composite electrode substrate can be made 
thinner than that of the conventional composite electrode substrate. 
Further, in the case of suitably interposing the flexible graphite sheet 
or the layer of fluorocarbon resin between the above-mentioned materials, 
the substrate of larger size than the conventional product is possibly 
produced without causing the problems of cracks, exfoliation, warps, etc. 
In addition, the composite electrode substrate formed by joining the 
materials by the flexible graphite sheet or the layer of the fluorocarbon 
resin into one body is excellent in resistance to phosphoric acid, and is 
particularly useful as the composite electrode substrate for a fuel cell 
of phosphoric acid-type. 
Furthermore, in the case where all of the peripheral sealers and the 
separator have been joined together via the flexible graphite sheet or the 
layer of the fluorocarbon resin, the amount of gas-leakage to outside 
through the peripheral sealer including the thus joined parts depends 
mainly on diffusion and is not so much affected by the pressure, however, 
it is preferable that an amount of gas-leakage is not more than 10.sup.-2 
ml/cm.hour.mmAq when an amount of gas-leakage per unit time per the 
peripheral length of the joined part under a differential pressure of 500 
mmAq is represented by [amount of gas-leakage/(side length of the 
periphery).multidot.(differential pressure)]. 
In the next place, the composite electrode substrate provided with the 
manifold for a fuel cell of the sixth embodiment according to the present 
invention is shown in FIGS. 5 to 7. 
FIG. 5 is a ground plan of the composite electrode substrate of the present 
invention, and FIGS. 6 and 7 are the respective cross-sectional figures 
corresponding to VI--VI and VII--VII of FIG. 5. 
The composite electrode substrate provided with the manifold according to 
the present invention has a structure comprising the two electrode 
substrates 1 and 1' consisting of the flexible carbon materials having the 
flow channels of a reactant gas 4 and 4', the separator 2 disposed between 
the above-mentioned two electrode substrate and the manifolds 5 and 5' 
each of which contacts with the periphery of the above-mentioned electrode 
substrates. 
The separator 2 is larger in surface area than the electrode substrates 1 
and 1' and as is shown in FIG. 5, the separator is extended beyond the 
periphery of the electrode substrate, and the manifolds 5 and 5' have been 
joined to the thus extended part of the separator 2. 
In the manifolds 5 and 5', the flow passages 6 and 6' for supplying a 
reactant gas have been provided while penetrating the manifolds including 
the separator. 
The above-mentioned flow passage 6 for supplying a reactant gas has been 
connected to the flow channel 4 of a reactant gas provided in the 
electrode substrate 1 via a flow passage 13 of a reactant gas disposed in 
the manifold 5, or has been directly connected to the flow channel 4 of a 
reactant gas disposed in the electrode substrate, and the other electrode 
substrate 1' consisting of the gas-diffusion part 1' and the rib 11' has 
been sealed by the manifold 5' (refer to FIG. 6). 
On the other hand, the flow passage 6' for supplying a reactant gas has 
been connected to the flow channel 4' of a reactant gas provided in the 
electrode substrate 1' via a flow passage 13' of a reactant gas provided 
in the manifold 5', or has been directly connected to the flow channel 4' 
of a reactant gas provided in the electrode substrate 1' and the other 
electrode substrate 1 has been sealed by the manifold 5 (refer to FIG. 7). 
The flow direction of the reactant gas is shown in FIGS. 6 and 7 by the 
arrow mark. 
As the electrode substrate in this case, any one of the ribbed flexible 
carbon materials in the embodiments shown in FIG. 2 and also in FIG. 3 may 
be used. 
It is preferable that the above-mentioned manifold is not less than 1.4 
g/cm.sup.3 in mean bulk density and not more than 10.sup.-4 
ml/cm.sup.2.hour.mmAq in gas-permeability. 
In order to produce the composite electrode substrate provided with the 
manifold for a fuel cell in the sixth embodiment according to the present 
invention, the electrode substrate material comprising the ribbed flexible 
carbon material (before or after calcination thereof) and the separator 
material are joined together while using an adhesive in the case where the 
ribbed flexible carbon material has been already calcined or while 
optionally using the adhesive in the case where the ribbed flexible carbon 
material has not yet been calcined. Thereafter, (1) after calcining the 
thus joined materials at a temperature of not lower than about 
1000.degree. C. under a reduced pressure and/or in an inert atmosphere in 
this stage, the manifold material is joined to the thus calcined materials 
or (2) except for the case where the manifold material is joined to the 
separator by a layer of the fluorocarbon resin, the manifold material is 
joined to the separator without calcination thereof and the thus joined 
materials may be calcined finally. The above-mentioned joining of the 
manifold material is carried out by joining the manifold material to the 
extended part of the separator material which has been extended beyond the 
electrode substrate material. 
Further, by the above-mentioned calcination, also the electrode substrate 
shown in FIGS. 5 to 7 forms the composite electrode substrate while coming 
into one body with the separator. 
In addition, the holes 6 and 6' which become the flow passage for supplying 
a reactant gas in the manifold may be made in the optional stage of the 
above-mentioned step, for instance, before or after joining each of the 
manifold materials to the separator material by a suitable means. Of 
course, it is desirable that the flow passages 13 and 13' which connect 
the above-mentioned holes 6 and 6' with the flow channels 4 and 4' of a 
reactant gas in the electrode substrate material are made suitable before 
joining the manifold material to the separator material. 
As the manifold material, a compact carbon material which shows the 
calcining shrinkage of not more than 0.2% when it is calcined at 
2000.degree. C. under a reduced pressure and/or in an inert atmosphere is 
desirable. 
Also in the above-mentioned embodiment according to the present invention, 
the joining of the materials may be carried out by interposing (1) a 
flexible graphite sheet between the ribbed flexible carbon material and 
the separator or (2) the flexible graphite sheet or the layer of the 
fluorocarbon resin between the manifold material and the separator. The 
conditions for the joining are the same as those described already. 
FIG. 10 shows the above-mentioned another example of the composite 
electrode substrate provided with the manifold in the six embodiment of 
the present invention. The electrode substrate shown in FIG. 10 has a 
construction formed by (1) two flexible carbon materials 1 and 1' on one 
side of each of which a plurality of mutually parallel flow channels 4 and 
4' have been provided by mechanical ribbing, the ribbed flexible carbon 
materials 1 and 1' being joined on both surfaces of a separator 2 via 
flexible graphite sheets 7 and 7' so that the respective top surfaces of 
said ribs 11 (not shown in FIG. 10) and 11' contact with the flexible 
graphite sheets 7 and 7' and flow channels of a reactant gas 4 in one of 
the ribbed flexible carbon material 1 are perpendicular to those 4' in 
another ribbed flexible carbon material 1', (2) the separator 2 having 
extended parts which extend beyond the flexible carbon materials 1 and 1' 
and (3) manifold materials 5 and 5' provided with a flow passage 6 for 
supplying a reactant gas, joined to the extended parts of the separator 2 
via flexible graphite sheets 8 and 8' or layers of a fluorocarbon resin 8 
and 8'. 
Furthermore, in the case wherein the composite electrode substrate for a 
fuel cell of the present invention, all the manifold and the separator 
have been joined together via the flexible graphite sheet or the layer of 
the fluorocarbon resin, the amount of gas-leakage to outside through the 
manifold part including the joining part is preferably not more than 
10.sup.-2 ml/cm.hour.mmAq when an amount of gas-leakage per the peripheral 
length of the joining part per unit time under a predetermined 
differential pressure is represented by the relationship of [amount of 
gas-leakage/(side length of the periphery).multidot.(differential 
pressure)]. 
The composite electrode substrate for a fuel cell according to the sxith 
embodiment respectively shown in FIGS. 5 to 7 and 10 of the present 
invention exhibits the already described effects, and since the manifold 
has been formed into one body with the substrate, the supply and discharge 
of the necessary gas can be carried out through the manifold parts of the 
respective composite materials of the stacked fuel cell as the whole cell 
when the reactant gas and the like is once introduced into the manifold. 
Accordingly, the above-mentioned composite electrode substrate exhibits 
another effect that it is not necessary to provide the outer manifold for 
supply and discharge of the reactant gas and the like, which has been 
necessitated in the ordinary fuel cell. 
Since in the electrode substrate for a fuel cell of the present invention, 
which has been precisely described as above, at least a part of the 
electrode substrate which contacts with the flow channel of a reactant gas 
has been composed of a flexible carbon material having a particular 
microstructure, and accordingly the above-mentioned electrode substrate 
exhibits an effect that the electrode substrate can be produced without 
causing cracks, exfoliation and warps at the time of joining it to the 
separator. 
The present invention will be explained more in detail while referring to 
the non-limitative examples as follows. 
EXAMPLE 1 and COMATIVE EXAMPLE 1 
Seven parts by weight of carbon fibers (made by KUREHA KAGAKU KOGYO Co., 
Ltd., under the trade name of C206S, 6 mm in length and from 14 to 16 
.mu.m in diameter, and produced by calcining isotropic pitch fibers at 
2000.degree. C.) and one part by weight of polyvinyl alcohol fibers (made 
by KURARE Co., Ltd., under the registered trade name of KURARE-VINYLON VBP 
105-2, 3 mm in length) were dispersed in water and manufactured into 
sheets of paper of a conventional paper machine and then dried. After 
impregnating the thus manufactured sheet of carbon fiber paper with a 20% 
by weight solution of a phenol resin dissolved in methanol, the solvent 
was removed from the sheet of carbon fiber paper by drying thereof. After 
thermally molding the thus treated sheet of carbon fiber paper in a 
prescribed metal mold at 130.degree. C. under a pressure of 10 
kgf/cm.sup.2 G for 20 min, the thus molded material was calcined at 
2000.degree. C. under a reduced pressure of several Torr and in a nitrogen 
atmosphere to obtain a thin plate-like electrode substrate of 0.3 mm in 
thickness. 
For comparison, a similar product of a thin plate form was prepared while 
using another carbon fibers (made by KUREHA KAGAKU KOGYO Co., Ltd. under 
the trade name of C106S, with a length of 6 mm and a diameter of from 14 
to 16 .mu.m, those prepared by calcining isotropic pitch at 850.degree. 
C.). 
The physical properties of the thus obtained products are shown in Table 2. 
TABLE 2 
______________________________________ 
Comparative 
Physical property Example 1 Example 1 
______________________________________ 
Flexibility (D/d)(cm/cm) 
35 &gt;500 
Bulk density (g/cm.sup.3) 
0.4 0.36 
Pore diameter (.mu.m) 
10-180 10-200 
Resistance (m.OMEGA. .multidot. cm) 
220 200 
Contact resistance with 
30 80 
the ribbed separator (m.OMEGA. .multidot. cm.sup.2) 
______________________________________ 
Note: 
In the case of subjecting the each products to "TEFLON .RTM.water 
repellent treatment and catalyst treatment, the product of Example 1 coul 
be handled extremely easily giving a favorable result, however, in the 
same treatments, the product of Comparative Example 1 formed the 
edgecracking in the rate of 10%. 
EXAMPLE 2 and COMATIVE EXAMPLE 2 
After dispersing the same carbon fibers and polyvinyl alcohol fibers as in 
Example 1 into water in the same weight ratio and manufacturing the carbon 
fiber paper sheet by using the ordinary paper machine, the thus obtained 
wet carbon fiber paper sheet was dried. 
After impregnating the dried carbon fiber paper sheets with a 20% 
methanolic solution of a phenol resin, the solvent was removed from the 
paper sheets by drying thereof. Thereafter, the thus impregnated carbon 
fiber paper sheets were thermally molded in a prescribed metal mold at 
130.degree. C. under a pressure of 10 kgf/cm.sup.2 G for 20 min, and then 
calcined at 2000.degree. C. under a reduced pressure of several Torr and 
in a nitrogen atmosphere to obtain an electrode substrate of a thick plate 
form of 3 mm in thickness. 
The thus obtained product was ribbed by a mechanical means to obtain a 
ribbed electrode substrate of 2 mm in the total thickness and 1.5 mm in 
the thickness of the rib. 
In addition, the mechanical ribbing can be carried out before calcining the 
material at 2000.degree. C. 
For comparison, a similar product was prepared while using C 106 S carbon 
fibers in Comparative Example 2. 
The physical properties of the thus obtained products are shown in Table 3. 
TABLE 3 
______________________________________ 
Comparative 
Physical property Example 2 Example 2 
______________________________________ 
Flexibility (D/d)(cm/cm) 
35 &gt;500 
Bulk density (g/cm.sup.3) 
0.4 0.36 
Pore diameter (.mu.m) 
10-180 10-200 
Resistance (m.OMEGA. .multidot. cm) 
200 180 
Contact resistance with 
30 80 
the separator (m.OMEGA. .multidot. cm.sup.2) 
______________________________________ 
Notes: 
In the case of subjecting the each products "TEFLON .RTM.water repellent 
treatment and catalyst treatment, the product of Example 2 could be 
handled extremely easily giving a favorable result, however, in the same 
treatments, the product of Comparative Example 2 formed the edgecracking 
in the rate of 10%. 
EXAMPLE 3 and COMATIVE EXAMPLE 3 
After dispersing the same carbon fibers and polyvinyl alcohol fibers as in 
Example 1 into water in the same weight ratio and manufacturing the carbon 
fiber paper sheet by using the ordinary paper machine, the thus obtained 
carbon fiber paper sheet was dried. 
After impregnating the dried carbon fiber paper sheets with a 20% 
methanolic solution of a phenol resin, the solvent was removed from the 
paper sheet by drying thereof. The thickness of the carbon paper sheet 
impregnated with the phenol resin was 0.4 mm. 
Separately, after blending 35% by weight of short carbon fibers (made by 
KUREHA KAGAKU KOGYO Co., Ltd. under the trade name of M-204 S, with the 
mean diameter of 14 .mu.m and the mean length of 400 .mu.m), 30% by weight 
of a phenol resin (made by ASAHI YUKIZAI Co., Ltd. under the trade name of 
RM-210) and 30% by weight of polyvinyl alcohol particles (made by NIHON 
GOSEI KAGAKU Co., Ltd. with the mean diameter of 180 .mu.m), the blend was 
supplied into a prescribed metal mold and molded under the conditions of 
the molding temperature of 135.degree. C., the molding pressure of 35 
kgf/cm.sup.2 G and the pressure holding time of 20 min to obtain a sheet 
of 1.5 mm in thickness. 
After joining the thus molded sheet and the above-mentioned carbon paper 
sheet impregnated with the phenol resin together by an adhesive, the 
molded sheet side of the thus joined materials was subjected to mechanical 
ribbing. Thereafter, the thus treated material was calcined at 
2000.degree. C. under a reduced pressure of several Torr and is a nitrogen 
atmosphere to produce a ribbed electrode substrate of 2 mm in width of the 
rib, 1.5 mm in thickness of the rib and 1.85 mm in the total thickness. 
For comparison, another electrode substrate was produced in the same manner 
as above except for using the C 106 S carbon fibers instead of the carbon 
fibers of Example 1. 
The physical properties of the products obtained in Example 3 and also in 
Comparative Example 3 are shown in Table 4. 
TABLE 4 
______________________________________ 
Comparative 
Example 3 Example 3 
gas- gas- 
diffusion diffusion 
Physical properties 
part rib part rib 
______________________________________ 
Flexibility(in the 
100 &gt;500 
direction parallel 
to the ditch) 
(D/d)(cm/cm) 
Bulk density(g/cm.sup.3) 
0.4 0.7 0.36 0.7 
Pore diameter(.mu.m) 
10-180 10-60 10-200 10-60 
Resistance(m.OMEGA. .multidot. cm) 
210 35 200 35 
______________________________________ 
Notes: 
Particularly, in the case of subjecting the each products to "TEFLON 
.RTM.water repellent treatment and catalyst treatment, the product of 
Example 3 could be handled extremely easily giving a favorable result, 
however, in the same treatments, the product of Comparative Example 3 was 
large in warping and showed cracks and exfoliation partially. 
EXAMPLE 4 and COMATIVE EXAMPLE 4 
The uncalcined flexible electrode substrates provided with the rib, 
produced in Example 2 was joined directly to the both surfaces of the 
separator so that the respective top surfaces of the ribs contact with the 
both surfaces of the separator and flow channels in one of the substrates 
are perpendicular to those in the another substrate, by using a phenol 
resin as the adhesive under the joining conditions of the temperature of 
130.degree. C. under a pressure of 10 kgf/cm.sup.2 G and the pressure 
holding time of 120 min. Thereafter, the thus joined materials were 
calcined at 2000.degree. C. under a reduced pressure of several Torr and 
in a nitrogen atmosphere. A favorable product was obtained by the 
above-mentioned procedures without causing any warps, cracks and 
exfoliation. 
For comparison, in Comparative Example 4, the conventional mold substrate 
provided with the rib was directly joined to the separator, and the thus 
joined materials were calcined. However, any satisfactory product was not 
obtained due to the occurrence of cracks in the composite electrode 
substrate. 
EXAMPLE 5 and COMATIVE EXAMPLE 5 
After directly joining the uncalcined flexible electrode substrates 
provided with the rib, produced in Example 3 to the both surfaces of the 
separator so that the respective top surfaces of the ribs contact both 
surfaces of the separator and flow channels in one of the substrates are 
perpendicular to those in the other substrate, while using a phenol resin 
as the adhesive under the same joining conditions as in Example 4, the 
thus joined materials were calcined at 2000.degree. C. under a reduced 
pressure of several Torr and in a nitrogen atmosphere. A favorable product 
was obtained by the above-mentioned procedures without causing any warps, 
cracks and exfoliation. 
For comparison, in Comparative Example 5, the conventional mold substrate 
provided with the rib was directly joined to the separator, and the thus 
joined materials were calcined. However, satisfactory product was not 
obtained due to the occurrence of cracks in the composite electrode 
substrate.