CA1314927C - Composite substrate for fuel cell and process for producing the same - Google Patents
Composite substrate for fuel cell and process for producing the sameInfo
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- CA1314927C CA1314927C CA000537161A CA537161A CA1314927C CA 1314927 C CA1314927 C CA 1314927C CA 000537161 A CA000537161 A CA 000537161A CA 537161 A CA537161 A CA 537161A CA 1314927 C CA1314927 C CA 1314927C
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- separator
- gas
- electrode substrate
- carbon
- joining
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
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Abstract
ABSTRACT OF THE DISCLOSURE:
Disclosed herein are a composite substrate for a fuel cell comprising (1) a separator, (2) two porous and carbonaceous electrode substrates which have been joined to the separator via a flexible carbon sheet and provided with, on one of the surfaces thereof, a plurality of grooves forming flow channels for reactant gases and (3a) a pair of peripheral sealers on the side of the electrode substrate, which comprise a gas-impermeable and compact carbon material or (3b) a pair of the peripheral sealers and a pair of gas-distributors on the side of the elec-trode substrate, which comprise a gas-impermeable and compact carbon material, the peripheral sealers (3a) or both the peripheral searlers and the gas-distributors (3b) being joined to an extended part of the separator beyond the periphery of the electrode substrate, via a fluorocarbon resin layer, and a process for producing the composite substrate for a fuel cell.
Disclosed herein are a composite substrate for a fuel cell comprising (1) a separator, (2) two porous and carbonaceous electrode substrates which have been joined to the separator via a flexible carbon sheet and provided with, on one of the surfaces thereof, a plurality of grooves forming flow channels for reactant gases and (3a) a pair of peripheral sealers on the side of the electrode substrate, which comprise a gas-impermeable and compact carbon material or (3b) a pair of the peripheral sealers and a pair of gas-distributors on the side of the elec-trode substrate, which comprise a gas-impermeable and compact carbon material, the peripheral sealers (3a) or both the peripheral searlers and the gas-distributors (3b) being joined to an extended part of the separator beyond the periphery of the electrode substrate, via a fluorocarbon resin layer, and a process for producing the composite substrate for a fuel cell.
Description
1~14q27 BACKGROUND OF THE INVENTION:
The present invention relates to a composite~
substrate for a fuel cell of phosphoric acid type and a process for producing the same. More in detail, the present invention relates to a composite substrate provided with two electrode substrates, a separator and (1) peripheral sealers or (2) both the peripheral sealers and gas-distri-butors (external manifold type), and a process for producing the same. In addition, "electrode substratei' in the pre-sent invention means all electrode substrates each of which becomes an electrode for a fuel cell by only applying a catalyst to the electrode substrate or only stacking on the electrode substrate a porous electrode carrying a catalyst which has been separately prepared.
In recent years, as an apparatus for generating clean energy or a freely switchable generator which can contribute to saving natural resources by a normalization of the operation of thermal power generation or water-power generation or an improvement of energy efficiency, a fuel cell and development and utilization of a system surrounding the fuel cell have been highly demanded.
Hitherto, as the fuel cell, a fuel cell of bipolar separator type in whLch a bipolar separator obtained by ribbing a gas-impermeable graphitio thin plate and a porous and carbonaceous plate are used in combination have been publicly known, however, contrary to the above-~r 1 31 ~27 mentioned, a fuel cell of monopolar type formed by stackingan electrode substrate which has been provided with ri~bs on one surface thereof and have a flat structure on the another surface thereof, a catalyst layer, a matrix impregnated wi~h an electrolyte and a separator sheet has been developed. In the fuel cell of monopolar type, a reactant gas (oxygen or hydrogen) diffuses from flow channels for reactant gases formed by the ribs provided on the electrode substrate to a flat surface of the elec-trode.
Although such an electrode substrate is usually made of a caxbonaceous material from the viewpoint of physical properties such as heat-resistance~ corrosion-resistance, electro-conductivity, mechanical strength, etc. and the ease of retaining poxosity therein and the electrode substrate is used by stacking them as has been stated above, it is difficult to make top surfaces of the ribs perfectly flat and therefore, the electric- and thermaI contact resistance between the ribs and the separator is too large to be disregarded.
Generally, it is said that the above-mentioned contact resistance is larger than the transmission resistance within the substrate by several times, and such contact resistance causes conclusive defects such as uneveness of distribution of the temperature between the cells and reduction of an efficiency of electric generation. ;
1 3 1 ~
In order to solve the above-mentioned problem of contact resistance, a composite substrate has been~
proposed wherein the electrode substrate, the separator, etc. of the stacked structure of the above-mentioned fuel cell have been adhered together by an adhesive and integrated into one body of carhon by calcination thereof.
Although in such a composite substrate, the contact resistance present on the contact surface can be made zero by joining them into one body, since the composite substrate is produced by adhering the carbonaceous materials together and carbonizing and calcining the thus adhered materials as has been stated, there are cases of exfoliation of the adhered surfaces during the calcining step due to a difference of rates of thermal expansion and shrinkage between the carbonaceous materials and the adhe,sive, and cases of causing warps, distortions or cracks in the product. In such cases, the reduction of the producti~e yield is caused, and accordingly, improvements of the product and process have been desired.
As a result of the present inventors' studies from the conception that the exfollation of the cOmpOSLte substrate for a fuel cell in the calcining step (to a maximum temperature of 3000C) is considered to be due to the difference of the thermal expansion between the porous and carbonaceous layer and the gas-impermeable layer (separator) in the temperature-raising step or to the .
131~q27 difference of shrinkage between the above-mentioned two layers in the cooling step to room temperature after `
completing calcination and that the difference of thermal expansion and shrinkage between the above-mentioned two layers may be reduced or removed by a buffer layer pro-vided between the two layers, it has been found by the present inventors that the above-mentioned problem of inter-layer exfoliation can be solved by inserting a -flexible carbon sheet which has a relatively large rate of thermal expansion and shrinkage, an adhesiveness to the adhesive, etc. and a relatively low gas-permeability, as a material for the buffer layer, between the above-mentioned porous and carbonaceous layer and the separator and joining the above-mentioned two layers via a carboni-zable adhesive (for instance, refer to U.S. Patent No.
4,579,789).
However, in general, the substate as the electrode in ~the fuel cell of phosphoric acid type is stacked 50 that one surface thereof contacts to the phosphoric acid matrix and the another surfaces thereof faces to the separator. Still more, in the case of stacking the elec-trode substrate for obtaining a fuel cell, a sealer .material is provided on the peripheral part thereof to prevent diffusion of the reactant gas from the side of the electrode substrate to outside thereof.
1 3 1 4'~27 Accordingly, particularly in the case where the composite substrate is formed of the porous and carbo~a-ceous electxode substrate up to the edge part thereof and the flow channels of reactant gases open directly at the edge part in the composite substrate of the external manifold type, the peripheral sealer which is compact and carbonaceous and the electrode substrate which is porous and carbonaceous are disposed opposite each other across the separator on the peripheral region of the separator, and there has been a problem of causing a certain degree of a warp or a strain in the joining part of the materials due to the difference of the thermal shrinkage between the mat~rials even by the intervention of the flexible carbon sheet. As the means for preventing the above-mentioned warp, the materials with an extrèmely small difference of the thermal shrinkage should be selected, and such a restriction has been the obstruction in the production of the composite substrate.
Furthermore, as a problem poin~ of the conventional fuel cell, the adhesion between the composite materials in the fuel cell has been carried out by using a carbon cement.
However~ since the carbon cement is eroded by phosphoric acid, ~here has been a possibility that exfolia-tion between the composite materials is caused and the reactant gas leaks through the joined parts.
~ 3 ~ ~927 In addition, there has been another problem in the point of mechanical strength of the electrode ~
substrate resulting in breaking on handling in the case where the area of the substrate is too large, because the electrode substrate is a thin plate.
Further, a method of joining porous electro-conductive materials wherein the gas-impermeability between the porous electroconductive materials has been increased, has been proposed recently. According to the proposed method, the porous electroconductive material is impregnated with a fluorinated ethylenepropylene copolymer, a polysulfone resin, etc., and the thus impregnated layer is joined as an interface to another electroconductive material by hot-pressing while maintaining electroconduc-tivity through the gas-impervious region (for instance, refer to U.S. Patent No. 4,505,992).
However, in the case of using the above-mentioned methods for sealing periphery of a composite substrate for a fuel cell, although the passage of~the gas between the ~wo carbonaceous materials is prevented by the thus resin-impregnated carbon layer, since the usable electro-conductive material is limited to the porous carbonaceous material and such a porous carbonaceous material is weak in mechanical strength, the usage of the thus~obtained composite material is limited.
.
1 31 ~9~7 On the other hand, even in the case where an electrode in a composite electrode substrate is produced by the above-mentioned method, the thus obtained resin-impregnated electrode is unsatisfactory in quali.ty for using it in the composite electrode substrate for a fuel cell, because the used thermoplastic resin is substantially large in resistance to thermal and electric conductivities.
As a result of the present inventors' studies for finding a process for producing a composite substrate for a fuel cell, which does not have the above-mentioned defects and is excellent in mechanical strength/ electrical properties and chemical resistance, it has been found out by the present inventors that the composite substrate having the above-mentioned excellent properties can be obtained in a high yield by joining a porous and carbona-ceous electrode substrate provided~with~flow channels for reactant gases and a gas-impermeable separator comprlsing~
a compact carbonaceous~material via a flexible carbon~sheet and further joining (1) a peripheral sealer comprising a gas-impermeable and compact carbon material or (2) both the peripheral sealer and a gas-distributor comprising~
a compact carbon material to the above-mentioned separator via a fluorocarbon resin layer, and on the basis of the ~:
above-mentioned flndings, the present inventors have attained the present invention.
t 3 1 4927 Namely, the first object of the present invention is to provide a composite substrate provided with peripheral sealers for a fuel cell, wherein the peripheral sealexs have been joined to a separator and the these materials have been integrated.
The second object of the present invention is to provide a composite substrate provided with peripheral sealers and gas-distributors (of the external manifold type) for a fuel cell, wherein porous and carbonaceous electrode substrates, peripheral sealers and gas-distributors have been joined to a separator and the above-mentioned materials have been integrated.
The third object of the pre:ent invention is to provide a composite substrate for a fuel cell, which has a structure that can prevent the generation of warps, distortions or cracks at the time ~f producing the composite substrate.
The fourth object of the present invention is to provide a composite substrate ~or a fuel cell o~ a phosphoric acid-type. ~
The fifth object of the present invention is to provide a composite substrate for a fuel cell, which is excellent in mechanical strength and handling properties at the time of producing the composite substrate.
The other objects and the merits of the present invention will be apparent to persons skilled in the art .... ~.; ~
1~i14927 from the following detailed description of the present invention.
SUMMARY OF THE INVENTION-In a first aspect of the present invention, there is provided a composite substrate for a fuel cell comprising (l) a separator, (2) two porous and carbonaceous electrode sub-strates which are provided with a plurality of grooves on one of surfaces thereof and have another flat surface, each of the electrode substrates being joined to the both surfaces of the separator via a flexible carbon sheet so that the grooves form flow channels for reactant gases and the flow channels in one of the elec-trode substrates are perpendicular to those in the~another -electrode substrate, the flexible carbon sheet being :
interposed only between the joining surfaces of..the separator and tops of ribs forming the grooves of the electrode substrate, and the sepa.rator having an extended part beyond a periphery of the eIectrode substrate,~and (3a) a:pair of peripheral sealers on the side of:
the electrode substrate parallel to the flow channels for reactant gases therein, which comprise a gas-impermeable and compact carbon material, or:
1 3 1 ~9~7 t3b) a pair of peripheral sealers on the side of the electrode substrate parallel to the flow channels for reactant gases therein, which comprise a gas-impermeable and compact carbon material and a pair of gas-distributor on the side of the electrode substrate perpendicular to the flow channels for reactant gases therein, which comprise a gas-impermeable and compact carbon material and are provided with a passage for distributing reactant gases, (3a) the peripheral sealers or (3b) the peri-pheral sealers and the gas-distributors being joined to the extended part of the separator beyond the electrode substrate, via a fluorocarbon resin layer.
In a second aspect of the present invention, there is provided a process for producing a composite substrate :
for a fuel cell, comprising steps of (1) adhering a flexible carbon sheet onto one surface of each of two electrode substrate materials of a fl~at plate-form without grooves and of the prescribed dimension by an adhesive, ~ :
(2) providing grooves of a desired dimension for forming flow channels of reactant gases on the joining:surface side of each of the electrode substrate materials by cut-processing, ~31~27 (3) joining a separator material to the surface of the fle~ible carbon sheet remaining on the thus cut-processed surface of each of the electrode substrate materials in face to face, (4) calcining the thus composed materials at a temperature of not lower than about 800C under a reduced pressure and/or in an inert atmosphere thereby producing a composite body comprising the electrode substrates and the separator, and (5a) joining a pair of peripheral sealers comprising a gas-impermeable and compact carbon material to an extended part of the separator, which extends be~ond a periphery of the electrode substrate parallel to the flow channels for reactant gases therein, via a sheet or a dispersion of fluorocarbon resin, or (5b) joining a pair of peripheral~sealers comprlsing a gas-impermeable and compact carbon material to an extended part of the separator, which extends beyond a periphery of the electrode substrate parallel to the flow channels for reactant gases therein, via a sheet or a dispersion of fluorocarbon resin and further joining a pair of gas-distributors comprising a gas-impermeable and compact carbon material and having grooves forming a passage for distributing reactant gases to an e~tended part o~ the separator, which extends beyond a periphery of the electrode substrate perpendicular to the flow channels 131~7 for reactant gases therein, via a sheet or a dispersion of fluorocarbon resin.
BRIEF EXPLANATION OF DRAWINGS:
of the attached drawings, Fig. 1 is an oblique view of the composite substrate provlded with the peripheral sealers according to the present invention and Figs. 2 and 3 are respectively the oblique views of the composite substrate provided with the peripheral sealers and the gas-distributors according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION:
The present invention rela-tes to a composite substrate for a fuel cell comprising (l) a separator, (2) two porous and carbonaceous electrode substrates which are provided with a plurality of grooves on one of surfaces thereof and have another flat surface, each of the electrode substrates being joined to the both surfaces of the separator via a flexible carbon sheet so that the grooves form flow channels for reactant gases and the flow channels in one of the electrode substrates are perpendicular to those in the another electrode substrate, the flexible carbon sheet being interposed only between the joining surfaces of the separator and tops of ribs forming the grooves of the 1 31 ~927 electrode substrate, and the separator having an extended part beyond a periphery oE the electrode substrate, and (3a) a pair of peripheral sealers on the side of the electrode substrate parallel to the flow channels for reactant gases therein, which comprise a gas-impermeable and compact carbon material, or (3b) a pair of peripheral sealers on the side of the el~ctrode substrate parallel to the flow channels for reactant gases therein, which comprise a gas-impermeable and compact carbon material and a palr of gas-distributor on the side of the electrode substrate perpendicular to the flow channels for reactant gases therein, which comprise a gas-impermeable and compact carbon material and are provided with a passage for ~:
reactant gases, (3a) the peripheral sealecs or (3b) the peripheral sealers and the gas-distributors being joined to the extended part of the separator beyond the electrode substrate, via a fluorocarbon resill layer. : :
: Still more, the present invention relates to a process for producing:a composite substrats for a fuel cell, comprising steps of ~l) adhering a flexible carbon sheet onto one surface of each of two electrode substrate materials of a~flat .
1 31 ~q27 plate-form without grooves and of the prescribed dimension by an adhesive, (2) providing grooves of a desired dimension for forming flow channels of reactant gases on the joining surface side of each of the electrode substrate materials by cut-processing, ~3) joining a separator material to the surface of the flexible carbon sheet remaining on the thus cut-processed surface of each of the electrode substrate materials in ace to face, (4) calcining the thus composed materials at a temperature of not lower than about 800C under a reduced pressure and/or in an inert atmosphere thereby producing a composite body comprising the electrode substrates and the separator, and ~
(5a) joining a pair of peripheral sealers comprising a gas-impermeable and compact carbon~material to an extended part of the separator, whlch extends beyond a:periphery of the electrode substrate parallel:to the flow c~annels for reactant gases therein, via a sheet or~a dispersion of fluorocarbon resin, or (5b) joining a pair of peripheral sealers comprising a gas-impermeable and compact carbon material to:an extended part of the separator, which extends beyond a periphery of the electrode substrate parallel to the flow channels for reactant gases therein, via a sheet or a dispersion of 1 3 1 ~927 fluorocarbon resin and ~urther joining a pair of gas-distributors comprising a gas-impermeable and compact~
carbon material and having grooves forming a passage for distributing reactant gases to an extended part of the separator, which extends beyond a periphery of the elec-trode substrate perpendicular to the flow channels for reactant gases therein, via a sheet or a dispersion of fluorocarbon resin.
Of the attached drawings, Fig. 1 is an oblique view of a composite substrate provided with the peripheral sealers according to the present invention. The composite substrate of Fig. 1 has a construction comprising a separator 1, two electrode substrates 2 which have grooves forming flow channels 6 for reactant gases together with the separator and are disposed on the both sides of the separator and peripheral sealers 3 which are disposed on the edge (namely, side) of the electrode substrate 2 in the parallel direction to the flow channels 6 for reactant gases of the electrode substrate.
The surface area of the separator 1 is larger than that of the electrode substrate 2, and the separator 1 has been extended beyond a periphery of the electrode substrate which is parallel to the flow channels 6 for reactant gases in each of the electrode subs~rates (the outer edge of the extended part coincides with the outer edge of the another electrode substrate). The peripheral t; 3 1 ~.q27 sealer 3 has been joined to the above-men-tioned extended part. Only between the joining surfaces of the separàtor 1 and tops of ribs forming the grooves of the electrode substrate 2, a flexible carbon sheet 4 has been interposed, and accordingly, the flow channels 6 for reactant gases have been prescribed by the grooves of the electrode substrate, the separator and the flexible carbon sheet.
The peripheral part of the separator, which has been extended beyond the electrode substrate and the peripheral sealer 3 have been joined via a fluorocarbon resin S.
Fig. 2 is an oblique view of a composite substrate provided with peripheral sealers and gas-distributors according to the present invention. Fig. 3 has been given to show a construction of the composite substrate according to the present invention and shows the same view as Fig. 2 except for inexistence of both (1) one of the gas-distri-butors 7 having grooves forming passage 8 for distrlbuting reactant gases, which will be explained later, and (2) the fluorocarbon resin 5 on the part to which the gas-distributor is ~oined.
In Figs. 2 and 3, the composite substrate according to the present invention has a construction comprising (1) the separator 1, (2) the two electrode substrates 2 which have the grooves ~orming the flow channels 6 for reactant gases together with the separator and are provided on the both sides of the separator so .
.
131~27 that the flow channels 6 in one of the electrode substrates are perpendicular to those in the another electrode substrates, (3) the peripheral sealers 3 which have been disposed on the edge (namely/ side) of the electrode substrate and (4) the gas-distributors 7.
The surface area of the separator 1 is larger than that of the electrode substrate 2 and as is seen in Figs.
2 and 3, the separator has been extended beyond a periphery of the electrode substrate, and the peripheral sealer 3 and the gas-distributor 7 have been joined to the above-mentioned extended part (the outer edge of the extended part of the separator coincides with the outer edge of the peripheral sealer and the gas-distributor after joining).
The gas-distributor 7, which is joined to the extended part of the above-mentioned separator beyond the periphery of the electrode substrate perpendicular to the 10w channel 6 for reactant gases therein, has grooves forming a flow passage 8 for distributing reactant gases together with the separa~or, and the peripheral sealer 3, which is joined to the extended part of the separator beyond the periphery of the electrode substrate parallel to the flow channel 6 therein, does not have the above~
mentioned grooves. Although the grooves in the gas-distributor 7 form the flow passage 8 for distributing reactant gases for the supply of the reactant gases from outside, it is not particularly necessary that the shape .
13~4~27 of the cross-section thereof coincides with that of the flow channel 6 for reactant gases, and further, it is~not necessary that all of the openings of the flow channels 6 open to the flow passage 8 for distributing reactant gases. Namely, the cross-sectional shape of the grooves of the gas-~istributor 7 may be selected so as to be sufficient for maintaining the flow volume of the gases necessary for operating the fuel cell provided with the composite substrate.
Between the separator 1 and the electrode substrate 2, a flexible carbon sheet 4 has been interposed. Still more, in E'igs. 2 and 3, the flexible carbon sheet 4 has been interposed only between the joining surfaces of the separator 1 and tops of the ribs of the electrode substrate 2, and accordingly, the flow channel 6 for reactant gases have been prescribed by the grooves of the electrode substrate, the separator and the flexible carbon sheet, and the flow passage 8 for distributing reactant gases has a shape prescribed by the grooves of the gas-distributor 7 r the separator 1 and the fluorocarbon resin 5.
In the production of the composite substrate of Figs. 2 and 3, the flexible carbon sheet 4 may be joined to the whole area of the separator facing to the electrode substrate (except for the surface area on which the peripheral sealer and the gas-distributor are joined vla a fluorocarbon resin layer) so that the size of the flexible 1; 3 1 ~7 carbon sheet is the same as that of the electrode substrate (such a situation has not been illustrated hereinJ. However, from the viewpoint of the thickness of the composite substrate, since the former structure can make the thickness of the composite substrate thinner than that of the latter structure by the thickness of the flexible carbon sheet while retaining the same cross-sectional area of the flow channels for reactant gases, the former structure is preferable.
In Figs. 2 and 3, the peripheral part (extended part) of the separator beyond the electrode substratej the peripheral sealer 3 and the gas-distributor 7 have been respectively joined via the fluorocarbon resin 5. Although the fluorocarbon resin may be interposed between the joining surface of the peripheral sealer and:the gas-distributor both of which are joined to the same side of the separator, it is not particularly necessary, because the gas-leakage does not become any problem:in the case where the product is used in combination with the external mani~old which is made so as to cover the above-mentioned joining part.
Still more in the composite substrate of Figs. 1 to 3, the separator 1, the:flexible carbon sheet 4 and the electrode substrate 2 have been made into one body by 1 3 1 ~927 carbonization and calcina-tion.
The electrode substrate used according to thè
present invention is a porous and carbonaceous material and preferably having the following specific properties, and also an electrode substrate material (namely, a material for the porous and carbonaceous electrode substrate) used in the present invention has preferably the same following specific properties after calcining the material at a temperature of not lower than 800C under a reduced pressure and/or in an inert atmosphere. That is, Mean bulk density of from 0.3 to 0.9 gjcc, Gas-permeability of not less than 200 ml/cm2.hour-mmAq and Electric resistivity of not more than 200 mQ-cm.
The separator used according to the present invention pre~erably has the following specific properties:
Mean bulk density of not less than 1.4 gjcc, Gas-permeability of not more than ~10 6~ml/cm2 houI 'IrlInAq, ` ~
Electric resistivity o~ not more than 10 mQ~cm and Thickness of not more than 2 mm.
The material of the peripheral sealer and the~
gas-distributor used in the composite substrate according to the present inventlon is preferably a compact carbon material of the following properties:
1 31 ~27 Mean bulk density of not less than 1.40 g/cc, Gas-permeability of not more than 10 4 ml/cm2~.
hour-mn~q and Difference of the thermal expansion coefficient thereof from that of the separator material is not more than 2 x 10 6/oC.
Particularly, the above-mentioned material is preferably a material subjected to calcination at a temperature of not lower than 800C under a reduced pres-sure and/or in an inert atmosphere.
As has been already described, in the composite substrate for a fuel cell accord:ng to the present invention, all of the peripheral sealers, all of the gas-distributors and the separator have been joined respectively ~ia a fluorocarbon re~in. Although an amount of gas leakage through the per~ipheral sealers including the joined parts~is controlled mainly by diffusion and is not so much influenced by the pressure~
.
the amount of gas leakage is preferably not more than 10 2 ml/cm-hour.mmAq in the case where the amount of gas leakage per unit time per unit length of the pariphery of the joining part under a differential pressure~of 500 mmAq. is represented by the relationship of [the amount of gas leakage/(side~length of periphery~-tdifferential pressure)].
~ 3 1 ~ 7 The ~luorocarbon resin used according to the present invention is a fluorocarbon resin of a melting point of not lower than 200C and is not particularly limited, however, for instance, a tetrafluoroethylene resin (an abbreviation of PTFE, a melting point of 327C, a thermal deformin~ temperature of 121C under 4.6 kgf/cm2G.), a copolymer resin of tetrafluoroethylene and hexafluoropropylene (an abbreviation of FEP, a melting point of from 250 to 280C, a thermal deforming temperature of 72C under 4.6 kgf/cm G.), a fluoroalkoxyethylene resin (an abbreviation of PFA, a melting point of from 300 to 310C, a thermal deformation temperature of 75C under 4.6 kgf/cm2G.) and a fluorinated copolymer resin of ethylene and propylene (an abbreviation of TFP, a melting point of from 290 to 300C) may be exemplified. The above-mentioned fluorocarbon resins are c:ommercialized.
Of the above-mentioned fluorocarbon resins, tetrafluoroethylene resin is preferably used particularly in the present invention and is commercialized under the trade name of TEFLO ~.
In the present invention, the above-mentioned fluorocarbon resin is used as, for instance, a sheet of about 50 ~m in thickness or a dispersion containing about 60% by weight of the resin. Into the dispersion, a small amount of a surfactant may be added.
As the electrode substrate material (namely, the 1~14~27 material for the porous and carbonaceous electrode substrate) used according to the present invention, the following materials may be mentioned:
(1) A material made by molding a mixture of short carbon fibers, a binder and an organic granular substance by heating under a pressure (for instance, refer to Canadian Patent No. 1,205,857). Particularly, the material obtained by molding a mixture of from 20 to 60~ by weight of short carbon fibers of not more than~2 mm in length, from 20 to 50% by weight of a phenol resin and from 20 to 50% by weight of an organic granular substance (a pore regulator) at a molding temperature of from 100 to 180C, under a molding pressure of from 2 to~
100 kgf/cm G. for from l to 60 min~ and (2) A material obtained by calcining the material shown in the above (1) at a temperature of not lower than 800C under a reduced pressure and/or in an inert atmosphere.
As a separator material (namely, the material for the separator) used according to the present invention, a compact carbon plate which shows a rate of calcining~
shrinkage of nct more than 0.2 % in the case where the material is calcined at 2000C under a reduced pressure and/or in an inert atmosphere is desirable. The separator material is usually in a flat plate form, and the area of one of the surfaces thereof is usually larger than that of the flat part of the electrode substrate material.
1314'~27 However, as will be described later, in the step of joining the separator material and the electrode substrate material, the surface area of the former may be the same as that of the latter.
As the flexible carbon sheet used for joining the electrode substrate material and the separator material in the composite substrate according to the present invention, a flexible graphite sheet of not more than 1 mm in thickness which has been 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 acid-treated particles, shows a bulk density of 1.0 to 1.5 g/cc and a rate of compression strain (namely, the rate of strain to the compression load of 1 kgf/cm2G.) of not more than 0.35 x 10 2 cm2/kgf and has a flexLbility that the sheet is not broken in the case of bending the sheet to 20 mm in the radius of curvature is preferable, and~of the commercialized flexible graphite sheets, GRAFOIL~made by U~C.C. is a suitable example.
The:flexible carbon sheet used also according to the present invention is produced by mlxing carbon fibers of not less than 1 mm in mean length whlch fibers have been thermally treated at a temperature of preferably not lower than l,000C, more preferably not lower than 1,500C under a reduced pressure and/or in an inert ~3~4~27 atmosphere, with a binder of not less than 10~ in the carbonizing yield, for instance, pouring the above binder into the matrix of the above carbon fibers, molding the thus composite materials by heating under a ~ressure and calcining and carbonizing the thus molded material at a temperature of not lower than 850C under a reduced pressure and/or in an inert atmosphere. The thus produced flexible carbon sheet has a thickness of no-t more than 1 mm, a bulk density of 0.2 to 1.3 g/cc and a rate of compression strain of not more than 2.0 x 10 1 cm~/kgf, wherein the carbon lumps derived from the above-mentioned binder have been dispersed in the matrix of the carbon fibers and restrain a plurality of the carbon fibers and by the carbon lumps the carbon fibers are slidably held to one another. The just-mentioned flexible carbon sheet has a flexibility of not being broken in the case of bending the sheet to 10 mm in the radius o~ curvature.
As the adhesive used on each of the joining surfaces in the case of joining the above~mentioned electrode substrate material to the separator material via the flexible carbon sheet, any adhesive usually used in joining carbon materials may be used, however, it is desirable that the adhesive is a thermosetting resin selected from the group consisting `
of phenol resins, epoxy resins and furan resins.
Although the thickness of the layer of the above-mentioned adhesive is not particularly limited, it is 131~927 desirable to apply the adhesive thereupon uniformly in the thickness of usually not more than 0.5 mm.
In addition, the joining by the above-mentioned adhesive can be carried out at a temperature or from 100 to 180~C under a press-pressure of from 1 to 50 kgf/cm2G.
for a press time of from 1 to 120 min.
After joining the electrode substrate material and the flexible carbon sheet while using the above-mentioned adhesive under the above-mentioned joining conditions, the grooves forming the flow channels for reactant gases are made by cut-processing in the desired dimensions on the surace to which the carbon sheet has been adhered. The cut-processing can be carried out in the optional means, ~
for instance, carried out by using a diamond blade.
After applying the adhesive on the suraces of the 1exible carbon sheets remaining on a pair of the electrode substrate materials to which the cut-processing have been finished, and joining the adhesive surfaces to the both surfaces of the separator so that the flow channels or reactant gases in one of the electrode substrate materials are perpendicular to those in the another elec-trode substrate material, as in the above-mentioned case of joining the electrode substrate materials and the , flexible carbon sheet, the thus joined materials are calcined at a temperature of not lower than 800C under a reduced pressure and/or in an inert atmosphere to produce a composite body comprising the electrode substrates and the separator.
Further, after joining the electrode substrate material and the flexible carbon sheet, the calcination thereof may be carried out under the same condition before subjecting the joined material to the cut-processing, namely the calcination is carried out two times, thereby ensuring the carbonization of the materials.
After joining the electrode substrate material and the separator material and calcining the thus joined materials in the case where the electrode substrate and the separator are of the same dimension (namely, the extended part of the separator beyond the electrode substrate is not provided thereupon), parts of the electrode substrate and the flexible carbon sheet facing to the extended part of the separator to be joined later are removed by cutting, thereby exposing the joining surface (the ex-tended part beyond the electrode substrate) of the separator to be joined to the peripheral sealer and the gas-distri-butor. Then, the thus exposed or previously provided extended part of the separator is used for the junction.
Namely, after interposing a sheet of fluorocarbon resi.n or applying a dispersion of fluorocarbon resin (1) between (i) the extended part (which is the joining surface to the peripheral sealer and extends beyond the periphery of the electrode substrate parallel to the flow channels for reactant gases) and (ii) the surface of the peripheral sealer to be joined thereto, or (2) between (i) the extended part (which is the joining surface to the peri-pheral sealer and extends beyond the periphery of the electrode substrate parallel to the flow channels for reactant gases) and (ii) the surface of the peripheral sealer to be joined thereto and between (i) the extanded part of the separator (which is the joining surface to the gas-distributor and extends beyond the periphery of the electrode substrate parpendicular to the flow channels for reactant gases) and (ii) the surface of the gas-distributor to be joined thereto, the thus treated materials are press-joined by melt-adhesion at:a temperature of not lower than the temperature of lower than the melting point of the fluorocarbon resin by 50C under a pressure of not less than 1 kgf/cm2G.
The grooves of the gas-distributor may be preli-1 31 ~927 minarily made by cut-processing in the desired dimenslons by an optional method as in the case of making the grooves on the above-mentioned porous and carbonaceous electrode substrateO
Further, the fluorocarbon resin may be prelimi-narily applied by melt-adhesion to the peripheral sealer or -the peripheral sealer and the gas-distributor.
In order to obtain the construction of the compo-site substrate wherein the flexible carbon sheet has been interposed only between the top surfaces of the ribs of the electrode substrate and the separator aacording to the present invention, various different methods can be~utilized.
For instance, after forming the groove by cut-processing the electrode substrate material, the flexible carbon sheet is joined only to the top surface of the thus formed rib, etc. However, it is the most practical method that after adhering the flexible carbon sheet to the not-yet cut-processed electrode substrate material, the cut-processing is carried out.
Since in the CQmpoSite substrate provided with the peripheral sealer or the peripheral sealer and the gas-distributor (external manifold type) for a fuel cell according to the present invention, which is obtained as .
1 31 ~q27 above, the periphera] sealer has been joined to the compo-site substrate and formed in one body, the thus composite substrate is excellent in preventing gas-leakage, and it is not necessary, of course, to provide any peripheral sealer for preventing the leakage of reactant gases on the side of the fuel cell. Moreover, the composlte substrate according to the present invention exhibits the following effect.
Namely, since the electrode substrate and the separator have been joined by the flexible carbon sheet into one body and the peripheral sealer or the peripheral sealer and the gas-distributor and the separator have been joined by the fluorocarbon resin into one body, respectively, the composite substrate according to the present invention is excellent ln resistance to phosphoric acid and is particularly useful as the composite electrode substrate for a fuel cell of phosphoric acid type.
Moreover, in the composite substrate provided with the peripheral sealer according to the present invention, since the peripheral sealers have been disposed and joined evenly on the both sides of the separator while holding the separator alternately in both sides, such a structure has a reinforcing e~fect and is excellent in handling property at the time of producing the~fuel cell.
Furthermore, in the composite substrate provided with the peripheral sealer and the gas-distributor according ~t~7 to the present invention, the peripheral sealer and the gas-distributor both of which have been made of the same material are opposite to each other across the separator and accordingly, the thermal expansion coefficient of the upper layer coincides with that of the lower layer. As a result, the thermal stress between the separator and the peripheral sealer becomes equal to that between the separator and the gas-distributor, thus resulting in the reduction of the warps and the distortion at the time of producing the composite substrate in addition to the effect obtained by interposing the flexible carbon sheet between the joining surface of the electrode substrate and the separator. -Still more, since in the peripheral region of the thin plate-like composite substrate,the peripheral sealer and the gas-distributor have been disposed and joined in face to face on the both sides of the separator while holding the separator, such a structure has a reinforcing effect and is excellent in the handling property at the time o~ producing the fuel cell.
Moreover, in the composite substrate according to the present invention, wherein the flexible carbon sheet is interposed only between the top surfaces of the ribs of the electrode substrate and the joining surface of the separator, the thickness of the flexible carbon sheet can be utilized as the effective height in the ribs of 13~927 the electrode substrate. Namely, in comparison to the composite substrate wherein the flexible carbon sheet~has been disposed on the whole area of the separator facing to the composite substrate, the thickness per one piece of the electrode substrate of from 3.8 to 4 mm may be reduced by from 0.3 to 0.5 mm, that is, from 7 to 13~
without any reduction of the cross section area of the flow channel or reactant gases therein.
The present invention will be explained more in detail while referring to the following non-limitative examples.
EXAMPLE 1:
(1) Electrode substrate material:
Two pieces of the porous and carbonaceous flat plate material preliminarily calcined at a temperature of not lower than 800C ~made by KUREHA KAGAKU KOGYO Co., Ltd., under the trade name of KES-400, 650 mm in length, 690 mm in width and 1.47 mm in thickness) were used as the elec-trode substrate material.
(2) The separator material:
A piece of the compact carbon plate (made by SHOWA DENKO Co., Ltd., under the trade name of SG-2, 0.6 mm in thickness) was cut into 690 mm both in length and width to prepare the separator material.
(3) Peripheral sealers:
A piece of the compact carbon plate (made by~
TOKAI Carbon Co., Ltd., 1.~5 g/cc in bulk density and 1.5 mm in thickness) was cut into 4 pieces (each 690 mm in length and 20 mm in width) to prepare the peripheral sealers.
(4) Fluorocarbon resin:
A piece of TEFLO ~ sheet (made by NICHIAS Co., Ltd., 0.05 mm in ~hickness) was cut into 4 pieces according to the dimensions of the peripheral sealer and the pieces were used for the purpose.
The present invention relates to a composite~
substrate for a fuel cell of phosphoric acid type and a process for producing the same. More in detail, the present invention relates to a composite substrate provided with two electrode substrates, a separator and (1) peripheral sealers or (2) both the peripheral sealers and gas-distri-butors (external manifold type), and a process for producing the same. In addition, "electrode substratei' in the pre-sent invention means all electrode substrates each of which becomes an electrode for a fuel cell by only applying a catalyst to the electrode substrate or only stacking on the electrode substrate a porous electrode carrying a catalyst which has been separately prepared.
In recent years, as an apparatus for generating clean energy or a freely switchable generator which can contribute to saving natural resources by a normalization of the operation of thermal power generation or water-power generation or an improvement of energy efficiency, a fuel cell and development and utilization of a system surrounding the fuel cell have been highly demanded.
Hitherto, as the fuel cell, a fuel cell of bipolar separator type in whLch a bipolar separator obtained by ribbing a gas-impermeable graphitio thin plate and a porous and carbonaceous plate are used in combination have been publicly known, however, contrary to the above-~r 1 31 ~27 mentioned, a fuel cell of monopolar type formed by stackingan electrode substrate which has been provided with ri~bs on one surface thereof and have a flat structure on the another surface thereof, a catalyst layer, a matrix impregnated wi~h an electrolyte and a separator sheet has been developed. In the fuel cell of monopolar type, a reactant gas (oxygen or hydrogen) diffuses from flow channels for reactant gases formed by the ribs provided on the electrode substrate to a flat surface of the elec-trode.
Although such an electrode substrate is usually made of a caxbonaceous material from the viewpoint of physical properties such as heat-resistance~ corrosion-resistance, electro-conductivity, mechanical strength, etc. and the ease of retaining poxosity therein and the electrode substrate is used by stacking them as has been stated above, it is difficult to make top surfaces of the ribs perfectly flat and therefore, the electric- and thermaI contact resistance between the ribs and the separator is too large to be disregarded.
Generally, it is said that the above-mentioned contact resistance is larger than the transmission resistance within the substrate by several times, and such contact resistance causes conclusive defects such as uneveness of distribution of the temperature between the cells and reduction of an efficiency of electric generation. ;
1 3 1 ~
In order to solve the above-mentioned problem of contact resistance, a composite substrate has been~
proposed wherein the electrode substrate, the separator, etc. of the stacked structure of the above-mentioned fuel cell have been adhered together by an adhesive and integrated into one body of carhon by calcination thereof.
Although in such a composite substrate, the contact resistance present on the contact surface can be made zero by joining them into one body, since the composite substrate is produced by adhering the carbonaceous materials together and carbonizing and calcining the thus adhered materials as has been stated, there are cases of exfoliation of the adhered surfaces during the calcining step due to a difference of rates of thermal expansion and shrinkage between the carbonaceous materials and the adhe,sive, and cases of causing warps, distortions or cracks in the product. In such cases, the reduction of the producti~e yield is caused, and accordingly, improvements of the product and process have been desired.
As a result of the present inventors' studies from the conception that the exfollation of the cOmpOSLte substrate for a fuel cell in the calcining step (to a maximum temperature of 3000C) is considered to be due to the difference of the thermal expansion between the porous and carbonaceous layer and the gas-impermeable layer (separator) in the temperature-raising step or to the .
131~q27 difference of shrinkage between the above-mentioned two layers in the cooling step to room temperature after `
completing calcination and that the difference of thermal expansion and shrinkage between the above-mentioned two layers may be reduced or removed by a buffer layer pro-vided between the two layers, it has been found by the present inventors that the above-mentioned problem of inter-layer exfoliation can be solved by inserting a -flexible carbon sheet which has a relatively large rate of thermal expansion and shrinkage, an adhesiveness to the adhesive, etc. and a relatively low gas-permeability, as a material for the buffer layer, between the above-mentioned porous and carbonaceous layer and the separator and joining the above-mentioned two layers via a carboni-zable adhesive (for instance, refer to U.S. Patent No.
4,579,789).
However, in general, the substate as the electrode in ~the fuel cell of phosphoric acid type is stacked 50 that one surface thereof contacts to the phosphoric acid matrix and the another surfaces thereof faces to the separator. Still more, in the case of stacking the elec-trode substrate for obtaining a fuel cell, a sealer .material is provided on the peripheral part thereof to prevent diffusion of the reactant gas from the side of the electrode substrate to outside thereof.
1 3 1 4'~27 Accordingly, particularly in the case where the composite substrate is formed of the porous and carbo~a-ceous electxode substrate up to the edge part thereof and the flow channels of reactant gases open directly at the edge part in the composite substrate of the external manifold type, the peripheral sealer which is compact and carbonaceous and the electrode substrate which is porous and carbonaceous are disposed opposite each other across the separator on the peripheral region of the separator, and there has been a problem of causing a certain degree of a warp or a strain in the joining part of the materials due to the difference of the thermal shrinkage between the mat~rials even by the intervention of the flexible carbon sheet. As the means for preventing the above-mentioned warp, the materials with an extrèmely small difference of the thermal shrinkage should be selected, and such a restriction has been the obstruction in the production of the composite substrate.
Furthermore, as a problem poin~ of the conventional fuel cell, the adhesion between the composite materials in the fuel cell has been carried out by using a carbon cement.
However~ since the carbon cement is eroded by phosphoric acid, ~here has been a possibility that exfolia-tion between the composite materials is caused and the reactant gas leaks through the joined parts.
~ 3 ~ ~927 In addition, there has been another problem in the point of mechanical strength of the electrode ~
substrate resulting in breaking on handling in the case where the area of the substrate is too large, because the electrode substrate is a thin plate.
Further, a method of joining porous electro-conductive materials wherein the gas-impermeability between the porous electroconductive materials has been increased, has been proposed recently. According to the proposed method, the porous electroconductive material is impregnated with a fluorinated ethylenepropylene copolymer, a polysulfone resin, etc., and the thus impregnated layer is joined as an interface to another electroconductive material by hot-pressing while maintaining electroconduc-tivity through the gas-impervious region (for instance, refer to U.S. Patent No. 4,505,992).
However, in the case of using the above-mentioned methods for sealing periphery of a composite substrate for a fuel cell, although the passage of~the gas between the ~wo carbonaceous materials is prevented by the thus resin-impregnated carbon layer, since the usable electro-conductive material is limited to the porous carbonaceous material and such a porous carbonaceous material is weak in mechanical strength, the usage of the thus~obtained composite material is limited.
.
1 31 ~9~7 On the other hand, even in the case where an electrode in a composite electrode substrate is produced by the above-mentioned method, the thus obtained resin-impregnated electrode is unsatisfactory in quali.ty for using it in the composite electrode substrate for a fuel cell, because the used thermoplastic resin is substantially large in resistance to thermal and electric conductivities.
As a result of the present inventors' studies for finding a process for producing a composite substrate for a fuel cell, which does not have the above-mentioned defects and is excellent in mechanical strength/ electrical properties and chemical resistance, it has been found out by the present inventors that the composite substrate having the above-mentioned excellent properties can be obtained in a high yield by joining a porous and carbona-ceous electrode substrate provided~with~flow channels for reactant gases and a gas-impermeable separator comprlsing~
a compact carbonaceous~material via a flexible carbon~sheet and further joining (1) a peripheral sealer comprising a gas-impermeable and compact carbon material or (2) both the peripheral sealer and a gas-distributor comprising~
a compact carbon material to the above-mentioned separator via a fluorocarbon resin layer, and on the basis of the ~:
above-mentioned flndings, the present inventors have attained the present invention.
t 3 1 4927 Namely, the first object of the present invention is to provide a composite substrate provided with peripheral sealers for a fuel cell, wherein the peripheral sealexs have been joined to a separator and the these materials have been integrated.
The second object of the present invention is to provide a composite substrate provided with peripheral sealers and gas-distributors (of the external manifold type) for a fuel cell, wherein porous and carbonaceous electrode substrates, peripheral sealers and gas-distributors have been joined to a separator and the above-mentioned materials have been integrated.
The third object of the pre:ent invention is to provide a composite substrate for a fuel cell, which has a structure that can prevent the generation of warps, distortions or cracks at the time ~f producing the composite substrate.
The fourth object of the present invention is to provide a composite substrate ~or a fuel cell o~ a phosphoric acid-type. ~
The fifth object of the present invention is to provide a composite substrate for a fuel cell, which is excellent in mechanical strength and handling properties at the time of producing the composite substrate.
The other objects and the merits of the present invention will be apparent to persons skilled in the art .... ~.; ~
1~i14927 from the following detailed description of the present invention.
SUMMARY OF THE INVENTION-In a first aspect of the present invention, there is provided a composite substrate for a fuel cell comprising (l) a separator, (2) two porous and carbonaceous electrode sub-strates which are provided with a plurality of grooves on one of surfaces thereof and have another flat surface, each of the electrode substrates being joined to the both surfaces of the separator via a flexible carbon sheet so that the grooves form flow channels for reactant gases and the flow channels in one of the elec-trode substrates are perpendicular to those in the~another -electrode substrate, the flexible carbon sheet being :
interposed only between the joining surfaces of..the separator and tops of ribs forming the grooves of the electrode substrate, and the sepa.rator having an extended part beyond a periphery of the eIectrode substrate,~and (3a) a:pair of peripheral sealers on the side of:
the electrode substrate parallel to the flow channels for reactant gases therein, which comprise a gas-impermeable and compact carbon material, or:
1 3 1 ~9~7 t3b) a pair of peripheral sealers on the side of the electrode substrate parallel to the flow channels for reactant gases therein, which comprise a gas-impermeable and compact carbon material and a pair of gas-distributor on the side of the electrode substrate perpendicular to the flow channels for reactant gases therein, which comprise a gas-impermeable and compact carbon material and are provided with a passage for distributing reactant gases, (3a) the peripheral sealers or (3b) the peri-pheral sealers and the gas-distributors being joined to the extended part of the separator beyond the electrode substrate, via a fluorocarbon resin layer.
In a second aspect of the present invention, there is provided a process for producing a composite substrate :
for a fuel cell, comprising steps of (1) adhering a flexible carbon sheet onto one surface of each of two electrode substrate materials of a fl~at plate-form without grooves and of the prescribed dimension by an adhesive, ~ :
(2) providing grooves of a desired dimension for forming flow channels of reactant gases on the joining:surface side of each of the electrode substrate materials by cut-processing, ~31~27 (3) joining a separator material to the surface of the fle~ible carbon sheet remaining on the thus cut-processed surface of each of the electrode substrate materials in face to face, (4) calcining the thus composed materials at a temperature of not lower than about 800C under a reduced pressure and/or in an inert atmosphere thereby producing a composite body comprising the electrode substrates and the separator, and (5a) joining a pair of peripheral sealers comprising a gas-impermeable and compact carbon material to an extended part of the separator, which extends be~ond a periphery of the electrode substrate parallel to the flow channels for reactant gases therein, via a sheet or a dispersion of fluorocarbon resin, or (5b) joining a pair of peripheral~sealers comprlsing a gas-impermeable and compact carbon material to an extended part of the separator, which extends beyond a periphery of the electrode substrate parallel to the flow channels for reactant gases therein, via a sheet or a dispersion of fluorocarbon resin and further joining a pair of gas-distributors comprising a gas-impermeable and compact carbon material and having grooves forming a passage for distributing reactant gases to an e~tended part o~ the separator, which extends beyond a periphery of the electrode substrate perpendicular to the flow channels 131~7 for reactant gases therein, via a sheet or a dispersion of fluorocarbon resin.
BRIEF EXPLANATION OF DRAWINGS:
of the attached drawings, Fig. 1 is an oblique view of the composite substrate provlded with the peripheral sealers according to the present invention and Figs. 2 and 3 are respectively the oblique views of the composite substrate provided with the peripheral sealers and the gas-distributors according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION:
The present invention rela-tes to a composite substrate for a fuel cell comprising (l) a separator, (2) two porous and carbonaceous electrode substrates which are provided with a plurality of grooves on one of surfaces thereof and have another flat surface, each of the electrode substrates being joined to the both surfaces of the separator via a flexible carbon sheet so that the grooves form flow channels for reactant gases and the flow channels in one of the electrode substrates are perpendicular to those in the another electrode substrate, the flexible carbon sheet being interposed only between the joining surfaces of the separator and tops of ribs forming the grooves of the 1 31 ~927 electrode substrate, and the separator having an extended part beyond a periphery oE the electrode substrate, and (3a) a pair of peripheral sealers on the side of the electrode substrate parallel to the flow channels for reactant gases therein, which comprise a gas-impermeable and compact carbon material, or (3b) a pair of peripheral sealers on the side of the el~ctrode substrate parallel to the flow channels for reactant gases therein, which comprise a gas-impermeable and compact carbon material and a palr of gas-distributor on the side of the electrode substrate perpendicular to the flow channels for reactant gases therein, which comprise a gas-impermeable and compact carbon material and are provided with a passage for ~:
reactant gases, (3a) the peripheral sealecs or (3b) the peripheral sealers and the gas-distributors being joined to the extended part of the separator beyond the electrode substrate, via a fluorocarbon resill layer. : :
: Still more, the present invention relates to a process for producing:a composite substrats for a fuel cell, comprising steps of ~l) adhering a flexible carbon sheet onto one surface of each of two electrode substrate materials of a~flat .
1 31 ~q27 plate-form without grooves and of the prescribed dimension by an adhesive, (2) providing grooves of a desired dimension for forming flow channels of reactant gases on the joining surface side of each of the electrode substrate materials by cut-processing, ~3) joining a separator material to the surface of the flexible carbon sheet remaining on the thus cut-processed surface of each of the electrode substrate materials in ace to face, (4) calcining the thus composed materials at a temperature of not lower than about 800C under a reduced pressure and/or in an inert atmosphere thereby producing a composite body comprising the electrode substrates and the separator, and ~
(5a) joining a pair of peripheral sealers comprising a gas-impermeable and compact carbon~material to an extended part of the separator, whlch extends beyond a:periphery of the electrode substrate parallel:to the flow c~annels for reactant gases therein, via a sheet or~a dispersion of fluorocarbon resin, or (5b) joining a pair of peripheral sealers comprising a gas-impermeable and compact carbon material to:an extended part of the separator, which extends beyond a periphery of the electrode substrate parallel to the flow channels for reactant gases therein, via a sheet or a dispersion of 1 3 1 ~927 fluorocarbon resin and ~urther joining a pair of gas-distributors comprising a gas-impermeable and compact~
carbon material and having grooves forming a passage for distributing reactant gases to an extended part of the separator, which extends beyond a periphery of the elec-trode substrate perpendicular to the flow channels for reactant gases therein, via a sheet or a dispersion of fluorocarbon resin.
Of the attached drawings, Fig. 1 is an oblique view of a composite substrate provided with the peripheral sealers according to the present invention. The composite substrate of Fig. 1 has a construction comprising a separator 1, two electrode substrates 2 which have grooves forming flow channels 6 for reactant gases together with the separator and are disposed on the both sides of the separator and peripheral sealers 3 which are disposed on the edge (namely, side) of the electrode substrate 2 in the parallel direction to the flow channels 6 for reactant gases of the electrode substrate.
The surface area of the separator 1 is larger than that of the electrode substrate 2, and the separator 1 has been extended beyond a periphery of the electrode substrate which is parallel to the flow channels 6 for reactant gases in each of the electrode subs~rates (the outer edge of the extended part coincides with the outer edge of the another electrode substrate). The peripheral t; 3 1 ~.q27 sealer 3 has been joined to the above-men-tioned extended part. Only between the joining surfaces of the separàtor 1 and tops of ribs forming the grooves of the electrode substrate 2, a flexible carbon sheet 4 has been interposed, and accordingly, the flow channels 6 for reactant gases have been prescribed by the grooves of the electrode substrate, the separator and the flexible carbon sheet.
The peripheral part of the separator, which has been extended beyond the electrode substrate and the peripheral sealer 3 have been joined via a fluorocarbon resin S.
Fig. 2 is an oblique view of a composite substrate provided with peripheral sealers and gas-distributors according to the present invention. Fig. 3 has been given to show a construction of the composite substrate according to the present invention and shows the same view as Fig. 2 except for inexistence of both (1) one of the gas-distri-butors 7 having grooves forming passage 8 for distrlbuting reactant gases, which will be explained later, and (2) the fluorocarbon resin 5 on the part to which the gas-distributor is ~oined.
In Figs. 2 and 3, the composite substrate according to the present invention has a construction comprising (1) the separator 1, (2) the two electrode substrates 2 which have the grooves ~orming the flow channels 6 for reactant gases together with the separator and are provided on the both sides of the separator so .
.
131~27 that the flow channels 6 in one of the electrode substrates are perpendicular to those in the another electrode substrates, (3) the peripheral sealers 3 which have been disposed on the edge (namely/ side) of the electrode substrate and (4) the gas-distributors 7.
The surface area of the separator 1 is larger than that of the electrode substrate 2 and as is seen in Figs.
2 and 3, the separator has been extended beyond a periphery of the electrode substrate, and the peripheral sealer 3 and the gas-distributor 7 have been joined to the above-mentioned extended part (the outer edge of the extended part of the separator coincides with the outer edge of the peripheral sealer and the gas-distributor after joining).
The gas-distributor 7, which is joined to the extended part of the above-mentioned separator beyond the periphery of the electrode substrate perpendicular to the 10w channel 6 for reactant gases therein, has grooves forming a flow passage 8 for distributing reactant gases together with the separa~or, and the peripheral sealer 3, which is joined to the extended part of the separator beyond the periphery of the electrode substrate parallel to the flow channel 6 therein, does not have the above~
mentioned grooves. Although the grooves in the gas-distributor 7 form the flow passage 8 for distributing reactant gases for the supply of the reactant gases from outside, it is not particularly necessary that the shape .
13~4~27 of the cross-section thereof coincides with that of the flow channel 6 for reactant gases, and further, it is~not necessary that all of the openings of the flow channels 6 open to the flow passage 8 for distributing reactant gases. Namely, the cross-sectional shape of the grooves of the gas-~istributor 7 may be selected so as to be sufficient for maintaining the flow volume of the gases necessary for operating the fuel cell provided with the composite substrate.
Between the separator 1 and the electrode substrate 2, a flexible carbon sheet 4 has been interposed. Still more, in E'igs. 2 and 3, the flexible carbon sheet 4 has been interposed only between the joining surfaces of the separator 1 and tops of the ribs of the electrode substrate 2, and accordingly, the flow channel 6 for reactant gases have been prescribed by the grooves of the electrode substrate, the separator and the flexible carbon sheet, and the flow passage 8 for distributing reactant gases has a shape prescribed by the grooves of the gas-distributor 7 r the separator 1 and the fluorocarbon resin 5.
In the production of the composite substrate of Figs. 2 and 3, the flexible carbon sheet 4 may be joined to the whole area of the separator facing to the electrode substrate (except for the surface area on which the peripheral sealer and the gas-distributor are joined vla a fluorocarbon resin layer) so that the size of the flexible 1; 3 1 ~7 carbon sheet is the same as that of the electrode substrate (such a situation has not been illustrated hereinJ. However, from the viewpoint of the thickness of the composite substrate, since the former structure can make the thickness of the composite substrate thinner than that of the latter structure by the thickness of the flexible carbon sheet while retaining the same cross-sectional area of the flow channels for reactant gases, the former structure is preferable.
In Figs. 2 and 3, the peripheral part (extended part) of the separator beyond the electrode substratej the peripheral sealer 3 and the gas-distributor 7 have been respectively joined via the fluorocarbon resin 5. Although the fluorocarbon resin may be interposed between the joining surface of the peripheral sealer and:the gas-distributor both of which are joined to the same side of the separator, it is not particularly necessary, because the gas-leakage does not become any problem:in the case where the product is used in combination with the external mani~old which is made so as to cover the above-mentioned joining part.
Still more in the composite substrate of Figs. 1 to 3, the separator 1, the:flexible carbon sheet 4 and the electrode substrate 2 have been made into one body by 1 3 1 ~927 carbonization and calcina-tion.
The electrode substrate used according to thè
present invention is a porous and carbonaceous material and preferably having the following specific properties, and also an electrode substrate material (namely, a material for the porous and carbonaceous electrode substrate) used in the present invention has preferably the same following specific properties after calcining the material at a temperature of not lower than 800C under a reduced pressure and/or in an inert atmosphere. That is, Mean bulk density of from 0.3 to 0.9 gjcc, Gas-permeability of not less than 200 ml/cm2.hour-mmAq and Electric resistivity of not more than 200 mQ-cm.
The separator used according to the present invention pre~erably has the following specific properties:
Mean bulk density of not less than 1.4 gjcc, Gas-permeability of not more than ~10 6~ml/cm2 houI 'IrlInAq, ` ~
Electric resistivity o~ not more than 10 mQ~cm and Thickness of not more than 2 mm.
The material of the peripheral sealer and the~
gas-distributor used in the composite substrate according to the present inventlon is preferably a compact carbon material of the following properties:
1 31 ~27 Mean bulk density of not less than 1.40 g/cc, Gas-permeability of not more than 10 4 ml/cm2~.
hour-mn~q and Difference of the thermal expansion coefficient thereof from that of the separator material is not more than 2 x 10 6/oC.
Particularly, the above-mentioned material is preferably a material subjected to calcination at a temperature of not lower than 800C under a reduced pres-sure and/or in an inert atmosphere.
As has been already described, in the composite substrate for a fuel cell accord:ng to the present invention, all of the peripheral sealers, all of the gas-distributors and the separator have been joined respectively ~ia a fluorocarbon re~in. Although an amount of gas leakage through the per~ipheral sealers including the joined parts~is controlled mainly by diffusion and is not so much influenced by the pressure~
.
the amount of gas leakage is preferably not more than 10 2 ml/cm-hour.mmAq in the case where the amount of gas leakage per unit time per unit length of the pariphery of the joining part under a differential pressure~of 500 mmAq. is represented by the relationship of [the amount of gas leakage/(side~length of periphery~-tdifferential pressure)].
~ 3 1 ~ 7 The ~luorocarbon resin used according to the present invention is a fluorocarbon resin of a melting point of not lower than 200C and is not particularly limited, however, for instance, a tetrafluoroethylene resin (an abbreviation of PTFE, a melting point of 327C, a thermal deformin~ temperature of 121C under 4.6 kgf/cm2G.), a copolymer resin of tetrafluoroethylene and hexafluoropropylene (an abbreviation of FEP, a melting point of from 250 to 280C, a thermal deforming temperature of 72C under 4.6 kgf/cm G.), a fluoroalkoxyethylene resin (an abbreviation of PFA, a melting point of from 300 to 310C, a thermal deformation temperature of 75C under 4.6 kgf/cm2G.) and a fluorinated copolymer resin of ethylene and propylene (an abbreviation of TFP, a melting point of from 290 to 300C) may be exemplified. The above-mentioned fluorocarbon resins are c:ommercialized.
Of the above-mentioned fluorocarbon resins, tetrafluoroethylene resin is preferably used particularly in the present invention and is commercialized under the trade name of TEFLO ~.
In the present invention, the above-mentioned fluorocarbon resin is used as, for instance, a sheet of about 50 ~m in thickness or a dispersion containing about 60% by weight of the resin. Into the dispersion, a small amount of a surfactant may be added.
As the electrode substrate material (namely, the 1~14~27 material for the porous and carbonaceous electrode substrate) used according to the present invention, the following materials may be mentioned:
(1) A material made by molding a mixture of short carbon fibers, a binder and an organic granular substance by heating under a pressure (for instance, refer to Canadian Patent No. 1,205,857). Particularly, the material obtained by molding a mixture of from 20 to 60~ by weight of short carbon fibers of not more than~2 mm in length, from 20 to 50% by weight of a phenol resin and from 20 to 50% by weight of an organic granular substance (a pore regulator) at a molding temperature of from 100 to 180C, under a molding pressure of from 2 to~
100 kgf/cm G. for from l to 60 min~ and (2) A material obtained by calcining the material shown in the above (1) at a temperature of not lower than 800C under a reduced pressure and/or in an inert atmosphere.
As a separator material (namely, the material for the separator) used according to the present invention, a compact carbon plate which shows a rate of calcining~
shrinkage of nct more than 0.2 % in the case where the material is calcined at 2000C under a reduced pressure and/or in an inert atmosphere is desirable. The separator material is usually in a flat plate form, and the area of one of the surfaces thereof is usually larger than that of the flat part of the electrode substrate material.
1314'~27 However, as will be described later, in the step of joining the separator material and the electrode substrate material, the surface area of the former may be the same as that of the latter.
As the flexible carbon sheet used for joining the electrode substrate material and the separator material in the composite substrate according to the present invention, a flexible graphite sheet of not more than 1 mm in thickness which has been 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 acid-treated particles, shows a bulk density of 1.0 to 1.5 g/cc and a rate of compression strain (namely, the rate of strain to the compression load of 1 kgf/cm2G.) of not more than 0.35 x 10 2 cm2/kgf and has a flexLbility that the sheet is not broken in the case of bending the sheet to 20 mm in the radius of curvature is preferable, and~of the commercialized flexible graphite sheets, GRAFOIL~made by U~C.C. is a suitable example.
The:flexible carbon sheet used also according to the present invention is produced by mlxing carbon fibers of not less than 1 mm in mean length whlch fibers have been thermally treated at a temperature of preferably not lower than l,000C, more preferably not lower than 1,500C under a reduced pressure and/or in an inert ~3~4~27 atmosphere, with a binder of not less than 10~ in the carbonizing yield, for instance, pouring the above binder into the matrix of the above carbon fibers, molding the thus composite materials by heating under a ~ressure and calcining and carbonizing the thus molded material at a temperature of not lower than 850C under a reduced pressure and/or in an inert atmosphere. The thus produced flexible carbon sheet has a thickness of no-t more than 1 mm, a bulk density of 0.2 to 1.3 g/cc and a rate of compression strain of not more than 2.0 x 10 1 cm~/kgf, wherein the carbon lumps derived from the above-mentioned binder have been dispersed in the matrix of the carbon fibers and restrain a plurality of the carbon fibers and by the carbon lumps the carbon fibers are slidably held to one another. The just-mentioned flexible carbon sheet has a flexibility of not being broken in the case of bending the sheet to 10 mm in the radius o~ curvature.
As the adhesive used on each of the joining surfaces in the case of joining the above~mentioned electrode substrate material to the separator material via the flexible carbon sheet, any adhesive usually used in joining carbon materials may be used, however, it is desirable that the adhesive is a thermosetting resin selected from the group consisting `
of phenol resins, epoxy resins and furan resins.
Although the thickness of the layer of the above-mentioned adhesive is not particularly limited, it is 131~927 desirable to apply the adhesive thereupon uniformly in the thickness of usually not more than 0.5 mm.
In addition, the joining by the above-mentioned adhesive can be carried out at a temperature or from 100 to 180~C under a press-pressure of from 1 to 50 kgf/cm2G.
for a press time of from 1 to 120 min.
After joining the electrode substrate material and the flexible carbon sheet while using the above-mentioned adhesive under the above-mentioned joining conditions, the grooves forming the flow channels for reactant gases are made by cut-processing in the desired dimensions on the surace to which the carbon sheet has been adhered. The cut-processing can be carried out in the optional means, ~
for instance, carried out by using a diamond blade.
After applying the adhesive on the suraces of the 1exible carbon sheets remaining on a pair of the electrode substrate materials to which the cut-processing have been finished, and joining the adhesive surfaces to the both surfaces of the separator so that the flow channels or reactant gases in one of the electrode substrate materials are perpendicular to those in the another elec-trode substrate material, as in the above-mentioned case of joining the electrode substrate materials and the , flexible carbon sheet, the thus joined materials are calcined at a temperature of not lower than 800C under a reduced pressure and/or in an inert atmosphere to produce a composite body comprising the electrode substrates and the separator.
Further, after joining the electrode substrate material and the flexible carbon sheet, the calcination thereof may be carried out under the same condition before subjecting the joined material to the cut-processing, namely the calcination is carried out two times, thereby ensuring the carbonization of the materials.
After joining the electrode substrate material and the separator material and calcining the thus joined materials in the case where the electrode substrate and the separator are of the same dimension (namely, the extended part of the separator beyond the electrode substrate is not provided thereupon), parts of the electrode substrate and the flexible carbon sheet facing to the extended part of the separator to be joined later are removed by cutting, thereby exposing the joining surface (the ex-tended part beyond the electrode substrate) of the separator to be joined to the peripheral sealer and the gas-distri-butor. Then, the thus exposed or previously provided extended part of the separator is used for the junction.
Namely, after interposing a sheet of fluorocarbon resi.n or applying a dispersion of fluorocarbon resin (1) between (i) the extended part (which is the joining surface to the peripheral sealer and extends beyond the periphery of the electrode substrate parallel to the flow channels for reactant gases) and (ii) the surface of the peripheral sealer to be joined thereto, or (2) between (i) the extended part (which is the joining surface to the peri-pheral sealer and extends beyond the periphery of the electrode substrate parallel to the flow channels for reactant gases) and (ii) the surface of the peripheral sealer to be joined thereto and between (i) the extanded part of the separator (which is the joining surface to the gas-distributor and extends beyond the periphery of the electrode substrate parpendicular to the flow channels for reactant gases) and (ii) the surface of the gas-distributor to be joined thereto, the thus treated materials are press-joined by melt-adhesion at:a temperature of not lower than the temperature of lower than the melting point of the fluorocarbon resin by 50C under a pressure of not less than 1 kgf/cm2G.
The grooves of the gas-distributor may be preli-1 31 ~927 minarily made by cut-processing in the desired dimenslons by an optional method as in the case of making the grooves on the above-mentioned porous and carbonaceous electrode substrateO
Further, the fluorocarbon resin may be prelimi-narily applied by melt-adhesion to the peripheral sealer or -the peripheral sealer and the gas-distributor.
In order to obtain the construction of the compo-site substrate wherein the flexible carbon sheet has been interposed only between the top surfaces of the ribs of the electrode substrate and the separator aacording to the present invention, various different methods can be~utilized.
For instance, after forming the groove by cut-processing the electrode substrate material, the flexible carbon sheet is joined only to the top surface of the thus formed rib, etc. However, it is the most practical method that after adhering the flexible carbon sheet to the not-yet cut-processed electrode substrate material, the cut-processing is carried out.
Since in the CQmpoSite substrate provided with the peripheral sealer or the peripheral sealer and the gas-distributor (external manifold type) for a fuel cell according to the present invention, which is obtained as .
1 31 ~q27 above, the periphera] sealer has been joined to the compo-site substrate and formed in one body, the thus composite substrate is excellent in preventing gas-leakage, and it is not necessary, of course, to provide any peripheral sealer for preventing the leakage of reactant gases on the side of the fuel cell. Moreover, the composlte substrate according to the present invention exhibits the following effect.
Namely, since the electrode substrate and the separator have been joined by the flexible carbon sheet into one body and the peripheral sealer or the peripheral sealer and the gas-distributor and the separator have been joined by the fluorocarbon resin into one body, respectively, the composite substrate according to the present invention is excellent ln resistance to phosphoric acid and is particularly useful as the composite electrode substrate for a fuel cell of phosphoric acid type.
Moreover, in the composite substrate provided with the peripheral sealer according to the present invention, since the peripheral sealers have been disposed and joined evenly on the both sides of the separator while holding the separator alternately in both sides, such a structure has a reinforcing e~fect and is excellent in handling property at the time of producing the~fuel cell.
Furthermore, in the composite substrate provided with the peripheral sealer and the gas-distributor according ~t~7 to the present invention, the peripheral sealer and the gas-distributor both of which have been made of the same material are opposite to each other across the separator and accordingly, the thermal expansion coefficient of the upper layer coincides with that of the lower layer. As a result, the thermal stress between the separator and the peripheral sealer becomes equal to that between the separator and the gas-distributor, thus resulting in the reduction of the warps and the distortion at the time of producing the composite substrate in addition to the effect obtained by interposing the flexible carbon sheet between the joining surface of the electrode substrate and the separator. -Still more, since in the peripheral region of the thin plate-like composite substrate,the peripheral sealer and the gas-distributor have been disposed and joined in face to face on the both sides of the separator while holding the separator, such a structure has a reinforcing effect and is excellent in the handling property at the time o~ producing the fuel cell.
Moreover, in the composite substrate according to the present invention, wherein the flexible carbon sheet is interposed only between the top surfaces of the ribs of the electrode substrate and the joining surface of the separator, the thickness of the flexible carbon sheet can be utilized as the effective height in the ribs of 13~927 the electrode substrate. Namely, in comparison to the composite substrate wherein the flexible carbon sheet~has been disposed on the whole area of the separator facing to the composite substrate, the thickness per one piece of the electrode substrate of from 3.8 to 4 mm may be reduced by from 0.3 to 0.5 mm, that is, from 7 to 13~
without any reduction of the cross section area of the flow channel or reactant gases therein.
The present invention will be explained more in detail while referring to the following non-limitative examples.
EXAMPLE 1:
(1) Electrode substrate material:
Two pieces of the porous and carbonaceous flat plate material preliminarily calcined at a temperature of not lower than 800C ~made by KUREHA KAGAKU KOGYO Co., Ltd., under the trade name of KES-400, 650 mm in length, 690 mm in width and 1.47 mm in thickness) were used as the elec-trode substrate material.
(2) The separator material:
A piece of the compact carbon plate (made by SHOWA DENKO Co., Ltd., under the trade name of SG-2, 0.6 mm in thickness) was cut into 690 mm both in length and width to prepare the separator material.
(3) Peripheral sealers:
A piece of the compact carbon plate (made by~
TOKAI Carbon Co., Ltd., 1.~5 g/cc in bulk density and 1.5 mm in thickness) was cut into 4 pieces (each 690 mm in length and 20 mm in width) to prepare the peripheral sealers.
(4) Fluorocarbon resin:
A piece of TEFLO ~ sheet (made by NICHIAS Co., Ltd., 0.05 mm in ~hickness) was cut into 4 pieces according to the dimensions of the peripheral sealer and the pieces were used for the purpose.
(5) Flexible carbon sheet:
A piece of GRAFOIL~ (made by U.C.C., 1.10 g/cc in bulk density and 0.13 mm in thickness) was suitably cùt into 2 pieces according to the dimension of the joining surface.
After applying an adhesive of phenol resin series on each one side of the two electrode substrate ma~erials and on one side of GRAFOIL~,the thus applied adhesive wa~s dried. Then, the electrode substrate material and GRAFOIL~9 were joined respectively under conditions of 140C, 10 k~f/cm2G. and 20 min. of pressure-holding time.
Then, a plurality of grooves having a rectangular cross section of 2 mm in width and 1 mm ln depth were prepared in parallel to each other at intervals of 4 mm on the GRAFOIL~-applied surface of each of the two sets - 3~ -1 ~ 1 4927 of the thus joined electrode subs-trate materials by cut-processing with a diamond blade.
Thereafter, on the GR~FOIL~surface remaining on the top of the rib forming the groove of the thus pro-cessed body, the above-mentioned adhesive was applied and dried.
In the same manner as above, the above-mentioned adhesive was applied on the surfaces of the separator material, and dried. Thereafter, the respective remaining GRAE'OIL~ surfaces of the two electrode substrate materials were joined to the both surfaces of the separator material so that the plurality of the mutually parallel grooves of one of the electrode substrate materials are perpendi-cular to those of the another electrode substrate material,~
under the conditions of 140C in joining temperature, 10 kgf/cm2G. in joining pressure and 20 min. in pressure-holding time. Then, the thus joined materials were calcined at 2000C under a reduced pressure of 5 Torr and~
in gaseous nitrogen.
After calcination of the joined materials, the part of the electrode substrate facing to the extended part of the separator to be joined to the peripheral sealer was cut off to expose the joining surface (extended part) of the separator to be joined to the peripheral sealer, and the TEFLO ~ sheet was lnterposed between the joining surfaces of the peripheral sealer and the separator.
Thereafter, the two materials were press-joined by melt-adhesion of the resin at 350C under a pressure of 20`kgf/
cm G. and the pressure-holding time of 20 min.
According to the above-mentioned procedures, a composite substrate of 3.8 mm in thickness was obtained.
In order to measure the adhesive strength of the melt-adhered and press-joined surface of the thus obtained composite substrate, a test piece taken from the product was joined to the measuring jig by an adhesive of epoxy resin, and the test piece was subjected to a tensile test.
Since the exfoliation was not caused at the joined part of the TEFLO ~ sheet and was caused at the joined part of the adhesive of epoxy resin, the adhesive strength was presumed to be not less than 90 kgf/cm2. B~ the above-mentioned test result, it can be said that the composite substrate obtained as above can sufficiently stand for the practical use as the composite substrate for a fuel cell.
EXAMPLE 2:
A composite substrate was prepared in the similar manner as in Example 1 only except for using the following flexible carbon sheet instead of GR~FOIL~ sheet used in Example 1.
Namely, after~dispersing 7 parts by weiyht of carbon fibers (made by KUREHA KAGAKU KOGYO Co., Ltd. by;
calcining isotropic pitch fihers at 2000C, under the trade name of C 206S, 6 mm in length and 14 to 16 ~m in diameter)~
:
::
and l part by weight of polyvinyl alcohol fibers (made by KURARE Co., I,td. under the registered trada name of KURARE VINYLO~ VBP 105-2, 3 mm in length) into water and manufacturing into paper sheets by using an ordinary paper machine, the thus manufactured carbon paper sheet was dried, and the thus dried carbon paper sheet was impreynated with a methanolic 20% solution of a phenol resin. After removing the solvent from the thus impregna-ted carbon paper sheet by drying~ the carbon paper sheet was thermally shaped in a metal mold at 130C under a pressure of lO kgf/cm2G. for 20 min. and then the thus shaped paper sheet was calcined at 2000C under a reduced pressure of 5 Torr and in gaseous nitrogen to obtain a thin plate-like sheet of 0.3 mm in thickness. The thus obtained sheet was 0.4 g/cc in bul~ density~ 8 x lO 2 cm2/kgf in rate of compression strain and 5. 3 mm in flexibility represented by radius of curvature. As in the case of Example l, the sheet was suitably cut into two pieces, each of them having the dimension corresponding to the dimension of the joining surface with the electrode substrate material.
By using the thus prepared flexible carbon sheet instead of the GRAFOIL~ sheet in Example l, it was ~oined to the electrode substrate material under the conditions of 130C, lO kgf/cm2G. and 20 min. of the pressure-holding time.
1 31 ~q27 Thereafter, as in the case of Example 1, after carrying out (1) preparing the groove by cut-processing the surface of the flexible carbon sheet adhered to each of the electrode substrate material, (2) press-joining the electrode substrate materials to the both surfaces of the separator material by heating by a pressure, (3) calcining the composed materials and (4) cutting and removing the part of the carbon sheet and the electrode substrate facing to the extended part OL the separator to be joined.to the peripheral sealer, the peripheral sealer and the separator were press-j.oined by melt-adhesion of the resin to obtain a composite substrate of 4.14 mm in thickness for a fuel cell. .:
However, the conditions in joining thè separator material and the electrode substrate material were 130C, 10 kgf/cm2G. and 120 min. of the p:ressure-holding:time.
: .. The thus obtained composite substrate was strong in adhesive strength as that in Example 1 and could be used actually. : ~ :
The following three kinds~of the composite ~
substrates mutually different~ln size were produced by using the following materials.~
(1) Electrode_substrate~material:
The same material as that used in Example 1 as-the electrode substrate material was cut into three pairs of square pieces respectively having the length of one side of 100, 300 and 600 mm, and each pair pieces of the same size were used as the electrode substrate material.
The thermal expansion coefficient of these materials up to 400C was 2.5 x 10 6/oC on the average.
(2) Sepaxator material:
A compact carbon plate (made by SHOWA DENKO Co., Ltd. of 0.6 mm in thickness) was cut into three square pieces having respectively the length of the side of 100, 300 and 600 mm to obtain the respective separator materials, the thermal expansion coefficient thereof being 3.0 x 10 /C.
(3) Peripheral sealer and gas-distributor:
.
A compact carbon plate (made by TOKAI Carbon Co., Ltd. of 1.85 g/cc in bulk density and 1.5 mm in thickness) was cut into 6 groups of pieces respectively having the length and width of 100 mm x 20 mm, 60 mm x 20 mm, 300 mm x 20 mm, 260 mm x 20 mm, 600 mm x 20 mm and 560 mm x 20~mm, one group consisting of four pieces, and these pieces were used as the peripheral sealer and the gas-distributor.
On the pleces having shorter length (namel~, 60 mm, 260 mm and 560 mm, respectively) used as the gas-distri-butor, after melt-adhering a TE~LO ~ sheet thereto, the grooves of 8 mm in width and 0.6 mm in depth were provided parallel to aach other with an interval of 12 mm by cut-processing. The thermal expansion coefficient of these 1 31 ~927 all pieces was 2.5 x 13 6/oC.
(4) Fluoro arbon resin:
A TEFLO ~ sheet (made by NICHIAS Co., Ltd., 0.05 mm in thickness) was cut into 4 pieces in accordance to the size of the peripheral sealer, and the pieces were used as the fluorocarbon resin.
(5) Flexible carbon sheet:
A GRAFOIL6~ (made by U.C.C., 1.10 g/cc in bulk density and 0.13 mm in thickness) was suitabiy cut into pieces in accordance to the size of the joining surface, and each two of them were used as the flexible carbon sheet.
After applying an adhesive of phenol resin series onto one of the surfaces of each of the two electrode substrate materials and one of the two surfaces of the GRAFOII.~ and drying the thus applied adhesive, the elec-trode substrate materials and the GRAFOIL~ were joined together under the conditions of~l40C, 10 kgf/cm2G. and 20 min. of the pressure-holding time.
In the next place, a plurality of grooves of 2 mm in width and 1 mm in depth parallel to each other and having~
a rectangular cross section were prepared at an interval of 4 mm on the surface of GRAFOIL~ sheet adhered to each of the two electrode substrate materials by cut-processing while using a diamond blade.
::
Thereafter, the ahove-mentioned adhesive was applied on the remaining GRAFOIL~ surface of the thus~
processed body and dried.
Then, the respective remaining GRAFOIL~ surfaces of the two electrode substrate materials were joined to the both surfaces of the separator material so that the plurality of the parallel grooves in one of the elec-trode substrate materials are perpendicular to those in the another electrode substrate material, under the joining conditions of 140C, 10 kgf/cm2G~ and 20 min. of the pres-sure-holding time, and the thus composed materials were calcined at 2000C under a reduced pressure of 5;Torr and in gaseous nitrogen.
After calcination, a part of the electrode substrate and the GRAFOIL~ facing to the~extended part of the separator to be joined to the peripheral sealer and the gas-distributor was removed by cutting to expose the joining surface of the saparator to be joined to the~
peripheral sealer and the gas-distributor, and a TEFLO
sheet was interposed between the ]oining surfaces of the peripheral sealer and the extended par~t of;the separator.;~
In addition, the gas-distributor to wh1ch ;a TEFLO ~ sheet had been preliminarily melt-adhered was piled while facing the TEFLO ~ sheet surface to the surface of the separator.
Thereafter, the thus composed materials were press-joined by melt-adhesion~under the conditions of 350C, 20~ kgf/cm2G.
1 3~ 4927 and 20 min. of the pressure-holding time.
By the above-mentioned procedures, three kinas of the composite substrate provided with the peripheral sealer and the gas-distributor for a fuel cell according to the present invention were obtained. The length of the side of the thus obtained products was respectively 100 mm, 300 mm or 600 mm, and the thickness thereof was 3.8 mm.
In the thus obtained composite substrate, the difference of the thermal expansion coefficient between the separator and the peripheral sealer and between the separa-tor and the gas-distributor was 0.5 x 10 6joC, respectively.
The results of measuring the extent of the warp of each of the thus obtained composite substrate were as follows:
.
Length of the side of the composite 100 300 600 substrate (mm) ~ _ ~ :
Warp (mm) 0 ~ 0.03 _0.05 : :
In addition, on measuring the adhesive strength of the melt-adhered surfaces under a pressure in tbe sam~
manner as in Example l, the same results as in Example 1 were obtained and according to the results, the adhesive strength was presumed to be not less than 90 kgf/cm2.
131'-Iq27 According to the above-mentioned measurements, it can be said that -the thus obtained composite suhstrate provided with the peripheral sealer and the gas-distributor for a fuel cell could be put to practical use sufficiently.
:, .,
A piece of GRAFOIL~ (made by U.C.C., 1.10 g/cc in bulk density and 0.13 mm in thickness) was suitably cùt into 2 pieces according to the dimension of the joining surface.
After applying an adhesive of phenol resin series on each one side of the two electrode substrate ma~erials and on one side of GRAFOIL~,the thus applied adhesive wa~s dried. Then, the electrode substrate material and GRAFOIL~9 were joined respectively under conditions of 140C, 10 k~f/cm2G. and 20 min. of pressure-holding time.
Then, a plurality of grooves having a rectangular cross section of 2 mm in width and 1 mm ln depth were prepared in parallel to each other at intervals of 4 mm on the GRAFOIL~-applied surface of each of the two sets - 3~ -1 ~ 1 4927 of the thus joined electrode subs-trate materials by cut-processing with a diamond blade.
Thereafter, on the GR~FOIL~surface remaining on the top of the rib forming the groove of the thus pro-cessed body, the above-mentioned adhesive was applied and dried.
In the same manner as above, the above-mentioned adhesive was applied on the surfaces of the separator material, and dried. Thereafter, the respective remaining GRAE'OIL~ surfaces of the two electrode substrate materials were joined to the both surfaces of the separator material so that the plurality of the mutually parallel grooves of one of the electrode substrate materials are perpendi-cular to those of the another electrode substrate material,~
under the conditions of 140C in joining temperature, 10 kgf/cm2G. in joining pressure and 20 min. in pressure-holding time. Then, the thus joined materials were calcined at 2000C under a reduced pressure of 5 Torr and~
in gaseous nitrogen.
After calcination of the joined materials, the part of the electrode substrate facing to the extended part of the separator to be joined to the peripheral sealer was cut off to expose the joining surface (extended part) of the separator to be joined to the peripheral sealer, and the TEFLO ~ sheet was lnterposed between the joining surfaces of the peripheral sealer and the separator.
Thereafter, the two materials were press-joined by melt-adhesion of the resin at 350C under a pressure of 20`kgf/
cm G. and the pressure-holding time of 20 min.
According to the above-mentioned procedures, a composite substrate of 3.8 mm in thickness was obtained.
In order to measure the adhesive strength of the melt-adhered and press-joined surface of the thus obtained composite substrate, a test piece taken from the product was joined to the measuring jig by an adhesive of epoxy resin, and the test piece was subjected to a tensile test.
Since the exfoliation was not caused at the joined part of the TEFLO ~ sheet and was caused at the joined part of the adhesive of epoxy resin, the adhesive strength was presumed to be not less than 90 kgf/cm2. B~ the above-mentioned test result, it can be said that the composite substrate obtained as above can sufficiently stand for the practical use as the composite substrate for a fuel cell.
EXAMPLE 2:
A composite substrate was prepared in the similar manner as in Example 1 only except for using the following flexible carbon sheet instead of GR~FOIL~ sheet used in Example 1.
Namely, after~dispersing 7 parts by weiyht of carbon fibers (made by KUREHA KAGAKU KOGYO Co., Ltd. by;
calcining isotropic pitch fihers at 2000C, under the trade name of C 206S, 6 mm in length and 14 to 16 ~m in diameter)~
:
::
and l part by weight of polyvinyl alcohol fibers (made by KURARE Co., I,td. under the registered trada name of KURARE VINYLO~ VBP 105-2, 3 mm in length) into water and manufacturing into paper sheets by using an ordinary paper machine, the thus manufactured carbon paper sheet was dried, and the thus dried carbon paper sheet was impreynated with a methanolic 20% solution of a phenol resin. After removing the solvent from the thus impregna-ted carbon paper sheet by drying~ the carbon paper sheet was thermally shaped in a metal mold at 130C under a pressure of lO kgf/cm2G. for 20 min. and then the thus shaped paper sheet was calcined at 2000C under a reduced pressure of 5 Torr and in gaseous nitrogen to obtain a thin plate-like sheet of 0.3 mm in thickness. The thus obtained sheet was 0.4 g/cc in bul~ density~ 8 x lO 2 cm2/kgf in rate of compression strain and 5. 3 mm in flexibility represented by radius of curvature. As in the case of Example l, the sheet was suitably cut into two pieces, each of them having the dimension corresponding to the dimension of the joining surface with the electrode substrate material.
By using the thus prepared flexible carbon sheet instead of the GRAFOIL~ sheet in Example l, it was ~oined to the electrode substrate material under the conditions of 130C, lO kgf/cm2G. and 20 min. of the pressure-holding time.
1 31 ~q27 Thereafter, as in the case of Example 1, after carrying out (1) preparing the groove by cut-processing the surface of the flexible carbon sheet adhered to each of the electrode substrate material, (2) press-joining the electrode substrate materials to the both surfaces of the separator material by heating by a pressure, (3) calcining the composed materials and (4) cutting and removing the part of the carbon sheet and the electrode substrate facing to the extended part OL the separator to be joined.to the peripheral sealer, the peripheral sealer and the separator were press-j.oined by melt-adhesion of the resin to obtain a composite substrate of 4.14 mm in thickness for a fuel cell. .:
However, the conditions in joining thè separator material and the electrode substrate material were 130C, 10 kgf/cm2G. and 120 min. of the p:ressure-holding:time.
: .. The thus obtained composite substrate was strong in adhesive strength as that in Example 1 and could be used actually. : ~ :
The following three kinds~of the composite ~
substrates mutually different~ln size were produced by using the following materials.~
(1) Electrode_substrate~material:
The same material as that used in Example 1 as-the electrode substrate material was cut into three pairs of square pieces respectively having the length of one side of 100, 300 and 600 mm, and each pair pieces of the same size were used as the electrode substrate material.
The thermal expansion coefficient of these materials up to 400C was 2.5 x 10 6/oC on the average.
(2) Sepaxator material:
A compact carbon plate (made by SHOWA DENKO Co., Ltd. of 0.6 mm in thickness) was cut into three square pieces having respectively the length of the side of 100, 300 and 600 mm to obtain the respective separator materials, the thermal expansion coefficient thereof being 3.0 x 10 /C.
(3) Peripheral sealer and gas-distributor:
.
A compact carbon plate (made by TOKAI Carbon Co., Ltd. of 1.85 g/cc in bulk density and 1.5 mm in thickness) was cut into 6 groups of pieces respectively having the length and width of 100 mm x 20 mm, 60 mm x 20 mm, 300 mm x 20 mm, 260 mm x 20 mm, 600 mm x 20 mm and 560 mm x 20~mm, one group consisting of four pieces, and these pieces were used as the peripheral sealer and the gas-distributor.
On the pleces having shorter length (namel~, 60 mm, 260 mm and 560 mm, respectively) used as the gas-distri-butor, after melt-adhering a TE~LO ~ sheet thereto, the grooves of 8 mm in width and 0.6 mm in depth were provided parallel to aach other with an interval of 12 mm by cut-processing. The thermal expansion coefficient of these 1 31 ~927 all pieces was 2.5 x 13 6/oC.
(4) Fluoro arbon resin:
A TEFLO ~ sheet (made by NICHIAS Co., Ltd., 0.05 mm in thickness) was cut into 4 pieces in accordance to the size of the peripheral sealer, and the pieces were used as the fluorocarbon resin.
(5) Flexible carbon sheet:
A GRAFOIL6~ (made by U.C.C., 1.10 g/cc in bulk density and 0.13 mm in thickness) was suitabiy cut into pieces in accordance to the size of the joining surface, and each two of them were used as the flexible carbon sheet.
After applying an adhesive of phenol resin series onto one of the surfaces of each of the two electrode substrate materials and one of the two surfaces of the GRAFOII.~ and drying the thus applied adhesive, the elec-trode substrate materials and the GRAFOIL~ were joined together under the conditions of~l40C, 10 kgf/cm2G. and 20 min. of the pressure-holding time.
In the next place, a plurality of grooves of 2 mm in width and 1 mm in depth parallel to each other and having~
a rectangular cross section were prepared at an interval of 4 mm on the surface of GRAFOIL~ sheet adhered to each of the two electrode substrate materials by cut-processing while using a diamond blade.
::
Thereafter, the ahove-mentioned adhesive was applied on the remaining GRAFOIL~ surface of the thus~
processed body and dried.
Then, the respective remaining GRAFOIL~ surfaces of the two electrode substrate materials were joined to the both surfaces of the separator material so that the plurality of the parallel grooves in one of the elec-trode substrate materials are perpendicular to those in the another electrode substrate material, under the joining conditions of 140C, 10 kgf/cm2G~ and 20 min. of the pres-sure-holding time, and the thus composed materials were calcined at 2000C under a reduced pressure of 5;Torr and in gaseous nitrogen.
After calcination, a part of the electrode substrate and the GRAFOIL~ facing to the~extended part of the separator to be joined to the peripheral sealer and the gas-distributor was removed by cutting to expose the joining surface of the saparator to be joined to the~
peripheral sealer and the gas-distributor, and a TEFLO
sheet was interposed between the ]oining surfaces of the peripheral sealer and the extended par~t of;the separator.;~
In addition, the gas-distributor to wh1ch ;a TEFLO ~ sheet had been preliminarily melt-adhered was piled while facing the TEFLO ~ sheet surface to the surface of the separator.
Thereafter, the thus composed materials were press-joined by melt-adhesion~under the conditions of 350C, 20~ kgf/cm2G.
1 3~ 4927 and 20 min. of the pressure-holding time.
By the above-mentioned procedures, three kinas of the composite substrate provided with the peripheral sealer and the gas-distributor for a fuel cell according to the present invention were obtained. The length of the side of the thus obtained products was respectively 100 mm, 300 mm or 600 mm, and the thickness thereof was 3.8 mm.
In the thus obtained composite substrate, the difference of the thermal expansion coefficient between the separator and the peripheral sealer and between the separa-tor and the gas-distributor was 0.5 x 10 6joC, respectively.
The results of measuring the extent of the warp of each of the thus obtained composite substrate were as follows:
.
Length of the side of the composite 100 300 600 substrate (mm) ~ _ ~ :
Warp (mm) 0 ~ 0.03 _0.05 : :
In addition, on measuring the adhesive strength of the melt-adhered surfaces under a pressure in tbe sam~
manner as in Example l, the same results as in Example 1 were obtained and according to the results, the adhesive strength was presumed to be not less than 90 kgf/cm2.
131'-Iq27 According to the above-mentioned measurements, it can be said that -the thus obtained composite suhstrate provided with the peripheral sealer and the gas-distributor for a fuel cell could be put to practical use sufficiently.
:, .,
Claims (15)
1. A composite substrate for a fuel cell comprising:
(1) a separator:
(2) two porous and carbonaceous electrode substrates which respectively are provided with a plurality of grooves on one of the surfaces thereof and have another flat surface, each of said electrode substrates being joined to both surfaces of said separator via a flexible carbon sheet so that said grooves form flow channels for reactant gases and said flow channels in one of said electrode substrates are perpendicular to those in another said electrode substrate, said flexible carbon sheet being interposed only between the joining surfaces of said separator and tops of ribs forming said grooves of said electrode substrate, said separator having extended parts beyond a periphery of said electrode substrate and being a compact carbon material having a mean bulk density of not less than 1.4g/cc, a gas-permeability of not more than 10-6ml/cm2-hour-mmAq, an electric resistivity of not more than 10 m.OMEGA.-cm and a thickness of not more than 2mm; and (3) a pair of peripheral sealers each of which is formed of a calcined gas-impermeable and compact carbon material and disposed on a side of said electrode substrate parallel to said flow channels for reactant gases therein, said peripheral sealers being joined to said extended parts of said separator beyond said electrode substrate via a tetrafluoroethylene resin layer and being a compact carbon material having a mean bulk density of not less than 1.40g/cc and a gas-permeability of not more than 10-4ml/cm2-hour-mmAq.
(1) a separator:
(2) two porous and carbonaceous electrode substrates which respectively are provided with a plurality of grooves on one of the surfaces thereof and have another flat surface, each of said electrode substrates being joined to both surfaces of said separator via a flexible carbon sheet so that said grooves form flow channels for reactant gases and said flow channels in one of said electrode substrates are perpendicular to those in another said electrode substrate, said flexible carbon sheet being interposed only between the joining surfaces of said separator and tops of ribs forming said grooves of said electrode substrate, said separator having extended parts beyond a periphery of said electrode substrate and being a compact carbon material having a mean bulk density of not less than 1.4g/cc, a gas-permeability of not more than 10-6ml/cm2-hour-mmAq, an electric resistivity of not more than 10 m.OMEGA.-cm and a thickness of not more than 2mm; and (3) a pair of peripheral sealers each of which is formed of a calcined gas-impermeable and compact carbon material and disposed on a side of said electrode substrate parallel to said flow channels for reactant gases therein, said peripheral sealers being joined to said extended parts of said separator beyond said electrode substrate via a tetrafluoroethylene resin layer and being a compact carbon material having a mean bulk density of not less than 1.40g/cc and a gas-permeability of not more than 10-4ml/cm2-hour-mmAq.
2. A composite substrate for a fuel cell comprising:
(1) a separator;
(2) two porous and carbonaceous electrode substrates which respectively are provided with a plurality of grooves on one of the surfaces thereof and have another flat surface, each of said electrode substrates being joined to both surfaces of said separator via a flexible carbon sheet so that said grooves form flow channels for reactant gases and said flow channels in one of said electrode substrates are perpendicular to those in another said electrode substrate, said flexible carbon sheet being interposed only between the joining surfaces of said separator and tops of ribs forming said grooves of said electrode substrate, said separator having extended parts beyond a periphery of said electrode substrate and being a compact carbon material having a mean bulk density of not less than 1.4g/cc, a gas-permeability of not more than 10-6 ml/cm2-hour-mmAq, an electric resistivity of not more than 10 m.OMEGA.-cm and a thickness of not more than 2mm;
(3) a pair of peripheral sealers each of which is formed of a calcined gas-impermeable and compact carbon material and disposed on a side of said electrode substrate parallel to said flow channels for reactant gases therein, said peripheral sealers being joined to said extended parts of said separator beyond said electrode substrate via a tetrafluoroethylene resin layer and being a compact carbon material having a mean bulk density of not less than 1.40g/cc and a gas-permeability of not more than 10-4ml/cm2-hour-mmAq; and (4) a pair of gas-distributors provided with a passage for distributing reactant gases, each of which is formed of a calcined gas-impermeable and compact carbon material and disposed on a side of said electrode substrate perpendicular to said flow channels for reactant gases therein, said gas-distributors being joined to said extended parts of said separator beyond said electrode substrate via a tetrafluoroethylene resin layer and being a compact carbon material having a mean bulk density of not less than 1.40g/cc and a gas-permeability of not more than 10-4ml/cm2-hour-mmAq.
(1) a separator;
(2) two porous and carbonaceous electrode substrates which respectively are provided with a plurality of grooves on one of the surfaces thereof and have another flat surface, each of said electrode substrates being joined to both surfaces of said separator via a flexible carbon sheet so that said grooves form flow channels for reactant gases and said flow channels in one of said electrode substrates are perpendicular to those in another said electrode substrate, said flexible carbon sheet being interposed only between the joining surfaces of said separator and tops of ribs forming said grooves of said electrode substrate, said separator having extended parts beyond a periphery of said electrode substrate and being a compact carbon material having a mean bulk density of not less than 1.4g/cc, a gas-permeability of not more than 10-6 ml/cm2-hour-mmAq, an electric resistivity of not more than 10 m.OMEGA.-cm and a thickness of not more than 2mm;
(3) a pair of peripheral sealers each of which is formed of a calcined gas-impermeable and compact carbon material and disposed on a side of said electrode substrate parallel to said flow channels for reactant gases therein, said peripheral sealers being joined to said extended parts of said separator beyond said electrode substrate via a tetrafluoroethylene resin layer and being a compact carbon material having a mean bulk density of not less than 1.40g/cc and a gas-permeability of not more than 10-4ml/cm2-hour-mmAq; and (4) a pair of gas-distributors provided with a passage for distributing reactant gases, each of which is formed of a calcined gas-impermeable and compact carbon material and disposed on a side of said electrode substrate perpendicular to said flow channels for reactant gases therein, said gas-distributors being joined to said extended parts of said separator beyond said electrode substrate via a tetrafluoroethylene resin layer and being a compact carbon material having a mean bulk density of not less than 1.40g/cc and a gas-permeability of not more than 10-4ml/cm2-hour-mmAq.
3. A composite substrate according to claim 1 or 2, wherein said porous and carbonaceous electrode substrate has a mean bulk density of from 0.3 to 0.9g/cc, a gas-permeability of not less than 200 ml/cm2-hour-mmAq and an electric resistivity of not more than 200 m.OMEGA.-cm.
4. A composite substrate according to claim 1 or 2, wherein said flexible carbon sheet is a product which has been produced by carbonizing a composite material comprising (1) a matrix of carbon fibers of not less than 1mm in mean length which fibers have been thermally treated at a temperature of not lower than 1000°C under reduced pressure, in an inert atmosphere, or under reduced pressure in an inert atmosphere, and (2) a binder, and has a thickness of not more than 1mm a bulk density of from 0.2 to 1.3g/cc, a rate of compression strain of not more than 2.0 x 10-1cm2/kgf and a flexibility of not being broken when bent to the radius of curvature of 10mm, and wherein in said flexible carbon sheet carbon lumps derived from said binder are dispersed in the matrix of said carbon fibers and restrain a plurality of said carbon fibers, and by said carbon lumps said carbon fibers are slidably held to one another.
5. A composite substrate according to claim 1 or 2, wherein said flexible carbon sheet is a product which has been produced by compressing expanded graphite particles obtained by subjecting graphite particles of not more than 5mm in diameter to acid-treatment and further heating the acid-treated particles, and has a thickness of not more than 1mm, a bulk density of 1.0 to 1.5g/cc, a rate of compression strain of not more than 0.35 x 10-2cm2/kgf and a flexibility of not being broken when bent to the radius of curvature of 20mm.
6. A process for producing a composite substrate for a fuel cell according to claim 1, comprising steps of:
(1) adhering a flexible carbon sheet onto one surface of each of two electrode substrate materials of a flat plate-form without grooves and of the prescribed dimension by an adhesive, (2) providing grooves of a desired dimension for forming flow channels of reactant gases on the joining surface side of each of said electrode substrate materials by cut-processing, (3) joining a separator material to the surface of said flexible carbon sheet remaining on the cut-processed surface of each of said electrode substrate materials in face to face, said separator material being a compact carbon plate which shows a calcining shrinkage rate of not more than 0.2% when said material is calcined at 2,000°C under a reduced pressure, in an inert atmosphere or under a reduced pressure in an inert atmosphere, (4) calcining the composed materials at a temperature of not lower than about 800°C under a reduced pressure, in an inert atmosphere or under a reduced pressure in an inert atmosphere thereby producing a composite body comprising said electrode substrates and said separator, said separator having a mean bulk density of not less than 1.4g/cc, a gas-permeability of not more than 10-6ml/cm2-hour-mmAq, and electric resistivity of not more than 10 m.OMEGA.-cm and a thickness of not more than 2mm, and (5) joining a pair of peripheral sealers formed of a calcined gas-impermeable and compact carbon material respectively to extended parts of said separator, which extend beyond a periphery of said electrode substrate parallel to said flow channels for reactant gases therein, via a sheet or a dispersion of tetrafluoroethylene resin, said peripheral sealer being a compact carbon material having a mean bulk density of not less than 1.40g/cc and a gas-permeability of not more than 10-4ml/cm2-hour-mmAq, the difference of thermal expansion coefficient of said peripheral sealer from said separator material being not more than 2 x 10-6/°C.
(1) adhering a flexible carbon sheet onto one surface of each of two electrode substrate materials of a flat plate-form without grooves and of the prescribed dimension by an adhesive, (2) providing grooves of a desired dimension for forming flow channels of reactant gases on the joining surface side of each of said electrode substrate materials by cut-processing, (3) joining a separator material to the surface of said flexible carbon sheet remaining on the cut-processed surface of each of said electrode substrate materials in face to face, said separator material being a compact carbon plate which shows a calcining shrinkage rate of not more than 0.2% when said material is calcined at 2,000°C under a reduced pressure, in an inert atmosphere or under a reduced pressure in an inert atmosphere, (4) calcining the composed materials at a temperature of not lower than about 800°C under a reduced pressure, in an inert atmosphere or under a reduced pressure in an inert atmosphere thereby producing a composite body comprising said electrode substrates and said separator, said separator having a mean bulk density of not less than 1.4g/cc, a gas-permeability of not more than 10-6ml/cm2-hour-mmAq, and electric resistivity of not more than 10 m.OMEGA.-cm and a thickness of not more than 2mm, and (5) joining a pair of peripheral sealers formed of a calcined gas-impermeable and compact carbon material respectively to extended parts of said separator, which extend beyond a periphery of said electrode substrate parallel to said flow channels for reactant gases therein, via a sheet or a dispersion of tetrafluoroethylene resin, said peripheral sealer being a compact carbon material having a mean bulk density of not less than 1.40g/cc and a gas-permeability of not more than 10-4ml/cm2-hour-mmAq, the difference of thermal expansion coefficient of said peripheral sealer from said separator material being not more than 2 x 10-6/°C.
7. A process for producing a composite substrate for a fuel cell according to claim 2, comprising steps of:
(1) adhering a flexible carbon sheet onto one surface of each of two electrode substrate materials of a flat plate-form without grooves and of the prescribed dimension by an adhesive, (2) providing grooves of a desired dimension for forming flow channels of reactant gases on the joining surface side of each of said electrode substrate materials by cut-processing.
(3) joining a separator material to the surface of said flexible carbon sheet remaining on the cut-processed surface of each said electrode substrate material in face to face, said separator material being a compact carbon plate which shows a calcining shrinkage rate of not more than 0.2% when said material is calcined at 2,000°C under a reduced pressure, in an inert atmosphere or under a reduced pressure in an inert atmosphere, (4) calcining the composed materials at a temperature of not lower than about 800°C under a reduced pressure, in an inert atmosphere or under a reduced pressure in an inert atmosphere thereby producing a composite body comprising said electrode substrates and said separator, said separator having a mean bulk density of not less than 1.4g/cc, a gas-permeability of not more than 10-6ml/cm2-hour-mmAq, and electric resistivity of not more than 10m.OMEGA.-cm and a thickness of not more than 2mm, and (5) joining a pair of peripheral sealers formed of a calcined gas-impermeable and compact carbon material respectively to the extended parts of said separator, which extend beyond a periphery of said electrode substrate parallel to said flow channels for reactant gases therein, via a sheet or a dispersion of tetrafluoroethylene resin and further joining a pair of gas distributors formed of a calcined gas-impermeable and compact carbon material and having grooves forming a passage for distributing reactant gases respectively to extended parts of said separator, which extend beyond a periphery of said electrode substrate perpendicular to said flow channels for reactant gases therein, via a sheet of a dispersion of tetrafluoroethylene resin, said peripheral sealer and said gas-distributor being respectively a compact carbon material having a mean bulk density of not less than 1.40g/cc and a gas-permeability of not more than 104ml/cm2-hour-mmAq, the difference of thermal expansion coefficient of said peripheral sealer from said separator material and the difference of thermal expansion coefficient of said gas-distributor from said separator material being respectively not more than 2 x 10-6/°C.
(1) adhering a flexible carbon sheet onto one surface of each of two electrode substrate materials of a flat plate-form without grooves and of the prescribed dimension by an adhesive, (2) providing grooves of a desired dimension for forming flow channels of reactant gases on the joining surface side of each of said electrode substrate materials by cut-processing.
(3) joining a separator material to the surface of said flexible carbon sheet remaining on the cut-processed surface of each said electrode substrate material in face to face, said separator material being a compact carbon plate which shows a calcining shrinkage rate of not more than 0.2% when said material is calcined at 2,000°C under a reduced pressure, in an inert atmosphere or under a reduced pressure in an inert atmosphere, (4) calcining the composed materials at a temperature of not lower than about 800°C under a reduced pressure, in an inert atmosphere or under a reduced pressure in an inert atmosphere thereby producing a composite body comprising said electrode substrates and said separator, said separator having a mean bulk density of not less than 1.4g/cc, a gas-permeability of not more than 10-6ml/cm2-hour-mmAq, and electric resistivity of not more than 10m.OMEGA.-cm and a thickness of not more than 2mm, and (5) joining a pair of peripheral sealers formed of a calcined gas-impermeable and compact carbon material respectively to the extended parts of said separator, which extend beyond a periphery of said electrode substrate parallel to said flow channels for reactant gases therein, via a sheet or a dispersion of tetrafluoroethylene resin and further joining a pair of gas distributors formed of a calcined gas-impermeable and compact carbon material and having grooves forming a passage for distributing reactant gases respectively to extended parts of said separator, which extend beyond a periphery of said electrode substrate perpendicular to said flow channels for reactant gases therein, via a sheet of a dispersion of tetrafluoroethylene resin, said peripheral sealer and said gas-distributor being respectively a compact carbon material having a mean bulk density of not less than 1.40g/cc and a gas-permeability of not more than 104ml/cm2-hour-mmAq, the difference of thermal expansion coefficient of said peripheral sealer from said separator material and the difference of thermal expansion coefficient of said gas-distributor from said separator material being respectively not more than 2 x 10-6/°C.
8. A process according to claim 6 or 7, wherein said electrode substrate material is selected from the group consisting of (1) molded materials obtained by molding a mixture of short carbon fibers, a binder and an organic granular substance by heating under a pressure into one body and (2) a calcined material obtained by calcining said material of the above (1).
9. A process according to claim 6 or 7, wherein said electrode substrate material has a mean bulk density of from 0.3 to 0.9g/cc, a gas-permeability of not less than 200ml/cm2-hour-mmAq and an electric resistivity of not more than 200m.OMEGA.-cm after having been calcined at a temperature of not lower than 800°C under reduced pressure, in an inert atmosphere, or under reduced pressure in an inert atmosphere.
10. A process according to claim 6 or 7, wherein said flexible carbon sheet is produced by (1) preparing a matrix of carbon fibers of not less than 1mm in mean length which fibers have been thermally treated at a temperature of not lower than 1000°C under a reduced pressure, in an inert atmosphere or under reduced pressure in an inert atmosphere, (2) mixing the matrix of said carbon fibers with a binder of not less than 10% in carbonizing yield to obtain a composite material, (3) molding the composite material by heating under a pressure and (4) calcining the obtained molded material at a temperature of not lower than 850°C under reduced pressure, in an inert atmosphere, or under reduced pressure in an inert atmosphere, and has a thickness of not more than 1mm, a bulk density of from 0.2 to 1.3g/cc, a rate of compression strain of not more than 2.0 x 10-1cm2/kgf and a flexibility of not being broken when bent to the radius of curvature of 10mm, and wherein in said flexible carbon sheet carbon lumps derived from said binder are dispersed in the matrix of said carbon fibers and restrain a plurality of said carbon fibers, and by said carbon lumps said carbon fibers are slidably held to one another.
11. A process according to claim 6 or 7, wherein said flexible carbon sheet is produced by compressing expanded graphite particles obtained by subjecting graphite particles of not more than 5mm in diameter to acid-treatment and further heating the acid-treated particles, and has a thickness of not more than 1mm, a bulk density of 1.0 to 1.5g/cc, a rate of compression strain of not more than 0.35 x 10-2cm2/kgf and a flexibility of not being broken when bent to the radius of curvature of 20mm.
12. A process according to claim 6 or 7, wherein said adhesive is a thermosetting resin selected from the group consisting of phenol resins, epoxy resins and furan resins.
13. A process according to claim 6 or 7, wherein the joining of said electrode substrate material and said separator material is carried out under conditions of a temperature of from 100 to 180°C, a press-pressure of from 1 to 50kgf/cm2G and a press-time of from 1 to 120 min.
14. A process according to claim 6, wherein the joining of said peripheral sealer to said separator is carried out under conditions of a pressure not less than lkgf/cm2G and a temperature not lower than the melting point of said tetrafluoroethylene resin by 50°C.
15. A process according to claim 7, wherein the joining of said peripheral sealer and said gas-distributor to said separator is carried out under condition of a pressure not less than 1kgf/cm2G and a temperature not lower than the melting point of said tetrafluoroethylene resin by 50°C.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61169525A JPH0622140B2 (en) | 1986-07-18 | 1986-07-18 | Composite electrode substrate for fuel cell and manufacturing method thereof |
| JP169525/86 | 1986-07-18 | ||
| JP184721/86 | 1986-08-06 | ||
| JP61184721A JPS6343268A (en) | 1986-08-06 | 1986-08-06 | Composite electrode plate for external manifold type fuel cell and manufacture thereof |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1314927C true CA1314927C (en) | 1993-03-23 |
Family
ID=26492808
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000537161A Expired - Fee Related CA1314927C (en) | 1986-07-18 | 1987-05-14 | Composite substrate for fuel cell and process for producing the same |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1314927C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009019193A1 (en) * | 2007-08-08 | 2009-02-12 | Sgl Carbon Ag | Laminate |
-
1987
- 1987-05-14 CA CA000537161A patent/CA1314927C/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009019193A1 (en) * | 2007-08-08 | 2009-02-12 | Sgl Carbon Ag | Laminate |
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