CA1273991A - Composite electrode substrate for a fuel cell and process for producing the same - Google Patents
Composite electrode substrate for a fuel cell and process for producing the sameInfo
- Publication number
- CA1273991A CA1273991A CA000519756A CA519756A CA1273991A CA 1273991 A CA1273991 A CA 1273991A CA 000519756 A CA000519756 A CA 000519756A CA 519756 A CA519756 A CA 519756A CA 1273991 A CA1273991 A CA 1273991A
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- CA
- Canada
- Prior art keywords
- separator
- electrode
- manifold
- joined
- gas
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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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
Abstract
TITLE OF THE INVENTION:
COMPOSITE ELECTRODE SUBSTRATE FOR A FUEL
CELL AND PROCESS FOR PRODUCING THE SAME
ABSTRACT OF THE DISCLOSURE:
Disclosed herein are a composite electrode substrate for a fuel cell in which a porous and carbonaceous electrode provided with flow channels for a reactant gas is joined to both surfaces of the separa-tor via a flexible graphite sheet, the separator has been extended beyond the electrode and to the thus extended part of the separator, (1) a peripheral sealer on the side of the electrode parallel to the flow channels therein, which comprises a gas-impermeable and compact carbonaceous material or (2) a manifold which comprises a gas-impermeable and compact carbonaceous material and is provided with a flow passage for supplying a reactant gas is joined via a layer of a fluorocarbon resin, and a process for producing the composite electrode substrate.
COMPOSITE ELECTRODE SUBSTRATE FOR A FUEL
CELL AND PROCESS FOR PRODUCING THE SAME
ABSTRACT OF THE DISCLOSURE:
Disclosed herein are a composite electrode substrate for a fuel cell in which a porous and carbonaceous electrode provided with flow channels for a reactant gas is joined to both surfaces of the separa-tor via a flexible graphite sheet, the separator has been extended beyond the electrode and to the thus extended part of the separator, (1) a peripheral sealer on the side of the electrode parallel to the flow channels therein, which comprises a gas-impermeable and compact carbonaceous material or (2) a manifold which comprises a gas-impermeable and compact carbonaceous material and is provided with a flow passage for supplying a reactant gas is joined via a layer of a fluorocarbon resin, and a process for producing the composite electrode substrate.
Description
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BAC~GROUND OF THE INVENTION:
The present invention relates to a co~posite electrode substrate for a fuel cell of phosphoric acid type, and more in detail, relates to a composite elec-trode substrate wherein a porous and carbonaceous electrode provided with flow channels of a reactant gas is joined to both surfaces of the separator via a flexible graphite sheet, the separator has been extended beyond the electrode and to the thus extended par'c of the separator, (1) a peripheral sealer on the side of the electrode parallel to the flow channels therein, which comprises a gas-impermeable, compact and carbonaceous material or (2) a manifold which comprises a gas-imperme-able, compact and carbonaceous material and is provided with a flow passage for supplying a reactant gas is joined via a layer of a fluorocarbon resin, and a process for producing the composite electrode substrate.
Generally, the electrode substrate as an elec-trode of a fuel cell of phosphoric acid type has been stacked so that one side thereof contacts to the phospho-ric acid matrix and the other side thereof faces to the separator.
In addition, in the case where the electrode substrates are stacked for making a fuel cell, (1) a sealer is provided at the edge (peripheral) part of the electrode substrate so as to prevent the diffusion of
BAC~GROUND OF THE INVENTION:
The present invention relates to a co~posite electrode substrate for a fuel cell of phosphoric acid type, and more in detail, relates to a composite elec-trode substrate wherein a porous and carbonaceous electrode provided with flow channels of a reactant gas is joined to both surfaces of the separator via a flexible graphite sheet, the separator has been extended beyond the electrode and to the thus extended par'c of the separator, (1) a peripheral sealer on the side of the electrode parallel to the flow channels therein, which comprises a gas-impermeable, compact and carbonaceous material or (2) a manifold which comprises a gas-imperme-able, compact and carbonaceous material and is provided with a flow passage for supplying a reactant gas is joined via a layer of a fluorocarbon resin, and a process for producing the composite electrode substrate.
Generally, the electrode substrate as an elec-trode of a fuel cell of phosphoric acid type has been stacked so that one side thereof contacts to the phospho-ric acid matrix and the other side thereof faces to the separator.
In addition, in the case where the electrode substrates are stacked for making a fuel cell, (1) a sealer is provided at the edge (peripheral) part of the electrode substrate so as to prevent the diffusion of
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the reactant gas from the side of the electrode substrate to outside or (2) a manifold is provided at the edge part of the electrode substrate so as to supply the reactant gas to the fuel cell and at the same time to prevent the diffusion of the reactant gas from the side of the elec-trode substrate to outside.
Hitherto, in such a fuel cell, the joining between the composite materials has been carried out by using a carbon cement. However, since the carbon cement is eroded by phosphoric acid, there has been a possibility of causing exfoliation between the jointed composite materials and gas leakage through the jointed part.
- In addition, since the electrode substrate is generally a thin plate type, there has been a problem in the point of mechanical strength that the elect~ode substrate is broken by handling, particularly in the case where the area of the electrode substrate is large.
Further, as a method of joining the porous electroconductive materials wherein the gas-impermeability between the porous electroconductive materials has been increased, a method has been proposed recently. According to the proposed method, the porous electroconductive material is impregnated with a fluorinated ethylene-propylene polymer, a polysulphone resin, etc., and the thus impregnated layer is joined as an interface to another electroconductive material by hot-pressing while maintaining 73~
electroconductivity 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 the peripheral sealer of the composite electrode substrate, although the passage of the gas between the two carbon materials is prevented by the thus resin-impregnated carbon layer, in the case where the electroconductive material is the porous carbon material, since such a carbon material is weak in mechanical strength, the usage of the thus obtained composite material is limited.
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 quality 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 obtaining a composite electrode substrate for a fuel cell wherein the above-mentioned demerits have been solved, it has been found by the present inventors that the com-posite electrode substrate provided with a peripheral sealer on the side of the electrode parallel to the flow channels therein, wherein the separator and the electrode are joined via a flexible graphite sheet and calcined to be one body as carbon, and the peripheral sealer and the separator are joined together via a fluorocarbon resin, is particularly excellent in resistance to phosphoric acid and at the same time, that since the peripheral sealer are evenly disposed and joined in a crossed state while holding the separator in both sides, there is a reinforcemental effect and the composite electrode , substrate of the above-mentioned structure is also excellent in handling. On the basis of the above-mentioned findings, the present inventors have attained the present invention.
Namely, the first object of the present invention is to provide a composite electrode substrate provided with a peripheral gas sealer on the side of the electrode parallel to the flow channels therein, wherein the peripheral gas-sealer is joined to the separator to form one body.
Still more, the present inventors have found that the composite electrode substrate provided with a manifold for a fuel cell, wherein all the composite materials are joined by carbon or a fluorocarbon resin, is particularly excellent in resistance to phosphoric acid and since the peripheral sealer material (hereinafter referred to as a manifold) which also serves as the gas manifold is joined to the peripheral part of the electrode ~273~
substrate, such a composite electrode substrate is excellent in handling.
Namely, the second object of the present invention is to provide a composite electrode substrate provided with a manifold for a fuel cell, wherein the manifold provided with a flow passage for supplying the reactant gas is joined to the separator in one body.
The third object of the present invention is to provide the above-mentioned composite electrode substrate for a fuel cell of phosphoric acid type, which is excellent in resistance to phosphoric acid.
The other objects of the present invention and the merits thereof will be clearly understood from the following description.
SUMMARY OF THE INVENTION: -In a first aspect of the present invention, thereis provided a composite electrode substrate for a fuel cell, comprising a porous and carbonaceous electrode provided with f'ow channels of the reactant gas and joined to both surfaces of a separator via a flexible graphite sheet, and peripheral sealer on the side of the electrode parallel to the flow channels therein, which comprises a gas-impermeable and compact carbon material or a manifold which comprises a gas-impermeable and compact carbon ~3~3~
plate and provided with a flow passaye for supplying the reactant gas, the peripheral sealer or manifold being joined to the extended part of the separator beyond the electrode via a fluorocarbon resin layer.
In a second aspect of the present invention, there is provided a process for produ~ing a composite electrode substrate for a fuel cell which process comprising (1) joining a porous and carbonaceous electrode material provided with flow channels of the reactant gas to a separator material which is larger in an surface area than the electrode material by an adhesive while interposing a flexible graphite sheet between the elec-trode material and the separator material so that said separator material is extended beyond the electrode material, (2) calcining the thus joined materials at a temperature of not less than about 1000C under a reduced pressure and/or in an inert atmosphere, thereby producing an electrode substrate part wherein the porous and carbonaceous electrode is joined to both surfaces of the separator via the flexible graphite sheet, and (3) joining a peripheral sealer on the side of the electrode parallel to the flow channels therein, which comprises a gas-impermeable carbon material or a manifold material comprising a gas-impermeable and compact carbon plate to ~ ~t7~
the extended part of the separator beyond -the electrode via a sheet or a dlspersion of a fluorocarbon resin.
BRIEF EXPLANATION OF DRAWINGS:
Of the attached drawings, Fiy. 1 shows an example of the composite electrode substrate provided with a peripheral sealer on the side of the electrode parallel to flow channels therein according to the present invention, Fig. 2 is a ground plan of the composite electrode substrate provided with a manifold for a fuel cell according to the present invention, Figs. 3 and 4 are respectively the sectional views of III - III and IV - IV of Fig. 2, and Fig. 5 shows the internal construction of the manifold of the composite electrode substrate provided with the manifold according to the present invention, the figures in the left side of Fig. 5 being the partial cross-section and the figures in the right side of Fig. 5 being the partial ground plan of the manifold.
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DETAILED DESCRIPTION OF THE INVENTION:
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The electrode used in the composite electrode substrate according to the present invention is porous and carboneous, and after being calcined at a ~empera-ture of not less than 1000C under a reduced pressureand/or in an inert atmosphere, the mean bulk density, the gas-permeability and the electric resistivity thereof are preferably from 0.3 to 0.9 g/cc, not less than 200 ml/cm .hour.mmAq, and not more than 200 mQ~cm, respectively.
The mean bulk density, the gas-permeability and the electric resistivity of the separator used ln the composite electrode substrate according to the present invention are preferably not less than 1.4 g/cc, not more than 10 6 ml/cm2.hour.mn~q and not more than 10 mQ.cm, respectively. The thickness of the same separator is preferably not more than 2 mm.
The mean bulk density and the gas-permeability of a peripheral sealer on the side of the electrode parallel to the flow channels therein and a manifold used in the composite electrode substrate according to the present invention are preferably not less than 1.4 g/cc and not more than 10 4 ml/cm2.hour.mmAq, respectively.
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In the composite electrode substrate provided with the peripheral sealer according to the present invention, the porous and carbonaceous electrode provided with flow channels of the reactant gas is joined to the both surfaces of the separator via a flexible yraphite sheet, and the peripheral sealer comprising a gas-impermeable, compact and carbonaceous material is joined to the above~mentioned separator via a layer of a fluorocarbon resin.
In addition, in the composite electrode substrate provided with the peripheral sealer according to the present invention, the both electrodes are joined to the both surfaces of the separator so that the flow channels of the reactant gas in one of the electrodes are perpendicular to those of the another electrode, and a pair of the peripheral sealers are joined to the extended part of the separator via a layer of a fluorocarbon resin while being adjacent to the periphery of the electrode parallel to the flow channels of the reactant gas in the electrode as are seen in Fig. 1. Namely, the separator shown in Flg. 1 extends beyond the periphery of the electrode parallel to the flow channels therein.
That is, Fig. 1 is an oblique view of the preferable composite elec-trode substrate provided with the peripheral sealer according to the present invention.
The composite electrode substrate provided with the peripheral sealer according to the present invention has a structure comprising the two electrodes 1, 1' provided with flow channels 5, 5' of the reactant gas, the separator 4 interposed between the two electrodes and the peripheral sealer 8 adjacent to periphery of the electrode parallel to the flow channels 5, 5' of the reactant gas in the above-mentioned electrodes.
The separator 4 is larger in a surface area than the electrodes _, 1' and as is shown in Fig. 1, it is extended beyond the periphery of the electrode parallel to the flow channel 5 or 5' of the reactant gas in one of the electrodes (the outer edge of the extended part being coincided with the outer edge of the another electrode), and the peripheral sealer 8 is joined to the extended part via a fluorocarbon resin 40. Between the separator 4 and the electrodes 1, 1' a flexible graphite sheet _ has been inserted, and the peripheral part (extended part) of the separator and the peripheral sealer 8 are mutually joined via a fluorocarbon resin 40.
As has been described, in the composite electrode substrate provided with the peripheral sealer according to the present invention, all the peripheral sealers and the separator are joined together via a fluorocarbon resin and although the amount of leakaye of the reactant gas to outside through the peripheral sealer including the joined part is subject to gas diffusion and is not so much influenced by the pressure of the reactant gas, the gaseous leakage per unit time per the peripheral length of the joined part under the differential pressure of 500 mmAq in the present invention is preferably not more than 10 ml/cm.hour.mmAq, when the gas leakage is represented by [the amount of lea~ed gas/~the side length) x (the differential pressure)].
In the composite electrode substrate provided with a manifold, which is another enforced mode of the present invention, the porous and carbonaceous electrode provided with the flow channels of the reactant gas is joined to both the surfaces of the separator via a flexible graphite sheet, the separator has been extended beyond the all periphery of the electrode and to the extended part of the separator, a manifold comprising a gas-impermeable, compact and carbonaceous plate provided with the flow passage for supplying the reactant gas is joined via a layer of a fluorocarbon resin.
Fig. 2 is a ground plan of the composite electrode substrate provided with the manifold accarding to the present invention, and Figs. 3 and 4 are respectively the cross-sectional views of III ~ III and IV - IV of Fig. 2.
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The composite electrode substrate provided with the manifold according to the present invention has a construction comprising the two electrodes 1, 1' provided with flow channels 5, 5' of the reactant gas, the separator 4 interposed between the two electrodes and the manifolds 2, 2' adjacent to the all periphery of the electrode.
The separator 4 is larger in a surface area than the electrodes 1, 1' and as is shown in Fig. 2, the separator has been extended beyond the periphery of the electrodes 1, 1' and the manifolds 2, 2' are joined to the thus extended part.
Between the separator and the electrode, a flexible graphite sheet 30 is inserted, and the peripheral part of the separator which has been extended beyond the periphery of the electrode, and the manifold are mutually joined via the fluorocarbon resin 40 (refer to Fig. 5).
In addition, in the.above-mentioned manifold 2, the flow passage 3 for supplying the reactant gas is provided while penetrating the separator 4 and the manifold 2, The flow passage 3 for supplying the reactant gas is (1) connected to the flow channel 5 of the reactant gas provided in the electrode 1 comprising the gas diffusion part 6 and rib 7, via a flow passage 11 of the reactant gas provided in the manifold 2 or (2) connected directly to the flow channel 5 of the reactant gas provided in the electrode 1, and the another electrode 1' is sealed by the manifold 2' (refer to Fig. 4).
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In Fig. 3, the flow passaye 3' for s~pplying the reactant gas is (1) connected to the flow channel 5' of the reactant gas provided in the electrode 1' ~ia a flow passage 11' of the reactant gas provided in the manifold 2' or (2) connected directly to the fIow channel 5' of the reactant gas provided in the electrode 1', and the another electrode 1 is sealed by the manifold 2.
The flow direction of the reactant gas is shown by arrows in Fig. 3 and Fig. 4.
The flow channel 5 of the reactant gas is prescribed by the gas diffusion part 6 and the rib 7 in the electrode 1 and the separator 4 or the flexible graphite sheet (refer to 30 of Fig. 5) which has been joined to the separator 4.
There are various types of the internal construc-tion of the manifold, and several instances thereof are shown in Fig. 5. The figures in the left half of Fig. 5 are the partial cross-sectional view thereof and those in the right half of Fig. 5 are the partial ground plans thereof.
In (1) of Fig. 5, the manifold has a construction of being divided into three parts 21, 22 and 23, and the rib 7 of one of the electrodes has a construction of entering a little under the manifold part 21 (for instance to the position 7''). The internal edge of the manifold - - -~273~
part 22 is shown by 22'. The two parts 21 and 22 of the manifold, 22 and the separator 4 and 23 and the separator 4 are mutually joined via a fluorocarbon resin as shown by 40 in (1) of Fig. 5, respectively.
In (2) of Fig. 5, the manifold parts 21 and 22 in the above (1) has been formed in one body and the manlfold consists of the two parts 21 and 23. The rib 7 ends in the same plane 7''as the edge surface of the gas-diffusion part 6. In addition, the surface corresponding to the inner edge 22' of (1) is shown by 21'.
In (3) and (4) of Fig. 5, a structure is shown wherein one of the electrodes joined to the separator has been extended to either end of the flow passage 3 for supplying the reactant gas (the end being shown by 1'') and contacts to the inner edge of the manifold part 21.
In every case the manifold and the separator have been joined together via the fluorocarbon resin.
In addition, each structure shown in Fig. 5 is only an instance of the present invention, and the internal construction of the manifold according to the present invention can take another mode different from those shown in Fig. 5.
As has been described above, in the composite ele~trode substrate provided with the manifold according to the present invention, all the manifold and the separa-tor have been joined together via a fluorocarbon resin, ~7~
however, when the amount of leakage of the reactant gas through the manifold per the peripheral length under a definite diferential pressure per unit time is repre-sented by [the amount of leaked gas/(the side length) x (the differential pressure)]the amount is preferably less than 10 2 ml/cm.hour.mmAq which value is the same as that in the composite electrode substrate provided with the peripheral sealer.
The fluorocarbon resin used for producing the composite electrode substrate according to the present invention is generally a fluorocarbon resin of not less than 200C in the melting point, and although it is not restricted, for instance, polytetrafluoroethylene resin (abbreviated to PTEE, a melting point of 327C and a thermally deforming temperature of 121C under 4.6 kgf/cm2G), a copolymer resin of ketrafluoroethylene and hexafluoropropylene (abbreviated to FEP, a melting point of 250 to 280C and a thermally deforming temperature of 72C under 4.6 kgf/cm2G), polyfluoroalkoxyethylene resin (abbreviated to PFA, a melting point of 300 to 310C, and a thermally deforming temperature of 75C under 4.6 kgf/cm2G), fluorinated copolymer resin of ethylene and propylene (abbreviated to TFP, a melting point of 290 -300C), etc. may be mentioned. These fluorocarbon resins are commerciallized. In the above fluorocarbon resins, polytetrafluoroethylene resin is most preferable for producing the product according to the present invention.
According to the present invention, the above-mentioned fluorocarbon resin is,for instance, used as a sheet of about 50 micrometers in thickness or a dispersion of about 60 % by weight. A small amount of a surfactant may be added to the above-mentioned dispersion.
For producing the composite electrode substrate for a fuel cell according to the present invention, the electrode material and the separator are joined together by inserting a flexible graphite sheet between the elec-trode material and the separator material and applying an adhesive on both sides of the flexible graphite sheet and after calcining the thus joined materials at a temper-ature of not less than 1000C under a reduced pressure and/or in an inert atmosphere, the extended part of the separator which has been extended beyond the periphery of the electrode and the peripheral sealer,or manifold material are joined together via a sheet of a fluorocarbon resin or a dispersion of a fluorocarbon resin.
In addition, the hole 3 which is used as the flow passage of the reactant gas in the manifold of the composite electrode substrate provided with the manifold may be made in any optional stage of the process for producing the composite electrode substrate according to the present invention, for instance, before or after joining each manifold material to the separator by a suitable means.
Of course, it is preferable to make a passage connecting the hole 3 to the flow channel 5 of the reactant gas in the electrode before joining the rnanifold material thereto.
As the electrode material of the composite elec-trode substrate according to the present invention, the following substances are used:
(1) A material made by thermally molding a mixture of short carbon fibers, a binder and an organic granular substance under a pressure (refer to ~apanese Patent Application Laid-Open No. 59-68170 (1984)).
Particularly, the material prepared by molding a mixture consisting of 20 to 60 % by weight of short carbon fibers of not more than 2 mm in length, 20 to 50 % by weight of a , . .
phenol resin and 20 to 50 % by weight of an organic granular substance ~a micro-pore regulator) at a molding temperature of 100 to 180C, under a molding pressure of 2 to 100 kgf/cm2G for one to 60 min.
(2) A material made by calcining the molded material of the above-mentioned (1) at a temperature of not less than 1000C under a reduced pressure and/or in an inert atmosphere.
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the reactant gas from the side of the electrode substrate to outside or (2) a manifold is provided at the edge part of the electrode substrate so as to supply the reactant gas to the fuel cell and at the same time to prevent the diffusion of the reactant gas from the side of the elec-trode substrate to outside.
Hitherto, in such a fuel cell, the joining between the composite materials has been carried out by using a carbon cement. However, since the carbon cement is eroded by phosphoric acid, there has been a possibility of causing exfoliation between the jointed composite materials and gas leakage through the jointed part.
- In addition, since the electrode substrate is generally a thin plate type, there has been a problem in the point of mechanical strength that the elect~ode substrate is broken by handling, particularly in the case where the area of the electrode substrate is large.
Further, as a method of joining the porous electroconductive materials wherein the gas-impermeability between the porous electroconductive materials has been increased, a method has been proposed recently. According to the proposed method, the porous electroconductive material is impregnated with a fluorinated ethylene-propylene polymer, a polysulphone resin, etc., and the thus impregnated layer is joined as an interface to another electroconductive material by hot-pressing while maintaining 73~
electroconductivity 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 the peripheral sealer of the composite electrode substrate, although the passage of the gas between the two carbon materials is prevented by the thus resin-impregnated carbon layer, in the case where the electroconductive material is the porous carbon material, since such a carbon material is weak in mechanical strength, the usage of the thus obtained composite material is limited.
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 quality 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 obtaining a composite electrode substrate for a fuel cell wherein the above-mentioned demerits have been solved, it has been found by the present inventors that the com-posite electrode substrate provided with a peripheral sealer on the side of the electrode parallel to the flow channels therein, wherein the separator and the electrode are joined via a flexible graphite sheet and calcined to be one body as carbon, and the peripheral sealer and the separator are joined together via a fluorocarbon resin, is particularly excellent in resistance to phosphoric acid and at the same time, that since the peripheral sealer are evenly disposed and joined in a crossed state while holding the separator in both sides, there is a reinforcemental effect and the composite electrode , substrate of the above-mentioned structure is also excellent in handling. On the basis of the above-mentioned findings, the present inventors have attained the present invention.
Namely, the first object of the present invention is to provide a composite electrode substrate provided with a peripheral gas sealer on the side of the electrode parallel to the flow channels therein, wherein the peripheral gas-sealer is joined to the separator to form one body.
Still more, the present inventors have found that the composite electrode substrate provided with a manifold for a fuel cell, wherein all the composite materials are joined by carbon or a fluorocarbon resin, is particularly excellent in resistance to phosphoric acid and since the peripheral sealer material (hereinafter referred to as a manifold) which also serves as the gas manifold is joined to the peripheral part of the electrode ~273~
substrate, such a composite electrode substrate is excellent in handling.
Namely, the second object of the present invention is to provide a composite electrode substrate provided with a manifold for a fuel cell, wherein the manifold provided with a flow passage for supplying the reactant gas is joined to the separator in one body.
The third object of the present invention is to provide the above-mentioned composite electrode substrate for a fuel cell of phosphoric acid type, which is excellent in resistance to phosphoric acid.
The other objects of the present invention and the merits thereof will be clearly understood from the following description.
SUMMARY OF THE INVENTION: -In a first aspect of the present invention, thereis provided a composite electrode substrate for a fuel cell, comprising a porous and carbonaceous electrode provided with f'ow channels of the reactant gas and joined to both surfaces of a separator via a flexible graphite sheet, and peripheral sealer on the side of the electrode parallel to the flow channels therein, which comprises a gas-impermeable and compact carbon material or a manifold which comprises a gas-impermeable and compact carbon ~3~3~
plate and provided with a flow passaye for supplying the reactant gas, the peripheral sealer or manifold being joined to the extended part of the separator beyond the electrode via a fluorocarbon resin layer.
In a second aspect of the present invention, there is provided a process for produ~ing a composite electrode substrate for a fuel cell which process comprising (1) joining a porous and carbonaceous electrode material provided with flow channels of the reactant gas to a separator material which is larger in an surface area than the electrode material by an adhesive while interposing a flexible graphite sheet between the elec-trode material and the separator material so that said separator material is extended beyond the electrode material, (2) calcining the thus joined materials at a temperature of not less than about 1000C under a reduced pressure and/or in an inert atmosphere, thereby producing an electrode substrate part wherein the porous and carbonaceous electrode is joined to both surfaces of the separator via the flexible graphite sheet, and (3) joining a peripheral sealer on the side of the electrode parallel to the flow channels therein, which comprises a gas-impermeable carbon material or a manifold material comprising a gas-impermeable and compact carbon plate to ~ ~t7~
the extended part of the separator beyond -the electrode via a sheet or a dlspersion of a fluorocarbon resin.
BRIEF EXPLANATION OF DRAWINGS:
Of the attached drawings, Fiy. 1 shows an example of the composite electrode substrate provided with a peripheral sealer on the side of the electrode parallel to flow channels therein according to the present invention, Fig. 2 is a ground plan of the composite electrode substrate provided with a manifold for a fuel cell according to the present invention, Figs. 3 and 4 are respectively the sectional views of III - III and IV - IV of Fig. 2, and Fig. 5 shows the internal construction of the manifold of the composite electrode substrate provided with the manifold according to the present invention, the figures in the left side of Fig. 5 being the partial cross-section and the figures in the right side of Fig. 5 being the partial ground plan of the manifold.
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DETAILED DESCRIPTION OF THE INVENTION:
. .
The electrode used in the composite electrode substrate according to the present invention is porous and carboneous, and after being calcined at a ~empera-ture of not less than 1000C under a reduced pressureand/or in an inert atmosphere, the mean bulk density, the gas-permeability and the electric resistivity thereof are preferably from 0.3 to 0.9 g/cc, not less than 200 ml/cm .hour.mmAq, and not more than 200 mQ~cm, respectively.
The mean bulk density, the gas-permeability and the electric resistivity of the separator used ln the composite electrode substrate according to the present invention are preferably not less than 1.4 g/cc, not more than 10 6 ml/cm2.hour.mn~q and not more than 10 mQ.cm, respectively. The thickness of the same separator is preferably not more than 2 mm.
The mean bulk density and the gas-permeability of a peripheral sealer on the side of the electrode parallel to the flow channels therein and a manifold used in the composite electrode substrate according to the present invention are preferably not less than 1.4 g/cc and not more than 10 4 ml/cm2.hour.mmAq, respectively.
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In the composite electrode substrate provided with the peripheral sealer according to the present invention, the porous and carbonaceous electrode provided with flow channels of the reactant gas is joined to the both surfaces of the separator via a flexible yraphite sheet, and the peripheral sealer comprising a gas-impermeable, compact and carbonaceous material is joined to the above~mentioned separator via a layer of a fluorocarbon resin.
In addition, in the composite electrode substrate provided with the peripheral sealer according to the present invention, the both electrodes are joined to the both surfaces of the separator so that the flow channels of the reactant gas in one of the electrodes are perpendicular to those of the another electrode, and a pair of the peripheral sealers are joined to the extended part of the separator via a layer of a fluorocarbon resin while being adjacent to the periphery of the electrode parallel to the flow channels of the reactant gas in the electrode as are seen in Fig. 1. Namely, the separator shown in Flg. 1 extends beyond the periphery of the electrode parallel to the flow channels therein.
That is, Fig. 1 is an oblique view of the preferable composite elec-trode substrate provided with the peripheral sealer according to the present invention.
The composite electrode substrate provided with the peripheral sealer according to the present invention has a structure comprising the two electrodes 1, 1' provided with flow channels 5, 5' of the reactant gas, the separator 4 interposed between the two electrodes and the peripheral sealer 8 adjacent to periphery of the electrode parallel to the flow channels 5, 5' of the reactant gas in the above-mentioned electrodes.
The separator 4 is larger in a surface area than the electrodes _, 1' and as is shown in Fig. 1, it is extended beyond the periphery of the electrode parallel to the flow channel 5 or 5' of the reactant gas in one of the electrodes (the outer edge of the extended part being coincided with the outer edge of the another electrode), and the peripheral sealer 8 is joined to the extended part via a fluorocarbon resin 40. Between the separator 4 and the electrodes 1, 1' a flexible graphite sheet _ has been inserted, and the peripheral part (extended part) of the separator and the peripheral sealer 8 are mutually joined via a fluorocarbon resin 40.
As has been described, in the composite electrode substrate provided with the peripheral sealer according to the present invention, all the peripheral sealers and the separator are joined together via a fluorocarbon resin and although the amount of leakaye of the reactant gas to outside through the peripheral sealer including the joined part is subject to gas diffusion and is not so much influenced by the pressure of the reactant gas, the gaseous leakage per unit time per the peripheral length of the joined part under the differential pressure of 500 mmAq in the present invention is preferably not more than 10 ml/cm.hour.mmAq, when the gas leakage is represented by [the amount of lea~ed gas/~the side length) x (the differential pressure)].
In the composite electrode substrate provided with a manifold, which is another enforced mode of the present invention, the porous and carbonaceous electrode provided with the flow channels of the reactant gas is joined to both the surfaces of the separator via a flexible graphite sheet, the separator has been extended beyond the all periphery of the electrode and to the extended part of the separator, a manifold comprising a gas-impermeable, compact and carbonaceous plate provided with the flow passage for supplying the reactant gas is joined via a layer of a fluorocarbon resin.
Fig. 2 is a ground plan of the composite electrode substrate provided with the manifold accarding to the present invention, and Figs. 3 and 4 are respectively the cross-sectional views of III ~ III and IV - IV of Fig. 2.
.
:
~2~
The composite electrode substrate provided with the manifold according to the present invention has a construction comprising the two electrodes 1, 1' provided with flow channels 5, 5' of the reactant gas, the separator 4 interposed between the two electrodes and the manifolds 2, 2' adjacent to the all periphery of the electrode.
The separator 4 is larger in a surface area than the electrodes 1, 1' and as is shown in Fig. 2, the separator has been extended beyond the periphery of the electrodes 1, 1' and the manifolds 2, 2' are joined to the thus extended part.
Between the separator and the electrode, a flexible graphite sheet 30 is inserted, and the peripheral part of the separator which has been extended beyond the periphery of the electrode, and the manifold are mutually joined via the fluorocarbon resin 40 (refer to Fig. 5).
In addition, in the.above-mentioned manifold 2, the flow passage 3 for supplying the reactant gas is provided while penetrating the separator 4 and the manifold 2, The flow passage 3 for supplying the reactant gas is (1) connected to the flow channel 5 of the reactant gas provided in the electrode 1 comprising the gas diffusion part 6 and rib 7, via a flow passage 11 of the reactant gas provided in the manifold 2 or (2) connected directly to the flow channel 5 of the reactant gas provided in the electrode 1, and the another electrode 1' is sealed by the manifold 2' (refer to Fig. 4).
... .
In Fig. 3, the flow passaye 3' for s~pplying the reactant gas is (1) connected to the flow channel 5' of the reactant gas provided in the electrode 1' ~ia a flow passage 11' of the reactant gas provided in the manifold 2' or (2) connected directly to the fIow channel 5' of the reactant gas provided in the electrode 1', and the another electrode 1 is sealed by the manifold 2.
The flow direction of the reactant gas is shown by arrows in Fig. 3 and Fig. 4.
The flow channel 5 of the reactant gas is prescribed by the gas diffusion part 6 and the rib 7 in the electrode 1 and the separator 4 or the flexible graphite sheet (refer to 30 of Fig. 5) which has been joined to the separator 4.
There are various types of the internal construc-tion of the manifold, and several instances thereof are shown in Fig. 5. The figures in the left half of Fig. 5 are the partial cross-sectional view thereof and those in the right half of Fig. 5 are the partial ground plans thereof.
In (1) of Fig. 5, the manifold has a construction of being divided into three parts 21, 22 and 23, and the rib 7 of one of the electrodes has a construction of entering a little under the manifold part 21 (for instance to the position 7''). The internal edge of the manifold - - -~273~
part 22 is shown by 22'. The two parts 21 and 22 of the manifold, 22 and the separator 4 and 23 and the separator 4 are mutually joined via a fluorocarbon resin as shown by 40 in (1) of Fig. 5, respectively.
In (2) of Fig. 5, the manifold parts 21 and 22 in the above (1) has been formed in one body and the manlfold consists of the two parts 21 and 23. The rib 7 ends in the same plane 7''as the edge surface of the gas-diffusion part 6. In addition, the surface corresponding to the inner edge 22' of (1) is shown by 21'.
In (3) and (4) of Fig. 5, a structure is shown wherein one of the electrodes joined to the separator has been extended to either end of the flow passage 3 for supplying the reactant gas (the end being shown by 1'') and contacts to the inner edge of the manifold part 21.
In every case the manifold and the separator have been joined together via the fluorocarbon resin.
In addition, each structure shown in Fig. 5 is only an instance of the present invention, and the internal construction of the manifold according to the present invention can take another mode different from those shown in Fig. 5.
As has been described above, in the composite ele~trode substrate provided with the manifold according to the present invention, all the manifold and the separa-tor have been joined together via a fluorocarbon resin, ~7~
however, when the amount of leakage of the reactant gas through the manifold per the peripheral length under a definite diferential pressure per unit time is repre-sented by [the amount of leaked gas/(the side length) x (the differential pressure)]the amount is preferably less than 10 2 ml/cm.hour.mmAq which value is the same as that in the composite electrode substrate provided with the peripheral sealer.
The fluorocarbon resin used for producing the composite electrode substrate according to the present invention is generally a fluorocarbon resin of not less than 200C in the melting point, and although it is not restricted, for instance, polytetrafluoroethylene resin (abbreviated to PTEE, a melting point of 327C and a thermally deforming temperature of 121C under 4.6 kgf/cm2G), a copolymer resin of ketrafluoroethylene and hexafluoropropylene (abbreviated to FEP, a melting point of 250 to 280C and a thermally deforming temperature of 72C under 4.6 kgf/cm2G), polyfluoroalkoxyethylene resin (abbreviated to PFA, a melting point of 300 to 310C, and a thermally deforming temperature of 75C under 4.6 kgf/cm2G), fluorinated copolymer resin of ethylene and propylene (abbreviated to TFP, a melting point of 290 -300C), etc. may be mentioned. These fluorocarbon resins are commerciallized. In the above fluorocarbon resins, polytetrafluoroethylene resin is most preferable for producing the product according to the present invention.
According to the present invention, the above-mentioned fluorocarbon resin is,for instance, used as a sheet of about 50 micrometers in thickness or a dispersion of about 60 % by weight. A small amount of a surfactant may be added to the above-mentioned dispersion.
For producing the composite electrode substrate for a fuel cell according to the present invention, the electrode material and the separator are joined together by inserting a flexible graphite sheet between the elec-trode material and the separator material and applying an adhesive on both sides of the flexible graphite sheet and after calcining the thus joined materials at a temper-ature of not less than 1000C under a reduced pressure and/or in an inert atmosphere, the extended part of the separator which has been extended beyond the periphery of the electrode and the peripheral sealer,or manifold material are joined together via a sheet of a fluorocarbon resin or a dispersion of a fluorocarbon resin.
In addition, the hole 3 which is used as the flow passage of the reactant gas in the manifold of the composite electrode substrate provided with the manifold may be made in any optional stage of the process for producing the composite electrode substrate according to the present invention, for instance, before or after joining each manifold material to the separator by a suitable means.
Of course, it is preferable to make a passage connecting the hole 3 to the flow channel 5 of the reactant gas in the electrode before joining the rnanifold material thereto.
As the electrode material of the composite elec-trode substrate according to the present invention, the following substances are used:
(1) A material made by thermally molding a mixture of short carbon fibers, a binder and an organic granular substance under a pressure (refer to ~apanese Patent Application Laid-Open No. 59-68170 (1984)).
Particularly, the material prepared by molding a mixture consisting of 20 to 60 % by weight of short carbon fibers of not more than 2 mm in length, 20 to 50 % by weight of a , . .
phenol resin and 20 to 50 % by weight of an organic granular substance ~a micro-pore regulator) at a molding temperature of 100 to 180C, under a molding pressure of 2 to 100 kgf/cm2G for one to 60 min.
(2) A material made by calcining the molded material of the above-mentioned (1) at a temperature of not less than 1000C under a reduced pressure and/or in an inert atmosphere.
(3) A molded body comprising (a) gas diffusion part made of the resin-impregnated paper sheet obtained ~73~
by impregnating a paper sheet obtained from a mixture of carbon fibers of not more than 20 mm in length, at least one kind of organic fibers selected from the yroup con-sisting of pulp, regenerated cellulose fibers, polyacry-lonitrile fibers, etc. and a paper-making binder (poly-vinyl alcohol fibers, etc.) by paper-manufacturing method with a solution of a phenol resin (for instance, refer to ~apanese Patent Publication No. 53-18603 (1978)) and (b) the rib prepared by using the raw material of the above-mentioned (1).
by impregnating a paper sheet obtained from a mixture of carbon fibers of not more than 20 mm in length, at least one kind of organic fibers selected from the yroup con-sisting of pulp, regenerated cellulose fibers, polyacry-lonitrile fibers, etc. and a paper-making binder (poly-vinyl alcohol fibers, etc.) by paper-manufacturing method with a solution of a phenol resin (for instance, refer to ~apanese Patent Publication No. 53-18603 (1978)) and (b) the rib prepared by using the raw material of the above-mentioned (1).
(4) A material obtained by calcining the molded body of the above-mentioned (3) at a temperature of not less than 1000C under a reduced pressure and/or in an inert atmosphere.
As the separator material used in producing the composite electrode substrate according to the present invention, a compact carbon plate of a calcining shrinkage of not more than 0.2 % in the case of calcining it at 2000C under a reduced pressure and/or in an inert atmosphere is preférable.
As the peripheral sealer and the manifold material, a compact carbon material of a calcining shrinkage of not more than 0.2 % in the case of calcining each of them at 2000C under a reduced pressure and/or in an inert atmosphere is preferable.
~7~
he flexible graphite sheet used for producing the composite electrode substrate according to the present invention 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 treated particles, and it is preferable that the flexible graphite sheet is not more than 1 mm in thickness, has a bulk density of 1.0 to 1.5 g/cc, shows a compression strain ratio (i.e. a strain ratio to the compression load of 1 kgf/cm2) of not more than 0.35 x 10 2 cm2/kgf and has a flexibility of not breaking in the case of bending the sheet to the radius of curvature of 20 mm. Of the commerciallized flexible graphite sheet, GRAFOIL~ (made by U.C.C.) is a suitable example. -As the adhesive used on each joining surface in joining the above-mentioned electrode material with the separator material via a flexible graphite sheet, an adhesive generally used in joining carbon materials may be used, however, particularly, a thermosetting resln selected from the group consisting of phenol resins, epoxy resins, furan resins, etc. is preferable.
Although the thickness of the layer of the adhe-sive is not particularly restricted, it is generally preferable to apply uniformly the adhesive in thickness of not more than 0.5 mm thereon.
~273~
In addition, the joininy by the above-mentioned adhesive can be carried out at a temperature of 100 to 180C, under a pressure of 1.5 to 50 kgf/cm2G for a pressing time of one to 120 min.
After joining the electrode material with the separator material via the flexible graphite sheet as mentioned above, the thus joined materials are calcined at a temperature of not less than about 1000C under a reduced pressure and/or in an inert atmosphere.
Thereafter, a sheet of a fluorocarbon resin is inserted or a dispersion of the fluorocarbon resin is applied between the extended part of the separator and the surface of the peripheral sealer or the manifold material which is to be joined to the extended part, and the thus composite materials are joined by melt-adhesion of the resin at a temperature of not lower than the temperature of lower by 50C than the melting point of the fluorocar~on resin under a pressure of not less than 2 kgf/cm G while holding the pressure for not less than 10 sec.
Since the peripheral sealer of the thus obtained composite electrode substrate provided with the peripheral sealer for a fuel cell according to the present invention is formed and joined to the substrate in one body, it is not necessary, as a matter of course, to provide a special peripheral sealer for preventing the leakage of the '3~
reactant gas to the fuel cell side (such a peripheral sealer is regarded necessary in a conventional fuel cell), and at the same time, such a construction according to -the present invention has the following effect.
Namely, since the electrode and the separator are joined together in one body via the flexible graphite sheet/and the peripheral sealer and the separator are joined together in one body via the fluorocarbon resin, the thus joined material is excellent in resistance to phosphoric acid and is particularly useful as -the composite electrode substrate for a fuel cell of phosphoric acid type. In addition, since the peripheral sealers are evenly disposed and joined around the thin pl.ate-like electrode substrate while holding the separator alternate-ly in both sides, such a structure has a reinforcing effect, and as a result, the composite electrode substrate is excellent in handling in the case of producing the fuel cell.
Since the manifold of the composite electrode substrate provided with the manifold for a fuel cell according tothe present invention has been joined to the substrate in one body, the supply and the discharge of the necessary gas is made possible as a whole fuel cell through the each manifold sections of the stacked fuel cell when the reactant gas is simply introduced into the manifold, and accordingly, it is not necessary, of course, ~2~3~3~
to provide an outer manifold for supply and discharye of the reaetant gas, etc. whieh is regarded neeessary in a eonventional fuel cell, and at the same time, such a construction has the following effect:
Namely, the electrode and the separator are joined together in one body via the flexible graphite sheet, and the manifold and the separator are joined together via the fluorocarbon resin, and accordingly, the thus joined materials are excellent in resistance to phosphoric acid, and such a construction is useful as a eomposite electrode substrate for a fuel cell of phospho-ric aeid type. In addition, since the manifold are uniformly disposed and joined around the thin-plate like electrode substrate, sueh a construetion has a reinforeing effeet. As a result, sueh a eonstruction is excellent in handling in the case of producing the fuel cell.
The present invention will be explained more in detail while referring to the non-limitative examples as follows:
EXAMPLE 1:
1-1: Electrode material:
After mixing 35 % by weight of short carbon fibers (made by KUREHA KAGAKU KOGYO Co., Ltd., under the trade name of M-204S, of a mean diameter of 14 ~m and a mean length of 400 ~m), 30 % by weight of a phenol resin (ASAHI-Y~KIZAI
Co., Ltd., under the trade name of RM-210) and 35 % by ~27;~
weight of granules of polyvinyl alcohol (made by NIPPON GOSEI
KAGAKU KOGYO Co., Ltd. of a mean diameter of 180 ~m), the mixture was supplied to a prescribed metal mold and molded under the conditions of the molding temperature of 135C, the molding pressure of 35 kgf/cm2G and the pressure holding time of 20 min to obtain a ribbed electrode material of 600 mm in width, 720 mm in length and 1.5 mm in thickness.
The thickness of the rib and the thickness of the gas-diffusion part thereof were 1.0 mm and 0.5 mm, respectively.
1-2: Separator materialc A compact carbon plate of 0.8 mm in thickness (made by SHOWA DENKO Co., Ltd.) was cut into a piece of 720 mm in length and 720 mm in width to obtain the separa-tor material.
1-3: Peripheral sealers:
., . A compact'carbon plate of a bulk density of 1.85 g/cc and of a thickness of 1.5 mm (made by TOKAI
Carbon Co., Ltd.) was cut into four pieces of 60 mm in width and 720 mm in length to obtain the peripheral sealers.
1-4: Fluorocarbon resin:
A TEFLON~ sheet ~made by NICHIAS Co., Ltd. of 0.05 mm in thickness) was used as the sheet of a fluoro-carbon resin.
1-5: Flexible graphite sheet:
A GRAFOIL~ sheet (made by U.C.C., of a bulk ~ ~27~
density of 1.10 g/cc and of a thickness of 0.13 mm) was cut into pieces according to the dimension of the joining surface suitably.
After applying the adhesive of phenol resin series onto the both surface of the separator material and onto one of the sides of the GRAFOIL sheet, the thus applied adhesive was dried and the two materials were joined together at a temperature of 135C under a pressure of 10 kgf/cm G for 20 min.
Thereafter, the same adhesive was applied onto the GRAFOIL surface of the thus joined separator material and dried, and in the same manner, the same adhesive was applied onto the rib surface of the electrode material and dried. Thereafter the thus treated joined separator material and the electrode material were joined together at 135C under a pressure of 10 kgf/cm G for 20 min, and the thus joined materials were calcined at 2000C under a reduced pressure of 1 Torr and in an inert gaseous atmosphere.
Thereafter, the TEFLON sheet was inserted between the peripheral sealer and the separator, and the thus combined materials were press-joined by melt-adhesion of the TEFLON at 360C under a pressure of 20 kgf/cm G.
In order to determine the adhesive strength of the press-joined surface by the melt-adhesion, the test piece was adhered to a measure jig with an adhesive of epoxy ~z~
resin series and a tensile test was carried out. Since the exfoliation did not occur at the joining part of the TEFLON sheet and occurred at the joining part of the adhesive of epoxy resin series, it was presumed that the adhesive strength was not less than 90 kgf/cm2. Such a large adhesive strength of not less than 90 kgf/crn2 is 30 times as large as 3 kgf/cm2 of the peeling strength in the case where carbon materials are adhered with a solution type adhesive of a conventional thermosetting resin together.
EX~PLE 2:
Instead of the TEFLON sheet of Example 1, a TEFLON
dispersion (made by MITSUI Fluorochemical Co., Ltd., with an abbreviated name of PTFE, an aqueous solution containing 60 % by weight of the TEFLON) is used and applied on the joining surface of the peripheral seaIer and the separator evenly and dried in air. Thereafter, the materials were press-joined by melt-adhesion of the TEFLON under a pressure of 20 kgf/cm G at 360C. The adhesive strength of the product was the same as that in Example 1.
EXAMPLE 3:
3-1: Electrode material:
A ribbed electrode materlal of 600 mm in width, 600 mm in length and 1.5 mm in thickness was produced by using the same materials under the same conditi.ons as in ~273~
Example 1. The thickness of the rib was 1.0 mm and the thickness of the gas-diffusion part was 0.05 mm.
3-2: Separator material:
As the separator material, the same material with the same dimensions as in Example 1 was used.
3-3: Manifold material:
A compact carbon plate (made by TOKAI Carbon Co., Ltd., of a bulk density of 1.85 g/cc and 1.5 mm in thickness) was cut into two pieces of 60 mm in width and 720 mm in length and two pieces of 60 mm in width and 600 mm in length, and the each parts in the thus obtained four pieces of the plates corresponding to the each flow passages for supplying the reactant gas were cut to provide the flow passages(holes)for supplying the reactant gas therein.
Then, a pair of the plates in the four pieces of the obtained plates with the holes were respectively provided with flow passages of the reactant gas for connecting the flow passage for supplying the reactant gas in the manifold to the flow channels of the reactant gas in the electrode, by cutting the parts corresponding thereto. Thus, the four pieces of manifold materials for joining to one surface of the separator were obtained. Also, by using the above-mentioned method and the same materials in quality and size as the above-mentioned manifold materials the four pieces of manifold materials for joining to the anot~er surface of the separator were obtained.
~;~7~9~
3-4: Fluorocarbon resin:
The same TEFLO ~ sheet as in Example 1 was used as the fluorocarbon resin.
3-5: Flexible graphite sheet:
The same GRAFOI ~ sheet as in Example 1 was cut into pieces according to the dimensions of the joining surface suitably.
After applying an adhesive of phenol resin series onto the both surfaces of the separator material and onto one of the surfaces of the GRAFOIL sheet, the thus applied adhesive was dried and the two materials were joined under the conditions of 135C, 10 kgf/cm2G and 20 min.
In the next step, the above-mentioned adhesive was applied onto the surface of the above-mentioned GRAFOIL sheet and dried.
In the same manner, the above-mentioned adhesive was applied onto the rib surface of the above-mentioned electrode substrate and dried. Thereafter, the two materials were joined under the conditions of 135C, 10 kgf/cm2G and 20 min., and the thus joined materials were calcined at 2000C under a reduced pressure of 1 Torr and in an inert gaseous atmosphere.
In the next step, between the joining surfaces of the manifold material and the separator, the TEFLO ~ sheet was inserted and was joined by melt-adhesion under a pressure of 20 kgf/cm G at 360C.
~;~73~3~
In order to determine the adhesive str~nyth of press-joined surface by the melt-adhesion, the same test as in Example 1 was carried out. Since the same results as in Example 1 was obtained,the adhesive strength was presumed to be not less than 90 kgf/cm2. Such a large adhesive strength of not less than 90 kgf/cm2 is 30 times as large as 3 kgf/cm of theadhesive strength in the case where the carbon materials are adhered with a solution type adhesive of a conventional thermosetting resin.
EXAMPLE 4:
Instead of the TEFLO ~ sheet of Example 3, a TEFLO ~ dispersion (the same as in Example 2) was used, and it was applied on the joining surfaces of the manifold material and the separator evenly an~ dried in air. Thereafter, the two materials were joined together by melt-adhesion at 360C under a pressure of 20 kgf/cm G.
The adhesivestrength was the same as in Exmaple 3.
_ 29 -
As the separator material used in producing the composite electrode substrate according to the present invention, a compact carbon plate of a calcining shrinkage of not more than 0.2 % in the case of calcining it at 2000C under a reduced pressure and/or in an inert atmosphere is preférable.
As the peripheral sealer and the manifold material, a compact carbon material of a calcining shrinkage of not more than 0.2 % in the case of calcining each of them at 2000C under a reduced pressure and/or in an inert atmosphere is preferable.
~7~
he flexible graphite sheet used for producing the composite electrode substrate according to the present invention 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 treated particles, and it is preferable that the flexible graphite sheet is not more than 1 mm in thickness, has a bulk density of 1.0 to 1.5 g/cc, shows a compression strain ratio (i.e. a strain ratio to the compression load of 1 kgf/cm2) of not more than 0.35 x 10 2 cm2/kgf and has a flexibility of not breaking in the case of bending the sheet to the radius of curvature of 20 mm. Of the commerciallized flexible graphite sheet, GRAFOIL~ (made by U.C.C.) is a suitable example. -As the adhesive used on each joining surface in joining the above-mentioned electrode material with the separator material via a flexible graphite sheet, an adhesive generally used in joining carbon materials may be used, however, particularly, a thermosetting resln selected from the group consisting of phenol resins, epoxy resins, furan resins, etc. is preferable.
Although the thickness of the layer of the adhe-sive is not particularly restricted, it is generally preferable to apply uniformly the adhesive in thickness of not more than 0.5 mm thereon.
~273~
In addition, the joininy by the above-mentioned adhesive can be carried out at a temperature of 100 to 180C, under a pressure of 1.5 to 50 kgf/cm2G for a pressing time of one to 120 min.
After joining the electrode material with the separator material via the flexible graphite sheet as mentioned above, the thus joined materials are calcined at a temperature of not less than about 1000C under a reduced pressure and/or in an inert atmosphere.
Thereafter, a sheet of a fluorocarbon resin is inserted or a dispersion of the fluorocarbon resin is applied between the extended part of the separator and the surface of the peripheral sealer or the manifold material which is to be joined to the extended part, and the thus composite materials are joined by melt-adhesion of the resin at a temperature of not lower than the temperature of lower by 50C than the melting point of the fluorocar~on resin under a pressure of not less than 2 kgf/cm G while holding the pressure for not less than 10 sec.
Since the peripheral sealer of the thus obtained composite electrode substrate provided with the peripheral sealer for a fuel cell according to the present invention is formed and joined to the substrate in one body, it is not necessary, as a matter of course, to provide a special peripheral sealer for preventing the leakage of the '3~
reactant gas to the fuel cell side (such a peripheral sealer is regarded necessary in a conventional fuel cell), and at the same time, such a construction according to -the present invention has the following effect.
Namely, since the electrode and the separator are joined together in one body via the flexible graphite sheet/and the peripheral sealer and the separator are joined together in one body via the fluorocarbon resin, the thus joined material is excellent in resistance to phosphoric acid and is particularly useful as -the composite electrode substrate for a fuel cell of phosphoric acid type. In addition, since the peripheral sealers are evenly disposed and joined around the thin pl.ate-like electrode substrate while holding the separator alternate-ly in both sides, such a structure has a reinforcing effect, and as a result, the composite electrode substrate is excellent in handling in the case of producing the fuel cell.
Since the manifold of the composite electrode substrate provided with the manifold for a fuel cell according tothe present invention has been joined to the substrate in one body, the supply and the discharge of the necessary gas is made possible as a whole fuel cell through the each manifold sections of the stacked fuel cell when the reactant gas is simply introduced into the manifold, and accordingly, it is not necessary, of course, ~2~3~3~
to provide an outer manifold for supply and discharye of the reaetant gas, etc. whieh is regarded neeessary in a eonventional fuel cell, and at the same time, such a construction has the following effect:
Namely, the electrode and the separator are joined together in one body via the flexible graphite sheet, and the manifold and the separator are joined together via the fluorocarbon resin, and accordingly, the thus joined materials are excellent in resistance to phosphoric acid, and such a construction is useful as a eomposite electrode substrate for a fuel cell of phospho-ric aeid type. In addition, since the manifold are uniformly disposed and joined around the thin-plate like electrode substrate, sueh a construetion has a reinforeing effeet. As a result, sueh a eonstruction is excellent in handling in the case of producing the fuel cell.
The present invention will be explained more in detail while referring to the non-limitative examples as follows:
EXAMPLE 1:
1-1: Electrode material:
After mixing 35 % by weight of short carbon fibers (made by KUREHA KAGAKU KOGYO Co., Ltd., under the trade name of M-204S, of a mean diameter of 14 ~m and a mean length of 400 ~m), 30 % by weight of a phenol resin (ASAHI-Y~KIZAI
Co., Ltd., under the trade name of RM-210) and 35 % by ~27;~
weight of granules of polyvinyl alcohol (made by NIPPON GOSEI
KAGAKU KOGYO Co., Ltd. of a mean diameter of 180 ~m), the mixture was supplied to a prescribed metal mold and molded under the conditions of the molding temperature of 135C, the molding pressure of 35 kgf/cm2G and the pressure holding time of 20 min to obtain a ribbed electrode material of 600 mm in width, 720 mm in length and 1.5 mm in thickness.
The thickness of the rib and the thickness of the gas-diffusion part thereof were 1.0 mm and 0.5 mm, respectively.
1-2: Separator materialc A compact carbon plate of 0.8 mm in thickness (made by SHOWA DENKO Co., Ltd.) was cut into a piece of 720 mm in length and 720 mm in width to obtain the separa-tor material.
1-3: Peripheral sealers:
., . A compact'carbon plate of a bulk density of 1.85 g/cc and of a thickness of 1.5 mm (made by TOKAI
Carbon Co., Ltd.) was cut into four pieces of 60 mm in width and 720 mm in length to obtain the peripheral sealers.
1-4: Fluorocarbon resin:
A TEFLON~ sheet ~made by NICHIAS Co., Ltd. of 0.05 mm in thickness) was used as the sheet of a fluoro-carbon resin.
1-5: Flexible graphite sheet:
A GRAFOIL~ sheet (made by U.C.C., of a bulk ~ ~27~
density of 1.10 g/cc and of a thickness of 0.13 mm) was cut into pieces according to the dimension of the joining surface suitably.
After applying the adhesive of phenol resin series onto the both surface of the separator material and onto one of the sides of the GRAFOIL sheet, the thus applied adhesive was dried and the two materials were joined together at a temperature of 135C under a pressure of 10 kgf/cm G for 20 min.
Thereafter, the same adhesive was applied onto the GRAFOIL surface of the thus joined separator material and dried, and in the same manner, the same adhesive was applied onto the rib surface of the electrode material and dried. Thereafter the thus treated joined separator material and the electrode material were joined together at 135C under a pressure of 10 kgf/cm G for 20 min, and the thus joined materials were calcined at 2000C under a reduced pressure of 1 Torr and in an inert gaseous atmosphere.
Thereafter, the TEFLON sheet was inserted between the peripheral sealer and the separator, and the thus combined materials were press-joined by melt-adhesion of the TEFLON at 360C under a pressure of 20 kgf/cm G.
In order to determine the adhesive strength of the press-joined surface by the melt-adhesion, the test piece was adhered to a measure jig with an adhesive of epoxy ~z~
resin series and a tensile test was carried out. Since the exfoliation did not occur at the joining part of the TEFLON sheet and occurred at the joining part of the adhesive of epoxy resin series, it was presumed that the adhesive strength was not less than 90 kgf/cm2. Such a large adhesive strength of not less than 90 kgf/crn2 is 30 times as large as 3 kgf/cm2 of the peeling strength in the case where carbon materials are adhered with a solution type adhesive of a conventional thermosetting resin together.
EX~PLE 2:
Instead of the TEFLON sheet of Example 1, a TEFLON
dispersion (made by MITSUI Fluorochemical Co., Ltd., with an abbreviated name of PTFE, an aqueous solution containing 60 % by weight of the TEFLON) is used and applied on the joining surface of the peripheral seaIer and the separator evenly and dried in air. Thereafter, the materials were press-joined by melt-adhesion of the TEFLON under a pressure of 20 kgf/cm G at 360C. The adhesive strength of the product was the same as that in Example 1.
EXAMPLE 3:
3-1: Electrode material:
A ribbed electrode materlal of 600 mm in width, 600 mm in length and 1.5 mm in thickness was produced by using the same materials under the same conditi.ons as in ~273~
Example 1. The thickness of the rib was 1.0 mm and the thickness of the gas-diffusion part was 0.05 mm.
3-2: Separator material:
As the separator material, the same material with the same dimensions as in Example 1 was used.
3-3: Manifold material:
A compact carbon plate (made by TOKAI Carbon Co., Ltd., of a bulk density of 1.85 g/cc and 1.5 mm in thickness) was cut into two pieces of 60 mm in width and 720 mm in length and two pieces of 60 mm in width and 600 mm in length, and the each parts in the thus obtained four pieces of the plates corresponding to the each flow passages for supplying the reactant gas were cut to provide the flow passages(holes)for supplying the reactant gas therein.
Then, a pair of the plates in the four pieces of the obtained plates with the holes were respectively provided with flow passages of the reactant gas for connecting the flow passage for supplying the reactant gas in the manifold to the flow channels of the reactant gas in the electrode, by cutting the parts corresponding thereto. Thus, the four pieces of manifold materials for joining to one surface of the separator were obtained. Also, by using the above-mentioned method and the same materials in quality and size as the above-mentioned manifold materials the four pieces of manifold materials for joining to the anot~er surface of the separator were obtained.
~;~7~9~
3-4: Fluorocarbon resin:
The same TEFLO ~ sheet as in Example 1 was used as the fluorocarbon resin.
3-5: Flexible graphite sheet:
The same GRAFOI ~ sheet as in Example 1 was cut into pieces according to the dimensions of the joining surface suitably.
After applying an adhesive of phenol resin series onto the both surfaces of the separator material and onto one of the surfaces of the GRAFOIL sheet, the thus applied adhesive was dried and the two materials were joined under the conditions of 135C, 10 kgf/cm2G and 20 min.
In the next step, the above-mentioned adhesive was applied onto the surface of the above-mentioned GRAFOIL sheet and dried.
In the same manner, the above-mentioned adhesive was applied onto the rib surface of the above-mentioned electrode substrate and dried. Thereafter, the two materials were joined under the conditions of 135C, 10 kgf/cm2G and 20 min., and the thus joined materials were calcined at 2000C under a reduced pressure of 1 Torr and in an inert gaseous atmosphere.
In the next step, between the joining surfaces of the manifold material and the separator, the TEFLO ~ sheet was inserted and was joined by melt-adhesion under a pressure of 20 kgf/cm G at 360C.
~;~73~3~
In order to determine the adhesive str~nyth of press-joined surface by the melt-adhesion, the same test as in Example 1 was carried out. Since the same results as in Example 1 was obtained,the adhesive strength was presumed to be not less than 90 kgf/cm2. Such a large adhesive strength of not less than 90 kgf/cm2 is 30 times as large as 3 kgf/cm of theadhesive strength in the case where the carbon materials are adhered with a solution type adhesive of a conventional thermosetting resin.
EXAMPLE 4:
Instead of the TEFLO ~ sheet of Example 3, a TEFLO ~ dispersion (the same as in Example 2) was used, and it was applied on the joining surfaces of the manifold material and the separator evenly an~ dried in air. Thereafter, the two materials were joined together by melt-adhesion at 360C under a pressure of 20 kgf/cm G.
The adhesivestrength was the same as in Exmaple 3.
_ 29 -
Claims (20)
1. A composite electrode substrate for a fuel cell comprising (1) a separator, (2) a porous carbonaceous electrode provided with flow channels for reactant gas, said electrode being joined to both surfaces of said separator via a flexible graphite sheet so that said separator extends beyond the periphery of said electrode, and (3) a peripheral sealer comprising compact gas-impermeable carbon material disposed on a side of said electrode parallel to said flow channels therein or a manifold comprising a compact gas-impermeable carbon plate and provided with a flow passage for supplying reactant gas, said peripheral sealer or manifold being joined to the extended part of said separator via tetrafluoroethylene resin layer.
2. A composite electrode substrate according to claim 1, wherein said porous carbonaceous electrode has a bulk density of 0.3 to 0.9 g/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 after having been calcined at a temperature of not less than 1000°C
under a reduced pressure and/or in an inert atmosphere.
under a reduced pressure and/or in an inert atmosphere.
3. A composite electrode substrate according to claim 1, wherein said separator has a bulk density of not less than 1.4 g/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 2 mm.
4. A composite electrode substrate according to claim 1, wherein said peripheral sealer and said manifold respectively have a bulk density of not less than 1.4 g/cc and a gas permeability of not more than 10-4 ml/cm2.hour.mmAq.
5. A composite electrode substrate according to claim 1, wherein said manifold has been formed by joining compact gas-impermeable carbon materials via said tetrafluoroethylene resin layer.
6. A composite electrode substrate according to claim 1, wherein said flexible graphite sheet has been produced by compressing expanded graphite particles.
7. A composite electrode substrate according to claim 1, wherein said flexible graphite sheet has been produced by compressing 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, and has a thickness of not more than 1 mm, a bulk density of 1.0 to 1.5 g/cc, a rate of compression strain of not more than 0.35 x 10-2 cm2/kgf and a flexibility of not being broken when bent to the radius of curvature of 20 mm.
8. A composite electrode substrate according to claim 1, wherein said porous carbonaceous electrodes have been joined to both surfaces of said separator via said flexible graphite sheet so that flow channels for reactant gas in one of said electrodes are perpendicular to those in another said electrode, and a pair of said peripheral sealers have been joined to the extended parts of said separator via said tetrafluoroethylene resin layer so that said peripheral sealer is disposed on a side of said electrode parallel to said flow channels therein.
9. A process for producing a composite electrode substrate for a fuel cell comprising (1) preparing (A) a separator material; (B) a porous carbonaceous electrode material provided with flow channels for reactant gas and having smaller area than the separator material; (C) a peripheral sealer comprising a compact gas-impermeable carbon material;
(D) a manifold comprising a compact gas-impermeable carbon material; (E) a flexible graphite sheet; (F) a tetrafluoroethylene resin and (G) an adhesive, (2) joining said electrode material to both surfaces of said separator material by said adhesive while interposing said graphite sheet between said electrode material and said separator material so that said separator material extends beyond the periphery of said electrode material, (3) calcining the thus joined materials at a temperature of not less than 1000°C under a reduced pressure and/or in an inert atmosphere, thereby producing an electrode substrate part material wherein a porous carbonaceous electrode is joined to both surfaces of a separator via said flexible graphite sheet, and (4) joining said peripheral sealer or said manifold to the extended part of said separator via said tetrafluoroethylene resin, wherein said peripheral sealer is disposed on a side of said electrode parallel to flow channels therein.
(D) a manifold comprising a compact gas-impermeable carbon material; (E) a flexible graphite sheet; (F) a tetrafluoroethylene resin and (G) an adhesive, (2) joining said electrode material to both surfaces of said separator material by said adhesive while interposing said graphite sheet between said electrode material and said separator material so that said separator material extends beyond the periphery of said electrode material, (3) calcining the thus joined materials at a temperature of not less than 1000°C under a reduced pressure and/or in an inert atmosphere, thereby producing an electrode substrate part material wherein a porous carbonaceous electrode is joined to both surfaces of a separator via said flexible graphite sheet, and (4) joining said peripheral sealer or said manifold to the extended part of said separator via said tetrafluoroethylene resin, wherein said peripheral sealer is disposed on a side of said electrode parallel to flow channels therein.
10. A process according to claim 9, wherein said porous carbonaceous electrode material is formed by a process selected from the group consisting of:
(1) thermally molding a mixture of short carbon fibers, a binder and an organic granular substance under a pressure into one body, (2) calcining a molded material formed by the process (1) above under a reduced pressure and/or in an inert atmosphere, (3) joining (a) a gas-diffusion part comprising resin impregnated paper sheet prepared by impregnating with a solution of phenol resin a paper sheet obtained from short carbon fibers, at least one kind of organic fibers selected from the group consisting of pulp, regenerated cellulose fibers and polyacrylonitrile fibers and a binder for paper-making by paper-manufacturing methods and (b) a rib formed by a process as in (1) above, and (4) calcining a material formed by the process (3) above under a reduced pressure and/or in an inert atmosphere.
(1) thermally molding a mixture of short carbon fibers, a binder and an organic granular substance under a pressure into one body, (2) calcining a molded material formed by the process (1) above under a reduced pressure and/or in an inert atmosphere, (3) joining (a) a gas-diffusion part comprising resin impregnated paper sheet prepared by impregnating with a solution of phenol resin a paper sheet obtained from short carbon fibers, at least one kind of organic fibers selected from the group consisting of pulp, regenerated cellulose fibers and polyacrylonitrile fibers and a binder for paper-making by paper-manufacturing methods and (b) a rib formed by a process as in (1) above, and (4) calcining a material formed by the process (3) above under a reduced pressure and/or in an inert atmosphere.
11. A process according to claim 9, wherein said separator material is formed of a compact carbon plate which shows a calcining shrinkage of not more than 0.2 when it is calcined at 2000°C under a reduced pressure and/or in an inert atmosphere.
12. A process according to claim 9, wherein said peripheral sealer and said manifold are respectively formed of a compact carbon material which shows a calcining shrinkage of not more than 0.2% when it is calcined at 2000°C under a reduced pressure and/or in an inert atmosphere.
13. A process according to claim 9, wherein said flexible graphite sheet is produced by compressing expanded graphite particles.
14. A process according to claim 9, wherein said flexible graphite sheet is produced by compressing 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, and has a thickness of not more than 1 mm, a bulk density of 1.0 to 1.5 g/cc, a rate of compression strain of not more than 0.35 x 10-2 cm2/kgf and a flexibility of not being broken when bent to the radius of curvature of 20 mm.
15. A process according to claim 9, wherein said adhesive for joining said electrode material to said separator material is a thermosetting resin selected from the group consisting of phenol resins, epoxy resins and furan resins.
16. A process according to claim 9, wherein said electrode material is joined to the surface of said separator material by said adhesive via said graphite sheet by pressing them under a condition of a temperature of 100 to 180°C, a pressure of 1.5 to 50 kgf/cm2G and a pressure holding time of 1 to 120 min.
17. A process according to claim 9, wherein said peripheral sealer and said manifold are respectively joined to the extended parts of said separator via said tetrafluoroethylene resin by pressing them under a condition of a pressure of not less than 2 kgf/cm2G and a temperature of not lower than the temperature which is lower by 50°C than the melting temperature of said tetrafluoroethylene resin.
18. A process according to claim 9, wherein said porous carbonaceous electrode materials are joined to both surfaces of said separator material via said flexible graphite sheet so that flow channels for reactant gas in one of said electrode material are perpendicular to those in another said electrode material, and a pair of said peripheral sealers are joined to the extended parts of said separator material via said tetrafluoroethylene resin so that said peripheral sealer is disposed on a side of said electrode parallel to said flow channels therein.
19. A process according to claim 9, which process further comprising making a flow passage for supplying reactant gas in said manifold before or after joining said manifold to the extended part of said separator.
20. A process according to claim 9, wherein said manifold is formed by joining compact gas-impermeable carbon materials together via said tetrafluoroethylene resin.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP60221439A JPS6282664A (en) | 1985-10-04 | 1985-10-04 | Electrode substrate for manifold mounted fuel cell and its manufacture |
| JP221439/85 | 1985-10-04 | ||
| JP60238684A JPS6298570A (en) | 1985-10-25 | 1985-10-25 | Electrode substrate for end seal-mounting fuel cell and its manufacture |
| JP238684/85 | 1985-10-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1273991A true CA1273991A (en) | 1990-09-11 |
Family
ID=26524301
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000519756A Expired - Fee Related CA1273991A (en) | 1985-10-04 | 1986-10-03 | Composite electrode substrate for a fuel cell and process for producing the same |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1273991A (en) |
-
1986
- 1986-10-03 CA CA000519756A patent/CA1273991A/en not_active Expired - Fee Related
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