JP2002088251A - Proton electroconductive polymer composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a proton electroconductive polymer composition excellent in proton eleetroconductivity and durability and inexpensively producible. SOLUTION: The proton electroconductive polymer composition comprises a sulfonated polymer having a sulfonic group density of at least 2 mg equivalent/g, and a polymer matrix, Preferably, the sulfonated polymer is one obtained by sulfonating a polymer of an aromatic compound having an unsaturated bond. A solid electrolyte film for a fuel cell can be composed of this proton electroconductive polymer composition. This solid electyolyte film has proton electroconductivity excellent enough to give a fuel cell formed thereof having high output.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel cell, a solid electrolyte membrane for a fuel cell, and a proton conductive polymer composition applicable to the solid electrolyte membrane. More specifically,
The present invention relates to a proton-conductive polymer composition having high proton conductivity, excellent durability, excellent strength when formed into a membrane, and which can be synthesized at low cost.

[0002]

2. Description of the Related Art Solid electrolyte membrane fuel cells can use hydrogen, alcohols such as methanol and ethanol, and hydrocarbons such as octane and decane as fuel. And high emission of harmful substances such as sulfur oxides and nitrogen oxides. Therefore, it is expected to be applied to automobiles and the like as a clean and highly efficient power generator.

[0003] The solid electrolyte membrane fuel cell here comprises a solid electrolyte membrane having ion exchange capacity and two electrodes arranged in contact with both sides thereof. As a specific example, a case where hydrogen is used as fuel to burn with oxygen is illustrated.
When hydrogen is supplied to the hydrogen electrode side and oxygen is supplied to the oxygen electrode side,
Hydrogen is electrochemically oxidized at the hydrogen electrode to generate protons and electrons, and the generated electrons move through a load connected to the battery toward the oxygen electrode to generate a current. At this time, the generated protons move in the solid electrolyte membrane toward the oxygen electrode, where the transferred protons and electrons react with oxygen to generate water.

The performance of a solid electrolyte membrane fuel cell particularly depends on the performance of a gas diffusion electrode used for a hydrogen electrode, an oxygen electrode and the like, and the performance of a solid electrolyte membrane. Here, the performance required for the solid electrolyte membrane is proton conductivity, that is, the proton generated at an electrode such as a hydrogen electrode is caused to flow to the oxygen electrode side. For this reason, it is considered important to introduce a large number of functional groups imparting ion exchange capability into the solid electrolyte membrane. For this reason, a fluorinated resin having a sulfonic acid group (trade name: Nafion) developed by DuPont or an analog thereof has been used as a typical example of a solid electrolyte membrane. Here, Nafion is based on a copolymer of tetrafluoroethylene and perfluorovinyl ether and has a sulfonic acid group as an ion exchange group.

[0005]

However, the upper limit of the ion exchange capacity of Nafion that can be used as a solid electrolyte membrane is 1.1 mg equivalent / g, and it cannot be said that the proton conductivity is sufficient. On the other hand, fluorine-based resins are very expensive, which leads to an increase in the cost of fuel cells and solid electrolyte membranes, which hinders practical use.

When hydrogen is supplied as a fuel to the hydrogen electrode, protons are generated at the hydrogen electrode as described above. However, hydration water of the generated protons (H ⁺ ) is simultaneously transported to the oxygen electrode side. In particular, the hydrogen electrode side of the solid electrolyte membrane may be dried. However, since the solid electrolyte membrane shows proton conductivity only in a wet state, in a dry state, the proton conductivity is significantly reduced, and the operation of the fuel cell may become impossible. In order to solve such a dry state, there is also a method of supporting a very small amount of ultrafine platinum catalysts or ultrafine oxide particles in a solid electrolyte membrane. Has become.

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a proton conductive polymer composition in which a sulfonated polymer is dispersed or mixed in a polymer matrix,
The inventors have found that they have excellent proton conductivity and durability, and also have excellent strength when formed into a solid electrolyte membrane, and can be manufactured at low cost, and have completed the present invention.

That is, the present invention provides the following (1) to (11).

(1) The sulfonic acid group density is 2 mg equivalent /
A proton conductive polymer composition containing at least g of a sulfonated polymer and a polymer matrix.

(2) The proton conductive polymer composition according to the above (1), wherein the sulfonated polymer is obtained by sulfonating a polymer of an aromatic compound having an unsaturated bond.

(3) The proton conductive polymer composition according to the above (2), wherein the aromatic compound polymer having an unsaturated bond is a polymer of a monomer mixture containing styrene as a main component. .

(4) The proton conductive polymer composition according to the above (1), wherein the sulfonated polymer is in the form of particles.

(5) The proton conductive polymer composition according to the above (4), wherein the sulfonated polymer has an average particle size of 1 to 100 μm.

(6) The proton conductive polymer according to any one of (1) to (5), wherein the ion exchange capacity of the sulfonated polymer is larger than the ion exchange capacity of the polymer matrix. Molecular composition.

(7) All or part of the polymer matrix is selected from the group consisting of fluororesin, polyimide, modified polyphenylene ether, polyphenylene sulfide, polyetherimide, polyethersulfone, polyetherketone and polyamideimide. The proton conductive polymer composition according to any one of the above (1) to (6), which is at least one kind.

(8) The proton conductive polymer composition according to any one of (1) to (7), wherein the polymer matrix has a sulfonic acid group and / or a carboxylic acid group.

(9) The compounding ratio of the sulfonated polymer to the polymer matrix is 5 to 5000 parts by mass for the former with respect to 100 parts by mass of the latter. The proton conductive polymer composition according to any one of the above).

(10) A solid electrolyte membrane for a fuel cell, comprising the proton conductive polymer composition according to any one of the above (1) to (9).

(11) A fuel cell using the solid electrolyte membrane for a fuel cell according to the above (10).

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention has a sulfonic acid group density of 2
It is a proton conductive polymer composition containing a sulfonated polymer of not less than mg equivalent / g and a polymer matrix. Conventionally, a compound containing a perfluorocarbon sulfonic acid group having a cluster structure, such as a poly (tetrafluoroethylene-perfluorovinyl ether) copolymer, has been frequently used because of its excellent proton conductivity. Proton conductivity is not yet sufficient. However, since the composition used in the present invention has a sulfonic acid group density of 2 mg equivalent / g or more, it can be produced at low cost despite having excellent proton conductivity. For this reason, it is possible to provide a composition having better proton conductivity at lower cost than before. Moreover, if the sulfonated polymer to be compounded is in the form of particles of a specific size, a composition having excellent proton conductivity without lowering the adhesiveness with the gas diffusion electrode of the polymer matrix and the chemical and physical strength. Can be provided. Furthermore, since the sulfonic acid group present on the particle surface has hydrophilicity, it is resistant to drying, and a decrease in proton conductivity due to drying can be prevented. Therefore, a solid electrolyte membrane can be prepared from such a composition, and a fuel cell having excellent proton conductivity provided with the solid electrolyte membrane can be provided. Hereinafter, the present invention will be described in detail.

(1) Sulfonated Polymer The sulfonated polymer constituting the proton conductive polymer composition of the present invention needs to have a sulfonic acid group density of 2 mg equivalent / g or more. This is because the sulfonic acid group has proton conductivity, and if it is less than 2 mg equivalent / g, the resulting composition has insufficient proton conductivity. More preferably, it is 2.5 to 8 mg equivalent / g, particularly 3 to 6 mg equivalent / g. If the sulfonic acid group density exceeds 8 mg equivalent / g, sufficient strength may not be obtained when the solid electrolyte membrane is used. The reason is that the organic portion in the polymer is reduced, and it is difficult to maintain the shape of the polymer.

The sulfonated polymer is preferably a sulfonated polymer of an aromatic compound having an unsaturated bond. By using a polymer of an aromatic compound, the sulfonic acid group content per unit mass can be improved. Thereby, excellent proton conductivity is exhibited.

Examples of the aromatic compound having an unsaturated bond include styrene, α-methylstyrene and ethylstyrene. In the present invention, one of these may be used alone, or two or more of them may be used in combination. As the aromatic compound used in the present invention, among these, a polymer of a monomer mixture containing styrene as a main component is preferable. This is because sulfonation is easy and the chemical strength is excellent. Further, as a monomer mixture, in addition to styrene, α-methylstyrene, ethylstyrene, and vinylbenzene, a polymer obtained by blending divinylbenzene, trivinylbenzene, or the like is crosslinked in the molecule, and a particulate sulfonated polymer is obtained. Is particularly preferable because it can be easily obtained.

The above-mentioned sulfonated polymer is preferably in the form of particles. At this time, the average particle size is 1 to 100 μm,
More preferably, the thickness is 1 to 20 μm. If the average particle diameter is less than 1 μm, the sulfonated polymer moves in the polymer matrix and moves to the oxygen electrode side together with water, thereby lowering proton conductivity. On the other hand, if the average particle diameter exceeds 100 μm, sufficient strength may not be obtained when the solid electrolyte membrane is used, which is not preferable.

(2) Method for Producing a Sulfonated Polymer The method for producing a sulfonated polymer used in the present invention is not particularly limited, but a polymer obtained by polymerizing an aromatic compound may be prepared by a conventional method. It can be obtained by sulfonation using a known sulfonating agent. Hereinafter, the case where the aromatic compound polymer is sulfonated will be described.

(I) Aromatic polymer In order to obtain an aromatic polymer, an aromatic compound can be polymerized by a known polymerization method such as suspension polymerization, emulsion polymerization and solution polymerization. Particularly preferred is suspension polymerization. This is because, by the suspension polymerization, a particulate aromatic polymer can be easily obtained. Further, a radical polymerization initiator is added to the solvent system of the aromatic compound, and the reaction can be carried out at 40 to 100 ° C, more preferably 50 to 90 ° C. Examples of the polymerization initiator include azo compounds such as azobis-2-methylpropionamidine hydrochloride and azoisobutyronitrile, and peroxides such as t-butyl hydroperoxide and benzoyl peroxide.

As the polymerization solvent, water is preferable. Also,
If necessary, ether solvents such as tetrahydrofuran and dioxane, amide solvents such as dimethylacetamide and dimethylformamide, alcohols such as methanol, ethanol and isopropanol, acetonitrile, acetone, 2-butanone, dimethyl sulfoxide, polyvinyl alcohol, etc. Can be added.

The polymerization reaction temperature is preferably 40 to 100 ° C.
Particularly, 50 to 90 ° C. is preferable. This is because an aromatic polymer having excellent strength can be obtained in this range.

An emulsifier can be used in the polymerization reaction. As the emulsifier, any of an anionic surfactant, a nonionic surfactant, and a polymer surfactant may be used.

Examples of the above anionic surfactant include alkyl sulfate salts such as sodium dodecyl sulfate, potassium dodecyl sulfate and ammonium alkyl sulfate; sodium dodecyl polyglycol ether sulfate; sodium sulfolinosinoate; sulfonated paraffin salts and the like. Alkyl sulfonates such as sodium dodecylbenzene sulfonate, alkali metal sulfate of alkali phenol hydroxyethylene; high alkyl naphthalene sulfonate; naphthalene sulfonic acid formalin condensate, sodium laurate, triethanolamine oleate, triethanolamine Fatty acid salts such as ahiate; polyoxyalkyl ether sulfates; poly Reactive anionic emulsifiers having a double bond such as xylethylene carboxylate sulfate, polyoxyethylene phenyl ether sulfate; dialkyl succinate sulfonate; polyoxyethylene alkylaryl sulfate, etc. can be used. .

Examples of the nonionic surfactant include polyoxyethylene alkyl ether; polyoxyethylene alkyl aryl ether; sorbitan aliphatic ester; polyoxyethylene sorbitan aliphatic ester; and glycerol monolaurate. Aliphatic monoglyceride; polyoxyethyleneoxypropylene copolymer, ethylene oxide and aliphatic amine,
Condensation products with amides or acids can be used.

As the above-mentioned polymer surfactant, for example,
Polyvinyl alcohol and modified products thereof; (meth) acrylic acid-based water-soluble polymer; hydroxyethyl (meth) acrylic acid-based water-soluble polymer; hydroxypropyl (meth) acrylic acid-based water-soluble polymer; .

Further, in such a polymerization reaction, known compounds such as a chain transfer agent chelating agent which can be used in suspension polymerization can be used.

(Ii) Sulfonation As the sulfonation, the aromatic compound polymer can be sulfonated using a sulfonating agent such as concentrated sulfuric acid, chlorosulfuric acid, and fuming sulfuric acid.

The amount of the sulfonating agent used for the sulfonation reaction is 500 parts by mass per 100 parts by mass of the aromatic compound polymer.
It is preferable to use it in a proportion of at least part by mass. The reaction is
In the absence of a solvent or in the presence of a non-swelling solvent for an aromatic polymer or for an aromatic polymer,
It can be performed in the presence of a swellable solvent.

The solvent which does not swell with respect to the aromatic compound polymer may be any solvent which does not swell the aromatic compound polymer and which is inert to the sulfonating agent, such as hexane and cyclohexane. And aliphatic hydrocarbons such as ligroin. The solvent that swells with respect to the aromatic compound polymer may be any solvent that does not swell the aromatic compound polymer and is inactive with respect to the sulfonating agent. For example, 1,1,2,2- Examples include tetrachloroethane, 1,2-dichloroethane, dichloromethane, carbon tetrachloride and the like. The amount of these solvents used is 100 parts by mass per 100 parts by mass of the aromatic compound polymer.
It is preferable to use it in a proportion of 0 parts by mass or more.

The reaction temperature for sulfonation is from -20 to 100.
℃ is good, and it is performed for about 0.3 to 100 hours. Preferably, the reaction is performed at a temperature of 70 to 100 ° C. for 1 to 24 hours.

(3) Polymer matrix The proton conductive polymer composition of the present invention is obtained by mixing or dispersing the above-mentioned sulfonated polymer in a polymer matrix.

The polymer matrix that can be used in the present invention is not particularly limited, but preferably has a hydrophilic group such as a sulfone group, a carboxylic acid group, an ether group, an ester group, and a hydroxyl group. These are 1
In addition to the case of having a kind, the case of having two or more kinds such as a sulfone group and a carboxylic acid group may be used. Particularly, the polymer matrix preferably has a sulfonic acid group or a carboxylic acid group. This is because, due to the presence of the hydrophilic group, the affinity between the polymer matrix and the sulfonated polymer becomes good, the proton conductivity becomes excellent, and a proton conductive polymer composition having excellent chemical and physical strength is obtained. .

As the polymer matrix, fluorine resin,
Polyimide, polyamide, polyacetal, polycarbonate, modified polyphenylene ether, polyphenylene sulfide, polysulfone, amorphous polyarylate, polyetherimide, polyethersulfone, polyetherketone, polyamideimide, silicone resin, polyurethane, phenolic resin, unsaturated polyester resin, Epoxy resin, methacrylic resin, polyvinylidyl alcohol, polystyrene, ABS resin, polyvinylidene chloride, polyvinyl chloride, polypropylene, polyethylene, polyisobutyl, natural rubber, butyl rubber, polyisoprene, styrene-butadiene rubber, nitrile rubber, vinyl chloride, Examples include fatty acid vinyl ester copolymers, ethylene-propylene rubber, ethylene-propylene-diene rubber, and the like. One of these may be used alone, or two or more may be used in combination. In the present invention, all or part of the polymer matrix is preferably a fluororesin, polyimide, modified polyphenylene ether, polyphenylene sulfide, polyetherimide, polyether sulfone, polyether ketone, or polyamide imide. Prepare a solid electrolyte membrane from the composition, when using this in a fuel cell, it is preferable that the operating temperature is higher in order to improve the catalyst efficiency, but that it has excellent heat resistance when using a solid fuel cell, Also, when the solid electrolyte membrane is prepared, the adhesion to the gas diffusion electrode is excellent.

The ion exchange capacity of the polymer matrix used in the present invention is preferably smaller than the ion exchange capacity of the sulfonated polymer. If a material having a large ion exchange capacity is used as the polymer matrix, the strength of the obtained solid electrolyte membrane may be insufficient. The reason is that the amount of organic substances in the material is reduced, and it is difficult to maintain the shape of the material. The ion exchange capacity is a value measured by a neutralization titration method.

The polymer matrix used in the present invention is a polymer into which a heat-resistant and hydrophilic group has been introduced, such as a fluororesin into which a hydrophilic group such as a sulfonic acid group or a carboxylic acid group has been introduced. be able to. Specifically, poly (tetrafluoroethylene-perfluorovinyl ether) copolymer, poly (vinylidene fluoride), poly (hexafluoropropylene-vinylidene fluoride) copolymer, poly (perfluorovinyl ether-vinylidene fluoride) Copolymer, poly (tetrafluoroethylene-vinylidene fluoride) copolymer, poly (hexafluoropropylene oxide-vinylidene fluoride) copolymer, poly (hexafluoropropylene-
Homologues such as a tetrafluoroethylene-vinylidene fluoride copolymer, a poly (hexafluoropropylene-tetrafluoroethylene-vinylidene fluoride) copolymer, and a poly (fluoroethylene-vinylidene fluoride) copolymer or components thereof Examples thereof include those obtained by introducing a sulfonic acid group based on a mixture of the above. In particular, those containing a perfluorocarbon sulfonic acid group exhibiting a cluster structure, such as a poly (tetrafluoroethylene-perfluorovinyl ether) copolymer, are preferable. This is because protons are quickly transmitted by the cluster structure and proton conductivity is excellent.

(4) Proton-Conducting Polymer Composition In the proton-conducting polymer composition of the present invention, the mixing ratio of the sulfonated polymer to the polymer matrix is 5 parts per 100 parts by mass of the latter. The range is preferably from 5,000 to 5000 parts by mass, more preferably from 10 to 1,000 parts by mass, particularly preferably from 100 to 600 parts by mass. If the amount is less than 5 parts by mass, the proton conductivity may be insufficient.
If the amount exceeds 0 parts by mass, the strength of the obtained solid electrolyte membrane may be insufficient. Although various proton conductive polymer compositions of the present invention have been used,
The ion exchange rate is not yet sufficient. Therefore, by adding a sulfonated polymer having an excellent ion exchange rate to a conventional polymer matrix, the ion exchange rate can be further improved. In addition, the cost can be reduced by blending an inexpensive sulfonated polymer.

The proton conductive polymer composition of the present invention may contain other additives which have been conventionally added to such an extent that the proton conductivity is not impaired. Such additives include catalysts, oxide ultrafine particles, hygroscopic inorganic porous materials,
Plasticizers and the like.

As the catalyst, there is a platinum ultrafine particle catalyst,
Ultrafine oxide particles include titanium oxide. Examples of the hygroscopic inorganic porous material include silica gel and synthetic zeolite. Further, as the plasticizer, cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate, dimethyl carbonate, chain carbonates such as methyl ethyl carbonate and methyl ether carbonate, ethers such as tetrahydrofuran and methyltetrahydrofuran, γ-butyl lactone, pro Piolactone, esters such as methyl acetate, acetonitrile, nitrile compounds such as propionitrile, organic low molecular compounds such as hydrocarbons, silicone oil, oligoethylene glycol, polyethylene oxide, aliphatic ether compounds such as polypropylene oxide, polyacrylonitrile, Examples include polar group-containing polymer compounds such as aliphatic polyesters and aliphatic polycarbonates.

The proton conductive polymer composition of the present invention comprises
Since a sulfonated polymer having a hydrophilic group is blended with a polymer matrix having excellent physical properties such as heat resistance, it has excellent water retention and also excellent adhesion to a gas diffusion electrode.

(5) Solid Electrolyte Membrane for Fuel Cell The solid electrolyte membrane for fuel cell of the present invention can be prepared by forming the proton conductive polymer composition into a membrane by a known method. For example, a method in which the proton conductive polymer composition is dissolved in a solvent and blended, and then formed into a film by casting, a method in which a polymer matrix and a sulfonated polymer are blended and then subjected to pressure and molded. is there. Examples of such a solvent include amide solvents such as dimethylacetamide and dimethylformamide, dimethylsulfoxide, a mixed solution of ethanol and water, a mixed solution of propanol and water, and the like.

The resin component is preferably dissolved in the solvent at a concentration of 0.5 to 50% by mass, more preferably 1 to 40% by mass, and particularly preferably 5 to 30% by mass. Resin concentration is 50
If the amount is more than 10% by mass, the viscosity of the solution is too high to uniformly mix the sulfonated polymer, and air bubbles are mixed into the solution to generate pores that lower the proton conductivity. On the other hand, if the resin concentration is less than 0.5% by mass, it may be difficult to form a film.

Next, the mixed solution is cast and then dried to obtain the solid electrolyte membrane for a fuel cell of the present invention. The cast surface is not particularly limited, and the surface may be smooth or uneven. When a vacuum drying method is adopted as the drying method, the drying time is shortened, and the phase separation between the perfluorocarbon sulfonic acid resin and the sulfonated polymer can be prevented. Since the proton conductive polymer composition for preparing the solid electrolyte membrane of the present invention contains a sulfonic acid group which is a hydrophilic group, the proton conductive polymer composition has excellent proton conductivity and excellent hydrophilicity. Moreover, the polymer matrix has excellent chemical strength and physical strength. If the sulfonated polymer compounded in this is in the form of particles, the polymer matrix has excellent adhesion with the gas diffusion electrode,
As a whole, a solid electrolyte membrane for a fuel cell having excellent proton conductivity can be obtained. Since the hydrophilicity is improved by blending the sulfonated polymer, it is particularly excellent in that the decrease in proton conductivity due to drying can be prevented.

(6) Fuel Cell The fuel cell of the present invention is characterized by using the above-mentioned solid electrolyte membrane for a fuel cell. A fuel cell has two gas diffusion electrodes, an anode and a cathode, and a fuel cell solid electrolyte membrane. Here, in order to obtain a joined body of the solid electrolyte membrane and the gas diffusion electrode, it can be prepared by the following method.

First, a gas-diffusion electrode was prepared by dissolving a fluorine-based polymer having a sulfonic acid group as a proton-conductive material similar to the proton-conductive polymer composition in a mixed solution of alcohols and water. Apply a fixed amount to the contact surface and dry. Two such gas diffusion electrodes are prepared, the fuel cell solid electrolyte membrane is interposed therebetween, and the contact surfaces of the electrodes are joined by hot pressing toward the fuel cell solid electrolyte membrane.
The temperature of the hot press varies depending on the type of the solid electrolyte membrane for a fuel cell, but is usually 100 ° C. or higher, and particularly
It is preferable that it is above. Moisture in the fuel cell solid electrolyte membrane evaporates due to the heat press, causing the fuel cell solid electrolyte membrane to shrink, making it difficult to achieve uniform joining.
At this temperature, drying of the solid electrolyte membrane for a fuel cell due to evaporation of water can be prevented.

The fuel cell of the present invention has a solid electrolyte membrane for a fuel cell and a gas diffusion electrode which have been assembled as described above. This assembly is inserted between a current collector and a graphite or metal flange provided with a gas inlet and a gas outlet, and assembled. One gas diffusion electrode is supplied with hydrogen gas as a fuel, and the other gas diffusion electrode is provided. By supplying a gas containing oxygen to the fuel cell, a fuel cell can be obtained.

The higher the operating temperature of the fuel cell, the higher the catalytic activity of the electrode and the lower the electrode overvoltage. However, since the solid electrolyte membrane for a fuel cell does not exhibit proton conductivity without water, it does not exhibit proton conductivity at a temperature at which water can be controlled. Activate. For this reason 50 ~
It is operated at 120C, more preferably at 60-100C.

As the gas to be used, it is preferable to use oxygen or air containing saturated steam at a temperature close to the temperature at which the fuel cell operates, as the oxidant gas, and to use a fuel gas which is saturated with steam under the same conditions as the fuel gas. . For this reason, when air or low-pressure oxygen is used, the oxygen partial pressure is low, and the output as a fuel cell is low.However, the solid electrolyte membrane for a fuel cell of the present invention has excellent proton conductivity, so that it can be applied to other fuel cells even at low pressure. The output can be increased by comparison.

As for the gas supply amount, the higher the supply amount, the higher the output of the fuel cell is, which is efficient. On the other hand, hydrogen gas and oxygen gas may mix and explode through the solid electrolyte membrane for the fuel cell. There is. For this reason, although it depends on the thickness of the solid electrolyte membrane for a fuel cell, when the thickness is 100 μm, it is 50 to 1000 kpa, more preferably 100 kPa.
Supply gas at ~ 500 kpa. If it is within this range,
This is because the gas is hardly supplied to the catalyst layer through the gas diffusion electrode, so that the output of the fuel cell is not significantly impaired, and there is no danger of explosion due to breakage of the membrane.

It is unclear why the solid electrolyte membrane of the present invention has excellent proton conductivity and the output of a fuel cell incorporating the solid electrolyte membrane is improved. However, the proton conductive polymer composition constituting the solid electrolyte membrane contains a sulfonated polymer having a high sulfonic acid group density, and a composition having excellent proton conductivity due to the proton conductivity of the sulfonic acid group is obtained. It is thought that it was possible. In order to improve the sulfonic acid group density, those obtained by sulfonating a polymer of an aromatic compound can be easily used, but in particular, when the sulfonated polymer is in the form of particles, In combination with the hydrophilicity, more water molecules are retained in the conductor, and the ions are hydrated by the water molecules, so that the ions are easily conducted. In a narrow space in the resin, water molecules are pressed against each other, so that a force for pushing out hydrated ions also acts. Therefore, the movement speed of ions on the ion exchange group is improved, and proton conductivity is promoted. It is believed that these interactions result in improved proton conductivity in the solid electrolyte membrane and improved output in the fuel cell.

[0057]

EXAMPLES The proton conductive polymer composition of the present invention will be further described based on examples. Note that the present invention is not limited to the embodiments.

(Synthesis Example 1) 1.2 liters of water was charged into a 3 liter four-neck separable flask equipped with a stirrer, a reflux condenser and a thermometer, and charged with polyvinyl alcohol (Kuraray Co., Ltd., Kuraray Poval PVA-). 205) 1
After adding and dissolving 6.0 g, 260 g of styrene is further added.
(2.5 mol), 40 g of industrial divinylbenzene (a mixture of 55 mass% of divinylbenzene, 35 mass% of ethylstyrene, etc., manufactured by Wako Pure Chemical Industries, Ltd.) (0.31 mol)
l) and a mixture consisting of 10 g of benzoyl peroxide. Thereafter, the contents in the flask were dispersed at a stirring speed of 5000 rpm using a disperser, and polymerized at 75 ° C. for 10 hours. The obtained solid was separated by filtration, washed sufficiently, and dried at 80 ° C. for 10 hours using a hot air drier to obtain 286 g of a spherical polymer crosslinked product.

The crosslinked polymer 5 was placed in a 2-liter four-neck separable flask equipped with a stirrer, thermometer and dropping funnel.
0 g was charged and cooled on ice. Thereto, 500 g of fuming sulfuric acid was added to obtain a uniform dispersion. After the temperature of the reaction mixture was gradually raised to 80 ° C., the mixture was stirred while heating at the same temperature for 24 hours to carry out a sulfonation reaction. Then, the reaction mixture was cooled to 0 ° C.
And filtered off, and then washed with water and acetone.
Then, using a vacuum dryer, dried at 80 ° C for 10 hours,
95 g of a particulate sulfonated polymer was obtained.

The average particle size of the obtained sulfonated polymer was measured by a laser diffraction type particle size distribution analyzer (Shimadzu Corporation, SA)
It was 10 μm when measured using LD-1000). When the ion exchange capacity of the sulfonated polymer was measured by neutralization titration, it was 5.0 mg equivalent / g.

Example 1 2 g of the sulfonated polymer obtained in Synthesis Example 1 was mixed with 40 g of a methanol solution containing 5% by mass of a fluororesin having a sulfonic acid group introduced therein (Nafion Solution SE-5112 manufactured by DuPont). And stirred well. After a concentrated solution obtained by partially removing methanol from the mixture was spread on a glass substrate, methanol was evaporated to obtain a solid electrolyte membrane (1) of the present invention in a film form.

The ion exchange capacity of the obtained solid electrolyte membrane (1) when dried was 2.5 mg equivalent / g.

[0063]

According to the present invention, a fuel cell, a solid electrolyte membrane for a fuel cell, and a proton conductive polymer composition applicable to the solid electrolyte membrane are provided. In particular, since it has high proton conductivity and excellent durability, it can be synthesized at a low cost and excellent strength when formed into a membrane.

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Claims (5)

[Claims] 1. A proton conductive polymer composition containing a sulfonated polymer having a sulfonic acid group density of 2 mg equivalent / g or more and a polymer matrix. 2. The proton conductive polymer composition according to claim 1, wherein the sulfonated polymer is obtained by sulfonating a polymer of an aromatic compound having an unsaturated bond. 3. The proton conductive polymer composition according to claim 1, wherein the ion exchange capacity of the sulfonated polymer is larger than the ion exchange capacity of the polymer matrix. 4. A solid electrolyte membrane for a fuel cell, comprising the proton conductive polymer composition according to claim 1. 5. A fuel cell using the solid electrolyte membrane for a fuel cell according to claim 4.