WO2007102418A1

WO2007102418A1 - Solid polymer electrolyte membrane for fuel cell and fuel cell

Info

Publication number: WO2007102418A1
Application number: PCT/JP2007/054011
Authority: WO
Inventors: Junichi Tsukada; Toshio Ohba; Nobuo Kawada
Original assignee: Shin-Etsu Chemical Co., Ltd.
Priority date: 2006-03-06
Filing date: 2007-03-02
Publication date: 2007-09-13
Also published as: JP2009151938A

Abstract

Disclosed is a solid polymer electrolyte membrane for fuel cells which is characterized by being obtained by graft-polymerizing a polymerizable monomer to a resin film irradiated with a radiation in such a manner that the number of units of the graft chain is not more than 30, and then sulfonating the resulting film. Since the solid polymer electrolyte membrane produced by such a radiation graft polymerization has high ion conductivity and low methanol permeability, it is suitable as an electrolyte membrane for fuel cells, especially an electrolyte membrane for direct methanol fuel cells.

Description

Specification

Solid polymer electrolyte membrane for fuel cell and fuel cell

Technical field

The present invention relates to a solid polymer electrolyte membrane for a fuel cell and a fuel cell.

Background art

[0002] Fuel cells using solid polymer electrolyte type ion exchange membranes have been widely put into practical use as power sources for electric vehicles and simple auxiliary power sources because of their high energy density, with operating temperatures as low as 100 ° C or lower. Expected. In this fuel cell, there are important elemental technologies relating to solid polymer electrolyte membranes, platinum-based catalysts, gas diffusion electrodes, and polymer electrolyte membrane-electrode assemblies. However, the development of solid polymer electrolyte membranes with good characteristics as fuel cells is one of the most important technologies.

[0003] In a solid polymer electrolyte membrane fuel cell, gas diffusion electrodes are combined on both sides of the electrolyte membrane, and the membrane and the electrode have a substantially integrated structure. For this reason, the electrolyte membrane acts as an electrolyte for conducting protons, and also has a role as a diaphragm for preventing hydrogen or methanol as a fuel and an oxidizing agent from being directly mixed even under pressure. Such an electrolyte membrane is required to have a high proton exchange rate and high ion exchange capacity as an electrolyte, and a constant and high water holding capacity in order to keep electric resistance low. On the other hand, due to its role as a diaphragm, its mechanical strength is high, its dimensional stability is excellent, its chemical stability for long-term use is excellent, and hydrogen as a fuel It is required not to be permeable to gas, methanol, or oxygen gas, which is an oxidant.

[0004] As such a solid polymer electrolyte membrane, a fluorine resin-based perfluorosulfonic acid membrane “Nafion (registered trademark of DuPont)” developed by DuPont and the like has been generally used.

However, conventional fluororesin-based electrolyte membranes such as “Nafion” have excellent chemical durability and stability, but in direct methanol fuel cells (D MFC) using methanol as fuel, methanol Causes a crossover phenomenon that passes through the electrolyte membrane, resulting in low output There was a problem. Furthermore, since the fluororesin-based electrolyte membrane starts from the synthetic ability of the monomer, it has a problem in that it requires a large number of manufacturing steps and increases the cost, which is a major obstacle to practical use.

For this reason, a technique for producing a solid polymer electrolyte membrane replacing the “naphth ion” or the like has been studied. As one of such techniques, a fluorocarbon resin, a hydrocarbon monomer such as styrene, Preparation of an electrolyte membrane obtained by radiation graft polymerization of a fluorine-based monomer partially containing hydrocarbons (JP 2001-348439 A, JP 2002 3133 64 A, JP 2003-82129 A). Etc.).

[0005] In these radiation graft polymerizations, styrene Z dibutene benzene co-graft membranes that are co-graft polymerized by simultaneously charging two or more types of graft raw materials such as styrene and dibutene benzene and fluorine resin irradiated with radiation are: Although proton conductivity is equivalent to or higher than that of “naphth ion” and methanol permeability is lower than that of “naphth ion”, an electrolyte membrane can be obtained, but further reduction of methanol permeability is required. However, in order to reduce the methanol permeability of such a styrene Z dibutene benzene co-graft membrane, if the amount of dibutene benzene as a cross-linking agent is increased or the graft ratio is reduced, methanol is reduced. Although the permeability decreases, at the same time, the proton conductivity significantly decreases, so it is impossible to obtain a solid polymer electrolyte membrane having both high proton conductivity and low methanol permeability! there were.

Disclosure of the invention

Problems to be solved by the invention

[0006] Accordingly, an object of the present invention is to provide a solid polymer electrolyte membrane and a fuel cell produced by a radiation graft polymerization method and having both high proton conductivity and low methanol permeability.

Means for solving the problem

[0007] As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that the polymerizable monomer is adjusted so that the number of graft chain units is 30 or less on the resin film irradiated with radiation. It is found that a solid polymer electrolyte membrane having both high proton conductivity and low methanol permeability can be obtained by sulfonating after graft polymerization of the polymer. It came.

Accordingly, the present invention provides the following solid polymer electrolyte membrane for fuel cell and fuel cell.

Claim 1:

A solid polymer for a fuel cell, characterized in that a polymerized monomer is graft-polymerized on a resin film irradiated with radiation so that the graft chain has a Nut number of 30 or less and is sulfonated. Electrolyte membrane.

Claim 2:

Resin film strength Polytetrafluoroethylene, tetrafluoroethylene perfluorinated alkyl butyl ether copolymer, tetrafluoroethylene monohexafluoropropylene copolymer and ethylene-tetrafluoroethylene copolymer strength 2. The solid polymer electrolyte membrane according to claim 1, which is at least one type of fluorine resin film selected. Claim 3:

3. The solid polymer electrolyte membrane according to claim 1, wherein the polymerizable monomer is a styrene monomer.

Claim 4:

4. The solid polymer electrolyte membrane according to claim 1, 2 or 3, wherein the absorbed dose of radiation applied to the resin film is not less than lOkGy and the graft ratio is not more than 60%.

Claim 5:

The solid polymer electrolyte membrane according to any one of claims 1 to 4, wherein the radiation is an electron beam.

Claim 6:

6. A fuel cell, wherein the solid polymer electrolyte membrane according to claim 1 is provided between a fuel electrode and an air electrode.

Claim 7:

7. The fuel cell according to claim 6, wherein the fuel cell is a direct methanol type using methanol as a fuel.

The invention's effect [0009] The solid polymer electrolyte membrane produced by the radiation grafting of the present invention exhibits high ionic conductivity and low methanol permeability. Therefore, the electrolyte membrane for fuel cells, particularly for direct methanol fuel cells. Suitable as electrolyte membrane.

BEST MODE FOR CARRYING OUT THE INVENTION

[0010] The solid polymer electrolyte membrane for a fuel cell of the present invention is such that the number of graft chain units is 30 or less, preferably 5 to 25, more preferably 10 to 20 on the resin film irradiated with radiation. In this case, as the resin film, polytetrafluoroethylene, tetrafluoroethylene perfluoroalkyl butyl ether copolymer is used. Fluorine resin films such as tetrafluoroethylene monohexafluoropropylene copolymer and ethylene-tetrafluoroethylene copolymer, or hydrocarbon resin films such as polyethylene and polypropylene. It is done.

[0011] On the other hand, in order to graft polymerize a polymerizable monomer so that the number of graft chain units is 30 or less on a resin film irradiated with radiation, the absorbed dose of radiation applied to the resin film is increased. This is possible by controlling the grafting ratio of the polymerizable monomer to a certain ratio (usually 60% or less, more preferably 20 to 50%, still more preferably 30 to 40%) after generating a large amount of radicals. become. Examples of the control of the graft ratio include a method of adjusting the polymerizable monomer concentration, oxygen concentration, etc. during graft polymerization.

[0012] As the polymerizable monomer, a styrene monomer such as styrene, α-methylstyrene, ρ funoleite rostyrene, styrene sulphonic acid, sodium styrene sulphonate, and the like, which are preferably monofunctional polymerizable monomers, is desirable. Acrylic monomers such as sodium acrylamidomethylpropanesulfonate can also be used alone or in appropriate combination. It is also possible to use a polyfunctional polymerizable monomer in combination.

Radiation graft polymerization is a method in which radicals are generated by irradiating a resin film with radiation, and a polymerizable monomer is grafted using the radical as a graft point. Radiation is preliminarily applied to the main chain of the resin film. Then, after generating radicals that will be the starting point of grafting, the pre-irradiation method in which the resin is brought into contact with the monomer to carry out the grafting reaction, and simultaneous irradiation with radiation in the coexistence of the polymerizable monomer and the resin film Although there is an irradiation method, in the present invention, A deviation method can also be adopted. In this case, the film thickness of the resin film is not particularly limited. Repulsive force 15-: LOO / zm Especially, the force of 25-60 / zm is preferable!

Examples of the radiation irradiated for graft polymerization in the present invention include γ-rays, X-rays, electron beams, ion beams, ultraviolet rays, and the like. In particular, γ-rays and electrons are used because of the ease of radical generation. Lines are preferred.

[0015] It is preferable that the absorbed dose of radiation is greater than or equal to lOkGy. Desirably, the absorbed dose is 20 to 300 kGy, and more desirably, the absorbed dose is 150 to 250 kGy. If it is less than 10 kGy, the number of monomer units in the graft chain must be increased in order to obtain the desired ionic conductivity with less radical generation. If it exceeds 300 kGy, the mechanical properties such as elongation and strength of the resin film may deteriorate.

[0016] Further, the irradiation with radiation is preferably performed in an inert gas atmosphere such as helium, nitrogen, and argon gas. The oxygen concentration in the gas is preferably lOOppm or less, particularly preferably 50ppm or less. There is no need to do this in the absence of oxygen.

[0017] Here, the amount of polymerizable monomer grafted on the irradiated resin is 100 mass% of the resin final, whereas the polymerization '14 monomer is 1,000,000 to 100,000 mass%. It is preferable to use 4,000 to 20,000 parts by mass. If the amount of the monomer is too small, the contact may be insufficient. If the amount is too large, the monomer may not be used efficiently.

[0018] In graft polymerization of these polymerizable monomers, a polymerization initiator such as azobisisoptyl-tolyl may be appropriately used as long as the object of the present invention is not impaired.

[0019] Furthermore, a solvent can be used at the time of the grafting reaction, and it is preferable to use a solvent that uniformly dissolves the monomer, for example, ketones such as acetone and methyl ethyl ketone, ethyl acetate, butyl acetate and the like. Esters, alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, ethers such as tetrahydrofuran, dioxane, N, N-dimethylformamide, N, N-dimethylacetamide, benzene, toluene, xylene, etc. Aromatic hydrocarbons, aliphatic or alicyclic hydrocarbons such as n-heptane, n-hexane, and cyclohexane, or a mixed solvent thereof can be used. The monomer Z solvent (mass ratio) is preferably 0.01 to 1. If the monomer Z solvent (mass ratio) is greater than 1, it will be difficult to adjust the number of monomer units in the graft chain, and if less than 0.01, The graft rate may be too low. A more desirable range is 0.03 to 0.5.

[0020] 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. It can be carried out in an inert gas atmosphere such as nitrogen or argon, or at an oxygen concentration of 0.01 to 20 Vol%.

As described above, a solid polymer electrolyte membrane can be obtained by graft polymerization of a polymerizable monomer to a resin film irradiated with radiation and further sulfonation.

[0022] The grafted membrane can be introduced with chlorosulfonic acid groups by immersing it in monodichloroethane chlorosulfonate. The membrane reacted with chlorosulfonic acid can be sulfonated by reacting in an aqueous solution of sodium hydroxide or sodium hydroxide to form an alkali salt of sulfonic acid, followed by acid treatment with hydrochloric acid or the like.

[0023] The solid polymer 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 on both sides of the solid polymer electrolyte membrane. By disposing the fuel diffusion layer and the separator, it is possible to obtain a fuel cell that is suitably used as an electrolyte membrane for a direct methanol fuel cell and excellent in battery characteristics without a methanol crossover. The configuration of the fuel electrode and the air electrode, the material, and the configuration of the fuel cell can be known.

Example

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, the number of graft chain units is the force determined by ¹³ CN MR. The specific conditions were determined by quantifying the C = C bond of styrene at the graft chain terminal site and calculating the graft chain mass force.

[Example 1]

5cm long, 6cm wide, 50m thick ethylene-tetrafluoroethylene copolymer (ETF E, manufactured by Norton) 0. 12g per room temperature, under nitrogen atmosphere, acceleration voltage lOOkV electron beam on both sides 20kGy each Immediately after irradiation, immerse in a 30 ml container equipped with a three-way cock containing 6 g of styrene and 18 g of toluene, publish nitrogen for 15 minutes at room temperature, and then heat at 60 ° C for 16 hours to obtain a graft rate of 42%. A styrene graft membrane was obtained.

Graft rate = [(film weight after grafting-film weight before grafting) before Z grafting Film mass] χ ιοο (%)

The film weight after grafting was the weight after the grafted film was washed once with toluene and three times with acetone and dried under reduced pressure at 60 ° C for 2 hours.

The average number of styrene units per graft chain of the styrene graft chain determined by ¹³ C NMR was 20.

The graft polymerized membrane is immersed in a mixed solution of 30 g of chlorosulfonic acid and 70 g of 1,2-dichloroethane, heated at 50 ° C for 2 hours, and then immersed in a 1N aqueous solution of caustic potassium at 90 ° C for 2 hours for hydrolysis. Subsequently, after being immersed in 2N hydrochloric acid at 90 ° C. for 2 hours, it was washed 3 times with pure water to obtain a solid polymer electrolyte membrane containing sulfonic acid groups. Table 1 shows the results of measuring the characteristics of the electrolyte membrane by the following method.

[0026] 1. Ion exchange capacity

After immersing the H-type electrolyte membrane in 0.02M aqueous sodium hydroxide solution for 24 hours, remove the membrane and use the solution. Determined by neutralization titration with 02M hydrochloric acid.

2.Moisture content

The difference between the weight of the water-containing film after immersion in pure water at room temperature and the weight of the dried film after drying at 100 ° C under reduced pressure was also determined.

3. Ionic conductivity

Using an impedance analyzer (Solartron 1260), the resistance in the longitudinal direction of the strip sample (width lcm) was measured at room temperature by the 4-terminal AC impedance method.

4.Methanol permeability coefficient

10M methanol water and pure water were separated by a membrane, and the amount of methanol that permeated the methanol water side membrane at the room temperature and exited to the pure water side was determined by gas chromatography.

[0027] [Comparative Example 1]

5cm long, 6cm wide, 50m thick ethylene-tetrafluoroethylene copolymer (ETF E, manufactured by Norton) 0. 12g at room temperature in a nitrogen atmosphere, acceleration voltage lOOkV electron beam irradiated on both sides 2kGy each Immediately after that, it is immersed in a 30 ml container equipped with a three-way cock containing 20 g of styrene, and after nitrogen publishing at room temperature for 15 minutes, it is heated at 60 ° C for 16 hours to graft. A styrene graft membrane having a rate of 45% was obtained.

Graft rate = [(film weight after grafting-film weight before grafting) Z film weight before grafting] X 100 (%)

The average number of styrene units per graft chain of the styrene graft chain determined by ¹³ C NMR was about 170.

The graft polymerized membrane is immersed in a mixed solution of 30 g of chlorosulfonic acid and 70 g of 1,2-dichloroethane, heated at 50 ° C for 2 hours, and then immersed in a 1N aqueous solution of caustic potassium at 90 ° C for 2 hours for hydrolysis. Subsequently, after being immersed in 2N hydrochloric acid at 90 ° C. for 2 hours, it was washed 3 times with pure water to obtain a solid polymer electrolyte membrane containing sulfonic acid groups. Table 1 shows the results of measurement by the method of Example 1 for the characteristics of this electrolyte membrane.

Examples [0028] From the results of Comparative Example 1, when the graft ratio is almost the same, the graft membrane with a high absorbed dose of electron beams has the same ionic conductivity with a small number of grafted monomer units, and has a methanol permeability. It was confirmed that the coefficient was small! / ヽ.

[0029] [Comparative Example 2]

The ethylene-tetrafluoroethylene copolymer used in Example 1 was irradiated with 0.1 g at room temperature under a nitrogen atmosphere at an acceleration voltage of 10 kV electron beams on both sides at 2 kGy each, and immediately after that, 20.0 g of styrene and dibutenebenzene were used. 2. Immerse it in a 30ml container equipped with 4g of a three-way cock, publish nitrogen for 15 minutes at room temperature, and then heat at 60 ° C for 16 hours. The graft ratio determined in the same manner as in Example 1 was 52%.

[0030] [Comparative Example 3]

According to the characteristics of Nafion 112 (manufactured by DuPont), the results measured by the method of Example 1 are Table 1 shows.

[table 1]

Claims

The scope of the claims

[1] A solid polymer for a fuel cell, characterized in that a polymerized monomer is graft-polymerized on a resin film irradiated with radiation so that the number of graft chain units is 30 or less and is sulfonated. Electrolyte membrane.

[2] Resin film strength Polytetrafluoroethylene, tetrafluoroethylene, perfluoroalkyl alkyl ether, tetrafluoroethylene-hexafluoropropylene, and ethylene-tetrafluoroethylene 2. The solid polymer electrolyte membrane according to claim 1, which is at least one type of fluororesin film selected.

[3] The polymer electrolyte membrane according to claim 1 or 2, wherein the polymerizable monomer is a styrene monomer.

[4] The solid polymer electrolyte membrane according to [1], [2] or [3], wherein the absorbed dose of radiation applied to the resin film is lOkGy or more and the graft ratio is 60% or less.

5. The solid polymer electrolyte membrane according to any one of claims 1 to 4, wherein the radiation is an electron beam.

[6] A fuel cell, wherein the solid polymer electrolyte membrane according to any one of claims 1 to 5 is provided between a fuel electrode and an air electrode.