JP2002105200A - Proton conductive membrane for direct type alcohol fuel cell and direct type alcohol fuel cell utilizing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a proton conductive membrane for direct type alcohol fuel cell having a high proton conductivity and excellent blocking property to alcohol. SOLUTION: This proton conductive membrane for direct type alcohol fuel cell mainly comprises a polyimide partly including a proton conductive substituent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a polymer electrolyte fuel cell using a proton conductive membrane as an electrolyte,
The present invention relates to a proton conductive membrane for a direct alcohol fuel cell using an alcohol such as methanol as a direct fuel, and a direct alcohol fuel cell using the same.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell is provided with two electrodes on both sides of an electrolyte comprising a polymer membrane having proton conductivity, and supplies an oxidizing gas (oxidizing agent) such as oxygen or air to one electrode. Then, a fuel (reducing agent) such as hydrogen or hydrocarbon is supplied to the other electrode to cause an electrochemical reaction to generate electricity.

[0003] There are several types of fuel cells depending on the type of electrolyte and fuel used. Particularly, those using methanol directly as a fuel are direct methanol fuel cells (hereinafter, referred to as fuel cells).
DMFC). DMFC feeds methanol directly to the anode electrode, which makes it easier to handle fuel, makes the equipment simpler, and makes it easier for households to use, compared to many fuel cells that use hydrogen or hydrocarbon-modified hydrogen. It is expected to be used as a power source with a relatively small output for industrial and industrial use. In particular, direct methanol fuel cells are considered promising as a future power source for consumer portable devices such as mobile phones and notebook computers.

[0004] The theoretical output voltage of a methanol-oxygen fuel cell is 1.2 V (25
° C), and in principle, the same characteristics as a hydrogen-oxygen fuel cell can be expected. DMFC using solid polymer electrolyte
Has been studied a lot and its performance is considerably improved as compared with the initial one, but its performance is insufficient compared with the performance of the hydrogen-oxygen fuel cell. This is due to the fact that a catalyst having sufficient methanol oxidizing activity has not been found, and the methanol permeability of the electrolyte membrane is high.

Conventionally, as a solid polymer electrolyte, Du has been used.
Perfluorosulfonic acid membranes represented by Nafion (registered trademark) of Pont have been mainly studied. These membranes generally have low methanol barrier properties,
When used as a membrane for use, crossover of methanol occurs and desired battery characteristics are not exhibited (JT Wang, JS Wainright,
R. F. Savinelland M. Litt J. et al.
Appl. Electrochem. , 26,751
(1996). ). In order to solve the above problems, DMFCs using these membranes set the reaction temperature to 100 ° C. or higher, increase the methanol oxidation rate, supply methanol in the gas phase, and reduce the methanol concentration on the anode side of the membrane. Although methods for lowering the properties have been reported, sufficient properties have not been obtained. Another method for improving the methanol permeability of a polymer electrolyte membrane is to use a membrane obtained by thermally cross-linking a polymer compound containing polystyrene sulfonic acid and polyvinyl alcohol on a porous support (see Japanese Patent Application Laid-Open No. HEI-5-205). 174856), a method of providing a layer for trapping methanol in an electrolyte membrane and discharging the same to the outside (Japanese Patent Laid-Open No.
No. 1-3724, JP-A-11-26005), a method using an anion exchange membrane (JP-A-11-1)
JP-A-35137, JP-A-11-144745,
Japanese Patent Application Laid-Open No. 11-273695) has been studied, but sufficient characteristics have not been obtained in terms of battery characteristics and long-term stability of the electrolyte membrane.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a low-permeability and high-proton protons for alcohols such as methanol, which can be used as an electrolyte membrane for a direct alcohol fuel cell such as a direct methanol fuel cell. An object of the present invention is to provide a proton conductive membrane for a direct alcohol fuel cell having conductivity, and a direct alcohol fuel cell and a direct methanol fuel cell using the same.

[0007]

That is, the present invention relates to a proton conductive membrane for a direct alcohol fuel cell which comprises a polyimide containing a repeating unit represented by the following general formula (I) as a main component.

[0008]

Embedded image [In the formula, X represents at least one kind of tetravalent organic group, Y represents at least one kind of divalent organic group, and a part of X and Y contains a proton conductive substituent. As the proton-conductive substituent, at least one selected from the group consisting of a phenolic hydroxyl group, a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group can be used.

The polyimide has the following general formula (II):
It is preferably a polyimide containing a repeating unit represented by the formula:

[0010]

Embedded image [Wherein X ₁ and X ₂ are the same or different tetravalent organic groups, Y
₁ is a divalent organic group containing a proton conductive substituent, Y ₂
Represents a divalent organic group containing no proton conductive substituent. m is an integer of 1 or more, and n is an integer of 0 or more. In the present invention, the repeating unit of m of the polyimide is 2
0 to 85 mol%, the repeating unit of n is 15 to 80 mol%
The polyimide preferably contains a polyfunctional component having three or more amino groups and a repeating structural unit obtained by polycondensation of tetracarboxylic dianhydride.

The repeating structural unit obtained by polycondensation of a polyfunctional component containing three or more amino groups and a tetracarboxylic dianhydride is preferably in the range of 0.1 to 20 mol%. A tetracarboxylic dianhydride and a diamine containing a proton conductive substituent, and / or
Alternatively, a polyimide obtained by polycondensation of a diamine containing no proton conductive substituent is preferable.

The tetracarboxylic dianhydrides are 1,4
5,8-Naphthalenetetracarboxylic dianhydride is preferred. Examples of the diamine having a proton conductive substituent include 2,2′-benzidinesulfonic acid and 2,4-diamine.
At least one selected from the group consisting of diaminobenzenesulfonic acid, 2,5-diaminobenzenesulfonic acid, and 3,3′-dimethyl-4,4′-diaminobiphenyl-6,6′-disulfonic acid Is preferred. On the other hand, the diamine containing no proton conductive substituent is
9,9-bis (4-aminophenyl) fluorene, 4,
It is preferably at least one selected from the group consisting of 4'-diaminodiphenyl ether, paraphenylenediamine and 2,2'-bis [4- (4-aminophenoxy) phenyl] propane.

The fuel cell of the present invention is a direct alcohol fuel cell using the above-mentioned proton conductive membrane, and its operating temperature is preferably 50 ° C. or lower.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a proton conductive membrane for a direct alcohol fuel cell and a direct alcohol fuel cell and a direct methanol fuel cell using the same according to the present invention will be described in detail.

The proton conductive membrane of the present invention preferably comprises a polyimide having any one of the following formulas (I) and (II) as a main component.

[0016]

Embedded image [In the formula, X represents at least one kind of tetravalent organic group, Y represents at least one kind of divalent organic group, and a part of X and Y contains a proton conductive substituent. ] The polyimide containing the repeating unit represented by these.

[0017]

Embedded image [Wherein X ₁ and X ₂ are the same or different tetravalent organic groups, Y
₁ is a divalent organic group containing a proton conductive substituent, Y ₂
Represents a divalent organic group containing no proton conductive substituent. m is an integer of 1 or more, and n is an integer of 0 or more. ] The polyimide containing the repeating unit represented by these.

The substituent having proton conductivity according to the present invention includes, for example, a phenolic hydroxyl group, a sulfonic acid group, a carboxylic acid group and a phosphoric acid group. In particular, a sulfonic acid group or a phosphoric acid group from which protons are easily dissociated is preferable from the viewpoint of expressing high proton conductivity. When a polyimide containing an aromatic ring or the like is used as a method for introducing a proton conductive substituent such as a sulfonic acid group, a known sulfonation method of an aromatic compound can be used. As such a method, a polyimide organic solvent solution or suspension is prepared, a sulfonating agent is added and mixed to prepare a polyimide into which a sulfonic acid group is introduced, and then a proton conductive membrane is formed by forming a film. And a method of immersing a polyimide membrane in an organic solvent and adding a sulfonating agent to obtain a proton conductive membrane. Examples of the sulfonating agent usable in the present invention include sulfuric acid, a mixed solution of sulfuric acid and an aliphatic acid anhydride, chlorosulfonic acid, a mixed solution of chlorosulfonic acid and trimethylsilyl chloride, sulfur trioxide, sulfur trioxide and triethyl. Phosphates and aromatic organic sulfonic acids typified by 2,4,6-trimethylbenzenesulfonic acid can be exemplified. Examples of the organic solvent to be used include halogenated hydrocarbons such as methylene chloride, linear aliphatic hydrocarbons such as hexane, and cyclic aliphatic hydrocarbons such as cyclohexane. These sulfonating agents and organic solvents may be appropriately selected from a plurality of combinations as necessary.

Further, polyimide is synthesized and formed into a film by using a monomer component having a proton conductive substituent,
A method for obtaining a proton conductive membrane is more convenient and preferable.
In particular, the use of a polyimide obtained by polycondensation of a tetracarboxylic dianhydride and a diamine containing a proton conductive substituent, and / or a diamine containing no proton conductive substituent can simplify the production and When the proton conductive substituent is surely and uniformly dispersed, characteristics are easily developed, which is preferable.

The proton conductive membrane of the present invention preferably contains a repeating structural unit obtained by a polycondensation reaction between a polyfunctional component having three or more amino groups and a tetracarboxylic dianhydride. By containing such a component, the proton conductivity is significantly improved.

The tetracarboxylic dianhydride used in the present invention includes, for example, para-terphenyl-3,4,4
3 ″, 4 ″ -tetracarboxylic dianhydride, pyromellitic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, 3,3 ′, 4,4′- Biphenyl ether tetracarboxylic dianhydride, 1,2,2
5,6-naphthalenetetracarboxylic dianhydride, 2,
3,6,7-naphthalenetetracarboxylic dianhydride,
2,3,5,6-pyridinetetracarboxylic dianhydride,
1,4,5,8-naphthalenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 4,4′-sulfonyldiphthalic dianhydride, 3,
3 ′, 4,4′-tetraphenylsilanetetracarboxylic dianhydride, meta-terphenyl-3,3 ″, 4
4 ″ -tetracarboxylic dianhydride, 3,3 ′, 4
4'-diphenyl ether tetracarboxylic dianhydride,
1,3-bis (3,4-dicarboxyphenyl) -1,
1,3,3-tetramethyldisiloxane dianhydride, 1-
(2,3-dicarboxyphenyl) -3- (3,4-dicarboxyphenyl) -1,1,3,3-tetramethyldisiloxane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) Phenyl) hexafluoropropanoic acid dianhydride,
1,2,3,4-butanetetracarboxylic dianhydride,
1,3,3a, 4,5,9b-Hexahydro-5- (tetrahydro-2,5-dioxo-3-furanyl) -naphtho [1,2-c] furan-1,3-dione. However, the present invention is not limited to this. In particular, in the present invention, chemical stability when used as a proton conductive membrane for a direct alcohol fuel cell, particularly water resistance (acid)
In consideration of the properties, 1,4,5,8-naphthalenetetracarboxylic dianhydride is preferred.

Examples of the diamine containing a substituent having proton conductivity include, for example, the following compounds, but are not limited thereto.

[0023]

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[0024]

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[0025]

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[0026]

Embedded image In particular, in the present invention, considering the stability of the compound, industrial availability, ease of polyimide synthesis, proton conductivity and the like, 2,2 represented by the following chemical formulas (III) to (VI) '-Benzidinesulfonic acid (III),
2,4-diaminobenzenesulfonic acid (IV), 2,5
It is preferably at least one selected from -diaminobenzenesulfonic acid (V) and 3,3'-dimethyl-4,4'-diaminobiphenyl-6,6'-disulfonic acid (VI).

[0027]

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[0028]

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[0029]

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[0030]

Embedded image As a diamine containing no proton conductive substituent,
For example, 4,4′-diaminodiphenyl ether,
4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfide, benzidine, metaphenylenediamine, paraphenylenediamine, 1,5-naphthalenediamine, 2,6-naphthalenediamine, bis [4-
(4-aminophenoxy) phenyl] sulfone, bis-
(4-aminophenoxyphenyl) sulfide, bis-
(4-aminophenoxyphenyl) biphenyl, 1,4
-Bis- (4-aminophenoxy) benzene, 1,3-
Bis- (4-aminophenoxy) benzene, 3,4'-
Diaminodiphenyl ether, 4,4′-diaminodiphenylether-3-sulfonamide, 3,4′-diaminodiphenylether-4-sulfonamide, 3,
4'-diaminodiphenylether-3'-sulfonamide, 3,3'-diaminodiphenylether-4-sulfonamide, 4,4'-diaminodiphenylsulfone-3-sulfonamide, 3,4'-diaminodiphenylsulfone-4- Sulfonamide, 3,4'-diaminodiphenylsulfone-3'-sulfonamide, 3,3'-
Diaminodiphenylsulfone-4-sulfonamide,
4,4'-diaminodiphenylsulfide-3-sulfonamide, 3,4'-diaminodiphenylsulfide-4-sulfonamide, 3,3'-diaminodiphenylsulfide-4-sulfonamide, 3,4'-diaminodiphenylsulfide -3'-sulfonamide,
1,4-diaminobenzene-2-sulfonamide, 4,
4'-diaminodiphenylether-3-carbonamide, 3,4'-diaminodiphenylether-4-carbonamide, 3,4'-diaminodiphenylether-
3'-carbonamide, 3,3'-diaminodiphenylether-4-carbonamide, 4,4'-diaminodiphenylmethane-3-carbonamide, 3,4'-diaminodiphenylmethane-4-carbonamide, 3,4 '
-Diaminodiphenylmethane-3'-carbonamide,
3,3'-diaminodiphenylmethane-4-carbonamide, 4,4'-diaminodiphenylsulfone-3-carbonamide, 3,4'-diaminodiphenylsulfone-4-carbonamide, 3,4'-diaminodiphenylsulfone- 3'-carbonamide, 3,3'-diaminodiphenylsulfone-4-carbonamide, 4,4'-
Diaminodiphenyl sulfide-3-carbonamide, 3,4'-diaminodiphenyl sulfide-4-
Carbonamide, 3,3'-diaminodiphenylsulfide-4-carbonamide, 3,4'-diaminodiphenylsulfide-3'-sulfonamide, 1,4-
Diaminobenzene-2-carbonamide, 4,4'-bis (4-aminophenoxy) biphenyl, bis @ 4-
(3-aminophenoxy) phenyl} sulfone, 9,9
-Bis (4-aminophenyl) fluorene, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2, Examples include, but are not limited to, 2'-bis (trifluoromethyl) -benzidine. These may be used in combination of two or more kinds as long as desired properties of the proton conductive membrane such as physical properties and chemical properties are not impaired.

In particular, as the diamine containing no proton conductive substituent used in the present invention, the following chemical formulas (VII) to (VII) are considered in consideration of easiness of synthesis of polyimide, easiness of film formation and proton conductivity. 9,9- represented by X)
Bis (4-aminophenyl) fluorene (VII),
4,4′-diaminodiphenyl ether (VIII),
Paraphenylenediamine (IX), 2,2'-bis [4
-(4-aminophenoxy) phenyl] propane (X)
It is preferably at least one selected from

[0032]

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[0033]

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[0034]

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[0035]

Embedded image Examples of the polyfunctional component containing three or more amino groups include, for example,
3,3 ′ diaminobenzidine, 3,3 ′, 4,4′-tetraaminodiphenylmethane, 1,2,4,5-tetraaminobenzene, 3,3 ′, 4,4′-tetraaminodiphenylisopropylidene, , 3 ', 4,4'-Tetraaminodiphenylhexafluoroisopropylidene,
In addition, the following compounds may be mentioned, but the present invention is not limited thereto.

[0036]

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[0037]

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[0038]

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[0039]

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[0040]

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[0041]

Embedded image In particular, in the present invention, considering the stability of the compound, industrial availability, ease of synthesis of the polyimide resin composition, ease of film processing, physical properties of the film, etc., the following chemical formula (XI) Preferably, it is the 3,3'-diaminobenzidine represented.

[0042]

Embedded image Where the following general formula (II)

[0043]

Embedded image [Wherein X ₁ and X ₂ are the same or different tetravalent organic groups, Y
₁ is a divalent organic group containing a proton conductive substituent, Y ₂
Represents a divalent organic group containing no proton conductive substituent. m is an integer of 1 or more, and n is an integer of 0 or more. In the polyimide containing a repeating unit represented by the formula:
It is preferable that the repeating unit of the above has a constituent component ratio of 15 to 80 mol%. When the repeating unit of m is smaller than this range, the obtained proton conductive membrane has a low ion exchange capacity and does not exhibit sufficient proton conduction, depending on the monomer component used. On the other hand, if it is larger than this range, the processability of the obtained polyimide resin composition may be reduced, or the polyimide resin composition may become water-soluble, and may not be used depending on the application. In practice, the ratio of these constituents depends on the monomer components used (tetracarboxylic dianhydride, diamine containing a proton conductive substituent, diamine not containing a proton conductive substituent), the required proton conductivity,
It may be appropriately set in consideration of the processability (film formability) of the obtained polyimide, the mechanical strength of the obtained film, the alcohol barrier property, and the like.
0 to 70 mol%, 30 to 70 mol% of n repeating units
It is.

The content of the repeating structural unit obtained by polycondensation of a polyfunctional component containing three or more amino groups and tetracarboxylic dianhydride is preferably in the range of 0.1 to 20 mol%. If it is smaller than this range, the number of branched structures and crosslinked structures due to the polyfunctional components in the composition becomes relatively small, and the effect is not sufficient. In addition, when it is larger than this range, the processability of the proton conductive membrane may decrease, making it difficult to obtain the membrane, or the physical properties such as elastic modulus and strength of the obtained membrane may decrease. is there.

The ion exchange capacity of the proton conductive membrane of the present invention is preferably 0.50 meq / g or more.
If the ion exchange capacity is lower than this range, there is a possibility that the proton conductive membrane does not exhibit sufficient proton conductivity.

The proton conductivity of the proton conductive membrane of the present invention at room temperature is preferably 1.0 × 10 ⁻² S / cm or more. If the proton conductivity is lower than this range, a direct alcohol fuel cell using the same may not exhibit sufficient power generation characteristics.

The proton conductive membrane of the present invention can be used at room temperature.
The tanol permeability coefficient is 1.3 × 10 ^-12(Cm^Three・ Cm)
/ (Cm^Two.S.Pa) or less. Me
If the tanol permeability coefficient is larger than this range,
Methano equivalent to perfluorosulfonic acid membranes such as Zion
Cut off due to methanol crossover
Battery characteristics may be degraded.

The polyimide as a component of the proton conductive membrane of the present invention may be synthesized by any known method. 1) Synthesizing a polyamic acid in an organic solvent and removing the solvent by a method such as reduced pressure, or isolating the polyamic acid by discharging the obtained polyamic acid solution into a poor solvent or the like, and then isolating the polyamic acid. A method in which a polyimide resin composition is obtained by imidization by heating. 2) A polyamic acid is obtained in the same manner as in 1), a dehydrating agent such as acetic anhydride is further added, and if necessary, a catalyst is added to chemically imidize the compound. A method of isolating, washing and drying as necessary. 3) A method in which, after obtaining a polyamic acid solution in the same manner as in 1), the solvent is removed under reduced pressure or heating, and at the same time, thermal imidization is performed. 4) A method in which a raw material is charged into an organic solvent, followed by heating to simultaneously perform synthesis of a polyamic acid and an imidization reaction, and coexist with a catalyst, an azeotropic agent, a dehydrating agent and the like as necessary. And the like.

The solvent used for the polymerization of polyimide includes, for example, sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide, formamide solvents such as N, N-dimethylformamide and N, N-diethylformamide, and N, N-dimethylformamide. N-dimethylacetamide,
Acetamide solvents such as N, N-diethylacetamide, pyrrolidone solvents such as N-methyl-2-pyrrolidone and N-vinyl-2-pyrrolidone, phenol, o-cresol, m-cresol, p-cresol, m-cresol Examples include acid, xylenol, halogenated phenols such as p-chlorophenol, phenol solvents such as catechol, hexamethylphosphoramide, and γ-butyrolactone. These organic solvents may be used alone or in combination of two or more. Further, some of aromatic hydrocarbons such as xylene and toluene can be used.

When a diamine having a proton conductive substituent such as a sulfonic acid group is used as a monomer, an aliphatic tertiary amine such as triethylamine and an aromatic tertiary amine such as dimethylaniline are used. ,
Heterocyclic tertiary compounds such as pyridine, picoline and isoquinoline
A secondary amine is added to the above organic solvent to form an ammonium salt of a proton-conductive substituent, followed by a polymerization method, or by replacing a hydrogen atom of a sulfonic acid group with an alkali metal such as sodium in advance to obtain a sulfonate. A method of preparing an alkali metal salt of an acid and then polymerizing the salt can be exemplified. When the polyimide is polymerized by these methods, when the polyimide is recovered or after the film is formed, the polyimide is immersed in a predetermined concentration of sulfuric acid, hydrochloric acid, or the like, and converted into the original state of the proton conductive substituent such as a sulfonic acid group. It is necessary.

A more specific example of the synthesis of the polyimide resin composition of the present invention is shown below. Synthesis Example At least one of an organic solvent and a diamine containing a proton conductive substituent is taken in a container in a predetermined amount. An aliphatic tertiary amine in an amount equal to or more than the equivalent of the diamine containing a proton conductive substituent is added, and the mixture is stirred at room temperature for preferably 15 minutes or more. Predetermined amounts of tetracarboxylic dianhydride and diamine containing no proton conductive substituent are added. A predetermined amount of toluene or the like is added, and the reaction solution is heated to 120 ° C. or higher. Remove the generated water while azeotroping with toluene etc.,
Preferably, stirring is performed for 2 hours or more. After removing toluene and the like by reflux, the reaction solution is cooled to room temperature. The reaction solution is dropped into a mixture of a strong acid such as hydrochloric acid and a poor solvent such as methanol to precipitate. The precipitate is washed with a poor solvent such as methanol. Dry under reduced pressure at 120 ° C. to obtain polyimide.

The polyimide obtained by the above method can be obtained by processing into a film by any known method. That is, a) Polyimide synthesized by the above method is dissolved in an organic solvent at a predetermined concentration, cast or coated on a support such as glass to form a film, and the solvent is removed under predetermined conditions. A method for obtaining a proton conductive membrane. B) A method in which the polyimide polymerization solution synthesized by the above method is cast or coated on a support such as glass to form a film, and the solvent is removed under predetermined conditions to obtain a proton conductive film. C) Polyamic acid, which is a precursor of the polyimide synthesized by the above method, is dissolved in an organic solvent at a predetermined concentration, cast or coated on a support such as glass to form a film, and under predetermined conditions. A method of obtaining a proton conductive membrane by imidation and solvent removal. D) Polyamic acid polymerization solution, which is a precursor of polyimide synthesized by the above method, is cast or coated on a support such as glass to form a film, and is subjected to imidization and solvent removal under predetermined conditions. A method for obtaining a proton conductive membrane. And the like.

The proton conductive membrane obtained by the above method is
By converting into the state of the proton conductive substituent by the method described above, the performance as a proton conductive membrane is exhibited.

As the organic solvent used in the above method, those similar to those used in the polymerization of the polyimide resin composition can be used. For example, sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide, and N, N-
Formamide solvents such as dimethylformamide and N, N-diethylformamide; acetamido solvents such as N, N-dimethylacetamide and N, N-diethylacetamide; N-methyl-2-pyrrolidone; N-vinyl-
A pyrrolidone solvent such as 2-pyrrolidone, phenol,
o-cresol, m-cresol, p-cresol, m
-Halogenated phenols such as cresylic acid, xylenol, p-chlorophenol, phenolic solvents such as catechol, or hexamethylphosphoramide, γ
-Butyrolactone and the like. These organic solvents may be used alone or in combination of two or more. Further, some of aromatic hydrocarbons such as xylene and toluene can be used. In addition to the above, any material can be used as long as it can be uniformly dissolved without decomposing the structure of the polyimide or the polyamic acid.

In the above method, the imidization and the solvent removal method can be carried out in combination with any method. As the imidation method, any of a method by a thermal treatment and a method by a chemical treatment using a dehydrating agent such as acetic anhydride can be used. The solvent may be removed under conditions in which the solvent can be sufficiently removed under normal pressure or reduced pressure. However, it is necessary to select conditions in which the proton conductive substituent is not eliminated or denatured.

The thickness of the proton conductive membrane of the present invention can be appropriately selected. However, when it is used directly as a proton conductive membrane for an alcohol fuel cell, 10 to 5 times.
00 μm is preferable, and 10 μm to 100 μm is more preferable. If the film thickness exceeds 500 μm, the resistance of the film increases, and if it is less than 10 μm, the mechanical strength of the film and the barrier property against alcohols such as methanol may be insufficient.

Next, a direct alcohol fuel cell using the proton conductive membrane of the present invention will be described as an example with reference to the drawings.

FIG. 1 is a sectional view of a principal part of a direct alcohol fuel cell using the proton conductive membrane of the present invention. This is because the proton conductive membrane (1) of the present invention, the catalyst-carrying gas diffusion electrode (2) in contact with the membrane of (1), the fuel gas or liquid formed on the separator (4), and the oxidizing agent It has a configuration of a flow path (3) for feeding.

As a method for joining the catalyst-carrying gas diffusion electrode (2) to the proton conductive membrane (1), for example, a known method performed with a proton conductive membrane composed of a perfluorocarbon sulfonic acid membrane can be applied. .

Specifically, a commercially available gas diffusion electrode (US E.
-TEK, etc.), but the method is not limited thereto.

As a practical method, the catalyst-supporting gas diffusion is performed by using a binder such as an alcohol solution of a perfluorosulfonic acid polymer or an organic solvent solution of the polyimide of the present invention on both sides of the proton conductive membrane (1) of the present invention. Electrode (2)
The surfaces on the catalyst layer side are generally aligned with each other using a press machine such as a hot press machine or a roll press machine.
Joining can be performed at a press temperature of about 50 ° C. Alternatively, the catalyst-carrying gas diffusion electrode (2) may be separately prepared by using a material as described below and bonded to the proton conductive membrane (1).

Here, as a material used for preparing the catalyst-supporting gas diffusion electrode (2), as a catalyst, a metal such as platinum or ruthenium, which promotes an oxidation reaction of a fuel and a reduction reaction of oxygen, or a metal thereof. Alloys, conductive materials, such as conductive materials such as fine-particle carbon materials, binders, such as water-repellent fluorine-containing resins, if necessary, as a support of the above materials, such as carbon cloth or carbon paper, Further, as the impregnating / coating material, a perfluorosulfonic acid-based polymer can be exemplified, but the present invention is not limited to this.

The assembly of the proton conductive membrane (1) obtained by the above-described method and the catalyst-carrying gas diffusion electrode (2) is connected to a flow path (3) for feeding a fuel gas or liquid and an oxidizing agent. The direct alcohol fuel cell according to the present invention is obtained by inserting it between a pair of gas separators (4) made of graphite or the like in which is formed. When methanol is used as fuel,
A direct methanol fuel cell according to claim 11 is obtained. As a fuel, a liquid of an alcohol such as methanol or a vaporized gas, and a gas containing oxygen as an oxidizing agent (oxygen or air) are supplied from separate flow paths (3) through a catalyst-supporting gas diffusion electrode (3). By supplying to 2), the fuel cell operates.

The direct alcohol fuel cell of the present invention may be used alone or in a plurality of layers to form a stack and used, or a fuel cell system incorporating them may be used.

As the fuel for the direct alcohol fuel cell of the present invention, alcohols such as methanol and ethanol are used. As the fuel directly used for the fuel cell, formalin, hydrazine, dimethyl ether, and the like have been studied in addition to the alcohols described above. Considering fuel safety, industrial availability, fuel performance, etc. Then, alcohols are preferable, and it is particularly preferable to use methanol and ethanol.

Examples of the method for supplying alcohols include a method of directly supplying an aqueous solution having a predetermined concentration, and then supplying the liquid as it is, and a method of supplying the liquid in a gaseous state after vaporization, and any method can be used. .

The operating temperature of the direct alcohol fuel cell according to the present invention can be set at any temperature from room temperature to 100 ° C. or higher. In general, as the operating temperature of a fuel cell increases, the cell characteristics tend to improve. However, if it is attempted to operate at a temperature of 100 ° C. or higher, for example, it is necessary to pressurize the cell in order to suppress drying of the proton conductive membrane. In addition, high durability is also required for the proton conductive membrane and constituent members of the cell to be used. on the other hand,
As the operating temperature is set at a low temperature such as room temperature, the tendency is opposite to that at the high temperature. In particular, assuming application to consumer portable devices such as notebook PCs and mobile phones, the demand for smaller and simpler fuel cells and peripheral devices is higher than for high cell characteristics, so low temperature such as room temperature The operation temperature of the direct methanol fuel cell is preferably 50 ° C. or lower, since it is one of the preferable modes to operate the fuel cell.

[0068]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples, and can be appropriately modified without departing from the scope of the invention. In the examples, BDSA is 2,
2′-benzidinesulfonic acid, NTDA 1,4,5,
8-naphthalenetetracarboxylic dianhydride, FDA is 9,9-bis (4-aminophenyl) fluorene, NM
P represents N-methyl-2-pyrrolidone.

The measurement method and the like will be described prior to the examples.

(Method for Measuring Ion Exchange Capacity) A test sample is immersed in a saturated aqueous solution of sodium chloride and reacted in a water bath at 60 ° C. for 3 hours. After cooling to room temperature, the sample was sufficiently washed with ion-exchanged water, and titrated with a 0.01 N aqueous sodium hydroxide solution using a phenolphthalein solution as an indicator to calculate the ion exchange capacity.

(Proton conductivity) A test specimen (10 mm × 40 mm) stored in ion-exchanged water is taken out, and water on the surface of the test specimen is wiped off with a filter paper. A test piece was mounted between platinum electrodes at a distance between the electrodes of 30 mm, and placed in a two-pole unsealed Teflon (registered trademark) cell.
Under the conditions of AC impedance method (frequency: 42 Hz to
5 MHz), the membrane resistance of the specimen was measured, and the proton conductivity was calculated.

(Methanol Permeability Coefficient) FIG. 2 is a flow chart of the apparatus for measuring the amount of methanol permeated. Proton conductive membrane (1
1), the methanol solution (9) heated to about 60 ° C. in a water bath (10) from a nitrogen cylinder (6) was placed in a measuring cell divided into two chambers, an upper part (12) and a lower part (13). ) Is supplied with nitrogen gas and bubbling is performed to flow methanol-nitrogen gas obtained through the upper portion (12) of the cell. Methanol permeating through the proton conductive membrane (11) was analyzed by a gas chromatograph (14) into the lower part (13) of the cell purged with helium gas supplied from the helium cylinder (7). At this time, the temperature of the measurement cell was maintained at 25 ° C. From the obtained methanol permeation amount, the methanol permeation coefficient of the proton conductive membrane (11) was calculated.

Example 1 A proton conductive membrane of the present invention was obtained according to the following method.

BDSA was placed in a 0.5 L separable flask.
4.30 g (0.0125 mol) and phenol 1
05 g, 70 g of p-chlorophenol, and 15.18 g (0.15 mol) of triethylamine were stirred at room temperature under a nitrogen stream for 0.5 hour. Next, NTDA was changed to 6.
70 g (0.025 mol), 4.36 g of FDA
(0.0125mol) Add all at once and add 50g of toluene
added. The mixture was stirred at 150 ° C. for 5 hours under a nitrogen stream. At this time, generated water was removed while azeotropic distillation with toluene. At this time, 0.9 mL of produced water was collected and removed. Then, toluene was removed by reflux, the separable flask was cooled with ice, and the reaction solution was cooled to room temperature. The reaction solution was gradually added dropwise while vigorously stirring a mixed solution of 26.1 g of hydrochloric acid and 1 L of methanol. At this time, a linear brown precipitate was formed. The obtained precipitate is washed with 0.5 L of methanol for 2 hours.
After washing twice, it was dried under reduced pressure at 120 ° C. for 3 hours to obtain a polyimide.

A 20 wt% NMP solution of the obtained polyimide was prepared, applied on a float glass to a thickness of 300 μm, and then reduced pressure at 50 ° C., 100 ° C., 150 ° C., 200 ° C.
The solvent is removed at a temperature of
m was obtained. Table 1 shows the ion exchange capacity and proton conductivity of this proton conductive membrane. Table 2 shows the methanol permeability coefficient.

Comparative Example 1 Nafion 112 (Du P
ont, registered trademark) was measured. The results are shown in Table 2.

[0077]

[Table 1]

[0078]

[Table 2] Table 1 shows that the proton conductive membrane of the present invention has high proton conductivity.

From a comparison between Example 1 and Comparative Example 1 in Table 2, it was revealed that the proton conductive membrane of the present invention had excellent methanol barrier properties.

From the above results, it can be seen that the proton conductive membrane of the present invention has high proton conductivity capable of expressing sufficient performance as a membrane for a direct alcohol fuel cell, and excellent methanol barrier properties. It has been shown.

[0081]

According to the present invention, the following general formula (I)

[0082]

Embedded image [In the formula, X represents at least one kind of tetravalent organic group, Y represents at least one kind of divalent organic group, and a part of X and Y contains a proton conductive substituent. A proton-conducting membrane for direct alcohol fuel cells containing polyimide as a main component containing a repeating unit represented by the following formula:
A proton conductive membrane for a direct alcohol fuel cell having high proton conductivity and excellent alcohol barrier properties can be provided. Further, a direct alcohol fuel cell using the same is particularly useful as a direct methanol fuel cell.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a direct alcohol fuel cell according to the present invention.

FIG. 2 is a flowchart of a methanol permeation amount measuring apparatus.

[Explanation of symbols]

 1: Proton conductive membrane 2: Catalyst supported gas diffusion electrode 3: Flow path 4: Separator 5: Gasket 6: Nitrogen cylinder 7: Helium cylinder 8: Bubbler 9: Methanol solution 10: Water trap 11: Proton conductive membrane 12: Cell upper part 13: Cell lower part 14: Gas chromatograph

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4J043 PA04 PC066 PC186 PC206 QB15 QB26 QB31 RA34 SA06 SA07 SA08 SA62 SA71 SA82 SA87 SB02 TA14 TA22 TB01 UA121 UA131 UA151 UA262 UB011 UB021 UB121 ZA41 ZA44 ZB47 5H0AH05 A03 A0506 A05 HH06 HH08

Claims (18)

[Claims] 1. A proton conductive membrane for a direct alcohol fuel cell comprising a polyimide containing a repeating unit represented by the following general formula (I) as a main component. Embedded image [In the formula, X represents at least one kind of tetravalent organic group, Y represents at least one kind of divalent organic group, and a part of X and Y contains a proton conductive substituent. ] 2. The proton conductive substituent is at least one selected from the group consisting of a phenolic hydroxyl group, a sulfonic acid group, a carboxylic acid group and a phosphoric acid group.
The proton conductive membrane for a direct alcohol fuel cell according to the above. 3. The proton conductive membrane for a direct alcohol fuel cell according to claim 1, wherein the polyimide is a polyimide containing a repeating unit represented by the following general formula (II). Embedded image [Wherein X ₁ and X ₂ are the same or different tetravalent organic groups, Y
₁ is a divalent organic group containing a proton conductive substituent, Y ₂
Represents a divalent organic group containing no proton conductive substituent. m is an integer of 1 or more, and n is an integer of 0 or more. ] 4. The polyimide, wherein m is 20 to 8 repeating units.
4. The proton conductive membrane for a direct alcohol fuel cell according to claim 3, wherein the repeating unit of 5 mol% and n is 15 to 80 mol%. 5. The polyimide according to claim 1, wherein the polyimide contains a polyfunctional component having three or more amino groups and a repeating structural unit obtained by polycondensation of tetracarboxylic dianhydride. 3. The proton conductive membrane for a direct alcohol fuel cell according to item 1. 6. The repeating structural unit obtained by polycondensation of a polyfunctional component containing three or more amino groups and tetracarboxylic dianhydride is in the range of 0.1 to 20 mol%.
The proton conductive membrane for a direct alcohol fuel cell according to the above. 7. The polyimide according to claim 1, wherein the polyimide is a tetracarboxylic dianhydride and a diamine containing a proton conductive substituent.
The proton conductive membrane for a direct alcohol fuel cell according to any one of claims 3 to 6, which is a polyimide obtained by polycondensation of a diamine containing no proton conductive substituent. 8. The method according to claim 1, wherein the tetracarboxylic dianhydride is 1,2.
The proton conductive membrane for a direct alcohol fuel cell according to claim 7, wherein the proton conductive membrane is 4,5,8-naphthalenetetracarboxylic dianhydride. 9. The diamine containing a proton conductive substituent is 2,2'-benzidinesulfonic acid, 2,4-diaminobenzenesulfonic acid, 2,5-diaminobenzenesulfonic acid, and 3,3'-dimethyl. The proton conductive membrane for a direct alcohol fuel cell according to claim 7, which is at least one member selected from the group consisting of -4,4'-diaminobiphenyl-6,6'-disulfonic acid. 10. A diamine containing no proton-conducting substituent is 9,9-bis (4-aminophenyl) fluorene, 4,4'-diaminodiphenyl ether, paraphenylenediamine, and 2,2'-bis [4 The proton conductive membrane for a direct alcohol fuel cell according to claim 7, which is at least one member selected from the group consisting of-(4-aminophenoxy) phenyl] propane. 11. A polyfunctional component containing three or more amino groups,
7. The proton conductive membrane for a direct alcohol fuel cell according to claim 5, which is 3,3'-diaminobenzidine. 12. 12. The proton conductive membrane for a direct alcohol fuel cell according to claim 1, wherein the proton exchange membrane has an ion exchange capacity of 0.50 meq / g or more. 13. The proton conductive membrane at room temperature having a proton conductivity of 1.0 × 10 ⁻² S / cm or more.
13. The proton conductive membrane for a direct alcohol fuel cell according to any one of items 1 to 12. Methanol permeability coefficient 14. The proton conducting membrane ^{is, 1.3 × 10 -1 2 (cm} 3 · cm) / (cm 2 · s ·
The proton conductive membrane for a direct alcohol fuel cell according to any one of claims 1 to 13, which is not higher than Pa). 15. A direct alcohol fuel cell using the proton conductive membrane according to claim 1. 16. The direct alcohol fuel cell according to claim 15, wherein the direct alcohol fuel cell is a direct methanol fuel cell. 17. The direct alcohol fuel cell according to claim 15, wherein the direct alcohol fuel cell is a direct ethanol fuel cell. 18. The direct alcohol fuel cell according to claim 15, wherein the operating temperature of the direct alcohol fuel cell is 50 ° C. or less.