JP2006164628A - Electrolyte film and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive electrolyte film of high productivity, by restraining permeation of fuel in the case that the electrolyte film for a fuel cell of a structure of an electrolyte polymer filled in pores of a porous base material is directly applied to a methanol fuel cell, and solving a problem in which durability is low. <P>SOLUTION: Of the electrolyte film made by filling a polymer having an ion-exchange group as an electrolyte polymer 13 in pores of the porous base material 12, a part contributing to power generation alone pinched by a pair of electrodes is to be an ion-conductive part, with the surroundings made non-ion-conductive, whereby, unnecessary fuel crossover is restrained, and at the same time, durability is improved in case of operation as a fuel cell. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrolyte membrane and a fuel cell, and the electrolyte membrane is suitable for electrochemical devices, particularly for fuel cells, and more specifically for direct alcohol fuel cell applications.

  Fuel cells, a type of electrochemical device that uses polymer electrolyte membranes, have recently gained attention as low-pollution automotive power sources and high-efficiency power generation methods due to the remarkable improvement in performance due to the development of electrolyte membranes and catalyst technology. . A fuel cell (polymer electrolyte fuel cell) using a polymer electrolyte membrane has a structure in which reaction layers (electrodes) having oxidation and reduction catalysts are formed on both sides of the membrane. In a polymer electrolyte fuel cell, a reaction occurs in which hydrogen molecules are decomposed into protons and electrons at the fuel electrode, and the generated electrons are transported to the oxygen electrode side by operating electrical components through electric wires. Water is generated from oxygen, protons, and electrons carried from the fuel electrode through electric wires. In a direct methanol fuel cell (DMFC, Direct Methanol Fuel Cell), methanol and water are supplied to the fuel electrode, and protons are extracted by reacting methanol and water with a catalyst in the vicinity of the membrane. In these fuel cells, an electrolyte membrane made of polyperfluoroalkylsulfonic acid is usually used.

  However, when a polyperfluoroalkylsulfonic acid membrane is used in a fuel cell that directly supplies a solution fuel such as DMFC to a battery cell, there is a problem that fuel such as methanol passes through the membrane and energy loss occurs. In addition, since the membrane area is greatly changed by swelling with a fuel such as methanol, there is a problem that the fuel concentration cannot be increased because the junction between the electrode and the membrane is easily peeled off. In addition, since it has fluorine atoms, there is an economic problem that the material itself is expensive, and the manufacturing process is complicated and the productivity is low.

  For this reason, there has been a demand for a polymer electrolyte membrane made of a hydrocarbon skeleton, which suppresses methanol permeation when DMFC is used. The electrolyte membrane for fuel cells disclosed in Patent Document 1 by the present inventors is formed by filling a porous base material with an inexpensive proton conductive polymer, and the porous base material is polyimide, crosslinked polyethylene, etc. In contrast, the proton conductive polymer filled in the pores can be prevented from excessive swelling due to the methanol aqueous solution, and as a result, the permeation of methanol can be suppressed. is there.

  Such an electrolyte membrane is characterized in that methanol permeation can be suppressed, but permeation cannot be completely suppressed. Further, as a result of studies by the present inventors, it was found that methanol was permeated from the outside of the portion in contact with the electrode when a membrane electrode assembly (MEA) was formed. That is, a normal DMFC has a gap (6) at the boundary between the electrode and gasket as shown in FIG. 1 when the MEA is assembled in the battery, so that gas or fuel flows directly into the gap, carbon paper, carbon cloth, etc. It oozes out from the electrode composed of the electrode and easily comes into direct contact with the electrolyte membrane, from which fuel and gas may permeate to the opposite electrode. Further, when this gap is narrowed so that the electrode and the gasket are in contact with each other, the permeation amount of methanol is reduced, but it is permeated from the boundary portion by an action such as capillary action.

  When such an electrolyte membrane is operated as a DMFC for a long time until the voltage drops, and the membrane inside the fuel cell is examined in detail, it contributes to power generation in which the electrolyte membrane corresponding to 10 in FIG. 1 is sandwiched between electrodes. As shown in FIG. 2, the electrolyte polymer filled in the pores of the porous substrate was sufficiently retained. Compared to this, the outer portion of the electrode corresponding to the portion 11 in FIG. 1 deteriorates quickly, and the electrolyte polymer escapes from the pores of the porous substrate as shown in FIG. It has been found that there is a problem that the oxidant easily passes through the membrane.

  Further, in Patent Document 2, it has been proposed to integrate an electrolyte membrane filled with electrolyte in pores of a porous substrate and a gasket. In this case, water in the electrolyte evaporates and the gasket and the electrolyte membrane are separated. The purpose is to prevent the gap from peeling off, and it is not described that the gap between the gasket and the electrode, which is one form of the proposal in the present invention, is not described, and is different from the purpose of preventing the deterioration of the electrolyte membrane. It is.

  Patent Document 3 describes a method in which an electrolyte membrane is divided into a porous portion and a non-porous portion. However, the method for forming an electrolyte membrane is that a micropore itself is formed by photolithography, which is a porous substrate. The material is limited to a photosensitive material and has a problem in productivity.

  Patent Document 4 proposes a method of laminating a cover sheet film with a hot-melt layer formed by hollowing out an electrode portion when forming an MEA with an electrolyte membrane protruding from the electrode. The electrolyte membrane is not referred to, but the wrinkles of the electrolyte membrane are eliminated so that the gas does not leak out from the wrinkled portion.

JP 2002-83612 A JP 2003-229140 A WO2002 / 059996 JP-A-11-45729

  The present invention has a problem that the permeation of fuel is suppressed and the durability is low when the electrolyte membrane for a fuel cell having a structure in which the electrolyte polymer is filled in the pores of the porous substrate as described above is applied to DMFC. In order to eliminate this point, the present inventors have studied to provide an electrolyte membrane that is highly productive and inexpensive.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have made a pair of electrodes out of an electrolyte membrane formed by filling a pore of a porous substrate with a polymer having an ion exchange group as an electrolyte polymer. Only the part that contributes to the sandwiched power generation is made into an ionic conduction part, and its periphery is made into a non-ion conduction part, so that unnecessary fuel crossover can be suppressed and at the same time the durability when operated as a fuel cell can be improved. I found. Further, it has been found that the same effect can be obtained by filling the boundary between the gasket and the electrode with a nonionic conductive polymer when the MEA is incorporated into the fuel cell without forming the nonionic conductive portion in the electrolyte membrane. The present invention has been completed.

  The electrolyte membrane of the present invention can suppress methanol permeation, which has been a problem when using an electrolyte membrane in which a porous base material is filled with a conventionally used hydrocarbon-based electrolyte polymer, and is durable. This is an improvement of the problem. Therefore, the electrolyte membrane of the present invention has both output characteristics and durability as a fuel cell and is extremely useful for applications such as a fuel cell.

The present invention will be described in detail below.
The electrolyte membrane and the fuel cell of the present invention provide a crossover of fuel when a polymer electrolyte membrane formed by filling a pore of a porous substrate with a polymer having an ion exchange group (electrolyte polymer) is used for a fuel cell. In addition, the durability is improved as compared with the conventional electrolyte membrane and fuel cell.

  The porous substrate used in the present invention is preferably a material that does not substantially swell with respect to methanol and water, and it is desirable that there is little or almost no change in area when wetted with water, especially when dry. The area increase rate when the porous substrate is immersed in methanol or water varies depending on the immersion time and temperature. In the present invention, the area increase rate when immersed in pure water at 25 ° C. for 1 hour is compared with that at the time of drying. Therefore, it is preferably 20% or less at the maximum.

  As the material of the porous substrate, a polyolefin-based polymer is chemically stable, and a substrate having fine pores can be continuously produced by a stretching method, which is preferable. In addition, since it is easy to close the pores by heating, it is also preferable in that the step of closing the pores of the porous base material can be easily performed in order to form the nonionic conductive portion. Those made of polyolefin which has been cross-linked after stretching are preferred because of good mechanical properties such as strength.

  The porosity of the porous substrate used in the present invention is preferably 5 to 95%, more preferably 5 to 90%, and particularly preferably 20 to 60%. Moreover, it is preferable that an average hole diameter exists in the range of 0.001-100 micrometers, More preferably, it is the range of 0.01-1 micrometer. If the porosity is too small, the number of ion exchange groups per area is too small and the output of the fuel cell is low, and if it is too large, the membrane strength decreases, which is not preferable. The thickness of the substrate is preferably 200 μm or less, more preferably 1 to 150 μm, still more preferably 5 to 100 μm, and particularly preferably 10 to 50 μm. If the film thickness is too thin, the film strength decreases and the amount of permeated methanol also increases. If the film thickness is too thick, the film resistance becomes too large and the output of the fuel cell is low, which is not preferable.

  In the present invention, when the fuel cell MEA is formed, the portion sandwiched between the electrodes has ion conductivity, and the ion conduction portion is filled with a polymer having an ion exchange group in the pores of the porous substrate. Become. There are two methods for forming such a structure, one of which is to make the electrolyte membrane itself divided into an ionic conduction part and a non-ion conduction part, and the second is that the entire surface has ionic conductivity. This is a method of protecting a predetermined pattern such as a portion other than a portion sandwiched between electrodes with a non-ion conductive polymer.

When the electrolyte membrane is prepared by dividing it into an ionic conductive part and a non-ionic conductive part, the method is to use a non-ionic conductive polymer in advance in the part corresponding to the part to be the non-ionic conductive part in the porous substrate. A method of filling or coating or fusing, a method of closing pores, and the like can be used. FIG. 4 shows a cross-sectional view when an electrolyte membrane filled with a nonionic conductive polymer is incorporated in a battery. A portion corresponding to the gap between the electrode and the gasket in the electrolyte membrane has a non-ion conducting portion, and fuel crossover hardly occurs in this portion.
The non-ion conductive polymer filled in the non-ion conductive part does not contain an ion exchange group, or even if it contains a small amount, it does not substantially exhibit ionic conductivity. Moreover, it is preferable that it is hydrophobic.

  As a method of filling the nonionic conductive part with a nonionic conductive polymer, a predetermined pattern is obtained after filling with an active energy ray-curable compound that becomes a nonionic conductive polymer by irradiation of active energy rays such as ultraviolet rays. Thus, after exposing and developing to expose the porous substrate, there is a method of forming an electrolyte polymer in the pores that are not closed. In addition, a nonionic conductive polymer that can be melted by heating is melted and applied to a predetermined pattern of a porous substrate, or a nonionic conductive polymer that is not in the form of a sheet is formed into a predetermined pattern of a porous substrate. And a method of laminating and thermocompression bonding. Alternatively, a method of closing the pores by heating in a predetermined pattern at a temperature near the melting point of the porous substrate can be used.

  Among the above methods, a nonionic conductive polymer that can be melted by heating is melted and applied in a predetermined pattern, or a sheet-like nonionic conductive polymer is laminated on a predetermined pattern of a porous substrate and thermocompression bonded Then, a hot melt adhesive or a polyethylene film can be preferably used, and a polyolefin hot melt adhesive (for example, trade name PPET, manufactured by Toagosei Co., Ltd.) can be preferably used.

  On the other hand, when impregnating a porous substrate with a compound that can become a non-ion conductive polymer for polymerization, a pattern is formed by a photolithographic method using an active energy ray curable compound (hereinafter referred to as a photocurable resin). It is preferable to do. When the monomer is filled only in a predetermined pattern of the porous substrate by a method such as coating, the monomer may soak into the portion to be filled with the electrolyte polymer later by capillary action to obtain the necessary shape. Have difficulty. For this reason, the method using a photocurable resin can be used preferably. The photo-curable resin is used for various applications such as a photoresist. For example, a radical polymerization type such as an acrylic resin and a cationic polymerization type such as an epoxy, oxetane, and a vinyl ether resin can be preferably used. When using a photo-curing resin, impregnate the entire porous substrate once, and use a photomask or the like to prevent the light from hitting the part corresponding to the place where the electrolyte polymer is filled, such as active energy such as ultraviolet rays. Irradiate the line to cure the necessary parts. Next, the porous substrate corresponding to the place where the electrolyte polymer is filled is exposed by dissolving and developing the uncured portion that is not exposed to the active energy ray using a solvent or the like.

  In this way, by creating a base material in which a porous portion is mixed with a porous portion or a porous portion, and filling the porous portion with an electrolyte polymer or polymerizing the electrolyte polymer precursor after filling An electrolyte membrane having an ionic conduction part and a non-ion conduction part is obtained.

  The method of filling the electrolyte polymer into the pores of the porous substrate is not particularly limited, but a method of filling the electrolyte polymer by dissolving it in a solvent and removing the solvent by volatilization. Alternatively, it can be obtained by impregnating a porous substrate with a polymer precursor and then polymerizing it. At that time, the electrolyte precursor to be filled may contain a polymerization initiator, a catalyst, a curing agent, a surfactant, and the like, if necessary.

  Also, for the purpose of improving the durability of the electrolyte membrane by forming a chemical bond between the porous substrate and the electrolyte polymer filled inside, the porous substrate is irradiated with radiation, electron beams, ultraviolet rays, etc., or plasma , Ozone, corona discharge treatment or a combination thereof may be used.

  When the electrolyte polymer filled in the pores of the porous substrate is polymerized before filling, any electrolyte polymer having proton conductivity can be used. Preferred examples include aromatic polysulfone, aromatic Examples thereof include an electrolyte polymer obtained by sulfonating a benzene ring such as polyether ketone.

The electrolyte polymer filled in the pores of the porous substrate is a polymer precursor such as a monomer or a cross-linking agent (hereinafter simply referred to as “polymer precursor”) before filling, and this is introduced into the pores. When the electrolyte polymer is polymerized after filling, the ion-exchange group-containing monomer, which is a component of the polymer precursor used in the present invention, has the performance when the proton acidic group-containing monomer is used as an electrolyte membrane for a fuel cell. Well preferred. This monomer is a compound having a polymerizable functional group and a protonic acid in one molecule. Specific examples thereof include 2- (meth) acrylamide-2-methylpropanesulfonic acid, 2- (meth) acrylamide-2-methylpropanephosphonic acid, styrenesulfonic acid, (meth) allylsulfonic acid, vinylsulfonic acid, isoprene. Examples thereof include sulfonic acid, (meth) acrylic acid, maleic acid, crotonic acid, vinylphosphonic acid, acidic phosphoric acid group-containing (meth) acrylate and the like.
Moreover, the monomer which has a functional group which can be converted into an ion exchange group is a salt, an anhydride, an ester or the like of the above compound. When the acid residue of the monomer to be used is a derivative such as a salt, an anhydride, or an ester, proton conductivity can be imparted by forming a protonic acid type after polymerization.
Further, as a monomer having a site capable of introducing an ion exchange group after polymerization, a benzene ring-containing monomer such as styrene, α-methylstyrene, chloromethylstyrene, or t-butylstyrene can be preferably used. Examples of the method for introducing an ion exchange group into these include a method of sulfonation with a sulfonating agent such as chlorosulfonic acid, concentrated sulfuric acid and sulfur trioxide.
“(Meth) acryl” means “acryl and / or methacryl”, “(meth) allyl” means “allyl and / or methallyl”, and “(meth) acrylate” means “acrylate and / or methacrylate”. ing.
Among these compounds, a sulfonic acid group-containing vinyl compound or a phosphoric acid group-containing vinyl compound is preferable because of excellent proton conductivity, and 2-methylpropane-2- (meth) acrylamide sulfonic acid has high polymerizability. More preferred.

As a polymer precursor used by this invention, the mixture which mix | blended the crosslinking agent with the ion exchange group containing monomer is preferable. A compound that can be used as a crosslinking agent has two or more polymerizable functional groups in one molecule, and is crosslinked in the polymer by blending with the above proton acidic group-containing monomer or a salt thereof for polymerization. Dots are formed, and the polymer can be made into an insoluble and infusible three-dimensional network structure.
Specific examples thereof include N, N′-methylenebis (meth) acrylamide, N, N′-ethylenebis (meth) acrylamide, N, N′-propylenebis (meth) acrylamide, and N, N′-butylenebis (meth). Acrylamide, tri (meth) acryloyl formal, bis (meth) acrylamide piperazine, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, trimethylolpropane diallyl ether, pentaerythritol triallyl ether, divinylbenzene, bisphenol di ( (Meth) acrylate, isocyanuric acid di (meth) acrylate, tetraallyloxyethane, triallylamine, N, N, N ′, N′tetraallyl-1,4-diaminobutane, triallyl isocyanurate Diallyloxyacetic acid salts and the like. Moreover, you may use the compound which has a polymerizable double bond and the functional group which can perform another crosslinking reaction in 1 molecule. Examples of such compounds include N-methylol acrylamide, N-methoxymethyl acrylamide, N-butoxymethyl acrylamide, and the like. After radical polymerization of a polymerizable double bond, heating is performed to cause a condensation reaction. It is possible to cause the same crosslinking reaction by crosslinking or heating simultaneously with radical polymerization.
In addition, the crosslinkable functional group is not limited to those having a carbon-carbon double bond, but is inferior in that the polymerization reaction rate is slow, but a bifunctional or higher epoxy compound, a phenyl group having a hydroxymethyl group, etc. are also used. be able to. When an epoxy compound is used, it may be crosslinked by reacting with an acid such as a carboxyl group in the polymer, or a copolymerizable compound having a hydroxyl group or the like as a third component may be added to the polymer precursor. These cross-linking agents can be used alone or in combination of two or more as required.

  The polymer precursor used in the present invention can be blended with a third copolymer component having no proton acidic group, if necessary, for adjusting the swelling property of the polymer. The third component is not particularly limited as long as it can be copolymerized with the ion exchange group-containing monomer and the crosslinking agent used in the present invention, but (meth) acrylonitrile, (meth) acrylic acid esters, (meth) acrylamides, Maleimides, styrenes, organic acid vinyls, allyl compounds, methallyl compounds and the like can be mentioned.

In the present invention, the method of polymerizing the ion-exchange group-containing monomer in the polymer precursor inside the pores of the porous substrate is polymerization by irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, or heating. However, after polymerization, a post-curing step may be added by heating or irradiation with ultraviolet rays if necessary.
Examples of the radical polymerization initiator for heat-initiated polymerization and redox-initiated polymerization that can be used in the heat polymerization include the following.
Azo compounds such as 2,2′-azobis (2-amidinopropane) dihydrochloride; ammonium persulfate, potassium persulfate, sodium persulfate, hydrogen peroxide, benzoyl peroxide, cumene hydroperoxide, di-t-butylperoxide A peroxide such as oxide; a redox initiator in which the above-mentioned peroxide is combined with a reducing agent such as sulfite, bisulfite, thiosulfate, formamidinesulfinic acid, ascorbic acid; 2,2′-azobis- Azo radical polymerization initiators such as (2-amidinopropane) dihydrochloride and azobiscyanovaleric acid. These radical polymerization initiators may be used alone or in combination of two or more.

Among the above-described polymerization means, photoinitiated polymerization with ultraviolet rays is desirable because the polymerization reaction is easily controlled and a desired electrolyte membrane can be obtained with a relatively simple process and high productivity. In the case of further photoinitiating polymerization, the radical photopolymerization initiator is more preferably dissolved or dispersed in advance in a monomer, a solution or dispersion thereof.
Examples of radical photopolymerization initiators include benzoin, benzyl, acetophenone, benzophenone, thioxanthone, thioacridone, and derivatives thereof generally used for ultraviolet polymerization. Specifically, as benzophenone series, o-benzoylbenzoate Acid methyl, 4-phenylbenzophenone, 4-benzoyl-4′-methyldiphenyl sulfide, 3,3 ′, 4,4′-tetra (t-butylperoxycarbonyl) benzophenone, 2,4,6-trimethylbenzophenone, 4 -Benzoyl-N, N-dimethyl-N- [2- (1-oxy-2-propenyloxy) ethyl] benzenemethananium bromide, (4-benzoylbenzyl) trimethylammonium chloride, 4,4'-dimethylaminobenzophenone , 4,4'-di Thioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, 2-ethylthioxanthone, etc .; thioacridone, thioacridone, etc .; benzoin, benzoin, benzoin methyl ether, benzoin isopropyl ether, benzoin ethyl ether Benzoin isobutyl ether and the like; acetophenone, acetophenone, propiophenone, diethoxyacetophenone, 2,2-dimethoxy-1,2-diphenylethane-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1- ( 4- (Methylthio) phenyl) -2-monfolinopropane-1,2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) bu Thanone-1, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1- (4- (2-hydroxyethoxy) -phenyl) -2-hydroxydi-2-methyl-1-propane-1 -On and the like; benzylic compounds such as benzyl are mentioned.

  The amount of these photopolymerization initiators used is preferably 0.001 to 1 mass%, more preferably 0.001 to 0.5 mass%, based on the total mass of the ion-exchange group-containing monomer and the third component unsaturated monomer. %, Particularly preferably 0.01 to 0.5% by mass. Of these, aromatic ketone radical polymerization initiators such as benzophenone, thioxanthone, and thioacridone can generate radicals by extracting hydrogen from carbon-hydrogen bonds, so they can be used in combination with organic materials such as polyolefins as porous substrates. Then, a chemical bond can be formed between the base material surface and the filled polymer, which is preferable.

In the present invention, when the porous substrate is impregnated with the polymer precursor, it is preferable that a monomer, a cross-linking agent, and a polymerization initiator, if necessary, are mixed to form a liquid or a solution or dispersion because filling becomes easier. . When the polymer precursor is a low-viscosity liquid, it can be used for impregnation as it is, but a concentration of 10 to 90% is preferable, and a solution of 20 to 70% is more preferable.
In addition, if the components used are insoluble in water, some or all of the water may be replaced with an organic solvent, but when using an organic solvent, remove all the organic solvent before joining the electrodes. An aqueous solution is preferred because it is necessary. The reason for impregnation in the form of a solution in this way is that it is easy to impregnate a porous substrate having fine pores by dissolving in water or a solvent and using it for impregnation, and that a pre-swollen gel is removed from the pores. This is because, when the produced electrolyte membrane is made into a fuel cell, it has an effect of preventing the polymer from falling off due to excessive swelling of the polymer in the pores by water or methanol.

  For the purpose of facilitating the impregnation operation, hydrophilic treatment of the porous substrate, addition of a surfactant to the polymer precursor, or ultrasonic irradiation during the impregnation can be performed.

  When the porous substrate is impregnated with the polymer precursor and then sandwiched between the films, the impregnated polymer precursor is prevented from falling off the pores of the porous substrate, and a uniform electrolyte membrane can be obtained after polymerization. When the polymer precursor is radically polymerizable, it also has an effect of blocking oxygen in the air that inhibits radical polymerization. The material of such a film is not particularly limited, but plastic or the like can be used. Preferred are plastic films such as PET, polyethylene, polypropylene, cellophane, polycarbonate, and polyvinylidene chloride. The surface of these films may be treated with a release agent such as silicone.

  The electrolyte membrane prepared by the method of the present invention can be preferably used particularly for a direct methanol fuel cell. When an electrolyte membrane is used in such a fuel cell, an electrolyte membrane electrode assembly (MEA) is obtained by sandwiching the electrolyte membrane between two electrodes provided with a catalyst typified by platinum and integrated by a heating press or the like. It is widely known to be used by being incorporated in a battery cell, and the electrolyte membrane according to the present invention can also be used by preparing an MEA by a similar method and incorporating it in a fuel cell.

  In the present invention, as described above, the electrolyte membrane itself is not divided into an ionic conduction part and a non-ion conduction part, and the same effect, that is, when MEA is used, the fuel permeates from other than the part sandwiched between the electrodes, Examples of methods for reducing the fuel utilization efficiency and preventing the phenomenon that the electrolyte inside the pores fall off due to direct contact with the fuel to form through holes are given. One is that when the MEA is incorporated into a battery, at least on one side of the MEA, the gap between the electrode and gasket is a non-ion that is durable against fuel and oxidant as shown in the cross-sectional view of FIG. It is filled with a conductive polymer. In addition, as shown in the cross-sectional view of FIG. 6, a nonionic conductive polymer that is durable against fuel and oxidant is attached to one or both sides of the electrolyte membrane that protrudes outside the MEA electrode before attaching the gasket. Or can be applied.

  Hydrophobic nonionic conductive polymer that is applied to one side or both sides of the electrolyte membrane that fills the gap between the electrode and gasket, or protrudes outside the MEA electrode before the gasket is attached. Examples thereof include fluorine-based sealants (for example, trade name Eight Seal manufactured by Asahi Glass Co., Ltd.), silicone RTV rubbers, types with a crosslinking reaction such as epoxy resins, and hot melt polymers (hot melt polymers). A type in which the heat-melted product is cooled and solidified can be preferably used. Among them, silicone RTV rubber (for example, trade name KE42 manufactured by Shin-Etsu Chemical Co., Ltd.) as a crosslinkable polymer, and polyolefin-based hot melt adhesive (for example, product name PPET manufactured by Toagosei Co., Ltd.) as a heat-meltable polymer. Can be suitably used as a fuel cell application because of its high durability against fuel and oxidant and little permeation of water and fuel.

  When using a heat-meltable polymer, the softening temperature is preferably the R & B softening temperature specified in JIS K2207 in the range of 80 ° C to 200 ° C. Furthermore, the range of 100-170 degreeC is preferable. DMFC is often used at 80 ° C. or lower, and if the softening temperature is too low, it is not preferable because it melts inside the battery and closes the flow path. If the softening temperature is too high, the processing temperature becomes too high and the electrolyte membrane becomes Neither is preferred because it deteriorates.

  In the electrolyte membrane of the present invention, it is preferable that only the portion sandwiched between the electrodes has ionic conductivity and the outside of the electrode is a hydrophobic nonionic conductive portion, but at the boundary portion, the nonionic conductive portion is below the electrode. If the polymer forming the non-ion conducting portion is slightly penetrated into the end portion of the electrode, the fuel crossover is further suppressed. In this case, if the overlapping width of the electrode and the non-ion conducting portion is too wide, the portion where the electrode catalyst is wasted increases, which is not preferable. If the overlap width is narrow, the overlapping catalyst can also contribute to power generation, so the overlap width is preferably 2 mm or less.

By these methods, the fuel leaking out of the electrode does not directly contact the portion filled with the electrolyte, and the electrolyte inside the pores cannot escape, so that the battery performance can be maintained for a long time.
In the electrolyte membrane of the present invention, only the boundary portion, that is, the vicinity of the tangent line between the outer periphery of the electrode and the gasket may be formed into a non-ion conducting portion in a strip shape. Thereby, deterioration of the gasket by the liquid which permeates from the interface between the membrane and the gasket can be prevented.

  When the electrolyte membrane or fuel cell prepared by the method of the present invention is assembled in a fuel cell and generates power, only the portion sandwiched between the electrodes is in contact with the fuel, and the other membrane portion does not contain an electrolyte polymer or is non-greasy. The fuel does not come into contact because it is protected by an ion conducting polymer. For this reason, fuel oozes from the outside of the electrode to the cathode side to lower the cell performance, or the electrolyte filled in the pores of the electrolyte membrane drops from the inside of the pores and penetrates, and the fuel and oxidant on the anode side and cathode side Can be prevented from mixing directly.

Example 1
A crosslinked polyethylene porous membrane (thickness 16 μm, porosity 40%, average pore diameter about 0.1 μm) prepared by a stretching method was prepared as a porous substrate. Next, in a polymer precursor solution consisting of 50 g of 2-acrylamido-2-methylpropanesulfonic acid, 5 g of N, N′-methylenebisacrylamide, 0.005 g of a surfactant, 0.005 g of an ultraviolet radical polymerization initiator, and 50 g of water, The porous membrane was immersed and filled with the solution. Next, after lifting the porous substrate from the solution, it was sandwiched between two 50 μm thick PET films. Next, ultraviolet rays were irradiated on both sides of the PET film using a high-pressure mercury lamp on each side at 1000 mJ / cm ² to polymerize the polymer precursor. Next, this PET film was peeled off and washed with distilled water to obtain an electrolyte membrane.
This membrane is sandwiched between a pair of electrodes (square, 22 mm long) and hot-pressed at 120 ° C. to create an MEA, and the electrode part is further cut into a square of 24 mm on each side. I sandwiched it between two sheets. Further, a one-component RTV rubber (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KE42) was embedded in the gap formed between the silicone rubber gasket and the electrode, and left until the RTV rubber was cured. This was installed in a fuel cell and operated for 10 hours a day, and the change in voltage was tracked. As a result, the voltage drop rate at a total operation time of 500 hours and the amount of methanol permeated from the fuel electrode side to the oxygen electrode side inside the cell were measured. The results are summarized in Table 1.

(Example 2)
A crosslinked polyethylene porous membrane (thickness 16 μm, porosity 40%, average pore diameter about 0.1 μm) prepared by a stretching method was prepared as a porous substrate. The pores were closed by sandwiching the outer portion with a heat sealer heated to about 140 ° C., leaving a square shape with a side slightly smaller than the electrode used for this substrate being 21.5 mm. The remaining porous portion was filled with an electrolyte polymer in the same manner as in Example 1 to obtain an electrolyte membrane. Silicone rubber in which an electrolyte membrane is sandwiched between a pair of electrodes (square, 22 mm long) so that it just overlaps the electrolyte-filled portion of this membrane, and the electrode portion is cut into a square of 24 mm on each side It was sandwiched between two gaskets. The results of evaluation similar to Example 1 for this MEA are summarized in Table 1.

(Example 3)
A crosslinked polyethylene porous membrane (thickness 16 μm, porosity 40%, average pore diameter about 0.1 μm) prepared by a stretching method was prepared as a porous substrate. Next, 1 g of xylylene oxetane (manufactured by Toagosei Co., Ltd., trade name Aron Oxetane OXT-121), 1 g of dioxetane (manufactured by Toagosei Co., Ltd., trade name Aron Oxetane OXT-221), and 0.1 g of cationic polymerization catalyst are mixed. The porous membrane was immersed in the liquid and impregnated with the oxetane resin mixed liquid. This was sandwiched between PET films, and a photomask on which a square black pattern with a side of 21.5 mm was formed was placed thereon, and ultraviolet irradiation at 2000 mJ / cm ² was performed from above using a high-pressure mercury lamp. When the photomask and the PET film were removed, and the porous film filled with oxetane resin and polymerized was washed with acetone, the original porous film was exposed only in the square part with a side of 22 mm that was not exposed to ultraviolet rays, and the other part was filled. The oxetane resin hardened and the holes were plugged. The exposed porous portion was filled with an electrolyte polymer in the same manner as in Example 1 to obtain an electrolyte membrane. An MEA was created by sandwiching the electrolyte membrane with a pair of electrodes (square, 22 mm long) so that it overlaps with the electrolyte polymer-filled portion of this membrane, and the electrode portion was further cut into a square with a side of 24 mm. It was sandwiched between two silicone rubber gaskets. The results of evaluation similar to Example 1 for this MEA are summarized in Table 1.

Example 4
When the electrodes were bonded to the electrolyte membrane prepared in Example 1, a sheet-like hot melt adhesive (Toagosei Co., Ltd.) formed in advance to a thickness of about 0.05 mm and hollowed out with a square pattern of 22 mm on one side. ), Trade name PPET2109, R & B softening point 140 ° C.) The electrolyte membrane was sandwiched so that the two cut-out portions overlapped. Further, from above and below, a MEA was prepared by sandwiching a catalyst in the form of a square with a side of 22 mm and sandwiching it with a carbon paper electrode with a side of 23 mm and hot pressing. At that time, the overlapping portion of the end portion of the carbon paper and the hot melt adhesive was fused. Further, the electrode portion was sandwiched between two silicone rubber gaskets that were cut out into a square with a side of 24 mm, and evaluation was performed in a fuel cell. The results of evaluation similar to Example 1 for this MEA are summarized in Table 1.

(Comparative Example 1)
The MEA was created by sandwiching the electrolyte membrane prepared in Example 1 with a pair of electrodes (square and 22 mm in length) and hot pressing at 120 ° C., and the electrode part was made into a square with a side of 24 mm. It was sandwiched between two silicone rubber gaskets. Table 1 summarizes the results of evaluations similar to those of Example 1 incorporated in a fuel cell. Compared to the Examples, the amount of methanol permeated from the fuel electrode to the air electrode was large, and the voltage drop during continuous operation was large.

(Evaluation method of the created film)
(1. Evaluation of methanol permeability)
A method described in the literature "Methanol Transport Through Nafion Embranes" (Journal of The Electronic Society, 2000, 147, No. 2, p. 466-474, by the American Electrochemical Society, Xiaming Ren et al.) did. Each MEA was incorporated in a fuel cell, and a 1 mol / l aqueous methanol solution was flowed to one electrode, and nitrogen was flowed to the other electrode, and the cell was kept at 50 ° C. Next, the negative electrode was connected to the methanol electrode, and the positive electrode was connected to the nitrogen flow side to increase the voltage, and the current value flowing at this time was monitored. The current value began to rise from around 0.5V and became constant around 0.7 to 1.0V, so the current values that became constant were compared. That is, as the voltage is increased, methanol leaking to the nitrogen side electrode is oxidized and releases protons and electrons, so that the higher the observed current value, the more methanol leaked.

(Fuel cell performance evaluation method)
(1. Creation of MEA)
Platinum-supported carbon (Tanaka Kikinzoku Co., Ltd .: TEC10E50E) is used for the oxygen electrode, and platinum ruthenium alloy-supported carbon (Tanaka Kikinzoku Kogyo Co., Ltd .: TEC61E54) is used for the fuel electrode. A molecular electrolyte solution (manufactured by DuPont: Nafion 5% solution) and polytetrafluoroethylene dispersion were blended, and water was appropriately added and stirred to obtain a reaction layer coating material. This was printed on one side of carbon paper (manufactured by Toray Industries, Inc .: TGP-H-060) by screen printing and dried to obtain an electrode. At that time, the platinum amount on the oxygen electrode side was 1 mg / cm ² , and the total amount of platinum and ruthenium on the fuel electrode side was 3 mg / cm ² . Unless otherwise specified in the Examples and Comparative Examples, these were superposed on the center of the electrolyte membrane with the paint surface inside, and heated and pressed at 120 ° C. to prepare a fuel cell membrane electrode assembly (MEA). This was installed in a single fuel cell and operated to confirm the performance.
(2. Fuel cell evaluation)
The operating conditions when the MEAs created in the examples and comparative examples are incorporated in a DMFC single cell are as follows. The fuel was a 3 mol / l aqueous methanol solution, and the oxidant was pure oxygen. The cell temperature was 50 ° C. Current-voltage characteristics were measured by changing the current with an electronic loader, and the maximum value of the output expressed as current × voltage was determined. Comparison of the performance of each electrolyte membrane was compared by the maximum output and summarized in Table 1. In addition, using 1 mol / l of fuel, intermittent operation for 10 hours a day while applying a load of 0.1 A / cm ² at a cell temperature of 60 ° C., and examining the voltage maintenance rate after a total of 300 hours of operation. The results are summarized in Table 1.

The electrolyte membrane of the present invention and a fuel cell using the electrolyte membrane are extremely useful for DMFC applications because they have excellent output characteristics and durability and high fuel utilization efficiency.

1 is a cross-sectional view showing a direct methanol fuel cell using an electrolyte membrane manufactured by filling a porous substrate with an electrolyte polymer. Sectional drawing of the electrolyte membrane pinched | interposed between the electrodes in the fuel cell of the structure shown by FIG. Even if it is operated for a long time and the performance deteriorates, the resin remains filled. FIG. 2 is a cross-sectional view of an electrolyte membrane corresponding to a gap portion between an electrode and a gasket in the fuel cell having the structure shown in FIG. 1. Sectional drawing which shows the state which carried out long time and the performance fell. The electrolyte polymer has fallen off and there are many voids. The portion corresponding to the electrolyte membrane in FIG. 1 is filled with a nonionic conductive polymer except for the portion sandwiched by the electrodes, or the porous substrate other than the portion sandwiched by the electrodes is also thermally melted to close the pores. Sectional drawing which shows the state made to do. Sectional drawing which shows the state which filled the clearance gap formed between the electrode and gasket of FIG. 1 with the nonionic conductive polymer. Sectional drawing which shows the state which apply | coated or bonded nonionic conductive polymer on the electrolyte membrane other than the part which the electrode of FIG. 1 is contacting

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a Oxidant gas flow path 1b Fuel flow path 2 Carbon member 3 Gasket 4a Electrode with cathode side catalyst 4b Electrode with anode side catalyst 5 Electrolyte membrane 6 Gap formed between gasket and electrode 7 Nonionic conductive polymer 8 Porous group A part that is filled with a non-ion conductive polymer or is made non-ion conductive by closing the pores.
9 Non-ion conductive polymer 10 Electrolyte membrane 11 sandwiched between electrodes Electrolyte membrane 12 in gap between electrode and gasket Porous substrate 13 Electrolyte polymer 14 Porosity formed by dropping electrolyte polymer

Claims (10)

An electrolyte membrane in which pores of a porous base material are filled with an electrolyte polymer, wherein a non-ion conducting portion having a predetermined pattern is formed. In the formation of the non-ion conductive portion of a predetermined pattern, the non-ion conductive polymer is applied or fused in a predetermined pattern on one or both surfaces of the electrolyte membrane in which the pores of the porous substrate are filled with the electrolyte polymer. The electrolyte membrane according to claim 1, which is obtained by a method. The electrolyte membrane according to claim 1 or 2, wherein the non-ion conductive polymer is a crosslinkable polymer or a heat-meltable polymer. 2. The electrolyte membrane according to claim 1, wherein the pores of the porous substrate are thermally melted and closed in a predetermined pattern, and the electrolyte polymer is filled in the pores that are not closed. The electrolyte membrane of Claim 1 obtained by the following process using an active energy ray hardening compound.
1) A step of filling active energy ray-curable compounds that can become nonionic conductive after polymerization into the pores of a porous substrate.
2) A step of polymerizing the compound by irradiating a predetermined pattern with active energy rays.
3) A step of exposing the porous substrate by dissolving and removing the compound in the unpolymerized portion with a solvent.
4) A step of filling the electrolyte polymer into the pores of the exposed porous substrate or filling the electrolyte polymer precursor and then forming the electrolyte polymer. 6. The electrolyte membrane according to claim 1, wherein the porous substrate is obtained by stretching polyolefin. When the predetermined pattern forming the non-ion conducting part is in contact with or bonded to both surfaces of the electrolyte membrane to form a membrane electrode assembly or a fuel cell, the outer part and / or the boundary of the contacted or bonded part with the electrode The electrolyte membrane according to claim 1, which is a portion. The predetermined pattern forming the non-ion conducting part is a boundary part between the outer peripheral part of the electrode and the gasket when the electrode is brought into contact with or bonded to both surfaces of the electrolyte membrane and a gasket is arranged around the electrode. 8. The electrolyte membrane according to claim 1, wherein: 9. A fuel cell in which an electrode is contacted or bonded to both surfaces of an electrolyte membrane according to claim 1 and a gasket is arranged around the electrode, and a non-ion conducting portion of the electrolyte membrane is provided at a boundary portion between the outer periphery of the electrode and the gasket. A fuel cell, wherein the fuel cell is in contact with each other. In a fuel cell in which electrodes are brought into contact with or bonded to both surfaces of an electrolyte membrane in which pores of a porous substrate are filled with an electrolyte polymer, and a gasket is disposed around the electrodes, an outer peripheral portion of the electrode of the electrolyte membrane and a gasket A fuel cell, wherein a nonionic conductive polymer is applied or fused to a portion in contact with a boundary portion of the electrode, or a nonionic conductive polymer is filled in a boundary portion between an electrode outer peripheral portion and a gasket.

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