JP2017216187A - Composite nanofiber and electrolyte membrane including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop a novel nanofiber for forming a composite electrolyte membrane to provide an electrolyte membrane having enough ion conductivity (proton conductivity) and a satisfactory gas barrier property even if it is arranged in a thin form of 30 μm or smaller.SOLUTION: Disclosed are: a composite nanofiber comprising an electrolyte polymer and a basic polymer, provided that the electrolyte polymer has proton conductivity; an electrolyte membrane comprising the nanofiber; and a method for manufacturing a composite membrane. The method for manufacturing a composite membrane comprises the steps of: forming the composite nanofiber and a nonwoven fabric including the composite nanofiber; performing an after-treatment on the nonwoven fabric; filling a matrix polymer in cavities of the nonwoven fabric, thereby integrating the composite nanofiber with the matrix polymer; and performing an after-treatment on an electrolyte membrane including the composite nanofiber.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrolyte membrane obtained by introducing a matrix polymer into nanofibers and nanofiber nonwoven fabrics, and more particularly to a polymer electrolyte membrane useful for a polymer electrolyte fuel cell or the like.

Composite membranes in which various substances are introduced into a nonwoven fabric have been applied to various fields, and in recent years have attracted attention as electrolyte membranes in polymer electrolyte fuel cells.
A polymer electrolyte membrane has been proposed as an electrolyte membrane in a polymer electrolyte fuel cell, and an example thereof is a fluorine-based electrolyte typified by Nafion (registered trademark). However, these fluorine-based electrolyte membranes have poor power generation performance due to reduced proton conductivity under low humidification conditions, induce membrane and catalyst deterioration by side reactions accompanying fuel gas permeation, have poor membrane strength, and undergo dimensional changes. There are problems such as poor long-term stability and high cost due to the use of fluorine.

  On the other hand, development of a hydrocarbon-based polymer electrolyte membrane that does not use a fluorine material is also being studied. In hydrocarbon-based polymer electrolyte membranes, it has been proposed to increase the number of sulfonic acid groups in order to increase ionic conductivity. However, in this proposal, the membrane is easily deformed due to water swelling, and mechanical strength is increased. However, it is difficult to obtain a film having excellent long-term stability.

Accordingly, various developments have been made, and among them, sulfonated polyimide has been proposed as a high-performance electrolyte material because it has high thermal stability and mechanical strength and is excellent in film forming properties (Patent Documents 1 to 4). ). However, the sulfonated polyimide according to these proposals has a problem that the ionic conductivity becomes low under high temperature and low humidity, so that it shows high ionic conductivity in a wide temperature range, and as a polymer electrolyte membrane excellent in mechanical strength. A phosphoric acid doped sulfonated polyimide / polybenzimidazole blend membrane has been proposed (Patent Document 5).
Such a film is characterized by high ion conductivity in a wide temperature range from a low temperature of about −20 ° C. to a high temperature of about 120 ° C., and excellent ion conductivity even under low humidification conditions with little moisture in the film. .
However, in recent years, polymer electrolyte membranes are required to have high ion conductivity without being humidified, and the thickness tends to be lowered for the purpose of reducing membrane resistance. Since the blend film has a rigid structure in the main chain, it exhibits high mechanical strength. However, since it is brittle, there is a problem that handling becomes difficult when the film is thinned. Further, since the gas permeability is increased by reducing the film thickness and hydrogen peroxide is generated in a large amount, the oxidation stability is poor and the film is not stable in the long term.

Therefore, in Patent Document 6, a proposal has been made to provide a composite membrane that exhibits high ion conductivity in a wide range of temperature and humidity, is excellent in handleability even in a thin film, and has excellent long-term stability, and a method for producing the same.

JP 2002-358978 A JP-A-2005-232236 JP 2005-272666 A JP 2007-302741 A JP 2011-68872 A JP 2012-238590 A

However, at present, there is a demand to further reduce the film thickness, more specifically, to reduce the film thickness to 20 μm or less, compared with the proposal of Patent Document 6 described above. With such a film thickness, problems such as insufficient ion conductivity (proton conductivity) and difficulty in keeping gas permeability low have occurred.
In short, in the conventionally proposed composite membranes, it is difficult to achieve both sufficient ion conductivity (proton conductivity) and gas barrier properties when the film thickness is reduced as much as currently required, and is 20 μm or less. In the present situation, there is a demand for the development of a composite membrane having sufficient ion conductivity (proton conductivity) and gas barrier properties even when the film thickness is reduced.

  Accordingly, an object of the present invention is to develop an electrolyte membrane having sufficient ion conductivity (proton conductivity) and gas barrier property even when a new nanofiber constituting the composite electrolyte membrane is developed and thinned to 20 μm or less. It is to provide.

The present inventors thought that the above-mentioned problems could be solved by devising a material constituting the nanofiber constituting the nonwoven fabric and a method for producing the nanofiber. As a result of examining various substances, a nanofiber was produced by combining a basic polymer having a basic functional group capable of interacting with a cation exchange group with an electrolyte polymer having a cation exchange group, It has been found that the above object can be achieved by filling the voids with a matrix polymer, and the present invention has been completed.
That is, the present invention provides the following inventions.
1. A composite nanofiber comprising an electrolyte polymer and a basic polymer,
The composite nanofiber, wherein the electrolyte polymer has proton conductivity.
2. 2. The composite nanofiber according to 1, wherein the electrolyte polymer has the following structures A) and B).
A) The main chain contains a repeating unit containing an aromatic group or a fluorine-containing aliphatic group.
B) The repeating unit has a side chain into which a cation exchange group has been introduced.
3. The electrolyte polymer has a structure in which the main chain skeleton is selected from the group consisting of a polyarylene ether skeleton, a polyimide skeleton, a polystyrene skeleton, or a fluoroethylene skeleton,
The composite nanofiber according to 1-2, wherein the side chain has a structure in which a cation exchange group selected from the group consisting of a sulfonic acid group, a phosphonic acid group, and a carboxylic acid group is introduced.
4). 2. The composite nanofiber according to 1, wherein the basic polymer has the following structures A) and B).
A) The main chain contains a repeating unit containing an aromatic group and / or an aliphatic group.
B) The main chain skeleton or the side chain functional group has a basic functional group capable of interacting with a cation exchange group.
5. The abundance ratio of the electrolyte polymer is 1 to 99% by mass in the entire composite nanofiber,
The fiber diameter of the composite nanofiber is 500 nm or less,
The composite nanofiber according to 1 to 4, which is characterized by the following.
6). The abundance ratio of the composite nanofiber is 1 to 50% by mass in the entire electrolyte membrane,
The thickness of the electrolyte membrane containing the composite nanofiber is 30 μm or less,
An electrolyte membrane comprising the composite nanofiber according to any one of 1 to 5.
7). Forming a composite nanofiber and a nonwoven fabric comprising the composite nanofiber,
Post-processing the nonwoven fabric,
A method for producing a composite membrane, comprising: filling a void in the nonwoven fabric with a matrix polymer to integrate the composite nanofiber and the matrix polymer; and post-treating an electrolyte membrane containing the composite nanofiber.
A membrane / electrode assembly for a polymer electrolyte fuel cell, comprising an electrolyte membrane containing the composite nanofiber according to 8.1 to 7.
A polymer electrolyte fuel cell comprising the membrane electrode assembly according to 9.8.

  The composite nanofiber of the present invention exceeds the properties of nanofibers conventionally used in composite membranes, and the electrolyte membrane containing the nanofibers has sufficient ion conductivity (proton) even when thinned to 20 μm or less. Conductivity), gas barrier properties, and film strength.

FIG. 1 is a schematic diagram schematically showing a composite nanofiber of the present invention and an electrolyte membrane containing the nanofiber. FIG. 2 is a schematic diagram schematically showing each step in the method for producing the composite nanofiber of the present invention and the electrolyte membrane containing the nanofiber. FIG. 3 is a SEM photograph (drawing substitute photograph) of the composite nanofiber nonwoven fabric obtained in Example 1. FIG. 4 is an SEM photograph (drawing substitute photograph) of the composite nanofiber nonwoven fabric obtained in Example 3. FIG. 5 is a SEM photograph (drawing substitute photograph) of the composite nanofiber nonwoven fabric obtained in Example 4. 6 is a SEM photograph (drawing substitute photograph) of the composite nanofiber nonwoven fabric obtained in Example 5. FIG.

1: composite nanofiber, 2: electrolyte polymer, 3: basic polymer, 5: post-treatment solution of composite nanofiber, 6: matrix polymer, 7: post-treatment solution of electrolyte membrane

Hereinafter, the present invention will be described in more detail.
The composite nanofiber of the present invention comprises an electrolyte polymer and a basic polymer,
The electrolyte membrane includes the composite nanofiber and a matrix polymer that exists in contact with the composite nanofiber.
Hereinafter, the components will be described first.

<Constituents>
(Electrolyte polymer)
The electrolyte polymer is a substance that conducts protons and exhibits the main function as an electrolyte membrane when the electrolyte membrane of the present invention is used as a polymer electrolyte membrane for a polymer electrolyte fuel cell. The specific substance as the electrolyte polymer is a proton conductive substance having a repeating unit containing an aromatic group or a fluorine-containing aliphatic group in the main chain, and having a side chain in which a cation exchange group is introduced into the repeating unit. Preferably there is.
Here, the main chain skeleton includes polyarylene ether (PAE) shown below, polyimide (PI) shown below, polystyrene and copolymer (PSt) shown below, polybenzimidazole (PBI), polyphenylene (PP). Polyphenylene oxide (PPO), polyphenylene sulfide (SPPS), polyvinyl sulfonic acid and its copolymer (PVS), and the like can be used.
Examples of the cation exchange group include acid functional groups such as a sulfonic acid group, a phosphonic acid group, and a carboxylic acid group, which can be used by being introduced at any position of the main chain skeleton.
Further, Nafion (registered trademark) having a fluoroalkyl main chain and a fluoroalkylsulfonic acid group can be used.
In use, the electrolyte polymer can be used alone or as a mixture of a plurality of electrolyte polymers.
Among these, sulfonated polyarylene ether (SPAE) such as sulfonated polyarylene ether sulfone is excellent in proton conductivity, thermal stability and mechanical strength, and also has a relatively good ability to form nanofibers. Therefore, it is preferable.
When mixing with a basic polymer to produce a composite nanofiber, the counter cation bonded to the cation exchange group must be a proton to prevent insolubilization due to the interaction between the two polymers in solution. No, any counter ion species can be selected by ion exchange. Examples thereof include sodium, potassium, triethylammonium, imidazolium and the like.
Preferred examples of the electrolyte polymer include compounds represented by the following chemical formulas.

Polyarylene ether (PAE)

(In the formula, n represents a number of 2 to 5000, and m represents a number of 2 to 5000))

Polyimide (PI)
(In the formula, n represents a number of 2 to 5000)

Polystyrene and its copolymers (PSt),
(In the formula, R represents a linear or branched hydrocarbon group having 1 to 18 carbon atoms, or a hydrocarbon group having a hydroxyl group or the like. (Wherein n represents a number of 2 to 5000, m represents Indicate a number between 2 and 5000))

  Examples of the sulfonated polyarylene ether (SPAE) include the following polymers.

(Wherein X and Y are divalent groups having at least one aromatic ring, such as a benzene ring or naphthalene ring, which may be substituted with a substituent such as a hydroxyl group, an alkyl group or a sulfonic acid group) aromatic rings, nitrogen-containing heterocyclic ring such as pyridine ring, two benzene rings is a direct _{bond, -O -, - CO -,} - SO 2 -, - S -, - CH 2 -, - C (CH 3 ) _2- , -C (CF ₃ ) _2- and the like, and a divalent group containing a benzene ring or the like linked by,
Having at least one sulfonic acid group, phosphonic acid group, carboxylic acid group, or other acid functional group in the aromatic ring of X and / or Y;
n is preferably an integer of 2 to 5000, more preferably 100 to 500.
Examples of the acid functional group counter cation include protons, sodium, potassium, triethylammonium, imidazolium, and other arbitrary cation species. )

Moreover, the polymer which has the following block structures which can introduce | transduce an acid functional group locally can also be used.

(In the formula, the repeating unit represented by a is a hydrophilic part,
X1 is a divalent group having at least one aromatic ring, for example, an aromatic ring such as a benzene ring or a naphthalene ring, which may be substituted with a substituent such as a hydroxyl group, an alkyl group, or a sulfonic acid group, A nitrogen-containing heterocycle such as a pyridine ring, two benzene rings are directly bonded, —O—, —CO—, —SO ₂ —, —S—, —CH ₂ —, —C (CH ₃ ) ₂ —, — A divalent group containing a benzene ring connected by C (CF ₃ ) _2- and the like,
In the formula, Y1 is also a divalent group having at least one aromatic ring, for example, an aromatic group such as a benzene ring or a naphthalene ring, which may be substituted with a substituent such as a hydroxyl group, an alkyl group, or a sulfonic acid group. A nitrogen-containing heterocycle such as a ring or a pyridine ring, two benzene rings are directly bonded, —O—, —CO—, —SO ₂ —, —S—, —CH ₂ —, —C (CH ₃ ) ₂ — , A divalent group containing a benzene ring linked by —C (CF ₃ ) ₂ — and the like,
X1 and / or Y1 has at least one, preferably many, for example, 2 to 4 acid functional groups such as a sulfonic acid group, a phosphonic acid group, and a carboxylic acid group in the aromatic ring,
a is preferably an integer of 1 to 500, more preferably 4 to 50. )
(In the formula, the repeating unit represented by b is a hydrophobic part,
X1 is a divalent group having at least one aromatic ring, for example, an aromatic ring such as a benzene ring or a naphthalene ring, a pyridine ring, which may be substituted with a substituent such as an alkyl group or a fluoroalkyl group nitrogen-containing heterocyclic ring such as two benzene rings is a direct _{bond, -O -, - CO -,} - SO 2 -, - S -, - CH 2 -, - C (CH 3) 2 -, - C ( A divalent group containing a benzene ring linked by CF ₃ ) _2- and the like,
In the formula, Y1 is also a divalent group having at least one aromatic ring, for example, an aromatic ring such as a benzene ring or a naphthalene ring, which may be substituted with a substituent such as an alkyl group or a fluoroalkyl group, A nitrogen-containing heterocycle such as a pyridine ring, two benzene rings are directly bonded, —O—, —CO—, —SO ₂ —, —S—, —CH ₂ —, —C (CH ₃ ) ₂ —, — A divalent group containing a benzene ring connected by C (CF ₃ ) _2- and the like,
The aromatic ring of X1 and Y1 does not contain an acid functional group, and b is preferably an integer of 1 to 500, more preferably 4 to 50. )
N is preferably an integer of 1 to 1000, more preferably 1 to 100, and particularly preferably 8 to 100. )
Furthermore, a polymer having the following graft structure capable of introducing a sulfonic acid group locally can also be used.

(X1, Y1, X2, Y2, X3 and Y3 are the same or different groups, each being a divalent group having at least one aromatic ring, for example, a substituent such as a hydroxyl group, an alkyl group or a sulfonic acid group. An aromatic ring such as a benzene ring or a naphthalene ring, a nitrogen-containing heterocyclic ring such as a pyridine ring, two benzene rings directly bonded, —O—, —CO—, —SO ₂ —, A divalent group containing a benzene ring connected by —S—, —CH ₂ —, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ — and the like,
X1, Y1, X2, Y2, X3, and Y3 have at least one, preferably many, for example, 2 to 4 acid functional groups such as sulfonic acid group, phosphonic acid group, and carboxylic acid group,
a, b and c each represent an integer of 1 to 500.
The repeating units represented by a and b may have the above-described block structure. )
More specifically, the following polymers can be used.

(x and y are each an integer of 1 to 1000)
The SPAE can be obtained as follows, for example, if it is sulfonated poly (arylene ether sulfone) (SPAES).
That is, using a polymerization solvent such as N, N-dimethylacetamide and an azeotropic agent (toluene, etc.) under a nitrogen atmosphere, 4,4′-bisfluorophenylsulfone-3,3′-sodium disulfonate, 4,4 ′ -Bisfluorophenylsulfone, 4,4'-biphenol and potassium carbonate are added, and the mixture is stirred for 1 to 10 hours at a temperature of 100 ° C or higher, and then further heated to 1 to 10 hours after raising the temperature.

In addition, a weight average molecular weight and a polymerization degree can be measured and calculated by GPC (gel permeation chromatography) by the following methods, and are polystyrene conversion values.
<Measurement method of molecular weight by GPC>
Using dimethylformamide (hereinafter referred to as “DMF”) to which a small amount of LiBr (10 mM) is added, the molecular weight of the synthesized polymer is measured in terms of polystyrene. The sample solution is prepared by dissolving the polymer in DMF supplemented with lithium bromide at a concentration of 1 mg / ml.

<Constituents>
(Basic polymer)
The basic polymer is a polymer having a functional group capable of interacting with an acid substituent of the electrolyte polymer. Here, the “interaction” includes not only the formation of ionic bonds and hydrogen bonds, but also the formation of covalent bonds, charge transfer complexes, and hydrophobic interactions.
Examples of the functional group capable of reacting with the acid substituent of the electrolyte polymer include —NH ₂ group,> NH group,> N-group, and ═N-group.
Examples of the polymer include polybenzimidazole, polybenzoxazole, polybenzthioazole, polyindole, polyquinoline, polyvinylimidazole, polyallylamine, polyethyleneimine and the like having the following structural formula.
Among these, polybenzimidazole is preferable because it has excellent chemical stability and mechanical properties, can improve the mechanical strength and heat resistance of the electrolyte membrane, and can contribute to thinning of the electrolyte membrane.

(X in the formula includes O, CO, SO ₂ , S, CH ₂ , C (CH ₃ ) ₂ , C (CF ₃ ) ₂ , etc.,
Y is a divalent group having at least one aromatic ring or aliphatic hydrocarbon, such as a benzene ring or naphthalene ring, which may be substituted with a substituent such as a hydroxyl group, an alkyl group, or a sulfonic acid group. A divalent group including a nitrogen-containing heterocyclic ring such as an aromatic ring, a pyridine ring, a benzene ring in which two benzene rings are directly bonded, connected by —O—, —CO—, —SO ₂ —, etc. Are mentioned,
n is preferably an integer of 2 to 5000, more preferably 100 to 500. )
Specific examples of the PBI include the following compounds.

Said PBI can be manufactured according to the manufacturing method of Unexamined-Japanese-Patent No. 2012-238590, 0018-0021.

Moreover, the mass average molecular weight (Mw) of the polymer is preferably 5.0 × 10 ^{4 to} 1.0 × 10 ⁶ , and the ratio Mw / Mn of the mass average molecular weight (Mw) to the number average molecular weight (Mn). Is preferably 1-5. By setting these within this range, a more uniform composite nanofiber can be produced with a wide mixing ratio with SPAES.

The fiber diameter of the composite nanofiber is preferably 500 nm or less from the viewpoint of reducing the thickness of the composite membrane and improving proton conductivity, and more preferably 50 to 300 nm.
A method for producing such a fiber will be described later.

<Constituents>
(Proton conducting material)
It is also possible to dope the composite nanofibers with a proton conducting material by post-treatment of the composite nanofibers.
The proton-transmitting substance is a substance that conducts protons and exhibits the main function as an electrolyte membrane when the composite membrane of the present invention is used as a polymer electrolyte membrane.
The proton conductive material is preferably a material that can interact with the basic polymer contained in the composite nanofiber and can contribute to proton conduction as an acid functional group. The substance is an acidic substance having two or more acid substituents. Here, examples of the acid substituent include a phosphoric acid group, a sulfonic acid group, a carboxylic acid group, a nitric acid group, a vinylic carboxylic acid group, and a Lewis acid group.
Examples of the acidic substance include polyphosphoric acid, phytic acid, polyvinyl phosphonic acid, polyvinyl sulfonic acid, naphthalene disulfonic acid, oxalic acid, squaric acid, and the like. Among these, phytic acid has a large molecular weight, is difficult to diffuse due to the acid-base interaction with the composite nanofiber described later, and has a relatively low solubility in water and is difficult to elute in the presence of water. Therefore, it is preferable.
Other materials that can be used in the composite nanofiber post-treatment step include only one acidic group in addition to the proton transfer material having two or more acidic groups that can be used in the composite membrane of the present invention described above. An acidic substance can also be used. For example, in addition to the acidic substance that can be used for the composite membrane of the present invention described above, specifically, phosphoric acid, methanephosphonic acid, sulfuric acid, methanesulfonic acid, benzenesulfonic acid, trifluoromethanesulfonic acid, sulfinic acid, Formic acid, acetic acid, nitric acid, hydrochloric acid, ascorbic acid, chromic acid, tetrafluoroboric acid, hexafluorophosphoric acid and the like can be mentioned.

<Constituents>
(Matrix polymer)
The matrix polymer is preferably a polymer that can improve the membrane strength when a composite membrane is formed, and is excellent in proton conductivity, such as sulfonated polyarylene ether (SPAE), Nafion (registered trademark) shown below. Perfluorosulfonic acid polymers such as sulfonated polyimide (SPI) shown below, sulfonated polybenzimidazole (SPBI) shown below, sulfonated polyphenylene (SPP) shown below, and sulfonated polyphenylene oxide (SPPO) shown below. Polyphenylene sulfide (SPPS) shown below, sulfonated polystyrene shown below and a copolymer thereof (SPSt), polyvinyl sulfonic acid shown below and a copolymer thereof (PVS), and the like can be used. In use, they can be used alone or as a mixture.

As an example of a typical perfluorosulfonic acid polymer, the structure of Nafion (registered trademark) is shown below.
In the formula, x represents 5 to 13.5, and y represents 1000.
m represents an integer of 2 or more, and n represents 2.

As the sulfonated polyimide (SPI), any sulfonated polyimide can be used, including sulfonated polyimides conventionally proposed for constituting polymer electrolyte membranes. Examples of the sulfonated polyimide preferably used in the present invention include a sulfonated polyimide represented by the following formula (2).

In the formula (2), R ³ represents a tetravalent group having at least one aromatic ring, such as an aromatic tetravalent residue such as a benzene ring or a naphthalene ring, a benzene ring, a naphthalene ring or the like. tetravalent aromatic residue of a compound in which two aromatic rings are linked directly, two benzene rings _{-C (CF 3) 2 -,} - SO 2 -, - CO 2 - is linked by a group such as Preferred examples of the compound include tetravalent residues and the like, and more preferred are tetravalent residues of compounds having two aromatic rings.

In Formula (2), R ⁴ represents a divalent group having a sulfonic acid group and having at least one aromatic ring. For example, two benzene rings are directly bonded, —O—, > CR ⁶ (R ⁶ forms a fluorene ring structure with a carbon atom) and the like, and is a divalent residue of a sulfonated aromatic compound having a sulfonic acid group as a benzene ring or a substituent of the benzene ring And the like are preferable. Preferred examples of the substituent on the benzene ring include an alkyl group, an alkyloxy group, and a phenyl group.

Further, in the formula (2), R ⁵ represents a divalent group having at least one aromatic ring and having no sulfonic acid group. For example, a heterocyclic ring such as a benzene ring or a nitrogen-containing heterocyclic ring is included in the structure. Preferred examples include divalent residues of non-sulfonated compounds. In formula (2), n is 1 or more, preferably an integer of 50 or more, for example 50 to 2000, and m is 0 or 1 or more, preferably 30 or more, for example, 30 to 1000. More specifically, examples of R ³ , R ⁴ , and R ⁵ include the following groups.

The sulfonated polyimide represented by the formula (2) used in the present invention is, for example, an aromatic carboxylic dianhydride, a sulfonated aromatic diamine, and an optional non-sulfone as shown in the following reaction formula: It can be synthesized from a monomer of an aromatic diamine.

In the formula, R ³ , R ⁴ , R ⁵ , n and m are as defined above.
Examples of the aromatic carboxylic dianhydride include 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane, 4 , 4′-bisphthyl-1,1 ′, 8,8′-tetracarboxylic dianhydride is preferred. Examples of the sulfonated aromatic diamine include a main chain type monomer whose main chain is modified with a sulfonic acid group, and a side chain type monomer whose side chain is modified with a sulfonic acid group. Preferable examples of the sulfonated aromatic diamine include, for example, 2,2-benzidine disulfonic acid, 4,4′-diaminophenyl ether disulfonic acid, 3,3′-bis (3-sulfopropoxy) benzidine, 9,9 ′. -Bis (4-aminophenyl) fluorene-2,7-disulfonic acid, 2,2'-bis (4-sulfophenyl) benzidine and the like. Preferred examples of the non-sulfonated aromatic diamine include 4,4′-hexafluoroisopropylidenebis (p-phenyleneoxy) diamine, 2,2-diaminodiphenylhexafluoropropane, and 9,9′-bis. (4-aminophenyl) fluorene and 2,5-diaminopyridine are mentioned. By using a non-sulfonated aromatic diamine monomer, film stability and acid retention ability can be imparted.
A sulfonated copolymerized polyimide is obtained by using a combination of a sulfonated aromatic diamine monomer and a non-sulfonated aromatic diamine monomer, and the copolymer may be a random copolymer or a block copolymer.
The ratio n / m of the sulfonated diamine monomer (n) to the non-sulfonated aromatic diamine monomer (m) during the copolymerization is preferably 30/70 to 100/0. When n / m is less than 30/70, the proton conductivity of the composite membrane is low, and it becomes difficult to obtain a suitable composite membrane. In order to obtain high proton conductivity, it is desirable that n / m is 70/30 to 100/0.
The mass average molecular weight (Mw) of the sulfonated polyimide is preferably 1.0 × 10 ^{4 to} 1.0 × 10 ⁶ from the viewpoint of film forming properties, and the mass average molecular weight (Mw) relative to the number average molecular weight (Mn). The ratio Mw / Mn is preferably 1 to 5 in terms of strength.

(SPI)
Further, as the SPI, those having the block structure shown below can be used.

(In the formula, A represents an aromatic group having 6 to 30 carbon atoms having a sulfonic acid group, B represents an aromatic group having 6 to 30 carbon atoms having a polyimide side chain having a sulfonic acid group, and C represents a substituted group. Represents an aromatic group having 6 to 30 carbon atoms which may have a group, m and n are integers of 1 or more, r is 0 or an integer of 1 or more, and Y is a number of 1 or more. Also, m / (n + r) is in the range of 90/10 to 10/90, and is a block polymer.)
The sulfonic acid group in the above group A may be directly substituted with an aromatic group, for example, via an —O (CH 2) — group, —C 6 H 4 (phenyl) group, —O—C 6 H 4 — group, etc. It may be introduced into the chain. As the aromatic group, a benzene ring, a naphthalene ring or the like may be used alone, but two or more rings may be directly bonded or via an —O—, —SO 2 —, —C (CF 3) 2 — group or the like. It may be combined.
Examples of the group A include the following groups as preferable examples.

  On the other hand, as described above, the group B represents an aromatic group having 6 to 30 carbon atoms having a polyimide side chain having a sulfonic acid group, and the group C has 6 to 30 carbon atoms which may have a substituent. Represents an aromatic group. The polyimide side chain having a sulfonic acid group is linked to an aromatic group having 6 to 30 carbon atoms directly or via —O—, —CO—, —NH— group or the like. Examples of the substituent of the group C include groups such as —OH, —COOH, and —NH 2. Examples of the group B which is an aromatic group having 6 to 30 carbon atoms including the direct bond portion or a —O—, —CO—, —NH— group include the following groups as preferred ones. As the group C which is an aromatic group having 6 to 30 carbon atoms which may have a group, in the following group, the group -D- is -H, -D-H or -D-OH. Such groups are preferred.

(In the formula, D represents —O—, —CO—, —NH—, —CO—NH—, —CO (═O) — or a direct bond.)

  Moreover, as said SPI, the graft polymer formed by introduce | transducing group represented by following (2) to the polymer represented by said Formula (1) can also be used. In this case, the polymer represented by (1) can employ either a random polymer or a block polymer. In the case of a random polymer, the polymer becomes a graft polymer, and in the case of a block polymer, a block graft. It becomes a polymer.

(In the formula, R represents an aromatic group having 6 to 30 carbon atoms having a sulfonic acid group, and x represents an integer of 1 or more.)
Preferred examples of the group R in the above formula (2) include the same groups as the group A in the above formula (1). The group A and the group R may be the same or different. Specifically, the following groups are preferable.

M and n + r are preferably integers of 1 to 100, m / (n + r) is preferably in the range of 90/10 to 10/90, and Y is preferably a number of 1 to 150. The weight average molecular weight (Mw) of the polyimide resin constituting the main chain is preferably 50,000 to 500,000. Moreover, as for the weight average molecular weight (Mw) of the polyimide resin which comprises a side chain, 5,000-500,000 are preferable.

  Further, the ratio of the weight average molecular weight of the graft side chain to the weight average molecular weight of the main chain is 0.01 <Mw (graft side chain) / Mw (main chain) <20, and the side chain polymer relative to the main chain polymer The graft ratio is preferably 1 <graft ratio <100.

Here, the graft ratio is a ratio calculated with 100% as the side chain introduced into all side chain introduction sites in the main chain, and is [n / (n + r)] × 100. For example, in Examples 3 and 4 to be described later, 100% when the amino group at the side chain partial terminal prepared in Synthesis Example 3 reacts with all the carboxylic acid groups of DABA used in Synthesis Example 1 or 2 to form an amide bond. It is. Specifically, it is calculated by the following formula.
IEC (ion exchange capacity) = sulfonic acid group equivalent × graft rate / (main chain unit molecular weight− (side chain molecular weight × graft rate)) Graft rate (%) = {(main chain unit molecular weight × IEC) / [sulfonic acid group Equivalent- (Side chain molecular weight × IEC)]} × 100

Examples of the sulfonated polybenzimidazole (SPBI) include polymers having the following structures.

(X in the formula includes O, CO, SO ₂ , S, CH ₂ , C (CH ₃ ) ₂ , C (CF ₃ ) ₂ , etc.,
Y is a divalent group having at least one aromatic ring, substituted with at least one sulfonic acid group, an aromatic ring such as a benzene ring or a naphthalene ring, a nitrogen-containing heterocyclic ring such as a pyridine ring, 2 A divalent group including a benzene ring in which the benzene ring is directly bonded, -O-, -CO-, -SO _2- and the like,
n is preferably an integer of 2 to 5000, more preferably 100 to 500. )

Specifically, the following polymers can be used.
The SPBI can be obtained as follows if it is disulfonated poly (benzimidazole), for example.
That is, in a nitrogen atmosphere, using polyphosphoric acid as a solvent and a condensing agent, 3,3′-diaminobenzidine and 4,8-disulfonyl-2,6-naphthalenedicarboxylic acid are added, and the temperature is 1 to 2 at a temperature of 80 ° C. or higher. The mixture can be obtained by stirring for a period of time, further raising the temperature, stirring at 200 ° C. for 8 to 10 hours, dropping into water, and washing and collecting the precipitate with a 10% by weight aqueous potassium hydroxide solution.

Examples of the sulfonated polyphenylene (SPP) include the following polymers.

(N is as described above)

(Wherein R1, R2, R3 and R4 are a hydrogen group, an alkyl group, a hydroxyl group, a sulfonic acid group, or a divalent group in which a monovalent or plural aromatic rings having an aromatic ring are linked, such as a sulfonic acid group, etc. Substituted, aromatic rings such as benzene ring and naphthalene ring, nitrogen-containing heterocycles such as pyridine ring, two benzene rings are directly bonded, connected by —O—, —CO—, —SO ₂ —, etc. And monovalent or divalent groups containing a benzene ring or the like, and n represents an integer of 1 to 5000.)

Specifically, the following polymers can be used.
(N is as described above)

  Examples of the sulfonated polyphenylene oxide (SPPO include the following polymers).

(Wherein R1, R2, R3 and R4 are a hydrogen group, an alkyl group, a hydroxyl group, a sulfonic acid group, or a divalent group in which a monovalent or plural aromatic rings having an aromatic ring are linked, such as a sulfonic acid group, etc. Substituted, aromatic rings such as benzene ring and naphthalene ring, nitrogen-containing heterocycles such as pyridine ring, two benzene rings are directly bonded, connected by —O—, —CO—, —SO ₂ —, etc. And monovalent or divalent groups containing a benzene ring or the like, and n represents an integer of 1 to 5000.)

Specifically, the following polymers can be used.
(N is as described above)

(SPPS)
Examples of the polyphenylene sulfide (SPPS) include the polymers shown below.

(Wherein R1, R2, R3 and R4 are a hydrogen group, an alkyl group, a hydroxyl group, a sulfonic acid group, or a divalent group in which a monovalent or plural aromatic rings having an aromatic ring are linked, such as a sulfonic acid group, etc. Substituted, aromatic rings such as benzene ring and naphthalene ring, nitrogen-containing heterocycles such as pyridine ring, two benzene rings are directly bonded, connected by —O—, —CO—, —SO ₂ —, etc. A monovalent or divalent group containing a benzene ring or the like,
n represents an integer of 1 to 5000. )
Specifically, the following polymers can be mentioned.

(N is as described above)

Examples of the sulfonated polystyrene and its copolymer (SPSt) include the following polymers.

(R is an aromatic ring such as alkyl, alkyl ester, and benzene, and includes all vinyl monomers copolymerizable with styrene, sulfonated styrene, or sulfonated ester-substituted styrene, and m and n each represent an integer of 1 to 10,000. Show.)

Examples of the polyvinyl sulfonic acid and its copolymer (PVS) include the following polymers.

(R is an aromatic ring such as alkyl, alkyl ester, and benzene, and includes all vinyl monomers copolymerizable with vinyl sulfonic acid or vinyl sulfonic acid ester, and m and n each represent an integer of 1 to 10,000.)

(Other ingredients)
In addition to the components described above, various additives can be added to the composite membrane of the present invention as long as the spirit of the present invention is not impaired. For example, inorganic particles such as silica particles may be included in order to improve the mechanical properties of the composite film. The particle diameter of the inorganic particles is preferably 1 nm to 1 μm in order to maintain film uniformity, more preferably 100 nm or less, and still more preferably 20 nm or less.

<Composite membrane form>
(overall structure)
The thickness of the composite film of the present invention is preferably 2 to 40 μm from the viewpoint of satisfying a recently required thickness, more preferably 2 to 30 μm, and most preferably 2 to 10 μm.
The composite membrane of the present invention will be described with reference to FIG. 1. In the composite membrane of the present invention, a composite nanofiber 1 composed of an electrolyte polymer and a basic polymer is in a nonwoven fabric form in which each nanofiber is entangled. Existing. And the matrix polymer is provided so that the space | interval of the composite nanofiber 1 may be filled and the external shape of a composite film may be formed, and in this embodiment, it consists only of a matrix polymer in the front and back both sides of the nonwoven fabric consisting of the composite nanofiber 1. A polymer layer 6 is formed.
Furthermore, it is possible to dope the nanofibers with a proton conducting material by means of a composite nanofiber post-treatment solution. In the composite membrane of the present invention, as described above, the proton transfer material has two or more acid functional groups, and the basic polymer in the composite nanofiber 1 has a substituent capable of reacting with the acid functional groups. Therefore, the proton-transmitting substance not only reacts with the basic polymer to be bonded to the composite nanofiber 1 but also bonds to the composite nanofiber 1 at two or more places to form a kind of bridge structure.
By forming such a bridging structure, it is possible to form a strong nonwoven structure even if the film thickness is thinner than the conventional one, and because the composite nanofiber and the proton transfer substance are in a combined state. It is also advantageous in terms of proton transmission performance.
The non-woven fabric formed by the composite nanofibers has a porosity of 50 to 90% before contacting with the matrix polymer in terms of proton conductivity and membrane strength and gas barrier properties when used as a composite membrane. preferable. In particular, it is preferable to use a composite nanofiber having the above-described fiber diameter that is made into a non-woven fabric with a porosity in this range in order to exhibit the desired effect of the present invention. The measurement of the porosity will be described later.
Here, the porosity before contacting with the matrix polymer means that the nonwoven fabric is first produced with composite nanofibers, and then the matrix polymer is added to the obtained nonwoven fabric, as described in the production method described later. It is the ratio of the space which exists between each composite nanofiber in the state of the nonwoven fabric before being immersed in the solution of a matrix polymer, and shape | molding in a desired shape before being immersed in this solution. That is, the porosity is the ratio of the space to the volume of the virtual solid circumscribing the nonwoven fabric, and is represented by (total volume of the space / volume of the virtual solid) × 100.

(Quantity ratio relationship)
Since the proton transfer material and the composite nanofiber both have the above-described structure, sufficient proton transfer performance can be obtained without increasing the amount of the proton transfer material. The content of the composite membrane of the present invention is preferably 0.1 to 20% by mass, and more preferably 1 to 10% by mass. If it is less than 1% by mass, the ionic conductivity may be insufficient, and if it exceeds 10% by mass, the proton-transmitting substance may be eluted over time, so it is preferably within the above range.
Thus, when the amount of proton-transmitting substance is small, there is very little seepage to the composite membrane surface. Therefore, for example, when used as a polymer electrolyte membrane for a fuel cell, the catalyst is hardly poisoned, which is advantageous in this respect.
The matrix polymer may be present in an amount sufficient to fill the voids existing between the composite nanofibers existing at the porosity and form the outer shape of the composite film, but preferably the composite nanofibers. And the total amount is 100 to 50% by mass.

<Manufacturing method>
Next, the manufacturing method of the composite film of this invention is demonstrated.
The production method of the present invention is preferably a method of producing the composite membrane of the present invention, as shown in FIG.
A step of forming a nonwoven fabric comprising the composite nanofiber and the composite nanofiber (A in FIG. 2);
A step of post-processing the nonwoven fabric (FIG. 2B),
The step of filling the voids of the nonwoven fabric with a matrix polymer to integrate the composite nanofiber and the matrix polymer (C in FIG. 2), and the step of post-treating the electrolyte membrane containing the composite nanofiber (not shown)
It can be implemented by performing.
Further explanation will be given.

(Process for forming a nonwoven fabric, FIG. 2A)
The step of forming the nonwoven fabric is formed by discharging a spinning solution obtained by dissolving an electrolyte polymer and a basic polymer, which are raw materials of the composite nanofiber, in a solvent onto the collector 30 using the discharger 10. Can do.
The ratio of the electrolyte polymer in the whole raw material polymer is preferably 1 to 99% by mass, and more preferably 20 to 80% by mass.
The production of non-woven fabric of fine fibers using a discharger is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 2003-73964, 2004-238749, and 2005-194675. Hereinafter, description will be made according to an example using the manufacturing apparatus disclosed in Japanese Patent Application Laid-Open No. 2005-194675.

A discharger 10 shown in FIG. 2 includes a nozzle 11 that discharges the spinning solution and a tank 12 that stores the spinning solution. It also has a grounded collector 30 located opposite the nozzle 11. For this reason, when an electric field is formed between the nozzle 11 and the collector 30 by being applied by a voltage application device (not shown), the fibers discharged from the nozzle 11 and stretched by the electric field fly toward the collector 30. The nonwoven fabric 20 made of composite nanofibers is deposited on the collector 30.
Examples of the solvent include dimethyl sulfoxide (DMSO), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP). 1 to 30% by mass, more preferably 5 to 20% by mass. The viscosity of the spinning solution is preferably 100 to 10000 mPa · s, and more preferably 500 to 5000 mPa · s.
When the above apparatus is used, the spinning solution is pushed out from the nozzle 11 toward the collecting body 30 and is subjected to a stretching action by an electric field between the grounded collecting body 30 and the nozzle 11 applied by the voltage application device, While flying into fiber, it flies toward the collecting body 30 (so-called electrostatic spinning method). The flying fibers are directly accumulated on the collecting body 30 to form a nonwoven fabric. The spinning solution is supplied from the tank 12 to the nozzle 11 by, for example, a syringe pump, a tube pump, a dispenser, or the like. In addition, the details of the apparatus used for spinning are appropriately described in JP 2012-238590 A.
The thickness of the nonwoven fabric obtained here is preferably 25 μm or less from the viewpoint of reducing the thickness of the entire composite membrane, and more preferably 5 μm or less.

(Step of post-processing the nonwoven fabric, FIG. 2B)
The resulting nonwoven fabric is then post-treated. The present invention is characterized in that the step of post-treating the composite nanofiber is performed before the step of contacting with the matrix. This makes it possible to remove the excess proton transfer material while adsorbing the necessary proton transfer material to the composite nanofiber (including adsorption by reaction), reducing the film thickness, gas barrier properties and high conductivity (especially gas barrier properties). Can be achieved.
As shown in FIG. 2B, the post-treatment is performed by putting the obtained non-woven fabric into an arbitrary container 40, injecting a proton transfer substance-containing solution from another injection container 50 into the container 40, and immersing in the proton transfer substance-containing solution. This can be done.
The concentration of the proton transfer substance in the proton transfer substance-containing solution is 5 to 95% by mass, preferably 10 to 85% by mass. The dipping conditions are preferably 15 to 80 ° C. and 0.5 to 3 hours.
And after completion | finish of immersion, it is preferable to wash | clean in order to remove an excess proton-transmitting substance. In particular, in the above-described electrolyte membrane of the present invention, since the proton transfer substance is bonded to the composite nanofiber as described above, it is better to remove the unbonded proton transfer substance from the viewpoint of film strength and gas barrier properties, Because there are very few free proton mediators, elution of proton mediators is unlikely to occur even in the presence of moisture. For example, when used as a polymer electrolyte membrane for fuel cells, catalyst poisoning does not occur. It is preferable from the viewpoint, and even if it is removed, there is no problem because it exhibits sufficient proton transferability by being bonded. Washing is preferably performed at 15 to 80 ° C. for 5 to 20 hours using a washing liquid such as water.
After washing, it is preferable to dry the film sufficiently by vacuum drying for 5 to 15 hours at 50 to 150 ° C.
The dope amount of proton-transmitting substance (adsorption amount to the composite nanofiber) can be calculated by measuring the mass change or ion exchange capacity of the nonwoven fabric before and after the post-treatment.
As the proton transfer substance that can be used in this step, an acidic substance having only one acid functional group can be used in addition to the proton transfer substance having two or more acid functional groups described above. For example, when nitric acid or the like having one acid functional group is used, the acidic substance is used to ion-exchange counter ions of the acid functional group of the electrolyte polymer to proton form. Many of the acidic substances having only one acid functional group that does not interact with the basic polymer can be removed by a washing operation.

(Process of filling the non-woven fabric with a matrix polymer and integrating the composite nanofiber and the matrix polymer, FIG. 2C)
In this step, the non-woven fabric after the post-treatment obtained in the previous step is put in a container 40 ′, a solution of a matrix polymer is put into the container 40 ′ from another injection container 50 ′, and the non-woven fabric is immersed in this solution. To do.
The solvent used in the matrix polymer solution is arbitrary depending on the matrix polymer to be used, but water, methanol, ethanol, 2-propanol, dimethyl sulfoxide (DMSO), N, N-dimethylformamide (DMF), N, N- Examples include dimethylacetamide (DMAc) and N-methyl-2-pyrrolidone (NMP), which may be used in combination with other solvents. Moreover, it is preferable that the density | concentration of the matrix polymer in the said solution shall be 2-20 mass%.
The composite film of the present invention can be obtained by evaporating the solvent after being immersed. The solvent can be evaporated by, for example, natural drying at 15 to 150 ° C., vacuum drying, or treatment in a hot air oven for 1 to 48 hours.
Further, in order to stabilize the polymer, the matrix polymer can be once converted into a salt and then treated as the above solution. In this case, it is preferable to acid-treat the composite film obtained after completion of the above evaporation treatment.

(Process to post-process electrolyte membrane containing composite nanofiber)
Post-treatment of electrolyte membranes containing composite nanofibers removes residual solvents and small molecules, exchanges acid functional group counter ions for protons, densifies membranes and improves stability and gas barrier properties, etc. The effect can be expected.
As post-treatment, there are mainly solution treatment and heat treatment. Examples of the substance used for the solution treatment include an aqueous hydrogen peroxide solution, an aqueous hydrochloric acid solution, an ethanol / hydrochloric acid mixed solution, and an ethanol / nitric acid mixed solution. After completion of the solution treatment, the heat treatment can be performed by performing a vacuum drying treatment at 50 to 150 ° C. for 1 to 48 hours.

<Use modes and advantages>
The electrolyte membrane of the present invention can be used as a polymer electrolyte membrane of a polymer electrolyte fuel cell used by being sandwiched between a positive electrode and a negative electrode, and is a thin film as described above, and is generated at the negative electrode. The protons thus conducted can be stably conducted to the positive electrode.
Such a polymer electrolyte is required to have low membrane resistance (membrane resistance (Ω · cm ² ) = film thickness (cm) / proton conductivity (s / cm): s = 1 / Ω). The electrolyte membrane of the invention exhibits excellent low membrane resistance close to the required value (<0.025 Ω · cm ² under high temperature and low humidification). In particular, it exhibits excellent film resistance (for example, 0.22 Ω · cm ² ) under high temperature and low humidity conditions (80 ° C., 30% RH).
In addition, it is required to have a high gas barrier property, that is, a low gas permeation flow rate (O ₂ : <1.3 × 10 ⁻⁹ (cm ³ / (cm ² sec kPa)) at 80 ° C. and 95% RH). In addition, it is also required that the film stability (chemical, mechanical, thermal) is high. The nanofiber composite film of the present invention satisfies these performances even when the film thickness is thinner than the conventional film. To do.
It is not clear why the electrolyte membrane of the present invention is a well-balanced composite membrane that has a low membrane resistance and a high gas barrier property as compared with conventional composite membranes. However, the following reasons can be considered.
By combining the basic polymer with the electrolyte polymer constituting the nanofiber, the acid functional group in the electrolyte interacts with the basic polymer to promote proton dissociation. In particular, the effect becomes conspicuous under low humidity conditions where proton dissociation is difficult and proton conductivity is lowered.
Moreover, it is possible to increase the substance which contributes to proton conduction by doping the composite nanofiber with an acidic substance having two or more acid functional groups. Most of the acidic substances are present on the surface of the composite nanofiber and exist so as to connect the composite nanofibers. Therefore, it becomes difficult for the composite nanofibers to spread when integrated with the matrix polymer.
Furthermore, the presence of the composite nanofiber containing the basic polymer suggests that the acid functional groups of the matrix polymer spontaneously gather in the vicinity of the nanofiber surface when forming the electrolyte membrane to form a kind of acid condensed layer. Since protons can move through nanofibers without being dispersed, it is considered that proton transfer performance is improved also in the film thickness direction. Furthermore, it is considered that the strength and gas barrier properties of the electrolyte membrane are improved by the presence of composite nanofibers in the electrolyte membrane that form an interaction inside and are excellent in the ga dynamic strength and the barrier properties.
The electrolyte membrane of the present invention thus configured not only has the effect of being excellent in each of the above performance balances, but also has no free acidic substance, and poisoning of the platinum catalyst by the acidic substance in the fuel cell. Therefore, it is possible to greatly suppress deterioration of characteristics. Note that the density of the fine fibers can be increased by pressing the nonwoven fabric with a hot press or the like, and further thinning can be achieved.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not restrict | limited at all by these.

<< Synthesis Example 1: Synthesis of 3,3'-disulfo-4,4'-difluorobenzophenone-sodium salt (SDFB) >>
Under a nitrogen atmosphere, 16 ml of fuming sulfuric acid was added to 4.36 g (20.0 mmol) of 4,4′-difluorobenzophenone, and the mixture was stirred at 110 ° C. for 6 hours. After standing to cool, the solution was poured into 100 ml of distilled water, and the pH was adjusted to 10 with sodium hydroxide while stirring. The solution was slowly poured into 1 L ethanol, and the precipitate was separated by suction filtration. The filtrate was concentrated by evaporation, 2-propanol was added, and the precipitate was collected by suction filtration. The collected SDFB was dried at 80 ° C. for 18 hours to completely remove the solvent.

<< Synthesis Example 2: Synthesis of sulfonated polyarylene ether (SPAES) >>
3,3′-Disulfo-4,4′-difluorobenzophenone-sodium obtained in Synthesis Example 1 in a three-necked flask having a Dean-Stark tube using 30 ml of N, N-dimethylacetamide (dehydrated) as a polymerization solvent under a nitrogen atmosphere 2.28 g (5.4 mmol) of salt (SDFB), 1.68 g (6.6 mmol) of bis (4-fluorophenyl) sulfone (FPS), 2.23 g (12.0) of 4,4′-biphenol (BP) , 2.2 times equivalent potassium carbonate and toluene (dehydrated) 15 ml were added and stirred at 140 ° C. for 4 hours. After removing water and toluene in the Dean-Stark tube, the mixture was further stirred at 170 ° C. for 15 hours. Arylene ether sulfone (SPAES) sodium salt was synthesized. The synthesized SPAES was poured into hot water, precipitated and purified, and then washed repeatedly with distilled water and recovered. The recovered SPAES (sodium salt) was vacuum-dried at 60 ° C. for 15 hours to completely remove the solvent.

The ¹ H-NMR spectrum of the sulfonated polyarylene ether (sodium salt) was measured using an NMR apparatus Burker AVANCE III500 (manufactured by Bruker Biospin). ¹ H-NMR spectrum It was confirmed that the target polymer was obtained.
The molecular weight of the sulfonated polyarylene ether salt was measured using gel permeation chromatography (GPC, HPLC pump PU-2080PLUS manufactured by JASCO Corporation). In addition, the molecular weight of polystyrene conversion was measured from the 1 mg / mL sulfonated polyarylene ether salt solution prepared using the carrier using DMF to which a small amount of lithium bromide (10 mmol / L) was added as a GPC solvent. As a result, Mw was 6.0 × 10 ⁵ and Mw / Mn was 1.7.

<< Synthesis Example 3: Synthesis of polybenzimidazole (PBI) >>
Under a nitrogen atmosphere, polyphosphoric acid (PPA) was used as a polymerization solvent, and 3,3′-diaminobenzidine (DAB) 2.27 g (10.6 mmol), 4,4′-oxybisbenzoic acid (OBBA) 2.73 g (10 .6 mmol) was weighed and polyphosphoric acid (PPA) was added to give a 3% by mass solution, the temperature was gradually raised while stirring, and the mixture was stirred at 140 ° C. for 12 hours to synthesize polybenzimidazole. The obtained polymer solution was poured into ion exchange water and reprecipitated, then neutralized with a sodium hydroxide solution and washed. Polybenzimidazole was collected by suction filtration, naturally dried for 24 hours, and then vacuum dried at 100 ° C.

The ¹ H-NMR spectrum of polybenzimidazole was measured and the structure was confirmed.
From the gel permeation chromatography (GPC) measurement, Mw of polybenzimidazole was 1.6 × 10 ⁵ and Mw / Mn was 2.1.

<< Example 1: Preparation of SPAES / PBI (50/50) composite nanofiber nonwoven fabric >>
Add the sulfonated polyarylene ether sulfone salt of Synthesis Example 2 and the polybenzimidazole of Synthesis Example 3 to the vial so that the weight ratio is 50/50, and dehydrated so that the polymer weight is 16% by mass of the total weight. N, N-dimethylformamide (DMF) was added. The vial was filled with nitrogen and stirred overnight to dissolve to prepare a polymer solution. An aluminum foil is installed in the collector part of the electrospinning apparatus ES-2000S (manufactured by Fuence), a syringe filled with the polymer solution is set in the electrospinning apparatus, and the release amount of the polymer solution is 0.12 mL / hour. Electrospinning was performed. The distance between the syringe and the collector was 10 cm, and a voltage of 30 kv was applied to the syringe. Thereby, SPAES / PBI (50/50) composite nanofiber nonwoven fabric was laminated on the aluminum foil. The obtained composite nanofiber was vacuum-dried at 60 ° C. for 15 hours.
The resulting composite nanofiber was post-treated for acid treatment and acid doping. The composite nanofiber was immersed in hydrochloric acid (0.1M) at room temperature for 15 hours and repeatedly washed with pure water. Subsequently, it was immersed in an aqueous phytic acid solution (50 wt%) at room temperature for 1 hour, and then washed in pure water at 80 ° C. for a total of 24 hours to remove undoped phytic acid. The acid-doped composite nanofiber was vacuum-dried at 60 ° C. for 15 hours. By the post-treatment, the SPAES sodium salt can be replaced with proton form, and the basic polymer can be doped with phytic acid.
After a part of the nanofiber was coated with osmium, it was observed with a scanning electron microscope (SEM, JSM-6100 manufactured by JEOL), and the fiber diameter of the nanofiber produced from the obtained SEM image was calculated. FIG. 3 shows an SEM image of the nanofiber of Example 1 (release time 60 seconds). From the SEM image results, it was confirmed that uniform nanofibers could be produced, and the fiber diameter was 326 ± 27 nm.
The porosity is determined by cutting the fiber mat into 3 cm square, the apparent volume (V) calculated from the dry mass (W) and the film thickness measured by the film thickness meter, the specific gravity of SPAES / PBI (50/50) (1.5 g / Cm ³ ) and calculated from the following formula.
Porosity (%) = (1− (W / (V × 1.5)) × 100
The calculated porosity was about 89%.

<< Example 2: Production of uniaxially arranged SPAES / PBI (50/50) composite nanofiber and measurement of proton conductivity >>
In order to measure the proton conductivity of a single nanofiber, a uniaxially aligned nanofiber was fabricated. As in Example 1, the polymer solution was adjusted to 16% by mass, and electrospinning was performed using ES-1000 (manufactured by Fusion). In addition, the collector used the glass substrate in which the two aluminum electrodes were installed in the both ends. The distance between the syringe and the collector was 10 cm, the amount of the polymer solution released was 0.12 mL / hour, and a voltage of 17 kv was applied to the syringe. Thereby, the uniaxially oriented nanofiber assembly was produced on the glass substrate. The collector was removed when the polymer solution release time was 60 seconds. Hydrochloric acid (0.1M) was added dropwise to the uniaxially arranged nanofibers, allowed to stand at room temperature for 1 hour, and then repeatedly washed with pure water. Subsequently, an aqueous phytic acid solution (50 wt%) was added dropwise, allowed to stand at room temperature for 1 hour, and washed repeatedly with pure water at room temperature to remove undoped phytic acid. Vacuum drying was performed at 60 ° C. for 15 hours to obtain acid-doped uniaxially aligned nanofibers.

[Measurement of proton conductivity of uniaxially arranged SPAES / PBI (50/50) composite nanofiber]
Using an impedance analyzer 3532-50 (manufactured by Hioki), the frequency response from 50 kHz to 5 MHz was measured, and the resistance of the nanofiber integrated body (distance between electrodes 0.5 cm) was measured. In addition, the temperature and humidity at the time of resistance measurement were kept at 90 ° C. and 95% RH, respectively, using a thermo-hygrostat SH-221 (manufactured by ESPEC).
Furthermore, the uniaxially aligned nanofibers after impedance measurement were coated with gold and observed with an SEM. The average diameter and the number of uniaxially arranged nanofibers existing between the electrodes are obtained from the SEM image, and the expression is based on the distance between electrodes [cm] / (cross-sectional area of one fiber [cm ² ] × number of nanofibers × resistance [Ω]). The proton conductivity [S / cm] was calculated. The results are shown in Table 1.

<< Comparative Example 1: Preparation of SPAES / PBI (50/50) blend membrane and measurement of proton conductivity >>
To the vial, add the sulfonated polyarylene ether sodium salt of Synthesis Example 2 and the polybenzimidazole of Synthesis Example 3 to a weight ratio of 50/50, and then add N, N-dimethylformamide (DMF). Stir overnight to prepare a blend polymer solution. The blend polymer solution was poured into a glass petri dish, naturally dried at 60 ° C., and then vacuum dried at 60 ° C. for 15 hours to obtain a SPAES / PBI (50/50) blend film. The film thickness was 64 μm. The obtained blend film was immersed in hydrochloric acid (0.1 M) at room temperature for 15 hours and repeatedly washed with pure water. Subsequently, it was immersed in an aqueous phytic acid solution (50 wt%) at room temperature for 1 hour, and then washed in pure water at 80 ° C. for a total of 24 hours to remove undoped phytic acid. The acid-doped blend film was vacuum dried at 60 ° C. for 15 hours.

[Measurement of proton conductivity of SPAES / PBI (50/50) blend membrane]
Using an impedance analyzer 3532-50 (manufactured by Hioki Co., Ltd.), the frequency response from 50 kHz to 5 MHz was measured, and the resistance of the nanofiber integrated body (distance between electrodes: 1.0 cm) was measured. In addition, the temperature and humidity at the time of resistance measurement were kept at 90 ° C. and 95% RH, respectively, using a thermo-hygrostat SH-221 (manufactured by ESPEC). Using the resistance [Ω] obtained by impedance measurement, the distance between electrodes [cm], and the membrane cross-sectional area [cm ² ], the formula Inter-electrode distance [cm] / (membrane cross-sectional area [cm ² ] × resistance [Ω]) From the above, proton conductivity [S / cm] was calculated. The results are shown in Table 1.
Compared with the nanofibers having the same composition as in Example 2, the conductivity of the blend film was very low. This is presumably because the sulfonic acid group in SPAES, which is an electrolyte polymer, interacted with PBI, which is a basic polymer, in the membrane, and the concentration of acid functional groups capable of proton conduction decreased. Further, it is presumed that phytic acid, which is a dope acid, has a relatively large molecular size and was doped in PBI existing in the vicinity of the film surface, but was not doped inside. On the other hand, in the case of nanofibers, it is considered that the diameter was as thin as several hundreds of nanometers, and phytic acid was sufficiently doped into the inside, and the formation of an efficient proton conduction channel unique to nanofibers led to high conductivity. .

<< Example 3: Production of SPAES / PBI (20/80) composite nanofiber nonwoven fabric >>
To the vial, the sulfonated polyarylene ether sulfone of Synthesis Example 2 and the polybenzimidazole of Synthesis Example 3 are added in a weight ratio of 20/80 so that the polymer weight is 14.3% by mass of the total weight. Dehydrated N, N-dimethylformamide (DMF) was added. The vial was filled with nitrogen and stirred overnight to dissolve to prepare a polymer solution. An aluminum foil is installed in the collector part of the electrospinning apparatus ES-2000S (manufactured by Fuence), a syringe filled with the polymer solution is set in the electrospinning apparatus, and the release amount of the polymer solution is 0.12 mL / hour. Electrospinning was performed. The distance between the syringe and the collector was 10 cm, and a voltage of 30 kv was applied to the syringe. As a result, the SPAES / PBI (20/80) composite nanofiber nonwoven fabric was laminated on the aluminum foil. Subsequently, post-treatment and drying were performed under the same conditions as in Example 1.
The SEM observation results are shown in FIG. The fiber diameter of the nanofiber produced from the SEM image was 323 ± 20 nm. The porosity was about 86%.

Example 4: Production of uniaxially arranged SPAES / PBI (20/80) composite nanofiber and measurement of proton conductivity
Similarly to Example 3, the polymer solution was adjusted to 14.3% by mass, and electrospinning was performed using ES-1000 (Fuence). In addition, the collector used the glass substrate in which the two aluminum electrodes were installed in the both ends. The distance between the syringe and the collector was 10 cm, the amount of the polymer solution released was 0.12 mL / hour, and a voltage of 20 kv was applied to the syringe. Thereby, the uniaxially oriented nanofiber assembly was produced on the glass substrate. The collector was removed when the polymer solution release time was 60 seconds. The post-process similar to Example 2 was performed, and the acid-doped uniaxially arranged nanofiber was obtained.
In the same manner as in Example 2, proton conductivity of the uniaxially arranged SPAES / PBI (20/80) composite nanofiber was measured. The results are shown in Table 1.
The SEM observation results are shown in FIG.

<< Example 5: Production of SPAES / PBI (80/20) composite nanofiber nonwoven fabric >>
To the vial, the sulfonated polyarylene ether sulfone of Synthesis Example 2 and the polybenzimidazole of Synthesis Example 3 are added so that the weight ratio is 80/20, and the polymer weight is 15.5% by mass of the total weight. Dehydrated N, N-dimethylformamide (DMF) was added. The vial was filled with nitrogen and stirred overnight to dissolve to prepare a polymer solution. An aluminum foil is installed in the collector part of the electrospinning apparatus ES-2000S (manufactured by Fuence), a syringe filled with the polymer solution is set in the electrospinning apparatus, and the release amount of the polymer solution is 0.12 mL / hour. Electrospinning was performed. The distance between the syringe and the collector was 10 cm, and a voltage of 30 kv was applied to the syringe. As a result, the SPAES / PBI (20/80) composite nanofiber nonwoven fabric was laminated on the aluminum foil. Subsequently, post-treatment and drying were performed under the same conditions as in Example 1.
The SEM observation result is shown in FIG. The fiber diameter of the nanofiber produced from the SEM image was 274 ± 25 nm. The porosity was about 85%.

<< Example 6: Preparation of uniaxially arranged SPAES / PBI (80/20) composite nanofiber and measurement of proton conductivity >>
Similarly to Example 5, the polymer solution was adjusted to 15.5% by mass, and electrospinning was performed using ES-1000 (Fuence). In addition, the collector used the glass substrate in which the two aluminum electrodes were installed in the both ends. The distance between the syringe and the collector was 10 cm, the amount of the polymer solution released was 0.12 mL / hour, and a voltage of 20 kv was applied to the syringe. Thereby, the uniaxially oriented nanofiber assembly was produced on the glass substrate. The collector was removed when the polymer solution release time was 60 seconds. The post-process similar to Example 2 was performed, and the acid-doped uniaxially arranged nanofiber was obtained.
In the same manner as in Example 2, proton conductivity of the uniaxially arranged SPAES / PBI (20/80) composite nanofiber was measured. The results are shown in Table 1.

<< Comparative Example 2: Production of SPAES single nanofiber nonwoven fabric >>
To the vial, the sulfonated polyarylene ether sulfone of Synthesis Example 2 was added with dehydrated N, N-dimethylformamide (DMF) so that the polymer weight was 14% by mass. The vial was filled with nitrogen and stirred overnight to dissolve to prepare a polymer solution. An aluminum foil is installed in the collector part of the electrospinning apparatus ES-2000S (manufactured by Fuence), a syringe filled with the polymer solution is set in the electrospinning apparatus, and the release amount of the polymer solution is 0.12 mL / hour. Electrospinning was performed. The distance between the syringe and the collector was 10 cm, and a voltage of 30 kv was applied to the syringe. Thereby, the SPAES single nanofiber nonwoven fabric was laminated on the aluminum foil. Subsequently, post-treatment and drying were performed under the same conditions as in Example 1.
The fiber diameter of the nanofiber prepared from the SEM image was 124 ± 29 nm. The porosity was about 82%.

<< Comparative Example 3: Preparation of uniaxially arranged SPAES single nanofiber and measurement of proton conductivity >>
As in Comparative Example 2, the polymer solution was adjusted to 14 mass%, and electrospinning was performed using ES-1000 (manufactured by Fusion). In addition, the collector used the glass substrate in which the two aluminum electrodes were installed in the both ends. The distance between the syringe and the collector was 10 cm, the amount of the polymer solution released was 0.12 mL / hour, and a voltage of 17 kv was applied to the syringe. Thereby, the uniaxially oriented nanofiber assembly was produced on the glass substrate. The collector was removed when the polymer solution release time was 60 seconds. The post-process similar to Example 2 was performed, and the acid-doped uniaxially arranged nanofiber was obtained.
In the same manner as in Example 2, proton conductivity of the uniaxially arranged SPAES / PBI (20/80) composite nanofiber was measured. The results are shown in Table 1.

<< Comparative Example 4: Production of PBI single nanofiber nonwoven fabric >>
To the vial, polybenzimidazole of Synthesis Example 3 and dehydrated N, N-dimethylformamide (DMF) were added so that the polymer weight was 8% by mass. The vial was filled with nitrogen and stirred overnight to dissolve to prepare a polymer solution. An aluminum foil is installed in the collector part of the electrospinning apparatus ES-2000S (manufactured by Fuence), a syringe filled with the polymer solution is set in the electrospinning apparatus, and the release amount of the polymer solution is 0.12 mL / hour. Electrospinning was performed. The distance between the syringe and the collector was 10 cm, and a voltage of 30 kv was applied to the syringe. Thereby, the PBI single nanofiber nonwoven fabric was laminated on the aluminum foil. Subsequently, post-treatment and drying were performed under the same conditions as in Example 1.
The fiber diameter of the nanofiber prepared from the SEM image was 113 ± 16 nm. The porosity was about 75%.

<< Comparative Example 5: Production of uniaxially arranged PBI single nanofiber >>
As in Comparative Example 4, the polymer solution was adjusted to 8% by mass, and electrospinning was performed using ES-1000 (Fuence). In addition, the collector used the glass substrate in which the two aluminum electrodes were installed in the both ends. The distance between the syringe and the collector was 10 cm, the amount of the polymer solution released was 0.12 mL / hour, and a voltage of 17 kv was applied to the syringe. As a result, an attempt was made to produce a monoaxially oriented nanofiber assembly on a glass substrate. However, although various conditions were examined, uniaxially aligned nanofibers could not be obtained with PBI alone.

<< Example 7: Preparation of SPAES / PBI (20/80) composite nanofiber nonwoven fabric / Nafion electrolyte membrane and measurement of proton conductivity >>
The mass ratio of the SPAES / PBI (20/80) composite nanofiber nonwoven fabric and Nafion was set to 10/100 in consideration of the porosity and specific gravity.
The SPAES / PBI (20/80) composite nanofiber nonwoven fabric with a film thickness of about 25 μm obtained in Example 3 is placed in a glass petri dish, a commercially available Nafion dispersion is cast, and the solvent is slowly evaporated at room temperature in the atmosphere. It was. Then, the electrolyte membrane was obtained by making it vacuum-dry at 60 degreeC for 15 hours. In addition, since the film thickness of a nonwoven fabric becomes substantially the same as the film thickness of a composite film, the film thickness of the composite film was made into the film thickness of a nonwoven fabric.
The obtained electrolyte membrane was immersed in 3% aqueous hydrogen peroxide at 80 ° C. for 1 hour, washed with pure water, then immersed in nitric acid (1M) at 80 ° C. for 1 hour, and repeatedly washed with pure water. Vacuum drying was performed at 60 ° C. for 15 hours to obtain a SPAES / PBI (20/80) composite nanofiber nonwoven fabric / Nafion electrolyte membrane having the form shown in FIG.
The film thickness of the produced electrolyte membrane is about 25 μm, and it is considered to be a composite membrane in which a Nafion matrix layer is formed on both the front and back surfaces of the nonwoven fabric as shown in FIG.

Proton conductivity measurement is performed using a thermo-hygrostat SH-221 (manufactured by ESPEC), keeping the temperature and humidity constant, and using an impedance analyzer 3532-50 (manufactured by Hioki), frequency response from 50 kHz to 5 MHz. The proton conductivity was calculated from the resistance of the SPAES / PBI (20/80) composite nanofiber nonwoven fabric / Nafion electrolyte membrane. The proton conductivities at 80 ° C.-30% RH and 90 ° C.-95% RH were calculated to be 5.5 × 10 ⁻⁴ and 3.8 × 10 ⁻² Scm ⁻¹ , respectively. The results are shown in Table 1. In particular, the proton conductivity was excellent under low humidity conditions.

<< Comparative Example 6: Production of nanofiber-free Nafion (registered trademark) single membrane and measurement of proton conductivity >>
A nanofiber mat was not used, and only a commercially available Nafion (registered trademark) dispersion was used to form a film in the same manner as in Example 7. The proton conductivity of the obtained Nafion single membrane was measured. The results are shown in Table 1. The proton conductivities at 80 ° C.-30% RH and 90 ° C.-95% RH were 2.8 × 10 ⁻⁴ and 7.4 × 10 ⁻² Scm ⁻¹ , respectively.

Claims (9)

A composite nanofiber comprising an electrolyte polymer and a basic polymer,
The composite nanofiber, wherein the electrolyte polymer has proton conductivity. The composite electrolyte nanofiber according to claim 1, wherein the electrolyte polymer has the following structures A) and B).
A) The main chain contains a repeating unit containing an aromatic group or a fluorine-containing aliphatic group.
B) The repeating unit has a side chain into which a cation exchange group has been introduced. The electrolyte polymer has a structure in which the main chain skeleton is selected from the group consisting of a polyarylene ether skeleton, a polyimide skeleton, a polystyrene skeleton, or a fluoroethylene skeleton,
3. The composite nanofiber according to claim 1, which has a structure in which a cation exchange group selected from the group consisting of a sulfonic acid group, a phosphonic acid group, and a carboxylic acid group is introduced into a side chain. The composite nanofiber according to claim 1, wherein the basic polymer has the following structures A) and B).
A) The main chain contains a repeating unit containing an aromatic group and / or an aliphatic group.
B) The main chain skeleton or the side chain functional group has a basic functional group capable of interacting with a cation exchange group. The abundance ratio of the electrolyte polymer is 1 to 99% by mass in the entire composite nanofiber,
The fiber diameter of the composite nanofiber is 500 nm or less,
The composite nanofiber according to claim 1, wherein: The abundance ratio of the composite nanofiber is 1 to 50% by mass in the entire electrolyte membrane,
The thickness of the electrolyte membrane containing the composite nanofiber is 30 μm or less,
An electrolyte membrane comprising the composite nanofiber according to claim 1. Forming a composite nanofiber and a nonwoven fabric comprising the composite nanofiber,
Post-processing the nonwoven fabric,
A method for producing a composite membrane, comprising: filling a void in the nonwoven fabric with a matrix polymer to integrate the composite nanofiber and the matrix polymer; and post-treating an electrolyte membrane containing the composite nanofiber. A membrane electrode assembly for a polymer electrolyte fuel cell, comprising an electrolyte membrane containing the composite nanofiber according to claim 1. A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 8.