Coating processes – Electrical product produced – Fuel cell part
Reexamination Certificate
2003-05-29
2004-02-03
Talbot, Brian K. (Department: 1762)
Coating processes
Electrical product produced
Fuel cell part
C427S372200, C427S388400, C427S402000, C029S623500
Reexamination Certificate
active
06685984
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for the production of a multilayer of an electrode and an electrolyte membrane suitable for use in fuel cells.
BACKGROUND OF THE INVENTION
In general, fuel cells include a unit of an electrode and an electrolyte membrane.
It is a conventional practice in producing the electrode-electrolyte units that a hydrogen reduction catalyst carried on carbon is mixed with an electrolyte, the resultant electrode paste is applied on carbon paper and heated to form an electrode, and an electrolyte filmy membrane is sandwiched between two electrodes so that a three-layered anode/electrolyte/cathode unit is obtained by hot pressing the superposed membranes.
However, such three-layer bonding methods as mentioned above have technical problems that, for example, interlaminar adhesion is poor, the three-layer integral bonding takes long to complete and mass production cannot be expected since the layers have to be produced individually.
Further, the electrolyte membrane of high heat resistance, for which a demand has been growing recently, has a problem that its thermoplasticity is so insufficient that some restrictions should apply in thermal adhesion.
With such a problem, it has been proposed that a coating solution obtained by dissolving a compound for forming an electrolyte membrane in a solvent can be applied on a previously prepared electrode and thereafter dried.
However, such coating solutions containing the dissolved electrolyte of high heat resistance, will penetrate into the electrodes upon application thereon so that sufficient power generation properties cannot be obtained.
OBJECT OF THE INVENTION
It is an object of the invention to obtain multilayers capable of satisfactory power generation properties as an electrode structure by forming an electrolyte membrane on an electrode without causing any penetration of electrolyte into the electrode.
SUMMARY OF THE INVENTION
The invention provides the following method of producing a multilayer to achieve the above object.
(1) A method for the production of a multilayer comprising an electrode and an electrolyte membrane, the method comprising:
applying a coating solution (I) which comprises a dissolved or dispersed proton-conductive polymer and a solvent (Is) containing water in amounts from 25 to 60 wt % and an organic solvent in amounts from 75 down to 40 wt %, on an electrode;
applying a coating solution (II) which comprises a dissolved or dispersed proton-conductive polymer and a solvent (IIs) containing water in amounts from 0 to less than 25 wt % and an organic solvent in amounts above 75 wt %, on the first coating without any drying of the first coating; and
drying the coatings to form an electrolyte membrane.
(2) The method for the production of an multilayer according to above (1), wherein the proton-conductive polymer is sulfonated polyarylene.
(3) The method for the production of a multilayer according to above (1) or (2), wherein the solvent (Is) contains water in amounts from 30 to 50 wt % and an organic solvent in amounts from 70 down to 50 wt %.
(4) The method for the production of a multilayer according to any of above (1) to (3), wherein the solvent (IIs) contains water in amounts from 10 to 20 wt % and an organic solvent in amounts from 90 down to 80 wt %.
(5) The method for the production of a multilayer according to any of above (1) to (4), wherein the coating solution (I) contains the proton-conductive polymer in amounts from 0.1 to 10 wt %.
(6) The method for the production of a multilayer according to any of above (1) to (5), wherein the coating solution (II) contains the proton-conductive polymer in amounts from 5 to 20 wt %.
(7) The method for the production of a multilayer according to any of above (1) to (6), wherein the organic solvent is at least one solvent selected from the group consisting of tetrahydrofuran, cyclohexanone, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, &ggr;-butyrolactone and &ggr;-butyrolactam, preferably from the group consisting of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide and N-methyl-2-pyrrolidone.
PREFERRED EMBODIMENTS OF THE INVENTION
The methods for the production of multilayers of the invention will be described in detail hereinafter.
In the methods, two kinds of coating solutions are used. They are obtained by dissolving or dispersing the proton-conductive polymer in the solvent which is different from the other in the water content. The coating solution with larger water content is first applied on an electrode, the one with smaller water content is thereafter applied on the undried first coating, and these coatings are dried to form an electrolyte membrane, thus a multilayer comprising the electrode and the electrolyte membrane is obtained.
Electrode
The electrode for use in the invention is obtained by coating a gas diffusion electrode substrate with a paste which comprises fine particles of catalyst capable of hydrogen reduction supported on conductive porous particles and a proton-conductive polyelectrolyte component.
The conductive porous particles used herein have high structures and large surface areas, e.g., Ketjen black and acetylene black. Examples of the catalyst capable of hydrogen reduction include noble metals, such as platinum, palladium, ruthenium and rhodium; and alloys of these metals and other metals such as chromium, molybdenum, tungsten, titanium, zirconium and cobalt. The amount of the catalyst supported is usually in the range of 10 to 60 wt % based on the conductive porous particles. The paste is applied to a porous gas diffusion electrode substrate, such as carbon paper or carbon cloth, by means of a doctor blade or a spray, so that the electrode is obtained.
The electrode generally ranges from 5 to 100 &mgr;m, preferably 5 to 50 &mgr;m in the thickness.
Proton-conductive Polymer
Examples of the proton-conductive polymer for the electrolyte membrane include sulfonated polyarylene, sulfonated polyarylene ether, sulfonated polyarylene ketone, sulfonated polybenzimidazole and tetrafluoroethylene copolymers. Of these, sulfonated polyarylene is preferred in order to obtain an electrode structure having good electric characteristics.
The sulfonated polyarylene is prepared by sulfonating a polymer which results from the reaction of a monomer (A) of the following formula (A) with at least one monomer (B) selected from the following monomers (B-1) to (B-4).
In the formula (A), R and R′, which may be the same or different, are independently a halogen atom other than a fluorine atom or a —OSO
2
Z group (Z is an alkyl group, a fluorine-substituted alkyl group or an aryl group).
Examples of the alkyl group indicated by Z include methyl and ethyl; those of the fluorine-substituted alkyl group include trifluoromethyl; and those of the aryl group include phenyl and p-tolyl.
R
1
to R
8
, which may be the same or different, are independently at, least one atom or group selected from the group consisting of hydrogen, a fluorine atom, and alkyl, fluorine-substituted alkyl, allyl and aryl groups.
Examples of the alkyl groups include methyl, ethyl, propyl, butyl, amyl and hexyl. Of these, methyl, ethyl and the like are preferred.
Examples of the fluorine-substituted alkyl groups include trifluoromethyl, perfluoroethyl, perfluoropropyl, perfluorobutyl, perfluoropentyl and perfluorohexyl. Of these, trifluoromethyl, pentafluoroethyl and the like are preferred.
Examples of, the allyl groups include propenyl.
Examples of the aryl groups include phenyl and pentafluorophenyl.
X is a divalent electron attracting group, e.g., —CO—, —CONH—, —(CF
2
)
p
— (p is an integer of 1 to 10), —C(CF
3
)
2
—, —COO—, —SO— and —SO
2
—.
The electron attracting group can be defined as having a Hammett substituent constant of not less than 0.06 in the case of a phenyl group at the m-position and not less than 0.01 in the case of the p-position.
Y is a divalent electron donating group, e.g., —O—, —S—, —CH═CH—, —C≡C— and groups represented by the following form
Asano Yoichi
Goto Kohei
Higami Makoto
Kakutani Osamu
Okiyama Gen
Arent Fox Kintner & Plotkin & Kahn, PLLC
JSR Corporation
Talbot Brian K.
LandOfFree
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