JPWO2005076396A1 - Electrolyte membrane and fuel cell using the electrolyte membrane - Google Patents

Abstract

It can be used for electrochemical device applications such as polymer electrolyte fuel cells, has high proton conductivity, has excellent methanol permeation prevention performance when used as a DMFC, and has excellent durability when operated as a fuel cell. An electrolyte membrane is provided. An electrolyte membrane obtained by filling an electrolyte polymer having proton conductivity into pores of a porous base material that does not substantially swell with an organic solvent containing methanol and water, and the membrane is 1 at 25 ° C. An electrolyte membrane, wherein a water swelling ratio represented by the following formula (a) when immersed in water for a period of time is 0.1 to 2.0. Water swelling ratio = (AB) / (BC) (a) where A is the weight of the electrolyte membrane after being immersed in water, B is the weight of the electrolyte membrane when dried, and C is the weight of the porous substrate. Show.

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, this patent document does not mention at all the water swelling rate of the electrolyte polymer filled in the electrolyte membrane, and the durability of the electrolyte membrane 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 diligent study, the inventors of the present invention, in an electrolyte membrane formed by filling an electrolyte polymer having proton conductivity in the pores of a porous substrate, were immersed in water at 25 ° C. for 1 hour. When the mass ratio between the amount of water in the membrane and the filled electrolyte polymer is in a specific range, the membrane is found to be excellent in proton conductivity, methanol permeation-preventing property, and improved in durability. It came to be completed.

That is, the present invention is an electrolyte membrane in which an electrolyte polymer having proton conductivity is filled in pores of a porous substrate that does not substantially swell with an organic solvent containing methanol and water, Has a water swell ratio represented by the following formula (a) (hereinafter referred to as “water swell ratio represented by formula (a)”) when immersed in water at 25 ° C. for 1 hour: 0.1-2. An electrolyte membrane characterized by zero.
Water swelling rate = (AB) / (BC) (a)
However, A represents the mass of the electrolyte membrane after being immersed in water, B represents the mass of the electrolyte membrane during drying, and C represents the mass of the porous substrate.
Further, the proton conductivity determined by the alternating current impedance method is 5 mS / cm or more, and the methanol permeability coefficient at 25 ° C. determined by the dialysis method is 50 (μm · kg) / (m ² · h) or less. .
In addition, the electrolyte polymer is a polymer containing a sulfonic acid group, and further, a crosslinked electrolyte polymer having a carbon-carbon double bond polymerizable in one molecule and a sulfonic acid group or a salt thereof as an essential constituent monomer An electrolyte membrane characterized in that 2-acrylamido-2-methylpropanesulfonic acid and / or 2-methacrylamide-2-methylpropanesulfonic acid (hereinafter referred to as “2- (meth) acrylamide— It is referred to as “2-methylpropanesulfonic acid”) or a salt thereof.
In the present invention, the electrolyte membrane includes (1) a step of filling a monomer constituting the electrolyte polymer or a solution or dispersion thereof in the pores of the porous substrate, and (2) a step of polymerizing 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 specifying the swelling ratio of the filled electrolytic mass when immersed in water within a specific range. Further, since it is an electrolyte membrane excellent in proton conductivity and methanol permeation blocking performance, it can be suitably used as an electrolyte membrane for a polymer electrolyte fuel cell, particularly a direct methanol polymer electrolyte fuel cell.

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

Hereinafter, the present invention will be described in detail.
In the electrolyte membrane of the present invention, an electrolyte polymer having proton conductivity is filled in the pores of a porous base material that does not substantially swell with an organic solvent containing methanol and water. This improves the durability of the conductive electrolyte membrane.

  The electrolyte polymer having proton conductivity used for the electrolyte membrane of the present invention is not particularly limited, but preferably contains a sulfonic acid group from the viewpoint of high proton conductivity. Examples of such electrolyte polymers include sulfonated polyetheretherketone, sulfonated polyphenylene, sulfonated polyethersulfone, sulfonated polyimide, and alkylsulfonated polybenzimidazole. Therefore, a cross-linked electrolyte polymer having a compound having a carbon-carbon double bond and a sulfonic acid group polymerizable in one molecule or a salt thereof as an essential constituent monomer is preferable. Specific examples of such monomers include 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, (meth) Examples thereof include monomers such as allyl sulfonic acid and vinyl sulfone, and salts thereof. 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, vinyl sulfonic acid has the highest sulfonic acid content per molecular weight, so it is preferable to use it as a copolymerization component because proton conductivity of the electrolyte membrane is improved. “(Meth) acryloyl” means “acryloyl and / or methacryloyl”, and “(meth) acryl” means “acryl and / or methacryl”.

The monomer constituting the electrolyte polymer used in the present invention preferably contains a compound having a carbon-carbon double bond polymerizable in one molecule and a sulfonic acid group or a salt thereof as essential components, but if necessary, further. Thus, other monomers can be used in combination. The monomer is not particularly limited as long as it is copolymerizable with the monomer. For example, as a water-soluble monomer, (meth) acrylic acid, (anhydrous) maleic acid, fumaric acid, crotonic acid, itaconic acid, vinyl Acidic monomers such as phosphonic acid and acidic phosphoric acid group-containing (meth) acrylate and salts thereof; (meth) acrylamide, N-substituted (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate , Monomers such as methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, N-vinylpyrrolidone, N-vinylacetamide; N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meta ) Acrylate, N, - and dimethyl amino propyl (meth) quaternized product basic monomers and their acrylamide such specifically.
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.
“(Meth) allyl” represents “allyl and / or methallyl”, and “(meth) acrylate” represents “acrylate and / or methacrylate”.

  The electrolyte polymer used in the electrolyte membrane of the present invention preferably has a crosslinked structure introduced in order to improve durability. A method for introducing a crosslinked structure is not particularly limited, and a known method can be used. 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 cross-linking agent include N, N-methylenebis (meth) acrylamide, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, and triglyceride. Methylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, trimethylolpropane diallyl ether, pentaerythritol tri Allyl ether, divinylbenzene, bisphenol di (meth) acrylate, isocyanuric acid di (meth) acrylate, tetra ali Okishietan, triallylamine, diallyloxy acetate, 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 (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, etc., and heating after radical polymerization of polymerizable double bonds. Then, a condensation reaction or the like is caused to crosslink, or the same crosslinking reaction can be caused by 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 preferably 0.1 to 50% by mass with respect to the total mass of unsaturated monomers in all monomers (hereinafter referred to as “polymer precursor”) constituting the electrolyte polymer, 0.1-40 mass% is more preferable, Especially preferably, it is 1-40 mass%. If the amount of the crosslinking agent is too small, the water swelling ratio represented by the formula (a) when the obtained electrolyte membrane is immersed in water at 25 ° C. for 1 hour tends to exceed 2.0, and the effect of the present invention is obtained. This is not preferable. On the other hand, when the amount is too large, the amount of the sulfonic acid group-containing monomer is relatively lowered, the proton conductivity is 5 mS / cm or less, and it is difficult to obtain the effects of the present invention.

As a method for obtaining an electrolyte polymer by copolymerizing a 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. Peroxides such as ammonium persulfate, potassium persulfate, sodium persulfate, hydrogen peroxide, benzoyl peroxide, cumene hydroperoxide, di-t-butyl peroxide; the above peroxides and sulfites, bisulfites, Redox initiator combined with a reducing agent such as thiosulfate, formamidinesulfinic acid, ascorbic acid; or azo radical polymerization such as 2,2′-azobis- (2-amidinopropane) dihydrochloride, azobiscyanovaleric acid Initiators, etc.
These radical polymerization initiators may be used alone or in combination of two or more. Among these, peroxide radical polymerization initiators 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 electrolyte A chemical bond can be formed with the polymer, which is preferable.

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. In the case of further photoinitiating polymerization, the radical photopolymerization initiator is more preferably dissolved or dispersed in advance in the polymer precursor, a solution or dispersion thereof.
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 such 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 photopolymerization initiator is too small, there is a problem that the amount of unreacted monomers increases. If the amount is too large, the crosslink density of the polymer that is generated becomes too low, and the durability when the fuel cell is built and 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, it is preferable because a chemical bond can be formed between the substrate surface and the filled electrolyte polymer.

  The porous base material used in the present invention is a material which 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 easy workability of 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 for filling the 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 crosslinked electrolyte polymer having proton conductivity is chemically bonded to the surface of the porous substrate, particularly the surface inside the pores. 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, or irradiated with ultraviolet rays to simultaneously graft onto the substrate surface and polymer precursor polymerization 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.

  In addition, the membrane surface of the electrolyte membrane in the present invention may be either exposed from the porous base material portion or covered with the same or different proton conductive polymer as the filled polymer, but the surface contact resistance is reduced. Therefore, it is preferable that the membrane surface is covered with the filled electrolyte polymer.

The electrolyte membrane of the present invention is an electrolyte membrane obtained by filling an electrolyte polymer having proton conductivity into the pores of a porous substrate, and the water swelling rate when the membrane is immersed in water is specific. It is in the range. That is, the electrolyte membrane of the present invention is characterized in that when the electrolyte membrane is immersed in water at 25 ° C. for 1 hour, the water swelling ratio represented by the formula (a) is 0.1 to 2.0. . A preferred range is 0.1 to 1.5, more preferably 0.2 to 1.5.
Water swelling rate = (A−B) / (B−C) (a)
Here, (A) is the mass of the electrolyte membrane after being immersed in water, (B) is the mass of the electrolyte membrane during drying, and (C) is the mass (C) of the porous substrate.
It should be noted that the water swelling rate is a problem only for the electrolyte filled in the pores, and when the porous substrate portion is covered with the filled polymer as described above, the surface coating is wet. The amount of water shall be measured after scraping off the polymer.
It should be noted that the swelling ratio of the filled electrolyte when immersed in water (the amount of water in the filled electrolyte after immersion / the filled electrolytic mass) should be in a specific range, not the water swelling ratio represented by the formula (a). However, it is difficult to measure the amount of water in the filled electrolyte after immersion, and the porous membrane serving as the substrate hardly swells in water, so that the water swelling rate of the membrane is used instead.
When the value of the water swelling ratio represented by the formula (a) is too large, the durability of the membrane becomes insufficient, and there is a problem that the output decreases in a short time when operated as a fuel cell. However, both of them are not preferable because of the problem that the performance as a fuel cell deteriorates. The method for adjusting this ratio is not particularly limited. As a method of increasing the ratio, there are a method of increasing the amount of crosslinking to be filled, a method of reducing the crosslinking density of the electrolyte polymer to be filled, a method of reducing the amount of the electrolyte polymer to be filled, and a sulfonic acid group density of the electrolyte polymer to be filled. Examples of the method for decreasing the ratio include a method for increasing the crosslinking density of the filled electrolyte electrolyte, a method for increasing the hydrophobicity of the electrolyte polymer by means such as increasing the number of times of filling, etc. Is mentioned.

Further, the electrolyte membrane of the present invention has a proton conductivity of 5 mS / cm or more determined by the alternating current impedance method and a methanol permeability coefficient at 25 ° C. of 50 (μm · kg) / (m ² · h) or less determined by the dialysis method. It is preferable that If these two physical property values are out of the above range, the performance as a fuel cell is deteriorated, which is not preferable.

  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 obtained electrolyte membrane was evaluated for water swelling rate, proton conductivity, methanol permeability, and durability (forced deterioration test) as follows.

<Water swelling rate> The water swelling rate represented by the formula (a) at 25 ° C was measured. Moisture on the surface of the electrolyte membrane swollen by being immersed in pure water for 1 hour was wiped off, and the mass (A) was measured. Moreover, the electrolyte membrane mass (B) at the time of drying was also measured, and the water swelling rate represented by the formula (a) was calculated from the following formula. C in a formula shows the mass of a porous substrate.
Water swelling rate = (AB) / (BC)

  <Proton conductivity> The conductivity of the swollen sample at 25 ° C was measured. 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)> Instead of confirming the deterioration phenomenon of the electrolyte polymer due to hydrogen peroxide generated in the battery, durability was evaluated by forced deterioration. An aqueous solution containing 3.5% by mass hydrogen peroxide and 0.01% by mass ferric sulfate heptahydrate was prepared, and the electrolyte membrane was immersed therein, stirred at 25 ° C. for 6 hours, and then the electrolyte membrane was pulled up. . The elution rate of the filled electrolyte polymer in the electrolyte membrane was determined from the mass 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, N, N′-methylenebisacrylamide 5 parts, nonionic surfactant 0.5 part, 2-hydroxy-2-methyl-1-phenylpropane-1-one The porous substrate was immersed in an aqueous monomer solution composed of 0.05 part and 50 parts of water, and the aqueous solution was filled into the porous substrate. 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)
Example 1 is the same as Example 1 except that 45 parts of 2-acrylamido-2-methylpropanesulfonic acid is 54 parts, 5 parts of N, N′-methylenebisacrylamide is 6 parts, and 50 parts of water is 40 parts. Thus, an electrolyte membrane was obtained. Table 1 shows the evaluation results of the obtained film.

(Example 3)
In Example 1, 52 parts of 2-acrylamido-2-methylpropanesulfonic acid were 52 parts, 5 parts of N, N′-methylenebisacrylamide were 6.5 parts, and 50 parts of water were 35 parts. An electrolyte membrane was obtained in the same manner as in Example 1 except that 5 parts were added. Table 1 shows the evaluation results of the obtained film.

(Example 4)
The same porous substrate as in Example 1 was used. 2-acrylamido-2-methylpropanesulfonic acid 52 parts, N-methylolacrylamide 13 parts, nonionic surfactant 0.5 parts, 2-hydroxy-2-methyl-1-phenylpropan-1-one 0.05 parts The porous substrate was immersed in an aqueous monomer solution composed of 35 parts of water, and the porous substrate was filled with the aqueous 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. Thereafter, it was heated in an oven at 120 ° C. for 3 minutes to obtain an electrolyte membrane. Table 1 shows the evaluation results of the obtained film.

(Example 5)
The same porous substrate as in Example 1 was used. 2-acrylamido-2-methylpropanesulfonic acid 31.5 parts, N, N′-methylenebisacrylamide 3.5 parts, nonionic surfactant 0.5 parts, 2-hydroxy-2-methyl-1-phenylpropane The porous substrate was immersed in an aqueous monomer solution composed of 0.05 part of -1-one and 65 parts of water, and the aqueous solution was filled into the porous substrate. 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. Further, the obtained electrolyte membrane was prepared by using 31.5 parts of 2-acrylamido-2-methylpropanesulfonic acid, 3.5 parts of N, N′-methylenebisacrylamide, 2-hydroxy-2-methyl-1-phenylpropane-1 -It was immersed in an aqueous monomer solution consisting of 0.05 parts of ON and 65 parts of water, and the electrolyte membrane was swollen with the aqueous solution. Next, after the swollen electrolyte membrane was lifted from the solution, ultraviolet rays were irradiated for 2 minutes with a high-pressure mercury lamp to polymerize the monomers inside the electrolyte membrane, thereby obtaining an electrolyte membrane. The evaluation results of the obtained film are shown in Table 1.

(Comparative Example 1)
In Example 1, except that 45 parts of 2-acrylamido-2-methylpropanesulfonic acid was 31.5 parts, 5 parts of N, N′-methylenebisacrylamide was 3.5 parts, and 50 parts of water was 65 parts. An electrolyte membrane was obtained in the same manner as 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 1 except that 45 parts of 2-acrylamido-2-methylpropanesulfonic acid and 49 parts of N, N′-methylenebisacrylamide were 1 part 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., an aqueous methanol solution having a concentration of 1 mol / liter was supplied to the fuel electrode at 10 ml / min, and pure air was supplied to the oxygen electrode at 2 liter / min. The voltage was read while increasing the current value, and the current density-voltage curve of FIG. 1 was obtained.

  As is clear from Table 1, each example showed superior performance in the durability test as compared with the comparative example.

  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.

[Claims]
[Claim 1]
An electrolyte membrane formed by filling an electrolyte polymer having proton conductivity into pores of a porous base material that does not substantially expand with respect to an organic solvent containing methanol and water, the membrane being 1 at 25 ° C. An electrolyte membrane for a direct methanol fuel cell, wherein a water swelling ratio represented by the following formula (a) when immersed in water for a period of time is 0.1 to 2.0.
Water swelling rate = (AB) / (BC) (a)
However, A represents the mass of the electrolyte membrane after being immersed in water, B represents the mass of the electrolyte membrane during drying, and C represents the mass of the porous substrate.
[Claim 2]
Proton conductivity determined by AC impedance method is 5 mS / cm or more, and methanol permeability coefficient at 25 ° C. determined by dialysis method is 50 (μm · kg) / (m ² · h) or less. The electrolyte membrane for direct methanol fuel cells according to claim 1.
[Claim 3]
Claim 1 electrolyte polymer, characterized in that it is a 2-acrylamido-2-methylpropanesulfonic acid and / or 2-methacrylamide-2-methylpropanesulfonic acid or polymers of these salts as essential constituent monomers, Or an electrolyte membrane for a direct methanol fuel cell as described in 2 ;
[Claim 4]
Porous substrate, oriented polyolefin, crosslinked polyolefin, polyolefin is crosslinked after stretching, claims 1 to direct methanol fuel cell electrolyte membrane according to 3, characterized in that it consists of polyimides.
[Claim 5]
It claims 1 to direct direct methanol fuel cell comprising incorporating a methanol fuel cell electrolyte membrane according to 4.

The electrolyte membrane of the present invention is an electrolyte membrane obtained by filling an electrolyte polymer having proton conductivity into the pores of a porous substrate, and the water swelling rate when the membrane is immersed in water is specific. It is in the range. That is, the electrolyte membrane of the present invention is characterized in that when the electrolyte membrane is immersed in water at 25 ° C. for 1 hour, the water swelling ratio represented by the formula (a) is 0.1 to 2.0. . A preferred range is 0.1 to 1.5, more preferably 0.2 to 1.5.
Water swelling rate = (A−B) / (B−C) (a)
Here, (A) is the mass of the electrolyte membrane after being immersed in water, (B) is the mass of the electrolyte membrane during drying, and (C) is the mass (C) of the porous substrate.
It should be noted that the water swelling rate is a problem only for the electrolyte filled in the pores, and when the porous substrate portion is covered with the filled polymer as described above, the surface coating is wet. The amount of water shall be measured after scraping off the polymer.
It should be noted that the swelling ratio of the filled electrolyte when immersed in water (the amount of water in the filled electrolyte after immersion / the filled electrolytic mass) should be in a specific range, not the water swelling ratio represented by the formula (a). However, it is difficult to measure the amount of water in the filled electrolyte after immersion, and the porous membrane serving as the substrate hardly swells in water, so that the water swelling rate of the membrane is used instead.
When the value of the water swelling ratio represented by the formula (a) is too large, the durability of the membrane becomes insufficient, and there is a problem that the output decreases in a short time when operated as a fuel cell. However, both of them are not preferable because of the problem that the performance as a fuel cell deteriorates. The method for adjusting this ratio is not particularly limited. Examples of the method for increasing the ratio include a method for reducing the crosslinking density of the electrolyte polymer to be filled, a method for reducing the amount of the crosslinked electrolyte polymer to be filled, a method for increasing the density of the sulfonic acid group of the electrolyte polymer to be filled, and the like. Examples of the method for lowering the pH include a method of increasing the crosslinking density of the crosslinked electrolyte polymer to be filled and a method of increasing the hydrophobicity of the electrolyte polymer by means such as increasing the number of times of filling the crosslinked electrolyte polymer to be filled.

Claims (16)

An electrolyte membrane formed by filling an electrolyte polymer having proton conductivity into pores of a porous base material that does not substantially expand with respect to an organic solvent containing methanol and water, the membrane being 1 at 25 ° C. An electrolyte membrane, wherein a water swelling ratio represented by the following formula (a) when immersed in water for a period of time is 0.1 to 2.0.
Water swelling rate = (AB) / (BC) (a)
However, A represents the mass of the electrolyte membrane after being immersed in water, B represents the mass of the electrolyte membrane during drying, and C represents the mass of the porous substrate. The electrolyte membrane according to claim 1, wherein the water swelling ratio represented by the formula (a) is 0.1 to 1.5. The electrolyte membrane according to claim 2, wherein a water swelling ratio represented by the formula (a) is 0.2 to 1.5. Proton conductivity determined by AC impedance method is 5 mS / cm or more, and methanol permeability coefficient at 25 ° C. determined by dialysis method is 50 (μm · kg) / (m ² · h) or less. The electrolyte membrane according to claim 1. 5. The electrolyte membrane according to claim 1, wherein the electrolyte polymer is a polymer containing a sulfonic acid group. 6. The electrolyte according to claim 5, wherein the electrolyte polymer is an electrolyte polymer having a compound containing a carbon-carbon double bond and a sulfonic acid group polymerizable in one molecule or a salt thereof as an essential constituent monomer. film. The electrolyte membrane according to claim 6, wherein the essential constituent monomer is 2-acrylamido-2-methylpropanesulfonic acid and / or 2-methacrylamide-2-methylpropanesulfonic acid, or a salt thereof. . 8. The electrolyte membrane according to claim 1, wherein the electrolyte polymer is a polymer into which a crosslinked structure is introduced. 9. The electrolyte membrane according to claim 8, wherein the introduction of the crosslinked structure is a polymerization reaction using a crosslinking agent having two or more polymerizable double bonds. 10. The electrolyte membrane according to claim 9, wherein the amount of the crosslinking agent used is 0.1 to 40% by mass with respect to the total mass of unsaturated monomers in all monomers constituting the electrolyte polymer. 11. The electrolyte membrane according to claim 1, wherein the electrolyte polymer is a polymer obtained by photoinitiated polymerization with ultraviolet rays. The electrolyte membrane according to claim 11, wherein the photoinitiated polymerization by ultraviolet rays is a reaction performed by a photopolymerization initiator added to a monomer constituting the electrolyte polymer. 13. The electrolyte membrane according to claim 12, wherein the amount of the photopolymerization initiator used is 0.01 to 1% by mass with respect to the total mass of unsaturated monomers in all monomers constituting the electrolyte polymer. . 14. The electrolyte membrane according to claim 1, wherein the porous substrate is composed of a stretched polyolefin, a crosslinked polyolefin, a polyolefin crosslinked after stretching, and a polyimide. The electrolyte membrane according to claim 1, wherein the electrolyte membrane is obtained by a production method including the following steps.
(1) A step of filling the pores of the porous substrate with a monomer constituting the electrolyte polymer or a solution or dispersion thereof.
(2) A step of polymerizing the filled monomer. A fuel cell incorporating the electrolyte membrane according to claim 1.

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