JP6767034B2 - Composite nanofibers and electrolyte membranes containing the nanofibers - Google Patents

Description

The present invention relates to an electrolyte membrane obtained by introducing a matrix polymer into nanofibers and nanofiber non-woven fabric, and more particularly to a polymer electrolyte membrane useful for polymer electrolyte fuel cells and the like.

Composite membranes in which various substances are introduced into non-woven fabrics have been applied to various fields, and in recent years, they have been attracting 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 deterioration of the membrane and catalyst due to side reactions associated with fuel gas permeation, and have poor membrane strength and dimensional changes. There are problems such as poor long-term stability and high cost due to the use of fluorine.

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

Therefore, various developments have been carried out, and among them, sulfonated polyimide has been proposed as a high-performance electrolyte material because it has high thermal stability, mechanical strength, and excellent film-forming property (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 humidification, so that it exhibits high ionic conductivity in a wide temperature range and is used as a polymer electrolyte membrane having excellent mechanical strength. , Phosphoric acid-doped sulfonated polyimide / polybenzimidazole blend film has been proposed (Patent Document 5).
Such a membrane exhibits high ionic conductivity in a wide temperature range from a low temperature of about -20 ° C to a high temperature of about 120 ° C, and is characterized by excellent ionic conductivity even under low humidification conditions where there is little water in the membrane. ..
However, in recent years, polymer electrolyte membranes are required to have high ionic conductivity without humidification, and the film thickness tends to be lowered for the purpose of lowering the membrane resistance. Since the above-mentioned blend film has a rigid structure in the main chain, it exhibits high mechanical strength, but it has a problem that it becomes difficult to handle if it is thinned because it is brittle. Further, as the film thickness becomes thinner, the gas permeability increases and a large amount of hydrogen peroxide is generated, so that the oxidative stability is poor and the film is not stable for a long period of time.

Therefore, Patent Document 6 proposes to provide a composite membrane which exhibits high ionic conductivity in a wide temperature and humidity range, is excellent in handleability even in a thin film, and is excellent in long-term stability, and a method for producing the same.

JP-A-2002-358978 Japanese Unexamined Patent Publication No. 2005-232236 Japanese Unexamined Patent Publication No. 2005-272666 Japanese Unexamined Patent Publication No. 2007-302741 Japanese Unexamined Patent Publication No. 2011-68872 Japanese Unexamined Patent Publication No. 2012-238590

However, at present, there is a demand for further thinning, specifically, a film thickness of 20 μm or less, as compared with the case of the above-mentioned proposal of Patent Document 6. With such a film thickness, there have been problems such as insufficient ionic conductivity (proton conductivity) not being exhibited and difficulty in keeping gas permeability low.
In short, with the conventionally proposed composite membrane, it is difficult to achieve both sufficient ion conductivity (proton conductivity) and gas barrier property when the film thickness is thinned to the extent currently required, and it is 20 μm or less. At present, there is a demand for the development of a composite film having sufficient ion conductivity (proton conductivity) and gas barrier property even when the film is thinned.

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

The present inventors have considered that the above-mentioned problems can be solved by devising the substances constituting the nanofibers constituting the non-woven fabric and the method for producing the nanofibers. As a result of investigating various substances, nanofibers were produced by combining an electrolyte polymer having a cation exchange group with a basic polymer having a basic functional group capable of interacting with a cation exchange group to produce a composite nanofiber non-woven fabric. 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. 1. Composite nanofibers containing electrolyte polymers and basic polymers
The electrolyte polymer is a composite nanofiber characterized by having proton conductivity.
2. The composite nanofiber according to 1, wherein the electrolyte polymer has the structures of A) and B) below.
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. 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.
2. The composite nanofiber according to 1 to 2, 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.
4. The composite nanofiber according to 1, wherein the basic polymer has the structures of A) and B) below.
A) The main chain contains repeating units containing aromatic groups and / and aliphatic groups.
B) The main chain skeleton or side chain functional group has a basic functional group that can interact with a cation exchange group.
5. The abundance ratio of the electrolyte polymer is 1 to 99% by mass in the whole composite nanofibers.
The fiber diameter of the composite nanofiber is 500 nm or less.
1. The composite nanofiber according to 1 to 4.
6. The abundance ratio of the composite nanofibers is 1 to 50% by mass in the entire electrolyte membrane.
The thickness of the electrolyte membrane containing the composite nanofibers is 30 μm or less.
1. An electrolyte membrane containing the composite nanofibers according to 1 to 5.
7. The process of forming composite nanofibers and non-woven fabrics composed of composite nanofibers,
The step of post-treating the non-woven fabric,
A method for producing a composite membrane, comprising a step of filling the voids of the non-woven fabric with a matrix polymer to integrate the composite nanofibers with the matrix polymer, and a step of post-treating an electrolyte membrane containing the composite nanofibers.
A membrane electrode assembly for a polymer electrolyte fuel cell, which comprises the electrolyte membrane containing the composite nanofibers according to 8.1 to 7.
A polymer electrolyte fuel cell comprising the membrane electrode assembly according to 9.8.

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

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

1: Composite nanofiber 2: Electrolyte polymer 3: Basic polymer 5: Composite nanofiber post-treatment solution, 6: Matrix polymer, 7: Electrolyte membrane post-treatment solution

Hereinafter, the present invention will be described in more detail.
The composite nanofibers of the present invention consist of an electrolyte polymer and a basic polymer.
The electrolyte membrane is characterized by comprising the composite nanofibers and a matrix polymer that exists in contact with the composite nanofibers.
Hereinafter, the constituent components will be described first.

<Components>
(Electrolyte polymer)
The electrolyte polymer is a substance that conducts protons and exerts a 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. It is preferable to have it.
Here, the main chain skeleton includes polyarylene ether (PAE) shown below, polyimide (PI) shown below, polystyrene and its copolymer (PSt) shown below, polybenzimidazole (PBI), and polyphenylene (PP). , Polyphenylene oxide (PPO), polyphenylene sulfide (SPPS), polyvinylsulfonic 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 introduced and used at any position on the main chain skeleton.
Further, Nafion (registered trademark) having a fluoroalkyl main chain and a fluoroalkyl sulfonic acid group can be used.
In use, the electrolyte polymer alone or a mixture of a plurality of the electrolyte polymers can be used.
Among these, sulfonated polyarylene ether (SPAE) such as sulfonated polyarylene ether sulfone is excellent in proton conductivity, thermal stability, mechanical strength, and also has relatively good nanofiber forming ability. Therefore, it is suitable.
When mixing with a basic polymer for producing a composite nanofiber, the counter cation bonded to the cation exchange group must be a proton in order to prevent insolubilization due to the interaction between the two polymers in the solution state. However, any counterion species can be selected by ion exchange. For example, sodium, potassium, triethylammonium, imidazolium and the like can be mentioned.
As the electrolyte polymer, a compound represented by the following chemical formula can be preferably mentioned.

Polyarylen Eterre (PAE)

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

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

Polystyrene and its copolymer (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. (In the formula, n represents a number of 2 to 5000, and m represents a number of 2 to 5000. 2 to 5000 numbers are shown)))

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

(In the formula, X and Y are divalent groups having at least one aromatic ring, and may be substituted with a substituent such as a hydroxyl group, an alkyl group or a sulfonic acid group, such as a benzene ring and a naphthalene ring. Aromatic ring, nitrogen-containing heterocycle such as pyridine ring, two benzene rings are directly bonded, -O-, -CO-, -SO _2- , -S-, -CH _2- , -C (CH ₃₎ ) _2- , -C (CF ₃ ) 2-A divalent group containing a benzene ring connected by ₂ -etc.
It has at least one acid functional group such as a sulfonic acid group, a phosphonic acid group, or a carboxylic acid group in the aromatic ring of X and / or Y, and has
n preferably represents an integer of 2 to 5000, more preferably 100 to 500.
Examples of the counter cation of the acid functional group include any cation species such as proton, sodium, potassium, triethylammonium and imidazolium. )

It is also possible to use a polymer having the following block structure into which an acid functional group can be locally introduced.

(The repeating unit represented by a in the formula is the hydrophilic part,
X1 is a divalent group having at least one aromatic ring, and may be substituted with a substituent such as a hydroxyl group, an alkyl group or a sulfonic acid group, for example, an aromatic ring such as a benzene ring or a naphthalene ring. Nitrogen-containing heterocycles such as pyridine rings, two benzene rings directly bonded, -O-, -CO-, -SO _2- , -S-, -CH _2- , -C (CH ₃ ) ₂ -,- A divalent group containing a benzene ring or the like linked by C (CF ₃ ) _2- or the like can be mentioned.
Y1 in the formula is also a divalent group having at least one aromatic ring, and may be substituted with a substituent such as a hydroxyl group, an alkyl group or a sulfonic acid group, and is an aromatic group such as a benzene ring or a naphthalene ring. Nitrogen-containing heterocycles such as rings and pyridine rings, two benzene rings are directly bonded, -O-, -CO-, -SO _2- , -S-, -CH _2- , -C (CH ₃ ) _2- , -C (CF ₃ ) _2- and other divalent groups containing benzene rings, etc.
It has at least one, preferably a large number, eg, 2-4 acid functional groups such as sulfonic acid groups, phosphonic acid groups, carboxylic acid groups, etc. in the aromatic ring of X1 and / or Y1.
a preferably represents an integer of 1 to 500, more preferably 4 to 50. )
(The repeating unit represented by b in the formula is a hydrophobic part,
X1 is a divalent group having at least one aromatic ring, and may be substituted with a substituent such as an alkyl group or a fluoroalkyl group. An aromatic ring such as a benzene ring or a naphthalene ring, or a pyridine ring. Nitrogen-containing heterocycles such as, two benzene rings are directly bonded, -O-, -CO-, -SO _2- , -S-, -CH _2- , -C (CH ₃ ) _2- , -C ( CF ₃ ) A divalent group containing a benzene ring or the like linked by _2- or the like can be mentioned.
Y1 in the formula is also a divalent group having at least one aromatic ring, and may be substituted with a substituent such as an alkyl group or a fluoroalkyl group, for example, an aromatic ring such as a benzene ring or a naphthalene ring. Nitrogen-containing heterocycles such as pyridine rings, two benzene rings directly bonded, -O-, -CO-, -SO _2- , -S-, -CH _2- , -C (CH ₃ ) ₂ -,- A divalent group containing a benzene ring or the like linked by C (CF ₃ ) _2- or the like can be mentioned.
The aromatic rings of X1 and Y1 do not contain an acid functional group, and b preferably represents an integer of 1 to 500, more preferably 4 to 50. )
Further, n preferably represents 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 into which a sulfonic acid group can be locally introduced can also be used.

(X1, Y1, X2, Y2, X3, Y3 are divalent groups having the same or different groups and having at least one aromatic ring, and are substituents such as a hydroxyl group, an alkyl group and a sulfonic acid group. An aromatic ring such as a benzene ring or a naphthalene ring, a nitrogen-containing heterocycle such as a pyridine ring, and two benzene rings directly bonded to each other, which may be substituted with, -O-, -CO-, -SO _2- , Divalent groups containing a benzene ring or the like linked by −S−, −CH ₂₋ , −C (CH ₃ ) ₂₋ , −C (CF ₃ ) _2−, etc. can be mentioned.
It has at least one, preferably a large number, for example 2 to 4 sulfonic acid groups, phosphonic acid groups, carboxylic acid groups and other acid functional groups in the aromatic rings of X1, Y1, X2, Y2, X3 and Y3.
a, b, and c represent integers of 1 to 500, respectively.
The repeating unit represented by a and b may have the above-mentioned block structure. )
More specifically, the following polymers can be used.

(X and y represent integers of 1 to 1000, respectively)
The SPAE can be obtained, for example, in the case of sulfonated poly (arylene ether sulfone) (SPAES) as follows.
That is, in a nitrogen atmosphere, using a polymerization solvent such as N, N-dimethylacetamide and an azeotropic agent (toluene, etc.), 4,4'-bisfluorophenyl sulfone-3,3'-sodium disulfonate, 4,4'. It can be obtained by adding −bisfluorophenyl sulfone, 4,4′-biphenol and potassium carbonate and stirring at a temperature of 100 ° C. or higher for 1 to 10 hours, and then raising the temperature further and stirring for 1 to 10 hours.

The weight average molecular weight and the degree of polymerization can be measured and calculated by GPC (gel permeation chromatography) by the following method, and are polystyrene-equivalent 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 lithium bromide-added DMF at a concentration of 1 mg / ml.

<Components>
(Basic polymer)
The basic polymer is a polymer having a functional group that can interact with the acid substituent of the electrolyte polymer. Here, "interaction" includes not only the formation of ionic bonds and hydrogen bonds, but also the formation of covalent bonds and 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, = N- group and the like.
Examples of the polymer include polybenzimidazole, polybenzoxazole, polybenzthioazole, polyindole, polyquinolin, polyvinylimidazole, polyallylamine, and polyethyleneimine having structural formulas shown below.
Among these, polybenzimidazole is suitable 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 the 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 , and the like.
Y is a divalent group having at least one aromatic ring or an aliphatic hydrocarbon, and may be substituted with a substituent such as a hydroxyl group, an alkyl group or a sulfonic acid group, such as a benzene ring or a naphthalene ring. aromatic rings, nitrogen-containing heterocyclic ring such as pyridine ring, two benzene rings is a direct bond, -O -, - CO -, - SO 2 - 2 divalent group containing a benzene ring are linked by such Is mentioned,
n preferably represents an integer of 2 to 5000, more preferably 100 to 500. )
Specific examples of the PBI include the following compounds.

The PBI can be produced according to the production method described in JP2012-238590A.

Further, the weight average molecular weight of the polymer (Mw) of, 5.0 × ¹⁰ 4 is preferably 1.0 a × 10 ^6, the ratio Mw / Mn of weight-average molecular weight to number average molecular weight (Mn) (Mw) Is preferably 1 to 5. By setting these within this range, it becomes possible to produce more uniform composite nanofibers in 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 film thickness of the composite film and improving the proton conductivity, and more preferably 50 to 300 nm.
A method for producing such a fiber will be described later.

<Components>
(Proton conductive material)
It is also possible to dope the composite nanofibers with a proton conductive material by post-treatment of the composite nanofibers.
The proton transmitter is a substance that conducts protons and exerts a main function as an electrolyte membrane when the composite membrane of the present invention is used as a polymer electrolyte membrane.
As the proton conductive substance, a substance capable of interacting with a basic polymer contained in the composite nanofiber and capable of contributing to proton conduction as an acid functional group is preferable, and a specific proton conductive substance is specified. 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 nitrate group, a vinyl carboxylic acid group, a Lewis acid group and the like.
Examples of the acidic substance include polyphosphoric acid, phytic acid, polyvinylphosphonic acid, polyvinylsulfonic acid, naphthalenedisulfonic acid, oxalic acid, and squaric acid. Among these, phytic acid has a large molecular weight, is difficult to diffuse due to acid-base interaction with composite nanofibers described later, has relatively low solubility in water, and is difficult to elute in the presence of water. Therefore, it is suitable.
Other substances that can be used in the composite nanofiber post-treatment step include only one acidic group in addition to the above-mentioned proton transmitter having two or more acidic groups that can be used in the composite membrane of the present invention. Acidic substances can also be used. For example, in addition to the acidic substances that can be used for the composite film of the present invention described above, specifically, phosphoric acid, methanephosphonic acid, sulfuric acid, methanesulfonic acid, benzenesulfonic acid, trifluoromethanesulfonic acid, sulfinic acid, Examples thereof include formic acid, acetic acid, nitrate, hydrochloric acid, ascorbic acid, chromium acid, tetrafluoroboric acid, hexafluorophosphoric acid and the like.

<Components>
(Matrix polymer)
As the matrix polymer, a polymer capable of improving the film strength when a composite film is formed and having excellent proton conductivity is preferable, 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, sulfonated polyphenylene oxide (SPPO) shown below. , Polyphenylene sulfide (SPPS) shown below, sulfonated polystyrene and its copolymer (SPSt) shown below, polyvinyl sulfonic acid shown below and its copolymer (PVS) and the like can be used. In addition, it 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 the sulfonated polyimide conventionally proposed for forming a polymer electrolyte membrane. Examples of the sulfonated polyimide preferably used in the present invention include the sulfonated polyimide represented by the following formula (2).

In the above formula (2), R ³ represents a tetravalent group having at least one aromatic ring, and for example, an aromatic tetravalent residue such as a benzene ring or a naphthalene ring, a benzene ring, a naphthalene ring or the like. The tetravalent aromatic residue of the compound in which the two aromatic rings are directly linked, and the two benzene rings are linked by groups such as -C (CF ₃ ) _2- , -SO _2- , and -CO _2-. The tetravalent residue of the compound is preferred, and more preferably the tetravalent residue of the compound having two aromatic rings.

Further, in the 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−,. A divalent residue of a sulfonated aromatic compound linked by a group such as> CR ⁶ (R ⁶ forms a fluorene ring structure with a carbon atom) and having a sulfonic acid group on the benzene ring or on the substituent of the benzene ring. Etc. are preferable. Preferred examples of the substituent of 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, and for example, a heterocycle such as a benzene ring or a nitrogen-containing heterocycle is included in the structure. Divalent residues of the non-sulfonated compound having the same are preferable. Further, in the 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 an integer of 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 used in the present invention represented by the above formula (2) is, for example, an aromatic carboxylic acid dianhydride, a sulfonated aromatic diamine, and a non-sulfone which is an optional component, as shown in the following reaction formula. It can be synthesized from the monomer of carboxylic acid diamine.

In the formula, R ³ , R ⁴ , R ⁵ , n, and m are defined above.
Examples of the aromatic carboxylic acid dianhydride include 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,2'-bis (3,4-dicarboxyphenyl) hexafluoropropane, and 4 , 4'-Bisphtyl-1,1', 8,8'-tetracarboxylic dianhydride is preferred. Examples of the sulfonated aromatic diamine include a main chain type monomer in which the main chain is modified with a sulfonic acid group and a side chain type monomer in which the side chain is modified with a sulfonic acid group. Preferred examples of the sulfonated aromatic diamine are, for example, 2,2-benzidine disulfonic acid, 4,4'-diaminophenyl ether disulfonic acid, 3,3'-bis (3-sulfopropoxy) benzidine, 9,9'. Examples thereof include −bis (4-aminophenyl) fluorene-2,7-disulfonic acid and 2,2′-bis (4-sulfophenyl) benzidine. Preferred examples of the non-sulfonated aromatic diamine include, for example, 4,4'-hexafluoroisopropyridenebis (p-phenyleneoxy) diamine, 2,2-diaminodiphenylhexafluoropropane, 9,9'-bis. Examples thereof include (4-aminophenyl) fluorene and 2,5-diaminopyridine. By using a non-sulfonated aromatic diamine monomer, membrane stability and acid retention ability can be imparted.
A sulfonated copolymerized polyimide can be obtained by using a sulfonated aromatic diamine monomer and a non-sulfonated aromatic diamine monomer in combination, and the copolymer may be a random copolymer or a block copolymer.
The ratio n / m of the sulfonated diamine monomer (n) and the non-sulfonated aromatic diamine monomer (m) at the time of copolymerization is preferably 30/70 to 100/0. If 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 weight average molecular weight of the sulfonated polyimide (Mw) of, preferably from the viewpoint of film formability to be ^{1.0 × 10 4 ~1.0 × 10 6} , weight-average molecular weight to number average molecular weight (Mn) (Mw) The ratio of Mw / Mn is preferably 1 to 5 in terms of strength.

(SPI)
Further, as the SPI, one having the block structure shown below can also 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 substitution. 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. In addition, m / (n + r) is in the range of 90/10 to 10/90, which is a block polymer.)
The sulfonic acid group in the group A may be directly substituted with an aromatic group, or side via, for example, an -O (CH2) -group, a -C6H4- (phenyl) group, an -O-C6H4- group, or the like. It may be introduced into a chain. As the aromatic group, a benzene ring, a naphthalene ring or the like may be used alone, but two or more rings are directly bonded or via an -O-, -SO2-, -C (CF3) 2-group or the like. It may be combined.
As an example of the group A, for example, the following groups are preferable.

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 directly linked to an aromatic group having 6 to 30 carbon atoms or via an -O-, -CO-, -NH- group or the like. Examples of the substituent of the group C include groups such as -OH, -COOH and -NH2. As the group B which is an aromatic group having 6 to 30 carbon atoms including the direct bonding portion or the -O-, -CO-, -NH- group and the like, for example, the following groups are preferably mentioned and substituted. As the group C, which is an aromatic group having 6 to 30 carbon atoms which may have a group, the group −D− is −H, −DH or −D—OH in the following groups. Such groups are preferred.

(In the formula, D represents -O-, -CO-, -NH-, -CO-NH-, -CO (= O)-or direct binding.)

Further, as the SPI, a graft polymer obtained by introducing a group represented by the following (2) into the polymer represented by the above formula (1) can also be used. In this case, the polymer represented by (1) above can be either a random polymer or a block polymer, and in the case of a random polymer, it becomes a graft polymer, and in the case of a block polymer, it is a block graft. It becomes a polymer.

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

Further, 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. The weight average molecular weight (Mw) of the polyimide resin constituting the side chain is preferably 5,000 to 500,000.

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 with respect to the main chain polymer. The graft ratio of 1 <graft ratio <100 is preferable.

Here, the graft ratio is a ratio calculated assuming that the side chain is introduced into all the side chain introduction sites in the main chain as 100%, and is [n / (n + r)] × 100. For example, in Examples 3 and 4 described later, 100% when all the carboxylic acid groups of DABA used in Synthesis Example 1 or 2 are reacted with the amino group at the partial end of the side chain prepared in Synthesis Example 3 to form an amide bond. Is. Specifically, it is calculated by the following formula.
IEC (ion exchange capacity) = sulfonic acid group equivalent x graft ratio / (main chain unit molecular weight- (side chain molecular weight x graft ratio)] Graft rate (%) = {(main chain unit molecular weight x IEC) / [sulfonic acid group Equivalent- (side chain molecular weight x IEC)]} x 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 , and the like.
Y is a divalent group having at least one aromatic ring, and has at least one substituted sulfonic acid group, an aromatic ring such as a benzene ring or a naphthalene ring, or a nitrogen-containing heterocycle such as a pyridine ring. benzene rings directly bonded, -O -, - CO -, - SO 2 - include divalent group containing a benzene ring are linked by like,
n preferably represents an integer of 2 to 5000, more preferably 100 to 500. )

Specifically, the following polymers and the like can be used.
The SPBI can be obtained, for example, in the case of disulfonated poly (benzimidazole) as follows.
That is, in a nitrogen atmosphere, polyphosphoric acid was used as a solvent and a condensing agent, 3,3'-diaminobenzidine and 4,8-disulfonyl-2,6-naphthalenedicarboxylic acid were added, and 1 to 2 was added at a temperature of 80 ° C. or higher. It can be obtained by stirring for hours, then raising the temperature further, stirring at 200 ° C. for 8 to 10 hours, dropping into water, and then washing and recovering the precipitate with a 10 wt% potassium hydroxide aqueous solution.

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

(N is as described above)

(R1, R2, R3, R4 in the formula are a monovalent or divalent group having a hydrogen group, an alkyl group, a hydroxyl group, a sulfonic acid group, or an aromatic ring, and a sulfonic acid group or the like. Aromatic rings such as benzene ring and naphthalene ring, nitrogen-containing heterocycles such as pyridine ring, and two benzene rings are directly bonded and linked by -O-, -CO-, -SO _2-, etc. A monovalent or divalent group containing a benzene ring or the like is mentioned, and n represents an integer of 1 to 5000.)

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

Examples of the above-mentioned sulfonated polyphenylene sulfide (SPPO includes the following polymers and the like can be mentioned.

(R1, R2, R3, R4 in the formula are a monovalent or divalent group having a hydrogen group, an alkyl group, a hydroxyl group, a sulfonic acid group, or an aromatic ring, and a sulfonic acid group or the like. Aromatic rings such as benzene ring and naphthalene ring, nitrogen-containing heterocycles such as pyridine ring, and two benzene rings are directly bonded and linked by -O-, -CO-, -SO _2-, etc. A monovalent or divalent group containing a benzene ring or the like is mentioned, 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) can be mentioned.

(R1, R2, R3, R4 in the formula are a monovalent or divalent group having a hydrogen group, an alkyl group, a hydroxyl group, a sulfonic acid group, or an aromatic ring, and a sulfonic acid group or the like. Aromatic rings such as benzene ring and naphthalene ring, nitrogen-containing heterocycles such as pyridine ring, and two benzene rings are directly bonded and linked by -O-, -CO-, -SO _2-, etc. A monovalent or divalent group containing a benzene ring or the like is mentioned.
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, benzene, etc., and includes all vinyl monomers copolymerizable with styrene, sulfonated styrene, or sulfonated ester-substituted styrene, and m and n are integers of 1 to 10,000, respectively. 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, benzene, etc., and includes all vinyl monomers copolymerizable with vinyl sulfonic acid or vinyl sulfonic acid ester, and m and n represent integers of 1 to 10,000, respectively.)

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

<Composite membrane morphology>
(overall structure)
The thickness of the composite film of the present invention is preferably 2 to 40 μm in terms of satisfying the thickness required in recent years, 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, composite nanofibers 1 composed of an electrolyte polymer and a basic polymer are in the form of a non-woven fabric in which each nanofiber is entangled. Existing. A matrix polymer is provided so as to fill the space between the composite nanofibers 1 and form the outer shape of the composite film. In the present embodiment, the non-woven fabric made of the composite nanofibers 1 is composed of only the matrix polymer on both the front and back sides. The polymer layer 6 is formed.
Furthermore, it is possible to dope the composite nanofibers with a proton conductive material using a composite nanofiber post-treatment solution. In the composite film of the present invention, as described above, the proton transmitter 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 transmitter not only reacts with the basic polymer to be bound to the composite nanofiber 1, but also binds to the composite nanofiber 1 at two or more points to form a kind of bridging structure.
By forming such a bridge structure, a strong non-woven fabric structure can be formed even if the film thickness is thinner than that of the conventional one, and the composite nanofibers and the proton transmitter are bonded to each other. It is also advantageous in terms of proton transfer performance.
In the non-woven fabric form formed by the composite nanofibers, the porosity before contact with the matrix polymer is 50 to 90% in terms of proton conductivity, film strength when formed into a composite film, and gas barrier properties. preferable. In particular, it is preferable to use the above-mentioned composite nanofibers having a fiber diameter in which they are made into a non-woven fabric with a porosity in this range in terms of exhibiting the desired effects of the present invention. The measurement of porosity will be described later.
Here, the void ratio before contact with the matrix polymer is defined by first producing a non-woven fabric using composite nanofibers, and then adding the matrix polymer to the obtained non-woven fabric to form the non-woven fabric, as described in the manufacturing method described later. It is the ratio of the space existing between each composite nanofiber in the state of the non-woven fabric before being immersed in the solution of the matrix polymer and being formed into a desired shape. That is, the porosity is the ratio of the space to the volume of the virtual solid that is in contact with the non-woven fabric, and is represented by (total volume of the space / volume of the virtual solid) × 100.

(Quantity ratio relationship)
The abundance ratio of the proton transmitter is that the proton transmitter and the composite nanofiber both have the above-mentioned structures, so that sufficient proton transfer performance can be obtained without increasing the abundance of the proton transmitter. , It is preferable that it is 0.1 to 20% by mass, and more preferably 1 to 10% by mass in the whole composite film of the present invention. If it is less than 1% by mass, the ionic conductivity may be insufficient, and if it exceeds 10% by mass, the proton transmitter may be eluted over time. Therefore, it is preferably within the above range.
As described above, when the abundance of the proton transmitter is small, the exudation to the surface of the composite film is also very small. Therefore, for example, when it is used as a polymer electrolyte membrane for a fuel cell, the catalyst is less likely to be poisoned, which is also advantageous in this respect.
Further, the abundance ratio of the matrix polymer is sufficient as long as it fills the voids existing between the composite nanofibers existing at the porosity and forms the outer shape of the composite film, but the composite nanofibers are preferable. When the total amount of and is 100, it is 50 to 90% by mass.

<Manufacturing method>
Next, the method for producing the composite film of the present invention will be described.
The production method of the present invention is preferably the above-mentioned method for producing the composite film of the present invention, as shown in FIG.
Step of forming the composite nanofiber and the non-woven fabric composed of the composite nanofiber (A in FIG. 2),
Step of post-treating the non-woven fabric (B in FIG. 2),
A step of filling the voids of the non-woven fabric with a matrix polymer to integrate the composite nanofibers and the matrix polymer (C in FIG. 2), and a step of post-treating an electrolyte membrane containing the composite nanofibers (not shown).
It can be carried out by performing.
This will be further described.

(Step of forming non-woven fabric, FIG. 2A)
The step of forming the non-woven fabric is to form by discharging a spinning liquid obtained by dissolving the electrolyte polymer and the basic polymer, which are the raw materials of the composite nanofibers, in a solvent onto the collector 30 using a discharger 10. Can be done.
The ratio of the electrolyte polymer to the total raw material polymer is preferably 1 to 99% by mass, more preferably 20 to 80% by mass.
The production of a fine fiber non-woven fabric using a discharger is disclosed in, for example, JP-A-2003-73964, JP-A-2004-238949, and JP-A-2005-194675. Hereinafter, description will be given according to an example using the manufacturing apparatus disclosed in JP-A-2005-194675.

The discharger 10 shown in FIG. 2 has a nozzle 11 for discharging the spinning liquid and a tank 12 for storing the spinning liquid. It also has a grounded collector 30 that is located opposite the nozzle 11. Therefore, when an electric field is formed between the nozzle 11 and the collector 30 by applying a voltage application device (not shown), the fibers discharged from the nozzle 11 and stretched by the electric field fly toward the collector 30. , Accumulate on the collector 30 to form a non-woven fabric 20 made of composite nanofibers.
Examples of the solvent include dimethyl sulfoxide (DMSO), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), and the raw material polymer concentration is , 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, more preferably 500 to 5000 mPa · s.
When the above device is used, the spinning liquid is extruded from the nozzle 11 toward the collector 30, and is subjected to a stretching action by an electric field between the grounded collector 30 and the nozzle 11 applied by the voltage application device. It flies toward the collector 30 while becoming fibrous (so-called electrostatic spinning method). Then, the flying fibers are directly accumulated on the collector 30 to form a non-woven fabric. The spinning liquid 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 description of JP2012-238590A Nos. 0047 to 0056 is appropriately applied to the details of the apparatus used for spinning.
The thickness of the non-woven fabric obtained here is preferably 25 μm or less from the viewpoint of reducing the thickness of the entire composite film, and more preferably 5 μm or less.

(Step of post-treating the non-woven fabric, FIG. 2B)
The resulting non-woven 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. As a result, the necessary proton transmitters can be adsorbed on the composite nanofibers (including adsorption by reaction), and excess proton transmitters can be removed, resulting in thinning, gas barrier properties, and high conductivity (particularly gas barrier properties). It is possible to achieve compatibility with.
In the post-treatment, as shown in B of FIG. 2, the obtained non-woven fabric is placed in an arbitrary container 40, a proton transmitter-containing solution is injected into the container 40 from another injection container 50, and the solution is immersed in the proton transmitter-containing solution. It can be done by doing.
The concentration of the proton transmitter in the proton transmitter-containing solution is preferably 5 to 95% by mass, preferably 10 to 85% by mass. The immersion conditions are preferably a temperature of 15 to 80 ° C. and 0.5 to 3 hours.
Then, after the immersion is completed, it is preferable to perform washing in order to remove excess proton transmitter. In particular, in the above-mentioned electrolyte membrane of the present invention, since the proton-transmitting substance binds to the composite nanofiber as described above, it is better to remove the excess proton-transmitting substance that is not bound from the viewpoint of membrane strength and gas barrier property, and further. Since there are very few free proton transmitters, elution of proton transmitters is unlikely to occur even in the presence of water. 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 transmissibility due to the binding. The washing is preferably carried out at 15 to 80 ° C. for 5 to 20 hours using a washing liquid such as water.
After washing, it is preferable to sufficiently dry the product by vacuum drying at 50 to 150 ° C. for 5 to 15 hours.
The doping amount of the proton transfer material (adsorption amount to the composite nanofiber) can be calculated by measuring the mass change or ion exchange capacity of the non-woven fabric before and after the post-treatment.
As the proton transmitter that can be used in this step, in addition to the above-mentioned proton transmitter having two or more acid functional groups, an acidic substance having only one acid functional group can also be used. For example, when nitric acid having one acid functional group is used, the acidic substance is used to ion exchange the counter ion of the acid functional group of the electrolyte polymer into proton foam. Many acidic substances that have only one acid functional group that does not interact with the basic polymer can be removed by a washing operation.

(Step of filling the voids of the non-woven fabric with the matrix polymer to integrate the composite nanofibers and the matrix polymer, FIG. 2C)
In this step, the non-woven fabric after the post-treatment obtained in the previous step is put into a container 40', a solution of the 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 optional depending on the matrix polymer used, but is water, methanol, ethanol, 2-propanol, dimethyl sulfoxide (DMSO), N, N-dimethylformamide (DMF), N, N-. Examples thereof include dimethylacetamide (DMAc) and N-methyl-2-pyrrolidone (NMP), which may be used in combination with other solvents. The concentration of the matrix polymer in the solution is preferably 2 to 20% by mass.
The composite film of the present invention can be obtained by evaporating the solvent after the immersion state. Evaporation of the solvent can be carried out, for example, by air 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 salted and then treated as the above solution, but in this case, the composite membrane obtained after the completion of the above evaporation treatment is preferably acid-treated.

(Step of post-treatment of electrolyte membrane containing composite nanofibers)
Post-treatment of electrolyte membranes containing composite nanofibers removes residual solvents and small molecules, exchanges counter ions of acid functional groups with protons, densifies membranes and improves stability and gas barrier properties. The effect can be expected.
Post-treatment mainly includes 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 the solution treatment is completed, the heat treatment can be performed by performing a vacuum drying treatment at 50 to 150 ° C. for 1 to 48 hours.

<Usage and advantages>
The electrolyte membrane of the present invention can be used as a polymer electrolyte membrane of a polymer electrolyte fuel cell that is sandwiched between a positive electrode and a negative electrode, is a thin film as described above, and is generated at the negative electrode. The resulting protons 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 present invention exhibits excellent low membrane resistance close to the required value (<0.025Ω · cm ² ) under low humidity in a high temperature range. 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).
It is also required to have a high gas barrier property, that is, a low gas permeation flow rate (O ₂ : 80 ° C. 95% RH <1.3 × ^10-9 (cm ³ / (cm ² sec kPa))). In addition, high film stability (chemical, mechanical, thermal) is also required. The nanofiber composite film of the present invention satisfies these performances even if the film thickness is thinner than that of the conventional film. To do.
It is not clear why the electrolyte membrane of the present invention is a well-balanced composite membrane having higher film resistance as a thin film and also having a high gas barrier property as compared with the conventional composite membrane. However, the following reasons can be considered.
By combining the basic polymer with the electrolyte polymer that constitutes the nanofiber, the acid functional groups in the electrolyte interact with the basic polymer and promote the dissociation of protons. In particular, the effect becomes remarkable under low humidity conditions where proton dissociation is difficult and proton conductivity is lowered.
Further, by doping the composite nanofiber with an acidic substance having two or more acid functional groups, it is possible to increase the substance that contributes to proton conduction. Most of the acidic substances are abundant on the surface of the composite nanofibers and exist so as to connect the composite nanofibers to each other. Therefore, when integrated with the matrix polymer, it becomes difficult for the composite nanofibers to spread.
Furthermore, the presence of the composite nanofibers containing the basic polymer suggests that the acid functional groups of the matrix polymer spontaneously gather near the surface of the nanofibers during the fabrication of the electrolyte membrane to form a kind of acid condensed layer. Since the protons can move along the nanofibers without being dispersed, it is considered that the proton transfer performance is improved in the film thickness direction as well. Further, it is considered that the strength and gas barrier property of the electrolyte membrane are improved by the presence of the composite nanofibers which form an interaction inside and are excellent in the mechanical strength and the sbaria property in the electrolyte membrane.
The electrolyte membrane of the present invention configured in this way not only has the effect of being excellent in each of the above-mentioned performance balances, but also has no free acidic substance, and poisoning of the platinum catalyst by the acidic substance in the fuel cell. Since there is no such thing, deterioration of characteristics can be significantly suppressed. The non-woven fabric can be pressurized by a hot press or the like to increase the density of fine fibers, and further thinning is possible.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

<< 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 allowing to cool, the pH was adjusted to 10 with sodium hydroxide while pouring into 100 ml of distilled water and stirring. The solution was slowly poured into 1 L ethanol and the precipitate was filtered by suction filtration. The filtrate was concentrated by evaporation, 2-propanol was added, and the precipitate was collected by suction filtration. The recovered SDFB was dried at 80 ° C. for 18 hours to completely remove the solvent.

<< Synthesis Example 2: Synthesis of Sulfonized Polyarylene Ether (SPAES) >>
Under a nitrogen atmosphere, 30 ml of N, N-dimethylacetamide (dehydrated) was used as the polymerization solvent, and 3,3'-disulfo-4,4'-difluorobenzophenone-sodium obtained in Synthesis Example 1 was placed in a three-necked flask having a Dean-Stark tube. 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. Add 2 times the same amount of potassium carbonate and 15 ml of toluene (dehydrated), stir at 140 ° C. for 4 hours to remove water and toluene in the Dean-Stark tube, and then stir at 170 ° C. for another 15 hours to sulfonated poly. An arylene ether sulfone (SPAES) sodium salt was synthesized. The synthesized SPAES was poured into hot water for precipitation and purification, and then repeatedly washed with distilled water for recovery. The recovered SPAES (sodium salt) was vacuum dried at 60 ° C. for 15 hours to completely remove the solvent.

A ¹ H-NMR spectrum of sulfonated polyallerene ether (sodium salt) was measured using an NMR apparatus Burker AVANCE III500 (manufactured by Bruker Biospin). ^{1 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). Using DMF to which a small amount of lithium bromide (10 mmol / L) was added as the GPC solvent, the polystyrene-equivalent molecular weight was measured from a 1 mg / mL sulfonated polyarylene ether salt solution prepared using a carrier. As a result, Mw is 6.0 × 10 ^5, Mw / Mn was 1.7.

<< Synthesis Example 3: Synthesis of Polybenzimidazole (PBI) >>
Under a nitrogen atmosphere, using polyphosphoric acid (PPA) as the polymerization solvent, 2.27 g (10.6 mmol) of 3,3'-diaminobenzidine (DAB) and 2.73 g (10) of 4,4'-oxybis benzoic acid (OBBA). .6 mmol) was weighed, polyphosphoric acid (PPA) was added so as to be a 3 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-exchanged water and reprecipitated, then neutralized with sodium hydroxide solution and washed. Polybenzimidazole was recovered by suction filtration, air-dried for 24 hours, and then vacuum-dried at 100 ° C.

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

<< Example 1: Preparation of SPAES / PBI (50/50) composite nanofiber non-woven fabric >>
To the vial, the sulfonated polyarylene ether sulfone salt of Synthesis Example 2 and polybenzimidazole of Synthesis Example 3 were added in a weight ratio of 50/50, and dehydrated so that the polymer weight was 16% by weight 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 was placed in the collector part of the electrospinning device ES-2000S (manufactured by Finance), a syringe filled with the polymer solution was set in the electrospinning device, and the amount of the polymer solution released was 0.12 mL / hour. , Electrospinning was done. 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 (50/50) composite nanofiber non-woven fabric was laminated on the aluminum foil. The obtained composite nanofibers were vacuum dried at 60 ° C. for 15 hours.
Post-treatment was performed for acid treatment and acid doping of the obtained composite nanofibers. The composite nanofibers were immersed in hydrochloric acid (0.1 M) at room temperature for 15 hours and washed repeatedly with pure water. Subsequently, the mixture was immersed in an aqueous phytic acid solution (50 wt%) at room temperature for 1 hour, and then washed repeatedly in pure water at 80 ° C. for a total of 24 hours to remove undoped phytic acid. The acid-doped composite nanofibers were vacuum dried at 60 ° C. for 15 hours. By the above post-treatment, the SPAES sodium salt can be replaced with proton foam, and the basic polymer can be doped with phytic acid.
After osmium coating using a part of the nanofibers, the fiber diameter of the nanofibers prepared by observing with a scanning electron microscope (SEM, JSM-6100 manufactured by JEOL) and obtained was calculated. FIG. 3 shows an SEM image of the nanofiber (release time 60 seconds) of Example 1. From the results of the SEM image, it was confirmed that uniform nanofibers could be produced, and the fiber diameter was 326 ± 27 nm.
The porosity is the apparent volume (V) calculated from the dry mass (W) and the film thickness measured by a film thickness meter obtained by cutting a fiber mat into 3 cm squares, and the specific gravity (1.5 g) of SPAES / PBI (50/50). It was calculated from the following formula using / cm ³ ).
Porosity (%) = (1- (W / (V x 1.5)) x 100
The calculated porosity was about 89%.

<< Example 2: Fabrication of uniaxial array SPAES / PBI (50/50) composite nanofibers and measurement of proton conductivity >>
In order to measure the proton conductivity of nanofibers alone, uniaxially arranged nanofibers were prepared. Similar to Example 1, the polymer solution was adjusted to 16% by mass, and electrospinning was performed using ES-1000 (manufactured by Furniture). As the collector, a glass substrate having two aluminum electrodes installed at both ends was used. A voltage of 17 kv was applied to the syringe, with the distance between the syringe and the collector being 10 cm and the amount of polymer solution released being 0.12 mL / hour. As a result, a uniaxially oriented nanofiber aggregate was produced on a glass substrate. The collector was removed when the release time of the polymer solution was 60 seconds. Hydrochloric acid (0.1 M) was added dropwise to the uniaxially arranged nanofibers, and the mixture was 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, and the mixture was allowed to stand at room temperature for 1 hour and repeatedly washed 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 arranged nanofibers.

[Measurement of proton conductivity of uniaxial array SPAES / PBI (50/50) composite nanofibers]
The resistance of the nanofiber aggregate (distance between electrodes 0.5 cm) was measured by measuring the frequency response from 50 kHz to 5 MHz using an impedance analyzer 3532-50 (manufactured by Hioki Co., Ltd.). The temperature and humidity at the time of resistance measurement were maintained at 90 ° C. and 95% RH, respectively, using a constant temperature and humidity controller SH-221 (manufactured by ESPEC).
Further, the uniaxially arranged nanofibers after the impedance measurement were coated with gold and observed by SEM. Obtain the average diameter and number of uniaxially arranged nanofibers existing between the electrodes from the SEM image, and use the formula inter-electrode distance [cm] / (cross-sectional area of one fiber [cm ² ] x number of nanofibers x 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 polybenzimidazole of Synthesis Example 3 in a weight ratio of 50/50, and further add N, N-dimethylformamide (DMF). Stirred evening to prepare a blended polymer solution. The blended polymer solution was poured into a glass petri dish, air-dried at 60 ° C., and then vacuum-dried at 60 ° C. for 15 hours to obtain a SPAES / PBI (50/50) blended film. The film thickness was 64 μm. The obtained blend membrane was immersed in hydrochloric acid (0.1 M) at room temperature for 15 hours and repeatedly washed with pure water. Subsequently, the mixture was immersed in an aqueous phytic acid solution (50 wt%) at room temperature for 1 hour, and then washed repeatedly in pure water at 80 ° C. for a total of 24 hours to remove undoped phytic acid. The acid-doped blend membrane was vacuum dried at 60 ° C. for 15 hours.

[Measurement of proton conductivity of SPAES / PBI (50/50) blended membrane]
The frequency response from 50 kHz to 5 MHz was measured using an impedance analyzer 3532-50 (manufactured by Hioki Co., Ltd.), and the resistance of the nanofiber aggregate (distance between electrodes 1.0 cm) was measured. The temperature and humidity at the time of resistance measurement were maintained at 90 ° C. and 95% RH, respectively, using a constant temperature and humidity controller SH-221 (manufactured by ESPEC). Using the resistance [Ω], inter-electrode distance [cm], and film cross-sectional area [cm ² ] obtained by impedance measurement, the formula inter-electrode distance [cm] / (film cross-sectional area [cm ² ] x resistance [Ω]) From, the proton conductivity [S / cm] was calculated. The results are shown in Table 1.
Compared with the nanofibers having the same composition in Example 2, the conductivity of the blended film was a very low value. It is considered that this is because the sulfonic acid group in SPAES, which is an electrolyte polymer, interacts with PBI, which is a basic polymer, acid-base in the membrane, and the concentration of acid functional groups capable of proton conduction decreases. Further, it is presumed that phytic acid, which is a doping acid, has a relatively large molecular size, and although it was doped in PBI existing near the film surface, it was not doped inside. On the other hand, in the case of nanofibers, it is considered that the diameter was as small as several hundred nm and the phytic acid was sufficiently doped to the inside, and the formation of efficient proton conduction channels peculiar to nanofibers led to high conductivity. ..

<< Example 3: Preparation of SPAES / PBI (20/80) composite nanofiber non-woven fabric >>
Into the vial, the sulfonated polyarylene ether sulfone of Synthesis Example 2 and the polybenzimidazole of Synthesis Example 3 were added in a weight ratio of 20/80 so that the polymer weight was 14.3% by weight based on 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 was placed in the collector part of the electrospinning device ES-2000S (manufactured by Finance), a syringe filled with the polymer solution was set in the electrospinning device, and the amount of the polymer solution released was 0.12 mL / hour. , Electrospinning was done. 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 non-woven 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 nanofibers produced from the SEM image was 323 ± 20 nm. The porosity was about 86%.

<< Example 4: Fabrication of Uniaxial Array SPAES / PBI (20/80) Composite Nanofibers and Measurement of Proton Conductivity >>
Similar to Example 3, the polymer solution was adjusted to 14.3% by mass, and electrospinning was performed using ES-1000 (manufactured by Fusion). As the collector, a glass substrate having two aluminum electrodes installed at both ends was used. A voltage of 20 kv was applied to the syringe, with the distance between the syringe and the collector being 10 cm and the amount of polymer solution released being 0.12 mL / hour. As a result, a uniaxially oriented nanofiber aggregate was produced on a glass substrate. The collector was removed when the release time of the polymer solution was 60 seconds. The same post-treatment as in Example 2 was carried out to obtain acid-doped uniaxially arranged nanofibers.
In the same manner as in Example 2, the proton conductivity of the uniaxial array SPAES / PBI (20/80) composite nanofibers was measured. The results are shown in Table 1.
The SEM observation results are shown in FIG.

<< Example 5: Preparation of SPAES / PBI (80/20) Composite Nanofiber Nonwoven Fabric >>
Add the sulfonated polyarylene ether sulfone of Synthesis Example 2 and the polybenzimidazole of Synthesis Example 3 to the vial so that the weight ratio is 80/20, and the polymer weight is 15.5% by weight 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 was placed in the collector part of the electrospinning device ES-2000S (manufactured by Finance), a syringe filled with the polymer solution was set in the electrospinning device, and the amount of the polymer solution released was 0.12 mL / hour. , Electrospinning was done. 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 non-woven 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 nanofibers produced from the SEM image was 274 ± 25 nm. The porosity was about 85%.

<< Example 6: Fabrication of Uniaxial Array SPAES / PBI (80/20) Composite Nanofibers and Measurement of Proton Conductivity >>
Similar to Example 5, the polymer solution was adjusted to 15.5% by mass, and electrospinning was performed using ES-1000 (manufactured by Fusion). As the collector, a glass substrate having two aluminum electrodes installed at both ends was used. A voltage of 20 kv was applied to the syringe, with the distance between the syringe and the collector being 10 cm and the amount of polymer solution released being 0.12 mL / hour. As a result, a uniaxially oriented nanofiber aggregate was produced on a glass substrate. The collector was removed when the release time of the polymer solution was 60 seconds. The same post-treatment as in Example 2 was carried out to obtain acid-doped uniaxially arranged nanofibers.
In the same manner as in Example 2, the proton conductivity of the uniaxial array SPAES / PBI (20/80) composite nanofibers was measured. The results are shown in Table 1.

<< Comparative Example 2: Fabrication of SPAES Single Nanofiber Nonwoven Fabric >>
Dehydrated N, N-dimethylformamide (DMF) was added to the vial to the sulfonated polyarylene ether sulfone of Synthesis Example 2 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 was placed in the collector part of the electrospinning device ES-2000S (manufactured by Finance), a syringe filled with the polymer solution was set in the electrospinning device, and the amount of the polymer solution released was 0.12 mL / hour. , Electrospinning was done. 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 single nanofiber non-woven 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 nanofibers produced from the SEM image was 124 ± 29 nm. The porosity was about 82%.

<< Comparative Example 3: Fabrication of uniaxial array SPAES single nanofibers and measurement of proton conductivity >>
Similar to Comparative Example 2, the polymer solution was adjusted to 14% by mass, and electrospinning was performed using ES-1000 (manufactured by Furniture). As the collector, a glass substrate having two aluminum electrodes installed at both ends was used. A voltage of 17 kv was applied to the syringe, with the distance between the syringe and the collector being 10 cm and the amount of polymer solution released being 0.12 mL / hour. As a result, a uniaxially oriented nanofiber aggregate was produced on a glass substrate. The collector was removed when the release time of the polymer solution was 60 seconds. The same post-treatment as in Example 2 was carried out to obtain acid-doped uniaxially arranged nanofibers.
In the same manner as in Example 2, the proton conductivity of the uniaxial array SPAES / PBI (20/80) composite nanofibers was measured. The results are shown in Table 1.

<< Comparative Example 4: Fabrication of PBI Single Nanofiber Nonwoven Fabric >>
Polybenzimidazole of Synthesis Example 3 and dehydrated N, N-dimethylformamide (DMF) were added to the vial 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 was placed in the collector part of the electrospinning device ES-2000S (manufactured by Finance), a syringe filled with the polymer solution was set in the electrospinning device, and the amount of the polymer solution released was 0.12 mL / hour. , Electrospinning was done. 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 PBI-only nanofiber non-woven 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 nanofibers produced from the SEM image was 113 ± 16 nm. The porosity was about 75%.

<< Comparative Example 5: Fabrication of Uniaxial Array PBI Single Nanofiber >>
Similar to Comparative Example 4, the polymer solution was adjusted to 8% by mass, and electrospinning was performed using ES-1000 (manufactured by Furniture). As the collector, a glass substrate having two aluminum electrodes installed at both ends was used. A voltage of 17 kv was applied to the syringe, with the distance between the syringe and the collector being 10 cm and the amount of polymer solution released being 0.12 mL / hour. As a result, an attempt was made to prepare a uniaxially oriented nanofiber aggregate on a glass substrate. However, although various conditions were examined, uniaxially arranged nanofibers could not be obtained by 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 non-woven fabric and Nafion was set to 10/100 in consideration of porosity and specific gravity.
The SPAES / PBI (20/80) composite nanofiber non-woven fabric having a film thickness of about 25 μm obtained in Example 3 was placed in a glass petri dish, a commercially available Nafion dispersion was cast, and the solvent was slowly evaporated at room temperature in the air. It was. Then, it was vacuum dried at 60 degreeC for 15 hours to obtain an electrolyte membrane. Since the film thickness of the non-woven fabric is substantially the same as the film thickness of the composite film, the film thickness of the composite film was used as the film thickness of the non-woven fabric.
The obtained electrolyte membrane was immersed in 3% hydrogen peroxide solution 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 dried at 60 ° C. for 15 hours to obtain the SPAES / PBI (20/80) composite nanofiber non-woven fabric / Nafion electrolyte membrane in the form shown in FIG.
The thickness of the produced electrolyte membrane is about 25 μm, and it is considered that the electrolyte membrane is a composite membrane in which Nafion matrix layers are formed on both the front and back surfaces of the non-woven fabric as shown in FIG.

For proton conductivity measurement, keep the temperature and humidity constant using a thermo-hygrostat SH-221 (manufactured by ESPEC), and use an impedance analyzer 3532-50 (manufactured by Hioki) for frequency response from 50 kHz to 5 MHz. Was measured, and the proton conductivity was calculated from the resistance of the SPAES / PBI (20/80) composite nanofiber non-woven fabric / Nafion electrolyte membrane. When the proton conductivity at 80 ° C.-30% RH and 90 ° C.-95% RH were calculated, they were 5.5 × 10 ^-4 and 3.8 × 10 ^-2 Scm- ¹ , respectively. The results are shown in Table 1. Especially under low humidity conditions, it showed excellent proton conductivity.

<< Comparative Example 6: Fabrication of Nanofiber-Free Nafion® Single Membrane and Measurement of Proton Conductivity >>
A film was formed in the same manner as in Example 7 using only a commercially available Nafion (registered trademark) dispersion solution without using a nanofiber mat, and the proton conductivity of the obtained Nafion single film was measured. The results are shown in Table 1. The proton conductivity at 80 ° C.-30% RH and 90 ° C.-95% RH was 2.8 × 10 ^-4 and 7.4 × 10 ^-2 Scm- ¹ , respectively.

Claims (9)

A composite nanofiber containing an electrolyte polymer and a basic polymer, wherein the electrolyte polymer has proton conductivity. The composite nanofiber according to claim 1, wherein the electrolyte polymer has the structures of A) and B) below.
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, and a sulfonic acid group, a phosphonic acid group, and a carboxylic acid group in the side chain. The composite nanofiber according to any one of claims 1 and 2 , wherein it has a structure in which a cation exchange group selected from the group consisting of is introduced. The composite nanofiber according to claim 1, wherein the basic polymer has the structures of A) and B) below.
A) The main chain contains repeating units containing aromatic groups and / and aliphatic groups.
B) The main chain skeleton or side chain functional group has a basic functional group that can interact with a cation exchange group. The invention according to any one of claims 1 to 4, wherein the abundance ratio of the electrolyte polymer is 1 to 99% by mass in the entire composite nanofiber, and the fiber diameter of the composite nanofiber is 500 nm or less. Composite nanofibers. The proportion of the composite nanofibers is 1 to 50% by mass in the entire electrolyte membrane, and the thickness of the electrolyte membrane containing the composite nanofibers is 30 μm or less, according to claims 1 to 5 . An electrolyte membrane comprising the composite nanofibers according to any one . Forming a nonwoven fabric made of composite nanofibers according to claim 1, the step of post-processing the non-woven fabric, filled with the matrix polymer in the voids of the nonwoven fabric, the composite nano-fiber and the matrix polymer A method for producing a composite membrane, comprising a step of integrating and a step of post-treating an electrolyte membrane containing composite nanofibers. A membrane electrode assembly for a polymer electrolyte fuel cell, which comprises an electrolyte membrane containing the composite nanofiber according to any one of claims 1 to 5 . A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 8.