阅读说明：本技术 高分子电解质膜、膜电极接合体以及固体高分子型燃料电池 (Polymer electrolyte membrane, membrane electrode assembly, and solid polymer fuel cell ) 是由 多胡贵广 宫崎久远 于 2017-05-11 设计创作，主要内容包括：本发明的高分子电解质膜的特征在于,其包含全氟磺酸系树脂(A),在利用SEM-EDX观测到的膜表面的图像中,主要检测出氟原子的相和主要检测出碳原子的相具有相分离结构,在利用SEM观测到的膜截面的图像中,具有平均长厚比为1.5以上10以下的相。(The polymer electrolyte membrane of the present invention is characterized by comprising a perfluorosulfonic acid resin (A), wherein a phase in which a fluorine atom is mainly detected and a phase in which a carbon atom is mainly detected have a phase separation structure in an image of the membrane surface observed by SEM-EDX, and a phase having an average aspect ratio of 1.5 to 10 in an image of the membrane cross section observed by SEM.)

1. A polymer electrolyte membrane comprising a perfluorosulfonic acid resin (A),

in the image of the membrane surface observed by SEM-EDX, the phase in which the fluorine atom is mainly detected and the phase in which the carbon atom is mainly detected have a phase separation structure,

the image of the cross section of the film observed by SEM has a phase with an average length-thickness ratio of 1.5 to 10.

2. The polymer electrolyte membrane according to claim 1, wherein a ratio of a relative standard deviation of a C/F peak intensity ratio at a magnification of 1500 to a relative standard deviation of a C/F peak intensity ratio at a magnification of 150, that is, a relative standard deviation of 1500 times/a relative standard deviation of 150 times is 0.20 to 5.0 in the image of the membrane surface observed by SEM-EDX.

3. The polymer electrolyte membrane according to claim 2, wherein an average value of C/F peak intensity ratios at a magnification of 1500 times in the image of the membrane surface observed by SEM-EDX is 0.50 or more and 20 or less,

the hydrogen permeability coefficient at 80 ℃ and 30% RH was 5.0X 10^-9cc·cm/cm²s.cmHg or less.

4. The polymer electrolyte membrane according to any one of claims 1 to 3, wherein the phase separation structure is a sea-island structure.

5. The polymer electrolyte membrane according to any one of claims 1 to 4, wherein the polymer electrolyte membrane further comprises an aromatic hydrocarbon resin (B) having an acidic group.

6. The polymer electrolyte membrane according to claim 5, wherein the mass ratio of the perfluorosulfonic acid resin (A) to the aromatic hydrocarbon resin (B) having an acid group, i.e., the mass/(B) of (A) is 90/10 to 50/50.

7. The polymer electrolyte membrane according to claim 5 or 6, wherein the polymer electrolyte membrane further comprises a compatibilizer (C) of a perfluorosulfonic acid resin (A) and an aromatic hydrocarbon resin (B) having an acidic group.

8. The polymer electrolyte membrane according to any one of claims 5 to 7, wherein the polymer electrolyte membrane is produced by a step of mixing a solution containing a perfluorosulfonic acid resin (A) and a solution containing an aromatic hydrocarbon resin (B) having an acidic group.

9. The polymer electrolyte membrane according to claim 8, wherein the peak top of the scattering diameter in dynamic light scattering measurement of the solution containing the perfluorosulfonic acid-based resin (A) and the solution containing the aromatic hydrocarbon-based resin (B) having an acidic group is in a range of 10 μm to 200 μm.

10. The polymer electrolyte membrane according to claim 7, wherein the polymer electrolyte membrane is produced through a step of mixing a solution containing a perfluorosulfonic acid resin (A), a solution containing an aromatic hydrocarbon resin (B) having an acidic group, and a solution containing the compatibilizer (C).

11. The polymer electrolyte membrane according to claim 10, wherein a mixed solution of the solution containing the perfluorosulfonic acid resin (a), the solution containing the aromatic hydrocarbon resin (B) having an acidic group, and the solution containing the compatibilizer (C) has a transmittance of 90% T or more at a wavelength of 800nm in UV measurement.

12. The polymer electrolyte membrane according to claim 10 or 11, wherein a solid content concentration of the compatibilizer (C) in a mixed solution of the solution containing the perfluorosulfonic acid resin (a), the solution containing the aromatic hydrocarbon resin (B) having an acidic group, and the solution containing the compatibilizer (C) is 0.001 mass% or more and less than 1 mass%.

13. The polymer electrolyte membrane according to any one of claims 1 to 12, wherein the polymer electrolyte membrane comprises a layer containing a perfluorosulfonic acid resin (A) and an aromatic hydrocarbon resin (B) having an acidic group, and a layer containing a perfluorosulfonic acid resin (A).

14. A membrane-electrode assembly comprising the polymer electrolyte membrane according to any one of claims 1 to 13 and an electrode catalyst layer.

15. A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 14.

Technical Field

The present invention relates to a polymer electrolyte membrane, a membrane electrode assembly, and a solid polymer fuel cell.

Background

Fuel cells obtain electrical energy from a fuel (hydrogen source) and an oxidant (oxygen) through an electrochemical reaction within the cell. I.e. the chemical energy of the fuel is directly converted into electrical energy. As the fuel source, pure hydrogen is typically used, and petroleum, natural gas (such as methane), methanol, and the like containing hydrogen elements can be used.

The fuel cell itself has the following features: since there is no mechanical part, noise is less generated, and power can be generated semi-permanently in principle by continuously supplying fuel and oxidant from the outside.

The electrolyte is classified into a liquid electrolyte and a solid electrolyte, and among them, a fuel cell using a polymer electrolyte membrane as an electrolyte is a solid polymer type fuel cell.

In particular, polymer electrolyte fuel cells are expected to be used as alternative power sources for automobiles and the like, household cogeneration systems, and portable power generators because they operate at a lower temperature than other fuel cells.

The polymer electrolyte fuel cell comprises at least a membrane electrode assembly in which gas diffusion electrodes each formed by laminating an electrode catalyst layer and a gas diffusion layer are bonded to both surfaces of a proton exchange membrane. The proton exchange membrane described herein has a strong acidic group such as a sulfonic acid group or a carboxylic acid group in a polymer chain, and has a property of selectively transmitting protons. As such a proton exchange membrane, a perfluoro-type proton exchange membrane represented by Nafion (registered trademark, manufactured by dupont, usa) having high chemical stability is preferably used.

During operation of the fuel cell, fuel (e.g., hydrogen) is supplied to the gas diffusion electrode on the anode side, an oxidant (e.g., oxygen or air) is supplied to the gas diffusion electrode on the cathode side, and both electrodes are connected by an external circuit, thereby realizing operation of the fuel cell. Specifically, when hydrogen is used as the fuel, the hydrogen on the anode catalyst is oxidized to generate protons, and the protons pass through the proton-conductive polymer in the anode catalyst layer, then move through the proton exchange membrane, pass through the proton-conductive polymer in the cathode catalyst layer, and reach the cathode catalyst. On the other hand, electrons generated simultaneously with protons by the oxidation of hydrogen reach the cathode-side gas diffusion electrode through an external circuit, and the protons react with oxygen in the oxidant on the cathode catalyst to generate water, whereby electric energy can be obtained. In this case, the proton exchange membrane needs to function also as a gas barrier wall, and when the gas permeability of the proton exchange membrane is high, cross leakage, which is a case where hydrogen leaks from the anode side to the cathode side and oxygen leaks from the cathode side to the anode side, occurs, so that a so-called chemical short circuit state is formed, and thus a good voltage cannot be obtained and fuel efficiency is also reduced.

In addition, if the gas leaks across the proton exchange membrane, hydrogen peroxide is generated on the anode catalyst or the cathode catalyst, and hydroxyl radicals are generated from the hydrogen peroxide, which chemically deteriorate the membrane and finally cause pinholes in the membrane, and thus sufficient chemical durability cannot be obtained.

In recent years, thinning of an electrolyte membrane has been studied in order to reduce the internal resistance of a fuel cell and further improve the output. In addition, it is desirable to operate the fuel cell under high-temperature and low-humidity conditions (100 to 120 ℃ and 0 to 30% RH) in order to reduce the cost reduction due to the auxiliary devices such as the radiator and the humidifier. However, when the electrolyte membrane is thinned or high temperature conditions are applied, the gas barrier property is lowered, and the problems of voltage reduction, fuel efficiency reduction, and chemical durability reduction due to cross leakage of gas become serious. Further, since the mechanical strength of the electrolyte membrane is reduced, there is a problem in that: handling of the electrolyte membrane during fabrication of the membrane electrode assembly or during assembly of the cell becomes difficult, or water generated on the cathode side is included to cause dimensional change, resulting in rupture of the electrolyte membrane.

Patent document 1 describes the following: the polymer electrolyte membrane composed of perfluorosulfonic acid resin and basic resin forms a micro-dispersed sea-island structure, and cross leak of gas can be suppressed for a long time even in a chemical durability test under high-temperature and low-humidity conditions (100 ℃ C., 20% RH).

Patent document 2 describes the following: a polymer electrolyte membrane comprising a perfluorosulfonic acid resin and an aromatic hydrocarbon sulfonic acid resin has excellent gas barrier properties.

Disclosure of Invention

Problems to be solved by the invention

However, the polymer electrolyte membrane described in patent document 1 contains different types of resins in the perfluorosulfonic acid resin, and is therefore insufficient in terms of elongation at break and physical durability particularly under thin film, high-temperature, and low-humidity conditions.

The polymer electrolyte membrane described in patent document 2 has excellent initial gas barrier properties, but is only mixed with a filler of an aromatic hydrocarbon sulfonic acid resin, and therefore has a low elongation at break, and is insufficient in view of gas barrier properties over time and chemical durability.

Accordingly, an object of the present invention is to provide a polymer electrolyte membrane that can achieve both high elongation at break and high gas barrier properties (for example, hydrogen gas barrier properties) even when different types of resins are mixed, exhibits high physical durability, and exhibits high chemical durability even under high-temperature and low-humidity conditions.

Means for solving the problems

Namely, the present invention is as follows.

[1]

A polymer electrolyte membrane comprising a perfluorosulfonic acid resin (A),

in the image of the membrane surface observed by SEM-EDX, the phase in which the fluorine atom is mainly detected and the phase in which the carbon atom is mainly detected have a phase separation structure,

the image of the cross section of the film observed by SEM has a phase with an average length-thickness ratio of 1.5 to 10.

[2]

The polymer electrolyte membrane according to [1], wherein a ratio of a relative standard deviation of a C/F peak intensity ratio at a magnification of 1500 to a relative standard deviation of a C/F peak intensity ratio at a magnification of 150 (relative standard deviation at 1500 times/relative standard deviation at 150 times) in the image of the membrane surface observed by SEM-EDX is 0.20 to 5.0.

[3]

The polymer electrolyte membrane according to [2], wherein the average value of the C/F peak intensity ratio at a magnification of 1500 times in the image of the membrane surface observed by SEM-EDX is 0.50 to 20,

the hydrogen permeability coefficient at 80 ℃ and 30% RH was 5.0X 10^-9cc·cm/cm²s.cmHg or less.

[4]

The polymer electrolyte membrane according to any one of [1] to [3], wherein the phase separation structure is a sea-island structure.

[5]

The polymer electrolyte membrane according to any one of [1] to [4], wherein the polymer electrolyte membrane further contains an aromatic hydrocarbon resin (B) having an acidic group.

[6]

The polymer electrolyte membrane according to [5], wherein the mass ratio of the perfluorosulfonic acid resin (A) to the aromatic hydrocarbon resin (B) having an acid group ((mass of A/(mass of B)) is 90/10 to 50/50.

[7]

The polymer electrolyte membrane according to [5] or [6], wherein the polymer electrolyte membrane further comprises a compatibilizer (C) of a perfluorosulfonic acid resin (A) and an aromatic hydrocarbon resin (B) having an acidic group.

[8]

The polymer electrolyte membrane according to any one of [1] to [7], wherein the polymer electrolyte membrane further comprises an aromatic hydrocarbon resin (B) having an acidic group,

the resin composition is produced by a step of mixing a solution containing a perfluorosulfonic acid resin (A) with a solution containing an aromatic hydrocarbon resin (B) having an acidic group.

[9]

The polymer electrolyte membrane according to [8], wherein the peak top of the scattering diameter in dynamic light scattering measurement of the solution containing the perfluorosulfonic acid resin (A) and the solution containing the aromatic hydrocarbon resin (B) having an acidic group is in the range of 10 μm to 200 μm.

[10]

The polymer electrolyte membrane according to [7], wherein the polymer electrolyte membrane is produced by a step of mixing a solution containing a perfluorosulfonic acid resin (A), a solution containing an aromatic hydrocarbon resin (B) having an acidic group, and a solution containing the compatibilizer (C).

[11]

The polymer electrolyte membrane according to [10], wherein a mixed solution of the solution containing the perfluorosulfonic acid resin (A), the solution containing the aromatic hydrocarbon resin (B) having an acidic group, and the solution containing the compatibilizer (C) has a transmittance of 90% T or more at a wavelength of 800nm in UV measurement.

[12]

The polymer electrolyte membrane according to [10] or [11], wherein a mixed solution of the solution containing the perfluorosulfonic acid resin (A), the solution containing the aromatic hydrocarbon resin (B) having an acidic group, and the solution containing a compatibilizer (C) has a solid content concentration of the compatibilizer (C) of 0.001 mass% or more and less than 1 mass%.

[13]

The polymer electrolyte membrane according to any one of [1] to [12], wherein the polymer electrolyte membrane has a layer containing a perfluorosulfonic acid resin (A) and an aromatic hydrocarbon resin (B) having an acid group, and a layer containing a perfluorosulfonic acid resin (A).

[14]

A membrane-electrode assembly comprising the polymer electrolyte membrane according to any one of [1] to [13 ].

[15]

A polymer electrolyte fuel cell comprising the membrane electrode assembly according to [14 ].

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to provide a polymer electrolyte membrane that can achieve both high elongation at break and high gas barrier properties (for example, hydrogen gas barrier properties) even when different types of resins are mixed, exhibits high physical durability, and exhibits high chemical durability even under high-temperature and low-humidity conditions.

Detailed Description

Hereinafter, specific embodiments of the polymer electrolyte membrane, the membrane electrode assembly comprising the polymer electrolyte membrane, and the polymer electrolyte fuel cell comprising the membrane electrode assembly (hereinafter, simply referred to as "the present embodiment") according to the present invention will be described in detail.

[ Polymer electrolyte Membrane ]

The polymer electrolyte membrane of the present embodiment contains a perfluorosulfonic acid resin (a) (in the present specification, may be simply referred to as "resin (a)"), and in an image of the membrane surface observed by SEM-EDX, a phase in which a fluorine atom is mainly detected and a phase in which a carbon atom is mainly detected have a phase separation structure, and in an image of the membrane cross section observed by SEM, the average aspect ratio is 1.5 or more and 10 or less.

The polymer electrolyte membrane according to the present embodiment may further include an aromatic hydrocarbon resin (B) having an acidic group (in the present specification, it may be simply referred to as "resin (B)") and/or a compatibilizer (in the present specification, it may be simply referred to as "compatibilizer (C)") between the perfluorosulfonic acid resin (a) and the aromatic hydrocarbon resin (B) having an acidic group.

The resin (a), the resin (B), and the compatibilizer (C) may be used singly or in combination of two or more.

The present inventors have found that the polymer electrolyte membrane of the present embodiment has a high elongation at break and exhibits high physical durability even when an aromatic hydrocarbon sulfonic acid resin is mixed, and exhibits high chemical durability under high-temperature and low-humidity conditions while satisfying both high elongation at break and high gas barrier properties, as compared with a polymer electrolyte membrane which does not contain the resin (a), in which a phase in which fluorine atoms are mainly detected and a phase in which carbon atoms are mainly detected have a phase separation structure in an image of the membrane surface observed by SEM and the average aspect ratio is 1.5 or more and 10 or less in an image of a membrane cross section observed by SEM.

-perfluorosulfonic acid-based resin (A)

Examples of the perfluorosulfonic acid resin (a) include a polymer containing a repeating unit represented by the following general formula (1) and a repeating unit represented by the following general formula (2).

-[CX¹X²-CX³X⁴]-…(1)

(in the formula (1), X¹、X²、X³、X⁴Each independently a hydrogen atom, a halogen atom or a perfluoroalkyl group having 1 to 10 carbon atoms, X¹、X²、X³、X⁴At least one of the above groups is a fluorine atom or a perfluoroalkyl group having 1 to 10 carbon atoms. )

-[CF₂-CF(-(O_a-CF₂-(CFX⁵)_b)_c-O_d-(CF₂)_e-SO₃R)]-…(2)

(in the formula (2), X⁵Is a halogen atom or a perfluoroalkyl group having 1 to 4 carbon atoms, R is an alkali metal atom such as a hydrogen atom, a lithium atom, a sodium atom or a potassium atom, NH₄、NH₃R¹、NH₂R¹R²、NHR¹R²R³Or NR¹R²R³R⁴(R¹、R²、R³、R⁴Each independently represents an alkyl group or an aryl group having 1 to 10 carbon atoms). In addition, a is 0 or 1, b is 0 or 1, c is an integer of 0 to 8, d is 0 or 1, and e is an integer of 0 to 8. Wherein b and e are not 0 at the same time. )

When the perfluorosulfonic acid resin contains a plurality of repeating units represented by the above general formula (1) and/or a plurality of repeating units represented by the above general formula (2), the repeating units may be the same or different.

The perfluorosulfonic acid resin (a) is preferably a compound having at least one of the repeating units represented by the following general formulae (3) to (7).

-[CF₂-CX³X⁴]_f-[CF₂-CF(-O-CF₂-CFX⁵)_c-O_d-(CF₂)_e-SO₃R)]_g-…(3)

-[CF₂-CF₂]_f-[CF₂-CF(-O-CF₂-CF(CF₃))_c-O-(CF₂)_e-SO₃R)]_g-…(4)

-[CF₂-CF₂]_f-[CF₂-CF-O-(CF₂)_e-SO₃R)]_g-…(5)

-[CF₂-CF₂]_f-[CF₂-CF(-O-CF₂-CFX⁵)_c-O_d-(CF₂)_e-SO₃H]_g…(6)

-[CF₂-CF₂]_f-[CF₂-CF-(CF₂)_e-SO₃R)]_g-…(7)

(in formulae (3) to (7), X³、X⁴、X⁵And R is the same as the formulas (1) and (2). C, d and e are the same as those of the formulas (1) and (2), and f is not less than 0<1，0<g is less than or equal to 1, and f + g is 1. Wherein e is not 0 in the formulae (5) and (7). )

The perfluorosulfonic acid resin (a) may further contain a structural unit other than the repeating units represented by the general formulae (1) and (2). Examples of the other structural units include structural units represented by the following general formulae (I) and (II).

[ solution 1]

(in the formula (I), R¹Is a single bond or a C1-6 2-valent perfluoroorganic group (e.g., C1-6 perfluoroalkylene), R²Is a C1-6 2-valent perfluoroorganic group (e.g., C1-6 perfluoroalkylene). )

[ solution 2]

(in the formula (II), R is-C₆H₄CN、-C₆F₄CN、-C₆H₅、-C₆F₅or-OH. )

The perfluorosulfonic acid resin (a) is preferably a resin having a repeating unit represented by formula (4) or formula (5), and more preferably a resin composed of only a repeating unit represented by formula (5), from the viewpoint of obtaining a polymer electrolyte membrane which is easily permeable to protons and has a lower electric resistance.

The perfluorosulfonic acid resin (a) can be produced, for example, by synthesizing a precursor polymer, and then subjecting the precursor polymer to alkaline hydrolysis, acid treatment, or the like.

Examples of the precursor polymer include-SO of the formula (2)₃R is-SO₂And Y (Y is a halogen atom) polymer.

The precursor polymer can be produced, for example, by copolymerizing the fluorinated olefin compound described below with the sulfonic acid-based vinyl fluoride compound described below.

Examples of the fluorinated olefin compound include compounds represented by the following general formula (9).

CX¹X²＝CX³X⁴…(9)

(in the formula (9), X¹、X²、X³、X⁴The same as in formula (1). )

Specific examples of the fluorinated olefin compound include tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorotrifluoroethylene, dichlorodifluoroethylene, and perfluorobutylethylene (C)₄F₉CH＝CH₂) Perfluorohexylethylene (C)₆F₁₃CH＝CH₂) Perfluorooctylethylene (C)₈F₁₇CH＝CH₂) And the like. Among them, tetrafluoroethylene is preferable.

The fluorinated olefin compounds can be used alone in 1, can also be used in 2 or more combinations.

Examples of the sulfonic acid-based fluoroethylene compound include compounds represented by the following general formula (10).

CF₂＝CF(-(O_a-CF₂-(CFX⁵)_b)_c-O_d-(CF₂)_e-SO₂Y)…(10)

(in the formula (10), X⁵Y is a halogen atom in the same manner as in the formula (2). A, b, c, d and e are the same as those in formula (2). Wherein b and e are not 0 at the same time. )

Specific examples of the sulfonic acid-based fluoroethylene compound include CF₂＝CF-O-(CF₂)_q-SO₂F、CF₂＝CF-O-CF₂-CF(CF₃)-O-(CF₂)_q-SO₂F、CF₂＝CF-(CF₂)_q-SO₂F、CF₂＝CF-(OCF₂CF(CF₃))_q-(CF₂)_q-1-SO₂And F and the like.

In the above compound, q is an integer of 1 to 8.

The precursor polymer can be produced by a known copolymerization method, and examples of the copolymerization method include the following methods.

(i) A method of polymerizing a sulfonic acid-based fluoroethylene compound with a gas of a fluorinated olefin compound using a polymerization solvent such as a fluorine-containing hydrocarbon in a state of being dissolved in the polymerization solvent in a charged state (solution polymerization). Here, as the fluorine-containing hydrocarbon, for example, a compound selected from the group consisting of trichlorotrifluoroethane, 1,1,1,2,3,4,4,5,5, 5-decafluoropentane and the like, which are collectively called "freon", is suitably used.

(ii) A method of polymerizing a sulfonic acid-based vinyl fluoride compound by reacting with a gas of a fluorinated olefin compound without using a solvent such as a fluorine-containing hydrocarbon or the like as a polymerization solvent (bulk polymerization).

(iii) A method of polymerizing a sulfonic acid-based fluoroethylene compound and a fluorinated olefin compound in a state of being filled and dissolved in a polymerization solvent by using an aqueous solution of a surfactant as the polymerization solvent (emulsion polymerization).

(iv) A method of polymerizing a sulfonic acid-based fluoroethylene compound with a gas of a fluorinated olefin compound by using an aqueous solution of a co-emulsifier such as a surfactant and an alcohol, and in a state of being filled and emulsified in the aqueous solution (microemulsion polymerization ).

(v) A method of polymerizing a sulfonic acid-based fluoroethylene compound with a fluorinated olefin compound in a state filled and suspended in an aqueous solution of a suspension stabilizer by using a gas reaction (suspension polymerization).

The melt Mass Flow Rate (MFR) of the precursor polymer is preferably 0.01g/10 min or more, more preferably 0.1g/10 min or more, still more preferably 0.3g/10 min or more, and particularly preferably 1g/10 min or more. The upper limit of MFR is preferably 100g/10 min or less, more preferably 50g/10 min or less, still more preferably 10g/10 min or less, and particularly preferably 5g/10 min or less. By adjusting the MFR to a range of 0.01g/10 min to 100g/10 min, molding such as film formation tends to be performed satisfactorily.

The MFR of the precursor polymer was measured in accordance with JIS K7210. Specifically, the melt flow rate of the fluorine-containing ion exchange resin precursor measured at a temperature of 270 ℃ and a load of 2.16kg using an apparatus having an inner diameter of a hole of 2.09mm and a length of 8mm was used as the MFR (g/10 min) of the precursor polymer.

The precursor polymer may be, for example, immersed in an alkaline reaction liquid, subjected to hydrolysis treatment at 10 to 90 ℃ for 10 seconds to 100 hours, sufficiently washed with warm water or the like, and then subjected to acid treatment. The alkaline reaction liquid is preferably an aqueous solution of an alkali metal or alkaline earth metal hydroxide such as potassium hydroxide or sodium hydroxide.

The acid treatment protonates the precursor polymer to obtain a perfluorosulfonic acid resin.

An aromatic hydrocarbon resin (B) having an acid group

The hydrocarbon-based resin (B) having an acidic group includes a resin having a repeating unit derived from a hydrocarbon having an acidic group in the main chain, and among them, polyphenylene ether (PPE) having an acidic group, polyether ketone (PEK) having an acidic group, polyether ether ketone (PEEK) having an acidic group, polyether ether ketone (PEEKK) having an acidic group, Polybenzimidazole (PBI) having an acidic group, polyphenylene sulfide (PPSd) having an acidic group, polyether sulfone (PES) having an acidic group, polyether ether sulfone (PEES) having an acidic group, and polyphenylene sulfone (PPSn) having an acidic group are preferable in terms of further improving the durability of the polymer electrolyte membrane.

Examples of the acidic group in the acidic group-containing aromatic hydrocarbon resin (B) include a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group. Among them, sulfonic acid groups are preferable in terms of obtaining a polymer electrolyte membrane having higher proton conductivity.

In the present specification, the aromatic system includes not only monocyclic cyclic unsaturated compounds but also heterocyclic cyclic unsaturated compounds.

The polyphenylene ether having an acidic group includes resins having an aromatic ring formed in the main chain and an acidic group such as a sulfonic acid group, a carboxylic acid group, or a phosphoric acid group in an acyl group bonded to the aromatic ring, and specifically includes polymers containing constituent components represented by the following general formulae (11) and (12).

[ solution 3]

(in the formula (11), R¹～R³Each independently is at least one selected from the group consisting of a hydrogen atom, a halogen atom, an alkyl group, a fluoroalkyl group, an allyl group, an aryl group, and a cyano group; x is a divalent electron withdrawing group; ar (Ar)¹Is an aryl group which may be substituted with a group other than an acidic group. )

[ solution 4]

(in the formula (12), R⁴～R⁶Each independently is at least one selected from the group consisting of a hydrogen atom, a halogen atom, an alkyl group, a fluoroalkyl group, an allyl group, an aryl group, and a cyano group; x is a divalent electron withdrawing group; ar (Ar)²Is an aryl group substituted with at least 1 acidic group selected from the group consisting of a sulfonic acid group, a carboxylic acid group and a phosphoric acid group. )

Among the above polyphenylene ethers having an acidic group, the following is preferable in formula (11) and formula (12).

As R¹～R⁶The number of carbon atoms of the alkyl group and the fluorinated alkyl group in (1) is preferably 1 to 12, more preferably 1 to 4.

As R¹～R⁶The allyl group of (A) is preferably 2-propenyl, 2-methyl-2-propenyl or 2-hexenyl.

As R¹～R⁶The (i.e., backbone-side) aryl group of (b) is preferably phenyl or benzyl.

Examples of the divalent electron-withdrawing group of X include-C (O) - (carbonyl (keto group)), -S (O) - (sulfoxide), -S (O))₂- (sulfonyl), preferably-C (O) - (carbonyl (keto)).

As Ar²The aryl group (i.e., side chain side) of (1) is preferably a phenyl group, a naphthyl group, an anthryl group, or a benzyl group. As Ar²Among them, the aryl group substituted with an acidic group is preferably a sulfonated benzoyl group, a sulfonated naphthoyl group or the like.

In the above polyphenylene ether having an acidic group, Ar¹Can carry a substitution other than an acidic group. In addition, Ar²At least one of the substituents of the aromatic ring skeleton (2) is preferably a sulfonic acid group. Here, the bonding position in the aromatic ring skeleton of the sulfonic acid group is not particularly limited. The number of binding sites of the sulfonic acid group is not limited to one, and may be two or three.

In the polyphenylene ether having an acidic group, the sulfonic acid group can be inhibited from being detached by selectively introducing the sulfonic acid group into an aromatic ring other than the main chain of the polyphenylene ether. As a result, a polyphenylene ether having a thermally stable acidic group is obtained.

In the polyphenylene ether having an acidic group, it is preferable that the proportion of the constituent component represented by the general formula (11) is 60 to 95 mol% and the proportion of the constituent component represented by the general formula (12) is 5 to 40 mol% with respect to the constituent components represented by the general formulae (11) and (12) for the following reasons. The ratio of the constituent component represented by the general formula (12) to the constituent components represented by the general formulae (11) and (12) is also referred to as a sulfonation ratio.

When the sulfonation ratio is in the above range, high proton conductivity can be obtained and high membrane strength can be maintained when a polyphenylene ether having an acidic group is used as a solid polymer electrolyte membrane.

The sulfonation ratio is preferably 5 mol% or more, more preferably 15 mol% or more, and particularly preferably 25 mol% or more, from the viewpoint of improving the power generation efficiency of a fuel cell including a resin as a solid polymer electrolyte membrane, and is preferably 40 mol% or less, and more preferably 35% or less, from the viewpoint of reducing swelling of the solid polymer electrolyte membrane.

Unless otherwise specified, the sulfonation ratio of the resin means a value after drying the resin at room temperature (e.g., 30 ℃) for 24 hours.

The ion exchange capacity of the polyphenylene ether having an acidic group is not particularly limited as long as the desired proton conductivity can be exhibited, but is preferably 0.5 to 3.5meq/g (milliequivalents/g), more preferably 1.2 to 2.5meq/g, for the same reason as the sulfonation ratio.

The ion exchange capacity can be determined by a method described later.

When the sulfonation amount of the resin is too large, the water resistance of the resin is lowered, and dissolution or decomposition in water may occur, which is not preferable as a proton conductive membrane.

The ion exchange capacity can be adjusted by the amount or concentration of the sulfonating agent in the reaction solution, the reaction time or reaction temperature of the reaction with the sulfonating agent, and for example, when the ion exchange capacity is to be increased, the sulfonating agent may be increased and the reaction time with the sulfonating agent may be prolonged.

The polyphenylene ether having an acidic group has a structure of, for example, 1010 to 1080cm in the infrared absorption spectrum^-1About 1100-1230 cm^-1The presence or absence of an absorption peak of a sulfonic acid group in the vicinity was confirmed.

In addition, the above structure can also be realized by¹H-NMR.

The method for producing the polyphenylene ether having an acidic group is not particularly limited, and examples thereof include the following methods: the polyphenylene ether having an acidic group is synthesized by introducing a divalent electron-withdrawing group and an aryl group into a polyphenylene ether as a base to synthesize a modified polyphenylene ether, and then introducing a sulfonic acid group into the modified polyphenylene ether.

The method for synthesizing the modified polyphenylene ether is not particularly limited, and examples thereof include a method of introducing an acyl group (particularly, an acyl group having an aromatic hydrocarbon group) into the aromatic ring skeleton of polyphenylene ether by Friedel-crafts acylation reaction.

In the friedel-crafts acylation reaction, more specifically, polyphenylene ether is reacted with an acid halide or the like in the presence of a lewis acid (metal halide) such as aluminum chloride, tin chloride or the like.

As the reaction solvent, dichloromethane, chloroform, methylene dichloride, or the like is used.

As reaction conditions, Li, q; liu, l.; liang, s.; li, Q.; jin, b.; bai, r.; conditions described in Polymer.chem., 2014,5,2425-2432.

The polyphenylene ether as the base is not particularly limited, but is preferably a poly (2, 6-dimethyl-1, 4-phenylene ether), a block copolymer of a poly (2, 6-dimethyl-1, 4-phenylene ether) and a poly (2,3, 6-trimethyl-1, 4-phenylene ether) or a mixture thereof, or a random copolymer of 2, 6-dimethylphenol and 2,3, 6-trimethylphenol.

The acid halide is not particularly limited, and examples thereof include compounds represented by the following general formula (13).

[ solution 5]

(formula (I))13) In the formula (I), Y is a halogen atom other than a fluorine atom; r⁷～R¹¹Each independently is a hydrogen atom, a halogen atom, an alkyl group, a fluoroalkyl group, an allyl group, an aryl group, a cyano group, wherein R is⁷～R¹¹At least one of them is a hydrogen atom. )

In addition, the acid halide may include the following compounds: in the general formula (13), the side chain aromatic hydrocarbon group bonded to the carbonyl group is a polycyclic aromatic hydrocarbon group such as a naphthyl group or an anthryl group instead of the phenyl group.

Further, the following compounds may be mentioned: in the general formula (13), the group bonded to the carbonyl group is an aryl group (for example, benzyl group or the like) capable of linking the carbonyl group and the side-chain aromatic hydrocarbon group with an alkyl group interposed therebetween, instead of the phenyl group.

The acylation rate by the friedel-crafts acylation reaction is particularly preferably 100 mol%, more preferably 90 to 100 mol%, and preferably 85 to 100 mol%.

The acylation rate may be determined by¹H-NMR.

The intrinsic viscosity of the polyphenylene ether is preferably 0.25dL/g or more, more preferably 0.30dL/g or more, from the viewpoint of improving the separability from the solvent and the heat resistance at the time of introducing the sulfonic acid group, and is preferably 1.45dL/g or less, more preferably 0.70dL/g or less, from the viewpoint of preventing the solution viscosity at the time of introducing the sulfonic acid group from becoming excessively high and improving the handleability such as stirring and liquid feeding.

The intrinsic viscosity is determined as follows. That is, 0.5g of modified polyphenylene ether was dissolved in chloroform to obtain 2 or more solutions having different concentrations of 100mL or more (concentration of 0.5g/dL or less). Then, the specific viscosity of each solution at different concentrations was measured at 30 ℃ with an Ubbelohde viscometer, and the viscosity at the concentration of 0 was derived from the relationship between the specific viscosity and the concentration, and this viscosity was defined as the intrinsic viscosity.

As a method for introducing all or part of the acidic groups into the modified polyphenylene ether, there can be mentioned a method in which the modified polyphenylene ether is reacted with an acidifying agent such as fuming sulfuric acid, chlorosulfonic acid or the like in the absence of a solvent or in the presence of a solvent.

In the case of introducing a sulfonic acid group, in addition to the method of introducing a sulfonic acid group by the sulfonating agent, the following method may be employed: the sulfonic acid group is introduced by introducing a sulfonated metal salt, a sulfo ester group, a sulfonyl chloride group, or the like, followed by ion exchange, deesterification, hydrolysis, or the like.

As the solvent, halogenated hydrocarbons such as dichloroethane, tetrachloroethane, chloroform, and dichloromethane can be used.

The reaction temperature is not particularly limited, but is usually-20 to 180 ℃ and preferably 0 to 100 ℃.

The reaction time is usually 0.5 to 48 hours, preferably 1 to 10 hours.

Further, as a method for introducing a sulfonic acid group, for example, a method in which poly (2, 6-dimethyl-1, 4-phenylene ether) is dissolved in chloroform, chlorosulfonic acid is added dropwise to the solution, and the reaction is carried out at room temperature, whereby a sulfonic acid group-containing polyphenylene ether can be obtained. The sulfonic acid group-containing polyphenylene ether is insoluble in chloroform with the progress of sulfonation, precipitates in the form of an amorphous solid, and can be recovered by filtration.

In the above polyphenylene ether having an acidic group, a sulfonic acid group is introduced into an aromatic ring skeleton of a side chain bonded to the aromatic ring skeleton via an electron-withdrawing group, as compared with an aromatic ring skeleton of a main chain of the polyphenylene ether having a rich electron. Therefore, the effect of preventing the sulfonic acid group from being released by heat even under high temperature conditions (for example, 170 ℃ C.) can be obtained. Further, due to the above-mentioned effects, the ion exchange capacity of the polyphenylene ether having an acidic group after being left under high temperature conditions is increased as compared with the ion exchange capacity of the conventional sulfonic acid group-containing polyphenylene ether after being left under high temperature conditions.

The polyphenylene ether having an acidic group may contain other components in addition to the components represented by the general formulae (11) and (12), and the proportion of the other components is particularly preferably 0 mol%, more preferably 0 to 10 mol%, and most preferably 0 to 20 mol% with respect to 100 mol% of the components represented by the general formulae (11) and (12) and the other components.

Examples of the polyether ketone having an acidic group include sulfonated polyether ketones having a structure represented by the following general formula, and sulfonated polyether ketones having only a structure represented by the following general formula are preferable.

[ solution 6]

(in the formula, n represents an integer of 2 or more.)

Examples of the polyether ether ketone having an acidic group include sulfonated polyether ether ketones having a structure represented by the following general formula, and sulfonated polyether ether ketones having only a structure represented by the following general formula are preferable.

[ solution 7]

(in the formula, n represents an integer of 2 or more.)

Examples of the polyether ether ketone having an acidic group include sulfonated polyether ether ketone ketones having a structure represented by the following general formula, and sulfonated polyether ether ketone ketones having only a structure represented by the following general formula are preferable.

[ solution 8]

(in the formula, n represents an integer of 2 or more.)

Examples of the polybenzimidazole having an acidic group include sulfonated polybenzimidazole having a structure represented by the following general formula, and sulfonated polybenzimidazole having a structure represented by only the following general formula is preferable.

[ solution 9]

(in the formula, n represents an integer of 2 or more.)

Examples of the polyphenylene sulfide having an acidic group include sulfonated polyphenylene sulfides having a structure represented by the following general formula, and sulfonated polyphenylene sulfides composed only of a structure represented by the following general formula are preferable.

[ solution 10]

(in the formula, n represents an integer of 2 or more.)

Examples of the polyether sulfone having an acidic group include sulfonated polyether sulfones having a structure represented by the following general formula, and preferably sulfonated polyether sulfones composed only of a structure represented by the following general formula.

[ solution 11]

(in the formula, n represents an integer of 2 or more.)

Examples of the polyether ether sulfone having an acidic group include sulfonated polyether ether sulfones having a structure represented by the following general formula, and sulfonated polyether ether sulfones composed only of a structure represented by the following general formula are preferable.

[ solution 12]

(in the formula, n represents an integer of 2 or more.)

Examples of the polyphenylsulfone having an acidic group include sulfonated polyphenylsulfone having a structure represented by the following general formula, and sulfonated polyphenylsulfone having only a structure represented by the following general formula is preferable.

[ solution 13]

(in the formula, n represents an integer of 2 or more.)

In the polymer electrolyte membrane of the present embodiment, the mass ratio of the resin (a) to the resin (B) (mass of the resin (a)/mass of the resin (B)) is preferably 90/10 to 50/50, more preferably 85/15 to 60/40, and still more preferably 80/20 to 70/30, from the viewpoints of elongation at break and gas barrier property.

Compatibilizer (C)

In the present embodiment, it is preferable that the polymer electrolyte membrane contain a compatibilizer (C) for compatibilizing the resin (a) and the resin (B) in view of easy mixing of the resin (a) and the resin (B).

The means for compatibilizing may be a method of adding a hydrocarbon segment to the resin (a), a method of adding a fluorine segment to the resin (B), or the like, in addition to the method of adding the compatibilizer (C), and any method may be used as long as the resin (a) and the resin (B) can be compatibilized.

In the present specification, the polymer having a hydrocarbon segment added to the resin (a) and the polymer having a fluorine segment added to the resin (B) correspond to the resin (a) and the resin (B), respectively, not to the compatibilizer (C).

Examples of the compatibilizer (C) include monomers, oligomers, and polymers having both a fluorine-based segment and a hydrocarbon-based segment in one chain (for example, polyvinylidene fluoride), and compounds (for example, oxides and hydroxides) containing polyvalent metal atoms such as cerium, calcium, magnesium, aluminum, tungsten, copper, nickel, and iron.

Examples of the method for adding the hydrocarbon segment to the resin (A) include conversion of a part of the C-F bond of the perfluorosulfonic acid resin (A) into a C-H bond, introduction of a hydrocarbon segment into the side chain of the perfluorosulfonic acid resin (A), and the like. In addition to these, any method may be used as long as it is possible to add a hydrocarbon segment to the resin (a).

Examples of the method for adding the fluorine-based segment to the resin (B) include a method of converting a part of the C-H bond of the resin (B) into a C-F bond, a method of introducing a fluorine-based segment into a side chain of the resin (B), and the like. For example, R in the above general formula (13)⁷～R¹¹At least 1 (preferably R)⁷～R¹¹All the positions) are fluorine atoms, and a modified resin (for example, modified polyphenylene ether) modified with perfluoroalkoxyalkane or the like. In addition, any method may be used as long as it is preferable.

The content of the resin (C) in the polymer electrolyte membrane (100 parts by mass) of the present embodiment is preferably 0.01 to 10.0 parts by mass, and more preferably 0.1 to 5.0 parts by mass.

Other components (D) -

The polymer electrolyte membrane of the present embodiment may contain, in addition to the resin (a), the resin (B), and the compatibilizer (C), another component (D) such as a polymer such as a nitrogen-containing aliphatic basic polymer or a nitrogen-containing aromatic basic polymer.

Examples of the nitrogen-containing aliphatic basic polymer include polyethyleneimine.

Examples of the nitrogen-containing aromatic basic polymer include polyaniline; heterocyclic compounds such as polybenzimidazole, polypyridine, polypyrimidine, polyvinylpyridine, polyimidazole, polypyrrolidine, polyvinylimidazole, and polypyrrole; and the like. Among them, polybenzimidazole is preferred because it has an action of trapping radicals generated in the polymer and can give a polymer electrolyte membrane having more excellent durability.

Examples of the polybenzimidazole include a compound represented by general formula (14) or general formula (15), and poly-2, 5-benzimidazole represented by general formula (16).

[ solution 14]

(in the formula (14), R is

[ solution 15]

Alkylene or fluoroalkylene radical, R¹Each independently is a hydrogen atom, an alkyl group,Phenyl, or pyridyl. In addition, x is 10 or more and 1.0X 10⁷The following integers. )

[ solution 16]

(in formula (15), as R, R¹R, R in the formula (14)¹The same group, l is 10 or more and 1.0X 10⁷The following integers. )

[ solution 17]

(in the formula (16), R is¹R in the formula (14)¹The same group, m is 10 or more and 1.0X 10⁷The following integers. )

Among them, poly [2,2 '- (m-phenylene) -5, 5' -dibenzoimidazole ] represented by the following formula (17) is particularly preferable.

[ solution 18]

(in the formula (17), n is not less than 10 and is 1.0X 10⁷The following integers. )

The polymer as the other component (D) can be produced by a polymerization method described in a publicly known document (for example, see the laboratory chemical lecture 28, 4 th edition of Polymer Synthesis, edited by Japan chemical society, Takayama, Ltd.).

The weight average molecular weight of the polymer as the other component (D) is not particularly limited, but is preferably 10000 to 1000000, more preferably 20000 to 100000, and further preferably 50000 to 100000.

The weight average molecular weight can be measured by Gel Permeation Chromatography (GPC).

The intrinsic viscosity of the polymer as the other component (D) is preferably 0.1 to 10.0dL/g, more preferably 0.3 to 5.0dL/g, and still more preferably 0.5 to 1.0 dL/g.

The intrinsic viscosity is determined from the viscosity η P (mPa · S) of the obtained polymer solution, the viscosity η S (mPa · S) of the dimethylacetamide, and the concentration Cp (g/dL) of the polymer solution by the following formula, by dissolving the polymer in dimethylacetamide. The viscosity here means a value measured by a cone-plate type rotary viscometer (E-type viscometer) at 25 ℃.

Intrinsic viscosity ═ ln (η P/η S)/Cp

(wherein ln represents a natural logarithm.)

The polymer electrolyte membrane of the present embodiment may contain other component (D) such as a compound having a thioether group or a compound having an epoxy group.

Examples of the compound having a sulfide group include compounds having a formula- (R-S)_n(in the formula, S is a sulfur atom, R is a hydrocarbon group, n is an integer of 1 or more) and specific examples thereof include dialkyl sulfides such as dimethyl sulfide, diethyl sulfide, dipropyl sulfide, methyl ethyl sulfide, and methyl butyl sulfide; cyclic thioethers such as tetrahydrothiophene and tetrahydropyran; aromatic sulfides such as methyl phenyl sulfide, ethyl phenyl sulfide, diphenyl sulfide, and dibenzyl sulfide.

The compound having a sulfide group may be a monomer or a polymer such as polyphenylene sulfide (polyphenylene sulfide having no acidic group). Among these, from the viewpoint of durability, polymers (oligomers and polymers) in which n is an integer of 10 or more are preferable, and polymers in which n is an integer of 1,000 or more are more preferable.

As the compound having a sulfide group, polyphenylene sulfide (polyphenylene sulfide having no acidic group) is preferable in view of chemical stability. The polyphenylene sulfide preferably has a p-phenylene sulfide skeleton of 70 mol% or more, and more preferably has a p-phenylene sulfide skeleton of 90 mol% or more.

Examples of the method for producing polyphenylene sulfide as the other component (D) include a method of polymerizing a halogen-substituted aromatic compound (e.g., p-dichlorobenzene) in the presence of sulfur and sodium carbonate; a method of polymerizing a halogen-substituted aromatic compound in a polar solvent in the presence of sodium sulfide or sodium hydrosulfide and sodium hydroxide; a method of polymerizing a halogen-substituted aromatic compound in a polar solvent in the presence of hydrogen sulfide and sodium hydroxide or an aminoalkanoic acid sodium salt; self-condensation of p-chlorothiophenol; and so on. Among them, a method of reacting p-dichlorobenzene with sodium sulfide in an amide solvent such as N-methylpyrrolidone or dimethylacetamide or a sulfone solvent such as sulfolane is preferred.

As the method for producing polyphenylene sulfide as the other component (D), there can be specifically mentioned the production methods described in, for example, U.S. Pat. No. 2513188, Japanese patent publication No. 44-27671, Japanese patent publication No. 45-3368, Japanese patent publication No. 52-12240, Japanese patent publication No. 61-225217, U.S. Pat. No. 3274165, British patent No. 1160660, Japanese patent publication No. 46-27255, Belgian patent No. 29437, Japanese patent publication No. 5-222196, and the like, and the production methods of the prior art exemplified in these documents.

The amount of the oligomer extracted from polyphenylene sulfide as the other component (D) with methylene chloride is preferably 0.001 to 0.9% by mass, more preferably 0.001 to 0.8% by mass, and still more preferably 0.001 to 0.7% by mass.

Here, when the amount of the oligomer extracted with methylene chloride is in the above range, it is explained that the amount of the oligomer (about 10 to 30-mer) in the polyphenylene sulfide is small. When the oligomer extraction amount is set in the above range, bleeding is less likely to occur during film formation, and therefore, the oligomer extraction amount is preferable.

The amount of the above-mentioned oligomer extracted with methylene chloride can be measured by the following method. Specifically, 5g of polyphenylene sulfide powder was added to 80mL of methylene chloride, Soxhlet extraction was performed for 4 hours, the mixture was cooled to room temperature, and the methylene chloride solution after extraction was transferred to a weighing flask. The vessel used for the extraction was washed 3 times with a total of 60mL of methylene chloride, and the washing solution was collected into the weighing bottle. Subsequently, the polyphenylene sulfide was heated to about 80 ℃ to evaporate methylene chloride in the weighing flask, and the residue was weighed to determine the amount of oligomers present in the polyphenylene sulfide from the amount of the residue.

The polyphenylene sulfide as the other component (D) has a content of-SX groups (S is a sulfur atom and X is an alkali metal or a hydrogen atom) of preferably 10 to 10,000. mu. mol/g, more preferably 15 to 10,000. mu. mol/g, and still more preferably 20 to 10,000. mu. mol/g.

The SX group concentration falling within the above range means that the number of reactive sites is large. By using polyphenylene sulfide having an-SX group concentration satisfying the above range, the miscibility with the polymer electrolyte is improved, thereby improving the dispersibility and enabling higher durability under high-temperature and low-humidity conditions.

The amount of the-SX group can be determined by the following method. That is, after previously drying polyphenylene sulfide powder at 120 ℃ for 4 hours, 20g of the dried polyphenylene sulfide powder was added to 150g N-methyl-2-pyrrolidone, and vigorously stirred and mixed at room temperature for 30 minutes to eliminate agglomeration of the powder, resulting in a slurry state. After the slurry was filtered, it was repeatedly washed 7 times with 1L of warm water of about 80 ℃ each time. The obtained cake was slurried again in 200g of pure water, and 1N hydrochloric acid was added to adjust the pH of the slurry to 4.5. Subsequently, the mixture was stirred at 25 ℃ for 30 minutes, filtered, and washed with 1L of warm water at about 80 ℃ for 6 times. The obtained cake was slurried again in 200g of pure water, followed by titration with 1N sodium hydroxide, and the amount of-SX groups present in polyphenylene sulfide was determined from the amount of sodium hydroxide consumed.

The polyphenylene sulfide as the other component (D) has a melt viscosity at 320 ℃ (value when held for 6 minutes under conditions of 300 ℃ and a load of 196N, L/D (L: hole length, D: hole inner diameter) of 10/1 using a flow tester), and is preferably 1 to 10,000 poise, more preferably 100 to 10,000 poise, from the viewpoint of molding processability.

The polyphenylene sulfide as the other component (D) may be one in which an acidic functional group is introduced into a benzene ring and the introduced acidic functional group is replaced with a metal salt or an amine salt. The metal salt is preferably an alkali metal salt such as a sodium salt or a potassium salt, or an alkaline earth metal salt such as a calcium salt.

Examples of the compound having an epoxy group as the other component (D) include low molecular weight compounds having an epoxy group, homopolymers or copolymers of unsaturated monomers having an epoxy group, and epoxy resins. Among them, since a polymer compound is easy to handle at high temperature, a homopolymer or a copolymer of an unsaturated monomer having an epoxy group and an epoxy resin are preferable.

The epoxy group-containing low-molecular-weight compound is preferably a compound that is solid or liquid at 200 ℃. Specific examples thereof include 1, 2-epoxy-3-phenoxypropane, N- (2, 3-epoxypropyl) phthalimide, 3, 4-epoxytetrahydrothiophene-1, 1-dioxide, glycidyl 4-nonylphenyl ether, glycidyl tosylate, and glycidyl trityl ether.

The unsaturated monomer having an epoxy group, which constitutes a homopolymer or a copolymer of the unsaturated monomer having an epoxy group, is not particularly limited as long as it is an unsaturated monomer having an epoxy group, and examples thereof include glycidyl methacrylate, glycidyl acrylate, vinyl glycidyl ether, glycidyl ether of hydroxyalkyl (meth) acrylate, glycidyl ether of polyalkylene glycol (meth) acrylate, and glycidyl itaconate. Among them, glycidyl methacrylate is preferable.

In the case of a copolymer of an unsaturated monomer having an epoxy group, as another unsaturated monomer copolymerizable with the unsaturated monomer having an epoxy group, a vinyl aromatic compound such as styrene, a vinyl cyanide monomer such as acrylonitrile, vinyl acetate, (meth) acrylate, and the like are preferable. Examples of the copolymer obtained by copolymerizing these copolymerizable unsaturated monomers include styrene-glycidyl methacrylate copolymer, styrene-glycidyl methacrylate-methyl methacrylate copolymer, styrene-glycidyl methacrylate-acrylonitrile copolymer, and the like.

Among them, the copolymer containing an unsaturated monomer having an epoxy group and a styrene monomer preferably contains at least 65 mass% or more of a styrene monomer from the viewpoint of improving dispersibility. The epoxy-containing unsaturated monomer is preferably contained in an amount of 0.3 to 20% by mass, more preferably 1 to 15% by mass, and still more preferably 3 to 10% by mass.

Examples of the epoxy resin include cresol novolac type epoxy resins, bisphenol a type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, hydantoin type epoxy resins, biphenyl type epoxy resins, alicyclic epoxy resins, triphenylmethane type epoxy resins, phenol novolac type epoxy resins, and the like. Also, 1 or 2 or more selected from these may be used in combination. Among them, cresol novolak type epoxy resins and bisphenol a type epoxy resins are preferable from the viewpoint of compatibility with polyphenylene ether resins, and cresol novolak type epoxy resins are more preferable.

Physical Properties of Polymer electrolyte Membrane

The polymer electrolyte membrane of the present embodiment has a specific morphology in an image observed by SEM-EDX and SEM.

The polymer electrolyte membrane of the present embodiment has a phase with an average aspect ratio of 1.5 or more and 10 or less in an image of a membrane cross section observed by SEM (in this specification, may be simply referred to as "cross-sectional SEM"). The average length-to-thickness ratio is preferably 2 to 8, and more preferably 2.5 to 6. When the average length-to-thickness ratio is within the above range, high gas barrier properties and high elongation at break can be achieved at the same time, and physical durability is improved.

The average aspect ratio may be an average aspect ratio of phases constituting islands in the phase-separated structure, or an average aspect ratio of islands in which carbon atoms are mainly detected. Among these, the average length-to-thickness ratio of the phase constituting the island in which carbon atoms are mainly detected, such as the island containing the resin (B) and the island composed of only the resin (B), is preferable.

Here, the membrane cross section refers to a cross section perpendicular to the surface of the polymer electrolyte membrane (cross section in the thickness direction). The polymer electrolyte membrane is embedded with an epoxy adhesive or the like, and then cut with a microtome or the like to obtain a cross section of the polymer electrolyte membrane, and the cross section is observed with SEM to observe the form of the cross section. As shown in the examples, the cross-sectional SEM can be observed by evaporating (or dyeing) a sample with platinum, osmium, or the like. The aspect ratio can be obtained by observing the form of at least 2 phases by vapor deposition (or dyeing) and determining the diameter (major axis, minor axis) of the dispersed phase. The aspect ratio is preferably such that the diameter of the polymer electrolyte membrane in the thickness direction is defined as a minor axis and the diameter of the polymer electrolyte membrane in the direction perpendicular to the thickness direction is defined as a major axis. Specifically, the measurement can be performed by the method described in the examples below.

In order to set the average aspect ratio to 1.5 or more and 10 or less, for example, the following means can be mentioned as described above: as the perfluorosulfonic acid resin (a), a copolymer of a monomer containing fluorine and a monomer containing no fluorine is used; or blending other components not containing fluorine (for example, an aromatic hydrocarbon resin (B) having an acid group described later); and so on.

In the polymer electrolyte membrane of the present embodiment, the phase having the average aspect ratio in the above range may be observed in at least 1 membrane cross section, and is preferably observed in 2 or more membrane cross sections in terms of more excellent uniformity, elongation at break, and physical durability of the membrane.

In the polymer electrolyte membrane of the present embodiment, in an image of the membrane surface observed by SEM-EDX, a phase in which a fluorine atom is mainly detected and a phase in which a carbon atom is mainly detected have a phase separation structure. The membrane surface having the phase separation structure may be one membrane surface or two membrane surfaces, and preferably has the phase separation structure on both membrane surfaces in terms of more excellent elongation at break and physical durability. In the present specification, the membrane surface observed by SEM-EDX means the surface of a layer having a phase separation structure containing the resin (a).

The element distribution of the SEM image was performed using an SEM with an EDX (energy dispersive X-ray spectrometry) device, whereby a phase in which fluorine atoms were mainly detected and a phase in which carbon atoms were mainly detected could be observed.

In general, the perfluorosulfonic acid resin forms a phase in which fluorine atoms are mainly detected. The perfluorosulfonic acid resin may be a phase in which a carbon atom is mainly detected by copolymerizing a comonomer (e.g., an α -olefin such as ethylene or propylene) containing no fluorine atom, or by blending a hydrocarbon resin (e.g., the component (B) described later) with the perfluorosulfonic acid resin. When the hydrocarbon resin is blended, both aromatic and aliphatic resins are possible, and the aromatic hydrocarbon resin is preferable in terms of gas barrier properties. In addition, the polymer may be graphene oxide, carbon nanotube oxide, or the like. Further, among aromatic systems, the aromatic hydrocarbon-based resin (B) having an acidic group is preferable in terms of compatibility between the gas barrier property and the proton conductivity.

The phase in which fluorine atoms are mainly detected means a region in which fluorine atoms are the most abundant as an element detected by SEM-EDX under the conditions described in examples below, and may be a region in which the amount of fluorine atoms detected by SEM-EDX is 10 mass% or more.

The phase in which carbon atoms are mainly detected means a region in which carbon atoms are the most as an element detected in SEM-EDX under the conditions described in examples described later, and may be a region in which the amount of carbon atoms detected in SEM-EDX is 10 mass% or more.

The phrase "having a phase separation structure" means that at least 1 of a phase in which a fluorine atom is mainly detected and a phase in which a carbon atom is mainly detected are observed.

The phase separation structure may include a phase in which other atoms are mainly detected, in addition to a phase in which fluorine atoms are mainly detected and a phase in which carbon atoms are mainly detected. Among them, the phase separation structure is preferably composed of only a phase in which a fluorine atom is mainly detected and a phase in which a carbon atom is mainly detected.

In the polymer electrolyte membrane of the present embodiment, the phase separation structure is preferably a sea-island structure, and from the viewpoint of gas barrier properties, the island phase is more preferably a phase in which carbon atoms are mainly detected, and further preferably a phase containing the resin (B), a phase composed only of the resin (B), or the like, and particularly preferably a phase composed of the resin (B). Further, the phase of the island is preferably dense and finely dispersed.

In the polymer electrolyte membrane of the present embodiment, in an image observed by SEM-EDX on at least one membrane surface, the ratio of the relative standard deviation of the C/F peak intensity ratio (peak intensity of carbon atom/peak intensity of fluorine atom) in an image at a magnification of 1500 times to the relative standard deviation of the C/F peak intensity ratio in an image at a magnification of 150 times (relative standard deviation of 1500 times/relative standard deviation of 150 times) is preferably 0.20 to 5.0, more preferably 0.50 to 2.0, and still more preferably 0.80 to 1.2. When the ratio of the relative standard deviation is within the above range, the phase in which carbon atoms are mainly detected in the phase-separated structure is uniformly and finely dispersed, and a higher gas barrier property and a higher elongation at break can be achieved at the same time.

The ratio of the relative standard deviation can be determined by the method described in the examples below.

The ratio of the relative standard deviation described above preferably satisfies the above range on one film surface, and more preferably satisfies the above range on both film surfaces.

In the polymer electrolyte membrane of the present embodiment, in the image of the membrane surface observed by SEM-EDX, the average value of the C/F peak intensity ratio in the image at a magnification of 1500 times is preferably 0.50 to 20, and the hydrogen permeability coefficient under the conditions of 80 ℃ and 30% RH is preferably 5.0 × 10^-9cc·cm/cm²s-cmHg or less, more preferably 1.0 to 10 as the average value of the C/F peak intensity ratio, and a hydrogen permeability coefficient of 3.0X 10^-9cc·cm/cm²s-cmHg or less, and more preferably 2.0 to 5.0 in the average value of the C/F peak intensity ratio and 1.0X 10 in the hydrogen permeability coefficient^-9cc·cm/cm²s.cmHg or less. When the average value of the C/F peak intensity ratio and the hydrogen permeability coefficient are within the above ranges, the balance between the gas barrier property and the elongation at break can be further improved.

The hydrogen permeability coefficient can be measured by the method described in the examples below.

The polymer electrolyte membrane, which was observed by SEM-EDX at a 5mm square position, measured at arbitrary four corners 4 points and the center 1 point, and 5 points in total. By increasing the number of sites to be observed, the reliability of the numerical value with respect to the standard deviation can be improved.

The average value of the C/F peak intensity ratio in the image of 1500 × magnification preferably satisfies the above range on one film surface, and more preferably satisfies the above range on both film surfaces.

Method for forming polymer electrolyte membrane

The polymer electrolyte membrane of the present embodiment is preferably formed by using a solution containing the resin (a) as a raw material and forming the solution into a membrane by a method described later. The solution containing the resin (a) as used herein is a solution in which the resin (a) is dissolved in a solvent or a finely dispersed solution.

When the polymer electrolyte membrane of the present embodiment contains both the resin (a) and the resin (B), it is preferable to produce the polymer electrolyte membrane through a step of mixing a solution containing the resin (a) and a solution containing the resin (B) in order to uniformly and finely disperse the resin (a) and the resin (B) in the membrane.

Here, the solution containing the resin (a) is preferably a solution containing only the resin (a) as a resin component. The solution containing the resin (B) is preferably a solution containing only the resin (B) as a resin component.

Both the solution containing the resin (A) and the solution containing the resin (B) preferably have a peak top of a scattering diameter in the range of 10 to 200 μm in a dynamic light scattering measurement. As a result, in the mixed solution of the solution containing the resin (a) and the solution containing the resin (B), the interval between the aggregates of the resin (a) and the aggregates of the resin (B) is constant, the resin (a) and the resin (B) can be uniformly finely dispersed in the film, and both the gas barrier property and the elongation at break can be achieved. The peak of the scattering diameter of the solution containing the resin (a) and the peak of the scattering diameter of the solution containing the resin (B) may be the same or different.

The dynamic light scattering measurement can be performed by the method described in the examples below.

When the polymer electrolyte membrane of the present embodiment includes the resin (a), the resin (B), and the compatibilizer (C), the following steps are preferably performed: the solution containing the resin (a), the solution containing the resin (B), and the solution containing the compatibilizer (C) are mixed using a solution containing the compatibilizer in addition to the above. In addition, regarding the order of mixing, it is preferable to mix the solution containing the resin (a) and the solution containing the resin (B) first and then mix the solution containing the compatibilizer (C). Thus, the compatibilizer (C) easily enters a space formed at a certain interval between the aggregates of the resin (a) and the aggregates of the resin (B), and the resin (a) and the resin (B) can be more uniformly and finely dispersed in the film, and the gas barrier property and the elongation at break can be achieved at a higher level. The solution containing the compatibilizer (C) may be a homogeneously dissolved solution or only a dispersed dispersion.

The solution containing the compatibilizer (C) is preferably a solution containing only the compatibilizer (C) as the compatibilizers for the resin (a) and the resin (B).

The mixed solution of the solution containing the resin (a), the solution containing the resin (B), and the solution containing the compatibilizer (C) preferably has a transmittance of 90% T or more at a wavelength of 800nm in UV measurement. The transmittance is more preferably 95% T or more, and still more preferably 98% T or more. When the transmittance is in the above range, it is possible to determine the microdispersion of the solution, and a microdispersion film in which the size of the island phase in the phase separation structure of the film is reduced can be formed. The apparatus for UV measurement and other measurement conditions were as described in examples. The UV measurement can be performed by the method described in the examples below.

The solid content concentration of the compatibilizer is preferably 0.001 mass% or more and less than 1 mass%, more preferably 0.005 mass% or more and less than 0.5 mass%, and still more preferably 0.01 mass% or more and less than 0.1 mass%, relative to the weight (100 mass%) of the mixed solution of the solution containing the resin (a), the solution containing the resin (B), and the solution containing the compatibilizer (C).

Examples of the method for forming the polymer electrolyte membrane according to the present embodiment include the following methods: the polymer electrolyte membrane is formed by mixing a solution containing the resin (a), a solution containing the resin (B), and/or a solution containing the compatibilizer (C), further mixing a liquid medium containing a protic solvent as necessary to prepare a casting liquid, casting the casting liquid onto a support to form a liquid coating film on the support, and removing the liquid medium from the liquid coating film. The casting liquid preferably contains a protic solvent added at the time of preparing the solution containing the resin (a), the solution containing the resin (B), and/or the solution containing the compatibilizer (C).

The casting liquid may be, for example, an emulsion (a substance in which liquid particles are dispersed in a liquid in the form of colloidal particles or coarser particles to form a milk), a suspension (a substance in which solid particles are dispersed in a liquid in the form of colloidal particles or particles to the extent that they can be observed by a microscope), a colloidal liquid (a state in which giant molecules are dispersed), a micellar liquid (a lyophilic colloidal dispersion system in which a large number of small molecules are associated by intermolecular forces), or a composite system of these.

The casting liquid preferably contains a liquid medium containing a protic solvent. By using a casting liquid containing a liquid medium containing a protic solvent, a polymer electrolyte membrane in which the resin (a) and the resin (B) are more uniformly microdispersed can be formed.

Examples of the protic solvent include solvents having a functional group capable of releasing a proton, and examples thereof include water, alcohols (methanol, ethanol, propanol, isopropanol, etc.), phenols, and the like. Among them, water is preferred.

The amount of the protic solvent added is preferably 0.5 to 99.5% by mass, more preferably 1 to 90% by mass, and still more preferably 10 to 60% by mass, based on 100% by mass of the liquid medium in the casting liquid.

The protic solvent may be used in a proportion of 1 species or in a mixture of 2 or more species. Particularly, a mixed solvent of water and alcohol is preferably used, and more preferably, a mixed solvent of water/ethanol (volume ratio) 3/1 to 1/3 and water/isopropanol (volume ratio) 3/1 to 1/3 is used.

The liquid medium in the casting liquid preferably further contains an aprotic solvent. Here, the aprotic solvent refers to a solvent other than the protic solvent, and examples thereof include N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, dimethylsulfoxide, acetone, methyl ethyl ketone, and the like. Among them, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, and dimethylsulfoxide are preferable.

The aprotic solvent may be used in a mixture of 1 or 2 or more.

The amount of the aprotic solvent added is preferably 99.5 to 0.5% by mass, more preferably 99 to 10% by mass, and still more preferably 90 to 40% by mass, based on 100% by mass of the liquid medium in the casting liquid.

The content of the liquid medium in the casting liquid is preferably 20.000 to 99.989 mass%, more preferably 40.000 to 99.895 mass%, and still more preferably 75.000 to 98.990 mass% with respect to the casting liquid (100 mass%).

The content of the resin (a) in the casting liquid is preferably 0.10 to 30.00 mass%, more preferably 0.15 to 20.00 mass%, and still more preferably 0.15 to 10.00 mass% with respect to 100 mass% of the casting liquid.

The content of the resin (B) in the casting liquid is preferably 0.10 to 30.00 mass%, more preferably 0.15 to 20.00 mass%, and still more preferably 0.15 to 10.00 mass% with respect to 100 mass% of the casting liquid.

When the casting liquid further contains a compatibilizer, the mass ratio of the total amount of the resin (a) and the resin (B) to the compatibilizer (C) (total mass of the resin (a) and the resin (B): mass of the compatibilizer (C)) in the casting liquid is not particularly limited, and is preferably 99.99: 0.01-90.0: 10.0, more preferably 99.9: 0.1 to 95.0: 5.0.

by using such a casting liquid, the removal of the liquid medium becomes easy, and a polymer electrolyte membrane in which the resin (a) and the resin (B) are more uniformly microdispersed can be formed, showing better gas barrier properties and elongation at break, which are associated with higher chemical durability.

The casting liquid can be obtained, for example, by: a casting liquid can be obtained by adding and stirring a resin solution (hereinafter, referred to as "pre-stage solution L") in which a compatibilizer (C) is dissolved in an aprotic solvent such as dimethylacetamide and a resin solution (hereinafter, referred to as "pre-stage solution M") in which a resin (a) and a resin (B) are dissolved in an aprotic solvent such as dimethylacetamide, and further adding and stirring a resin solution (hereinafter, referred to as "pre-stage solution N") in which a resin (a) is dissolved in a protic solvent.

Examples of the method for preparing the pre-stage solution L include: putting the compatibilizer (C) and the aprotic solvent into an autoclave, and heating for 10 minutes to 100 hours at 40 to 300 ℃; and so on.

The content of the compatibilizer (C) in the pre-stage solution L is preferably 0.001 mass% or more and less than 1 mass%, more preferably 0.005 mass% or more and less than 0.5 mass%, and still more preferably 0.01 mass% or more and less than 0.1 mass% with respect to the pre-stage solution L (100 mass%). When the content of the compatibilizer (C) is in the above range, the finely dispersed compatibilizer easily enters a space formed at a certain interval between the resin (a) and the resin (B), and the resin (a) and the resin (B) can be more uniformly and finely dispersed in the film, and the gas barrier property and the elongation at break can be achieved at a higher level.

Examples of the method for preparing the pre-stage solution M include: a method of heating the resin (A) and the resin (B) in an aprotic solvent at 40 to 300 ℃ for 10 minutes to 100 hours in an autoclave; or a method of performing solvent replacement of the solution N in the previous stage (adding an aprotic solvent after evaporating a protic solvent); and so on.

The content of the resin (A) and the resin (B) in the pre-stage solution M is preferably 0.01 to 50 mass%, more preferably 0.1 to 30 mass%, and still more preferably 1 to 10 mass% with respect to 100 mass% of the pre-stage solution M.

The method for producing the solution N in the former stage includes a method in which the resin (a) and the protic solvent are placed in an autoclave and subjected to a heat treatment at 40 to 300 ℃ for 10 minutes to 100 hours. The solution mentioned here also includes a state in which the resin (a) is dispersed in a micelle form.

The content of the resin (A) in the pre-stage solution N is preferably 0.1 to 50 mass%, more preferably 0.1 to 30 mass%, and still more preferably 1 to 10 mass% with respect to 100 mass% of the pre-stage solution N.

When the pre-stage solution L and the pre-stage solution M produced as described above are mixed by a known stirring method and the concentration of the resin (a) is adjusted, the pre-stage solution N is added and stirred and mixed. Further, concentration may be carried out as desired. Thus, a casting solution was obtained.

Next, the casting liquid is poured onto a support to form a liquid coating film on the support, and then the liquid medium is removed from the liquid coating film, whereby a polymer electrolyte membrane can be obtained.

As a method of casting, a method such as a gravure roll coater, a natural roll coater, a reverse roll coater, a blade coater, or a dip coater, or a known coating method such as a spray method or a spin coating method can be used.

As the support for casting, plastic films such as a glass plate, a polyethylene terephthalate film, a polytetrafluoroethylene film, and a polyimide film, metal foils, substrates such as aluminum oxide and Si, and the like are suitably used. Such a support is removed from the polymer electrolyte membrane as desired when forming the membrane electrode assembly. In addition, a polymer electrolyte membrane including a reinforcement (such a porous membrane) can also be produced by infiltrating a casting solution into a porous membrane obtained by stretching a PTFE membrane and then removing the liquid medium, as described in japanese patent publication No. 5-75835. Further, a polymer electrolyte membrane reinforced with fibrillated fibers as shown in jp 53-149881 a and jp 63-61337 a can also be produced by adding fibrillated fibers made of PTFE or the like to a casting liquid and casting, and then removing the liquid medium.

The polymer electrolyte membrane thus obtained may be subjected to heat treatment (annealing) (the heat treatment can completely remove the liquid medium and stabilize the structure of the components in the polymer electrolyte membrane) at 40 to 300 ℃ (preferably 80 to 200 ℃). In order to sufficiently exert the original ion exchange capacity, an acid treatment with hydrochloric acid, nitric acid, or the like may be performed as desired (when a part of the ion exchange groups of the polymer electrolyte membrane is substituted with a salt, the ion exchange groups can be recovered by the acid treatment). In addition, by using a transverse uniaxial tenter together with a biaxial tenter, stretch orientation can be imparted.

The content of the resin (a) in the polymer electrolyte membrane is preferably 10 to 95% by mass, more preferably 20 to 80% by mass, based on 100% by mass of the polymer electrolyte membrane, from the viewpoint of obtaining a polymer electrolyte membrane having higher proton conductivity.

The content of the resin (B) in the polymer electrolyte membrane is preferably 5 to 90 mass%, more preferably 20 to 80 mass% based on 100 mass% of the polymer electrolyte membrane, from the viewpoint of obtaining a polymer electrolyte membrane having more excellent durability.

The mass ratio of the resin (B) to 100 parts by mass of the resin (a) in the polymer electrolyte membrane is preferably 5 to 900 parts by mass, more preferably 25 to 400 parts by mass, in order to obtain a polymer electrolyte membrane having more excellent gas barrier properties and durability and a higher cell voltage.

The content of the compatibilizer (C) in the polymer electrolyte membrane is preferably 0.01 to 10.0 mass%, more preferably 0.10 to 5.0 mass%, based on 100 mass% of the polymer electrolyte membrane, in order to facilitate the compatibility of the resin (a) with the resin (B) and to obtain a polymer electrolyte membrane having more excellent durability.

The resin (a) and the resin (B) are preferably uniformly dispersed in the polymer electrolyte membrane from the viewpoints of gas barrier properties, durability, and cell voltage.

The polymer electrolyte membrane of the present embodiment may be a laminate having a plurality of layers, and is preferably a polymer electrolyte membrane composed only of a layer containing the resin (a). The polymer electrolyte membrane of the present embodiment preferably has a layer containing the resin (a) and the resin (B) and a layer containing the resin (a), and more preferably a 2-layer laminate composed of only the layer containing the resin (a) and the resin (B) and the layer containing the resin (a).

The polymer electrolyte membrane of the present embodiment may be a laminate of layers containing the same or different resins (a) and (B).

When the polymer electrolyte membrane of the present embodiment is a laminate, at least one surface layer (preferably both surfaces) is preferably a layer containing at least the resin (a), more preferably a layer containing at least the resin (a) and the resin (B), and still more preferably a layer containing the resin (a), the resin (B), and the compatibilizer (C).

The present inventors have surprisingly found that the polymer electrolyte membrane of the present embodiment has significantly improved durability, is also superior in gas barrier properties, and has a higher cell voltage than a laminate of a layer of the resin (a) and a layer of the resin (B).

Although the detailed principle is not clear, it is considered that the hydrocarbon resin portion of the resin (B) contained in the layer containing the resin (a) and the resin (B) of the polymer electrolyte membrane of the present embodiment is related to the gas barrier property, and the acid group is related to the cell voltage. Further, since the layer containing the resin (a) and the resin (B) also contains the resin (a), it is considered that the layer is also excellent in proton conductivity and durability. Also, surprisingly, if the layer contains the resin (a) and the resin (B), a significant effect exceeding the effect obtained by combining the effects of the respective resin components can be obtained.

In the polymer electrolyte membrane of the present embodiment, it is preferable that the layer containing the resin (a) having excellent proton conductivity and the resin (B) having excellent gas barrier properties is used as the gas barrier layer, and the layer containing the resin (a) having excellent proton conductivity is used as the conductive layer.

The polymer electrolyte membrane of the present embodiment can be used for confirming the content of each layer using a fourier transform infrared spectrophotometer, for example.

The polymer electrolyte membrane of the present embodiment is preferably: when a cross section in the thickness direction of a polymer electrolyte membrane is measured using a Fourier transform infrared spectrophotometer, the cross section is observed to appear at 1000 to 1200cm over the entire area of the membrane cross section^-1The peak derived from the C-F bond in the vicinity is observed to appear at 1400 to 1600cm in a region of the cross section containing at least a layer comprising the resin (A) and the resin (B)^-1The sum of the sums of the^-1The intensity of the C-H bond-derived peak in the layer containing the resin (A) and the resin (B) is higher than that of the layer containing the resin (A) (the layer not containing the resin (B))) The intensity of the peak derived from the above C-H bond in (1).

Here, the expression occurs at 1000 to 1200cm^-1The peak derived from the C-F bond in the vicinity thereof includes, for example, a peak derived from the resin (A). As appearing at 1400-1600 cm^-1The sum of the sums of the^-1The peak derived from the C-H bond in the vicinity thereof includes, for example, a peak derived from the resin (B).

The polymer electrolyte membrane of the present embodiment is preferably: when a cross section in the thickness direction of the polymer electrolyte membrane is measured by a Fourier transform infrared spectrophotometer, the cross section appears in the range of 1400-1600 cm in a region containing at least a layer comprising a resin (A) and a resin (B)^-1The sum of the sums of the^-1A peak derived from a nearby C-H bond and appearing at 1010 to 1080cm^-1The sum of the near distance and the distance is 1100-1230 cm^-1nearby-SO₃H derived peak.

The thickness of the layer containing the resin (a) and the resin (B) in the polymer electrolyte membrane of the present embodiment is preferably not more than the thickness of the layer containing the resin (a).

The ion exchange capacity of the polymer electrolyte membrane is not particularly limited, but is preferably 0.50 to 4.00 milliequivalents/g, more preferably 0.83 to 4.00 milliequivalents/g, and still more preferably 1.00 to 1.50 milliequivalents/g, per 1 g. When the ion exchange capacity is high, the proton conductivity becomes higher under high-temperature and low-humidity conditions, and when the ion exchange capacity is used in a fuel cell, higher output can be obtained during operation.

The ion exchange capacity can be measured by the following method. First, the cut pieces were cut into 10cm²The left and right polymer electrolyte membranes were vacuum-dried at 110 ℃ to obtain the dry weight W (g). The polymer electrolyte membrane was immersed in 50mL of a 25 ℃ saturated NaCl aqueous solution to thereby obtain H⁺When phenolphthalein was released, neutralization titration was performed with a 0.01N aqueous solution of sodium hydroxide using phenolphthalein as an indicator, and the equivalent M (milliequivalent) of NaOH required for neutralization was determined. The value obtained by dividing M thus obtained by W was the ion exchange capacity (milliequivalent/g). Further, the value obtained by dividing W by M and multiplying by 1000 times is equivalent mass EW, which is the dry mass in grams per 1 equivalent of ion-exchange group.

The polymer electrolyte membrane of the present embodiment may be provided with a reinforcing layer for allowing the polymer electrolyte to permeate into the microporous membrane.

The material for the microporous membrane is not particularly limited, and examples thereof include: polyolefin resins such as polyethylene, polypropylene, ethylene-propylene copolymers, and polytetrafluoroethylene copolymers of fluorinated olefins such as tetrafluoroethylene and olefins such as ethylene and propylene; polysiloxanes such as polysiloxane; methacrylate resins such as polymethyl methacrylate (PMMA); styrene resins such AS polystyrene, acrylonitrile-styrene copolymer (AS resin), and acrylonitrile-butadiene-styrene copolymer (ABS resin); a polyamide; polyimide (PI); polyetherimide (PEI); a polyamide-imide; a polyester imide; polycarbonate (PC); a polyacetal; poly (arylene ethers) such as poly (phenylene oxide) (PPO); polyphenylene Sulfide (PPS); a polyarylate; a polyaryl group; polysulfones; polyethersulfone (PES); polyurethanes; polyester resins such as polyethylene terephthalate (PET); polyether ketones such as polyether ether ketone (PEEK) and polyether ketone (PEKK); polyacrylates such as polybutyl acrylate and polyethyl acrylate; polyvinyl esters such as polybutoxymethylene; a polysulfide species; polyphosphazenes; polytriazines; polycarboboranes; polynorbornene; an epoxy resin; polyvinyl alcohol; polyvinylpyrrolidone; polydienes such as polyisoprene and polybutadiene; polyolefins such as polyisobutylene; a vinylidene fluoride resin; a hexafluoropropylene-based resin; hexafluoroacetone-based resins, and the like.

The thickness of the polymer electrolyte membrane in the present embodiment is preferably 1 to 50 μm, more preferably 3 to 25 μm, and still more preferably 5 to 15 μm.

The polymer electrolyte membrane of the present embodiment can be used as a membrane electrode assembly, a component of a polymer electrolyte fuel cell, or the like.

(Membrane electrode Assembly)

The membrane electrode assembly of the present embodiment includes the polymer electrolyte membrane and the electrode catalyst layer.

A unit in which two electrode catalyst layers, an anode and a cathode, are joined to both surfaces of a polymer electrolyte membrane is called a membrane electrode assembly (hereinafter sometimes simply referred to as "MEA"). When a pair of gas diffusion layers are joined to face each other on the outer sides of the electrode catalyst layers, the MEA may be used. The MEA of the present embodiment is configured in the same manner as a known MEA, except that the polymer electrolyte membrane of the present embodiment is used as the polymer electrolyte membrane.

The electrode catalyst layer is composed of fine particles of a catalyst metal and a conductive agent supporting the fine particles, and contains a water repellent agent as needed.

The catalyst metal may be any metal that promotes the oxidation reaction of hydrogen and the reduction reaction of oxygen, and examples thereof include 1 or more selected from the group consisting of platinum, gold, silver, palladium, iridium, rhodium, ruthenium, iron, cobalt, nickel, chromium, tungsten, manganese, vanadium, and alloys thereof. Among them, platinum is preferable.

The polymer electrolyte membrane of the present embodiment can be used as a method for producing an MEA, and known production methods are used, and examples thereof include the following methods. First, an electrode binder ion exchange resin is dissolved in a mixed solution of alcohol and water, and platinum-supported carbon as an electrode material is dispersed therein to prepare a paste. It is coated onto a Polytetrafluoroethylene (PTFE) sheet in an amount and allowed to dry. Next, the coated surfaces of the PTFE sheets are opposed to each other with the polymer electrolyte membrane interposed therebetween, and hot pressing is performed at 100 to 200 ℃. As the electrode binder, a binder obtained by dissolving an ion exchange resin in a solvent (alcohol, water, or the like) is generally used, but the polymer electrolyte of the present embodiment may be used as the electrode binder, and the polymer electrolyte is preferably used in view of durability. The method for producing MEA may be, for example, the method described in JOURNAL OF APPLIED ELECTRECHEMISTRY, 22(1992) p.1-7, etc.

(Polymer electrolyte Fuel cell)

The polymer electrolyte fuel cell of the present embodiment includes the membrane electrode assembly.

The MEA obtained as described above, and optionally an MEA having a structure in which a pair of gas diffusion electrodes face each other further outside the electrode catalyst layer, is further combined with a constituent component used in a general polymer electrolyte fuel cell such as a bipolar plate or a support plate to constitute a polymer electrolyte fuel cell. Such a polymer electrolyte fuel cell may have the same configuration as a known polymer electrolyte fuel cell except that the MEA is used as the MEA.

The bipolar plate is a composite material of graphite and resin, a metal plate, or the like, in which grooves for flowing a gas such as a fuel or an oxidant are formed on the surface thereof. The bipolar plate has a function of supplying a fuel or an oxidizing agent to a flow path near the electrode catalyst, in addition to a function of transferring electrons to an external load circuit. The MEA is interposed between the bipolar plates, and two or more of the MEA are stacked to produce the polymer electrolyte fuel cell according to the present embodiment.

The polymer electrolyte fuel cell according to the present embodiment can be used, for example, in a fuel cell automobile, a household fuel cell, or the like.