JP2006032302A - Electrolyte film and fuel cell using the electrolyte film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost electrolyte film with high proton conductivity, excellent permeation-stopping power against methanol in case of using it as a DMFC, and excellent in durability in case of operating it as a fuel cell, which can be utilized for an electrochemical device such as a solid polymer fuel cell. <P>SOLUTION: The electrolyte film contains a crosslinking electrolyte polymer with (a) a compound or its salt having a carbon-carbon double bond and a sulfonic group in a molecule, and (b) multi-functional acrylic or a methallyl compound expressed in a specific structural formula, as an essential configuration monomer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  As global environmental protection activities become more active, so-called greenhouse gas and NOx emission prevention is strongly screamed. In order to reduce the total emission amount of these gases, it is considered that practical application of a fuel cell system for automobiles is very effective.

  A polymer electrolyte fuel cell (PEFC), which is a type of electrochemical device using a polymer electrolyte membrane, has excellent features such as low temperature operation, high output density, and low environmental impact. . Among them, PEFC, which is a methanol fuel, can be supplied as a liquid fuel in the same manner as gasoline, and thus is considered promising as a power source for electric vehicles and a power source for portable devices.

  When using methanol as a fuel, PEFC is divided into a reformed methanol type that uses a reformer to convert methanol into a hydrogen-based gas, and a direct methanol type that uses methanol directly without using a reformer (DMFC, It is divided into two types, Direct Methanol Polymer Fuel Cell). Since DMFC does not require a reformer, it has great advantages such as being able to reduce weight, and its practical use is expected.

  However, when an electrolyte membrane for DMFC is a perfluoroalkylsulfonic acid membrane that is an electrolyte membrane for PEFC using conventional hydrogen as a fuel, such as a Nafion (registered trademark) membrane manufactured by Du Pont, Since methanol permeates the membrane, there is a problem that the electromotive force decreases. Furthermore, these electrolyte membranes also have an economic problem that they are very expensive.

  As means for solving the above problem, Patent Document 1 proposes an electrolyte membrane in which a porous base material such as polyimide, crosslinked polyethylene, etc., which is inexpensive and hardly deformed by external force, is filled with a polymer having proton conductivity. Has been made. However, since the electrolyte membrane includes a step of subjecting the base material to plasma irradiation and graft polymerization of the polymer, there is a problem of an increase in manufacturing equipment cost. In addition, the durability when continuously operating as a fuel cell was not sufficient.

Furthermore, Patent Document 2 discloses an electrolyte membrane in which a first polymer having proton conductivity is filled in pores of a porous base material that does not substantially swell with an organic solvent containing methanol and water. An electrolyte membrane has been proposed in which the first polymer is a polymer derived from 2-acrylamido-2-methylpropanoic acid. However, the durability of the electrolyte membrane described in this patent document is still insufficient.
JP 2002-83612 A (pages 1-7, 9) International Publication No. 03/075385 Pamphlet

  The object of the present invention is to solve these problems, that is, it can be used for electrochemical device applications such as polymer electrolyte fuel cells, has high proton conductivity, and has excellent methanol permeation blocking performance when used as a DMFC, Another object is to provide an inexpensive electrolyte membrane that is excellent in durability when operated as a fuel cell.

  As a result of intensive studies, the present inventors have identified 2-acrylamido-2-methylpropanesulfonic acid and / or 2-methacrylamideamido-2-methylpropanesulfonic acid (hereinafter “acrylic and / or methacrylic” as “(meth)”. As for the method of introducing the crosslinked structure, a specific polyfunctional allyl compound is copolymerized with respect to the electrolyte membrane including a crosslinked electrolyte polymer obtained by polymerizing a monomer having a sulfonic acid group or a salt thereof as a main component. In this case, the electrolyte membrane was found to have excellent proton conductivity, methanol permeation-preventing performance, and good durability, and the present invention was completed.

式中、Ｒ₁は、アリル基もしくはメタリル基またはこれら基を含む炭素鎖もしくは環構造の一部を、Ｒ₂は、水素、アルキル基、アルキレン基、アリル基もしくはメタリル基またはアリル基もしくはメタリル基を含む炭素鎖もしくは環構造の一部を、Ｒ₃は、水素またはメチル基を表わす。 That is, the present invention relates to (a) a compound having a carbon-carbon double bond polymerizable in one molecule and a sulfonic acid group or a salt thereof, and (b) a polyfunctional allyl represented by the following structural formula (1): Methallyl compounds,
It is an electrolyte membrane characterized by containing the crosslinked electrolyte polymer which uses as an essential constituent monomer.

In the formula, R ₁ represents an allyl group or methallyl group or a part of a carbon chain or ring structure containing these groups, and R ₂ represents hydrogen, an alkyl group, an alkylene group, an allyl group or a methallyl group, an allyl group or a methallyl group. R ₃ represents a hydrogen or a methyl group.

As the monomer (b), R ₁ is an allyl group or methallyl group or a part of a carbon chain or ring structure containing these groups, and R ₂ is a part of a carbon chain or ring structure containing an allyl group or methallyl group. A polyfunctional allyl compound represented by the structural formula (1), which is characterized by being a polyfunctional allyl or methallyl compound represented by the structural formula (1), is used as the monomer (b). , Triallyl isocyanurate, trimethallyl isocyanurate, N, N, N ′, N′-tetraallyl-1,4-diaminobutane or N, N, N ′, N′-tetramethallyl-1,4-diaminobutane is used. Is.
Further, 2- (meth) acrylamide-2-methylpropanesulfonic acid or a salt thereof is used as the monomer (a).
The electrolyte membrane is characterized in that the ratio of the monomers (a) and (b) to the total monomers constituting the crosslinked electrolyte polymer is 20 to 99.9% by mass and 0.1 to 20% by mass, respectively. The electrolyte membrane is characterized in that the crosslinked electrolyte polymer is filled in pores of a porous substrate.
In the present invention, the electrolyte membrane comprises: (1) a step of filling a monomer constituting the crosslinked electrolyte polymer or a solution or dispersion thereof in the pores of the porous substrate; and (2) polymerization and crosslinking of the filled monomer. Further, the present invention relates to a fuel cell in which the above electrolyte membrane is incorporated.

  The electrolyte membrane of the present invention has improved durability by containing a crosslinked electrolyte polymer having a specific composition. Further, since it is an electrolyte membrane excellent in proton conductivity and methanol permeation blocking performance, it can be suitably used as an electrolyte for a polymer electrolyte fuel cell, particularly a direct methanol polymer electrolyte fuel cell.

Hereinafter, the present invention will be described in detail.
The electrolyte membrane of the present invention includes (a) a compound having a carbon-carbon double bond polymerizable in one molecule and a sulfonic acid group or a salt thereof, and (b) a polyfunctional allyl represented by the structural formula (1). Alternatively, it contains a crosslinked electrolyte polymer obtained by copolymerizing a monomer mixture (hereinafter referred to as “polymer precursor”) having a methallyl compound as an essential constituent monomer.

Here, the ratio of the essential constituent monomers (a) and (b) to the total monomers constituting the crosslinked electrolyte polymer is preferably 20 to 99.9% by mass and 0.1 to 20% by mass, respectively. . When the monomer (a) is lower than the lower limit of the above range, the proton conductivity of the obtained electrolyte membrane tends to be low, the output per area of the obtained electrolyte membrane tends to be low, and the incorporated fuel cell becomes large. . On the other hand, if it is higher than the upper limit of the above range, neither methanol permeation-preventing property nor durability is likely to be lowered, which is not preferable.
When the monomer (b) is lower than the lower limit of the above range, the resulting electrolyte membrane methanol permeation-preventing property and durability are likely to be low. On the other hand, when the monomer (b) is higher than the upper limit of the above range, the polymerizability becomes poor. Since proton conductivity tends to be low, neither is preferable.
A more preferable range is 60 to 95% by mass of the monomer (a) and 1 to 10% by mass of the monomer (b).

    The monomer (a) constituting the crosslinked electrolyte polymer used in the electrolyte membrane of the present invention is a compound having a polymerizable carbon-carbon double bond and a sulfonic acid group in one molecule or a salt thereof, and is not particularly limited. 2-acryloylethanesulfonic acid and / or 2-methacryloylethanesulfonic acid (hereinafter, “acryloyl and / or methacryloyl” is referred to as “(meth) acryloyl”), 2- (meth) acryloylpropanesulfonic acid, 2- (Meth) acrylamide-2-methylpropanesulfonic acid, styrenesulfonic acid, allylsulfonic acid and / or methallylsulfonic acid (hereinafter, “allyl and / or methallyl” is referred to as “(meth) allyl”), vinyl. Specific examples include monomers such as sulfones or salts thereof. Kill. These may be used alone or copolymerized, but 2- (meth) acrylamido-2-methylpropanesulfonic acid or a salt thereof is particularly preferable in terms of good polymerizability. Also, since vinyl sulfonic acid has the highest sulfonic acid content per molecular weight, it is preferable to use it as a copolymerization component because the proton conductivity of the electrolyte membrane is improved.

The monomer (b) constituting the crosslinked electrolyte polymer used in the electrolyte membrane of the present invention is a polyfunctional allyl compound or methallyl compound represented by the structural formula (1), and in particular, in the structural formula (1), R ₁ , R ₂ is preferably an allyl group or a methallyl group or a part of a carbon chain or ring structure containing these groups, more preferably R ₁ is an allyl group or a methallyl group or a carbon chain or ring structure containing these groups. In part, R ₂ is part of a carbon chain or ring structure containing an allyl or methallyl group.
Specific preferred compounds include tri (meth) allyl isocyanurate, tri (meth) allylamine, di (meth) allylamine, N, N, N ′, N′-tetra (meth) allyl-1,4-diaminobutane , N, N-di (meth) allylmelamine and the like.
These may be used alone or copolymerized. More preferable compounds include tri (meth) allyl isocyanurate, N, N, N ′, N′-tetra (meth) allyl-1,4-diaminobutane in terms of easy availability and improved durability. Is mentioned.

The monomer constituting the crosslinked electrolyte polymer used in the electrolyte membrane of the present invention contains monomers (a) and (b) as essential components, but other monomers can be used in combination as necessary. .
The monomer is not particularly limited as long as it is copolymerizable with the monomers (a) and (b). For example, as a water-soluble monomer, (meth) acrylic acid, (anhydrous) maleic acid, fumaric acid, Acidic monomers such as crotonic acid, itaconic acid, vinylphosphonic acid, acidic phosphoric acid group-containing acrylates and / or methacrylates (hereinafter referred to as “(meth) acrylates”) and salts thereof; (Meth) acrylamide, N-substituted (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, N-vinylpyrrolidone, N-vinyl acetate Monomers such as amides; basic monomers such as N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, and their quaternary Specific examples thereof include compounds.
Acrylic esters such as methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate, vinyl acetate, and vinyl propionate are also used to adjust the water absorption of the polymer filled in the pores. Hydrophobic monomers such as can also be used.

In the crosslinked electrolyte polymer used in the electrolyte membrane of the present invention, as a method for introducing a crosslinked structure, it is preferable to introduce a crosslinked structure derived from the essential constituent monomer (b).
As a method for introducing a crosslinked structure derived from the monomer (b), the polymer precursor is filled into the pores of the porous substrate and then subjected to a polymerization reaction, or simultaneously with the polymerization reaction to obtain a polymer, the monomer (b ) Or a method of polymerizing a polymer precursor in advance and filling the polymer solution into the pores of the porous substrate, followed by a crosslinking reaction. Among these methods, in the method of filling after the polymer is first prepared, gelation occurs at the time of polymerization, which makes it impossible to fill, and the yield is poor, and the viscosity of the polymer is higher than the polymer precursor solution. Since it takes time to fill the pores or the filling tends to be insufficient, a method of polymerizing and cross-linking after pre-filling the polymer precursor is preferable.
The crosslinking is preferably promoted by heating or active energy rays such as ultraviolet rays, electron beams, and gamma rays. The conditions are preferably 50 to 150 ° C. for 1 to 120 minutes in the case of heating, and 10 in the case of ultraviolet irradiation. ˜5000 mJ / cm ² is desirable.

In the crosslinked electrolyte polymer used for the electrolyte membrane of the present invention, a crosslinked structure other than the crosslinked structure derived from the essential constituent monomer (b) may be introduced, and the method is not particularly limited, and a known method is used. Can do.
Specifically, a method of performing a polymerization reaction in combination with a crosslinking agent having two or more polymerizable double bonds, a method of copolymerizing a monomer having a functional group capable of forming a crosslinked structure, a functional group in the polymer Using a crosslinking agent having two or more groups that react with the molecule in the molecule, utilizing self-crosslinking by hydrogen abstraction during polymerization, and irradiating the polymerized polymer with active energy rays such as electron beams and gamma rays Etc.

Among these methods, a method in which a polymerization reaction is carried out using a crosslinking agent having two or more polymerizable double bonds in combination is preferable because of the ease of introduction of a crosslinked structure. Examples of the crosslinking agent include N, N-methylenebisacrylamide, N, N-ethylenebisacrylamide, triacryl formal, bisacryloylpiperazine, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (Meth) acrylate, polypropylene glycol di (meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (Meth) acrylate, divinylbenzene, bisphenol diacrylate, isocyanuric acid (meth) diacrylate and the like. A method of copolymerizing a water-soluble monomer having a functional group capable of forming a crosslinked structure is also preferred from the viewpoint of easily increasing the crosslinking density. Examples of such compounds include N-methylol acrylamide, N-methoxymethyl acrylamide, N-butoxymethyl acrylamide, etc., and after carrying out radical polymerization of polymerizable double bonds, heating to cause a condensation reaction or the like. It is possible to cause the same crosslinking reaction by crosslinking or heating simultaneously with radical polymerization. These cross-linking agents can be used alone or in combination of two or more as required.
The amount of the copolymerizable crosslinking agent used is 0.01 to 20% by mass, preferably 0.1 to 20% by mass, more preferably 0.1 to 20% by mass with respect to the total mass of unsaturated monomers in the polymer precursor. 10% by mass. If the amount of the crosslinking agent is too small, the uncrosslinked polymer tends to be eluted, and there is a problem that the output decreases within a short time when operated as a fuel cell. If the amount is too large, the crosslinking agent component is difficult to be compatible. Neither is preferred because there is a problem of hindering conduction and reducing battery performance.

As a method for obtaining a crosslinked electrolyte polymer by copolymerizing the polymer precursor used in the electrolyte membrane of the present invention, a known aqueous solution radical polymerization technique can be used. Specific examples include redox-initiated polymerization, heat-initiated polymerization, electron beam-initiated polymerization, and photoinitiated polymerization such as ultraviolet rays.
Examples of the radical polymerization initiator for heat-initiated polymerization and redox-initiated 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; or 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 these, the peroxide radical polymerization initiator can generate radicals by extracting hydrogen from carbon-hydrogen bonds, so when used in combination with an organic material such as polyolefin as a porous substrate, the surface of the substrate and the filled polymer It is preferable because a chemical bond can be formed between the two.

Among the radical polymerization initiating means, photoinitiated polymerization by ultraviolet rays is desirable in that the polymerization reaction is easily controlled and a desired electrolyte membrane can be obtained with a relatively simple process and high productivity. Furthermore, when carrying out photoinitiated polymerization, it is more preferable to dissolve or disperse the radical photopolymerization initiator in advance in the polymer precursor, its solution or dispersion.
Examples of the radical photopolymerization initiator include benzoin, benzyl, acetophenone, benzophenone, quinone, thioxanthone, thioacridone, and derivatives thereof that are generally used for ultraviolet polymerization. Examples of the derivatives include benzoin-based benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether; acetophenone-based diethoxyacetophenone, 2,2-dimethoxy-1,2-diphenylethane-1- ON, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1- (4- (methylthio) phenyl) -2-montolinopropane-1, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) ) Butanone-1,2-hydroxy-2-methyl-1-phenylpropan-1-one, 1- (4- (2-hydroxyethoxy) -phenyl) -2-hydroxydi-2-methyl-1-propane- 1-one; as benzophenone, o-benzoy Methyl benzoate, 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′-dimethylamino Examples include benzophenone and 4,4′-diethylaminobenzophenone.

The amount of these photopolymerization initiators used is preferably 0.001 to 1% by mass, more preferably 0.001 to 0.5% by mass, particularly preferably the total mass of unsaturated monomers in the polymer precursor. 0.01 to 0.5% by mass. If the amount of the initiator is too small, there is a problem that the amount of unreacted monomers increases. If the amount is too large, the crosslinking density of the polymer to be formed becomes too low, and the durability when the fuel cell is operated is lowered. Therefore, neither is preferable.
Of these, aromatic ketone radical polymerization initiators such as benzophenone, thioxanthone, quinone, and thioacridone can generate radicals by extracting hydrogen from carbon-hydrogen bonds. When used together, a chemical bond can be formed between the substrate surface and the filled polymer, which is preferable.

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.
Although the area increase rate 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 preferably 20% or less at the maximum compared to the time of drying.

The porous substrate used in the present invention preferably has a tensile modulus of 500 to 5000 MPa, more preferably 1000 to 5000 MPa, and preferably has a breaking strength of 50 to 500 MPa, more preferably 100. ~ 500 MPa.
If these ranges are deviated to the lower side, the membrane tends to be deformed by the force of swelling of the filled polymer with methanol or water, and if it deviates to the higher side, the base material becomes too brittle and press molding and battery for electrode joining are performed. The film is liable to crack due to tightening during assembly.

Further, the porous substrate is preferably one having heat resistance against the temperature at which the fuel cell is operated, and one that does not easily extend even when an external force is applied.
Examples of the material having such a property include inorganic materials such as glass or ceramics such as alumina or silica. Examples of organic materials include engineering plastics such as aromatic polyimides, polyolefins that have been made difficult to be deformed such as being stretched against external forces by methods such as radiation irradiation and crosslinking or stretching by adding a crosslinking agent. It is done. These materials may be used alone or in combination by stacking two or more of them.

  Among these porous base materials, those made of stretched polyolefin, cross-linked polyolefin, cross-linked polyolefin after stretching, and polyimides are preferable from the viewpoint of good workability in the filling step and easy availability of the base material.

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 80%. 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, there are too few proton acidic groups, which are proton conductive groups per area, and the output of the fuel cell will be low.
Furthermore, the thickness of the substrate is preferably 200 μm or less. More preferably, it is 1-150 micrometers, More preferably, it is 5-100 micrometers, Most preferably, it is 5-50 micrometers. 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.

  There is no particular limitation on the method of filling the crosslinked electrolyte polymer in the pores of the porous substrate, and a known method can be used. For example, a method of impregnating a porous substrate with a polymer precursor or a solution or dispersion thereof, and then polymerizing and crosslinking the polymer precursor can be mentioned. At that time, the mixed liquid to be filled may contain a crosslinking agent, a polymerization initiator, a catalyst, a curing agent, a surfactant and the like, if necessary.

When the polymer precursor filled in the pores of the porous substrate has a low viscosity, it can be used for impregnation as it is, but otherwise it is preferably a solution or a dispersion. In particular, a solution with a concentration of 10 to 90% by mass is preferable, and a solution with a concentration of 20 to 70% by mass 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 pores by dissolving in water or a solvent and using it for impregnation, and that a pre-swelled gel is contained in the pores. This is because when the manufactured electrolyte membrane is made into a fuel cell, water or methanol has an effect of preventing the polymer in the pores from swelling too much and the polymer from falling off.
Further, for the purpose of facilitating the impregnation operation, hydrophilic treatment of the porous substrate, addition of a surfactant to the polymer precursor solution, or ultrasonic irradiation during the impregnation can be performed.

  In addition, it is preferable that a cross-linked electrolyte polymer having proton conductivity is chemically bonded to the surface of the porous substrate, particularly the inner surface of the pore. As a means for forming the bond, the polymer precursor to be filled is a radical. In the case of a polymerizable substance, the substrate is preliminarily irradiated with plasma, ultraviolet rays, electron beams, gamma rays, corona discharge, etc. to generate radicals on the surface, and when the filled polymer precursor is polymerized, it is grafted onto the substrate surface. A method that allows polymerization to occur simultaneously, a method that causes graft polymerization to the surface of the substrate and polymerization of the polymer precursor simultaneously by irradiating an electron beam after filling the polymer precursor to the substrate, radical extraction polymerization of hydrogen abstraction type Initiator is blended with polymer precursor, heated and irradiated with ultraviolet rays, and graft polymerization onto the substrate surface and polymerization of polymer precursor are performed simultaneously The method of causing, methods and the like using a coupling agent. These may be performed alone or a plurality of methods may be used in combination.

    The electrolyte membrane according to the present invention can have excellent proton conductivity by containing a crosslinked electrolyte polymer having a sulfonic acid group. Furthermore, since the crosslinked electrolyte polymer uses a specific polyfunctional allyl compound as a crosslinking agent, the electrolyte polymer is stable against hydrolysis. As a result, the electrolyte membrane has excellent durability.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, the scope of the present invention is not limited by these examples. Moreover, the part in an Example and a comparative example shall mean a mass part unless there is particular notice. The proton conductivity, methanol permeability, and durability (forced deterioration test) of the obtained electrolyte membrane were evaluated as follows.

  <Proton conductivity> Conductivity measurement of the swollen sample at 25 ° C was performed. An electrolyte membrane that was swollen by being immersed in pure water for 1 hour was sandwiched between two platinum plates to obtain a measurement sample. Thereafter, AC impedance measurement from 100 Hz to 40 MHz was performed to measure the conductivity. The higher the conductivity, the easier the protons move in the electrolyte membrane, indicating that the fuel cell is excellent.

  <Methanol Permeability> A permeation experiment at 25 ° C. was performed as follows. The electrolyte membrane was sandwiched between glass cells, 10% by mass aqueous methanol solution was placed in one cell, and pure water was placed in the other cell. The amount of methanol penetrating the pure water side was measured over time by gas chromatographic analysis, and the permeation coefficient when it reached a steady state was measured. A lower permeation coefficient indicates that methanol is less likely to pass through the electrolyte membrane and is suitable for fuel cell applications.

<Durability (Forced Degradation Test)> Durability was evaluated by forced degradation instead of confirming the polymer degradation phenomenon due to hydrolysis in the battery. The electrolyte membrane immersed in pure water was allowed to stand for 6 hours at 121 ° C. and 2 atmospheres. The elution rate of the filled polymer in the electrolyte membrane was determined from the weight change before and after the test. The larger the elution rate, the faster the deterioration when operated as a battery, and the smaller the dissolution rate, the less likely it is to deteriorate.
Example 1

A cross-linked polyethylene film (thickness 16 μm, porosity 38%) was used as the porous substrate. 2-acrylamido-2-methylpropanesulfonic acid 45 parts, triallyl isocyanurate 5 parts, nonionic surfactant 0.5 parts, 2-hydroxy-2-methyl-1-phenylpropan-1-one 0.05 parts The porous substrate was immersed in a monomer solution consisting of 15 parts of water and 35 parts of N, N-dimethylformamide, and the porous substrate was filled with the solution. Next, after pulling up the porous substrate from the solution, ultraviolet rays were irradiated for 2 minutes with a high-pressure mercury lamp to polymerize the monomers inside the pores to obtain an electrolyte membrane. Table 1 shows the evaluation results of the obtained film.
(Example 2)

An electrolyte membrane was obtained in the same manner as in Example 1 except that triallylamine was used instead of triallyl isocyanurate in Example 1. Table 1 shows the evaluation results of the obtained film.
Example 3

An electrolyte membrane was obtained in the same manner as in Example 1 except that N, N, N ′, N′-tetraallyl-1,4-diaminobutane was used instead of triallyl isocyanurate in Example 1. Table 1 shows the evaluation results of the obtained film.
Example 4

In Example 1, 45 parts of 2-acrylamido-2-methylpropanesulfonic acid, 24 parts of triallyl isocyanurate, 6 parts of water, 40 parts of water, and 35 parts of N, N-dimethylformamide were 0 parts. An electrolyte membrane was obtained in the same manner as in Example 1 except that 6 parts of N, N-methylenebisacrylamide and 24 parts of acrylic acid were newly added. Table 1 shows the evaluation results of the obtained film.
(Example 5)

An electrolyte membrane was obtained in the same manner as in Example 4 except that triallylamine was used instead of triallyl isocyanurate in Example 4. Table 1 shows the evaluation results of the obtained film.
(Comparative Example 1)

An electrolyte membrane was obtained in the same manner as in Example 1 except that N, N′-methylenebisacrylamide was used instead of triallyl isocyanurate in Example 1. Table 1 shows the evaluation results of the obtained film.
(Comparative Example 2)

An electrolyte membrane was obtained in the same manner as in Example 4 except that 6 parts of N, N′-methylenebisacrylamide was changed to 12 parts and 6 parts of triallyl isocyanurate were changed to 0 parts. Table 1 shows the evaluation results of the obtained film.
(Comparative Example 3)

An electrolyte membrane was obtained in the same manner as in Example 1 except that trimethylolpropane diallyl ether was used instead of triallyl isocyanurate in Example 1. Table 1 shows the evaluation results of the obtained film.
(Comparative Example 4)

An electrolyte membrane was obtained in the same manner as in Example 1 except that pentaerythritol triallyl ether was used instead of triallyl isocyanurate in Example 1. Table 1 shows the evaluation results of the obtained film.
(Example 6)

In order to confirm that the obtained membrane functions as a fuel cell, the membrane prepared in Example 1 was incorporated into a DMFC cell and evaluated.
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 . These were superposed on the center of the electrolyte membrane obtained in Example 1 with the paint surface inside, and heated and pressed at 120 ° C. to prepare a membrane electrode assembly (MEA) for fuel cells. This was installed in a DMFC single cell and operated to confirm the performance. The DMFC operating conditions were such that the cell temperature was 50 ° C., a 3 mol / l aqueous methanol solution was supplied to the fuel electrode at 10 ml / min, and oxygen was supplied to the oxygen electrode at 0.3 liter / min. The voltage was read while increasing the current value, and the current density-voltage curve of FIG. 1 was obtained.

  As can be seen from Table 1, the Examples exhibited better performance in the durability test than the Comparative Examples.

  The electrolyte membrane of the present invention can be applied not only to fuel cells, but also to electrochemical device elements such as various sensors and separation membranes for electrolysis.

10 is a graph showing a current density-voltage curve in the fuel cell of Example 6.

Claims (8)

(A) a compound having a carbon-carbon double bond polymerizable in one molecule and a sulfonic acid group or a salt thereof, and (b) a polyfunctional allyl or methallyl compound represented by the following structural formula (1):
An electrolyte membrane comprising a cross-linked electrolyte polymer having an essential constituent monomer.

In the formula, R ₁ represents an allyl group or methallyl group or a part of a carbon chain or ring structure containing these groups, and R ₂ represents hydrogen, an alkyl group, an alkylene group, an allyl group or a methallyl group, an allyl group or a methallyl group. R ₃ represents a hydrogen or a methyl group.
In the monomer (b), R ₁ is an allyl group or methallyl group or a part of a carbon chain or ring structure containing these groups, and R ₂ is a part of a carbon chain or ring structure containing an allyl group or methallyl group. 2. The electrolyte membrane according to claim 1, which is a polyfunctional allyl or methallyl compound represented by the structural formula (1).
Monomer (b) is triallyl isocyanurate, trimethallyl isocyanurate, N, N, N ′, N′-tetraallyl-1,4-diaminobutane or N, N, N ′, N′-tetramethallyl-1,4 The electrolyte membrane according to claim 1, wherein the electrolyte membrane is diaminobutane.
The monomer (a) is 2-acrylamido-2-methylpropanesulfonic acid and / or 2-methacrylamideamido-2-methylpropanesulfonic acid, or a salt thereof. Electrolyte membrane.
The ratios of the monomers (a) and (b) to the total monomers constituting the crosslinked electrolyte polymer are 20 to 99.9% by mass and 0.1 to 20% by mass, respectively. The electrolyte membrane described.
6. The electrolyte membrane according to claim 1, wherein the crosslinked electrolyte polymer is filled in pores of the porous substrate.
The electrolyte membrane according to claim 1, which is obtained by a production method including the following steps.
(1) A step of filling a monomer constituting the crosslinked electrolyte polymer or a solution or dispersion thereof into the pores of the porous substrate.
(2) A step of polymerizing and crosslinking the filled monomer.
A fuel cell in which the electrolyte membrane according to claim 1 is incorporated.

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