JP2011052078A - Polymer electrolyte composition, polymer electrolyte membrane, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an excellent polymer electrolyte composition which exhibits both durability and bondability with an electrode. <P>SOLUTION: The polymer electrolyte composition, comprising an aromatic polymer electrolyte and a biphenyl derivative represented by formula (A), is characterized in that, in 100 mass% in the total of the aromatic polymer electrolyte and the biphenyl derivative, the biphenyl derivative is 1-20 mass%. [In formula (A), R and R' are the same or different, and are each at least one group selected from the group consisting of hydrogen, alkyl, hydroxy, alkoxy, hydroxyalkyl and carbonylalkyl, with the proviso that R and R' are not simultaneously hydrogen; and m and n are each independently an integer of 1 or more and 5 or less]. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polymer electrolyte composition, particularly a polymer electrolyte composition suitably used for forming an electrolyte membrane of a fuel cell.

  Solid polymer fuel cells (PEFCs) and direct methanol fuel cells (DMFCs) that use polymer membranes as polymer electrolyte membranes are portable and can be miniaturized. Applications to power generation systems and power supplies for portable devices are being promoted. Currently, perfluorocarbon sulfonic acid polymer membranes represented by Nafion (registered trademark) manufactured by DuPont of the United States are widely used as polymer electrolyte membranes.

  However, since these membranes are softened at 100 ° C. or higher, the operating temperature of the fuel cell is limited to 80 ° C. or lower. Increasing the operating temperature has various advantages such as energy efficiency, downsizing of the apparatus, and improvement of catalytic activity, and therefore a polymer electrolyte membrane with higher heat resistance is required.

  As a heat-resistant polymer electrolyte membrane, a sulfonated polymer obtained by treating a heat-resistant polymer such as polysulfone or polyetherketone with a sulfonating agent such as fuming sulfuric acid is known (for example, Non-Patent Document 1). However, it is generally difficult to control the sulfonation reaction with a sulfonating agent. For this reason, the degree of sulfonation becomes excessive or excessive. In addition, there is a problem that the polymer is easily decomposed during sulfonation, and uneven sulfonation is likely to occur.

  For this reason, use of a polymer polymerized from a monomer having an acidic group such as a sulfonic acid group as a polymer electrolyte membrane has been studied. For example, Patent Document 1 discloses a polymer electrolyte obtained by reaction of 4,4′-dichlorodiphenylsulfone-3,3′-disulfonic acid soda and 4,4′-dichlorodiphenylsulfone with 4,4′-biphenol. Copolymers that can be obtained are disclosed. The polymer electrolyte membranes containing these polymers as constituent components have less sulfonic acid group heterogeneity as in the case of using the sulfonating agent described above, and the amount of sulfonic acid group introduced and the molecular weight of the polymer are easy to control. It was.

  However, a film containing a biphenyl group is not softened even at 250 ° C. or higher, and it is difficult to join the electrode with a hot press method. In order to solve this, use of an aromatic polymer electrolyte having a glass transition temperature (Tg) in the range of 100 to 250 ° C. as a polymer electrolyte membrane has been studied. For example, Patent Document 2 discloses a copolymer having a Tg in the range of 130 to 220 ° C. as a polymer electrolyte. However, the polymer substituted with the biphenyl group has a problem that the durability is lowered.

US Patent Application Publication No. 2002/0091225 JP 2006-342252 A

F. Lufrano et al., “Sulfolated Polysulfone as Prombling Membranes for Polymer Electrolite Fuel Cells,” Science), (USA), John Wiley & Sons, Inc., 2000, 77, p. 1250-1257

  In view of the above-described problems of the prior art, the present invention provides a polymer electrolyte composition capable of forming a high-performance polymer electrolyte membrane that can achieve both durability and bondability with an electrode. As an issue.

  As a result of intensive studies to achieve the above object, the present inventors have found that a polymer electrolyte membrane obtained from a polymer electrolyte composition comprising an aromatic polymer electrolyte and a biphenyl derivative having a specific structure is an electrode. As a result, the present invention has been found to be excellent in bondability with the resin, and also excellent in durability.

  That is, the polymer electrolyte composition of the present invention includes an aromatic polymer electrolyte and a biphenyl derivative represented by the following general formula (A), and a total of 100 masses of the aromatic polymer electrolyte and the biphenyl derivative. %, The biphenyl derivative is 1 to 20% by mass.

In the formula (A), R and R ′ are the same or different and each represents one or more groups selected from the group consisting of a hydrogen atom, an alkyl group, a hydroxy group, an alkoxy group, a hydroxyalkyl group and a carbonylalkyl group. To express. However, R and R ′ are not simultaneously hydrogen atoms. m and n each independently represent an integer of 1 to 5. ]

  The biphenyl derivative represented by the general formula (A) is preferably a para-substituted biphenyl represented by the following general formula (B).

[In Formula (B), P and Q are the same or different and each represents an alkyl group having 3 or more carbon atoms. ]

  The present invention includes a polymer electrolyte membrane obtained from the polymer electrolyte composition, a membrane electrode assembly in which the polymer electrolyte membrane and an electrode are joined, and a fuel cell using the membrane electrode assembly. .

  By using the polymer electrolyte composition of the present invention, it is possible to obtain a polymer electrolyte membrane that achieves both good bondability with the electrode and durability.

  The polymer electrolyte composition of the present invention is characterized in that it contains an aromatic polymer electrolyte and a biphenyl derivative having a specific structure. The biphenyl derivative is represented by the following formula (A). The biphenyl derivative has a high affinity with an aromatic polymer electrolyte described later, and plays a role in plasticizing the polymer electrolyte. For this reason, even if the Tg of the aromatic polymer electrolyte is high, it can be satisfactorily bonded to the electrode by the hot press method.

[In the formula (A), R and R ′ are the same or different and each represents one or more groups selected from the group consisting of a hydrogen atom, an alkyl group, a hydroxy group, an alkoxy group, a hydroxyalkyl group and a carbonylalkyl group. To express. However, R and R ′ are not simultaneously hydrogen atoms. m and n each independently represent an integer of 1 to 5. ]

  Examples of the biphenyl derivative represented by the formula (A) include 4-methylbiphenyl, 4,4′-dimethylbiphenyl, 4-n-propylbiphenyl, 4-isopropylbiphenyl, 4-tert-butylbiphenyl, 4-pentylbiphenyl, 4-acetylbiphenyl, 4,4'-diacetylbiphenyl, 4-propionylbiphenyl, 4,4'-dipropionylbiphenyl, 4-butyrylbiphenyl, 4,4'-butyrylbiphenyl, 4-phenylphenol, 4,4 Examples include '-biphenol. Two or more types of biphenyl derivatives may be used.

  Particularly preferred as the biphenyl derivative is para-substituted biphenyl represented by the following formula (B).

[P and Q in the formula (B) are the same or different and each represents an alkyl group having 3 or more carbon atoms. ]

  Examples of the para-substituted biphenyl represented by the formula (B) include 4,4′-diisopropylbiphenyl, 4,4′-di-tert-butylbiphenyl, 4,4′-dipentylbiphenyl, and the like. It is not limited to. Among these, 4,4'-diisopropylbiphenyl and 4,4'-di-tert-butylbiphenyl are preferable, and 4,4'-di-tert-butylbiphenyl is more preferable.

  In order to exert the plasticizing effect, it is preferable to use the biphenyl derivative in the range of 1 to 20% by mass in a total of 100% by mass of the polymer electrolyte and the biphenyl derivative. More preferably, it is 5-10 mass%. If the amount of the biphenyl derivative is too small, the effect of improving the bonding property with the electrode is reduced, which is not preferable. If the amount is too large, a uniform polymer electrolyte composition film (hereinafter simply referred to as a polymer electrolyte film) is obtained. It is sometimes not desirable.

[Aromatic polymer electrolyte]
The aromatic polyelectrolyte of the present invention has an aromatic ring in the polymer main chain, and this aromatic ring is a single bond, an ether bond, a sulfone bond, an imide bond, a heterocyclic bond, an ester bond, an amide bond, It is a non-fluorine or partially fluorinated ion conductive polymer having a structure bonded with at least one linking group selected from a urethane bond, a sulfide bond, a carbonate bond and a ketone bond.

  Examples of the aromatic polymer having such a structure include polyparaphenylene, polyphenylene oxide, polysulfone, polyethersulfone, polyimide, polyphenylquinoxaline, polybenzoxazole, polybenzthiazole, polybenzimidazole, aromatic polyester, aromatic Polyamide, aromatic polyurethane, polyphenylene sulfide, polyphenylene sulfide sulfone, aromatic polycarbonate, polyaryl ketone, polyether ketone (polyether ketone, polyether ketone ketone, polyether ether ketone, polyether ether ketone ketone, polyether ketone ether Ketone ketone, polyether ketone sulfone) and the like. The polymer electrolyte may be composed of these aromatic polymers alone or in combination of two or more. In particular, aromatic polymers include polyarylene polymers such as poly (p-phenylene) and poly (m-phenylene); polysulfone, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene oxide, polyether sulfone, polyether ketones, and the like. A polyarylene (thio) ether polymer; preferably the polyarylene / polyarylene (thio) ether copolymer, and may have a side chain composed of an aromatic group or an aliphatic group.

  The aromatic polymer constituting the polymer electrolyte of the present invention preferably has an acidic group. Examples of the acidic group include a sulfonic acid group, a phosphonic acid group, a carboxyl group, a sulfonamide group, a sulfonimide group, and derivatives thereof. The aromatic hydrocarbon polymer may be configured to have only one of these acidic groups, or may be configured to have two or more types. In the present invention, it preferably has a sulfonic acid group or a phosphonic acid group. The acidic group may be held at any position of the aromatic hydrocarbon polymer, for example, on the aromatic ring constituting the polymer main chain, on the aromatic group constituting the polymer side chain, or on the aliphatic group. The aspect which has an acidic group is mentioned. The acidic group may be a salt during the formation of the polymer or during the production of the polymer electrolyte membrane, but the salt is eventually converted into proton (H) to form a polymer electrolyte membrane. preferable. Examples of the cation constituting the salt include alkali metal ions such as lithium, sodium and potassium, and monovalent cations such as monoammonium salts. It may be composed of a single type of salt selected from the group of these monovalent cation salts, or may be composed of a plurality of types of salts obtained by combining two or more types.

  The polymer electrolyte used in the present invention may be a segmented block copolymer, a polymer having a long chain chain or a short chain branch (for example, a comb polymer) in addition to the homopolymer or random copolymer of the aromatic polymer. Etc.), and may have a higher order structure such as a star polymer. In particular, the use of a copolymer that can form a co-continuous structure by phase separation of a hydrophilic part and a hydrophobic part, such as a segmented block copolymer, improves the durability and proton conductivity of the polymer electrolyte membrane. Is preferable. Examples of such a segmented block copolymer include a copolymer of a hydrophilic segment having an acidic group or a salt thereof and a hydrophobic segment having no acidic group and a salt thereof. Such a segmented block copolymer can be obtained, for example, by polymerizing an oligomer constituting the segment directly or via another compound.

  Moreover, as a method of polymerizing a monomer component having an acidic group to obtain an aromatic hydrocarbon polymer having an acidic group, for example, an aromatic diamine having an acidic group (such as a sulfonic acid group or a phosphonic acid group) is included. A method of polymerizing a diamine and an aromatic tetracarboxylic dianhydride to obtain an acidic group-containing polyimide; a dicarboxylic acid containing an aromatic dicarboxylic acid having an acidic group, an aromatic diamine diol, an aromatic diamine dithiol, an aromatic A method of polymerizing an aromatic tetramine to obtain an acid group-containing polybenzoxazole, an acid group-containing polybenzthiazole, or an acid group-containing polybenzimidazole; In obtaining a polyetherketone, it has an aromatic dihalide having an acidic group or an acidic group. The method or the like using that aromatic diols. The degree of polymerization tends to be higher when an aromatic dihalide having an acidic group is used than when an aromatic diol having an acidic group is used, and the thermal stability of the aromatic hydrocarbon polymer having an acidic group is higher. Since it becomes high, it is preferable.

  The polymer electrolyte used in the present invention is particularly preferably an aromatic hydrocarbon polymer having a repeating unit represented by the general formula 1.

[In General Formula 1, X represents a —S (═O) ₂ — group or —C (═O) — group, Y represents H or a monovalent cation, Z ¹ represents either an O or S atom, Z ² represents any one of an O atom, an S atom, a —CH ₂ — group, a —C (CH ₃ ) ₂ — group, a —C (CF ₃ ) ₂ — group, a cyclohexylene group, and a direct bond; It represents the above integer. ]

In General Formula 1, when X is a —S (═O) ₂ — group, the solubility in a solvent is improved. When X is a —C (═O) — group, the softening temperature of the polymer can be lowered to further enhance the bonding property with the electrode, or the polymer electrolyte membrane can be imparted with photocrosslinkability. Y is preferably an alkali metal such as Na or K. This is because when Y is an H atom, it is easily decomposed by heat or the like during the production process of the polymer electrolyte membrane. In order to obtain a polymer electrolyte membrane excellent in proton conductivity, it is preferable to finally convert Y to H atoms to obtain a polymer electrolyte membrane. When Z ¹ is an O atom, there are advantages such as little coloring of the polymer and easy availability of raw materials. When Z ¹ is an S atom, the oxidation resistance is improved. When Z ² is an O atom or an S atom, the bondability with the electrode is further improved. When Z ² is a direct bond, the dimensional stability of the obtained polymer electrolyte membrane is improved. n1 is preferably in the range of 1-30. In n1 is 3 or more, and Z ² is the case of the O atoms, bonding between the polymer electrolyte membrane and the electrode is particularly enhanced. In addition, when n1 is 2 or more, Z ² may be composed of different bonding groups.

  The polymer electrolyte used in the present invention is preferably an aromatic polymer containing a repeating unit represented by the general formula 1 together with a repeating unit represented by the general formula 2. Such an aromatic polymer has an appropriate softening temperature, and when it is used as a polymer electrolyte membrane, it bonds well with an electrode.

[In General Formula 2, Ar ¹ represents a divalent aromatic group, Z ³ represents either an O atom or an S atom, Z ⁴ represents an O atom, an S atom, a —CH ₂ — group, —C (CH _{3) 2} - group, -C (CF _{3) 2} - group, cyclohexylene group, either a direct bond, n2 is an integer of 1 or more. ]

In the general formula 2, when Z ³ is an O atom, there are advantages such that the coloring of the polymer is small and the raw materials are easily available. When Z ³ is an S atom, the oxidation resistance is improved. When Z ⁴ is an O atom or an S atom, the bondability is further improved. When Z ⁴ is a direct bond, the dimensional stability of the resulting polymer electrolyte membrane is improved. n2 is preferably in the range of 1 to 30, and when n2 is 2 or more, Z ⁴ may be composed of different linking groups. When n2 is 3 or more and Z ⁴ is an O atom, the bondability between the polymer electrolyte membrane and the electrode is particularly improved.

Ar ¹ in the general formula 2 is preferably a divalent aromatic group having an electron-withdrawing group. The electron-withdrawing group may be a known electron-withdrawing group, and is not particularly limited. For example, sulfo group such as sulfone group, sulfonyl group, sulfonic acid group, sulfonic acid ester group, sulfonic acid amide group, sulfonic acid imide group and derivatives thereof; carboxyl group such as carboxyl group and carboxylic acid ester group and derivatives thereof; carbonyl A cyano group; a halogen group; a perfluoroalkyl group such as a trifluoromethyl group; a nitro group; a phosphine group. These electron withdrawing groups may be used alone or in combination of two or more.

Ar ¹ is preferably represented by the following general formulas 3 to 6. In the case of general formula 3, the solubility of the polymer can be increased. In the case of the general formula 4, the softening temperature of the polymer can be lowered to enhance the bonding property with the electrode, or the photocrosslinking property can be imparted. In the case of the general formulas 5 and 6, the swelling of the polymer can be reduced. Such an effect is larger in the general formula 6. Of the general formulas 3 to 6, the general formula 6 is most preferable.

The polymer electrolyte used in the present invention contains a repeating unit represented by the general formula 1 in addition to a repeating unit represented by the general formula 2, and both Z ¹ and Z ² in the general formula 1 are O atoms. More preferably, it is an aromatic polymer in which n1 is 3 or more. The polymer electrolyte membrane obtained using such an aromatic polymer has particularly improved bondability with the electrode.

In such an aromatic polymer, it is more preferable that Z ³ and Z ⁴ in the general formula 2 are both O atoms, and n2 is 3 or more. The polymer electrolyte membrane obtained by using such an aromatic polymer further improves the bondability with the electrode.

  When the polymer electrolyte used in the present invention is an aromatic polymer mainly composed of a repeating unit represented by the general formula 1 and a repeating unit represented by the general formula 2, the molar ratio of each repeating unit is: It is preferable that it is the range of 7: 93-70: 30. The molar ratio of 7:93 means that when the number of moles of the repeating unit represented by the general formula 1 is 7, the number of moles of the repeating unit represented by the general formula 2 is 93. When the number of repeating units represented by the general formula 1 is larger than the molar ratio of 70:30, the fuel permeability when used as a polymer electrolyte membrane may increase, which is not preferable. When the number of repeating units represented by the general formula 1 is less than the molar ratio of 7:93, it is not preferable because the proton conductivity when the polymer electrolyte membrane is made decreases and the resistance increases. The molar ratio is more preferably in the range of 10:90 to 50:50, and still more preferably in the range of 10:90 to 40:60.

  The polymer electrolyte used in the present invention is more preferably an aromatic hydrocarbon polymer containing a repeating unit represented by general formula 7 in addition to general formula 1 and general formula 2. By using such an aromatic hydrocarbon polymer, it is possible to improve the form stability of the membrane when it is used as a polymer electrolyte membrane.

[In General Formula 7, X represents a —S (═O) ₂ — group or —C (═O) — group, Y represents H or a monovalent cation, and Z ⁵ represents either an O or S atom. To express. ]

The reason why it is preferable that X, Y, and Z ^{5 in the} general formula 7 are the above-described embodiments is the same as the reason described for X, Y, and Z ¹ in the general formula ¹ , respectively.

Such an aromatic hydrocarbon-based polymer has a bonding property between a polymer electrolyte membrane and an electrode, and a membrane when Z ¹ and Z ² in formula 1 are O atoms or S atoms and n1 is 1. This is preferable because the morphological stability becomes better. Further, when Z ³ and Z ⁴ in the general formula 2 are O atoms or S atoms and n2 is 1, the bondability between the polymer electrolyte membrane and the electrode and the morphological stability of the membrane are further improved. This is preferable.

  The polymer electrolyte used in the present invention is an aromatic polymer containing a repeating unit represented by the general formula 8 in addition to the repeating units represented by the general formulas 1, 2, and 7. Further preferred. By using such an aromatic hydrocarbon polymer, the bondability between the polymer electrolyte membrane and the electrode and the morphological stability of the membrane can be greatly improved.

[In General Formula 8, Ar ² represents a divalent aromatic group, and Z ⁶ represents either an O atom or an S atom. ]

In General Formula 8, it is preferable that Z ⁶ is the above-described aspect, and a preferable specific aspect of Ar ² is the same as the reason described for Z ³ and Ar ¹ in General Formula 2, respectively.

  When the polymer electrolyte used in the present invention is an aromatic hydrocarbon polymer having all the repeating units represented by the general formulas 1, 2, 7, and 8, mol% of each repeating unit, and others It is preferable that the mol% of the repeating unit satisfies the following formulas 1 to 3.

0.9 ≦ (n3 + n4 + n5 + n6) / (n3 + n4 + n5 + n6 + n7)
≦ 1.0 (Formula 1)
0.05 ≦ (n3 + n4) / (n3 + n4 + n5 + n6)
≦ 0.7 (Formula 2)
0.01 ≦ (n4 + n6) / (n3 + n4 + n5 + n6)
≦ 0.95 (Formula 3)
(In the above formula, n3 is the mol% of the repeating unit represented by the general formula 7, n4 is the mol% of the repeating unit represented by the general formula 1, and n5 is the mol of the repeating unit represented by the general formula 8. %, N6 represents the mol% of the repeating unit represented by the general formula 2, and n7 represents the mol% of the other repeating unit.)

  If (n3 + n4 + n5 + n6) / (n3 + n4 + n5 + n6 + n7) is smaller than 0.9, good characteristics may not be obtained when a polymer electrolyte membrane is obtained. More preferred is a range of 0.95 to 1.0.

  If (n3 + n4) / (n3 + n4 + n5 + n6) is smaller than 0.05, sufficient proton conductivity may not be obtained when a polymer electrolyte membrane is obtained. On the other hand, if it is greater than 0.7, the swellability of the polymer electrolyte membrane may be remarkably increased.

  (N3 + n4) / (n3 + n4 + n5 + n6) is preferably in the range of 0.07 to 0.5, and more preferably in the range of 0.1 to 0.4.

  When (n4 + n6) / (n3 + n4 + n5 + n6) is less than 0.01, the bondability between the polymer electrolyte membrane and the electrode may be lowered. When it is larger than 0.95, the swelling property of the polymer electrolyte membrane may become too large. The range of 0.05-0.8 is more preferable, and the range of 0.4-0.8 is more preferable.

  In the aromatic polymer, the bonding mode of each repeating unit represented by each general formula is not particularly limited, and examples thereof include random bonding, alternating bonding, and bonding in a continuous block structure. The aromatic polymer may be composed of a single bonding mode or a combination of two or more bonding modes.

[Preferred example of production method of polymer electrolyte]
The aromatic polymer having a repeating unit represented by the above general formula 1 or the like is a monomer represented by the following general formulas 9 to 11 (for example, (activated) dihalogen aromatic compound, aromatic diol, aromatic dithiol. And a dinitroaromatic compound) can be produced by a known method (for example, a polymerization reaction by a known aromatic nucleophilic substitution reaction in the presence of a basic compound). Further, it is preferable to further use a monomer represented by the general formula 12 because physical properties such as film form stability are improved.

[In the general formulas 9 to 12, Z ⁷ and Z ¹⁰ are each independently any one of Cl atom, F atom, I atom, Br atom and nitro group, and Z ⁸ and Z ¹¹ are each independently OH Represents any of a group, SH group, -O-NH-C (= O) -R group, and -S-NH-C (= O) -R group. R represents an aromatic or aliphatic hydrocarbon group. X, Y, Z ² , n1 and Ar ¹ are the same as X, Y, Z ² , n1 and Ar ¹ , respectively. ]

The polymer electrolyte of the present invention preferably has a biphenyl structure. An electrolyte membrane with even better durability and electrode bondability can be obtained. The biphenyl structure may be introduced from any of a monomer in which X in the general formula 9 is a direct bond, a monomer in which Z ^{2 in the} general formula 10 is a direct bond, and a monomer represented by the general formula 12. Or may be introduced from two or more.

  Specific examples of the monomer represented by the general formula 9 include 3,3′-disulfo-4,4′-dichlorodiphenyl sulfone, 3,3′-disulfo-4,4′-difluorodiphenyl sulfone, 3,3 ′. -Disulfo-4,4'-dichlorodiphenyl ketone, 3,3'-disulfo-4,4'-difluorodiphenyl ketone, 3,3'-disulfobutyl-4,4'-dichlorodiphenyl sulfone, 3,3'-disulfobutyl Dihalogen aromatic compounds such as -4,4'-difluorodiphenyl sulfone, 3,3'-disulfobutyl-4,4'-dichlorodiphenyl ketone, 3,3'-disulfobutyl-4,4'-difluorodiphenyl ketone, and these In which the sulfonic acid group forms a salt with a monovalent cation. Specific examples of the cation are as described above.

  Examples of the compound represented by the general formula 9 in which the sulfonic acid group is a salt include sodium 3,3′-disulfonate-4,4′-dichlorodiphenylsulfone, 3,3′-disulfone Sodium salt-4,4′-difluorodiphenylsulfone, sodium 3,3′-disulfonate-4,4′-dichlorodiphenylketone, sodium 3,3′-disulfonate-4,4′-difluorodiphenylketone, 3, 3′-potassium disulfonate-4,4′-dichlorodiphenylsulfone, 3,3′-potassium disulfonate-4,4′-difluorodiphenylsulfone, 3,3′-potassium disulfonate-4,4′-dichlorodiphenyl Examples thereof include ketones and potassium 3,3′-disulfonate-4,4′-difluorodiphenyl ketone.

  Specific examples of the monomer represented by the general formula 10 include 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) methane, and 2,2-bis (4-hydroxyphenyl) hexafluoropropane. Bis (4-hydroxyphenyl) sulfide (4,4′-thiobisphenol), 4,4′-dihydroxydiphenyl ether, 1,1-bis (4-hydroxyphenyl) cyclohexane, 4,4′-dihydroxydiphenyl sulfone (bisphenol) S), aromatic diols such as terminal hydroxyl group-containing phenylene ether oligomers (structures represented by the following general formula 13); 4,4′-thiobisbenzenethiol, 4,4′-oxybisbenzenethiol, etc. Aromatic dithiols and the like, and in particular, bis (4- Hydroxyphenyl) sulfide, 1,1-bis (4-hydroxyphenyl) cyclohexane, terminal hydroxyl group-containing phenylene ether oligomer, 4,4'-thiobisbenzenethiol is preferred.

[In General Formula 13, n is an integer of 1 or more, and a mixture of a plurality of components with different n may be used. ]

  The monomer represented by the general formula 10 increases the flexibility of the polymer electrolyte membrane, and brings about effects such as prevention of breakage against deformation and improvement in bondability with an electrode due to a decrease in glass transition temperature.

  Examples of the monomer represented by the general formula 11 include monomers having a leaving group in a nucleophilic substitution reaction such as halogen or nitro group and an electron-withdrawing group that activates the same aromatic ring. Specifically, 2,6-dichlorobenzonitrile, 2,4-dichlorobenzonitrile, 2,6-difluorobenzonitrile, 2,4-difluorobenzonitrile, 4,4′-dichlorodiphenyl sulfone, 4,4′- Examples include, but are not limited to, activated dihalogen aromatic compounds such as difluorodiphenyl sulfone, 4,4′-difluorobenzophenone, 4,4′-dichlorobenzophenone, and decafluorobiphenyl. In addition, other aromatic dihalogen compounds, aromatic dinitro compounds, aromatic dicyano compounds and the like that are active in aromatic nucleophilic substitution can also be used.

  Examples of the monomer represented by the general formula 12 include aromatic diols such as 4,4'-biphenol and 4,4'-dimercaptobiphenol, and 4,4'-biphenol is particularly preferable.

  In the present invention, other various activated dihalogen aromatic compounds, dinitro aromatic compounds, bisphenol compounds, and bisthiophenol compounds can be used in combination with the monomers represented by the general formulas 9 to 12 as monomers. Examples of the bisphenol compound or bisthiophenol compound include 9,9-bis (4-hydroxyphenyl) fluorene, 9,9-bis (3-methyl-4-hydroxyphenyl) fluorene, and bis (4-hydroxyphenyl). Sulfone, 1,1-bis (4-hydroxyphenyl) ethane, 2,2-bis (4-hydroxyphenyl) butane, 3,3-bis (4-hydroxyphenyl) pentane, 2,2-bis (4-hydroxy) -3,5-dimethylphenyl) propane, bis (4-hydroxy-3,5-dimethylphenyl) methane, bis (4-hydroxy-2,5-dimethylphenyl) methane, bis (4-hydroxyphenyl) phenylmethane, Hydroquinone, resorcin, bis (4-hydroxyphenyl) ketone, 1,4-ben Njichioru, 1,3 benzenedithiol, phenolphthalein, 10- (2,5-dihydroxyphenyl) -9,10-dihydro-9-oxa-10-phosphatonin phenanthrene-10-oxide, and the like. In addition, various aromatic diols or various aromatic dithiols that can be used for polymerization of polyarylene ether compounds by aromatic nucleophilic substitution reaction may be used.

  In addition, as a raw material of the polymer of another embodiment constituting the polymer electrolyte of the present invention, aromatic tetraamino compounds such as 3,3 ′, 4,4′-tetraaminodiphenylsulfone, 3,3′-diaminobenzidine and the like And aromatic dicarboxylic acids having an ionic group such as monosodium 2,5-dicarboxybenzenesulfonate and 3,5-dicarboxyphenylphosphonic acid. Polycondensation can be performed using these monomers to obtain a polyazole polymer electrolyte such as polybenzimidazole.

  Among these, activated dihalogen aromatic compounds, dinitro aromatic compounds, aromatic diols and aromatic dithiols are used as raw materials in the presence of basic compounds such as potassium carbonate by known aromatic nucleophilic substitution reactions. It is preferable to use an aromatic polymer obtained by polymerization as a polymer electrolyte.

  The molecular weight of the polymer electrolyte is not particularly limited, but it is preferable that the number average molecular weight measured by using gel permeation chromatography with polyethylene glycol as a standard is in the range of 10,000 to 500,000. If it is less than 10,000, the physical properties of the film may deteriorate. The larger the molecular weight, the better from the viewpoint of mechanical properties, but if it is too large, the solid content concentration of the polymer electrolyte composition may be lowered when the polymer electrolyte membrane is produced using the polymer electrolyte composition. May not be obtained, and there may be a problem in removing the solvent.

  The softening temperature of the polymer electrolyte is preferably 120 ° C. or higher, and more preferably 140 to 300 ° C. The softening temperature of the mixture of the polymer electrolyte and the biphenyl derivative is also preferably 120 ° C. or higher, and more preferably 140 to 300 ° C.

[Production Method of Polymer Electrolyte Composition]
The method for producing the polymer electrolyte composition of the present invention is not particularly limited. For example, the method may be a method in which the biphenyl derivative is dissolved in the polymer electrolyte solution and then the solvent is removed. Alternatively, the solvent may be removed after mixing with the polymer electrolyte solution in a state of being dissolved or dispersed in advance in the solvent. Moreover, the composition with a solvent may be sufficient.

  Solvents that can be used at this time include aprotic polar solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, sulfolane, diphenylsulfone, N-methyl-2-pyrrolidone, and hexamethylphosphonamide. However, the present invention is not limited to these. Among these, it is preferable to dissolve in N-methyl-2-pyrrolidone, N, N-dimethylacetamide and the like. A plurality of these solvents may be used as a mixture within a possible range. The solid content concentration in the solution is preferably in the range of 0.1 to 50% by mass, more preferably in the range of 5 to 20% by mass, and still more preferably in the range of 5 to 15% by mass. If the solid content concentration in the solution is less than 0.1% by mass, it tends to be difficult to obtain a good molded product, and if it exceeds 50% by mass, the workability tends to deteriorate.

  In addition, when the polymer electrolyte composition of the present invention is produced, additives such as antioxidants, stabilizers, mold release agents and the like used in ordinary polymers are included within the range not contrary to the object of the present invention. It can also be made. Further, when the electrolyte composition of the present invention is produced, or when the electrolyte composition of the present invention is processed or formed into a film or the like, an intermolecular cross-linked structure can be introduced within a range that does not contradict the purpose of the present invention. The intermolecular cross-linked structure here means that the polymer chains are linked to each other by chemical bonds, and can be introduced by irradiating the electrolyte composition with a radiation source such as an electron beam, radiation, or ultraviolet rays. In that case, a well-known crosslinking agent can be used suitably. Further, a known plasticizer can be further contained.

[Method of forming polymer electrolyte composition]
The polymer electrolyte composition of the present invention can be formed into a molded body such as a fiber or a film by any method such as extrusion, spinning, rolling or casting. Among these, it is preferable to mold from a solution dissolved in an appropriate solvent.

  A method of obtaining a molded body from a solution can be performed using a conventionally known method. For example, in addition to heating and drying under reduced pressure, the polymer electrolyte and the biphenyl derivative can be mixed with a solvent (good solvent), but the polymer electrolyte and the biphenyl derivative are immersed in a solvent (poor solvent) that does not dissolve. It is preferable to further extract and remove the good solvent from the polymer electrolyte composition. The poor solvent is preferably distilled off by heating or drying under reduced pressure. At this time, it may be formed into various shapes such as a fiber shape, a film shape, a pellet shape, a plate shape, a rod shape, a pipe shape, a ball shape, and a block shape in a form combined with other compounds as required it can. When combined with a compound having a similar dissolution behavior, it is preferable in that good molding is possible. The acidic group in the molded product thus obtained may contain a salt form with a monovalent cation, but is converted to a free acidic group by acid treatment as necessary. You can also

[Production method of polymer electrolyte membrane]
A polymer electrolyte membrane can also be produced from the polymer electrolyte composition of the present invention. The polymer electrolyte membrane may be not only the polymer electrolyte composition of the present invention but also a composite membrane with a support such as a porous membrane, a nonwoven fabric, fibrils, and paper. The obtained polymer electrolyte membrane can be used as a polymer electrolyte membrane for fuel cells.

  The most preferable method for forming the polymer electrolyte membrane is a cast from a polymer electrolyte composition containing a good solvent. The polymer electrolyte membrane is obtained by removing the good solvent from the cast solution as described above. Can be obtained. The removal of the poor solvent is preferably by drying from the uniformity of the polymer electrolyte membrane. Moreover, in order to avoid decomposition | disassembly and alteration of a polymer electrolyte or a solvent, it can also be dried at the lowest possible temperature under reduced pressure. Further, when the viscosity of the polymer electrolyte composition is high, when the substrate or the composition is heated and cast at a high temperature, the viscosity of the composition is lowered and can be easily cast. The thickness of the cast film of the composition is not particularly limited, but is preferably 10 to 1000 μm. More preferably, it is 50-500 micrometers. If the cast membrane is thinner than 10 μm, it tends to be unable to maintain the form as a polymer electrolyte membrane, and if it is thicker than 1000 μm, a non-uniform polymer electrolyte membrane tends to be easily formed. As a method for controlling the thickness of the cast film, a known method can be used. For example, the thickness of the cast film can be controlled by the amount and concentration of the composition to be cast, such as by using an applicator or doctor blade to make the thickness constant, or using a glass petri dish to make the cast area constant. can do. The cast film can obtain a more uniform film by adjusting the solvent removal rate. For example, when heating, it is preferable to lower the evaporation rate at a low temperature in the first stage. In addition, when the cast film is immersed in a poor solvent such as water, the cast film is allowed to solidify at a suitable time before being immersed in an air atmosphere or an inert gas atmosphere. Can be adjusted.

[Polymer electrolyte membrane]
The polymer electrolyte membrane of the present invention can have any thickness depending on the purpose, but is preferably as thin as possible from the viewpoint of proton conductivity. Specifically, the thickness is preferably 5 to 200 μm, more preferably 5 to 100 μm, and most preferably 20 to 80 μm. If the thickness of the polymer electrolyte membrane is less than 5 μm, the handling of the polymer electrolyte membrane becomes difficult and a short circuit or the like tends to occur when a fuel cell is produced. If the thickness is greater than 200 μm, the electrical resistance value of the polymer electrolyte membrane is high. Therefore, the power generation performance of the fuel cell tends to decrease. When used as a polymer electrolyte membrane, the acidic group in the membrane may contain a monovalent cation salt, but can be converted to a free acidic group by an appropriate acid treatment. In this case, it is also effective to immerse the obtained film in an aqueous solution of sulfuric acid, hydrochloric acid or the like with or without heating. The proton conductivity of the polymer electrolyte membrane is preferably 1.0 × 10 ⁻³ S / cm or more. When the proton conductivity is 1.0 × 10 ⁻³ S / cm or more, a good output tends to be obtained in a fuel cell using the polymer electrolyte membrane, and 1.0 × 10 ⁻³ S If it is less than / cm, the output of the fuel cell tends to decrease.

[Membrane electrode assembly]
By joining the polymer electrolyte membrane of the present invention described above to an electrode, a joined body (membrane electrode assembly) of the polymer electrolyte membrane of the present invention and an electrode can be obtained. As a method for producing this joined body, a conventionally known method can be used. For example, a method of applying an adhesive to the electrode surface and bonding the polymer electrolyte membrane and the electrode, or a polymer electrolyte membrane and the electrode There is a method of heating and pressurizing (hot pressing method). Moreover, the adhesive which has the polymer electrolyte composition of this invention as a main component can also be apply | coated and adhere | attached on the electrode surface. The polymer electrolyte membrane of the present invention has a low softening temperature because the polymer electrolyte is plasticized with a biphenyl derivative. For this reason, a membrane electrode assembly can be easily produced if a hot press method is adopted. The heating temperature in the hot press method is preferably 100 to 250 ° C., and the pressure is preferably 100 to 1000 N / cm ² .

[Fuel cell]
A fuel cell can also be produced using the membrane electrode assembly described above. Since the polymer electrolyte membrane of the present invention is excellent in processability, proton conductivity, and durability, it can be easily produced, has a good output, and can provide a fuel cell excellent in durability. The polymer electrolyte membrane of the present invention is suitable not only for solid polymer fuel cells (PEFC) using hydrogen as a fuel but also for methanol direct fuel cells (DMFC) using methanol as a fuel. Further, it is also suitable for a fuel cell of a type in which hydrogen is extracted from a hydrocarbon such as methanol, gasoline, ether or the like by a reformer.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely using an Example, this invention is not limited to these Examples. Various measurements were performed as follows.

<Ion exchange capacity>
100 mg of the dried polymer electrolyte membrane was immersed in 50 mL of 0.01N NaOH aqueous solution and stirred overnight at 25 ° C. Then, neutralization titration with 0.05N HCl aqueous solution was performed. For neutralization titration, a potentiometric titrator (“COMMITE-980”; manufactured by Hiranuma Sangyo Co., Ltd.) was used. The ion exchange equivalent was calculated by the following formula. The greater the ion exchange capacity, the better the bondability with the electrode.
Ion exchange capacity [meq / g] = (10-titer [mL]) / 2

<Proton conductivity>
A platinum wire (diameter: 0.2 mm) is pressed on the surface of a strip-shaped film sample on a probe for self-made measurement (made of polytetrafluoroethylene), and a constant temperature / humidity oven (“LH-” at 80 ° C. and 95% RH) is used. 20-01 "(manufactured by Nagano Kagaku Kikai Seisakusho Co., Ltd.), and the impedance between the platinum wires was measured by a frequency response analyzer (FREQENCY RESPONSE ANALYSER 1250; manufactured by SOLARTRON). Measured by changing the distance between the electrodes, and calculated the conductivity by canceling the contact resistance between the film and the platinum wire from the slope of the distance measured between the electrodes and the resistance measurement value estimated from the CC plot. did.
Conductivity [S / cm] = 1 / (film width [cm] × film thickness [cm] × resistance interelectrode gradient [Ω / cm])

<Method for evaluating membrane electrode bondability>
After adding 5.0 g of ultrapure water to 2.0 g of a fuel cell catalyst (“TEC61E54”; manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) and stirring it lightly, a 20 mass% Nafion (registered trademark) solution (“Nafion Dispersion DE2021”; Dupont 3.75 g) and 5.0 g of special grade isopropanol were added. Next, a catalyst ink was prepared by stirring with a ball mill until the mixture was completely uniform. Next, the catalyst ink was applied to carbon paper (“TGPH-060”; manufactured by E-Tek) using a coater so that the catalyst amount was 1.0 mg-Pt / cm ^2, and a nitrogen stream The carbon paper in which the catalyst layer was formed was obtained by making it dry gradually under room temperature.

Thereafter, the polymer electrolyte membrane and the carbon paper on which the catalyst layer is formed are laminated so that the catalyst layer is in contact with the membrane surface, and then hot press (“SA-401”; Tester Sangyo Co., Ltd .; polymer electrolyte membrane electrode) Carbon for which a catalyst layer is thermally bonded to one side of a polymer electrolyte membrane by a high-precision hot press; pressure = 780 N / cm ² ; temperature = 200 ° C .; time = 3 minutes) for production of a joined body (abbreviation: MEA) The paper was joined. Thereafter, the carbon paper was peeled off. At this time, if the adhesive force at the interface between the polymer electrolyte membrane and the catalyst layer is weak, the carbon paper is peeled off together with the catalyst layer along with the operation of peeling the carbon paper. On the other hand, when the adhesive force between the polymer electrolyte membrane and the catalyst layer interface is sufficiently strong, only the carbon paper is peeled off.

  By utilizing this phenomenon, the bondability between the polymer electrolyte membrane and the catalyst layer was evaluated. In other words, the remaining ratio of the catalyst layer remaining on the surface of the polymer electrolyte membrane is used as an index for evaluating the adhesion between the polymer electrolyte membrane and the catalyst layer, and “Image J” (software name: version 1.38X) is used. Thus, the joining ratio of the electrode (catalyst layer) was quantified. Specifically, the MEA from which the carbon paper has been peeled is read using a scanner (Docu Center Color f450; manufactured by FUJI XEROX) under the conditions of gray scale and 600 dpi, and using Image J, Image> Rotate> Arbitally After adjusting the angle with, Process> Image Calculator is used to make two gradations, Edit> Invert to reverse the black and white, select the MEA location (720 x 720 pixels), and then calculate the% Area value calculated by Analyze> Measurement It was.

<Method for evaluating methanol resistance of membrane electrode assembly>
The MEA obtained above was immersed in an aqueous 10 mass% methanol solution at 70 ° C. for one week. The MEA after immersion was sandwiched between filter papers and dried, and the bonding ratio of the electrodes was quantified using the same method as in <Method for evaluating membrane electrode bondability>.

Production Example 1 [Polymer electrolyte (P1)]
Sodium 3,3′-disulfonate-4,4′-dichlorodiphenylsulfone (abbreviation: S-DCDPS) 60.4 g (123.0 mmol), 2,6-dichlorobenzonitrile (abbreviation: DCBN) 58.7 g (341) .1 mmol), 4,4′-biphenol (abbreviation: BP) 86.5 g (464.1 mmol), potassium carbonate 73.8 g (533.7 mmol), N-methyl-2-pyrrolidone (abbreviation: NMP) 500 mL, toluene 100 mL was put into a 1000 mL branch flask equipped with a nitrogen introduction tube, a stirring blade, a Dean-Stark trap, and a thermometer, and heated in a nitrogen stream while stirring in an oil bath. After dehydration by azeotropy with toluene at 140 ° C., all toluene was distilled off. Then, it heated up at 200 degreeC and heated for 5 hours. After the reaction solution was cooled to room temperature, it was poured into 3000 mL of pure water to solidify the polymer, and further washed 5 times with pure water to remove NMP and inorganic salts. After separation by filtration, the polymer electrolyte (P1) was obtained by drying under reduced pressure at 120 ° C. for 16 hours. The chemical structure of P1 is shown below. In the following formula, X is K. When the viscosity of P1 was measured with an E-type viscometer, it was about 230 Pa · s. In the following formula, m is 73.5, and n is 26.5.

Production Example 2 [Polymer electrolyte (P2)]
Production Example 1 using 54.1 g (110.1 mmol) of S-DCDPS, 63.5 g (368.5 mmol) of DCBN, 89.2 g (478.6 mmol) of BP, 76.1 g (550.3 mmol) of potassium carbonate, 500 mL of NMP, and 100 mL of toluene. In the same manner as above, a polymer electrolyte (P2) was obtained.

Production Example 3 [Polymer electrolyte (P3)]
S-DCDPS 56.47 g (115.0 mmol), DCBN 54.9 g (318.8 mmol), BP 40.42 g (216.9 mmol), 2,2-bis (4-hydroxyphenyl) hexafluoropropane (abbreviation: 6F-BisA) A polymer electrolyte (P3) was obtained in the same manner as in Production Example 1 using 72.92 g (216.9 mmol), potassium carbonate 65.95 g (477.2 mmol), NMP 500 mL, and toluene 100 mL. The chemical structure of P3 is shown below. In the following formula, X is K.

  That is,

Here, n is 23 and m is 50.

Production Example 4 [Polymer electrolyte (P4)]
S-DCDPS 15.2 g (31.0 mmol), DCBN 17.9 g (103.7 mmol), BP 22.6 g (121.2 mmol), 6F-BisA 4.53 g (13.5 mmol), potassium carbonate 18.4 g ( 133.3 mmol), 125 mL of NMP, and 25 mL of toluene were used in the same manner as in Production Example 1 to obtain a polymer electrolyte (P4). The repeating unit in the chemical structure of P4 is the same as P3, n is 23 and m is 10.

<Test biphenyl derivative>
DPB: 4,4′-diisopropylbiphenyl DTBB: 4,4′-di-tert-butylbiphenyl

Example 1 [Production of polymer electrolyte membrane comprising polymer electrolyte (P1) and biphenyl derivative DPB]
The total amount of biphenyl derivative DPB was 6.1% by mass in 100% by mass of P1 and biphenyl derivative DPB, the total amount was 3 g, and well mixed with 9.0 g of NMP to prepare a polymer electrolyte composition solution. This solution was cast on a glass plate to a thickness of 500 μm, and dried by heating at 100 ° C. for 1 hour and 150 ° C. for 1 hour. Thereafter, the glass plate with the cast film was allowed to cool to near room temperature, and the glass plate with the cast film was immersed in water to peel the film from the glass plate. The peeled membrane is immersed in pure water, then immersed in 1N sulfuric acid for 1 hour to convert the potassium base of sulfonic acid to sulfonic acid group, washed with pure water to remove free sulfuric acid, air dried and polymerized. An electrolyte membrane was obtained.

Examples 2 to 4 [Production of polymer electrolyte membrane comprising polymer electrolyte (P1) and biphenyl derivative]
A polymer electrolyte membrane was obtained in the same manner as in Example 1 except that the amount and type of the biphenyl derivative were changed.

Examples 5 to 6 [Production of polymer electrolyte membrane comprising polymer electrolyte (P3) and a biphenyl derivative]
Example 1 except that P3 was used in place of P1, DPB was 7.4% by mass, or DTBB was 8.2% by mass in a total of 100% by mass of P3 and a biphenyl derivative, and DPB or DTBB was added. In the same manner, a polymer electrolyte membrane was obtained.

Comparative Example 1 [Production of Polymer Electrolyte Membrane Consisting of Polymer Electrolyte (P1) Only]
A polymer electrolyte membrane was obtained in the same manner as in Example 1 except that no biphenyl derivative was added. The appearance of the obtained polymer electrolyte membrane was homogeneous.

Comparative Example 2 [Production of Polymer Electrolyte Membrane Consisting of Polymer Electrolyte (P2) Only]
A polymer electrolyte membrane was obtained in the same manner as in Example 1 except that P2 was used instead of P1 and no biphenyl derivative was added. The appearance of the obtained polymer electrolyte membrane was homogeneous.

Comparative Example 3 [Production of Polymer Electrolyte Membrane Consisting of Polymer Electrolyte (P3) Only]
A polymer electrolyte membrane was obtained in the same manner as in Example 1 except that P3 was used instead of P1 and no biphenyl derivative was added. The appearance of the obtained polymer electrolyte membrane was homogeneous.

Comparative Example 4 [Production of Polymer Electrolyte Membrane Consisting of Polymer Electrolyte (P4) Only]
A polymer electrolyte membrane was obtained in the same manner as in Example 1 except that P4 was used instead of P1 and no biphenyl derivative was added. The appearance of the obtained polymer electrolyte membrane was homogeneous.

  Table 1 shows the evaluation results of the polymer electrolyte membranes obtained in the examples and comparative examples.

  As shown in Table 1, the polymer electrolyte membrane of the present invention exhibits good proton conductivity and exfoliation when immersed in methanol, despite exhibiting proton conductivity equivalent to that of the polymer electrolyte membrane of the comparative example to which no biphenyl derivative is added. It can be seen that the polymer electrolyte membrane has excellent resistance. The electrolyte membranes of Examples 1 and 2 in which DPB was added as a biphenyl derivative plasticizer to the electrolyte membrane of Comparative Example 1 were (a) a high electrode joint ratio, (b) high even after methanol immersion, The bondability of the electrode to the electrolyte membrane was improved. Furthermore, the electrolyte membranes of Examples 3 and 4 using DTBB as a biphenyl derivative plasticizer had higher electrode bondability. This indicates that DTBB has a higher plasticizing effect. Further, from the comparison between Comparative Example 3 and Examples 5 and 6, even when the polymer electrolyte is P3 having a higher electrode bonding ratio than P1, the electrode bonding ratio after immersion in methanol is increased by the addition of DPB or DTBB. It shows that the bondability of the electrode is improved. These improvements in electrode bondability are considered to originate from the interaction between the biphenyl group and the biphenyl compound contained in the polymer electrolyte.

  The polymer electrolyte composition of the present invention can greatly facilitate the production of a polymer electrolyte membrane and an electrode assembly, and can provide a more stable membrane / electrode assembly, which greatly contributes to industrial development.

Claims (5)

An aromatic polymer electrolyte and a biphenyl derivative represented by the following general formula (A) are included, and the total amount of the aromatic polymer electrolyte and the biphenyl derivative is 100% by mass, and the biphenyl derivative is 1 to 20% by mass. A polymer electrolyte composition characterized by comprising:
In the formula (A), R and R ′ are the same or different and each represents one or more groups selected from the group consisting of a hydrogen atom, an alkyl group, a hydroxy group, an alkoxy group, a hydroxyalkyl group and a carbonylalkyl group. To express. However, R and R ′ are not simultaneously hydrogen atoms. m and n each independently represent an integer of 1 to 5. ] The polymer electrolyte composition according to claim 1, wherein the biphenyl derivative represented by the general formula (A) is a para-substituted biphenyl represented by the following general formula (B).
[In Formula (B), P and Q are the same or different and each represents an alkyl group having 3 or more carbon atoms. ]   A polymer electrolyte membrane obtained from the polymer electrolyte composition according to claim 1 or 2.   A membrane electrode assembly, wherein the polymer electrolyte membrane according to claim 3 and an electrode are joined.   A fuel cell comprising the membrane electrode assembly according to claim 4.