WO2009099041A1

WO2009099041A1 - Solid polymer electrolyte membrane and manufacturing method thereof, membrane electrode assembly for fuel cell, and fuel cell

Info

Publication number: WO2009099041A1
Application number: PCT/JP2009/051740
Authority: WO
Inventors: Mitsuhito Takahashi
Original assignee: Shin-Etsu Chemical Co., Ltd.
Priority date: 2008-02-05
Filing date: 2009-02-03
Publication date: 2009-08-13
Also published as: JP5326288B2; JP2009187726A

Abstract

A solid polymer electrolyte membrane is manufactured by applying radiation to a fluororesin or hydrocarbon-based resin and co-graft polymerizing at least α-methylstyrene and alkoxysilane containing styryl groups with said resin, and then sulfonating. The solid polymer electrolyte membrane of the present invention has excellent oxidation resistance. Said electrolyte membrane is placed between the fuel electrode and the air electrode of a fuel cell to form a fuel cell membrane electrode assembly. A fuel cell with extremely high performance can be produced by using said assembly in the fuel cell.

Description

Solid polymer electrolyte membrane, method for producing the same, membrane electrode assembly for fuel cell, and fuel cell

The present invention relates to a solid polymer electrolyte membrane excellent in oxidation resistance, a production method thereof, a membrane electrode assembly for a fuel cell using the solid polymer electrolyte membrane, and a fuel cell using the same.

A fuel cell using an electrolyte membrane for a polymer electrolyte fuel cell has a low operating temperature of 100 ° C. or lower, and its energy density is high. Therefore, it is expected to be widely put into practical use as a power source for electric vehicles and a simple auxiliary power source. . In this polymer electrolyte fuel cell, there are important elemental technologies related to an electrolyte membrane, a platinum-based catalyst, a gas diffusion electrode, and an electrolyte membrane-electrode assembly. Among these, there are electrolyte membranes and electrolyte membrane-electrode assemblies. The technology related to the joined body is one of the most important technologies involved in the characteristics as a fuel cell.

In a polymer electrolyte fuel cell, a fuel diffusion electrode and an air diffusion electrode are combined on both surfaces of an electrolyte membrane, and the electrolyte membrane and the electrode are substantially integrated. For this reason, the electrolyte membrane acts as an electrolyte for conducting protons, and also functions as a diaphragm to prevent direct mixing of hydrogen or methanol as a fuel with air or oxygen as an oxidant even under pressure. Have.

Such an electrolyte membrane is required to have a high proton transfer rate as an electrolyte, a high ion exchange capacity, and a constant and high water retention in order to keep electric resistance low. On the other hand, due to its role as a diaphragm, it has high mechanical strength and excellent dimensional stability, chemical stability for long-term use, especially oxidation resistance against hydroxy radicals generated at the cathode. It is required to be excellent and not to have excessive permeability to hydrogen gas or methanol as a fuel or oxygen gas as an oxidant.

Currently, fluororesin-based perfluorosulfonic acid membranes such as “Nafion (registered trademark)” developed mainly by DuPont are generally used as electrolyte membranes. However, the fluororesin-based electrolyte membrane must be started from the synthesis of the monomer, so that there are many manufacturing processes and there is a problem that the cost is high. This is a great obstacle to practical use.

Therefore, efforts are underway to develop low-cost electrolyte membranes that replace the “Nafion (registered trademark)” and the like. In the radiation graft polymerization method, a fluoropolymer film is irradiated with radiation, a radical active site is generated on the fluororesin, a hydrocarbon radical polymerizable monomer is grafted on the film, and the resulting polymer is sulfonated. A method for producing an electrolyte membrane is proposed in Japanese Patent Application Laid-Open No. 2002-313364 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2003-82129 (Patent Document 2).

However, a membrane obtained by graft polymerization of a hydrocarbon radical polymerizable monomer by a radiation graft polymerization method has a problem that it has poor oxidation resistance although high proton conductivity is obtained by achieving a high graft ratio. .

In order to improve this oxidation resistance, a highly durable solid polymer electrolyte membrane obtained by co-grafting α-methylstyrene is disclosed in Japanese Patent Application Laid-Open No. 2003-36864 (Patent Document 3). Since α-methylstyrene has a methyl group at the α-position of the benzene ring, radicals can be prevented from being generated at the α-position of the benzene ring, and a solid polymer electrolyte membrane having excellent durability can be obtained. However, since α-methylstyrene has poor radical polymerizability and graft polymerization alone does not proceed, it is necessary to co-graft with α-methylstyrene and a copolymerizable monomer. There was a problem of low conversion.

Japanese Patent Laid-Open No. 2006-313659 (Patent Document 4) discloses a solid polymer electrolyte membrane obtained by a production method in which a polymerizable monomer having an alkoxysilyl group and another polymerizable monomer are co-grafted. In this publication, the oxidation resistance of this film is not described.

JP 2002-313364 A JP 2003-82129 A JP 2003-36864 A JP 2006-313659 A

The present invention has been made in view of the above circumstances, and a solid polymer electrolyte membrane suitable for a fuel cell excellent in oxidation resistance, a method for producing the same, and a membrane electrode assembly for a fuel cell using the solid polymer electrolyte membrane And a fuel cell using the same.

As a result of intensive studies to achieve the above-mentioned object, the present inventors irradiate the resin with radiation, and co-graft polymerize a polymerizable monomer containing α-methylstyrene and a styryl group-containing alkoxysilane on the resin, It has been found that a solid polymer electrolyte membrane obtained by sulfonation has excellent oxidation resistance and is a useful solid polymer electrolyte membrane for fuel cells.

Further, by making the sulfonation rate of the styryl group-containing alkoxysilane 50% or less, the oxidation resistance is greatly improved. Further, if sulfonating at 60 ° C. or less, the sulfonation rate of the styryl group-containing alkoxysilane As a result, it was found that α-methylstyrene can be sulfonated almost quantitatively with the content being kept at 30% or less.

Accordingly, the present invention provides the following solid polymer electrolyte membrane, a production method thereof, a membrane electrode assembly for fuel cells, and a fuel cell.
[1] By irradiating a fluorine-based resin or a hydrocarbon-based resin, co-grafting a polymerizable monomer containing at least α-methylstyrene and a styryl group-containing alkoxysilane, and then sulfonating the resin. A solid polymer electrolyte membrane obtained.
[2] The solid polymer electrolyte membrane according to [1], wherein the sulfonation rate of the styryl group-containing alkoxysilane in the co-graft chain is 50% or less.
[3] The solid polymer electrolyte membrane according to [1] or [2], wherein the molar fraction of the styryl group-containing alkoxysilane in the polymerizable monomer is 30% or more.
[4] The solid polymer electrolyte membrane according to any one of [1] to [3], wherein the resin is a fluororesin.
[5] Irradiating the fluorine-based resin or hydrocarbon-based resin, and co-grafting a polymerizable monomer containing at least α-methylstyrene and a styryl group-containing alkoxysilane to the resin, followed by sulfonation. A method for producing a solid polymer electrolyte membrane.
[6] The method for producing a solid polymer electrolyte membrane according to [5], wherein the sulfonation rate of the styryl group-containing alkoxysilane in the co-graft chain is 50% or less.
[7] The method for producing a solid polymer electrolyte membrane according to [5] or [6], wherein the molar fraction of the styryl group-containing alkoxysilane in the polymerizable monomer is 30% or more.
[8] The method for producing a solid polymer electrolyte membrane according to any one of [5] to [7], wherein the resin is a fluororesin.
[9] The method for producing a solid polymer electrolyte membrane according to any one of [5] to [8], wherein the sulfonation is performed at 60 ° C. or lower.
[10] The method for producing a solid polymer electrolyte membrane according to any one of [5] to [8], wherein the sulfonation is performed at 30 ° C. or lower.
[11] A membrane electrode assembly for a fuel cell, characterized in that the solid polymer electrolyte membrane according to any one of [1] to [4] is provided between a fuel electrode and an air electrode.
[12] A fuel cell comprising the fuel cell membrane electrode assembly according to [11].
[13] The fuel cell according to [12], which is a direct methanol type using methanol as a fuel.

The solid polymer electrolyte membrane of the present invention has excellent oxidation resistance. This electrolyte membrane is provided between a fuel electrode and an air electrode of a fuel cell to form a membrane electrode assembly for a fuel cell. By using it for a fuel cell, the fuel cell can have a very high performance.

14 is a graph showing evaluation results of polarization characteristics (IV characteristics) of the fuel cell of Example 7.

Hereinafter, the present invention will be described in more detail.
The solid polymer electrolyte membrane of the present invention can be obtained by co-grafting a polymerizable monomer containing α-methylstyrene and a styryl group-containing alkoxysilane onto a resin irradiated with radiation and further sulfonating.

As the resin, fluorine resin or hydrocarbon resin is used. As the fluorine resin, tetrafluoroethylene-hexafluoropropylene copolymer resin (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin are used. Examples of hydrocarbon resins such as (PFA), tetrafluoroethylene-ethylene copolymer resin (ETFE), and vinylidene fluoride resin (PVDF) include polyethylene, polypropylene, polyetheretherketone (PEEK), and polyethersulfone (PES). Etc.), and one of these can be used alone or two or more of them can be used in combination. In particular, a fluorine-based resin is preferable because of its excellent durability. The shape is not particularly limited, but may be a film shape or the like.

In graft polymerization, the resin is irradiated with radiation in advance to generate radicals that serve as the starting point of grafting, and then the pre-irradiation method in which the resin is brought into contact with the monomer to carry out the grafting reaction, and radiation is applied in the presence of the monomer and resin. Although there is a simultaneous irradiation method of irradiation, any method can be adopted in the present invention. The film thickness of the resin film is not particularly limited, but is preferably 10 to 100 μm, particularly 10 to 50 μm.

Examples of the radiation used for graft polymerization of the radical polymerizable monomer on the resin in the present invention include γ rays, X rays, electron beams, ion beams, ultraviolet rays, etc., but γ rays, An electron beam is preferred.

The absorbed dose of radiation is preferably 1 kGy or more, particularly 1 to 200 kGy, particularly 1 to 100 kGy, and if it is less than 1 kGy, the amount of radical generation is small and grafting may be difficult, and if it exceeds 200 kGy, the graft rate is large. The mechanical strength of the electrolyte membrane obtained by becoming too small may be reduced.

Further, the irradiation with radiation is preferably performed in an inert gas atmosphere such as helium, nitrogen, and argon gas, and the oxygen concentration in the atmospheric gas is preferably 100 ppm or less, more preferably 50 ppm or less, but it is not necessarily in the absence of oxygen. There is no need to do it.

In the solid polymer electrolyte membrane of the present invention, a polymerizable monomer (radical polymerizable monomer) containing α-methylstyrene and a styryl group-containing alkoxysilane is co-grafted to the resin irradiated with radiation. The styryl group-containing alkoxysilane to co-graft polymerization and α- methyl styrene, styryl group in the molecule _{_{(CH 2 = CH-C 6}} H 4 -) styryl trimethoxysilane having, styryl triethoxysilane, styryl ethyltrimethoxysilane Examples include silane, styrylethyltriethoxysilane, vinylphenethyltrimethoxysilane, vinylphenethyltriethoxysilane, and the like. In particular, styryltrimethoxysilane is desirable because it has good copolymerizability with α-methylstyrene.

The molar fraction of α-methylstyrene in the polymerizable monomer in the present invention is preferably 10 to 90%, more preferably 20 to 70%, and if it exceeds 90%, a sufficient graft ratio may not be obtained. If it is less than 10%, the oxidation resistance of the film may be deteriorated.

Further, the molar fraction of the styryl group-containing alkoxysilane in the polymerizable monomer is preferably 10 to 90%, more preferably 30 to 80%, and if it exceeds 90%, the brittleness of the film may be deteriorated. If it is less than 10%, a sufficient graft rate may not be obtained. In particular, the oxidation resistance can be greatly improved by setting it to 30% or more.

The graft ratio of the polymerizable monomer in the solid polymer electrolyte membrane of the present invention is preferably 20 to 100%, particularly preferably 40 to 100%.

In addition, in the co-graft polymerization, another radical polymerizable monomer can be further co-grafted as long as the effects of the present invention are not impaired. In this case, the other radical polymerizable monomer is preferably a monofunctional polymerizable monomer, for example, having an ion conductive group such as a sulfonic acid group, a sulfonic acid amide group, a carboxylic acid group, a phosphoric acid group, or a quaternary ammonium base. Monomers (sodium acrylate, sodium acrylamidomethylpropanesulfonate, sodium styrenesulfonate, etc.) can be used alone or in appropriate combination. In addition, a polyfunctional polymerizable monomer can be used by utilizing the difference in the reactivity of the functional group.

Furthermore, if necessary, a crosslinkable monomer such as a monomer having a plurality of vinyl groups such as divinylbenzene can be mixed in an amount of 0.1 to 15 mol% with respect to the polymerizable monomer. Thus, by using a crosslinkable monomer together, a crosslinked structure can be introduced into the graft chain.

Here, the amount of the polymerizable monomer grafted to the resin irradiated with radiation is 1,000 to 100,000 parts by weight, particularly 5,000 to 30,000 parts by weight of the polymerizable monomer with respect to 100 parts by weight of the resin. It is preferable to use a part. If the amount of the polymerizable monomer is too small, the contact may be insufficient. If the amount is too large, the polymerizable monomer may not be used efficiently.

In the graft polymerization of these monomers, a polymerization initiator such as azobisisobutyronitrile may be appropriately used as long as the object of the present invention is not impaired.

Furthermore, in the present invention, a solvent can be used during the graft reaction. As the solvent, those that uniformly dissolve the radical polymerizable monomer are preferable, for example, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate and butyl acetate, alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, and butyl alcohol. , Ethers such as tetrahydrofuran and dioxane, aromatic hydrocarbons such as N, N-dimethylformamide, N, N-dimethylacetamide, benzene and toluene, aliphatics or fats such as n-heptane, n-hexane and cyclohexane A cyclic hydrocarbon or a mixed solvent thereof can be used.

In this case, the amount of solvent used is preferably monomer / solvent (mass ratio) = 0.01-20. If the monomer / solvent (mass ratio) is greater than 20, it may be difficult to adjust the number of monomer units in the graft chain, and if it is less than 0.01, the graft ratio may be too low. In particular, the monomer / solvent (mass ratio) is preferably 0.2 to 10.

In the present invention, it is preferable to adjust the oxygen concentration in the reaction atmosphere during graft polymerization to 0.05 to 5% by volume. It is considered that oxygen in the reaction atmosphere reacts with radicals in the system to become carbonyl radicals or peroxy radicals and acts to suppress further reactions. When the oxygen concentration is less than 0.05% by volume, the polymerizable monomer is polymerized in the solution and a gel insoluble in the solvent is generated. Therefore, the raw material is wasted and it takes time to remove the gel. If it exceeds 5% by volume, the graft ratio may decrease. A desirable oxygen concentration is 0.1 to 3% by volume, and a more desirable oxygen concentration is 0.1 to 1% by volume. In addition, as gas other than oxygen, inert gas, such as nitrogen and argon gas, is used.

The reaction conditions for the graft polymerization are preferably 0 to 100 ° C., particularly 40 to 80 ° C., and 1 to 40 hours, particularly 4 to 20 hours.

Sulfonated after co-graft polymerization as described above. Sulfonation is carried out by contacting the grafted membrane with a sulfonating agent in liquid or gas phase. Under the present circumstances, the sulfonation rate of a styryl group containing alkoxysilane is 50% or less, Preferably it is 30% or less, and when larger than 50%, there exists a possibility that the oxidation resistance of a film | membrane may worsen. This is probably because when the styryl group-containing alkoxysilane is sulfonated, hydrogen bonded to the α-carbon of the styryl group is easily extracted by the hydroxy radical. In addition, since the one where the sulfonation rate of a styryl group containing alkoxysilane is smaller is advantageous in the viewpoint of an oxidation-resistant improvement, the minimum is suitably 0%.

The reaction temperature of sulfonation is preferably 60 ° C. or lower, more preferably 30 ° C. or lower. In the sulfonation, α-methylstyrene (the benzene ring is monosubstituted) is more easily sulfonated than the styryl group-containing alkoxysilane (the benzene ring is disubstituted), but the selection ratio largely depends on the reaction temperature of the sulfonation. If the temperature is higher than 60 ° C., the styryl group-containing alkoxysilane is also sulfonated almost simultaneously with α-methylstyrene, and the oxidation resistance may not be sufficiently improved. In particular, at 30 ° C. or lower, α-methylstyrene is sulfonated, but styryl group-containing alkoxysilane is hardly sulfonated, so that the oxidation resistance is very good.

A well-known thing can be used for a sulfonating agent, For example, it can sulfonate by concentrated sulfuric acid, fuming sulfuric acid, sulfuric anhydride, mesitylene sulfonic acid, etc. Moreover, it can also sulfonate by making it hydrolyze in a pure water after reaction with chlorosulfonic acid (in this invention, the reaction temperature with chlorosulfonic acid is defined as sulfonation temperature in this case). The sulfonating agent may be appropriately diluted with a solvent such as dichloroethane or dichlorobenzene.

The sulfonation reaction time may be adjusted as appropriate to obtain a desired ion exchange capacity. If the reaction time is short, the inside of the membrane may not be sufficiently sulfonated, and if it is long, the styryl group-containing alkoxysilane may also be gradually sulfonated. More specifically, after immersing in a solution obtained by diluting chlorosulfonic acid with dichloroethane to a concentration of 0.02 to 6 mol / L at 0 to 60 ° C. for 3 to 24 hours, it is immersed in pure water at 50 to 90 ° C. for 6 to 48 hours. Is preferred.

Simultaneously with this sulfonation, hydrolysis and condensation of the alkoxysilyl group of the styryl group-containing alkoxysilane proceeds, and a cross-link is formed between the graft chains by the Si—O—Si bond. By this cross-linking, the graft chain has a three-dimensional network structure and is more excellent in oxidation resistance. In addition, before or after sulfonation, a separate hydrolysis / condensation step of alkoxysilyl groups may be carried out to form graft chain cross-linking by Si—O—Si bonds.

The solid polymer electrolyte membrane of the present invention is disposed adjacent to both electrodes between a first electrode on which a catalyst is supported and a second electrode (fuel electrode and air electrode), and is an electrolyte membrane for a fuel cell. Although formed as an electrode assembly (membrane electrode assembly), this electrolyte membrane / electrode assembly can be produced by the following method.

In the production of an electrolyte membrane / electrode assembly, electrodes serving as an anode (fuel electrode) and a cathode (air electrode) are joined to a solid polymer electrolyte membrane. In this case, the electrode comprises a porous support, a catalyst layer, and a catalyst layer. Formed from. As the porous support, carbon paper, carbon cloth or the like is preferably used. The catalyst layer preferably contains a fine particle catalyst and a proton conductive polymer electrolyte.

In this case, a platinum group metal fine particle catalyst or a platinum-containing alloy fine particle catalyst is used as the fine particle catalyst. As the platinum group metal fine particle catalyst, platinum, ruthenium, palladium, rhodium, iridium, osmium and the like are used, and as the platinum-containing alloy fine particle catalyst, for example, platinum and ruthenium, palladium, rhodium, iridium, osmium, molybdenum, tin, Examples thereof include alloys with at least one metal selected from cobalt, nickel, iron, chromium and the like. In this case, the platinum-containing alloy is preferably an alloy containing 5% by mass or more, particularly 10% by mass or more of platinum.

As the platinum group metal fine particle catalyst and the platinum-containing alloy fine particle catalyst, those having a particle diameter (average particle diameter) of 4 nm or less, preferably 1 to 4 nm, more preferably 2 to 3.5 nm are preferably used. When a catalyst having a particle diameter exceeding 4 nm is used, there is a concern that the specific surface area becomes small and the catalyst activity is lowered. The particle diameter is based on observation with a transmission electron microscope.

In this case, as the fine particle catalyst, one supported on carbon can be used, and a commercially available product can be used.

The catalyst amount of the fine particle catalyst is usually 0.05 to 10 mg / cm ² , preferably 0.3 to 5 mg / cm ² in each electrode catalyst layer. If the amount of the catalyst is too small, the catalyst effect may not be sufficiently obtained. If the amount is more than 10 mg / cm ² , the catalyst layer may be too thick and the output may be lowered.

In addition, as the proton conductive polymer electrolyte having a sulfonic acid group, a perfluoro-based electrolyte typified by Nafion [Nafion (trade name, manufactured by DuPont)], and a carbonized carbon typified by a styrenesulfonic acid-butadiene copolymer. Hydrogen-based electrolytes, inorganic / organic hybrid electrolytes typified by sulfonic acid group-containing alkoxysilanes and terminal silylated oligomers are preferably used. Furthermore, for the purpose of improving electron conductivity, carbon fine particles on which no catalyst is supported can be blended.

In addition, it is also possible to use a solvent for the catalyst paste which forms a catalyst layer in order to improve applicability | paintability, when applying a catalyst paste to an electrode and / or an electrolyte membrane. Examples of the solvent include alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, ethylene glycol and glycerol, ketones such as acetone and methyl ethyl ketone, and esters such as ethyl acetate and butyl acetate. , Ethers such as tetrahydrofuran and dioxane, aromatic hydrocarbons such as benzene and toluene, aliphatic to alicyclic hydrocarbons such as n-heptane, n-hexane and cyclohexane, water, dimethyl sulfoxide, N, N-dimethyl Examples include polar solvents such as formamide, N, N-dimethylacetamide, formamide, N-methylformamide, N-methylpyrrolidone, ethylene carbonate, and propylene carbonate. These can be used alone or in admixture of two or more. Among these, polar solvents such as isopropyl alcohol, water and N, N-dimethylformamide are desirable.

Fluorine resin can also be added to increase the porosity in the catalyst layer and facilitate water movement. Fluoropolymers include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polychlorotrifluoroethylene (PCTFE), ethylene-tetra Fluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), ethylene trifluoride-ethylene copolymer (ECTFE), and the like are used alone or in combination of two or more. Can do. As these fluororesins, commercially available products having a polystyrene equivalent number average molecular weight of 100,000 to 600,000 by GPC can be used.

The amount of the above-mentioned components can be selected within a wide range, but the proton conductive polymer electrolyte is 50 to 200 parts by mass and the solvent is 0 to 5,000 parts by mass, particularly 100 to 1, parts per 100 parts by mass of the catalyst particles. 000 parts by mass, and the fluororesin component is preferably used in an amount of 10 to 400 parts by mass, particularly 40 to 130 parts by mass.

The catalyst paste is applied onto the electrolyte membrane or the porous electrode substrate, and when a solvent is added to the paste, the solvent is removed and a catalyst layer is formed by a conventional method.

The catalyst layer is formed on at least one of the electrolyte membrane and the electrode substrate, and a membrane / electrode assembly can be obtained by sandwiching both surfaces of the electrolyte membrane with the electrode substrate and hot pressing. The temperature at the time of hot pressing is appropriately selected depending on the electrolyte membrane to be used or the components in the catalyst paste, the kind of fluorine resin and the blending ratio, but the desirable temperature range is 50 to 200 ° C., more desirably 80 to 180 ° C. is there. If it is less than 50 ° C, bonding may be insufficient, and if it exceeds 200 ° C, the resin component in the electrolyte membrane or the catalyst layer may be deteriorated. The pressure level is appropriately selected depending on the components in the electrolyte membrane and / or the catalyst paste, the type and blending ratio of the fluororesin, and the type of the porous electrode substrate, but the preferable pressure range is 1 to 100 kgf / cm ^2. More desirably, it is 10 to 100 kgf / cm ² . If it is less than 1 kgf / cm ² , the bonding may be insufficient, and if it exceeds 100 kgf / cm ² , the porosity of the catalyst layer and the electrode substrate may decrease, and the performance may deteriorate.

Thus, the electrolyte membrane of the present invention can be used as a solid polymer electrolyte membrane provided between a fuel electrode and an air electrode of a fuel cell, and a catalyst layer / fuel diffusion on both sides of the solid polymer electrolyte membrane. By disposing the layer and the separator, it is possible to obtain a fuel cell that is suitably used as an electrolyte membrane for a fuel cell, particularly a direct methanol fuel cell, and has excellent cell characteristics. In addition, the structure of the fuel cell other than that described above can be a known one.

Hereinafter, the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to the following examples. In the following examples, all parts are parts by mass.

[Example 1]
An electron beam with an accelerating voltage of 100 kV is converted to 100 kGy at room temperature in a nitrogen atmosphere by an electron beam (EB) irradiation device (Iwasaki Electric light beam L) on an ETFE film (thickness 25 μm, 6 × 5 cm square, 0.13 parts). Irradiated as follows. Film in a solution charged with 11.03 parts of α-methylstyrene, 8.97 parts of styryltrimethoxysilane, 3 parts of dimethylacetamide, and 0.001 part of azobisisobutyronitrile previously deoxygenated by bubbling with nitrogen Was immersed in a nitrogen atmosphere and heated at 60 ° C. for 20 hours to perform graft polymerization. As a result, the graft ratio was 67%.

The graft-polymerized film is immersed in a 0.2 mol / L chlorosulfonic acid / dichloroethane mixed solution, reacted at 60 ° C. for 6 hours, then immersed in pure water at 80 ° C. overnight, and hydrolyzed to obtain sulfonic acid. A film containing groups was obtained. This film was immersed in a 3% aqueous hydrogen peroxide solution at 80 ° C. The 10% mass loss time with respect to the initial stage of this film was 34 hours.

[Comparative Example 1]
An electron beam with an accelerating voltage of 100 kV is converted to 4 kGy at room temperature in a nitrogen atmosphere by an electron beam (EB) irradiation device (Light Beam L manufactured by Iwasaki Electric) on an ETFE film (thickness 25 μm, 6 × 5 cm square, 0.13 parts). Irradiated as follows. Immerse the film in a solution containing 2.6 parts of styrene, bubbling with nitrogen, 2.4 parts of styrene, 2.4 parts of styryltrimethoxysilane, 18 parts of dimethylacetamide, and 0.001 part of azobisisobutyronitrile. As a result of heating in a nitrogen atmosphere at 60 ° C. for 18 hours and graft polymerization, the graft ratio was 39%.

The graft-polymerized film is immersed in a 0.2 mol / L chlorosulfonic acid / dichloroethane mixed solution, reacted at 60 ° C. for 6 hours, then immersed in pure water at 80 ° C. overnight, and hydrolyzed to obtain sulfonic acid. A film containing groups was obtained. This film was immersed in a 3% aqueous hydrogen peroxide solution at 80 ° C. The 10% mass loss time with respect to the initial stage of this film was 6 hours.

[Comparative Example 2]
An electron beam with an acceleration voltage of 100 kV is 20 kGy at room temperature in a nitrogen atmosphere with an electron beam (EB) irradiation device (Iwasaki Electric light beam L) on an ETFE film (thickness 25 μm, 6 × 5 cm square, 0.13 parts). Irradiated as follows. The film is immersed in a solution prepared by previously charging 8.38 parts of α-methylstyrene, 1.62 parts of acrylonitrile, 11 parts of dimethylacetamide, and 0.001 part of azobisisobutyronitrile from which oxygen has been removed by bubbling with nitrogen in advance. As a result of heating in a nitrogen atmosphere at 60 ° C. for 18 hours and graft polymerization, the graft ratio was 41%.

The graft-polymerized film is immersed in a 0.2 mol / L chlorosulfonic acid / dichloroethane mixed solution, reacted at 60 ° C. for 6 hours, then immersed in pure water at 80 ° C. overnight, and hydrolyzed to obtain sulfonic acid. A film containing groups was obtained. This film was immersed in a 3% aqueous hydrogen peroxide solution at 80 ° C. The 10% mass loss time with respect to the initial stage of this film was 4 hours.

[Comparative Example 3]
An electron beam with an accelerating voltage of 100 kV is applied to an ETFE film (thickness 25 μm, 6 × 5 cm square, 0.13 parts) with an electron beam (EB) irradiation device (light beam L manufactured by Iwasaki Electric) at room temperature in a nitrogen atmosphere to 5 kGy. Irradiated as follows. The film was immersed in a solution containing 12 parts of styrene and 12 parts of toluene from which oxygen had previously been removed by bubbling with nitrogen, and heated at 60 ° C. for 18 hours in a nitrogen atmosphere. As a result of graft polymerization, the graft ratio was 42%. Met.

The graft-polymerized film is immersed in a 0.2 mol / L chlorosulfonic acid / dichloroethane mixed solution, reacted at 60 ° C. for 6 hours, then immersed in pure water at 80 ° C. overnight, and hydrolyzed to obtain sulfonic acid. A film containing groups was obtained. This film was immersed in a 3% aqueous hydrogen peroxide solution at 80 ° C. The 10% mass loss time with respect to the initial stage of this film was 3 hours.

The graft ratio and proton conductivity of the electrolyte membranes of Example 1 and Comparative Examples 1 to 3 were measured by the following methods. The results are shown in Table 1.

[Measurement of graft ratio]
The membrane mass before grafting and the membrane mass after grafting were measured and determined by the following formula.
Graft ratio = (post-graft membrane mass-pre-graft membrane mass) / pre-graft membrane mass

[Measurement of proton conductivity]
The electrolyte membrane is cut into a strip of 1 cm width, immersed in pure water at room temperature to swell, and then the platinum electrode is pressed in the swollen state, and the membrane is formed by an AC four-terminal method using an impedance analyzer (Solartron 1260). The longitudinal resistance was determined. From the membrane resistance, the distance between the electrodes, the film thickness at the time of swelling, and the sample width at the time of swelling, the proton conductivity was obtained by the following formula.
Proton conductivity = distance between electrodes / (membrane resistance × film thickness × sample width)

[Example 2]
An electron beam with an accelerating voltage of 100 kV is converted to 100 kGy at room temperature in a nitrogen atmosphere by an electron beam (EB) irradiation device (Iwasaki Electric light beam L) on an ETFE film (thickness 25 μm, 6 × 5 cm square, 0.13 parts). Irradiated as follows. A film in a solution charged with 14.25 parts of α-methylstyrene, 6.75 parts of styryltrimethoxysilane, 2 parts of dimethylacetamide, and 0.001 part of azobisisobutyronitrile previously deoxygenated by bubbling with nitrogen Was immersed, heated at 60 ° C. for 60 hours, and subjected to graft polymerization. As a result, the graft ratio was 65%.

The graft-polymerized film is immersed in a 0.2 mol / L chlorosulfonic acid / dichloroethane mixed solution, reacted at 25 ° C. for 6 hours, then immersed in pure water at 80 ° C. overnight, and hydrolyzed to obtain sulfonic acid. A film containing groups was obtained. This film was immersed in a 3% aqueous hydrogen peroxide solution at 80 ° C. The 10% mass loss time with respect to the initial stage of this film was 28 hours.

[Example 3]
An electron beam with an accelerating voltage of 100 kV is converted to 100 kGy at room temperature in a nitrogen atmosphere by an electron beam (EB) irradiation device (Iwasaki Electric light beam L) on an ETFE film (thickness 25 μm, 6 × 5 cm square, 0.13 parts). Irradiated as follows. A film in a solution charged with 6.56 parts of α-methylstyrene, 12.44 parts of styryltrimethoxysilane, 5 parts of dimethylacetamide, and 0.001 part of azobisisobutyronitrile previously deoxygenated by bubbling with nitrogen Was heated at 60 ° C. for 18 hours and graft polymerization was conducted. As a result, the graft ratio was 95%.

The graft-polymerized film is immersed in a 0.2 mol / L chlorosulfonic acid / dichloroethane mixed solution, reacted at 25 ° C. for 6 hours, then immersed in pure water at 80 ° C. overnight, and hydrolyzed to obtain sulfonic acid. A film containing groups was obtained. This film was immersed in a 3% aqueous hydrogen peroxide solution at 80 ° C. The 10% mass loss time with respect to the initial stage of this film was 62 hours.

[Example 4]
An electron beam with an accelerating voltage of 100 kV is converted to 100 kGy at room temperature in a nitrogen atmosphere by an electron beam (EB) irradiation device (Iwasaki Electric light beam L) on an ETFE film (thickness 25 μm, 6 × 5 cm square, 0.13 parts). Irradiated as follows. Film in a solution charged with 16.48 parts of α-methylstyrene, 5.52 parts of styryltrimethoxysilane, 1 part of dimethylacetamide, and 0.001 part of azobisisobutyronitrile previously deoxygenated by bubbling with nitrogen Was heated at 60 ° C. for 60 hours and graft polymerization was performed. As a result, the graft ratio was 53%.

[Example 5]
An electron beam with an accelerating voltage of 100 kV is converted to 100 kGy at room temperature in a nitrogen atmosphere by an electron beam (EB) irradiation device (Iwasaki Electric light beam L) on an ETFE film (thickness 25 μm, 6 × 5 cm square, 0.13 parts). Irradiated as follows. A film in a solution charged with 3.45 parts of α-methylstyrene, 6.55 parts of styryltrimethoxysilane, 13 parts of dimethylacetamide, and 0.001 part of azobisisobutyronitrile previously deoxygenated by bubbling with nitrogen Was heated at 60 ° C. for 18 hours and graft polymerization was performed. As a result, the graft ratio was 31%.

The graft polymerized film is immersed in a 0.2 mol / L chlorosulfonic acid / tetrachloroethane mixed solution, reacted at 80 ° C. for 6 hours, then immersed in pure water at 80 ° C. overnight, and hydrolyzed. A film containing acid groups was obtained. This film was immersed in a 3% aqueous hydrogen peroxide solution at 80 ° C. The 10% mass loss time with respect to the initial stage of this film was 12 hours.

[Example 6]
An electron beam with an accelerating voltage of 100 kV is converted to 100 kGy at room temperature in a nitrogen atmosphere by an electron beam (EB) irradiation device (Iwasaki Electric light beam L) on an ETFE film (thickness 25 μm, 6 × 5 cm square, 0.13 parts). Irradiated as follows. Film in a solution charged with 15.73 parts of α-methylstyrene, 5.27 parts of styryltrimethoxysilane, 2 parts of dimethylacetamide, and 0.001 part of azobisisobutyronitrile previously deoxygenated by bubbling with nitrogen And was heated at 60 ° C. for 18 hours and subjected to graft polymerization. As a result, the graft ratio was 25%.

The graft polymerized film is immersed in a 0.2 mol / L chlorosulfonic acid / tetrachloroethane mixed solution, reacted at 80 ° C. for 6 hours, then immersed in pure water at 80 ° C. overnight, and hydrolyzed. A film containing acid groups was obtained. This film was immersed in a 3% aqueous hydrogen peroxide solution at 80 ° C. The 10% mass reduction time with respect to the initial stage of this film was 10 hours.

For the electrolyte membranes of Examples 2 to 6, the graft ratio and proton conductivity were measured by the above methods, and the sulfonation ratio was measured by the following method. The results are shown in Table 2.

[Measurement of sulfonation rate]
After immersing the electrolyte membrane in 0.01N NaOH aqueous solution, the NaOH aqueous solution was titrated with 0.01N hydrochloric acid to determine the total sulfonic acid group concentration in the electrolyte membrane. On the other hand, the concentrations of α-methylstyrene and styryltrimethoxysilane in the electrolyte membrane were calculated from the graft ratio and copolymerization mole fraction. Since α-methylstyrene is sulfonated prior to styryltrimethoxysilane, the sulfonation rate α [%] of styryltrimethoxysilane was determined by the following formula.
α = 100 [C {(100-x) (gM _1s + 100M ₁ ) + x (gM _2c + 100M ₂ )}-(100-x) g] / [xg {1-C (M _2s -M _2c ) }]
C: Total sulfonic acid group concentration in the electrolyte membrane [mol / g]
g: Graft ratio [%]
x: mole fraction of styryltrimethoxysilane [%]
M ₁ : Molecular weight of α-methylstyrene [g / mol]
M _1s: molecular weight of α- methyl styrene after sulfonation [g / mol]
M ₂ : Molecular weight of styryltrimethoxysilane [g / mol]
M _2s : Molecular weight [g / mol] of styryltrimethoxysilane after sulfonation + condensation
M _2c : molecular weight [g / mol] of styryltrimethoxysilane after condensation

[Example 7]
In the graft polymerization, except that the concentration of the polymerizable monomer in the solution was lowered, the same procedure as in Example 3 was carried out, and a 25 μm ETFE film was co-grafted with 50 mol% α-methylstyrene and 50 mol% styryltrimethoxysilane. Sulfonated electrolyte membrane was prepared. The graft ratio of this membrane was 64%, and the proton conductivity was 0.05 S / cm. Next, a 5 cm ² anode catalyst layer containing 4 mg / cm ² of PtRu black (HiSPEC 6000 manufactured by Johnson Massey) is provided on one side of the membrane, and 6 mg / cm ² of Pt black (HiSPEC 1000 manufactured by Johnson Massey) is provided on the opposite side. A 5 cm ² cathode catalyst layer containing the catalyst is transferred, sandwiched between carbon papers (TGP-H-060 manufactured by Toray Industries, Inc.) and used as an MEA (membrane electrode assembly), and this is applied to a fuel cell (FC05-01SP manufactured by Electrochem). Attached.

1 mol / L methanol water was supplied to the anode side of the fuel cell at a rate of 0.5 mL / min, and dry air was supplied to the cathode side at a rate of 0.44 SLM (Standard Liter per Minute). Power generation was performed, an electronic load (890CL manufactured by Scribner) was connected, and polarization characteristics were measured. The results are shown in FIG. The voltage at a current density of 200 mA / cm ² was 0.392 V, and the maximum output density was 104 mW / cm ² .

Claims

It is obtained by irradiating a fluororesin or hydrocarbon resin with radiation, co-grafting a polymerizable monomer containing at least α-methylstyrene and a styryl group-containing alkoxysilane, and then sulfonating the resin. A solid polymer electrolyte membrane.
The solid polymer electrolyte membrane according to claim 1, wherein the sulfonation rate of the styryl group-containing alkoxysilane in the co-graft chain is 50% or less.
The solid polymer electrolyte membrane according to claim 1 or 2, wherein a molar fraction of the styryl group-containing alkoxysilane in the polymerizable monomer is 30% or more.
The solid polymer electrolyte membrane according to any one of claims 1 to 3, wherein the resin is a fluororesin.
It is characterized by irradiating a fluorine-based resin or a hydrocarbon-based resin with radiation, co-grafting a polymerizable monomer containing at least α-methylstyrene and a styryl group-containing alkoxysilane, and then sulfonating. A method for producing a solid polymer electrolyte membrane.
6. The method for producing a solid polymer electrolyte membrane according to claim 5, wherein the sulfonation rate of the styryl group-containing alkoxysilane in the co-graft chain is 50% or less.
The method for producing a solid polymer electrolyte membrane according to claim 5 or 6, wherein the molar fraction of the styryl group-containing alkoxysilane in the polymerizable monomer is 30% or more.
The method for producing a solid polymer electrolyte membrane according to any one of claims 5 to 7, wherein the resin is a fluororesin.
The method for producing a solid polymer electrolyte membrane according to any one of claims 5 to 8, wherein the sulfonation is carried out at 60 ° C or lower.
The method for producing a solid polymer electrolyte membrane according to any one of claims 5 to 8, wherein sulfonation is carried out at 30 ° C or lower.
A membrane electrode assembly for a fuel cell, wherein the solid polymer electrolyte membrane according to any one of claims 1 to 4 is provided between a fuel electrode and an air electrode.
A fuel cell comprising the fuel cell membrane electrode assembly according to claim 11.
The fuel cell according to claim 12, wherein the fuel cell is a direct methanol type using methanol as a fuel.