Electrolyte membrane and method for producing same, electrolyte membrane with catalyst layer, membrane electrode assembly, solid polymer fuel cell, and solid polymer water electrolysis device

Abstract

This electrolyte membrane includes a crosslinked body of a polymer having a structure represented by formula (1), and the crosslinked body has a crosslinking group directly bonded to an aromatic hydrocarbon ring in a polymer unit. (In formula (1), A1 represents a structural unit represented by formula (a1), A2 represents a structural unit represented by formula (a2), L1 and L2 each represent a single bond or the like, n is an integer of 10-100, and * represents a bond.) (In formula (a1), IExG represents an ion exchange group, L3 represents a single bond or the like, x is an integer of 2-10, and * represents a bond.) (In formula (a2), Ar represents an arylene group having no ion exchange groups, L4 represents a single bond or the like, y is an integer of 3-20, and * represents a bond.)

Description

Electrolyte membrane and method for manufacturing the same, electrolyte membrane with catalyst layer, membrane electrode assembly, polymer electrolyte fuel cell, and polymer electrolyte water electrolysis device.

[0001] This disclosure relates to an electrolyte membrane and a method for producing the same, an electrolyte membrane with a catalyst layer, a membrane electrode assembly, a polymer electrolyte fuel cell, and a polymer electrolyte water electrolysis device.

[0002] In recent years, fuel cells have been attracting attention as a highly energy-efficient new energy technology, driven by environmental concerns. Among them, polymer electrolyte fuel cells, which use polymer materials as electrolytes, are particularly noteworthy because they have a high maximum current density and operate at low temperatures, making them suitable as power sources for mobile devices such as automobiles and small-capacity power sources for portable electronic devices.

[0003] Fluorine-based polymers are known as electrolyte polymers used in polymer electrolyte fuel cells and water electrolysis (see, for example, Patent Document 1). Although fluorine-based polymers are widely used in electrolyte applications due to their high proton conductivity and excellent swelling resistance, they have the problems of being expensive and having a large environmental impact.

[0004] For these reasons, the development of electrolyte polymers that do not use fluorine is also progressing. For example, Patent Document 2 discloses an invention relating to a polymer electrolyte membrane made of a block copolymer containing one or more segments (A1) containing ionic groups and one or more segments (A2) that do not contain ionic groups.

[0005] Japanese Patent Publication No. 11-204119, International Publication No. 2013-031675

[0006] Young Moo Lee, et al., “Synthesis of Crosslinked Sulfonated Poly(phenylene sulfide sulfone nitrile) for Direct Methanol Fuel Cell Applications”, Macromol. Rapid Commun., 30, 2009, pp. 64-68. Matteo Gigli, et al., “Crosslinked sulfonated poly(phenylene sulfide sulfone) membranes for vanadium redox flow batteries”,Sustain. Mater. Technol.,28,2021,e00249.

[0007] However, polymer electrolyte membranes made of non-fluorinated polymers obtained by block copolymerization, as disclosed in Patent Document 2 above, do not necessarily have sufficient proton conductivity.

[0008] One aspect of this disclosure aims to provide an electrolyte membrane having excellent proton conductivity.

[0009] The present invention is as described in the claims, and the present disclosure provides, in several aspects, the following [1] to

[15] .

[0010] [1] The following formula (1): [In formula (1), A １ The following formula (a1): (In formula (a1), IExG indicates an ion exchange group, L ３ These are single bonds, -O-, -S-, -SO ２ - or -CO- is indicated, x is an integer from 2 to 10, and * indicates a combination. Multiple IExG may be the same or different from each other, and multiple L ３ These may be identical or different from each other.) The constituent units are shown as A ２ The following formula (a2): (In formula (a2), Ar represents an arylene group that does not have an ion exchange group, L ４represents a single bond, -O-, -S-, -SO ２ -, or -CO-, y represents an integer from 3 to 20, and * represents a bond. The plurality of Ars may be the same or different from each other, and the plurality of Ls ４ represents a structural unit represented by (where they may be the same or different from each other).) L １ and L ２ each independently represents a single bond, -O-, -S-, or -SO ２ -, n represents an integer from 10 to 100, and * represents a bond. The plurality of As １ may be the same or different from each other, and the plurality of As ２ may be the same or different from each other, and the plurality of Ls １ may be the same or different from each other, and the plurality of Ls ２ may be the same or different from each other. However, the difference in x in formula (a1) among the plurality of As １ is within 3, and the difference in y in formula (a2) among the plurality of As ２ is within 5.] It includes a crosslinked body of a polymer having a structure represented by, and the crosslinked body has a plurality of polymer units derived from the polymer and a crosslinking group that directly binds to the aromatic hydrocarbon ring in the polymer unit and crosslinks the plurality of polymer units to each other, an electrolyte membrane.

[0011] [2] As the crosslinking group, the following formula (c1): [In formula (c1), R １ represents any of a group consisting of an aliphatic hydrocarbon group, an aromatic hydrocarbon group, and a combination thereof, a z １ +1-valent organic group, z １ represents an integer of 1 or more, and * represents a bond. The organic group of R １ may have a part of the carbon atoms substituted with at least one heteroatom selected from the group consisting of an oxygen atom, a nitrogen atom, and a sulfur atom.] The electrolyte membrane according to [1], having a group represented by.

[0012] [3] The L １ and the L ２The electrolyte membrane according to [1] or [2], wherein each of the bonds is independently a single bond, -O-, or -S-.

[0013] [4] Said L ３ However, single bonds or -SO ２ - An electrolyte membrane as described in any of [1] to [3].

[0014] [5] The electrolyte membrane according to any one of [1] to [4], wherein the constituent unit represented by formula (a1) comprises at least one group selected from the group consisting of a sulfonic acid group, an alkyl sulfonic acid group, and a sulfonimide group, and salts thereof, as the ion exchange group.

[0015] [6] The electrolyte membrane according to any one of [1] to [5], wherein the constituent unit represented by formula (a2) comprises, as the arylene group, at least one group selected from the group consisting of a phenylene group, a naphthylene group, and a fluorene group, which may have substituents.

[0016] [7] An electrolyte membrane according to any one of [1] to [6], wherein the ion exchange capacity is 1.0 to 4.0 mmol / g.

[0017] [8] An electrolyte membrane according to any of [1] to [7], wherein the gel fraction obtained from the following formula (I) is 1 to 100%. Gel fraction = (W ２ / W １ ) × 100 ... (I) [In formula (I), W １ and W ２ These values ​​represent the mass of the electrolyte membrane before and after immersion in dimethyl sulfoxide at 25°C for 24 hours, respectively.

[0018] [9] The following formula (1): [In formula (1), A １ The following formula (a1): (In formula (a1), IExG indicates an ion exchange group, L ３ These are single bonds, -O-, -S-, -SO ２ - or -CO- is indicated, x is an integer from 2 to 10, and * indicates a combination. Multiple IExG may be the same or different from each other, and multiple L ３These may be identical or different from each other.) The constituent units are shown as A ２ The following formula (a2): (In formula (a2), Ar represents an arylene group that does not have an ion exchange group, L ４ These are single bonds, -O-, -S-, -SO ２ - or -CO- is indicated, y is an integer from 3 to 20, and * indicates a combination. Multiple Ars may be the same or different from each other, and multiple L ４ These may be identical or different from each other.) The constituent units are shown as L １ and L ２ These are, independently, a single bond, -O-, -S-, or -SO-. ２ - indicates a combination, n is an integer between 10 and 100, and * indicates a combination. Multiple A １ They may be the same or different from each other, and there are multiple A ２ These may be the same or different from each other, and there are multiple L １ These may be the same or different from each other, and there are multiple L ２ They may be the same or different from each other. However, multiple A １ The difference of x in equation (a1) is 3 or less, and multiple A ２ A method for producing an electrolyte membrane, comprising the steps of: preparing an uncrosslinked membrane containing a polymer having a structure represented by ] and a crosslinking agent; and crosslinking the polymer with the crosslinking agent by a Friedel-Crafts reaction.

[0019]

[10] The crosslinking agent is of the following formula (2): [In formula (2), R １ z is one of the following groups: an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof. １ It shows a +1 valent organic group, z １ X represents an integer greater than or equal to 1. １ R represents a halogen atom or a hydroxyl group. １The organic group may have some of its carbon atoms replaced by at least one heteroatom selected from the group consisting of oxygen, nitrogen, and sulfur atoms, and multiple X １ The method for producing an electrolyte membrane according to [9], comprising at least one selected from the group consisting of a compound represented by ] and an intramolecular condensate of said compound.

[0020]

[11] The method for producing an electrolyte membrane according to [9] or

[10] , wherein the content of the crosslinking agent in the uncrosslinked membrane is 0.01 to 20 parts by mass per 100 parts by mass of the polymer.

[0021]

[12] An electrolyte membrane with a catalyst layer, comprising an electrolyte membrane according to any one of [1] to [8] and a catalyst layer disposed on one or both sides of the electrolyte membrane.

[0022]

[13] A membrane electrode assembly comprising an electrolyte membrane according to any one of [1] to [8] and an electrode layer disposed on one or both sides of the electrolyte membrane.

[0023]

[14] A polymer electrolyte fuel cell comprising the membrane electrode assembly described in

[13] .

[0024]

[15] A solid polymer water electrolysis apparatus comprising the membrane electrode assembly described in

[13] .

[0025] According to one aspect of this disclosure, it is possible to provide an electrolyte membrane having excellent proton conductivity.

[0026] The following describes exemplary embodiments of this disclosure. However, this disclosure is not limited to the embodiments described below. In this specification, numerical ranges indicated using "~" indicate a range that includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively. Also, unless otherwise explicitly stated, the units of the numerical values ​​before and after "~" are the same. Furthermore, each configuration and parameter disclosed in this specification can be combined in any way, and the upper and lower limits described individually can be combined in any way.

[0027] <Electrolyte Membrane> The electrolyte membrane of one embodiment (hereinafter also referred to as "electrolyte membrane (E)") includes a crosslinked polymer (hereinafter also referred to as "polymer (P)") having a structure represented by the following formula (1). The crosslinked polymer (L) has a plurality of polymer units (hereinafter also referred to as "polymer units (P')") derived from polymer (P), and a crosslinking group that is directly bonded to an aromatic hydrocarbon ring in the polymer units (P') and crosslinks the plurality of polymer units (P') to each other.

[0028]

[0029] In formula (1), A １ This is a constituent unit represented by the following formula (a1) (hereinafter referred to as "constituent unit A １ It is also called ". ) and A ２ This is a constituent unit represented by the following formula (a2) (hereinafter referred to as "constituent unit A ２ It is also called ". ) indicates L １ and L ２ These are, independently, a single bond, -O-, -S-, or -SO-. ２ - indicates a combination, n is an integer between 10 and 100, and * indicates a combination. Multiple A １ They may be the same or different from each other, and there may be multiple A ２ These may be the same or different from each other, and there may be multiple L １ These may be the same or different from each other, and there may be multiple L ２ They may be the same or different from each other. However, multiple A １ The difference of x in equation (a1) in is 3 or less, and multiple A ２ The difference of y in equation (a2) is within 5.

[0030]

[0031] In formula (a1), IExG represents an ion exchange group, and L ３ These are single bonds, -O-, -S-, -SO ２ - or -CO- is indicated, x is an integer from 2 to 10, and * is an association. Multiple IExG may be the same or different from each other, and multiple L ３ They may be the same or different from one another.

[0032]

[0033] In formula (a2), Ar represents an arylene group that does not have an ion exchange group, and L ４ These are single bonds, -O-, -S-, -SO ２ - or -CO- is indicated, y is an integer from 3 to 20, and * indicates a combination. Multiple Ars may be the same or different from each other, and multiple L ４ They may be the same or different from one another.

[0034] The electrolyte membrane (E), containing a crosslinker (L), exhibits excellent proton conductivity, and tends to show even better proton conductivity in high-humidity environments (e.g., humidity above 80% RH). The reason for this effect is not clear, but it is speculated that the polymer (P) contains multiple A １ Since the difference of x in equation (a1) is within 3, multiple hydrophilic constituent units A １ These are identical or have similar molecular sizes, and multiple A ２ Since the difference of y in equation (a2) is within 5, multiple hydrophobic constituent units A ２ These are identical or have similar molecular sizes. In other words, polymer (P) is composed of multiple hydrophilic constituent units A that are identical or have similar molecular sizes. １ (Hydrophilic part) and multiple hydrophobic constituent units A that are identical to or have similar molecular sizes to each other. ２ The polymer has a structure in which hydrophobic regions are precisely arranged, and the ion exchange groups are arranged at approximately equal intervals. It is presumed that the ion exchange groups in the polymer unit self-assemble in a higher-order structure, inducing a microphase separation structure. This is presumed to result in the formation of good proton conduction paths within the crosslinked material (L), leading to excellent proton conductivity.

[0035] The proton conductivity of the electrolyte membrane (E) is, for example, 135 mS / cm or higher in an environment of 80°C and 100% relative humidity, and may be 150 mS / cm or higher, 170 mS / cm or higher, or 180 mS / cm or higher.

[0036] Furthermore, because the electrolyte membrane (E) contains a crosslinker (L), it tends to exhibit superior swelling resistance compared to a membrane made of polymer (P). For example, the volume swelling rate of the electrolyte membrane (E) measured by the method of the example may be 110% or less, 100% or less, 90% or less, 80% or less, or 50% or less. The reason why the crosslinker (L) provides superior swelling resistance is not clear, but it is presumed that crosslinking makes the polymer network denser, suppressing the penetration of water into the polymer, and that the amount of water that can be contained inside the polymer decreases due to the reduction in free volume. In addition, there is no particular lower limit to the volume swelling rate of the electrolyte membrane (E), but it may be 5% or more, 10% or more, 15% or more, or 20% or more. The volume swelling rate of the electrolyte membrane (E) may be 5 to 110%, and may also be 10 to 100%, 15 to 100%, 20 to 90%, 20 to 80%, or 20 to 50%.

[0037] (Polymer (P)) Polymer (P) is represented by the above formula (1), and is composed of constituent units A １ and constituent unit A ２ and the linking group (L １ or L ２ The structure has a continuous repeating structure (the structure in brackets in formula (1)) via a ). The number of repeats (n) of the structure is 10 to 100, and may be 15 or more, 20 or more, 80 or less, or 50 or less. When the number of repeats (n) is 15 or more, it tends to have excellent gas barrier properties, and when the number of repeats (n) is 50 or less, it tends to have excellent solubility in solvents and film-forming properties. From these viewpoints, the number of repeats (n) of the structure may be 15 to 80, or 20 to 50.

[0038] The polymer (P) forms a crosslinked product (L) by, for example, a Friedel-Crafts reaction with a crosslinking agent. This reaction is known in the art (for example, see Non-Patent Document 1 for the Friedel-Crafts acylation reaction and Non-Patent Document 2 for the Friedel-Crafts alkylation reaction). The specific conditions for this reaction may follow the conditions in the electrolyte membrane manufacturing method described later. When a crosslinked product (L) is formed by a Friedel-Crafts reaction, multiple Ls in the polymer (P)１ , L ２ and L ４ At least one of them is preferably a single bond, -O- or -S-. The carbon atoms of the arylene group adjacent to these linking groups (single bond, -O- or -S-) (for example, the carbon atoms located at the ortho position of the linking group) tend to have a high electron density and are likely to undergo a Friedel-Crafts reaction (electrophilic substitution reaction) with a crosslinking agent (acylating agent or alkylating agent).

[0039] [Structural unit A １ Structural unit A １ has a structure in which an aromatic ring having an ion exchange group (IExG) is continuous via a linking group (L ３ ). Here, the ion exchange group means a group having the property of being able to exchange ions with other ions by releasing an ion (for example, a cation), and is also called an ionic group. The ion exchange group may be a protonic acid group. Examples of the ion exchange group include a sulfonic acid group, an alkylsulfonic acid group, a perfluoroalkylsulfonic acid group, a sulfonimide group, a phosphonic acid group, a phosphoric acid group, and a carboxy group, and salts thereof. As described above, the ion exchange group includes those that form salts with metal ions and the like.

[0040] The sulfonic acid group and its salts are represented by, for example, -SO ３ M １／ｑ (M represents H or at least one selected from the group consisting of metals (for example, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Ti, Al, Fe, Pt, Rh, Ru, Ir, and Pd), and q represents the valence of M (for example, an integer of 1 to 4).). The metal represented by M exists as an ion (cation) and forms a salt with -SO ３ － .

[0041] The alkylsulfonic acid group and its salts are represented by, for example, -R ４ SO ３ M １／ｑ . R ４ is an alkanediyl group, and from the viewpoint of obtaining better proton conductivity, its carbon number is preferably 1 to 12 (an integer). R ４Specific examples thereof include, for example, a methylene group, a butane-1,4-diyl group, and a hexane-1,6-diyl group. M and q have the same meanings as described above.

[0042] The sulfonimide group and its salts are, for example, -SO ２ NM １／ｑ SO ２ R ５ represented by. R ５ is an alkyl group, and from the viewpoint of obtaining more excellent proton conductivity, the number of carbon atoms thereof is preferably 1 to 6 (integers). Specific examples of R ５ include a methyl group, an ethyl group, and a propyl group. M and q have the same meanings as described above.

[0043] The structural unit A １ preferably contains, as an ion exchange group, at least one group selected from the group consisting of a sulfonic acid group, an alkylsulfonic acid group, a sulfonimide group, and salts thereof, from the viewpoint of obtaining more excellent proton conductivity, and more preferably contains at least one group selected from the group consisting of a sulfonic acid group and its salts. When the structural unit A １ contains a sulfonic acid group as an ion exchange group, in addition to the above effects, the sulfonic acid group functions as an acid catalyst, and an effect such as the use of an acid catalyst in the above Friedel-Crafts reaction becomes unnecessary is also obtained. From the same viewpoint, it is more preferable that the majority of the plurality of ion exchange groups in the structural unit A １ are those in the above preferred embodiments, and it is particularly preferable that all of the plurality of ion exchange groups in the structural unit A １ are those in the above preferred embodiments.

[0044] The structural unit A １ preferably contains, as a linking group (L ３ ), at least one group selected from the group consisting of -SO ２ - and --CO--, from the viewpoint of obtaining more excellent proton conductivity, and more preferably contains -SO ２ -. From the same viewpoint, among the plurality of linking groups (L １ present in the structural unit A ３It is even more preferable that the majority of these are of the above-described preferred embodiment.

[0045] Constituent unit A １ The linking group inside (L ３ ) is used in order to improve proton conductivity and chemical durability, with single bonds or -SO ２ - is preferable.

[0046] Linking group (L ３ The bonding position of the constituent unit A is not particularly limited, but from the viewpoint of obtaining better proton conductivity and chemical durability, it is preferable that it be located in the ortho or meta position relative to the ion exchange group. １ It is preferable that it contains a 1,4-phenylene group having an ion exchange group.

[0047] Constituent unit A １ In formula (a1), the number of repeating structures (x) in brackets [ ] is preferably 2 to 8, more preferably 3 to 5, from the viewpoint of obtaining better proton conductivity, excellent resistance to hot water, and increasing the degree of crosslinking of the crosslinked material.

[0048] Constituent unit A １ From the viewpoint of obtaining superior proton conductivity, it is preferable that the structure includes at least one structure selected from the group consisting of the structure represented by the following formula (a1-1) (hereinafter referred to as "structure (a1-1)"), the structure represented by the following formula (a1-2) (hereinafter referred to as "structure (a1-2)"), and the structure represented by the following formula (a1-3) (hereinafter referred to as "structure (a1-3)").

[0049]

[0050]

[0051]

[0052] In formulas (a1-1), (a1-2), and (a1-3), IExG and * have the same meaning as described above. In formula (a1-3), L ３１ x represents -O- or -S-. Multiple IExGs may be the same or different from each other. １x represents an integer between 2 and 10, and x in equation (a1-2) ２ x represents an integer between 2 and 5, and x in equation (a1-3) ３ This represents an integer between 1 and 2. However, the constituent unit A １ If it includes two or more structures selected from the group consisting of structure (a1-1), structure (a1-2), and structure (a1-3), then x １ , 2x ２ (2 and x ２ (product of) and 4x ３ (4 and x) ３ The sum of the product of x is between 6 and 10. １ From the viewpoint of obtaining better proton conductivity, excellent resistance to hot water, and increasing the degree of crosslinking of the crosslinked material, it is preferably 2 to 5, more preferably 2 to 3. ２ From the viewpoint of obtaining better proton conductivity, excellent resistance to hot water, and increasing the degree of crosslinking of the crosslinked material, it is preferably 2 to 3, and more preferably 2. ３ From the viewpoint of obtaining better proton conductivity, excellent resistance to hot water, and increasing the degree of crosslinking of the crosslinked material, it is preferably 1.

[0053] Constituent unit A １ It may consist only of structure (a1-1), or it may include structure (a1-1) and structures other than structure (a1-1). In the latter case, structure (a1-1) and structures other than structure (a1-1) are linking groups (L ３ They may be connected by ). Similarly, constituent unit A １ It may consist only of structure (a1-2), or it may include structure (a1-2) and structures other than structure (a1-2). In the latter case, structure (a1-2) and structures other than structure (a1-2) are linking groups (L ３ They may be connected by ). Similarly, constituent unit A １ It may consist only of structure (a1-3), or it may include structure (a1-3) and structures other than structure (a1-3). In the latter case, structure (a1-3) and structures other than structure (a1-3) are linking groups (L ３ They may be connected by ).

[0054] Constituent unit A １This may be a constituent unit represented by any of the following formulas (A1-1) to (A1-4).

[0055]

[0056] IExG and * in formulas (A1-1) to (A1-4), and L in formulas (A1-2) to (A1-4). ３ This is synonymous with the above. Multiple IExG may be the same or different from each other. Multiple L ３ They may be the same or different from one another.

[0057] Constituent unit A １ From the viewpoint of obtaining better proton conductivity and excellent chemical durability, it is preferable that the constituent unit is one of those represented by formulas (A1-1) to (A1-4), and more preferably that it is the constituent unit represented by formula (A1-2). L in formula (A1-2) ３ From the viewpoint of improving proton conductivity and chemical durability, it is preferable that the bond be a single bond.

[0058] Multiple constituent units A in equation (1) １ At least one of them may be one of those exemplified above, and multiple constituent units A １ The majority of these may be those exemplified above, and multiple constituent units A １ All of these may be examples given above.

[0059] Multiple constituent units A in equation (1) １ This is a range where the difference of x in equation (a1) is 3 or less, and there are two or more constituent units A １ It may consist of multiple constituent units A. １ From the viewpoint of obtaining better proton conductivity, the number of types is preferably three or less, and more preferably two or less.

[0060] Multiple constituent units A in equation (1) １ The difference of x in equation (a1) is preferably as close to 0 as possible from the viewpoint of obtaining better proton conductivity, but may be within 2, within 1, or 0.

[0061] [Construction Unit A] ２ ] Component Unit A ２In this case, the arylene group (Ar) which does not have an ion exchange group is linked to the L group. ４ It has a continuous structure via ).

[0062] The arylene group is a divalent aromatic hydrocarbon group and has a structure obtained by removing two hydrogen atoms from a monocyclic or condensed polycyclic aromatic hydrocarbon. The number of aromatic rings in the arylene group is preferably 1 to 4, more preferably 1 to 2, and even more preferably 1, from the viewpoint of solubility in solvents, film-forming ability, and obtaining better proton conductivity. The arylene group may have substituents other than ion exchange groups. Examples of substituents include alkyl groups and aryl groups. The alkyl group may be at least one group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and dodecyl groups. An example of an aryl group is the phenyl group. When the arylene group has an aryl group as a substituent, the number of aromatic rings in the arylene group includes the number of aromatic rings in the substituent.

[0063] An unsubstituted arylene group may be at least one group selected from the group consisting of phenylene, naphthylene, fluorene, anthracylene, phenanthrylene, triphenylene, pyrenylene, and tetracenylene groups. A substituted arylene group may be at least one group selected from the group consisting of diphenylfluorene, methylphenylene, ethylphenylene, dimethylfluorene, diethylfluorene, dipropylfluorene, diisopropylfluorene, dibutylfluorene, dipentylfluorene, dihexylfluorene, diheptylfluorene, dioctylfluorene, dinonylfluorene, didecylfluorene, diundecylfluorene, and didodecylfluorene groups. Note that a fluorene group as an arylene group means a divalent fluorene group (for example, a fluorene-2,7-diyl group).

[0064] Constituent unit A ２From the viewpoint of solubility in the solvent, film-forming properties, and the degree of crosslinking of the crosslinked material, it is preferable that the arylene group contains at least one group selected from the group consisting of phenylene, naphthylene, and fluorene groups, which may have substituents, and it is more preferable that the arylene group contains at least one group selected from the group consisting of phenylene, naphthylene, and fluorene groups, which may have an aryl group as a substituent. Constituent Unit A ２ From the viewpoint of further improving solubility in the solvent and film-forming properties, it is more preferable to contain a phenylene group, and even more preferable to contain a 1,4-phenylene group. From a similar viewpoint, constituent unit A ２ It is particularly preferable that the majority of the multiple arylene groups present in the constituent unit A are of the above preferred embodiment. ２ It is extremely preferable that all of the multiple arylene groups present are independently phenylene groups, naphthylene groups, or fluorene groups, which may each have substituents.

[0065] Constituent unit A ２ From the viewpoint of increasing the degree of crosslinking of the crosslinked body, the linking group (L ４ It is preferable that the constituent unit A includes at least one group selected from the group consisting of a single bond, -O-, or -S-, and more preferably includes -O- or -S-. From a similar viewpoint, constituent unit A ２ Multiple linking groups (L) present inside ４ It is even more preferable that the majority of these are of the above-described preferred embodiment.

[0066] Constituent unit A ２ From the viewpoint of having excellent solubility in solvents and film-forming properties, as well as excellent mechanical strength of the electrolyte membrane, the linking group (L ４ ) as a single bond, -SO ２ Preferably, it contains at least one group selected from the group consisting of - and -CO-, and -SO ２ It is more preferable to include - or -CO-.

[0067] Constituent unit A ２ The linking group inside (L ４From the viewpoint of increasing the degree of crosslinking of the crosslinked material, and from the viewpoint of having excellent solubility in the solvent and film-forming properties, as well as excellent mechanical strength of the electrolyte membrane, the materials used are single bonds, -O-, -S-, or -SO ２ It is preferable that it be -, a single bond, -O- or -SO ２ - is preferable.

[0068] Constituent unit A ２ In formula (a2), the number of repeating structures (y) in the brackets [ ] is preferably 4 to 12, more preferably 5 to 10, from the viewpoint of obtaining better proton conductivity, excellent resistance to hot water, and increasing the degree of crosslinking of the crosslinked body.

[0069] Constituent unit A ２ In formula (a2), the number of repeating structures (y) in the brackets [ ] is preferably 2 to 7 more than the number of repeating structures (x) in formula (a1) (x + (2 to 7)), from the viewpoint of achieving both superior proton conductivity and resistance to hot water, and from the viewpoint of increasing the degree of crosslinking of the crosslinked body.

[0070] Constituent unit A ２ The number of aromatic rings in the main chain is preferably 4 to 21, more preferably 5 to 13, and even more preferably 6 to 11, from the viewpoint of obtaining better proton conductivity.

[0071] Constituent unit A ２ From the viewpoint of having excellent solubility in solvents and film-forming properties, as well as excellent mechanical strength of the electrolyte membrane, it is preferable that the material includes at least one structure selected from the group consisting of the structure represented by the following formula (a2-1) and the structure represented by the following formula (a2-2).

[0072]

[0073]

[0074] In formulas (a2-1) and (a2-2), Ar and * have the same meanings as described above. Multiple Ars may be the same or different from one another.

[0075] Constituent unit A including the above structure ２ A concrete example of this is the constituent unit represented by the following formula (A2-1).

[0076]

[0077] Ar, L in equation (A2-1) ４ And * are the same as above, Q indicates the base of the structure represented by formula (a2-1) or formula (a2-2), and y １ and y ２ Each of these independently represents an integer between 2 and 4. １ and y ２ From the viewpoint of obtaining better proton conductivity, excellent resistance to hot water, and increasing the degree of crosslinking of the crosslinked body, it is preferably 2 to 3. The multiple Ars may be the same or different from each other, and multiple L ４ They may be the same or different from one another.

[0078] Constituent unit A including the above structure ２ This may be a constituent unit represented by any of the following formulas (A2-2) to (A2-7).

[0079]

[0080] The * in equations (A2-2) to (A2-7) has the same meaning as above. The R in equations (A2-4) and (A2-6) ３ R represents an alkyl group, and from the viewpoint of obtaining better proton conductivity, its carbon number is preferably 1 to 12 (an integer). ３ Specific examples include methyl, ethyl, propyl, hexyl, and dodecyl groups. In formulas (A2-4) and (A2-6), multiple R ３ They may be the same or different from one another.

[0081] Multiple constituent units A in equation (1) ２ At least one of them may be one of those exemplified above, and multiple constituent units A ２ The majority of these may be those exemplified above, and multiple constituent units A ２ All of these may be examples given above.

[0082] Multiple constituent units A in equation (1) ２ This is a range where the difference of y in equation (a2) is 5 or less, and there are two or more constituent units A ２It may be composed of these elements.

[0083] Multiple constituent units A in equation (1) ２ In equation (a2), the difference of y is preferably as close to 0 as possible from the viewpoint of obtaining better proton conductivity, and may be 4 or less, 3 or less, 2 or less, 1 or less, or 0.

[0084] Multiple constituent units A in equation (1) ２ The difference in the number of aromatic rings in the main chain in formula (a2) is preferable to be close to 0 from the viewpoint of obtaining better proton conductivity, and may be 5 or less, 4 or less, 3 or less, 2 or less, 1 or less, or 0. From a similar viewpoint, the multiple constituent units A in formula (1) ２ The difference in the number of aromatic rings in formula (a2) is preferably as close to 0 as possible, and may be 5 or less, 4 or less, 3 or less, 2 or less, 1 or less, or 0.

[0085] [Connecting group] Polymer (P) is a constituent unit A from the viewpoint of increasing the degree of crosslinking of the crosslinked product. １ and constituent unit A ２ Linking group between (L １ or L ２ It is preferable that the polymer (P) contains at least one group selected from the group consisting of a single bond, -O-, or -S-. From a similar viewpoint, multiple constituent units A present in the polymer (P) １ and constituent unit A ２ Linking group between (L １ and L ２ It is more preferable that the majority of these are of the above preferred embodiment, and that there are multiple constituent units A in the polymer (P). １ and constituent unit A ２ Linking group between (L １ and L ２ It is even more preferable that all of ) are of the above preferred embodiment. That is, L １ and L ２ However, it is even more preferable that each of them be a single bond, -O-, or -S- independently.

[0086] The polymer (P) may consist of a structure represented by formula (1) and terminal structures bonded to the structure. The polymer (P) may be a compound represented by any of the following formulas (1-1) to (1-3).

[0087]

[0088] A in equations (1-1) to (1-3) １ A ２ , L １ , L ２ and n are the same as above. However, in equations (1-1) and (1-2), Z ２ L that joins ２ This is a single bond. Z １ and Z ２ Each of these independently represents a hydroxyl group, a thiol group, a halogen atom, a boronic acid group, an alkylborane group, or a boronic acid ester group. Examples of halogen atoms include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). Examples of alkylborane groups include diethylborane, diciamilborane, dicyclohexylborane, and 9-borabicyclo[3.3.1]nonane. Examples of boronic acid ester groups include pinacol boronic acid ester, 1,3-propanediol boronic acid ester, biscyclohexyldiol boronic acid ester, neopentyl glycol boronic acid ester, and catechol boronic acid ester.

[0089] Polymer (P) may contain a plurality of polymer units (hereinafter also referred to as "polymer unit A") that include the structure represented by formula (1). For example, polymer (P) may contain three or more polymer units A and terminal crosslinking groups that bond to the terminal structures of three or more polymer units A. Note that polymer unit A may, for example, have terminal groups Z from any of the compounds represented by formulas (1-1) to (1-3) above. １ and Z ２ The structure may have the excluding of the terminal crosslinking group. The terminal crosslinking group may be a group derived from a known crosslinkable compound (e.g., decafluorobiphenyl). If the terminal crosslinking group has an aromatic ring, the terminal structure of polymer unit A is either directly connected to the aromatic ring of the terminal crosslinking group, or to -O-, -S-, or -SO ２ They may be bonded via a -. The number of terminal crosslinking groups may be one or more. The multiple terminal crosslinking groups may be the same or different from each other.

[0090] The proportion of the structure represented by formula (1) in the entire polymer (P) is preferably 80% by mass or more, from the viewpoint of obtaining better proton conductivity. From a similar viewpoint, the proportion of the structure represented by formula (1) in the entire polymer (P) may be 85% by mass or more, or 90% by mass or more. The proportion of the structure represented by formula (1) in the entire polymer (P) may be less than 100% by mass. The proportion of the structure represented by formula (1) in the entire polymer (P) may be 80% by mass or more and less than 100% by mass, 85% by mass or more and less than 100% by mass, or 90% by mass or more and less than 100% by mass.

[0091] The polymer (P) may contain fluorine atoms, but the fluorine content in the polymer (P) is preferably 5% by mass or less, and it is preferable that the polymer (P) does not contain fluorine atoms (the fluorine content is below the detection limit).

[0092] The number-average molecular weight of the polymer (P) may be 20,000 or more, 25,000 or more, or 30,000 or more from the viewpoint of superior proton conductivity and superior mechanical strength of the electrolyte membrane, and may be 300,000 or less, 200,000 or less, or 150,000 or less from the viewpoint of superior solubility in the solvent and film formation. From these viewpoints, the number-average molecular weight of the polymer (P) may be 20,000 to 300,000, 25,000 to 200,000, or 30,000 to 150,000.

[0093] The weight-average molecular weight of polymer (P) may be 40,000 or more, 50,000 or more, 60,000 or more, or 100,000 or more from the viewpoint of superior proton conductivity and superior mechanical strength of the electrolyte membrane, and may be 500,000 or less, 300,000 or less, 200,000 or less, 120,000 or less, or 80,000 or less from the viewpoint of superior solubility in solvents and film formation. From these viewpoints, the weight-average molecular weight of polymer (P) may be 40,000 to 500,000, 50,000 to 300,000, 60,000 to 200,000, 60,000 to 120,000, 100,000 to 120,000, or 60,000 to 80,000.

[0094] The ratio of the weight-average molecular weight to the number-average molecular weight of the polymer (P) (polydispersity) may be 1.5 or higher, and may be 2.0 or higher, 2.5 or higher, or 2.8 or higher. When the polydispersity of the polymer (P) is 2.5 or higher, excellent swelling resistance tends to be obtained. From the viewpoint of solubility in the solvent, the polydispersity of the polymer (P) may be 20.0 or lower, and may be 15.0 or lower, 10.0 or lower, 5.0 or lower, or 2.5 or lower. The polydispersity of the polymer (P) may be 1.5 to 20.0, 2.0 to 20.0, 2.5 to 20.0, 2.5 to 15.0, 2.8 to 10.0, 1.5 to 5.0, or 1.5 to 2.5.

[0095] The number-average molecular weight and weight-average molecular weight of polymer (P) are measured by gel permeation chromatography (GPC) and are expressed as standard polyethylene glycol / oxide (PEG / PEO) equivalent values.

[0096] Polymer (P) can be obtained, for example, by reacting (polymerizing) a compound represented by the following formula (b1) (hereinafter also referred to as "compound (b1)") with a compound represented by the following formula (b2) (hereinafter also referred to as "compound (b2)"). That is, polymer (P) can be a polymer of compound (b1) and compound (b2).

[0097]

[0098] In formula (b1), A １ This is synonymous with the above, Y １ｂ and Y ２ｂ Each of these independently represents a halogen atom. Examples of halogen atoms include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

[0099]

[0100] In formula (b2), A ２ This is synonymous with the above, Z １ｂ and Z ２ｂEach of these independently represents a hydroxyl group, a thiol group, a halogen atom, a boronic acid group, an alkylborane group, or a boronic acid ester group. Examples of halogen atoms, alkylborane groups, and boronic acid ester groups are given above, Z １ and Z ２ These are the same examples as halogen atoms, alkylborane groups, and boronic acid ester groups represented by .

[0101] In the above method, constituent unit A １ and constituent unit A ２ A structure in which these are arranged alternately (a repeating structure) can be formed throughout the polymer. Therefore, according to the above method, the number of repeats n in formula (1) can be easily set to 10 or more.

[0102] According to the above method, L in equation (1) １ and L ２ A polymer (P) is obtained in which the bonds are -O-, -S-, or single bonds. Specifically, Z １ｂ and Z ２ｂ If at least one of them is a hydroxyl group, then L in formula (1) １ and L ２ A polymer (P) is obtained in which at least one of the elements is -O-, Z １ｂ and Z ２ｂ If at least one of them is a thiol group, then L in formula (1) １ and L ２ A polymer (P) is obtained in which at least one of the elements is -S-, Z １ｂ and Z ２ｂ If at least one of them is a halogen atom, a boronic acid group, an alkylborane group, or a boronic acid ester group, then L in formula (1) １ and L ２ A polymer (P) is obtained in which at least one of the bonds is a single bond.

[0103] In the above method, A is calculated within the range where the difference of x in equation (a1) is 3 or less. １ The method involves using multiple types of compounds (b1) with different structures, and ensuring that the difference in y in formula (a2) is within 5. ２ It is permissible to use multiple types of compounds (b2) with different structures. As for compound (b1), Y １ｂ and / or Y２ｂ Multiple types of compounds with different properties can be used. Similarly, as compound (b2), Z １ｂ and / or Z ２ｂ Multiple types of compounds with different properties can be used.

[0104] Compound (b1) and compound (b2) can be reacted (polymerized) by, for example, an aromatic nucleophilic substitution reaction in a solvent in the presence of a base.

[0105] The solvent used in the reaction is preferably one that is a good solvent for compound (b1), compound (b2), and polymer (P), and that allows for the high molecular weight of polymer (P) during polymerization. For example, N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, diphenyl sulfone, sulfolane, 1,3-dimethyl-2-imidazolidinone, and tetramethylurea are preferably used. These solvents may be used individually or as a mixture of two or more.

[0106] A base is used to enhance the nucleophilicity of compound (b2). The base is not particularly limited as long as it can deprotonate compound (b2). For example, alkali metal hydroxides and carbonates, alkaline earth metal hydroxides and carbonates, and organic bases such as amines can be used. The alkali metal may be lithium, sodium, potassium, rubidium, or cesium. The alkaline earth metal may be magnesium, calcium, strontium, or barium.

[0107] The reaction temperature in aromatic nucleophilic substitution reactions may be in the range of 25 to 350°C. From the viewpoint of excellent reaction rate, the reaction temperature is preferably 60°C or higher, and more preferably 100°C or higher. From the viewpoint of suppressing polymer decomposition, the reaction temperature is preferably 300°C or lower, and more preferably 250°C or lower. From these viewpoints, the reaction temperature is preferably 60 to 300°C, and more preferably 100 to 250°C.

[0108] Compound (b1) and compound (b2) can also be reacted (polymerized) by a cross-coupling reaction in a solvent in the presence of a catalyst. Examples of solvents that can be used in the reaction are the same as examples of solvents that can be used in the aromatic nucleophilic substitution reaction described above.

[0109] There are no particular restrictions on the catalyst as long as it can carry out the cross-coupling reaction, and conventionally known catalysts can be used. For coupling reactions between halogens, for example, copper catalysts, nickel catalysts, or palladium catalysts can be used. For coupling reactions between halogens and boronic acid groups, alkylborane groups, or boronic acid ester groups, for example, conventionally known catalysts used in the Suzuki-Miyaura coupling reaction (palladium catalysts, nickel catalysts, etc.) can be used.

[0110] The copper catalyst may be, for example, copper(I) 2-thiophenecarboxylate or tetrakis(acetonitrile)copper(I)hexafluorophosphate.

[0111] The nickel catalyst may be, for example, bis(1,5-cyclooctadiene)nickel(0), dibromobis(triphenylphosphine)nickel(II), or [1,1'-bis(diphenylphosphino)ferrocene]dichloronickel(II).

[0112] The palladium catalyst may be, for example, tetrakis(triphenylphosphine)palladium(0), palladium(II) acetate, bis(triphenylphosphine)palladium(II) dichloride, or [1,1'-bis(diphenylphosphine)ferrocene]dichloropalladium(II).

[0113] The reaction temperature in the cross-coupling reaction may be in the range of 0 to 350°C. From the viewpoint of improving the reaction rate, the reaction temperature is preferably 30°C or higher, and more preferably 60°C or higher. From the viewpoint of suppressing polymer decomposition, the reaction temperature is preferably 300°C or lower, and more preferably 250°C or lower. From these viewpoints, the reaction temperature is preferably 60 to 300°C, and more preferably 100 to 250°C.

[0114] In the aromatic nucleophilic substitution and cross-coupling reactions described above, it is preferable to remove water from the reaction system in order to increase the molecular weight of the polymer (P). The method of dehydration is not particularly limited, but examples include azeotropic dehydration by coexisting an azeotropic solvent in the reaction system, continuous removal from the reaction system by heating above the boiling point of water, and coexisting a water-absorbing agent such as a molecular sieve. The azeotropic solvent is not particularly limited as long as it can remove water, and for example, at least one selected from the group consisting of benzene, toluene, cyclohexane, and xylene may be used.

[0115] The above aromatic nucleophilic substitution and cross-coupling reactions are preferably carried out under an inert atmosphere (for example, under a nitrogen or argon atmosphere). After the polymerization reaction is complete, the polymer can be recovered from the reaction solution and purified to obtain the desired polymer. Methods for recovering the polymer from the reaction solution include, for example, adding the reaction solution to a solvent in which the polymer has low solubility, allowing the polymer to precipitate and be recovered as a solid, and removing the solvent from the reaction solution by evaporation and recovering the polymer as a solid. Methods for purifying the polymer include, for example, washing in a solvent in which the polymer has low solubility and the by-product inorganic salts and residual monomer-derived compounds have high solubility, and washing using a Soxhlet extractor. The methods for recovering and purifying the polymer are not limited to these methods.

[0116] Polymer (P) can also be obtained by oxidizing a polymer having the structure represented by formula (1) (for example, a polymer of compound (b1) and compound (b2)). More specifically, polymer (P) is obtained from among polymers having the structure represented by formula (1), L １ , L ２ , L ３ or L ４ It can be an oxide of a polymer containing a -S- (sulfide group) (hereinafter referred to as "sulfide-containing polymer").

[0117] Polymer (P) can also be obtained by reacting (polymerizing) a polymer of compound (b1) and compound (b2) or an oxide thereof with a known crosslinkable compound (e.g., decafluorobiphenyl) having three or more groups that react with the terminal structure of the polymer or oxide to form a crosslink. In other words, polymer (P) can be a reaction product of a polymer of compound (b1) and compound (b2) or an oxide thereof with a crosslinkable compound. This method makes it possible to obtain polymer (P) having a polymer of compound (b1) and compound (b2) or an oxide thereof as polymer units.

[0118] The polymer (P) may be obtained by a method that includes a step of protonating the ion exchange groups that form salts with metal ions. This step may involve immersing the polymer obtained by the method described above (for example, a polymer of compound (b1) and compound (b2) or an oxide thereof, or a reaction product of the polymer or oxide with a crosslinkable compound) in an acid (for example, hydrochloric acid) to protonate the ion exchange groups (for example, a salt of a sulfonic acid group). By washing and drying the compound (for example, a powder) after immersion, the metal ions of the polymer before immersion are replaced with protons, and a polymer (P) in which the ion exchange groups are protonated is obtained.

[0119] (Crosslinked material (L)) The crosslinked material (L) is a crosslinked material of polymer (P), and has a plurality of polymer units (P') derived from polymer (P), and a crosslinking group that is directly bonded to the aromatic hydrocarbon ring in the polymer unit (P') and crosslinks the plurality of polymer units (P') to each other.

[0120] The polymer unit (P') may have the same structure as the structure represented by formula (1) above, except that the hydrogen atom directly bonded to the aromatic hydrocarbon ring in the polymer (P) is replaced by a crosslinking group. Multiple polymer units (P') may be identical or different from one another.

[0121] [Crosslinking group] The crosslinking group may be a group formed by a Friedel-Crafts acylation reaction between the polymer (P) and a crosslinking agent (acylation agent), or a group formed by a Friedel-Crafts alkylation reaction between the polymer (P) and a crosslinking agent (alkylating agent).

[0122] Examples of groups formed by the Friedel-Crafts acylation reaction include the group represented by the following formula (c1) (hereinafter also referred to as the "crosslinking group (c1)").

[0123]

[0124] In formula (c1), R １ z is one of the following groups: an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof. １ It shows a +1 valent organic group, z １ represents an integer greater than or equal to 1, and * represents a combination.

[0125] R １ The organic group may have some of its carbon atoms replaced by at least one heteroatom selected from the group consisting of oxygen, nitrogen, and sulfur atoms. For example, R １ The organic group may have a divalent heterogroup. Examples of divalent heterogroups include -O-, -S-, and =O. Among these, R １ When the organic group has an ether group (-O-), higher swelling resistance tends to be obtained.

[0126] R １ The number of carbon atoms in the aliphatic hydrocarbon group is, for example, 1 to 12, preferably 1 to 6, and more preferably 2 to 4, from the viewpoint of obtaining better proton conductivity. The aliphatic hydrocarbon group may be linear or branched. １ The aromatic ring contained in the aromatic hydrocarbon group may be monocyclic or polycyclic.

[0127] R １ From the viewpoint of improving swelling resistance, it is preferable that it contains an aromatic hydrocarbon group, and more preferably a benzene ring. １ If it contains an aromatic hydrocarbon group, then R in formula (c1) １ The group that attaches to it (carbonyl group) is R １ It may be directly bonded to the aromatic ring inside.

[0128] R １From the viewpoint of obtaining better proton conductivity, it is preferable that the material contains an aliphatic hydrocarbon group, and more preferably that it contains an aliphatic hydrocarbon group in which some of the carbon atoms are replaced by oxygen atoms.

[0129] z １ z is, for example, 1 to 11, preferably 1 to 2, and more preferably 1, from the viewpoint of improving swelling resistance. １ If R is 1, １ From the viewpoint of obtaining better proton conductivity and better swelling resistance, it is preferable that it contains one or more arylene groups, and the formula is *-Ar １ -*, or formula: *-Ar ２ -L ５ -Ar ３ -*(in the formula, Ar １ ~Ar ３ Each of these independently represents an arylene group, L ５ It is more preferable that the group is a single bond, -O-, -S- or -CO-, and * indicates a bond. Specific examples of arylene groups include phenylene, naphthylene, fluorene, anthracylene, phenanthrylene, triphenylene, pyrenylene, and tetrasenylene.

[0130] Specific examples of the crosslinking group (c1) include the groups represented by the following formulas (C1-1) to (C1-6).

[0131]

[0132] In equations (C1-1) to (C1-6), the asterisk (*) indicates a coupling.

[0133] From the viewpoint of obtaining better proton conductivity and better swelling resistance, the crosslinking group (c1) is preferably one of the groups represented by formulas (C1-1) to (C1-6), more preferably one of the groups represented by formulas (C1-2), (C1-5), or (C1-6), even more preferably one of the groups represented by formulas (C1-2) or (C1-6), and particularly preferably one of the groups represented by formula (C1-6).

[0134] The crosslinking groups (c1) contained in the crosslinked body (L) may be of one type or multiple types. At least one of the multiple crosslinking groups (c1) in the crosslinked body (L) may be one of those exemplified above, a majority of the multiple crosslinking groups (c1) may be one of those exemplified above, or all of the multiple crosslinking groups (c1) may be one of those exemplified above.

[0135] The crosslinking group (c1) may be formed by a method other than the Friedel-Crafts acylation reaction.

[0136] Examples of groups formed by the Friedel-Crafts alkylation reaction include the group represented by the following formula (c2) (hereinafter also referred to as the "crosslinking group (c2)").

[0137]

[0138] In formula (c2), R １ This is synonymous with the above, R ２ z represents a hydrogen atom or a methyl group. ２ represents an integer greater than or equal to 1, and * represents a combination. Multiple R ２ They may be the same or different from one another.

[0139] z ２ z is, for example, 1 to 11, and is preferably 1 from the viewpoint of obtaining better proton conductivity. ２ If R is 1, １ From the viewpoint of obtaining better proton conductivity and better swelling resistance, it is preferable that it contains one or more arylene groups, and the formula is *-Ar ４ - * or formula: * - Ar ５ -L ６ -Ar ６ -*(in the formula, Ar ４ ~Ar ６ Each of these independently represents an arylene group, L ６ It is more preferable that the group is a single bond, -O-, -S-, or -CO-, and * indicates a bond. Specific examples of the arylene group are the same as in the case of the crosslinking group (c1).

[0140] Specific examples of the crosslinking group (c2) include the groups represented by the following formulas (C2-1) to (C2-4).

[0141]

[0142] In formulas (C2-1) to (C2-4), R ２ This is synonymous with the above, and * indicates a combination.

[0143] The crosslinking group (c2) is preferably a group represented by formulas (C2-1) to (C2-4), and more preferably a group represented by formula (C2-1), from the viewpoint of obtaining better proton conductivity and better swelling resistance.

[0144] The crosslinking group (c2) may be formed by a method other than the Friedel-Crafts alkylation reaction.

[0145] The crosslinking group (c2) contained in the crosslinked body (L) may be one type or multiple types.

[0146] The crosslinked body (L) may have either the crosslinking group (c1) or the crosslinking group (c2) alone, or it may have both. From the viewpoint of superior swelling resistance, it is preferable that the crosslinked body (L) has the crosslinking group (c1). Furthermore, the crosslinked body (L) may have groups other than the crosslinking group (c1) and the crosslinking group (c2).

[0147] The crosslinked material (L) may have a structure in which multiple polymer units (P') are three-dimensionally crosslinked via crosslinking groups, or it may have a structure in which other polymer units (P') are grafted onto the main chain of a polymer unit (P') via crosslinking groups.

[0148] The crosslinked product (L) may have crosslinkable groups. These crosslinkable groups may be derived from the crosslinking agent described later. That is, some of the crosslinkable groups of the crosslinking agent may remain unreacted in the crosslinked product (L).

[0149] (Electrolyte membrane (E)) The electrolyte membrane (E) may consist only of the crosslinked body (L), or it may contain components other than the crosslinked body (L). The components other than the crosslinked body (L) may be a polymer (P), a reaction product (uncrosslinked) of the polymer (P) and a crosslinking agent, a crosslinking agent, a catalyst, or an additive such as a water-retaining inorganic substance or a radical scavenger. The catalyst may be a catalyst for a crosslinking reaction (e.g., a Friedel-Crafts reaction). Specific examples of additives include water, silica, cerium oxide, and manganese oxide. These components may be used individually or in combination.

[0150] The content of the crosslinked material (L) may be 1 to 100% by mass, 5 to 95% by mass, 10 to 90% by mass, or 20 to 70% by mass, from the viewpoint of superior proton conductivity and swelling resistance. The above content is based on the total amount of solids in the electrolyte membrane (E).

[0151] The total content of polymer (P) and polymer (P)-derived components in the electrolyte membrane (E) may be 90 to 100% by mass, 94 to 100% by mass, or 97 to 100% by mass, from the viewpoint of superior proton conductivity and swelling resistance. Here, polymer (P)-derived components refer to the crosslinked material (L) and the reaction products (uncrosslinked material) of polymer (P) and the crosslinking agent. The above total content is based on the total solid content of the electrolyte membrane (E).

[0152] The ion exchange capacity (IEC) of the electrolyte membrane (E) may be 1.0 mmol / g or more, 1.5 mmol / g or more, 2.0 mmol / g or more, 2.2 mmol / g or more, or 2.4 mmol / g or more from the viewpoint of superior proton conductivity, and may be 4.0 mmol / g or less, 3.8 mmol / g or less, 3.5 mmol / g or less, 2.7 mmol / g or less, or 2.4 mmol / g or less from the viewpoint of superior swelling resistance. From these viewpoints, the ion exchange capacity of the electrolyte membrane (E) may be 1.0 to 4.0 mmol / g, 1.5 to 3.8 mmol / g, 2.0 to 3.5 mmol / g, 2.2 to 2.7 mmol / g, 2.4 to 2.7 mmol / g, or 2.2 to 2.4 mmol / g.

[0153] The ion exchange capacity of an electrolyte membrane is measured by the following procedure (1) to (4): (1) Dry the electrolyte membrane and determine its dry mass. Drying is carried out until the mass loss when the electrolyte membrane is heated at 80°C is 1% by mass / hour or less. For example, after vacuum drying, heat at 80°C for 12 hours or more. (2) Immerse the dried electrolyte membrane in a 20% by mass sodium chloride aqueous solution and stir for 24 hours to perform ion exchange. (3) Using the point where the pH becomes 7 as the endpoint, titrate the hydrochloric acid produced by the above ion exchange using a 0.01 M sodium hydroxide aqueous solution. (4) Calculate the ion exchange capacity (IEC) of the electrolyte membrane using the following formula: IEC (unit: mmol / g) = {Concentration of sodium hydroxide aqueous solution (unit: mol / L) × Droplet volume (unit: mL)} / Dry mass of electrolyte membrane (unit: g)

[0154] The gel fraction in the electrolyte membrane (E) is preferably 1 to 100%. By setting the gel fraction to 1% or more, it becomes easier to obtain an electrolyte membrane with superior swelling resistance. Furthermore, a better phase separation structure is more easily formed, making it easier to obtain an electrolyte membrane with superior proton conductivity. From the above viewpoint, the gel fraction of the electrolyte membrane (E) may be 5% or more, 10% or more, 20% or more, or 40% or more. The gel fraction of the electrolyte membrane (E) may also be 95% or less, 90% or less, 70% or less, 30% or less, or 10% or less, and may be 5 to 95%, 10 to 90%, 20 to 70%, 40 to 70%, 1 to 70%, 1 to 30%, or 1 to 10%. The gel fraction of the electrolyte membrane (E) is determined as the insoluble fraction of the electrolyte membrane with respect to dimethyl sulfoxide. The specific calculation method is described in the examples below. Generally, the gel fraction correlates with the degree of crosslinking of the electrolyte membrane. This is presumably because the more cross-linked portions there are in the electrolyte membrane, the lower the solubility in the solvent becomes, and the larger the amount of insoluble matter.

[0155] The gel fraction of the electrolyte membrane (E) is determined as the insoluble fraction of the electrolyte membrane in dimethyl sulfoxide (DMSO). Specifically, the electrolyte membrane is immersed in DMSO at 25°C for 24 hours and the value is calculated using the following formula (I). In formula (I), W １ and W ２ The values ​​represent the mass (in grams) of the electrolyte membrane before and after immersion in DMSO at 25°C for 24 hours, respectively. Gel fraction = (W ２ / W １ )×100...(I)

[0156] The thickness of the electrolyte membrane (E) is not particularly limited and can be changed according to the size of the fuel cell, etc. From the viewpoint of increasing the mechanical strength of the membrane while reducing membrane resistance, the thickness of the electrolyte membrane (E) may be, for example, 1 to 200 μm, or it may be 1 to 100 μm or 1 to 50 μm.

[0157] As described later, the electrolyte membrane (E) can be obtained by preparing a membrane containing a polymer (P) and a crosslinking agent (hereinafter also referred to as "uncrosslinked membrane (E')"), and crosslinking the polymer (P) in the uncrosslinked membrane (E') with the crosslinking agent (for example, a Friedel-Crafts reaction).

[0158] The electrolyte membrane (E) is suitably used in polymer electrolyte fuel cells and polymer electrolyte water electrolyzers. The electrolyte membrane (E) can also be used in redox flow batteries, electrochemical hydrogen pumps, chlor-alkali electrolyzers, solid acid catalysts, membrane-type humidity control devices, gas separation membranes, and the like.

[0159] The electrolyte membrane (E) can also be used in combination with a microporous membrane, nonwoven fabric, mesh, etc. That is, another embodiment of the present disclosure is a laminate comprising an electrolyte membrane (E) and another membrane (microporous membrane, nonwoven fabric, mesh, etc.).

[0160] <Method for Manufacturing an Electrolyte Membrane> One embodiment of the method for manufacturing an electrolyte membrane comprises the steps of: preparing a membrane (uncrosslinked membrane (E')) containing a polymer (P) and a crosslinking agent (hereinafter referred to as the "preparation step"); and crosslinking the polymer (P) by reaction with the crosslinking agent (hereinafter referred to as the "crosslinking step"). This method yields an electrolyte membrane with excellent proton conductivity. Below, the method for manufacturing an electrolyte membrane according to the above embodiment will be described using the case where the reaction in the crosslinking step is a Friedel-Crafts reaction as an example.

[0161] (Preparation Step) The uncrosslinked film (E') prepared in the preparation step contains a polymer (P) and a crosslinking agent. The crosslinking agent has at least two crosslinkable groups. Here, a crosslinkable group means a group that can react with the polymer (P) to form a crosslink. An example of a crosslinking agent is an acyling agent for the Friedel-Crafts reaction. An example of an acyling agent is a compound represented by the following formula (2) (hereinafter also referred to as "crosslinking agent (2)").

[0162]

[0163] In formula (2), R １ and z １ This is synonymous with the above, X１ X represents a halogen atom or a hydroxyl group. Multiple X １ These may be the same or different from each other. From the viewpoint of superior responsiveness, X １ It is preferable that it is a hydroxyl group. From a similar viewpoint, all X １ It is more preferable that it is a hydroxyl group.

[0164] The crosslinking agent (2) may be a compound represented by any of the following formulas (2-1) to (2-6).

[0165]

[0166] X in equations (2-1) to (2-6) １ This is synonymous with the above.

[0167] The acylating agent may be an intramolecular condensate of the crosslinking agent (2). The intramolecular condensate of the crosslinking agent (2) is an acid anhydride obtained by an intramolecular dehydration reaction or an intramolecular dehalogenation reaction of the crosslinking agent (2), and has, for example, a structure represented by the following formula (2').

[0168] In formula (2'), R １ and X １ This is synonymous with the above, z １ａ represents an integer greater than or equal to 1, and z １ｂ represents a non-negative integer. However, R １ The valence is 2z １ａ +z １ｂ That is the case.

[0169] As an acylation agent, it is preferable to use at least one selected from the group consisting of compounds represented by formulas (2-1) to (2-6) and their intramolecular condensates, from the viewpoint of making it easier to obtain an electrolyte membrane having better proton conductivity and better swelling resistance; more preferable to use at least one selected from the group consisting of compounds represented by formulas (2-2), (2-5), and (2-6) and their intramolecular condensates; even more preferable to use at least one selected from the group consisting of compounds represented by formulas (2-2) and (2-6) and their intramolecular condensates; and particularly preferable to use at least one selected from the group consisting of compounds represented by formula (2-6) and its intramolecular condensates.

[0170] The acylating agent may be used individually or in combination with other agents.

[0171] Another example of a crosslinking agent is an alkylating agent in the Friedel-Crafts reaction. Examples of alkylating agents include compounds represented by the following formula (3) (hereinafter also referred to as "crosslinking agent (3)").

[0172]

[0173] In formula (3), R １ and z ２ This is synonymous with the above, X ２ X represents a vinyl group, a monohalogenated methyl group, or a hydroxymethyl group. Multiple X ２ They may be the same or different from each other. From the viewpoint of obtaining higher reactivity, X ２ It is preferable that it is a monohalide methyl group. From a similar viewpoint, all X ２ It is more preferable that the group is a monohalogenated methyl group.

[0174] The crosslinking agent (3) may be a compound represented by any of the following formulas (3-1) to (3-4).

[0175]

[0176] X in equations (3-1) to (3-4) ２ This is synonymous with the above.

[0177] From the viewpoint of obtaining an electrolyte membrane having better proton conductivity and better swelling resistance, the alkylating agent is preferably one of the compounds represented by formulas (3-1) to (3-4), and more preferably the compound represented by formula (3-1).

[0178] Alkylating agents may be used individually or in combination of multiple types.

[0179] As the crosslinking agent, either the acyling agent or the alkylating agent may be used alone, or both may be used in combination. From the viewpoint of obtaining an electrolyte membrane with superior swelling resistance, it is preferable that the crosslinking agent includes an acyling agent (i.e., the reaction in the crosslinking step includes a Friedel-Crafts acylation reaction).

[0180] The polymer (P) content in the uncrosslinked membrane (E') may be 60 to 100% by mass, 70 to 100% by mass, or 75 to 100% by mass, based on the total solid content of the uncrosslinked membrane (E'), from the viewpoint of obtaining an electrolyte membrane with better proton conductivity.

[0181] From the viewpoint of making it easier to obtain an electrolyte membrane having better proton conductivity and better swelling resistance, the content of the crosslinking agent in the uncrosslinked membrane (E') may be 0.01 to 20 parts by mass per 100 parts by mass of polymer (P). From a similar viewpoint, the content of the crosslinking agent in the uncrosslinked membrane (E') may be 0.1 parts by mass or more, 0.3 parts by mass or more, 0.5 parts by mass or more, 2 parts by mass or more, or 4 parts by mass or more per 100 parts by mass of polymer (P), and may also be 15 parts by mass or less, 10 parts by mass or less, 7 parts by mass or less, or 5 parts by mass or less, and may be 0.1 to 15 parts by mass, 0.3 to 10 parts by mass, 0.5 to 5 parts by mass, 2 to 10 parts by mass, or 4 to 7 parts by mass.

[0182] The uncrosslinked film (E') may consist only of the polymer (P) and the crosslinking agent, or it may contain other components besides the polymer (P) and the crosslinking agent. Examples of other components include the catalyst for the Friedel-Crafts reaction, the solvent remaining in the film, and the additives mentioned above. These other components may be used individually or in combination.

[0183] The catalyst is not particularly limited as long as it facilitates the Friedel-Crafts reaction, and conventionally known catalysts can be used. For the Friedel-Crafts acylation reaction, for example, iron(III) chloride, aluminum(III) chloride, zinc(II) chloride, boron trifluoride, sulfuric acid, trifluoroacetic acid, and polyphosphate can be used. For the Friedel-Crafts alkylation reaction, for example, iron(III) chloride, aluminum(III) chloride, zinc(II) chloride, boron trifluoride, sulfuric acid, trifluoroacetic acid, and polyphosphate can be used. The amount of catalyst used may be, for example, 0 to 200 parts by mass, 0 to 150 parts by mass, or 0 to 100 parts by mass per 100 parts by mass of crosslinking agent.

[0184] The ion exchange capacity of the uncrosslinked membrane (E') may be 1.0 mmol / g or more, 1.5 mmol / g or more, or 2.0 mmol / g or more, from the viewpoint of making it easier to obtain an electrolyte membrane with superior proton conductivity, and may be 4.0 mmol / g or less, 3.8 mmol / g or less, 3.5 mmol / g or less, 3.0 mmol / g or less, or 2.6 mmol / g or less, from the viewpoint of making it easier to obtain an electrolyte membrane with superior swelling resistance. From these viewpoints, the ion exchange capacity of the uncrosslinked membrane (E') may be 1.0 to 4.0 mmol / g, 1.5 to 3.8 mmol / g, 2.0 to 3.5 mmol / g, 2.0 to 3.0 mmol / g, or 2.0 to 2.6 mmol / g. The ion exchange capacity of the uncrosslinked membrane (E') described above is a value measured by the same method as the method for measuring the ion exchange capacity of the electrolyte membrane described above.

[0185] The preparation step may be a step of preparing a pre-formed uncrosslinked film (E'), or it may be a step of forming an uncrosslinked film (E') (hereinafter referred to as the "film formation step").

[0186] In the film formation step, an uncrosslinked film (E') may be formed by a known method for forming an electrolyte polymer film (e.g., solution casting method or dispersion casting method). Specifically, for example, an uncrosslinked film (E') may be formed on the substrate by applying a liquid composition containing a polymer (P) and a crosslinking agent to the substrate and then drying the liquid composition. The liquid composition may contain a Friedel-Crafts reaction catalyst and the additives mentioned above.

[0187] In the solution casting method, the solvent is not particularly limited as long as it is capable of dissolving the polymer (P). For example, N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, diphenyl sulfone, sulfolane, 1,3-dimethyl-2-imidazolidinone, and tetramethylurea can be used. These may be used individually or in combination.

[0188] In the dispersion casting method, a dispersion medium capable of dispersing the polymer (P) is used. That is, the liquid composition contains a dispersion medium capable of dispersing the polymer (P). Examples of the dispersion medium include water, ethers, alcohols, ketones, esters, carboxylic acids, amines, acetonitrile, nitromethane, toluene, xylene, chlorobenzene, and chloroform. Examples of ethers include tetrahydrofuran and diethyl ether. Examples of alcohols include methanol, ethanol, 1-propanol, isopropyl alcohol, and 1-butanol. Examples of ketones include acetone and cyclohexanone. Examples of esters include methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, methyl lactate, and ethyl lactate. Examples of carboxylic acids include formic acid, acetic acid, and propionic acid. Examples of amines include dimethylamine, diethylamine, triethylamine, pyridine, triethanolamine, and piperazine. These may be used individually or in combination.

[0189] The amount of solids other than the crosslinking agent and catalyst in the liquid composition (for example, the amount of polymer (P)) may be 1 to 50% by mass, 2.5 to 40% by mass, or 5 to 30% by mass, based on the total amount of the liquid composition. The amount of crosslinking agent in the liquid composition may be 0.0001 to 10% by mass, 0.0025 to 6% by mass, or 0.025 to 3% by mass, based on the total amount of the liquid composition. The amount of Friedel-Crafts reaction catalyst in the liquid composition may be 0 to 20% by mass, 0 to 9% by mass, or 0 to 3% by mass, based on the total amount of the liquid composition.

[0190] The drying temperature and drying time for forming the uncrosslinked film (E') also depend on the amount of liquid medium (solvent, dispersion medium) used, but the drying temperature may be, for example, 25 to 180°C, 40 to 150°C, or 55 to 120°C, and the drying time may be, for example, 0.05 to 72 hours, 0.1 to 48 hours, or 0.25 to 24 hours.

[0191] (Crosslinking process) In the crosslinking process, the polymer (P) in the uncrosslinked film (E') reacts with the crosslinking agent (an electrophilic reactant in the Friedel-Crafts reaction), causing the polymer (P) to crosslink and generate a crosslinked product (L). That is, if the reaction in the crosslinking process is a Friedel-Crafts reaction, the electrolyte film (E) of the above embodiment is obtained. The progress of crosslinking of the polymer (P) can be confirmed, for example, by a change (increase) in the gel fraction of the electrolyte film (E).

[0192] The reaction between the polymer (P) and the crosslinking agent may be carried out, for example, by heating the uncrosslinked film (E'). The heating temperature and heating time of the uncrosslinked film (E') may be changed according to the type of crosslinking agent used, the desired degree of crosslinking, etc. The heating temperature of the uncrosslinked film (E') may be, for example, 25 to 200°C, 40 to 190°C, or 55 to 180°C. The heating time of the uncrosslinked film (E') may be, for example, 0.05 to 72 hours, 1 to 48 hours, or 0.25 to 24 hours. The heating of the uncrosslinked film (E') may be carried out under vacuum conditions (e.g., 0.1 kPa or less), or in air.

[0193] In addition to the above steps, the method for manufacturing an electrolyte membrane according to one embodiment may also include a step of washing the membrane obtained in the crosslinking step (the membrane after the crosslinking reaction) (hereinafter referred to as the "washing step"). The washing step may be performed for purposes such as removing residual solvent, unreacted crosslinking agent, catalyst, by-products, etc. from the membrane, and neutralizing the pH.

[0194] In the washing step, the film after the crosslinking reaction may be washed using a washing solution. In this case, the electrolyte film is obtained by drying the film after the washing step using a method such as vacuum drying. As the washing solution, a known washing solution suitable for the purpose of washing may be used. Specific examples of washing solutions include hydrogen peroxide, sulfuric acid, hydrochloric acid, nitric acid, and pure water. These may be used individually or in combination of two or more.

[0195] <Electrolyte membrane with catalyst layer> An electrolyte membrane with a catalyst layer according to one embodiment comprises the electrolyte membrane of the above embodiment and a catalyst layer disposed on one or both sides of the electrolyte membrane.

[0196] The catalyst layer is, for example, a layer composed of an anode catalyst or a cathode catalyst, such as in a polymer electrolyte fuel cell or polymer electrolyte water electrolysis device. Hereinafter, a layer composed of an anode catalyst will be referred to as the anode catalyst layer, and a layer composed of a cathode catalyst will be referred to as the cathode catalyst layer.

[0197] The composition of the catalyst layer is not particularly limited and can be a conventionally known configuration for catalyst layers (anode catalyst layer, cathode catalyst layer) in polymer electrolyte fuel cells and polymer electrolyte water electrolyzers. The catalyst layer may be formed of a conductive composition containing, for example, an anode catalyst or cathode catalyst and a conductive material. The catalyst layer may also contain an ionomer.

[0198] As an anode catalyst in a polymer electrolyte fuel cell, a metal catalyst capable of promoting the oxidation reaction of fuels such as hydrogen can be used. As an anode catalyst in a polymer electrolyte water electrolysis device, a metal catalyst capable of promoting the oxygen evolution reaction can be used. For example, platinum, gold, silver, palladium, iridium, rhodium, ruthenium, iron, cobalt, nickel, chromium, tungsten, manganese, and vanadium, as well as alloys of two or more of these, can be used. These may be used individually or in mixtures of two or more.

[0199] As a cathode catalyst in a polymer electrolyte fuel cell, a metal catalyst capable of promoting the reduction reaction of oxygen can be used, and as a cathode catalyst in a polymer electrolyte water electrolysis device, a metal catalyst capable of promoting the hydrogen evolution reaction can be used. For example, platinum, gold, silver, palladium, iridium, rhodium, ruthenium, iron, cobalt, nickel, chromium, tungsten, manganese, and vanadium, as well as alloys of two or more of these, can be used. These may be used individually or in mixtures of two or more.

[0200] Examples of conductive materials that can be used include carbon blacks such as furnace black, Ketjen black, channel black, and acetylene black, activated carbon, and graphite. These may be used individually or in combination of two or more.

[0201] Conventional known materials can be used as the ionomer; for example, an ionomer containing a perfluoro electrolyte can be used. Alternatively, the above-mentioned polymer (P) can be used as the ionomer. It is preferable to use a material with high oxygen permeability as the ionomer. There are no particular restrictions on the amount of ionomer added to the catalyst layer, but it is preferable to adjust the amount added within a range where oxygen diffusion is not easily inhibited.

[0202] The catalyst layer may further contain additives such as water repellents like fluorinated carbon, binders like fluororesins and hydrocarbon resins having sulfonic acid groups.

[0203] A laminate comprising an electrolyte membrane with an anode catalyst layer and a cathode catalyst layer on both sides (for example, a laminate with a layer configuration of "anode catalyst layer / electrolyte membrane / cathode catalyst layer") is also called a CCM (Catalist Coated Membrane) and is suitably used in polymer electrolyte fuel cells and polymer electrolyte water electrolyzers.

[0204] In the above embodiment, instead of the electrolyte membrane, a laminate comprising an electrolyte membrane and the other membranes mentioned above (microporous membrane, nonwoven fabric, mesh, etc.) can also be used.

[0205] <Membrane electrode assembly> A membrane electrode assembly according to one embodiment comprises the electrolyte membrane of the above embodiment and an electrode layer disposed on one or both sides of the electrolyte membrane.

[0206] The electrode layer comprises, for example, the catalyst layer (anode catalyst layer or cathode catalyst layer) in the electrolyte membrane with catalyst layer of the above embodiment. Hereinafter, an electrode layer comprising an anode catalyst layer will be referred to as the anode layer, and an electrode layer comprising a cathode catalyst layer will be referred to as the cathode layer.

[0207] The configuration of the electrode layer is not particularly limited and may be a configuration conventionally known as the electrode layer (anode layer, cathode layer) of a polymer electrolyte fuel cell or polymer electrolyte water electrolysis device. The electrode layer may consist, for example, of the catalyst layer (anode catalyst layer or cathode catalyst layer) and a gas diffusion substrate. If the catalyst layer itself has gas diffusivity, the electrode layer may consist only of the catalyst layer. As the gas diffusion substrate, for example, a porous membrane can be used. As the gas diffusion substrate, in addition to gas diffusivity, materials that have water repellency and conductivity can also be used (for example, carbon fiber substrates such as carbon nonwoven fabric or carbon paper, or titanium fiber sintered bodies).

[0208] A laminate comprising an electrolyte membrane with an anode layer and a cathode layer as electrode layers on both sides (for example, a laminate with a layer configuration of "gas diffusion substrate / anode catalyst layer / electrolyte membrane / cathode catalyst layer / gas diffusion substrate") is also called a MEA (Membrane Electrode Assembly) and is suitably used in polymer electrolyte fuel cells and polymer electrolyte water electrolyzers.

[0209] In the above embodiment, instead of the electrolyte membrane, a laminate comprising an electrolyte membrane and the other membranes mentioned above (microporous membrane, nonwoven fabric, mesh, etc.) can also be used.

[0210] <Solid Polymer Fuel Cell> A solid polymer fuel cell according to one embodiment comprises the membrane electrode assembly of the above embodiment.

[0211] The configuration of a polymer electrolyte fuel cell is not particularly limited and may be a conventionally known configuration, except that the membrane electrode assembly of the above embodiment is used. A polymer electrolyte fuel cell may, for example, comprise two or more membrane electrode assemblies. The two or more membrane electrode assemblies may be stacked (laminated) with a separator in between. A separator conventionally known for polymer electrolyte fuel cells can be used as the separator.

[0212] <Solid Polymer Water Electrolyzer> A solid polymer water electrolyzer according to one embodiment includes the membrane electrode assembly according to the above embodiment.

[0213] The configuration of the polymer electrolyte water electrolysis apparatus is not particularly limited, and can be a conventionally known configuration except for the use of the membrane electrode assembly of the above embodiment. The polymer electrolyte water electrolysis apparatus may, for example, further include a power supply element outside the membrane electrode assembly. It may also include two or more membrane electrode assemblies.

[0214] The contents of this disclosure will be described in more detail below using examples and comparative examples, but this disclosure is not limited to the following examples.

[0215] <Synthesis Example 1> (Synthesis of hydrophilic monomer (M1)) A 10 L flask equipped with a dropping funnel, reflux condenser, and mechanical stirrer was purged with nitrogen, and 101 g of 4,4'-bis[(4-chlorophenyl)sulfonyl]-1,1'-biphenyl and 4 L of anhydrous tetrahydrofuran were charged in, and stirring was started. The mixture was cooled to -70°C in a methanol-dry ice bath, and 320 mL of 2.6 mol / L n-butyllithium-hexane solution was added dropwise. The mixture was stirred for 1 hour while remaining cooled in the bath. 40 mL of sulfur dioxide gas was introduced into the flask with nitrogen gas. The mixture was stirred for 30 minutes while remaining cooled in the bath. After that, the bath was removed and the internal temperature was raised to 0°C. The precipitated solid was filtered off by suction filtration and washed with 200 mL of tetrahydrofuran. The recovered solid was dissolved in 2 L of pure water, 260 mL of 35% hydrogen peroxide solution was added, and the mixture was stirred for 18 hours. The solid was removed by suction filtration, and 600 g of sodium chloride was added to the recovered filtrate. The precipitated white solid was recovered by suction filtration and purified by recrystallization from water / isopropyl alcohol. The obtained solid was dried under reduced pressure to obtain a hydrophilic monomer (M1) represented by the following formula (M1). The yield was 65%.

[0216]

[0217] <Synthesis Example 2> (Synthesis of hydrophobic monomer (M2)) In a 200 mL flask equipped with a stirring bar, Dean-Stark tube, reflux condenser, and calcium chloride tube, 4.0 g of 4,4'-bis[(4-chlorophenyl)sulfonyl]-1,1'-biphenyl, 14.8 g of [1,1'-biphenyl]-4,4'-diol, and 13.2 g of potassium carbonate were charged, and 50 mL of N,N-dimethylacetamide (DMAc) and 50 mL of toluene were added. The mixture was heated to 160°C in an oil bath while stirring, and heating and stirring were continued for 4 hours. The toluene was removed from the Dean-Stark tube, and the mixture was heated to 180°C in an oil bath. After heating, heating and stirring were continued for 8 hours. After the reaction mixture was allowed to cool to room temperature (approximately 25°C), the reaction mixture was poured into 200 mL of 10% hydrochloric acid, and the precipitated white solid was filtered off. The filtered solid was washed with 300 mL of ethanol and dried. The dried solid was purified by recrystallization from N-methylpyrrolidone (NMP) / ethanol. The resulting solid was dried under reduced pressure to obtain a hydrophobic monomer (M2) represented by the following formula (M2). The yield was 50%.

[0218]

[0219] <Synthesis Example 3> (Synthesis of hydrophobic monomer (M3)) A 500 mL flask equipped with a stirring bar and condenser was purged with nitrogen. To this flask, 9.5 g of 2,7-dibromo-9,9-diphenylfluorene, 12.1 g of 4'-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)biphenyl-4-ol, 19 g of potassium carbonate, 2.0 g of tetrakis(triphenylphosphine)palladium(0), and 250 mL of tetrahydrofuran were added. The reaction mixture was heated to 90°C and stirred for 3 hours. After the reaction mixture was allowed to cool to room temperature, 200 mL of water and 500 mL of ethyl acetate were added and the mixture was separated, and the organic layer was recovered. The solvent was removed by evaporation using an evaporator, and the resulting crude product was purified by silica column chromatography using an ethyl acetate / hexane = 1 / 1 (volume ratio) mixed solvent as the developing solvent. The fraction containing the target product was recovered, and the solvent was removed by evaporation using an evaporator. The obtained solid was dried under reduced pressure to obtain a hydrophobic monomer (M3) represented by the following formula (M3). The yield was 53%.

[0220]

[0221] <Synthesis Example 4> (Synthesis of Polymer (P1)) 0.983 g of the hydrophobic monomer (M2) obtained in Synthesis Example 2, 1.181 g of the hydrophilic monomer (M1) obtained in Synthesis Example 1, and 0.507 g of potassium carbonate were added to a 100 mL three-necked flask equipped with a nitrogen inlet tube, a stirrer, and a Dean-Stark tube, and nitrogen purging was performed. Then, 10 mL of dimethyl sulfoxide (DMSO) and 10 mL of cyclohexane were added. After heating to 130 °C and reflux dehydration for 4 hours, the cyclohexane was removed from the Dean-Stark tube. Polymerization was carried out at 130 °C for 150 hours. After the reaction mixture was allowed to cool to room temperature, it was reprecipitated and purified with 300 mL of isopropyl alcohol (IPA), and the solid was recovered by suction filtration. The recovered solid was washed with water and dried under reduced pressure to obtain polymer (P1) having the structure represented by the following formula (P1). The yield was 97%. In formula (P1), n ​​was calculated from the number-average molecular weight described later.

[0222]

[0223] In equation (P1), M represents Na, K, or H, and n represents a positive number. In equation (P1), n ​​was approximately 20.

[0224] (Molecular Weight Measurement) The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of polymer (P1) were measured under the following conditions, and the polydispersity (Mw / Mn) was determined. Mn was 30,000, Mw was 61,000, and Mw / Mn was 2.0.

[0225] [Measurement Conditions] Polymer (P1) was dissolved at a concentration of 1 mg / mL in an eluent (N,N-dimethylformamide solvent containing 10 mmol / L of lithium bromide) to prepare the sample solution. A Tosoh HLC-8320GPC was used as the apparatus. Two Tosoh TSKgel SuperAWM-H columns (6.0 mm inner diameter, 15 cm length) were used. A differential refractometer was used as the detector. The flow rate was 0.6 mL / min and the temperature was 40°C. The number-average molecular weight (Mn) and weight-average molecular weight (Mw) were determined by converting to standard polyethylene glycol / oxide (PEG / PEO). Furthermore, the polydispersity (Mw / Mn) was determined by dividing the weight-average molecular weight (Mw) by the number-average molecular weight (Mn).

[0226] (Protonation of polymer) The obtained polymer (P1) is immersed in 1M hydrochloric acid for 24 hours to release metal ions (Na ＋ or K ＋ ) to proton (H ＋ After substitution with ), the polymer (P1') was thoroughly washed by immersion in pure water and dried under reduced pressure to obtain a polymer in which the sulfonic acid salt was protonated.

[0227] <Synthesis Example 5> (Synthesis of Polymer (P2)) 0.932 g of the hydrophobic monomer (M3) obtained in Synthesis Example 3, 1.297 g of the hydrophilic monomer (M1) obtained in Synthesis Example 1, and 0.593 g of potassium carbonate were added to a 100 mL three-necked flask equipped with a nitrogen inlet tube, a stirrer, and a Dean-Stark tube, and nitrogen purging was performed. Then, 10 mL of DMSO and 10 mL of cyclohexane were added. After heating to 130 °C and reflux dehydration for 4 hours, the cyclohexane was removed from the Dean-Stark tube. Polymerization was carried out by heating to 150 °C for 105 hours. After the reaction mixture was allowed to cool to room temperature, it was reprecipitated and purified from 300 mL of IPA, and the solid was recovered by suction filtration. The recovered solid was washed with water and dried under reduced pressure to obtain polymer (P2) having the structure represented by the following formula (P2). The yield was 90%. The polymer (P2), measured in the same manner as in Synthesis Example 4, had a Mn of 51,000, a Mw of 110,000, and a Mw / Mn ratio of 2.2.

[0228]

[0229] In equation (P2), M represents Na, K, or H, and n represents a positive number. The value of n in equation (P2) was approximately 30.

[0230] (Protonation of polymer) The obtained polymer (P2) is immersed in 1M hydrochloric acid for 24 hours to release metal ions (Na ＋ or K ＋ ) to proton (H ＋ After substitution with ), the polymer (P2') was thoroughly washed by immersion in pure water and dried under reduced pressure to obtain a polymer in which the sulfonic acid group salt was protonated.

[0231] <Comparative Example 1> In Comparative Example 1, a commercially available Nafion was used as the evaluation sample. ＴＭ Using NR211 (film thickness 25 μm), various measurements and evaluations (ion exchange capacity measurement, proton conductivity evaluation, and volume swelling rate measurement) were performed using the following methods.

[0232] (Ion Exchange Capacity Measurement) The proton-substituted electrolyte membrane was dried at 80°C for 12 hours or more, and its dry mass was determined. The dried electrolyte membrane was immersed in a 20% sodium chloride aqueous solution and stirred for 24 hours to perform ion exchange. The resulting hydrochloric acid was titrated using a 0.01 M sodium hydroxide aqueous solution. An automatic titrator COM-A19 manufactured by HIRANUMA Corporation was used for the titration, and the endpoint was set at a pH of 7. The ion exchange capacity (IEC) was calculated using the following formula. The IEC of this comparative example was 1.00 mmol / g. IEC (unit: mmol / g) = {Concentration of sodium hydroxide aqueous solution (unit: mol / L) × Dropping volume (unit: mL)} / Dry mass of electrolyte membrane (unit: g)

[0233] (Evaluation) [Proton Conductivity Evaluation] The proton conductivity of the obtained electrolyte membrane was measured by the following method. Using a Teflon® measurement cell (Scribner, BT-115), the fabricated electrolyte membrane was placed in the cell in contact with four platinum wires. After being held at 80°C and 20% relative humidity for 2 hours, the relative humidity was increased by 10% and held for 30 minutes. This operation was continued until the relative humidity reached 100%, and then DC resistance measurement was performed using the four-terminal method at 100% relative humidity. The proton conductivity in the planar direction of the electrolyte membrane was calculated from the obtained resistance value, the thickness of the electrolyte membrane, and the distance between terminals. The proton conductivity of the electrolyte membrane of Comparative Example 1 under conditions of 80°C and 100% relative humidity was 129 mS / cm. Hereafter, the proton conductivity in the examples and comparative examples represents the measured value under conditions of 80°C and 100% relative humidity. In the following examples, the above Nafion ＴＭ Using the proton conductivity of NR211 as a reference, an electrolyte membrane was evaluated as having excellent proton conductivity characteristics if its measured proton conductivity under conditions of 80°C and 100% relative humidity was 129 mS / cm or higher.

[0234] [Measurement of Volume Swelling Rate] A 3 cm square membrane was punched out from the obtained electrolyte membrane, and the punched-out membrane was immersed in 50 mL of pure water at 80°C for 1 hour. The volume of the membrane was calculated by measuring the dimensions before and after immersion in pure water. The volume swelling rate was calculated by dividing the change in the volume of the membrane before and after immersion in pure water ([Volume after pure water immersion] - [Volume before pure water immersion]) by the volume of the membrane before immersion in pure water. The volume swelling rate was 61%.

[0235] <Example 1> (Preparation of Electrolyte Membrane) The polymer (P1') obtained in Synthesis Example 4 and the crosslinking agent, 4,4'-dicarboxydiphenyl ether, were dissolved in DMAc to obtain a solution containing 10% by mass of polymer (P1') and 0.1% by mass of 4,4'-dicarboxydiphenyl ether. The obtained solution was cast onto a glass substrate and dried at 60°C for 20 hours to obtain the uncrosslinked film of Example 1 (film thickness 25 μm). The content of 4,4'-dicarboxydiphenyl ether in the uncrosslinked film was 1 part by mass per 100 parts by mass of polymer (P1'). The obtained uncrosslinked film was heated at 165°C for 10 hours under vacuum conditions, then washed sequentially with 10% sulfuric acid and pure water, and dried under reduced pressure to obtain the electrolyte membrane of Example 1 (film thickness 35 μm). The "film thickness" in this example was measured using PG-02 manufactured by TECLOK CORPORATION. When the ion exchange capacity was measured using the same method as in Comparative Example 1, the IEC of the electrolyte membrane in Example 1 was found to be 2.31 mmol / g.

[0236] (Gel fraction measurement) The obtained electrolyte membrane was immersed in DMSO at 25°C for 24 hours, and the gel fraction (%) was calculated using the following formula (I). The gel fraction of the electrolyte membrane in Example 1 was 25%, confirming that the polymer and crosslinking agent reacted to form crosslinks. Gel fraction = (W ２ / W １ ) × 100 ... (I) In equation (I), W １ and W ２ The values ​​represent the mass (in grams) of the electrolyte membrane before and after immersion in DMSO at 25°C for 24 hours, respectively.

[0237] (Evaluation) The electrolyte membrane of Example 1 was evaluated in the same manner as in Comparative Example 1 (proton conductivity evaluation and volume swelling rate measurement). The proton conductivity was 178 mS / cm, confirming that the electrolyte membrane of Example 1 has good proton conductivity. The volume swelling rate was 105%.

[0238] <Example 2> (Preparation of Electrolyte Membrane) An electrolyte membrane (thickness 35 μm) of Example 2 was obtained using the same method as in Example 1, except that the content of 4,4'-dicarboxydiphenyl ether in the uncrosslinked membrane was 3 parts by mass per 100 parts by mass of polymer (P1'). When the ion exchange capacity was measured using the same method as in Comparative Example 1, the IEC of the electrolyte membrane of Example 2 was 2.32 mmol / g. The gel fraction of the electrolyte membrane of Example 2, calculated using the same method as in Example 1, was 64%, confirming that the polymer and crosslinking agent reacted to form crosslinks.

[0239] (Evaluation) The electrolyte membrane of Example 2 was evaluated in the same manner as in Comparative Example 1 (proton conductivity evaluation and volume swelling rate measurement). The proton conductivity was 169 mS / cm, confirming that the electrolyte membrane of Example 2 has good proton conductivity. The volume swelling rate was 79%.

[0240] <Example 3> (Preparation of electrolyte membrane) An electrolyte membrane (thickness 35 μm) of Example 3 was obtained using the same method as in Example 1, except that the crosslinking agent was changed to adipic acid and the adipic acid content in the uncrosslinked membrane was set to 3 parts by mass per 100 parts by mass of polymer (P1'). When the ion exchange capacity was measured using the same method as in Comparative Example 1, the IEC of the electrolyte membrane of Example 3 was 2.36 mmol / g. The gel fraction of the electrolyte membrane of Example 3, calculated using the same method as in Example 1, was 2%, confirming that the polymer and crosslinking agent reacted to form crosslinks.

[0241] (Evaluation) The electrolyte membrane of Example 3 was evaluated in the same manner as in Comparative Example 1 (proton conductivity evaluation and volume swelling rate measurement). The proton conductivity was 184 mS / cm, confirming that the electrolyte membrane of Example 3 has good proton conductivity. The volume swelling rate was 93%.

[0242] <Example 4> (Preparation of Electrolyte Membrane) An electrolyte membrane (thickness 35 μm) of Example 4 was obtained using the same method as in Example 3, except that the adipic acid content in the uncrosslinked membrane was 5 parts by mass per 100 parts by mass of polymer (P1'). When the ion exchange capacity was measured using the same method as in Comparative Example 1, the IEC of the electrolyte membrane of Example 4 was 2.44 mmol / g. The gel fraction of the electrolyte membrane of Example 4, calculated using the same method as in Example 1, was 5%, confirming that the polymer and crosslinking agent reacted to form crosslinks.

[0243] (Evaluation) The electrolyte membrane of Example 4 was evaluated in the same manner as in Comparative Example 1 (proton conductivity evaluation and volume swelling rate measurement). The proton conductivity was 203 mS / cm, confirming that the electrolyte membrane of Example 4 has good proton conductivity. The volume swelling rate was 89%.

[0244] <Example 5> (Preparation of Electrolyte Membrane) An electrolyte membrane (thickness 35 μm) of Example 5 was obtained using the same method as in Example 1, except that the crosslinking agent was changed to diglycolic acid and the content of diglycolic acid in the uncrosslinked membrane was set to 3 parts by mass per 100 parts by mass of polymer (P1'). When the ion exchange capacity was measured using the same method as in Comparative Example 1, the IEC of the electrolyte membrane of Example 5 was 2.24 mmol / g. The gel fraction of the electrolyte membrane of Example 5, calculated using the same method as in Example 1, was 1%, confirming that the polymer and crosslinking agent reacted to form crosslinks.

[0245] (Evaluation) The electrolyte membrane of Example 5 was evaluated in the same manner as in Comparative Example 1 (proton conductivity evaluation and volume swelling rate measurement). The proton conductivity was 191 mS / cm, confirming that the electrolyte membrane of Example 5 has good proton conductivity. The volume swelling rate was 87%.

[0246] <Example 6> (Preparation of Electrolyte Membrane) An electrolyte membrane (thickness 35 μm) of Example 6 was obtained using the same method as in Example 5, except that the content of diglycolic acid in the uncrosslinked membrane was 5 parts by mass per 100 parts by mass of polymer (P1'). When the ion exchange capacity was measured using the same method as in Comparative Example 1, the IEC of the electrolyte membrane of Example 6 was 2.17 mmol / g. The gel fraction of the electrolyte membrane of Example 6, calculated using the same method as in Example 1, was 54%, confirming that the polymer and crosslinking agent reacted to form crosslinks.

[0247] (Evaluation) The electrolyte membrane of Example 6 was evaluated in the same manner as in Comparative Example 1 (proton conductivity evaluation and volume swelling rate measurement). The proton conductivity was 200 mS / cm, confirming that the electrolyte membrane of Example 6 has good proton conductivity. The volume swelling rate was 69%.

[0248] <Example 7> (Preparation of Electrolyte Membrane) An electrolyte membrane (thickness 35 μm) of Example 7 was obtained using the same method as in Example 1, except that the polymer was changed to the polymer (P2') obtained in Synthesis Example 5, and the content of 4,4'-dicarboxydiphenyl ether in the uncrosslinked membrane was set to 1 part by mass per 100 parts by mass of polymer (P2'). When the ion exchange capacity was measured using the same method as in Comparative Example 1, the IEC of the electrolyte membrane of Example 7 was 2.53 mmol / g. The gel fraction of the electrolyte membrane of Example 7, calculated using the same method as in Example 1, was 3%, confirming that the polymer and crosslinking agent reacted to form crosslinks.

[0249] (Evaluation) The electrolyte membrane of Example 7 was evaluated in the same manner as in Comparative Example 1 (proton conductivity evaluation and volume swelling rate measurement). The proton conductivity was 155 mS / cm, confirming that the electrolyte membrane of Example 7 has good proton conductivity. The volume swelling rate was 46%, confirming that the electrolyte membrane of Example 7 has excellent swelling resistance.

[0250] <Example 8> (Preparation of Electrolyte Membrane) An electrolyte membrane (thickness 35 μm) of Example 8 was obtained using the same method as in Example 7, except that the content of 4,4'-dicarboxydiphenyl ether in the uncrosslinked membrane was 3 parts by mass per 100 parts by mass of polymer (P2'). When the ion exchange capacity was measured using the same method as in Comparative Example 1, the IEC of the electrolyte membrane of Example 8 was 2.51 mmol / g. The gel fraction of the electrolyte membrane of Example 8, calculated using the same method as in Example 1, was 8%, confirming that the polymer and crosslinking agent reacted to form crosslinks.

[0251] (Evaluation) The electrolyte membrane of Example 8 was evaluated in the same manner as in Comparative Example 1 (proton conductivity evaluation and volume swelling rate measurement). The proton conductivity was 166 mS / cm, confirming that the electrolyte membrane of Example 8 has good proton conductivity. The volume swelling rate was 47%, confirming that the electrolyte membrane of Example 8 has excellent swelling resistance.

[0252] <Example 9> (Preparation of Electrolyte Membrane) An electrolyte membrane (thickness 35 μm) of Example 9 was obtained using the same method as in Example 7, except that the content of 4,4'-dicarboxydiphenyl ether in the uncrosslinked membrane was 5 parts by mass per 100 parts by mass of polymer (P2'). When the ion exchange capacity was measured using the same method as in Comparative Example 1, the IEC of the electrolyte membrane of Example 9 was 2.62 mmol / g. The gel fraction of the electrolyte membrane of Example 9, calculated using the same method as in Example 1, was 6%, confirming that the polymer and crosslinking agent reacted to form crosslinks.

[0253] (Evaluation) The electrolyte membrane of Example 9 was evaluated in the same manner as in Comparative Example 1 (proton conductivity evaluation and volume swelling rate measurement). The proton conductivity was 179 mS / cm, confirming that the electrolyte membrane of Example 9 has good proton conductivity. The volume swelling rate was 43%, confirming that the electrolyte membrane of Example 9 has excellent swelling resistance.

[0254] <Example 10> (Preparation of Electrolyte Membrane) An electrolyte membrane (thickness 35 μm) of Example 10 was obtained using the same method as in Example 7, except that the crosslinking agent was changed to diglycolic acid and the content of diglycolic acid in the uncrosslinked membrane was set to 3 parts by mass per 100 parts by mass of polymer (P2'). When the ion exchange capacity was measured using the same method as in Comparative Example 1, the IEC of the electrolyte membrane of Example 10 was 2.55 mmol / g. The gel fraction of the electrolyte membrane of Example 10, calculated using the same method as in Example 1, was 42%, confirming that the polymer and crosslinking agent reacted to form crosslinks.

[0255] (Evaluation) The electrolyte membrane of Example 10 was evaluated in the same manner as in Comparative Example 1 (proton conductivity evaluation and volume swelling rate measurement). The proton conductivity was 157 mS / cm, confirming that the electrolyte membrane of Example 10 has good proton conductivity. The volume swelling rate was 38%, confirming that the electrolyte membrane of Example 10 has excellent swelling resistance.

[0256]

[0257] This application is based on Japanese Patent Application No. 2024-169425, filed on 27 September 2024, which is incorporated by reference in its entirety. All references cited herein are incorporated as a whole.

Claims

1. The following formula (1): [In formula (1), A １ represents a structural unit represented by the following formula (a1): (In formula (a1), IExG represents an ion-exchange group, L ３ represents a single bond, -O-, -S-, -SO ２ -, or -CO-, x represents an integer from 2 to 10, and * represents a bond. A plurality of IExG may be the same or different from each other, and a plurality of L ３ may be the same or different from each other.) represents a structural unit, and A ２ represents a structural unit represented by the following formula (a2): (In formula (a2), Ar represents an arylene group having no ion-exchange group, L ４ represents a single bond, -O-, -S-, -SO ２ -, or -CO-, y represents an integer from 3 to 20, and * represents a bond. A plurality of Ar may be the same or different from each other, and a plurality of L ４ may be the same or different from each other.) represents a structural unit, and L １ and L ２ each independently represent a single bond, -O-, -S-, or -SO ２ -, n represents an integer from 10 to 100, and * represents a bond. A plurality of A １ may be the same or different from each other, a plurality of A ２ may be the same or different from each other, a plurality of L １ may be the same or different from each other, and a plurality of L ２ may be the same or different from each other. However, the difference in x in formula (a1) among a plurality of A １ is within 3, and the difference in y in formula (a2) among a plurality of A ２ is within 5.] contains a crosslinked body of a polymer having the structure represented by the formula, and the crosslinked body has a plurality of polymer units derived from the polymer and a crosslinking group that is directly bonded to the aromatic hydrocarbon ring in the polymer unit and crosslinks the plurality of polymer units with each other, an electrolyte membrane.

2. The crosslinking base is given by the following formula (c1): [In formula (c1), R １ z is one of the following groups: an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof. １ It shows a +1 valent organic group, z １ represents an integer greater than or equal to 1, and * represents a combination. R １ The electrolyte membrane according to claim 1, having a group represented by ], wherein a portion of the carbon atoms of the organic group may be substituted with at least one heteroatom selected from the group consisting of oxygen atoms, nitrogen atoms, and sulfur atoms.

3. Said L １ and L ２ The electrolyte membrane according to claim 1 or 2, wherein each of these is independently a single bond, -O-, or -S-.

4. Said L ３ However, single bonds or -SO ２ - The electrolyte membrane according to any one of claims 1 to 3.

5. The electrolyte membrane according to any one of claims 1 to 4, wherein the constituent unit represented by formula (a1) comprises at least one group selected from the group consisting of a sulfonic acid group, an alkyl sulfonic acid group, a sulfonimide group, and salts thereof, as the ion exchange group.

6. The electrolyte membrane according to any one of claims 1 to 5, wherein the constituent unit represented by formula (a2) comprises, as the arylene group, at least one group selected from the group consisting of a phenylene group, a naphthylene group, and a fluorene group, which may have substituents.

7. An electrolyte membrane according to any one of claims 1 to 6, wherein the ion exchange capacity is 1.0 to 4.0 mmol / g.

8. An electrolyte membrane according to any one of claims 1 to 7, wherein the gel fraction obtained from the following formula (I) is 1 to 100%. Gel fraction = (W ２ / W １ ) × 100 ... (I) [In formula (I), W １ and W ２ These values ​​represent the mass of the electrolyte membrane before and after immersion in dimethyl sulfoxide at 25°C for 24 hours, respectively.

9. The following formula (1): [In formula (1), A １ The following formula (a1): (In formula (a1), IExG indicates an ion exchange group, L ３ These are single bonds, -O-, -S-, -SO ２ - or -CO- is indicated, x is an integer from 2 to 10, and * indicates a combination. Multiple IExG may be the same or different from each other, and multiple L ３ These may be identical or different from each other.) The constituent units are shown as A ２ The following formula (a2): (In formula (a2), Ar represents an arylene group that does not have an ion exchange group, L ４ These are single bonds, -O-, -S-, -SO ２ - or -CO- is indicated, y is an integer from 3 to 20, and * indicates a combination. Multiple Ars may be the same or different from each other, and multiple L ４ These may be identical or different from each other.) The constituent units are shown as L １ and L ２ These are, independently, a single bond, -O-, -S-, or -SO-. ２ - indicates a combination, n is an integer between 10 and 100, and * indicates a combination. Multiple A １ They may be the same or different from each other, and there are multiple A ２ These may be the same or different from each other, and there are multiple L １ These may be the same or different from each other, and there are multiple L ２ They may be the same or different from each other. However, multiple A １ The difference of x in equation (a1) is 3 or less, and multiple A ２ A method for producing an electrolyte membrane, comprising the steps of: preparing an uncrosslinked membrane containing a polymer having a structure represented by ] and a crosslinking agent; and crosslinking the polymer with the crosslinking agent by a Friedel-Crafts reaction.

10. The crosslinking agent is of the following formula (2): [In formula (2), R １ z is one of the following groups: an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a combination thereof. １ It shows a +1 valent organic group, z １ X represents an integer greater than or equal to 1. １ R represents a halogen atom or a hydroxyl group. １ The organic group may have some of its carbon atoms replaced by at least one heteroatom selected from the group consisting of oxygen, nitrogen, and sulfur atoms, and multiple X １ The method for producing an electrolyte membrane according to claim 9, comprising at least one selected from the group consisting of a compound represented by ] and an intramolecular condensate of said compound.

11. The method for producing an electrolyte membrane according to claim 9 or 10, wherein the content of the crosslinking agent in the uncrosslinked membrane is 0.01 to 20 parts by mass per 100 parts by mass of the polymer.

12. An electrolyte membrane with a catalyst layer, comprising an electrolyte membrane according to any one of claims 1 to 8, and a catalyst layer disposed on one or both sides of the electrolyte membrane.

13. A membrane electrode assembly comprising an electrolyte membrane according to any one of claims 1 to 8, and an electrode layer disposed on one or both sides of the electrolyte membrane.

14. A polymer electrolyte fuel cell comprising the membrane electrode assembly described in claim 13.

15. A solid polymer water electrolysis apparatus comprising the membrane electrode assembly described in claim 13.

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