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

An electrolyte membrane includes a crosslinked body of a polymer having a structure represented by formula (1). The crosslinked body has a structure in which a plurality of polymer units derived from the polymer are crosslinked with each other via a sulfonyl group. [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 represents a single bond or the like, n represents an integer of 10-100, and * represents a bond.] [In formula (a1), IExG represents at least one group selected from the group consisting of sulfonic acid groups, which are ion exchange groups, and salts thereof, L３ represents a single bond or the like, x represents an integer of 2-10, and * represents a bond.] [In formula (a2), Ar represents an arylene group having no ion exchange group, L4 represents a single bond or the like, (y) represents 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] Di Vona et al., “Cross-Linking of Sulfonated Poly(ether ether ketone) by Thermal Treatment: How Does the Reaction Occur?”, Fuel Cells, 13, 2013, pp. 107-117.

[0007] However, the polymer electrolyte membrane made of a non-fluorine-based polymer obtained by block copolymerization as disclosed in the above Patent Document 2 does not necessarily have sufficient proton conductivity.

[0008] In contrast, the present inventors have found a method for precisely arranging hydrophilic structural units (hydrophilic parts) and hydrophobic structural units (hydrophobic parts) in an electrolyte polymer, and thereby succeeded in synthesizing an electrolyte polymer having excellent proton conductivity. However, the electrolyte polymer had room for improvement in terms of swelling resistance.

[0009] One aspect of the present disclosure aims to provide an electrolyte membrane having excellent proton conductivity and excellent swelling resistance.

[0010] The present invention is as described in the claims, and the present disclosure provides the following [1] to

[13] in some aspects.

[0011] [1] The following formula (1): [In formula (1), A １ represents the following formula (a1): (In formula (a1), IExG represents at least one group selected from the group consisting of a sulfonic acid group which is an ion exchange group and its salts, L ３ represents a single bond, -O-, -S-, -SO ２ -, or -CO-, x represents an integer of 2 to 10, and * represents a bond. A plurality of Ls ３ may be the same as or different from each other.) represents a structural unit represented by, A ２ represents 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 of 3 to 20, and * represents a bond. A plurality of Ars may be the same as or different from each other, and a plurality of Ls ４ may be the same as or different from each other.) represents a structural unit represented by, L １ and L ２These 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 The difference of y in equation (a2) is within 5, and multiple L １ , L ２ and L ４ An electrolyte membrane comprising a crosslinked polymer having a structure represented by ], wherein the crosslinked polymer has a structure in which a plurality of polymer units derived from the polymer are crosslinked with each other via sulfonyl groups derived from the sulfonic acid group or a salt thereof.

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

[0013] [3] Said L ３ However, single bonds or -SO ２ - The electrolyte membrane according to [1] or [2].

[0014] [4] The electrolyte membrane according to any one of [1] to [3], 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 a substituent.

[0015] [5] An electrolyte membrane according to any one of [1] to [4], wherein the ion exchange capacity is 1.0 to 4.0 mmol / g.

[0016] [6] An electrolyte membrane according to any of [1] to [5], wherein the gel fraction obtained from the following formula (I) is 10 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.

[0017] [7] The following formula (1): [In formula (1), A １ The following formula (a1): (In formula (a1), IExG represents at least one group selected from the group consisting of sulfonic acid groups and salts thereof, which are ion exchange groups, 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 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 A１ The difference of x in equation (a1) is 3 or less, and multiple A ２ The difference of y in equation (a2) is within 5, and multiple L １ , L ２ and L ４ A method for producing an electrolyte membrane, comprising the step of heating a membrane containing a polymer having a structure represented by [ ] and dimethyl sulfoxide at 140 to 200°C, wherein at least one of the members is a single bond, -O-, or -S-.

[0018] [8] The method for producing an electrolyte membrane according to [7], wherein the amount of dimethyl sulfoxide in the heated membrane is 1 to 20 parts by mass per 100 parts by mass of the polymer.

[0019] [9] The method for producing an electrolyte membrane according to [7] or [8], wherein the degree of crosslinking of the electrolyte membrane, determined from the following formula (II), is 0.1 to 15%. Degree of crosslinking = (C １ -C ２ ) / C １ ×100...(II) [In formula (II), C １ represents the ion exchange capacity of the heated membrane, C ２ This represents the ion exchange capacity of the electrolyte membrane.

[0020]

[10] An electrolyte membrane with a catalyst layer, comprising an electrolyte membrane according to any one of [1] to [6], and a catalyst layer disposed on one or both sides of the electrolyte membrane.

[0021]

[11] A membrane electrode assembly comprising an electrolyte membrane according to any one of [1] to [6] and an electrode layer disposed on one or both sides of the electrolyte membrane.

[0022]

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

[11] .

[0023]

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

[11] .

[0024] According to one aspect of this disclosure, it is possible to provide an electrolyte membrane that has excellent proton conductivity and excellent swelling resistance.

[0025] 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.

[0026] <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 structure in which a plurality of polymer units derived from polymer (P) are crosslinked with each other via sulfonyl groups derived from sulfonic acid groups or salts thereof.

[0027]

[0028] 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) is 3 or less, and multiple A ２ The difference of y in equation (a2) is within 5, and multiple L １ , L ２ and L４ At least one of them is a single bond, -O-, or -S-.

[0029]

[0030] In formula (a1), IExG represents at least one group selected from the group consisting of sulfonic acid groups and salts thereof, which are ion exchange groups, and 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 L ３ They may be the same or different from one another.

[0031]

[0032] 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.

[0033] 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 presumed to be as follows: In the polymer (P), 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. ２The polymer has a structure in which hydrophobic parts are precisely arranged, and the sulfonic acid groups or salts thereof, which are ion exchange groups, are arranged at approximately equal intervals. It is presumed that the sulfonic acid groups or salts thereof in the polymer unit self-assemble in a higher-order structure, inducing a microphase separation structure. This is presumed to form good proton conduction paths within the crosslinked body (L), resulting in excellent proton conductivity.

[0034] The proton conductivity of the electrolyte membrane (E) is, for example, 135 mS / cm or higher, and may be 150 mS / cm or higher or 180 mS / cm or higher, in an environment of 80°C and 100% relative humidity.

[0035] Furthermore, the electrolyte membrane (E) exhibits excellent swelling resistance due to the inclusion of the crosslinked material (L). For example, the volume swelling rate of the electrolyte membrane (E) measured by the method of the examples may be 60% or less, 55% or less, 50% or less, or 45% or less. Also, 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 60%, or 10 to 55%. The reason why the crosslinked material (L) provides excellent swelling resistance is not clear, but it is presumed that crosslinking by sulfonyl groups 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.

[0036] (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 or 20 or more, or 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 formation properties. From these viewpoints, the number of repeats (n) of the structure is preferably 15 to 80, and more preferably 20 to 50.

[0037] The polymer (P) has at least one group (—SO ３ M １／ｑ ) selected from the group consisting of sulfonic acid groups and their salts, and at least one of the plurality of L １ , L ２ and L ４ is a single bond, —O—, or —S—, so that it reacts by heating in the presence of dimethyl sulfoxide to form a crosslinked product (L). This reaction is known in the art (see, for example, Non-Patent Document 1), and an electrophilic sulfonium ion group (—SO ２ ＋ ) is generated from some of the sulfonic acid groups in the polymer (P), and then the sulfonium ion group and the carbon atom of the arylene group adjacent to the above linking group (single bond, —O—, or —S—) (for example, the carbon atom located at the ortho position of the linking group) or the carbon atom at the position where the sulfonic acid group is present (ipso position) undergo an aromatic electrophilic substitution reaction to form a crosslink by a sulfonyl group. It is considered that this reaction does not require the addition of a transition metal catalyst or the like, so it is useful in an industrial production process. The specific conditions (heating temperature, heating time, etc.) of this reaction may follow the conditions in the method for producing an electrolyte membrane described later.

[0038] [Structural unit A １ ] The structural unit A １ has a structure in which an aromatic ring having at least one group selected from the group consisting of sulfonic acid groups and their salts as 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 ions (for example, cations), and is also called an ionic group. Generally, the ion exchange group may be a protonic acid group. Examples of general ion exchange groups include sulfonic acid groups, alkylsulfonic acid groups, perfluoroalkylsulfonic acid groups, sulfonimide groups, phosphonic acid groups, phosphoric acid groups, and carboxy groups, and their salts. As described above, the ion exchange groups include those that form salts with metal ions and the like.

[0039] The sulfonic acid group and its salts are, for example, -SO ３ M １／ｑ (where M represents H or at least one metal selected from the group consisting of 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 (an integer of 1 to 4).). The metal represented by M exists as an ion (cation) and forms a salt with -SO ３ － .

[0040] The structural unit A １ preferably contains, from the viewpoint of obtaining better proton conductivity, at least one group selected from the group consisting of -SO ３ - and -CO- as the linking group (L ２ ), and more preferably contains -SO ２ . From the same viewpoint, it is more preferable that the majority of the linking groups (L １ ) present in the structural unit A ３ are in the above preferred form.

[0041] The linking group (L １ ) in the structural unit A ３ is preferably a single bond or -SO ２ - from the viewpoints of improving proton conductivity and chemical durability.

[0042] The bonding position of the linking group (L ３ ) is not particularly limited, but is preferably located at the ortho or meta position with respect to the ion-exchange group (sulfonic acid group or its salt) from the viewpoints of obtaining better proton conductivity and chemical durability. That is, the structural unit A １ preferably contains a 1,4-phenylene group having at least one group selected from the group consisting of a sulfonic acid group and its salts.

[0043] The repetition number (x) of the structure within [ ] in the formula (a1) in the structural unit A １ is preferably 2 to 8, more preferably 3 to 5, from the viewpoints of obtaining better proton conductivity, excellent heat and water resistance, and increasing the crosslinking degree of the crosslinked body.

[0044] 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)").

[0045]

[0046]

[0047]

[0048] 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. １ x 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.

[0049] 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 ).

[0050] Constituent unit A １ This may be a constituent unit represented by any of the following formulas (A1-1) to (A1-4).

[0051]

[0052] 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.

[0053] 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.

[0054] Multiple constituent units A in equation (1) １At 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.

[0055] 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.

[0056] 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.

[0057] [Construction Unit A] ２ ] Component Unit A ２ In 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 ).

[0058] 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 the solvent, 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.

[0059] 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).

[0060] Constituent unit A ２ From 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.

[0061] Constituent unit A ２ From the viewpoint of increasing the degree of crosslinking of the crosslinked body, the linking group (L ４It 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.

[0062] 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-. The above sulfonium ion group (-SO ２ ＋ The electrophilic substitution reaction by ) is -SO ２ Since this can also occur at the meta position of electron-withdrawing groups such as - or -CO-, the constituent unit A ２ is a linking group (L ４ ) as -SO ２ The degree of crosslinking of the crosslinked material may be increased by including - or -CO-.

[0063] Constituent unit A ２ The linking group inside (L ４ From 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.

[0064] 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.

[0065] Constituent unit A ２In 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.

[0066] 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.

[0067] 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).

[0068]

[0069]

[0070] 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.

[0071] Constituent unit A including the above structure ２ A concrete example of this is the constituent unit represented by the following formula (A2-1).

[0072]

[0073] 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 ４They may be the same or different from one another.

[0074] 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).

[0075]

[0076] 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 identical or different from one another.

[0077] 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.

[0078] 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 ２ It may be composed of these elements.

[0079] 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.

[0080] 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) ２The 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.

[0081] [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.

[0082] 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).

[0083]

[0084] A in equations (1-1) to (1-3) １ A ２ , L １ , L ２ and n are as defined above. However, in equations (1-1) and (1-2), Z ２ L that joins ２ This is a single bond. Z １ and Z ２Each 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.

[0085] Polymer (P) may contain multiple 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 crosslinking groups that bond to three or more polymer units A. 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 be one that excludes the crosslinking group. The crosslinking group may be a group derived from a known crosslinkable compound (e.g., decafluorobiphenyl). If the crosslinking group has an aromatic ring, polymer unit A may be directly attached to the aromatic ring of the crosslinking group, or to -O-, -S-, or -SO ２ They may be bonded via a cross-linking group. The number of cross-linking groups may be one or more. The multiple cross-linking groups may be the same or different from each other.

[0086] 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.

[0087] 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).

[0088] 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.

[0089] The weight-average molecular weight of polymer (P) may be 40,000 or more, 50,000 or more, 60,000 or more, or 70,000 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, 80,000 or less, or 70,000 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 80,000, 70,000 to 80,000, or 60,000 to 70,000.

[0090] 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, better 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 3.0 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 3.0.

[0091] 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.

[0092] 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).

[0093]

[0094] In formula (b1), A １ This is synonymous with the above, X １ｂ and X ２ｂ Each of these independently represents a halogen atom. Examples of halogen atoms include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

[0095]

[0096] 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 .

[0097] 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.

[0098] 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.

[0099] 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), X １ｂ and / or X２ｂ 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] The copper catalyst may be, for example, copper(I) 2-thiophenecarboxylate or tetrakis(acetonitrile)copper(I)hexafluorophosphate.

[0107] 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).

[0108] 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).

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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").

[0113] 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 polymer or its 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.

[0114] 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.

[0115] (Crosslinked material (L)) Crosslinked material (L) is a crosslinked material of polymer (P), and has a plurality of polymer units derived from polymer (P) and sulfonyl groups that crosslink these polymer units with each other.

[0116] Polymer units derived from polymer (P) may have the same structure as the structure represented by formula (1) above, except that some or all of the sulfonic acid groups or their salts are converted to sulfonyl groups, and some of the hydrogen atoms bonded to carbon atoms are substituted with sulfonyl groups. Multiple polymer units may be identical or different from one another.

[0117] Since the sulfonyl group originates from the sulfonic acid group or a salt thereof of the polymer (P) above, one end of the sulfonyl group is bonded to a carbon atom on the benzene ring to which the sulfonic acid group or salt thereof was bonded. The other end of the sulfonyl group may be bonded to a carbon atom of the arylene group adjacent to the single bond, -O-, or -S- which is the linking group (for example, the carbon atom located in the ortho position of the linking group), or it may be bonded to a carbon atom at the position where the sulfonic acid group or salt thereof exists (the ipso position). Constituent unit A ２ is a linking group (L ４ ) as -SO ２ If a - or -CO- is included, the other end of the sulfonyl group may be bonded to the meta position of these linking groups.

[0118] (Electrolyte membrane (E)) The electrolyte membrane (E) may consist only of a 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), or they may be additives such as water-retaining inorganic substances or radical scavengers. Specific examples of additives include water, silica, cerium oxide, and manganese oxide. These components may be used individually or in combination.

[0119] The content of the crosslinking agent (L) 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. The above content is based on the total amount of solids in the electrolyte membrane (E).

[0120] The total content of the crosslinked material (L) and polymer (P) 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. The above total content is based on the total amount of solids in the electrolyte membrane (E).

[0121] 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, 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, 3.0 mmol / g or less, or 2.3 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, 1.0 to 3.8 mmol / g, 1.0 to 3.5 mmol / g, 1.5 to 3.8 mmol / g, 2.0 to 3.5 mmol / g, 2.0 to 3.0 mmol / g, 2.0 to 2.3 mmol / g, or 2.4 to 3.0 mmol / g.

[0122] 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)

[0123] The gel fraction of the electrolyte membrane (E) may be 10% or more, 15% or more, 20% or more, 40% or more, or 80% or more. A gel fraction of 10% or more makes it easier to obtain an electrolyte membrane with superior swelling resistance. Furthermore, it becomes easier to form a better phase separation structure, making it easier to obtain an electrolyte membrane with superior proton conductivity. The gel fraction of the electrolyte membrane (E) may also be 100% or less, or 90% or less. A gel fraction of 90% or less makes it easier to obtain an electrolyte membrane with superior flexibility. Furthermore, it becomes easier to increase the ion exchange capacity, making it easier to obtain an electrolyte membrane with superior proton conductivity. From these viewpoints, the gel fraction of the electrolyte membrane (E) may be 10-100%, 15-100%, 20-100%, 40-100%, 80-100%, 20-90%, or 40-90%. 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.

[0124] 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)

[0125] 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.

[0126] As described later, the electrolyte membrane (E) can be obtained by heating a membrane containing polymer (P) and dimethyl sulfoxide (hereinafter also referred to as "the treated membrane (E')") at 140 to 200°C to crosslink the polymer (P).

[0127] 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.

[0128] 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.).

[0129] <Method for Manufacturing an Electrolyte Membrane> One embodiment of the method for manufacturing an electrolyte membrane comprises a step of heating a membrane containing a polymer (P) and dimethyl sulfoxide (the membrane to be treated (E')) at 140 to 200°C (hereinafter referred to as the "heating step"). This method yields an electrolyte membrane that has excellent proton conductivity and excellent swelling resistance.

[0130] In the above method, during the heating step, the polymer (P) in the treated film (E') is heated in the presence of dimethyl sulfoxide, which promotes crosslinking of the polymer (P) (electrophilic substitution reaction by sulfonium ion groups), and a crosslinked product (L) may be formed. Therefore, the electrolyte membrane obtained by the above method may be the electrolyte membrane (E) of the above embodiment. The progress of crosslinking of the polymer (P) can be confirmed, for example, by a change (decrease) in the ion exchange capacity of the membrane and a change (increase) in the gel fraction.

[0131] The treated film (E') may consist only of polymer (P) and dimethyl sulfoxide, or it may contain components other than polymer (P) and dimethyl sulfoxide. Examples of components other than polymer (P) and dimethyl sulfoxide include the additives mentioned above. These components may be used individually or in combination.

[0132] The polymer (P) content in the treated film (E') may be 90 to 100% by mass, 94 to 100% by mass, or 97 to 100% by mass, based on the total solid content of the treated film (E'), from the viewpoint of obtaining an electrolyte film with superior proton conductivity and swelling resistance.

[0133] The dimethyl sulfoxide content in the treated film (E') may be 1 to 20 parts by mass per 100 parts by mass of polymer (P), from the viewpoint of facilitating the formation of crosslinked bodies (L) with a higher degree of crosslinking, and thus making it easier to obtain an electrolyte film with superior proton conductivity and swelling resistance. From a similar viewpoint, the dimethyl sulfoxide content in the treated film (E') may be 3 parts by mass or more, or 6 parts by mass or more, or 18 parts by mass or less, or 15 parts by mass or less, or 3 to 18 parts by mass or 6 to 15 parts by mass per 100 parts by mass of polymer (P).

[0134] The ion exchange capacity of the treated membrane (E') may be 1.1 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, 3.5 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 treated membrane (E') may be 1.1 to 4.0 mmol / g, 1.5 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 treated membrane (E') is a value measured by the same method as the method for measuring the ion exchange capacity of the electrolyte membrane described above.

[0135] The heating process may be carried out according to the method and conditions described in Non-Patent Document 1. The degree of crosslinking of the electrolyte membrane can be adjusted by adjusting the heating conditions. Longer heating times tend to result in higher crosslinking, and higher heating temperatures tend to result in higher crosslinking. The heating temperature and heating time of the film to be treated (E') may be changed according to the desired degree of crosslinking. The heating temperature of the film to be treated (E') may be 150°C or higher, 160°C or higher, or 170°C or higher, or 190°C or lower, or 150-200°C, 160-200°C, or 170-190°C. The heating time of the film to be treated (E') may be, for example, 0.1-120 hours, 0.5-90 hours, 1-72 hours, 6-36 hours, 10-24 hours, or 20-36 hours. Heating may be carried out in air.

[0136] The degree of crosslinking of the electrolyte membrane can be determined from the following formula (II): Degree of crosslinking = (C １ -C ２ ) / C １ ×100...(II) [In formula (II), C １ This represents the ion exchange capacity of the heated film (the film being treated (E')), and C ２ This represents the ion exchange capacity of the resulting electrolyte membrane.

[0137] The degree of crosslinking of the electrolyte membrane is preferably 0.1 to 15%. By setting the degree of crosslinking to 0.1% 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. On the other hand, if the degree of crosslinking is 15% or less, it becomes easier to obtain an electrolyte membrane with superior flexibility. Furthermore, the ion exchange capacity tends to increase, making it easier to obtain an electrolyte membrane with superior proton conductivity. From these viewpoints, the degree of crosslinking of the electrolyte membrane may be 0.5% or more, 1.0% or more, 3.0% or more, or 5.0% or more, or 12% or less, 11% or less, 10% or less, or 6.0% or less, or 0.5 to 12%, 1.0 to 11%, 1.0 to 10%, 3.0 to 10%, 1.0 to 6.0%, or 5.0 to 11%.

[0138] In one embodiment, the method for manufacturing an electrolyte membrane may include, in addition to the heating step described above, a step of forming the membrane to be treated (E') (hereinafter referred to as the "membrane formation step").

[0139] In the film formation step, the film to be treated (E') may be formed by a known method for forming an electrolyte polymer film (for example, a solution casting method or a dispersion casting method). Specifically, for example, a liquid composition containing polymer (P) and dimethyl sulfoxide may be applied to a substrate, and then the liquid composition may be dried to form the film to be treated (E') on the substrate. The liquid composition may contain the additives mentioned above.

[0140] In the solution casting method, dimethyl sulfoxide may be used alone as the solvent, or dimethyl sulfoxide may be used in combination with other solvents. That is, the liquid composition may further contain other solvents. The other solvent is not particularly limited as long as it is a solvent that can dissolve the polymer (P), and for example, N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, diphenyl sulfone, sulfolane, 1,3-dimethyl-2-imidazolidinone, and tetramethylurea can be used. These may be used individually or in combination.

[0141] 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.

[0142] The solid content in the liquid composition (for example, the content of polymer (P)) may be 1% by mass or more, 5% by mass or more, or 10% by mass or more, and may be 50% by mass or less, 40% by mass or less, or 30% by mass or less, based on the total amount of the liquid composition. The solid content in the liquid composition may be 1 to 50% by mass, 5 to 40% by mass or 10 to 30% by mass. The dimethyl sulfoxide content in the liquid composition may be 1% by mass or more, 10% by mass or more, or 20% by mass or more, and may be 99% by mass or less, 95% by mass or less, or 90% by mass or less, based on the total amount of the liquid composition. The dimethyl sulfoxide content in the liquid composition may be 1 to 99% by mass, 10 to 95% by mass or 20 to 90% by mass.

[0143] The drying temperature and drying time for forming the treated film (E') may be adjusted so that the dimethyl sulfoxide content in the resulting treated film (E') falls within the above range. Depending on the amount of liquid medium (solvent, dispersion medium) used, the drying temperature may be, for example, 25 to 130°C, 40 to 120°C, or 55 to 110°C, and the drying time may be, for example, 0.05 to 48 hours, 0.1 to 24 hours, or 0.25 to 12 hours.

[0144] In one embodiment, the method for producing an electrolyte membrane may include, in addition to the heating step, a step of washing the membrane obtained in the heating step (the membrane after heat treatment) (hereinafter referred to as the "washing step"). The washing step may be performed for purposes such as removing residual dimethyl sulfoxide, by-products, etc., from the membrane, and neutralizing the pH.

[0145] In the cleaning process, the heat-treated film may be cleaned using a cleaning solution. In this case, the electrolyte film is obtained by drying the film after the cleaning process using methods such as vacuum drying. As the cleaning solution, a known cleaning solution suitable for the purpose of cleaning may be used. Specific examples of cleaning 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.

[0146] <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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] The catalyst layer may further contain additives such as water repellents like fluorinated carbon, binders like fluororesins and hydrocarbon resins having sulfonic acid groups.

[0154] 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.

[0155] 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.

[0156] <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.

[0157] 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.

[0158] 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).

[0159] 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.

[0160] 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.

[0161] <Solid Polymer Fuel Cell> A solid polymer fuel cell according to one embodiment comprises the membrane electrode assembly of the above embodiment.

[0162] The configuration of a polymer electrolyte fuel cell is not particularly limited and can be a conventionally known configuration, except that it uses the membrane electrode assembly of the above embodiment. 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.

[0163] <Solid Polymer Water Electrolyzer> A solid polymer water electrolyzer according to one embodiment includes the membrane electrode assembly according to the above embodiment.

[0164] 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.

[0165] 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.

[0166] <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%.

[0167]

[0168] <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%.

[0169]

[0170] <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%.

[0171]

[0172] <Comparative Example 1> (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 solution was allowed to cool to room temperature, it was reprecipitated and purified from 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.

[0173]

[0174] In equation (P1), M represents Na, K, or H, and n represents a positive number. In equation (P1), n ​​was approximately 20.

[0175] (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.

[0176] [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).

[0177] (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.

[0178] (Preparation of Electrolyte Membrane) The obtained polymer (P1') was dissolved in DMSO to obtain a solution containing 10% by mass of polymer (P1'). The obtained solution was cast onto a glass substrate and dried at 120°C for 1 hour to obtain the electrolyte membrane of Comparative Example 1 (film thickness 25 μm). The DMSO content in the electrolyte membrane, calculated from the mass loss rate due to drying, was 11 parts by mass per 100 parts by mass of polymer (P1'). Note that the "film thickness" in this example was measured using PG-02 manufactured by TECLOK CORPORATION.

[0179] (Ion Exchange Capacity Measurement) The obtained 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 was 2.21 mmol / g. IEC (unit: mmol / g) = {Concentration of sodium hydroxide aqueous solution (unit: mol / L) × Droplet volume (unit: mL)} / Dry mass of electrolyte membrane (unit: g)

[0180] (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 of Comparative Example 1 was 0%. 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.

[0181] (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 165 mS / cm. Hereinafter, the proton conductivity in the examples and comparative examples represents the measured value under conditions of 80°C and 100% relative humidity.

[0182] [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 72%.

[0183] <Example 1> (Preparation of electrolyte membrane) The electrolyte membrane of Comparative Example 1 (thickness 25 μm) was heated at 180°C for 12 hours, then washed sequentially with 3% hydrogen peroxide solution, 5M sulfuric acid, and pure water, and dried under reduced pressure to obtain the electrolyte membrane of Example 1 (thickness 25 μm). When the ion exchange capacity was measured using the same method as in Comparative Example 1, the IEC of the electrolyte membrane of Example 1 was 2.18 mmol / g, and the gel fraction of the electrolyte membrane of Example 1, calculated using the same method as in Comparative Example 1, was 42%, confirming that some of the sulfonic acid groups reacted to form crosslinks with sulfonyl groups.

[0184] (Degree of Crosslinking) The degree of crosslinking (%) of the electrolyte membrane in Example 1 was calculated using the following formula (IIa). The degree of crosslinking was 1.4%. Degree of Crosslinking = (C １ａ -C ２ａ ) / C １ａ ×100...(IIa) In formula (IIa), C １ａ The IEC (unit: mmol / g) of the electrolyte membrane in Comparative Example 1 is shown, and C ２ａ This represents the IEC (unit: mmol / g) of the electrolyte membrane in Example 1.

[0185] (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 169 mS / cm, confirming that the electrolyte membrane of this example has good proton conductivity. The volume swelling rate was 51%, confirming that the electrolyte membrane of this example has excellent swelling resistance.

[0186] <Example 2> (Preparation of Electrolyte Membrane) An electrolyte membrane (thickness 25 μm) of Example 2 was obtained using the same method as in Example 1, except that the heating time was 24 hours. 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 2.09 mmol / g, and the gel fraction of the electrolyte membrane of Example 2, calculated using the same method as in Comparative Example 1, was 90%, confirming that some of the sulfonic acid groups reacted to form crosslinks with sulfonyl groups. C ２ａ The degree of crosslinking of the electrolyte membrane in Example 2 was calculated using the same method as in Example 1, except that the IEC of the electrolyte membrane in Example 2 was used. The degree of crosslinking of the electrolyte membrane in Example 2 was 5.4%.

[0187] (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 155 mS / cm, confirming that the electrolyte membrane of this example has good proton conductivity. The volume swelling rate was 43%, confirming that the electrolyte membrane of this example has excellent swelling resistance.

[0188] <Comparative Example 2> In Comparative Example 2, 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 same method as in Comparative Example 1. The IEC was 1.0 mmol / g, the proton conductivity was 130 mS / cm, and the volume swelling rate was 61%.

[0189] <Reference Example 1> (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 Comparative Example 1, had a Mn of 35,000, a Mw of 71,000, and a Mw / Mn ratio of 2.0.

[0190]

[0191] In equation (P2), M represents Na, K, or H, and n represents a positive number. In equation (P2), n was approximately 20.

[0192] (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.

[0193] (Preparation of Electrolyte Membrane) The obtained polymer (P2') was dissolved in DMSO to obtain a solution containing 10% by mass of polymer (P2'). The obtained solution was cast onto a glass substrate and dried at 120°C for 1 hour to obtain the electrolyte membrane of Reference Example 1 (film thickness 24 μm). The DMSO content in the electrolyte membrane, calculated from the mass loss rate due to drying, was 12 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 Reference Example 1 was 2.53 mmol / g, and the gel fraction of the electrolyte membrane of Reference Example 1, calculated using the same method as in Comparative Example 1, was 0%.

[0194] <Example 3> (Preparation of Electrolyte Membrane) The electrolyte membrane of Reference Example 1 (thickness 24 μm) was heated at 180°C for 1 hour, then washed sequentially with 3% hydrogen peroxide solution, 5M sulfuric acid, and pure water, and dried under reduced pressure to obtain the electrolyte membrane of Example 3 (thickness 24 μm). 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 2.51 mmol / g, and the gel fraction of the electrolyte membrane of Example 3, calculated using the same method as in Comparative Example 1, was 39%, confirming that some of the sulfonic acid groups reacted to form crosslinks with sulfonyl groups. C １ａ Using the IEC of the electrolyte membrane in Reference Example 1, C ２ａ The degree of crosslinking of the electrolyte membrane in Example 3 was calculated using the same method as in Example 1, except that the IEC of the electrolyte membrane in Example 3 was used. The degree of crosslinking of the electrolyte membrane in Example 3 was 0.8%.

[0195] (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 193 mS / cm, confirming that the electrolyte membrane of this example has good proton conductivity. The volume swelling rate was 45%, confirming that the electrolyte membrane of this example has excellent swelling resistance.

[0196] <Example 4> (Preparation of Electrolyte Membrane) An electrolyte membrane (thickness 24 μm) of Example 4 was obtained using the same method as in Example 3, except that the heating time was 6 hours. 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 2.49 mmol / g, and the gel fraction of the electrolyte membrane of Example 4, calculated using the same method as in Comparative Example 1, was 93%, confirming that some of the sulfonic acid groups reacted to form crosslinks with sulfonyl groups. C ２ａ The degree of crosslinking of the electrolyte membrane in Example 4 was calculated using the same method as in Example 3, except that the IEC of the electrolyte membrane in Example 4 was used. The degree of crosslinking of the electrolyte membrane in Example 4 was 1.6%.

[0197] (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 167 mS / cm, confirming that the electrolyte membrane of this example has good proton conductivity. The volume swelling rate was 42%, confirming that the electrolyte membrane of this example has excellent swelling resistance.

[0198] <Example 5> (Preparation of Electrolyte Membrane) An electrolyte membrane (thickness 24 μm) of Example 5 was obtained using the same method as in Example 3, except that the heating time was 12 hours. 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 2.48 mmol / g, and the gel fraction of the electrolyte membrane of Example 5, calculated using the same method as in Comparative Example 1, was 100%, confirming that some of the sulfonic acid groups reacted to form crosslinks with sulfonyl groups. C ２ａ The degree of crosslinking of the electrolyte membrane in Example 5 was calculated using the same method as in Example 3, except that the IEC of the electrolyte membrane in Example 5 was used. The degree of crosslinking of the electrolyte membrane in Example 5 was 2.0%.

[0199] (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 162 mS / cm, confirming that the electrolyte membrane of this example has good proton conductivity. The volume swelling rate was 42%, confirming that the electrolyte membrane of this example has excellent swelling resistance.

[0200] <Example 6> (Preparation of Electrolyte Membrane) An electrolyte membrane (thickness 24 μm) of Example 6 was obtained using the same method as in Example 3, except that the heating time was 24 hours. 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 2.26 mmol / g, and the gel fraction of the electrolyte membrane of Example 6, calculated using the same method as in Comparative Example 1, was 100%, confirming that some of the sulfonic acid groups reacted to form crosslinks with sulfonyl groups. C ２ａ The degree of crosslinking of the electrolyte membrane in Example 6 was calculated using the same method as in Example 3, except that the IEC of the electrolyte membrane in Example 6 was used. The degree of crosslinking of the electrolyte membrane in Example 6 was 10.8%.

[0201] (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 142 mS / cm, confirming that the electrolyte membrane of this example has good proton conductivity. The volume swelling rate was 39%, confirming that the electrolyte membrane of this example has excellent swelling resistance.

[0202]

[0203] This application is based on Japanese Patent Application No. 2024-169418, 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 the following formula (a1): (In formula (a1), IExG represents at least one group selected from the group consisting of a sulfonic acid group which is an ion exchange group and its salts, and 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 L ３ may be the same as or different from each other.) represents a structural unit, and A ２ represents the following formula (a2): (In formula (a2), Ar represents an arylene group having no ion exchange group, and 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 as or different from each other, and a plurality of L ４ may be the same as 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 as or different from each other, a plurality of A<s ２ may be the same as or different from each other, a plurality of L １ may be the same as or different from each other, a plurality of L ２ may be the same as or different from each other. However, the difference in x in formula (a1) among a plurality of A １ is within 3, the difference in y in formula (a2) among a plurality of A ２ is within 5, and a plurality of L １ , L ２ and L ４ An electrolyte membrane comprising a crosslinked polymer having a structure represented by ], wherein the crosslinked polymer has a structure in which a plurality of polymer units derived from the polymer are crosslinked with each other via sulfonyl groups derived from the sulfonic acid group or a salt thereof.

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

3. Said L ３ However, single bonds or -SO ２ - The electrolyte membrane according to claim 1 or 2.

4. The electrolyte membrane according to any one of claims 1 to 3, 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.

5. An electrolyte membrane according to any one of claims 1 to 4, wherein the ion exchange capacity is 1.0 to 4.0 mmol / g.

6. An electrolyte membrane according to any one of claims 1 to 5, wherein the gel fraction obtained from the following formula (I) is 10 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.

7. The following formula (1): [In formula (1), A １ The following formula (a1): (In formula (a1), IExG represents at least one group selected from the group consisting of sulfonic acid groups and salts thereof, which are ion exchange groups, 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 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 The difference of y in equation (a2) is within 5, and multiple L １ , L ２ and L ４ A method for producing an electrolyte membrane, comprising the step of heating a membrane containing a polymer having a structure represented by ] and dimethyl sulfoxide at 140 to 200°C, wherein at least one of the elements is a single bond, -O-, or -S-.

8. The method for producing an electrolyte membrane according to claim 7, wherein the content of the dimethyl sulfoxide in the heated membrane is 1 to 20 parts by mass per 100 parts by mass of the polymer.

9. The method for producing an electrolyte membrane according to claim 7 or 8, wherein the degree of crosslinking of the electrolyte membrane, as determined by the following formula (II), is 0.1 to 15%. Degree of crosslinking = (C １ -C ２ ) / C １ ×100...(II) [In formula (II), C １ represents the ion exchange capacity of the heated membrane, C ２ This represents the ion exchange capacity of the electrolyte membrane.

10. An electrolyte membrane with a catalyst layer, comprising an electrolyte membrane according to any one of claims 1 to 6, and a catalyst layer disposed on one or both sides of the electrolyte membrane.

11. A membrane electrode assembly comprising an electrolyte membrane according to any one of claims 1 to 6, and an electrode layer disposed on one or both sides of the electrolyte membrane.

12. A polymer electrolyte fuel cell comprising the membrane electrode assembly described in claim 11.

13. A solid polymer water electrolysis apparatus comprising the membrane electrode assembly described in claim 11.

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