JP2012084278A - Fluorine system polyelectrolyte film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyelectrolyte film which suppresses a dimensional change ratio in water at 80°C and which is excellent in chemical durability and physical durability.SOLUTION: A polyelectrolyte film includes a fluorine system polyelectrolyte composition in a microporous film gap. The pore distribution of the microporous film has at least two distribution centers within a pore size of 0.07 μm to 0.4 μm. The fluorine system polyelectrolyte composition includes a fluorine system polyelectrolyte (A component) and a thioether compound (B component).

Description

    The present invention relates to a fluorine-based polymer electrolyte membrane.

A fuel cell is one that converts the chemical energy of the fuel directly into electrical energy by electrochemically oxidizing fuel such as hydrogen and methanol in the battery, and is a clean electrical energy supply source. Attention has been paid. In particular, solid polymer electrolyte fuel cells are expected to be used as alternative power sources for automobiles, home cogeneration systems, portable generators, and the like because they operate at a lower temperature than other fuel cells.
Such a solid polymer electrolyte fuel cell has a membrane electrode in which gas diffusion electrodes having a structure in which an electrode catalyst layer (anode catalyst layer, cathode catalyst layer) and a gas diffusion layer are laminated are bonded to both surfaces of a proton exchange membrane. At least a joined body is provided. The proton exchange membrane here is a polymer electrolyte membrane made of a composition having a strongly acidic group such as a sulfonic acid group or a carboxylic acid group in a polymer chain and a property of selectively transmitting protons. Examples of the composition used for such a proton exchange membrane include a perfluoro proton composition typified by Nafion (registered trademark, manufactured by DuPont) having high chemical stability, and a proton exchange membrane using the same. Are preferably used.

During operation of the fuel cell, fuel (eg, hydrogen) is supplied to the gas diffusion electrode on the anode side, and oxidant (eg, oxygen or air) is supplied to the gas diffusion electrode on the cathode side. The operation of the fuel cell is realized by connecting both electrodes with an external circuit. Specifically, when hydrogen is used as fuel, hydrogen is oxidized on the anode catalyst in the anode catalyst layer to generate protons. After passing through the proton conductive polymer in the anode catalyst layer, the proton moves in the proton exchange membrane and reaches the cathode catalyst in the same layer through the proton conductive polymer in the cathode catalyst layer. On the other hand, electrons generated simultaneously with protons due to oxidation of hydrogen reach the gas diffusion electrode on the cathode side through an external circuit. On the cathode catalyst in the cathode electrode layer, the proton and oxygen in the oxidant react to generate water. At this time, electric energy is extracted.
At this time, the proton exchange membrane must also serve as a gas barrier partition by lowering the gas permeability. When the gas permeability of the proton exchange membrane is high, leakage of anode-side hydrogen to the cathode and leakage of cathode-side oxygen to the anode, that is, cross-leakage occurs. When a cross leak occurs, a so-called chemical short circuit occurs and a good voltage cannot be taken out. There is also a problem that the hydrogen on the anode side reacts with the oxygen on the cathode side to generate hydrogen peroxide to chemically degrade the proton exchange membrane. In order to solve these problems, a proton exchange membrane with improved chemical durability has been proposed by combining additives such as polybenzimidazole and polyphenylene sulfide, which have an inhibitory effect on the generation of hydrogen peroxide, with an ion exchange resin. Has been. (See Patent Documents 1 and 2)

On the other hand, from the viewpoint of reducing the internal resistance of the battery and increasing the output, it has been studied to reduce the thickness of the proton exchange membrane that is an electrolyte. However, if this proton exchange membrane is thinned, the effect as a gas barrier partition is reduced, and the problem of cross leak becomes more serious. Furthermore, since the mechanical strength of the membrane itself is reduced by reducing the thickness of the proton exchange membrane, it becomes difficult to handle the membrane during fabrication of the membrane electrode assembly and cell assembly, and water generated on the cathode side. There is a physical problem that the film is torn by changing the dimensions including.
In order to solve such problems, proton exchange membranes in which a porous membrane is filled with an ion exchange resin have been proposed (see Patent Documents 3 to 5).

  In addition, in recent years, due to further increase in fuel cell operation time, and further increase in temperature and humidity, physical durability in which a porous membrane is filled with an ion exchange resin compounded with additives such as polybenzimidazole and polyphenylene sulfide. A film having both chemical durability has been proposed (see Patent Document 6).

International Publication No. 2005/000949 Pamphlet International Publication No. 2008/102851 Pamphlet Japanese Patent Publication No. 5-75835 Japanese Examined Patent Publication No. 7-68377 Japanese Patent No. 4402625 JP 2009-242688 A

However, the proton exchange membranes disclosed in Patent Documents 1 and 2 have long-term chemical durability, but are still from the viewpoint of improving physical durability that can withstand repeated dimensional changes. There was room for improvement. In addition, since none of the proton exchange membranes disclosed in Patent Documents 3 to 5 can suppress deterioration of the membrane due to generation of hydrogen peroxide or the like, from the viewpoint of improving the chemical durability of the proton exchange membrane. There was still room for improvement.
Furthermore, the proton exchange membrane disclosed in Patent Document 6 is provided with means for achieving both chemical durability and physical durability, but in order to prevent flatting, the pore diameter of the porous membrane may be increased. On the other hand, if the pore size is increased, it becomes difficult to suppress the volume swelling of the electrolyte with the mechanical strength of the porous membrane, so there is still room for improvement from the viewpoint of achieving both chemical durability and physical durability. . Further, when the pore diameter is reduced, there is a problem that it is difficult to fill with additives such as polybenzimidazole and polyphenylene sulfide, and voids are generated in the film.
Accordingly, an object of the present invention is to provide an excellent fluorine-based polymer electrolyte membrane that has both chemical durability and physical durability.

As a result of intensive studies in view of the above circumstances, the present inventor, as a polymer electrolyte membrane in which the pores of the microporous membrane are filled with the polymer electrolyte composition, contains a fluorine-based polymer electrolyte and a thioether compound as the polymer electrolyte composition. In addition, by using a microporous membrane having a specific pore distribution as a microporous membrane, the dimensional change in water at 80 ° C. is suppressed, and the generation of hydrogen peroxide and the like is further suppressed. The inventors have found that a molecular electrolyte membrane can be realized, and have completed the present invention.
That is, the present invention provides the following fluoropolymer electrolyte membrane.
A polymer electrolyte membrane comprising a microporous membrane containing a fluorine-based polymer electrolyte composition, wherein the pore distribution of the microporous membrane is at least 2 within a pore diameter range of 0.07 μm to 0.4 μm. A polymer electrolyte membrane having two distribution centers, wherein the fluorine-based polymer electrolyte composition contains a fluorine-based polymer electrolyte (component A) and a thioether compound (component B).

  According to the present invention, it is possible to provide a polymer electrolyte membrane excellent in chemical durability and physical durability, in which a dimensional change ratio in water at 80 ° C. is suppressed and generation of hydrogen peroxide and the like is suppressed.

It is a pore distribution curve of the microporous membrane used for the Example and comparative example of this invention.

Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiment, and can be implemented with various modifications within the scope of the gist.
The polymer electrolyte membrane of the present embodiment is a fluoropolymer electrolyte membrane in which a fluoropolymer electrolyte composition is contained in the voids of the microporous membrane, and the microporous membrane has a microporous structure having a specific structure. It is a film | membrane and the said fluorine-type polymer electrolyte composition contains a thioether compound.

[Fluoropolymer electrolyte composition]
(Fluoropolymer electrolyte)
The fluorine-based polymer electrolyte is a polymer electrolyte having a fluorine atom in at least one repeating unit. As a specific example, a perfluorocarbon polymer compound having a structural unit represented by the following general formula (1) is used. Can be mentioned.
_{^{- [CF 2 CX 1 X 2}} ] a - [CF 2 -CF ((- O-CF 2 -CF (CF 2 X 3)) b -O c - (CFR 1) d - (CFR 2) e - ( CF) _f -X ⁴ )] _g- (1)
Here, in the formula (1), X ¹ , X ² and X ³ are each independently selected from the group consisting of a halogen atom and a C 1 to C 3 perfluoroalkyl group. A chlorine atom, a bromine atom, and an iodine atom are mentioned, It is preferable that they are a fluorine atom or a chlorine atom.
X ⁴ is COOZ, SO ₃ Z, PO ₃ Z ₂ or PO ₃ HZ. Z is a hydrogen atom, lithium atom, alkali metal atom such as sodium atom or potassium atom; alkaline earth metal atom such as calcium atom or magnesium atom or amines (NH ₄ , NH ₃ R ₁ , NH ₂ R ₁ R ₂ , NHR ₁ R ₂ R ₃ , NR ₁ R ₂ R ₃ R ₄ ). R ₁ , R ₂ , R ₃ and R ₄ are each independently selected from the group consisting of alkyl groups and arene groups. When X ⁴ is PO ₃ Z ₂ , Z may be the same or different.
The alkyl group is not particularly limited, and is a monovalent group represented by the general formula C _n H _{2n + 1} (n represents an integer of 1 or more, and may be an integer of 1 to 20). Preferably, it is an integer of 1 to 10. More specifically, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, and the like can be mentioned and substituted. Also good. The arene group may also be substituted.
R ¹ and R ² are each independently selected from the group consisting of a halogen atom, a C 1-10 perfluoroalkyl group and a fluorochloroalkyl group, and the halogen atom includes a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. An atom is mentioned, It is preferable that it is a fluorine atom or a chlorine atom.
a and g are numbers satisfying 0 ≦ a <1, 0 <g ≦ 1, and a + g = 1.
b is an integer of 0-8.
c is 0 or 1;
d, e and f are each independently an integer of 0 to 6 (provided that d, e and f are not 0 at the same time).

In the above general formula (1), when Z is an alkaline earth metal, for example (COO) ₂ Z or (SO ₃ ) ₂ Z, the two X ⁴ are an alkaline earth metal and a salt. It may be formed.
Among these, a perfluorocarbon sulfonic acid polymer represented by the following general formula (3) or (4) or a metal salt thereof is particularly preferable.
_{- [CF 2 CF 2] a} - [CF 2 -CF ((- O-CF 2 -CF (CF 3)) b -O- (CF 2) h -SO 3 X)] g - (3)
In the formula, a and g are numbers satisfying 0 ≦ a <1, 0 <g ≦ 1, a + g = 1, b is an integer of 1 to 3, h is an integer of 1 to 8, and X is It is a hydrogen atom or an alkali metal atom.
_{- [CF 2 CF 2] a} - [CF 2 -CF (-O- (CF 2) h -SO 3 X)] g - (4)
In the formula, a and g are numbers satisfying 0 ≦ a <1, 0 <g ≦ 1, and a + g = 1, h is an integer of 1 to 8, and X is a hydrogen atom or an alkali metal atom.

The perfluorocarbon polymer compound having an ion exchange group that can be used in the present embodiment is, for example, polymerized a precursor polymer represented by the following general formula (5), and then subjected to alkali hydrolysis, acid treatment, and the like. Can be manufactured.
_{^{- [CF 2 CX 1 X 2}} ] a - [CF 2 -CF ((- O-CF 2 -CF (CF 2 X 3)) b -O c - (CFR 1) d - (CFR 2) e - ( ^{_{CF 2) f -X 5)]}} g - (5)
In the formula, X ¹ , X ² and X ³ are each independently selected from the group consisting of a halogen atom and a C 1 to C 3 perfluoroalkyl group, and as the halogen atom, a fluorine atom, a chlorine atom, a bromine atom and An iodine atom is mentioned, It is preferable that they are a fluorine atom or a chlorine atom.
X ⁵ is COOR ³ , COR ⁴ or SO ₂ R ⁴ . R ³ is a hydrocarbon alkyl group having 1 to ³ carbon atoms. R ⁴ is a halogen atom.
R ₁ and R ₂ are each independently selected from the group consisting of a halogen atom, a C 1-10 perfluoroalkyl group and a fluorochloroalkyl group, and the halogen atom includes a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. An atom is mentioned, It is preferable that it is a fluorine atom or a chlorine atom.
a and g are numbers satisfying 0 ≦ a <1, 0 <g ≦ 1, and a + g = 1.
b is an integer of 0-8.
c is 0 or 1;
d, e and f are each independently an integer of 0 to 6 (provided that d, e and f are not 0 at the same time).
The precursor polymer represented by the general formula (5) can be produced, for example, by copolymerizing a fluorinated olefin compound and a vinyl fluoride compound.

Here, as a fluorinated olefin compound, the compound represented by the following general formula (1a) is mentioned, for example.
CF ₂ = CX ¹ X ² (1a)
In the formula, X ¹ and X ² are as described above for the general formula (5).
_{Specifically, CF 2 = CF 2, CF} 2 = CFCl, CF 2 = CCl 2 , and the like.
Moreover, as a vinyl fluoride compound, the compound represented by the following general formula (1b) is mentioned, for example.
_{CF 2 = CF ((- O} -CF 2 -CF (CF 2 X 3)) b -O c - (CFR 1) d - (CFR 2) e - (CF 2) f -X 5) (1b)
In the formula, X ³ , X ⁵ , R ¹ , R ² , b, c, d, e, and f are as described above for the general formula (5).
_{Specifically, CF 2 = CFO (CF 2} ) j -SO 2 F, CF 2 = CFOCF 2 CF (CF 3) O (CF 2) j -SO 2 F, CF 2 = CF (OCF 2 CF (CF _{3)) j - (CF 2} ) j-1 -SO 2 F, CF 2 = CFO (CF 2) j -CO 2 R, CF 2 = CFOCF 2 CF (CF 3) O (CF 2) j -CO 2 _{R, CF 2 = CF (CF} 2) j -CO 2 R, CF 2 = CF (OCF 2 CF (CF 3)) j - (CF 2) 2 -CO 2 R ( where, j is 1 to 8 Integer, R represents a hydrocarbon alkyl group having 1 to 3 carbon atoms.) And the like.

The precursor polymer as described above can be synthesized by a known method. The synthesis method is not particularly limited, and examples thereof include the following methods.
(I) A method (solution polymerization) in which a polymerization solvent such as fluorine-containing hydrocarbon is used, and polymerization is performed by reacting a vinyl fluoride compound and a fluorinated olefin gas in a state where the polymerization solvent is filled and dissolved. Examples of the fluorine-containing hydrocarbon include a group of compounds collectively referred to as “fluorocarbon” such as trichlorotrifluoroethane, 1, 1, 1, 2, 3, 4, 4, 5, 5, 5-decafluoropentane, and the like. It can be preferably used.
(Ii) A method in which a vinyl fluoride compound is polymerized using a vinyl fluoride compound itself as a polymerization solvent without using a solvent such as a fluorine-containing hydrocarbon (bulk polymerization).
(Iii) A method (emulsion polymerization) in which an aqueous solution of a surfactant is used as a polymerization solvent and a vinyl fluoride compound and a fluorinated olefin gas are reacted in a state of being charged and dissolved in the polymerization solvent.
(Iv) A method in which an aqueous solution of an interfacial polymerizer and an auxiliary emulsifier such as alcohol is used, and polymerization is performed by reacting a vinyl fluoride compound and a fluorinated olefin gas in a state where the aqueous solution is filled and emulsified (miniemulsion polymerization, Microemulsion polymerization).
(V) A method (suspension polymerization) in which an aqueous solution of a suspension stabilizer is used, and polymerization is performed by reacting a vinyl fluoride compound and a fluorinated olefin gas in a state of being filled and suspended in the aqueous solution.

In the present embodiment, a melt mass flow rate (hereinafter sometimes abbreviated as “MFR”) can be used as an index of the polymerization degree of the precursor polymer. In the present embodiment, from the viewpoint of molding processing, the MFR of the precursor polymer is preferably 0.01 or more, more preferably 0.1 or more, and further preferably 0.3 or more. Although the upper limit of MFR is not specifically limited, From a viewpoint of a shaping | molding process, 100 or less are preferable, 50 or less are more preferable, and 10 or less are more preferable.
The precursor polymer produced as described above is hydrolyzed in a basic reaction liquid, sufficiently washed with warm water or the like, and acid-treated. By this hydrolysis treatment and acid treatment, for example, the perfluorocarbon sulfonic acid resin precursor is protonated to become a perfluorocarbon sulfonic acid resin that is an SO ₃ H form.

  In the present embodiment, the content of the fluorine-based polymer electrolyte is preferably 100% by mass with respect to the whole polymer used as the polymer electrolyte, from the viewpoint of chemical durability, but for example, a hydrocarbon-based polymer electrolyte Etc. may be included in any proportion. Examples of the hydrocarbon polymer electrolyte include polyphenylene sulfide, polyphenylene ether, polysulfone, polyether sulfone, polyether ether sulfone, polyether ketone, polyether ether ketone, polythioether ether sulfone, polythioether ketone, and polythioether ether ketone. , Polybenzimidazole, polybenzoxazole, polyoxadiazole, polybenzoxazinone, polyxylylene, polyphenylene, polythiophene, polypyrrole, polyaniline, polyacene, polycyanogen, polynaphthyridine, polyphenylene sulfide sulfone, polyphenylene sulfone, polyimide, polyetherimide, polyester Imide, polyamideimide, polyarylate, aromatic poly De, polystyrene, polyester, polycarbonate, and the like. The content of the hydrocarbon-based polymer electrolyte is preferably 50% by mass or less, more preferably 20% by mass or less, with respect to the entire polymer electrolyte.

  In the present embodiment, the fluorinated polymer electrolyte preferably has an ion exchange capacity of 0.5 to 3.0 meq / g, and preferably has an ion exchange group so as to satisfy this condition. . By setting the ion exchange capacity to 3.0 meq / g or less, swelling of the polymer electrolyte membrane containing the polymer electrolyte under high temperature and high humidity during fuel cell operation tends to be reduced. Reduction of the swelling of the polymer electrolyte membrane causes problems such as a decrease in strength of the polymer electrolyte membrane, generation of wrinkles and separation from the electrode, and a problem of reduced gas barrier properties. Can improve. On the other hand, by setting the ion exchange capacity to 0.5 meq / g or more, the fuel cell equipped with the polymer electrolyte membrane satisfying such conditions can maintain its power generation capability well. From these viewpoints, the ion exchange capacity of the fluorine-based polymer electrolyte (component A) is more preferably 0.65 to 2.8 meq / g, further preferably 1.3 to 2.5 meq / g. is there.

In addition, the ion exchange capacity of the fluorine-based polymer electrolyte in the present embodiment is measured as follows.
First, a membrane made of a polymer electrolyte in which the counter ion of the ion exchange group is in a proton state is immersed in a saturated NaCl aqueous solution at 25 ° C., and the aqueous solution is stirred for a sufficient time. Subsequently, the proton in the saturated NaCl aqueous solution is neutralized and titrated with a 0.01N sodium hydroxide aqueous solution. A membrane made of a polymer electrolyte in which the counter ion of the ion exchange group obtained by filtration after neutralization is in the form of sodium ions is rinsed with pure water, further vacuum-dried, and weighed. The amount of sodium hydroxide required for neutralization is M (mmol), the mass of a membrane made of a polymer electrolyte in which the counter ion of the ion exchange group is sodium ion is W (mg), and the equivalent mass EW ( g / equivalent).
EW = (W / M) −22

Furthermore, the ion exchange capacity (milli equivalent / g) is calculated by taking the reciprocal of the obtained EW value and multiplying it by 1000.
Therefore, the fluorine-based polymer electrolyte in the present embodiment has an equivalent weight (EW) value of preferably 330 to 2000 g / equivalent, more preferably 355 to 1540 g / equivalent, and further preferably 400 to 770 g / equivalent. It is.
This ion exchange capacity can be adjusted to fall within the above numerical range by adjusting the number of ion exchange groups present in the fluorine-based polymer electrolyte membrane 1g.

  In the present embodiment, the fluoropolymer electrolyte composition has a glass transition temperature of preferably 80 ° C. or higher, more preferably 100 ° C. or higher, more preferably 120 ° C. or higher, from the viewpoint of heat resistance during fuel cell operation. Especially preferably, it is 130 degreeC or more. Here, the glass transition temperature of the polymer electrolyte is measured according to JIS-C-6481. Specifically, the polymer electrolyte molded into a film shape is cut into a width of 5 mm, and the test piece is heated from room temperature at a rate of 2 ° C./minute using a dynamic viscoelasticity measuring device. The dynamic viscoelasticity and loss tangent of the specimen are measured. The measured peak temperature of loss tangent is defined as the glass transition temperature. The glass transition temperature can be adjusted by controlling the structural formula, molecular weight, ion exchange capacity, etc. of the polymer electrolyte contained in the fluorine-based polymer electrolyte composition.

The polymer electrolyte membrane according to this embodiment preferably has a water content at 80 ° C. of 5% by mass to 150% by mass, more preferably 10% by mass to 100% by mass, and still more preferably 20% by mass to 80% by mass. It is mass%, Most preferably, it is 30 mass%-70 mass%. When the water content of the polymer electrolyte is adjusted to the above range, there is an effect that long-term dimensional change stability and high battery performance are exhibited even under high temperature and low humidification conditions. When the water content at 80 ° C. is 5% by mass or more, there is sufficient water for proton transfer, so that excellent battery performance is exhibited when used in a fuel cell. On the other hand, when the water content at 80 ° C. is 150% by mass or less, the polymer electrolyte is less likely to be in a gel state and can be easily formed as a film.
The water content of the polymer electrolyte membrane at 80 ° C. is the molecular weight, MFR, crystallinity and ion exchange capacity of the polymer electrolyte, the hydrophilic treatment area of the microporous membrane surface, the heat treatment temperature and time of the polymer electrolyte membrane, etc. It can be adjusted by adjusting.
Examples of means for increasing the water content at 80 ° C. include increasing the ion exchange group density of the polymer electrolyte, increasing the MFR of the polymer electrolyte precursor polymer, and decreasing the heat treatment temperature and heat treatment time to increase the polymer content. For example, the surface of the microporous membrane that suppresses crystallization of the electrolyte may be modified with a hydrophilic group. On the other hand, as means for lowering the moisture content at 80 ° C., for example, the ion exchange group density of the polymer electrolyte is lowered, the MFR of the polymer electrolyte precursor polymer is lowered, or the polymer electrolyte membrane is removed by an electron beam or the like. Crosslinking may be mentioned.

(Thioether compound)
The fluorine-based polymer electrolyte composition used in the present invention contains a thioether compound (B). The thioether compound is a compound having a chemical structure of — (R—S) _r — (S is a sulfur atom, R is a hydrocarbon group, and r is an integer of 1 or more). Specific examples of the compound having such a chemical structure include dialkyl thioethers such as dimethylthioether, diethylthioether, dipropylthioether, methylethylthioether, and methylbutylthioether, tetrahydrothiophene, and tetrahydroapiran. Examples thereof include aromatic thioethers such as cyclic thioether, methylphenyl sulfide, ethylphenyl sulfide, diphenyl sulfide, and dibenzyl sulfide. In addition, you may use what was illustrated here as a thioether compound as it is, for example, you may use the polymer obtained by using what was illustrated for a monomer like a polyphenylene sulfide (PPS) as a thioether compound.

From the viewpoint of durability, the thioether compound is preferably a polymer (oligomer or polymer) having r of 10 or more, more preferably a polymer having r of 1,000 or more. A particularly preferred thioether compound is polyphenylene sulfide (PPS).
Here, polyphenylene sulfide will be described. Examples of the polyphenylene sulfide that can be used in the present embodiment include polyphenylene sulfide having a paraphenylene sulfide skeleton of preferably 70 mol% or more, more preferably 90 mol% or more.
The method for producing the polyphenylene sulfide is not particularly limited. For example, a method in which a halogen-substituted aromatic compound (p-dichlorobenzene or the like) is polymerized in the presence of sulfur and sodium carbonate, a halogen-substituted aromatic compound in a polar solvent. Is polymerized in the presence of sodium sulfide or sodium hydrogen sulfide and sodium hydroxide, a method of polymerizing a halogen-substituted aromatic compound in the presence of hydrogen sulfide and sodium hydroxide or sodium aminoalkanoate in a polar solvent, or Examples include a method by self-condensation of p-chlorothiophenol. Among these, a method of reacting sodium sulfide and p-dichlorobenzene in an amide solvent such as N-methylpyrrolidone or dimethylacetamide or a sulfone solvent such as sulfolane is preferably used.

Further, the content of -SX group (S is a sulfur atom, X is an alkali metal atom or a hydrogen atom) in polyphenylene sulfide is preferably usually 10 μmol / g to 10,000 μmol / g, more preferably 15 μmol / g. g to 10,000 μmol / g, more preferably 20 μmol / g to 10,000 μmol / g.
That the content of the —SX group is in the above range means that there are many reaction active sites. -By using polyphenylene sulfide in which the content concentration of the SX group satisfies the above range, the dispersibility is improved as the miscibility with the polymer electrolyte according to the present embodiment is improved, and high temperature and low humidification conditions are satisfied. It is considered that higher durability can be obtained.

Moreover, as the thioether compound, those having an acidic functional group introduced at the terminal can be suitably used. The acidic functional group to be introduced is selected from the group consisting of sulfonic acid group, phosphoric acid group, carboxylic acid group, maleic acid group, maleic anhydride group, fumaric acid group, itaconic acid group, acrylic acid group, and methacrylic acid group. Are preferred, and sulfonic acid groups are particularly preferred.
In addition, the introduction method of an acidic functional group is not specifically limited, A general method is used. For example, when introducing a sulfonic acid group into a thioether compound, it can be introduced under known conditions using a sulfonating agent such as sulfuric anhydride or fuming sulfuric acid. More specifically, for example, K.K. Hu, T .; Xu, W .; Yang, Y. et al. Fu, Journal of Applied Polymer Science, Vol. 91, E.E. Montoneri, Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 27, 3043-3051 (1989).
Further, those in which the introduced acidic functional group is further substituted with a metal salt or an amine salt are also suitably used as the thioether compound. The metal salt is preferably an alkali metal salt such as sodium salt or potassium salt, or an alkaline earth metal salt such as calcium salt.

Furthermore, when the thioether compound is used in a powder form, the average particle diameter of the thioether compound is 0.01 μm to from the viewpoint of favorably realizing an effect such as a long life by improving dispersibility in the polymer electrolyte. The thickness is preferably 2.0 μm, more preferably 0.01 μm to 1.0 μm, still more preferably 0.01 μm to 0.5 μm, and particularly preferably 0.01 μm to 0.1 μm. This average particle size is a value measured by a laser diffraction / scattering particle size distribution measuring device (for example, model number: LA-950, manufactured by Horiba, Ltd.).
As a method of finely dispersing the thioether compound in the polymer electrolyte, for example, a method of pulverizing and finely dispersing by applying high shear at the time of melt kneading with the polymer electrolyte, etc., after obtaining a polymer electrolyte solution described later, Examples thereof include a method of filtering the solution to remove coarse thioether compound particles and using the solution after filtration. From the viewpoint of molding processability, the melt viscosity of polyphenylene sulfide suitably used for melt kneading is preferably 1 to 10,000 poise, more preferably 100 to 10,000 poise. The melt viscosity is a value obtained by holding for 6 minutes at 300 ° C., a load of 196 N, L / D (L: orifice length, D: orifice inner diameter) = 10/1 using a flow tester.

  The ratio (Wa / Wd) of the mass (Wa) of the polymer electrolyte (the total amount of the polymer electrolyte contained in the polymer electrolyte membrane) to the mass (Wd) of the thioether compound is 60/40 to 99.99 / 0.01. 70/30 to 99.95 / 0.05 is more preferable, 80/20 to 99.9 / 0.1 is still more preferable, and 90/10 to 99.5 / 0.5 is particularly preferable. . By setting the mass ratio of the polymer electrolyte to 60 or more, better ion conductivity can be realized, and better battery characteristics can be realized. On the other hand, by setting the mass ratio of the thioether compound to 40 or less, durability in battery operation under high temperature and low humidity conditions can be improved.

  The polymer electrolyte membrane of the present embodiment may contain an additive such as a polyazole compound for the purpose of improving durability. These additives are used singly or in combination of two or more.

(Polyazole compound)
Examples of polyazole compounds that can be used in the present embodiment include polyimidazole compounds, polybenzimidazole compounds, polybenzobisimidazole compounds, polybenzoxazole compounds, polyoxazole compounds, polythiazole compounds, and polybenzothiazoles. Examples thereof include a polymer of a compound having a hetero five-membered ring containing one or more nitrogen atoms in the ring, such as a system compound. The hetero five-membered ring may contain an oxygen atom, a sulfur atom or the like in addition to the nitrogen atom.
Moreover, it is preferable that the molecular weight of a polyazole compound is 300-500,000 (polystyrene conversion) as a weight average molecular weight at the time of GPC measurement.
Examples of the compound having the five-membered ring as a constituent element include p-phenylene group, m-phenylene group, naphthalene group, diphenylene ether group, diphenylene sulfone group, biphenylene group, terphenyl group, and 2,2-bis. From the viewpoint of obtaining heat resistance, it is preferable to use a compound in which a divalent aromatic group represented by (4-carboxyphenylene) hexafluoropropane group is bonded to a hetero five-membered ring. Specifically, polybenzimidazole is preferably used as the polyazole compound.

In addition, the polyazole compound may be a compound in which an ion exchange group is introduced (modified polyazole compound) using the following general modification method. Examples of such modified polyazole compounds include those obtained by introducing one or more groups selected from the group consisting of amino groups, quaternary ammonium groups, carboxyl groups, sulfonic acid groups, and phosphonic acid groups into the polyazole compounds. In addition, by introducing an anionic ion exchange group into the polyazole compound, the ion exchange capacity of the entire polymer electrolyte membrane of the present embodiment can be increased, resulting in high output during fuel cell operation. It is useful because it can. The ion exchange capacity of the modified polyazole compound is preferably 0.1 to 3.5 meq / g.
The modification method of the polyazole compound is not particularly limited. For example, fuming sulfuric acid, concentrated sulfuric acid, sulfuric anhydride and its complex, sultone such as propane sultone, α-bromotoluenesulfonic acid, chloroalkylsulfonic acid, etc. Examples thereof include a method of introducing an ion exchange group into the polyazole compound, a method of polymerizing by adding an ion exchange group at the time of monomer synthesis of the polyazole compound, and the like.

  The polyazole compound is preferably dispersed in islands in the polymer electrolyte phase. Here, “is dispersed in the form of islands” means a state in which a phase containing a polyazole compound is dispersed in the form of particles in a polymer electrolyte phase when TEM observation is performed without performing a staining treatment. means. Dispersion in such a state indicates that the portion containing the polyazole compound is uniformly finely dispersed in the portion mainly composed of the polymer electrolyte, which is preferable from the viewpoint of durability.

Further, the polymer electrolyte and the polyazole compound may form, for example, an ion-bonded ion-base complex or a covalent bond. That is, for example, when the polymer electrolyte has a sulfonic acid group and the polyazole compound has a reactive group such as an imidazole group, an oxazole group, or a thiazole group, the sulfonic acid group in the polymer electrolyte and each reaction in the polyazole compound A nitrogen atom of the group may be bonded to each other by an ionic bond or a covalent bond.
Whether or not the ionic bond or the covalent bond exists can be confirmed using a Fourier-Transform Infrared Spectrometer (hereinafter referred to as FT-IR). For example, when a perfluorocarbon sulfonic acid resin is used as the polymer electrolyte and poly [2,2 ′ (m-phenylene) -5,5′-benzimidazole] (hereinafter referred to as “PBI”) is used as the polyazole compound, FT is used. When measured by -IR, shifted absorption peaks derived from the chemical bond between the sulfonic acid group in the polymer electrolyte and the imidazole group in PBI show 1458 cm ^-1 , 1567 cm ^-1 , 1634 cm ^-1. Recognized.

  In addition, when a polymer electrolyte membrane to which PBI was added as a polyazole compound was prepared and a dynamic viscoelasticity test was performed on the membrane, a peak temperature (Tg) of a loss tangent (Tanδ) obtained in a temperature rising process from room temperature to 200 ° C. ) Is higher than that of a polymer electrolyte membrane to which PBI is not added. Such an increase in Tg is preferable because the heat resistance and mechanical strength of the polymer electrolyte membrane can be improved.

  The ratio (Wc / Wd) of the mass (Wc) of the polyazole compound to the mass (Wd) of the thioether compound is preferably 1/99 to 99/1. Further, from the viewpoint of the balance between chemical stability and durability (dispersibility), Wc / Wd is more preferably 5/95 to 95/5, further preferably 10/90 to 90/10, and 20/80 to 80/20 is particularly preferred.

  Furthermore, the proportion of the total mass of the polyazole compound and the thioether compound in the polymer electrolyte membrane is preferably 0.01% by mass to 50% by mass. From the viewpoint of balance between ion conductivity and durability (dispersibility), the total mass is more preferably 0.05% by mass to 45% by mass, and further preferably 0.1% by mass to 40% by mass. 0.2 mass% to 35 mass% is even more preferable, and 0.3 mass% to 30 mass% is particularly preferable.

[Microporous membrane]
The raw material of the microporous membrane according to the present embodiment is not limited, and for example, a simple substance such as polytetrafluoroethylene, polyamide, polyimide, polyolefin, polycarbonate, or a mixture thereof may be used, but it may be made of polytetrafluoroethylene (PTFE). It is preferable that
The method for producing a PTFE microporous membrane preferably used in the present embodiment is not particularly limited, but is preferably an expanded PTFE microporous membrane from the viewpoint of suppressing the dimensional change of the polymer electrolyte membrane. The expanded PTFE microporous membrane is produced by a known method as disclosed in, for example, JP-A-51-30277, JP-A-1-01876 and JP-A-10-30031. be able to. Specifically, first, a liquid lubricant such as solvent naphtha and white oil is added to fine powder obtained by coagulating an aqueous PTFE emulsion polymerization dispersion, and paste extrusion is performed in a rod shape. Thereafter, this rod-like paste extrudate (cake) is rolled to obtain a PTFE green body. The green tape at this time is stretched at an arbitrary magnification in the longitudinal direction (MD direction) and / or the width direction (TD direction). At the time of stretching or after stretching, the liquid lubricant filled at the time of extrusion can be removed by overheating or extraction to obtain a stretched PTFE microporous membrane.

  In addition, the microporous membrane in the present embodiment is a known additive such as a non-fibrinated material (for example, low molecular weight PTFE), an ultraviolet absorber, a light stabilizer, an antistatic agent, an antifogging agent, and a coloring pigment as necessary. May be contained within a range that does not impair the achievement and effects of the present invention.

The microporous membrane in the present embodiment is characterized in that the pore distribution has at least two distribution centers (peaks) in a pore diameter range of 0.07 μm to 0.4 μm. When the pore distribution of the microporous membrane has two distribution centers, (i) pores having a pore diameter near the larger distribution center play a role in promoting discharge of reaction product water and easy filling of additives. (Ii) The pore having a pore diameter near the smaller distribution center plays a role of maintaining the mechanical strength of the electrolyte membrane by suppressing volume swelling in the membrane plane direction of the electrolyte filled in the pore. Therefore, the polymer electrolyte membrane using the microporous membrane can easily achieve both chemical durability and physical durability.
Here, the pore distribution of the microporous membrane refers to a value measured by a bubble point half dry method using a bubble point method described in JIS-K-3832.
If the distribution center of the smaller pore diameter is 0.07 μm or more, it is easy to fill with an additive or an electrolyte solution having a hydrogen peroxide suppressing effect, and voids are formed in the polymer electrolyte membrane while exhibiting the hydrogen peroxide suppressing effect. It is possible to suppress the occurrence and the processability is excellent because the filling speed can be increased. Further, when the distribution center of the larger pore diameter is 0.4 μm or less, the dimensional change of the polymer electrolyte membrane can be suppressed, so that the membrane reinforcing effect is excellent.
The pore distribution of the microporous membrane preferably has at least two distribution centers in the pore diameter range of 0.1 μm to 0.4 μm, and has at least two distribution centers in the pore diameter range of 0.15 μm to 0.4 μm. More preferably.
The smaller distribution center may be in the range of 0.1 to 0.2 μm or in the range of 0.15 to 0.2 μm. The larger distribution center may be in the range of 0.2 to 0.4 μm, or may be in the range of 0.22 to 0.3 μm.

The pore distribution of the microporous membrane in the present embodiment is such that the ratio of pores having a pore diameter of 0.2 μm or less to the pore distribution having a pore diameter of 0.07 μm to 0.4 μm is 0.1 or more (quantity ratio). In addition, it is preferable that the ratio of pores larger than the pore diameter of 0.2 μm is 0.5 or more (quantity ratio).
When the ratio of the microporous membrane to the pores having a pore diameter of 0.2 μm or less with respect to the pores having a pore diameter of 0.07 μm to 0.4 μm is adjusted to 0.1 or more (quantity ratio), the dimensional change of the polymer electrolyte membrane Since it becomes easy to suppress, a polymer electrolyte tends to express high physical durability. On the other hand, the ratio of the pores having a pore diameter of 0.2 μm or less to the pores having a pore diameter of 0.07 μm to 0.4 μm is preferably 0.5 or less (quantity ratio).
In addition, when the ratio of the microporous membrane with respect to the pores having a pore diameter of 0.07 μm to 0.4 μm to the pores having a diameter of 0.2 μm or more is adjusted to 0.5 or more (quantity ratio), the reaction generated during fuel cell operation Since water can be discharged smoothly and the microporous membrane can be easily filled with the additive, voids are hardly generated in the membrane, and the additive can be uniformly dispersed in the membrane. Molecular electrolyte membranes tend to exhibit high chemical durability. On the other hand, the ratio of 0.2 μm or more pores to pores having a pore diameter of 0.07 μm to 0.4 μm is preferably 0.9 or less (quantity ratio).

The pore size of the microporous membrane is the type of lubricant used in manufacturing, the amount of lubricant added, the dispersibility of the lubricant, the stretch ratio of the microporous membrane, the lubricant extraction solvent, the heat treatment temperature, the heat treatment time, the extraction time and the extraction. The numerical value can be adjusted to the above range depending on the temperature.
For example, the pore distribution as in the present embodiment can be achieved by adjusting the amount of lubricant added and sequentially performing biaxial stretching while changing the stretching ratio of MD and TD.

  In addition, the microporous membrane in the present embodiment may be a single layer or may be composed of multiple layers as necessary. By adopting a multilayer structure, a multilayer is preferable from the viewpoint that defects do not propagate even if defects such as voids and pinholes occur in each single layer. On the other hand, a single layer is preferable from the viewpoint of the fillability of the electrolyte and the additive. Examples of the method of forming a PTFE microporous membrane as a multilayer include a method of bonding two or more single layers by thermal lamination, a method of rolling a plurality of cakes, and the like.

The microporous membrane according to this embodiment preferably has an elastic modulus of at least 250 MPa or less in the machine flow direction (MD) and the direction perpendicular to the machine flow direction (MD). By setting the elastic modulus of the microporous membrane to 250 MPa or less, the dimensional stability of the polymer electrolyte membrane is improved. Here, the elastic modulus of the microporous membrane refers to a value measured according to JIS-K7113.
Proton conduction in the fluorine-based polymer electrolyte is made possible by the water absorption of the fluorine-based polymer electrolyte and hydration of the ion exchange groups. Therefore, the conductivity at the same humidity increases as the ion exchange group density increases and the ion exchange capacity increases. Also, the higher the humidity, the higher the conductivity.
The fluorine-based polymer electrolyte in the present embodiment has a high conductivity even under low humidity when the sulfone group density is high, but has a problem of extremely containing water under high humidity.
For example, in the operation of a household fuel cell, starting and stopping are usually performed once or more once a day, and the polymer electrolyte membrane repeatedly swells and contracts due to a change in humidity at that time. It is negative in terms of both performance and durability that the polymer electrolyte membrane repeats such changes in wet and dry dimensions. When the ion exchange capacity of the fluorine-based polymer electrolyte in the present embodiment is high, it is easy to contain water, and when the film is formed as it is, the wet and dry dimensional change is large. By using a microporous membrane having flexibility with an elastic modulus of 250 MPa or less, it is possible to relieve stress due to the volume change of the membrane by the flexibility of the microporous membrane and suppress dimensional changes.
Therefore, the elastic modulus of the microporous membrane is more preferably 1 to 250 MPa, further preferably 5 to 200 MPa, and most preferably 10 to 150 MPa.

The microporous membrane according to this embodiment preferably has a porosity of 50% to 90%, more preferably 60% to 90%, still more preferably 60% to 85%, and 50% to 90%. 85% is particularly preferable. When the porosity is in the range of 50% to 90%, the ionic conductivity of the polymer electrolyte membrane, the strength of the polymer electrolyte membrane, and the suppression of dimensional change tend to be compatible. Here, the porosity of the microporous film refers to a value measured by a mercury porosimeter (for example, manufactured by Shimadzu Corporation, trade name: Autopore IV 9520, initial pressure of about 20 kPa) by a mercury intrusion method.
The numerical value of the porosity of the microporous membrane can be adjusted to the above range depending on the number of pores in the microporous membrane, the pore diameter, the pore shape, the draw ratio, the amount of liquid lubricant added, and the type of liquid lubricant. As a means for increasing the porosity of the microporous film, for example, a method of adjusting the addition amount of the liquid lubricant to 5 to 50% by mass can be mentioned. By adjusting the addition amount of the liquid lubricant within this range, the moldability of the resin constituting the microporous membrane is maintained and the plasticizing effect is sufficient. It can be highly fibrillated in the biaxial direction and can efficiently increase the draw ratio. On the other hand, examples of means for lowering the porosity include reducing the amount of liquid lubricant and decreasing the draw ratio.

The microporous membrane in this embodiment preferably has a thickness of 0.1 μm to 50 μm, more preferably 0.5 μm to 30 μm, still more preferably 1.0 μm to 20 μm, and 2.0 μm to 20 μm. Is particularly preferred. When the film thickness is in the range of 0.1 μm to 50 μm, the polymer electrolyte tends to fill the pores in the microporous membrane, and the dimensional change of the polymer electrolyte tends to be suppressed. Here, the film thickness of the microporous membrane is determined by sufficiently allowing the membrane to stand in a constant temperature and humidity room of 50% RH, and then using a known film thickness meter (for example, trade name “B-1 manufactured by Toyo Seiki Seisakusho”). ") Means the value measured using.
The value of the film thickness of the microporous film can be adjusted to the above range by the solid content of the cast solution, the amount of the extruded resin, the extrusion speed, and the stretching ratio of the microporous film.

  It is preferable that the microporous membrane in the present embodiment is further subjected to a heat setting treatment to reduce shrinkage. By performing this heat setting treatment, shrinkage of the microporous membrane in a high temperature atmosphere can be reduced, and the dimensional change of the polymer electrolyte membrane can be reduced. The heat setting is performed on the microporous film by, for example, relaxing the stress in the TD (width direction) direction in a temperature range below the melting point of the microporous film raw material with a TD (width direction) tenter. In the case of PTFE preferably used in the present embodiment, a preferable stress relaxation temperature range is 200 ° C to 420 ° C.

  In addition, the microporous membrane in the present embodiment may be subjected to surface treatment such as application of a surfactant or chemical modification, as necessary, within a range that does not impair the problems and effects of the present invention. By performing the surface treatment, the surface of the microporous membrane can be hydrophilized, and in addition to the effect of high filling of the polymer electrolyte solution, the water content of the polymer electrolyte membrane can be adjusted.

[Polymer electrolyte membrane]
The polymer electrolyte membrane of this embodiment can be obtained by filling the voids of the microporous membrane with a fluorine-based polymer electrolyte composition.
In the present embodiment, the thickness of the polymer electrolyte membrane is preferably 1 μm to 500 μm, more preferably 2 μm to 100 μm, still more preferably 5 μm to 50 μm, and particularly preferably 5 μm to 35 μm. Adjusting the film thickness to the above range can reduce inconveniences such as direct reaction between hydrogen and oxygen, resulting in differential pressure and distortion during handling during fuel cell production and during fuel cell operation. However, it is preferable in that the film is hardly damaged. Furthermore, from the viewpoint of maintaining the ion permeability of the polymer electrolyte membrane and maintaining the performance as a solid polymer electrolyte membrane, it is preferable to adjust the film thickness to the above range.

In the present embodiment, the dimensional change in the planar direction of the polymer electrolyte membrane in 80 ° C. water is preferably 15% or less, more preferably 13% or less, and even more preferably 11% or less.
Here, the dimensional change in the planar direction in 80 ° C. water of the present embodiment is measured as follows.
The film sample was cut into a rectangular film of 4 cm × 3 cm, left in a constant temperature and humidity room (23 ° C., 50% RH) for 1 hour or longer, and then each dimension of the dried rectangular film sample in the planar direction was measured.
Next, the rectangular membrane sample whose dimensions were measured was boiled in hot water at 80 ° C. for 1 hour, so that the mass change due to moisture in the electrolyte membrane was 5% or less (volume swelling due to moisture absorption was saturated). Fully absorbed water). At this time, the film was taken out from the hot water, and it was confirmed that the amount of mass change was 5% or less with an electronic balance in a state where water on the surface was sufficiently removed. A wet membrane sample which absorbed water and expanded was taken out from the hot water, and each dimension in the plane direction (longitudinal (MD) direction, width (TD) direction) was measured. Taking each dimension in the planar direction in the dry state as a reference, taking the average of the increment of each dimension (MD direction and TD direction) in the planar direction in the wet state from each dimension in the dry state, %).
The dimensional change in the planar direction can be adjusted to the above range by adjusting the structure of the microporous membrane, the elastic modulus and film thickness, the EW of the fluorine-based polymer electrolyte, the heat treatment temperature of the polymer electrolyte membrane, and the like.

[Production method of polymer electrolyte membrane]
Next, the manufacturing method of the polymer electrolyte membrane of this embodiment is demonstrated. The polymer electrolyte membrane of the present embodiment can be obtained by filling fine pores of a microporous membrane with a fluorine-based polymer electrolyte composition.
The method for filling the pores of the microporous membrane with the fluorine-based polymer electrolyte composition is not particularly limited. For example, a method of applying a polymer electrolyte solution described later to the microporous membrane, or a polymer electrolyte solution A method of drying after impregnating the microporous membrane is exemplified. For example, a film of a polyelectrolyte solution is formed on a moving or stationary elongate casting substrate (sheet), and an elongate microporous membrane is brought into contact with the solution to form an unfinished composite structure. Make it. The incomplete composite structure is dried in a hot air circulation tank. Next, a method of forming a polymer electrolyte membrane by further forming a film of a polymer electrolyte solution on the dried incomplete composite structure is raised. The contact between the polymer electrolyte solution and the microporous membrane may be performed in a dry state, in an undried state or in a wet state. Moreover, when contacting, you may carry out pressure bonding with a rubber roller, or controlling the tension | tensile_strength of a microporous film. Further, a sheet containing a polymer electrolyte may be preliminarily formed by extrusion molding, cast molding, or the like, and this sheet may be filled by hot pressing with a microporous film.

  Further, for the purpose of improving the conductivity and mechanical strength of the polymer electrolyte membrane, one or more layers containing the polymer electrolyte are laminated on at least one main surface of the polymer electrolyte membrane thus produced. May be. Moreover, in the polymer electrolyte membrane of this embodiment, you may bridge | crosslink the compounds contained there using a crosslinking agent, an ultraviolet-ray, an electron beam, a radiation.

  The polymer electrolyte membrane of the present embodiment is preferably subjected to a heat treatment after being manufactured as described above. By this heat treatment, the crystal part and the polymer solid electrolyte part in the polymer electrolyte membrane are firmly bonded, and as a result, the mechanical strength can be stabilized. The temperature of this heat treatment is preferably 100 ° C to 230 ° C, more preferably 110 ° C to 230 ° C, and still more preferably 120 ° C to 200 ° C. By adjusting the temperature of the heat treatment to the above range, the adhesion between the crystal part and the electrolyte composition part tends to be improved. Moreover, the said temperature range is suitable also from a viewpoint of maintaining the high moisture content and mechanical strength of a polymer electrolyte membrane. Although depending on the temperature of the heat treatment, the heat treatment time is preferably 5 minutes to 3 hours, more preferably 10 minutes to 2 hours from the viewpoint of obtaining a highly durable polymer electrolyte membrane.

(Polymer electrolyte solution)
The polymer electrolyte solution that can be used when producing the polymer electrolyte membrane according to the present embodiment contains the polymer electrolyte, the thioether compound, the solvent, and other additives as necessary. This polymer electrolyte solution is used as it is or after passing through processes such as filtration and concentration, as a filling liquid for the microporous membrane. Alternatively, this solution can be used alone or mixed with another electrolyte solution.
A method for producing the polymer electrolyte solution will be described. The method for producing the polymer electrolyte solution is not particularly limited. For example, after obtaining a solution in which the polymer electrolyte is dissolved or dispersed in a solvent, the additive is dispersed in the solution as necessary. Alternatively, first, the polymer electrolyte is melt-extruded, and the polymer electrolyte and the additive are mixed through a process such as stretching, and the mixture is dissolved or dispersed in a solvent. In this way, a polymer electrolyte solution is obtained.

  More specifically, first, a molded product made of a polymer electrolyte precursor polymer is immersed in a basic reaction liquid and hydrolyzed. By this hydrolysis treatment, the precursor polymer of the polymer electrolyte is converted into a polymer electrolyte. Next, the hydrolyzed molded product is sufficiently washed with warm water or the like, and then the molded product is subjected to an acid treatment. The acid used for the acid treatment is not particularly limited, but mineral acids such as hydrochloric acid, sulfuric acid and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid and trifluoroacetic acid are preferred. By this acid treatment, the precursor polymer of the polymer electrolyte is protonated, and a polymer electrolyte such as a perfluorocarbon sulfonic acid resin is obtained.

The above-mentioned molded product (molded product containing a polymer electrolyte) treated with an acid as described above is dissolved or suspended in a solvent (solvent having good affinity with the resin) that can dissolve or suspend the polymer electrolyte. It is. Examples of such solvents include protic organic solvents such as water, ethanol, methanol, n-propanol, isopropyl alcohol, butanol, and glycerin, N, N-dimethylformamide, N, N-dimethylacetamide, and N-methyl. And aprotic organic solvents such as pyrrolidone. These are used singly or in combination of two or more. In particular, when one kind of solvent is used, the solvent is preferably water. Moreover, when using combining 2 or more types, the mixed solvent of water and a protic organic solvent is preferable.
The method for dissolving or suspending the polymer electrolyte in the solvent is not particularly limited. For example, the polymer electrolyte may be dissolved or dispersed as it is in the above solvent, but the polymer electrolyte may be dissolved in a temperature range of 0 to 250 ° C. under atmospheric pressure or under conditions of airtight pressure in an autoclave or the like. It is preferable to dissolve or disperse in. In particular, when water and a protic organic solvent are used as the solvent, the mixing ratio of water and the protic organic solvent depends on the dissolution method, dissolution conditions, type of polymer electrolyte, total solid content concentration, dissolution temperature, stirring speed, etc. The ratio of the mass of the protic organic solvent with respect to water is preferably 0.1 to 10 with respect to water 1, and more preferably with respect to water 1. 0.1-5.

  Polyelectrolyte solutions include emulsions (in which liquid particles are dispersed as colloidal particles or coarser particles to form a milky state), suspensions (solid particles in a liquid are colloidal particles) Or dispersed as particles that can be seen with a microscope), colloidal liquid (macromolecule dispersed state), micellar liquid (a lyophilic colloidal dispersion system formed by associating many small molecules with intermolecular force), etc. 1 type (s) or 2 or more types are included.

  In addition, the polymer electrolyte solution can be concentrated or filtered according to the molding method and application of the polymer electrolyte membrane. The concentration method is not particularly limited, and examples thereof include a method of heating a polymer electrolyte solution to evaporate a solvent and a method of concentrating under reduced pressure. When the polymer electrolyte solution is used as a coating solution, if the solid content of the polymer electrolyte solution is too high, the viscosity tends to increase and it becomes difficult to handle, whereas if it is too low, the productivity tends to decrease. Therefore, it is preferably 0.5% by mass to 50% by mass. The method for filtering the polymer electrolyte solution is not particularly limited, but a typical example is a method of pressure filtration using a filter. It is preferable to use a filter medium having a 90% collection particle size of 10 to 100 times the average particle size of solid particles contained in the polymer electrolyte solution. Examples of the material of the filter medium include paper and metal. In particular, when the filter medium is paper, the 90% collection particle diameter is preferably 10 to 50 times the average particle diameter of the solid particles. When using a metal filter, it is preferable that the 90% collection particle diameter is 50 to 100 times the average particle diameter of the solid particles. Setting the 90% collection particle size to 10 times or more of the average particle size suppresses that the pressure required for liquid feeding becomes too high or that the filter is blocked in a short period of time. Can be suppressed. On the other hand, setting the 90% collection particle size to 100 times or less of the average particle size is preferable from the viewpoint of satisfactorily removing particle agglomerates and resin undissolved materials that cause foreign matters on the film.

[Membrane electrode assembly]
The polymer electrolyte membrane of this embodiment can be used as a constituent member of a membrane electrode assembly and a solid polymer electrolyte fuel cell. A unit in which two types of electrode catalyst layers of an anode and a cathode are bonded to both surfaces of a polymer electrolyte membrane is called a membrane electrode assembly (hereinafter sometimes abbreviated as “MEA”). A material in which a pair of gas diffusion layers are bonded to the outer side of the electrode catalyst layer so as to face each other may be referred to as MEA. The MEA according to this embodiment may have the same configuration as that of a known MEA except that the polymer electrolyte membrane according to this embodiment is adopted.
The electrode catalyst layer is generally composed of fine particles of a catalytic metal and a conductive agent carrying the catalyst metal, and a water repellent is included as necessary. The catalyst may be any metal that promotes the oxidation reaction of hydrogen and the reduction reaction of oxygen. Platinum, gold, silver, palladium, iridium, rhodium, ruthenium, iron, cobalt, nickel, chromium, tungsten, manganese, vanadium And one or more selected from the group consisting of these alloys. Of these, platinum is mainly preferred.
As a manufacturing method of MEA, a known manufacturing method can be adopted using the polymer electrolyte membrane of the present embodiment, and examples thereof include the following methods. First, platinum-supported carbon serving as an electrode material is dispersed in a solution obtained by dissolving an electrode binder ion exchange resin in a mixed solution of alcohol and water to obtain a paste. A certain amount of this is applied to a PTFE sheet and dried. Next, the application surface of the PTFE sheet is faced to each other, and a polymer electrolyte membrane is sandwiched therebetween, and bonded by hot pressing at 100 ° C. to 200 ° C. to obtain an MEA. The electrode binder is generally prepared by dissolving an ion exchange resin in a solvent (alcohol, water, etc.), but the polymer electrolyte solution of the present embodiment can also be used, and this polymer electrolyte solution is used from the viewpoint of durability. Is preferred.

[Solid polymer electrolyte fuel cell]
The MEA obtained as described above, and in some cases, a MEA having a structure in which a pair of gas diffusion electrodes are further opposed to the outer side of the electrode catalyst layer, is a common solid polymer electrolyte such as a bipolar plate or a backing plate. A solid polymer electrolyte fuel cell is configured in combination with components used in the fuel cell. Such a solid polymer electrolyte fuel cell may have the same configuration as a known one except that the above MEA is adopted as the MEA.
The bipolar plate means a composite material of graphite and resin having a groove for flowing a gas such as fuel or oxidant on its surface, or a metal plate. In addition to the function of transmitting electrons to an external load circuit, the bipolar plate has a function of a flow path for supplying fuel and oxidant to the vicinity of the electrode catalyst. A solid polymer electrolyte fuel cell according to this embodiment is manufactured by inserting a plurality of the MEAs between the bipolar plates and stacking them.
The polymer electrolyte membrane of the present embodiment described above has a high water content, is excellent in dimensional stability, mechanical strength, and physical durability, and is suitable as an electrolyte material for a solid polymer electrolyte fuel cell.
As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to the said this embodiment. The present invention can be variously modified without departing from the gist thereof.
Unless otherwise specified, the various parameters described above are measured according to the measurement methods in the following examples.

EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited only to these Examples. Measurement methods and evaluation methods for various physical properties in Examples and the like are as follows.
(1) Pore distribution of microporous membrane The pore distribution of the microporous membrane was measured as follows. First, a microporous membrane sample was cut into a size of φ25 mm, and measurement was performed using a through pore distribution / gas, fluid permeability analyzer (manufactured by Xonics Corporation, apparatus name: Porometer 3G). The measurement of this apparatus is based on the bubble point method described in JIS-K-3832, and after the pore volume of the microporous membrane is first completely filled with a test liquid (porofil (registered trademark)) In this method, the pressure applied to the porous membrane is gradually increased to obtain the pore distribution from the surface tension of the test liquid, the pressure of the applied gas, and the supply flow rate (bubble point half-dry method).
The pore distribution of the microporous membrane was measured with a pore measurement range: 0.07 μm to 0.4 μm, a flow rate gas: compressed air.

(2) Moisture content The moisture content of the polymer electrolyte membrane at 80 ° C was measured as follows. First, a sample was cut out from the polymer electrolyte membrane into a 30 mm × 40 mm square, and the film thickness was measured. Next, the membrane sample was immersed in ion exchange water heated to 80 ° C. After 1 hour, the membrane was taken out from the ion-exchanged water at 80 ° C., sandwiched between filter papers, lightly pressed twice or three times to wipe off the water adhering to the membrane sample surface, the weight was measured with an electronic balance, and W1 (g ). Next, the membrane sample was dried in a constant temperature and humidity chamber (23 ° C., 50% RH). After 1 hour or more had elapsed, the membrane sample was placed in a halogen moisture meter (HB43, manufactured by METTLER TOLEDO Co., Ltd.), dried at 160 ° C. for 1 minute, and the weight of the membrane sample was measured. The absolute dry weight of this membrane sample was set to W2 (g). The water content of the polymer electrolyte membrane at 80 ° C. was calculated from the above W1 and W2 by the following formula.
Moisture content = (W1-W2) / W2 × 100

(3) Ion-exchange capacity A membrane is formed from a polymer electrolyte in which the counter-ion of the ion-exchange group is in a proton state (with one main surface area of about ² to 20 cm ² ), and saturated at 25 ° C. It was immersed in 30 mL of NaCl aqueous solution and left for 30 minutes with stirring. Subsequently, the proton in the saturated NaCl aqueous solution was neutralized and titrated as a 0.01N sodium hydroxide aqueous solution using phenolphthalein as an indicator. The polymer electrolyte membrane in which the counter ion of the ion exchange group obtained by filtration after neutralization was in the state of sodium ion was rinsed with pure water, further vacuum dried and weighed. The amount of sodium hydroxide required for neutralization is M (mmol), the mass of a membrane made of a polymer electrolyte membrane whose ion exchange group counter ion is sodium ion is W (mg), and the equivalent mass EW ( g / equivalent).
EW = (W / M) −22
Furthermore, the ion exchange capacity (milli equivalent / g) was calculated by taking the inverse of the obtained EW value and multiplying it by 1000.

(4) Film thickness After the film sample was allowed to stand in a constant temperature and humidity room at 23 ° C. and 50% RH for 1 hour or longer, the film was measured using a film thickness meter (trade name “B-1” manufactured by Toyo Seiki Seisakusho). The thickness was measured.
(5) Tensile strength and elastic modulus A film sample was cut into a rectangular film of 70 mm x 10 mm, and its tensile strength and elastic modulus were measured according to JIS K-7127.
(6) Dimensional change in plane direction A film sample was cut into a 4 cm x 3 cm rectangular film, left in a constant temperature and humidity room (23 ° C, 50% RH) for 1 hour or longer, and then the planar direction of the dried rectangular film sample Each dimension of was measured.
Next, the rectangular membrane sample whose dimensions were measured was boiled in hot water at 80 ° C. for 1 hour, and water was sufficiently absorbed so that the amount of mass change due to moisture in the electrolyte membrane was 5% or less. At this time, the film was taken out from the hot water, and it was confirmed that the amount of change in mass was 5% or less with an electronic balance in a state where water on the surface was sufficiently removed. The wet membrane sample which absorbed water and expanded was taken out from the hot water, and each dimension in the planar direction (longitudinal (MD) direction and width (TD) direction) was measured. Taking each dimension in the plane direction in the dry state as a reference, the average of the increments of each dimension in the plane direction in the wet state from each dimension in the dry state was taken as the dimensional change (%) in the plane direction.

(7) Glass transition temperature The glass transition temperature of the fluorine-type polymer electrolyte composition was measured based on JIS-C-6481. First, a film made of a fluorine-based polymer electrolyte composition is formed, cut into a width of 5 mm, and a test piece is removed from room temperature using a dynamic viscoelasticity measuring device (model number: DVA-225, manufactured by IT Measurement Control). The temperature was raised at a rate of ° C./min, and the dynamic viscoelasticity and loss tangent of the test piece were measured with a viscoelasticity measuring device. The measured peak temperature of loss tangent was defined as the glass transition temperature.
(8) Porosity The porosity of the microporous membrane was measured by a mercury porosimetry using a mercury porosimeter (manufactured by Shimadzu Corporation, product name: Autopore IV 9520). First, one microporous membrane was cut into a size of about 25 mm width, about 0.08 to 0.12 g was collected, folded, and placed in a standard cell. The initial pressure was measured at about 25 kpa. The porosity value obtained from the measurement was taken as the porosity of the microporous membrane.

(9) Fuel cell evaluation The fuel cell evaluation of the polymer electrolyte membrane was performed as follows. First, an electrode catalyst layer was prepared as follows. 5 mass% perfluorosulfonic acid polymer solution SS-910 (manufactured by Asahi Kasei E-materials, equivalent mass (EW): 910) for 1.00 g of Pt-supported carbon (TEC10E40E, Tanaka Kikinzoku Co., Ltd., TEC10E40E, Pt36.4%) : Ethanol / water = 50/50 (mass ratio)) was added to a polymer solution of 3.31 g, and further 3.24 g of ethanol was added, and then mixed well with a homogenizer to obtain an electrode ink. . This electrode ink was applied on a PTFE sheet by a screen printing method. The coating amount was set to two types: a coating amount at which both the Pt loading amount and the polymer loading amount were 0.15 mg / cm ^2, and a coating amount at which both the Pt loading amount and the polymer loading amount were 0.30 mg / cm ² . After coating, the electrode catalyst layer having a thickness of about 10 μm was obtained by drying at room temperature for 1 hour and in air at 120 ° C. for 1 hour. Of these electrode catalyst layers, those having both Pt loading and polymer loading of 0.15 mg / cm ² are used as the anode catalyst layer, and those having both Pt loading and polymer loading of 0.30 mg / cm ² are the cathode catalyst layer. It was.
The anode catalyst layer and the cathode catalyst layer thus obtained are faced to each other, a polymer electrolyte membrane is sandwiched between them, and hot pressing is performed at 160 ° C. and a surface pressure of 0.1 MPa. An MEA was produced by transferring and joining to a polymer electrolyte membrane.
A carbon cloth (ELAT (registered trademark) B-1 manufactured by DE NORA NORTH AMERICA) was set as a gas diffusion layer on both sides of the MEA (outer surfaces of the anode catalyst layer and the cathode catalyst layer) and incorporated in an evaluation cell. This evaluation cell was set in a fuel cell evaluation system 890CL manufactured by Toyo Technica and heated to 80 ° C., then hydrogen gas was supplied to the anode side at 260 cc / min and air gas was supplied to the cathode side at 880 cc / min. The cathode side was pressurized at 0.20 MPa (absolute pressure). A water bubbling method was used for gas humidification, and the initial characteristics were examined by measuring a current-voltage curve in a state where the gas was humidified at 90 ° C. and the air gas was humidified at 80 ° C. and supplied to the cell.
Next, a durability test was performed at a cell of 80 ° C. The gas humidification temperatures of the anode and cathode were 45 ° C. and 80 ° C., respectively. Electric power was generated for 1 minute at a current density of 0.1 A / cm ² with the anode side pressurized at 0.10 MPa (absolute pressure) and the cathode side pressurized at 0.05 MPa (absolute pressure). Thereafter, the circuit was opened for 3 minutes to reduce the current value to 0, and the OCV (open circuit voltage) was examined. This power generation-OCV was repeated to make a durability test. This test promotes chemical degradation of the polymer electrolyte membrane when it is maintained in the OCV state while causing dry and wet dimensional changes in the polymer electrolyte by repeating power generation-OCV to promote physical degradation. is there.
In the durability test, when a pinhole is generated in the polymer electrolyte membrane, a phenomenon called cross leak occurs in which a large amount of hydrogen gas leaks to the cathode side. In order to examine the amount of cross leak, the hydrogen concentration in the cathode side exhaust gas was measured with a micro GC (manufactured by Varian, model number: CP4900), and the test was terminated when the measured value exceeded 10,000 ppm. In this durability test, the longer the time from the start of the test to the end of the test, the more the polymer electrolyte membrane has both chemical durability and physical durability. The time from the start of the test to the end of the test was used for the evaluation of the durability test, and the durability was determined according to the following criteria.
A: Durability of 500 Hr or more was shown.
○: Durability of 400Hr or more and less than 500Hr was shown.
(Triangle | delta): The durability of 100Hr or more and less than 400Hr was shown.
X: Durability of less than 100 Hr was exhibited.

[Example 1]
(Preparation of polymer electrolyte solution)
First, a precursor of perfluorosulfonic acid resin obtained from tetrafluoroethylene and CF ₂ ═CFO (CF ₂ ) ₂ —SO ₂ F, which is a polymer polymer precursor polymer (EW after hydrolysis and acid treatment) : 730 g / equivalent) pellets were prepared. Next, the precursor pellets were made of polyphenylene sulfide (manufactured by Sigma Aldrich Japan, melt viscosity of 275 poise at 310 ° C.) and a mass ratio of 90/10, twin screw extruder (manufactured by WERNER & PELEIDER, model number: ZSK-40, kneading temperature 280). ˜310 ° C., screw rotation speed 200 rpm). The melt-kneaded resin was cut through a strand die to obtain cylindrical pellets having a diameter of about 2 mm and a length of about 2 mm. The cylindrical pellet was brought into contact with an aqueous solution in which potassium hydroxide (15% by mass) and methyl alcohol (50% by mass) were dissolved at 80 ° C. for 20 hours for hydrolysis treatment. Then, the pellet was immersed in 60 degreeC water for 5 hours. Next, the treatment of immersing the pellets immersed in water in a 2N aqueous hydrochloric acid solution at 60 ° C. for 1 hour was repeated 5 times, each time replacing the aqueous hydrochloric acid solution with a new one. And the pellet after having been repeatedly immersed in hydrochloric acid aqueous solution was washed with ion-exchange water and dried. As a result, pellets of perfluorocarbon sulfonic acid resin (PFSA), which is a polymer electrolyte, were obtained.
The pellet was placed in a 5 L autoclave together with an aqueous ethanol solution (water: ethanol = 50.0: 50.0 (mass ratio)), sealed, heated to 160 ° C. with stirring with a blade, and held for 5 hours. Thereafter, the autoclave was naturally cooled to obtain a uniform perfluorosulfonic acid resin solution having a solid content concentration of 5% by mass. In this perfluorosulfonic acid resin solution, the polyphenylene sulfide particle size is measured by a laser diffraction / scattering particle size distribution measuring device (manufactured by Horiba, model number: LA-950, the measurement sample is diluted with water and used with a refractive index of 1). .33), the median diameter of the dispersed polyphenylene sulfide particles was 0.23 μm. This was concentrated under reduced pressure at 80 ° C., diluted with water and ethanol to prepare a solution of ethanol: water = 60: 40 (mass ratio) having a viscosity of 500 cP and a solid content of 15.1% by mass, Solution 1 was obtained.
(Preparation of microporous membrane)
For each 1 kg of PTFE fine powder having a number average molecular weight of 6.5 million, 406 mL of hydrocarbon oil as an extruded liquid lubricating oil was added at 20 ° C. and mixed.
Next, the round bar-like molded body obtained by extruding this mixture by paste extrusion was molded into a film shape by a calender roll heated to 70 ° C. to obtain a PTFE film. This film was passed through a hot air drying oven at 250 ° C. to evaporate and remove the extrusion aid, and an unfired film having an average thickness of 500 μm and an average width of 150 mm was obtained.
Next, this unsintered PTFE film was stretched in the longitudinal direction (MD direction) at a stretch ratio of 5 and wound up.
The obtained MD direction stretched PTFE film was clipped at both ends, stretched in the width direction (TD direction) at a stretch ratio of 8 times, heat fixed, and a stretched PTFE film was obtained. The stretching temperature at this time was 290 ° C., and the heat setting temperature was 360 ° C. The produced PTFE microporous membrane was designated as microporous membrane 1. The pore distribution of the obtained microporous membrane 1 is shown in FIG.
(Production of polymer electrolyte membrane)
The above solution 1 was applied on a base film using a bar coater (manufactured by Matsuo Sangyo, bar No. 200, WET film thickness 200 μm) (application area: width about 200 mm × length about 500 mm), and then solution 1 was dried. In an unfinished state, PTFE microporous membrane 1 (film thickness: 10 μm, porosity: 73%, sample size: width 200 mm × length 500 mm) is laminated on solution 1 and a rubber roller is used from above the microporous membrane. Then, the solution 1 and the microporous membrane were pressure-bonded. At this time, after visually confirming that a part of the microporous membrane was filled with the solution, this membrane was dried in an oven at 90 ° C. for 20 minutes. Next, the solution 1 is laminated again in the same manner from above the PTFE microporous membrane of the obtained membrane to sufficiently fill the voids of the microporous membrane with the solution 1, and this membrane is further heated in an oven at 90 ° C. for 20 minutes. Dried. The thus obtained “PTFE microporous membrane sufficiently impregnated with solution 1” was heat-treated in an oven at 170 ° C. for 1 hour to obtain a polymer electrolyte membrane having a thickness of about 25 μm. Table 1 shows the evaluation results of the polymer electrolyte membrane.

[Example 2]
(Preparation of polymer electrolyte solution)
A precursor pellet of a perfluorosulfonic acid resin obtained from tetrafluoroethylene and CF ₂ ═CFO (CF ₂ ) ₂ —SO ₂ F, which is a polymer polymer precursor polymer, polyphenylene sulfide (manufactured by Sigma-Aldrich Japan, The mixture was melt kneaded using a twin screw extruder (manufactured by WERNER & PELEIDER, model number: ZSK-40, kneading temperature 280 to 310 ° C., screw rotation speed 200 rpm) at a mass ratio of 90/10 at a melt viscosity of 310 ° C. The melt-kneaded resin was cut through a strand die to obtain cylindrical pellets having a diameter of about 2 mm and a length of about 2 mm. This cylindrical pellet was hydrolyzed and acid-treated in the same manner as in Example 1, and then dissolved in a 5 L autoclave to obtain a solution A having a solid content concentration of 5%. Laser diffractive / scattering particle size distribution measuring device (manufactured by Horiba, model number: LA-950, measurement sample is used by diluting the solution with water, refractive index 1.33). As a result, the median diameter of the dispersed polyphenylene sulfide particles was 0.23 μm.
Next, a 5 mass% perfluorocarbon acid polymer solution (Aciplex-SS (registered trademark), manufactured by Asahi Kasei E-Materials, EW720, solvent composition (mass ratio): ethanol / water = 50/50) (solution B-1) Dimethylacetamide (DMAC) was added to the mixture, and the mixture was refluxed at 120 ° C. for 1 hour, and then concentrated under reduced pressure with an evaporator to obtain a solution having a mass ratio of perfluorocarbon sulfonic acid resin to DMAC of 1.5 / 98.5 (Solution B). -2).
Further, poly [2,2 ′-(m-phenylene) -5,5′-bibenzimidazole] (PBI) (manufactured by Sigma-Aldrich Japan, weight average molecular weight 27,000) is put together with DMAC in an autoclave and sealed. The temperature was raised to 200 ° C. and held for 5 hours. Thereafter, the autoclave was naturally cooled to obtain a PBI solution having a mass ratio of PBI to DMAC of 10/90. Further, this PBI solution was diluted 10 times with DMAC to prepare a 1% by mass uniform PBI solution.
The above solutions were mixed at Solution A / Solution B-1 / Solution B-2 / Solution C = 30.6 / 14.9 / 46.9 / 7.6 (mass ratio), and stirred until the solution was uniform. Thus, a mixed solution of perfluorocarbon sulfonic acid resin / polyphenylene sulfide resin / PBI = 92.5 / 5 / 2.5 (mass ratio) was obtained. This was designated as Solution 2.
(Production of polymer electrolyte membrane)
A polymer electrolyte membrane having a film thickness of 25 μm was obtained in the same manner as in Example 1 except that the above solution 2 was used as the polymer electrolyte solution. The evaluation results of the obtained polymer electrolyte membrane are shown in Table 1.

[Comparative Example 1]
(Preparation of polymer electrolyte solution)
Solution 2 was prepared in the same manner as Example 2.
(Production of polymer electrolyte membrane)
About 42 g of the above “Solution 2” was poured into a petri dish having a diameter of 154 mm, and dried on a hot plate at 90 ° C. for 1 hour. Next, the petri dish was placed in an oven and heat treated at 170 ° C. for 1 hour. Thereafter, the petri dish in which the membrane was formed was taken out of the oven and cooled, and then ion-exchanged water was poured into the petri dish to peel off the membrane to obtain a polymer electrolyte membrane having a thickness of about 30 μm. Table 1 shows the evaluation results of the polymer electrolyte membrane.
[Example 3]
(Preparation of polymer electrolyte solution)
Solution 2 was prepared in the same manner as Example 2.
(Preparation of microporous membrane)
0.375 parts by mass of an antioxidant was added to 100 parts by mass of a polyolefin composition consisting only of polypropylene having a weight average molecular weight of 4 × 10 5 to obtain a polyolefin composition. 30 parts by mass of this polyolefin composition was put into a twin screw extruder (58 mmφ, L / D = 42, strong kneading type). Moreover, 70 mass parts of liquid paraffin was supplied from the side feeder of this twin-screw extruder, and it melt-kneaded at 200 rpm, and prepared the polyolefin solution in an extruder.
Subsequently, a melt-kneaded product was extruded at 220 ° C. from a T die installed at the tip of the extruder, and a sheet was formed while being taken up by a cooling roll. Next, the formed sheet was sequentially biaxially stretched 7 × 5 at 110 ° C. to obtain a stretched film. The obtained stretched membrane was washed with methylene chloride to extract and remove the remaining liquid paraffin, followed by drying and heat treatment to obtain a polyolefin microporous membrane. The pore distribution of the obtained microporous membrane is shown in FIG.
(Production of polymer electrolyte membrane)
A polymer electrolyte with a film thickness of 30 μm was used in the same manner as in Example 1 except that the polyolefin microporous film (film thickness: 12 μm, porosity: 50%) obtained as described above was used as the microporous film. A membrane was obtained. Table 1 shows the evaluation results of the polymer electrolyte membrane.

(A) Pore distribution curve of microporous membrane of Examples 1 and 2 (b) Pore distribution curve of porous membrane of Example 3

Claims (7)

A polymer electrolyte membrane in which a fluorine-based polymer electrolyte composition is contained in a void of a microporous membrane,
The pore distribution of the microporous membrane has at least two distribution centers in the pore diameter range of 0.07 μm to 0.4 μm,
The fluorine-based polymer electrolyte composition contains a fluorine-based polymer electrolyte (A component) and a thioether compound (B component).
Polymer electrolyte membrane.   In the pore distribution of the microporous membrane, the proportion of pores having a pore diameter of 0.2 μm or less to pores having a pore diameter of 0.07 μm to 0.4 μm is 0.1 or more (quantity ratio), and 2. The polymer electrolyte membrane according to claim 1, wherein the proportion of pores having a pore diameter of 0.2 μm or more is 0.5 or more (quantity ratio).   The polymer electrolyte membrane according to claim 1 or 2, wherein the ion exchange capacity of the fluorine-based polymer electrolyte is 0.5 to 3.0 meq / g.   The polymer electrolyte membrane according to any one of claims 1 to 3, wherein the fluorine-based polymer electrolyte composition further contains a polyazole compound (component C).   The polymer electrolyte membrane according to any one of claims 1 to 4, wherein the microporous membrane is made of polytetrafluoroethylene.   The membrane electrode assembly (MEA) containing the polymer electrolyte membrane of any one of Claims 1-5.   A solid polymer electrolyte fuel cell comprising the polymer electrolyte membrane according to any one of claims 1 to 5.