JPH11273695A - Solid high polymer electrolyte methanol fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery having high output by using a polymer by introducing an anion exchange group into a polymer having a repeating unit containing an aromatic ring as an ion exchange membrane where a methanol electrode is joined to one surface and an air electrode is joined to the other. SOLUTION: A polymer by introducing an anion exchange group into a polymer (a polymer A) having a repeating unit expressed by -X-Ar-Y- is used as an ion exchange membrane. In the formula, X and Y are -O-, -S-, Ar is a formula I, a formula II and a formula III. In the formula I to III, W is a single bond, -O-, -S- and -CR<6> R<7> (R<6> and R<7> are H and a 1-6C alkyl group), R<1-6> is a 1-8C alkyl group, (a) is 0 to 3, (b+c) are 0 to 7, and (d+e) are 0 to 5. The polymer has desirably a cross-linked structure. Aromatic sulfone, aromatic polysulfone, aromatic polyether and aromatic polyimide are cited as the polymer A. The obtained ion exchange membrane having low methanol permeability is used as an electrolyte of a methanol fuel cell.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid polymer electrolyte type methanol fuel cell using an anion exchange membrane as an electrolyte.

[0002]

2. Description of the Related Art A methanol fuel cell using methanol as a fuel is expected to be a relatively small-output power source for home use and industrial use because of easy handling and low cost of fuel. The theoretical output voltage of a methanol fuel cell is 1.2 V (2
5 ° C.), and similar performance can be expected in principle. However, although many studies have been made on the anodic oxidation reaction of methanol, sufficient performance has not yet been obtained.

[0003] The reason for this is that no oxidation catalyst for methanol having sufficient activity has been found, and the ion exchange membrane usually used as an electrolyte has a very high methanol permeability, so that the utilization efficiency of methanol is low. In addition, methanol reaching the air electrode which is the counter electrode of the methanol electrode reacts on the surface of the air electrode, so that the overvoltage increases and the output voltage decreases.

As a method of solving the above problem, an electrode-membrane assembly using a perfluorocarbon polymer membrane having a sulfonic acid group is used, the reaction temperature is set to 100 ° C. or higher, and the reaction between the methanol electrode and the air electrode is performed. There has been reported a method of increasing the speed and supplying methanol in the gas phase to lower the methanol concentration on the methanol electrode side of the membrane, but this method has not been able to provide sufficient performance.

When the ion exchange membrane serving as the electrolyte is a cation exchange membrane, the supplied methanol does not react at the methanol electrode, but reaches the air electrode as it passes through the electrolyte. There is a problem of an increase in the amount and an increase in overvoltage due to the acidic atmosphere of the air electrode.

[0006]

An object of the present invention is to provide a high-output methanol fuel cell by using an ion exchange membrane having low methanol permeability.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a solid polymer electrolyte type methanol comprising a methanol electrode joined to one surface of an ion exchange membrane which is a solid polymer electrolyte and an air electrode joined to the other surface. A fuel cell, wherein the ion exchange membrane is -X-Ar-Y- (X and Y are each independently-
O- or -S-. Ar is a group represented by Formula 1, Formula 2 or Formula 3. The present invention provides a solid polymer electrolyte type methanol fuel cell comprising a polymer having an anion exchange group introduced into a polymer having a repeating unit represented by the formula (1).

[0008]

Embedded image

However, in equations 1, 2 and 3, W
It is a single bond, -O -, - S-, or -CR ⁶ R ⁷ - (alkyl R ⁶ and R ⁷ each independently represent a hydrogen atom or 1 to 6 carbon atoms.). R ¹ , R ² , R ³ , R ⁴ and R ⁵ are each independently an alkyl group having 1 to 8 carbon atoms. a is an integer of 0-3. b + c is an integer of 0-7. d + e is an integer of 0-5.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The electrolyte constituting the solid polymer electrolyte type methanol fuel cell of the present invention is -X-Ar-Y-
(X and Y are each independently -O- or -S-; Ar is a group represented by Formula 1, Formula 2 or Formula 3) (hereinafter referred to as polymer A). ) Is an ion exchange membrane made of a polymer having an anion exchange group introduced therein. This ion exchange membrane is preferable because it has excellent mechanical strength and heat resistance.

In the polymer A, the content of aromatic rings not bonded to an electron-withdrawing functional group such as —SO ₂ — is at least 10 mol% in all the aromatic rings of the polymer A, particularly Is 2
It is preferably 0 to 50 mol%. In this specification, an aromatic ring refers to a benzene ring or a condensed benzene ring such as a naphthalene ring. When the content of the aromatic ring not bonded to the electron-withdrawing functional group is less than 10 mol%, a chloromethyl group or the like which is a group of a precursor of an anion exchange group is hardly introduced into the aromatic ring. It becomes difficult to obtain a polymer having a high ion exchange capacity.

Examples of the polymer A include polymers such as aromatic polysulfone, aromatic polyether, aromatic polyimide, and aromatic polyetherimide, and a polymer represented by Formula 4 is particularly preferable.

[0013]

Embedded image

However, in the formula 4, X and Y are each independently -O- or -S-. Ar is represented by Formula 1, Formula 2 or Formula 3
Group represented by Z is -SO ₂ -, - O- or -S-. R
⁸ , R ⁹ , R ¹⁰ and R ¹¹ are each independently an alkyl group having 1 to 8 carbon atoms. f, g, h, and i are each independently an integer of 0 to 4. m and n are each independently an integer of 2 to 200. m /
n is 0.1-100.

Examples of the polymer represented by Formula 4 include polyphenylene oxide / polyether sulfone copolymer, polyphenylene sulfide / polyether sulfone copolymer, polyaryl ether sulfone / polyether sulfone copolymer, and polyaryl ether sulfone. / Aromatic block copolymers such as polythioether sulfone copolymers. These block copolymers can be obtained by the methods described in JP-A-1-215348, JP-A-2-24535 and JP-A-2-248434.

In the above aromatic block copolymer, since the chloromethyl group is locally introduced into the segment into which the chloromethyl group is easily introduced, the anion exchange group is also locally arranged. Therefore, even if the ion exchange capacity is increased, the strength of the copolymer in the segment into which the chloromethyl group is not easily introduced is not impaired, and thus the strength of the entire ion exchange membrane is preferably not reduced.

The polymer constituting the ion exchange membrane in the present invention preferably has a crosslinked structure. The site having a crosslinked structure may be present at least in a part of the ion exchange membrane. However, in order to further prevent the permeation of methanol, the site is preferably present in a layer in the ion exchange membrane. The thickness of the layer where the site having the crosslinked structure exists,
It is particularly preferable that the thickness be 1 μm or more.

The ion exchange capacity of the ion exchange membrane in the present invention is preferably from 0.8 to 4.5 meq / g dry resin, particularly preferably from 0.9 to 2.8 meq / g dry resin. If the ion exchange capacity is smaller than 0.8 meq / g dry resin, the membrane resistance is increased, and if the ion exchange capacity is larger than 4.5 meq / g dry resin, the membrane strength is significantly reduced.

The thickness of the ion exchange membrane is 10 to 100 μm.
m, particularly preferably 30 to 80 μm. 10 μm thick
If the thickness is smaller, the permeation of methanol cannot be sufficiently prevented, and the amount of cross leak increases, which is not preferable. Also, if the thickness is 1
If the thickness is larger than 00 μm, the film resistance increases, which is not preferable. The ion exchange membrane is preferably used after being reinforced with a reinforcing cloth. In this case, the total thickness of the ion exchange membrane including the thickness of the reinforcing cloth is preferably within the above range.

The method for obtaining the ion exchange membrane in the present invention includes the following methods. (1) A method in which the polymer A is chloromethylated, converted into a solution, cast, formed into a film, and then aminated. (2) A method in which the polymer A is chloromethylated, converted into a solution, aminated, cast, and formed into a film. In the present invention, since amination is preferably performed to introduce an anion exchange group and to perform crosslinking, the method (1) in which molding is performed before amination is generally used.

The chloromethylation is carried out by reacting the polymer A with a chloromethylating agent. Examples of the chloromethylating agent include (chloromethoxy) methane, 1,4-
Bis (chloromethoxy) butane, 1-chloromethoxy-
4-chlorobutane, formaldehyde-hydrogen chloride, paraformaldehyde-hydrogen chloride and the like can be used. By reacting the chloromethylated product of the polymer A thus obtained with an amine compound to aminate, anion exchange groups are introduced and crosslinking is performed.

As the amine compound, a monoamine can be used. Specifically, in addition to ammonia, monoalkylamines such as methylamine, ethylamine, propylamine and butylamine; dialkylamines such as dimethylamine and diethylamine; aniline; -Aromatic amines such as methylaniline, heterocyclic amines such as pyrrolidine, piperazine and morpholine, and alcohol amines such as ethanolamine and diethanolamine. These amine compounds lose one active hydrogen by reacting with one chloromethyl group and then are quaternized, or the remaining active hydrogen reacts with another chloromethyl group to crosslink polymer A .

However, when the above-mentioned monoamine is used, there is a possibility that the monoamine is not sufficiently crosslinked. Therefore, as the amine compound, a polyamine compound having two or more amino groups in one molecule is preferably used. Specific examples of the polyamine compound include m-phenylenediamine, pyridazine, pyrimidine, pyrazine, 1-methylimidazole, N, N′-dimethylpiperazine, 1,4-
Polyamine compounds having an aromatic ring, polyamine compounds having a heterocycle, or polyamine compounds having a heterocyclic ring, such as diazabicyclo [2.2.2] octane, polyethyleneimine such as diethylenetriamine, triethylenetetramine and tetraethyleneheptamine, and hexamethylenetetramine. No.

Among polyamine compounds, diaminoalkanes having amino groups at both ends of an alkylene chain (either linear or branched) may react with an aromatic polymer having a chloromethyl group. Is particularly preferable because it is easier to crosslink. As the diaminoalkane, specifically, diaminomethane, 1,2
-Diaminoethane, 1,3-diaminopropane, 1,4
-Diaminobutane, 1,5-diaminopentane, 1,6
-Diaminohexane, 1,7-diaminoheptane, 1,
8-diaminooctane, 1,9-diaminononane, 1,
Compounds having primary amines at both terminals, such as 10-diaminodecane, are exemplified.

Further, diaminoalkanes having a secondary or tertiary amine at both terminals can also be used. Specifically, 3- (methylamino) propylamine, 3,3-bis (methylamino) propylamine, 3,3 -Bis (ethylamino) propylamine, 3,3 bis (butylamino) propylamine, N, N, N ', N'-tetramethyl-1,2-diaminoethane, N- (2-aminoethyl) ethanolamine , N, N, N ', N'-tetramethyl-1,3-diaminopropane, N, N, N', N'-tetramethyl-
1,6-diaminohexane and the like.

Further, as another preferred method for producing the ion exchange membrane in the present invention, the following method is also used. (3) A method of reacting with a small amount of a tertiary monoamine after the chloromethylation of the polymer A to form a partially aminated polymer containing a chloromethyl group, and then reacting with a polyamine. Examples of the tertiary monoamine include trialkylamines such as trimethylamine, triethylamine and tributylamine; aromatic tertiary amines such as N, N-dimethylbenzylamine; and tertiary alcoholamines such as triethanolamine.

The methanol electrode and the air electrode constituting the solid polymer electrolyte type methanol fuel cell of the present invention can be manufactured according to ordinary known techniques. For example, it is preferable that a catalyst for imparting activity as a methanol electrode or an air electrode is held by a hydrophobic resin binder such as polytetrafluoroethylene (PTFE) to form a porous sheet-shaped gas diffusion electrode. . Further, it can also be produced by a method of spraying, applying and filtering a dispersion mixture of materials constituting the gas diffusion electrode.

Known catalysts for electrodes can be used. For example, the catalyst for the methanol electrode includes a platinum catalyst, an alloy catalyst such as a platinum-ruthenium alloy or a platinum-tin alloy, or a supported catalyst in which fine particles of these catalysts are dispersed and supported on a carrier such as carbon. As the catalyst for the air electrode, a platinum catalyst, a platinum alloy-based catalyst, a supported catalyst, or the like similar to the methanol electrode is used.

As a method of manufacturing a joined body of a gas diffusion electrode and an ion exchange membrane, a method of directly forming a gas diffusion electrode on an ion exchange membrane, and a method of forming a gas diffusion electrode once on a base material such as a PTFE film. After that, various methods can be applied, such as a method of transferring this to an ion exchange membrane, a method of hot pressing the gas diffusion electrode and the ion exchange membrane, and a method of forming the gas diffusion electrode and the ion exchange membrane in close contact with an adhesive liquid.

[0030]

The reason why the permeability of methanol is high in the conventional ion exchange membrane is not clear, but the perfluorocarbon sulfonic acid membrane which is usually used easily swells and further swells due to the interaction between methanol and water. In addition, when protons move from the methanol electrode side to the air electrode side, several molecules of water per atom of protons accompany, and it is considered that methanol moves with the movement of the water.

On the other hand, the ion exchange membrane in the present invention is an anion exchange membrane, and it is considered that methanol does not move since anions move from the air electrode side to the methanol electrode side when electricity is supplied. In addition, the ion exchange membrane of the present invention can be used at high temperatures because of its excellent heat resistance,
The reaction speed of the methanol electrode and the air electrode can be increased. Further, it is considered that by supplying methanol in a gas phase, the methanol concentration on the anode side of the membrane can be reduced, and the permeation of methanol is reduced.

[0032]

[Example 1] In the same manner as in the synthesis method described in JP-A-61-168629, 4,4'-diphenol 0.1.
36 mol and 0.396 mol of dichlorodiphenyl sulfone are reacted to synthesize 0.36 mol of a precursor composed of repeating units of aromatic polysulfone.
By reacting 36 moles, 0.324 moles of dichlorodiphenyl sulfone and 0.378 moles of sodium sulfide, 220 g of an aromatic polysulfone-polythioether sulfone copolymer represented by the formula 5 (hereinafter referred to as copolymer a) is obtained. Was. In addition, in Formula 5, p / q = 1/1, and the intrinsic viscosity of the copolymer a was 0.50. The content of the aromatic ring not bonded to —SO ₂ — as the electron-withdrawing group was 33 mol% in the whole aromatic ring of the copolymer a.

[0033]

Embedded image

Next, 75 g of the copolymer a was added to 1,1,2,2
After dissolving in 1 liter of 2-tetrachloroethane, 400 g of (chloromethoxy) methane and 4.5 ml of anhydrous tin chloride were obtained.
g was added and a chloromethylation reaction was performed at 110 ° C. for 4 hours. Next, the reaction product was precipitated with 5 liters of methanol, and the reaction product was washed to obtain 85 g of a chloromethylated copolymer (hereinafter, referred to as copolymer b). The introduction rate of chloromethyl groups in the copolymer b was about 1.9 per repeating unit. When all the chloromethyl groups were aminated with trimethylamine, the ion exchange capacity was 2.2 meq / g dry. It was a resin.

50 g of the copolymer b was dissolved in 283 g of N, N-dimethylformamide to prepare a 15% by weight solution. While stirring the solution at 0 ° C., 50 ml of a 1 mol / liter solution of trimethylamine in N, N-dimethylformamide was slowly dropped, and 10 g of 2-methoxyethanol was added.

The solution thus obtained is heated at 60 ° C., 2
The film was cast in a short time to obtain a film having a thickness of 50 μm. Next, the above film was treated with 1 mol / liter of N, N, N ', N'-
It was immersed in a methanol solution of tetramethyl-1,3-diaminopropane at 50 ° C. for 4 hours to obtain a crosslinked anion exchange membrane. The ion exchange capacity of the obtained anion exchange membrane was 2.4 meq / g dry resin.

[Example 2] Instead of immersing the film obtained by casting in a methanol solution of N, N, N ', N'-tetramethyl-1,3-diaminopropane, N, N
Immersion in methanol of N, N ′, N′-tetramethyl-1,6-diaminohexane at 50 ° C. for 0.5 hours, followed by 4 mol / l of a solution of trimethylamine in methanol.
A crosslinked anion exchange membrane was obtained in the same manner as in Example 1 except that the membrane was immersed for an hour. The ion exchange capacity of the obtained anion exchange membrane was 2.5 meq / g dry resin.

Example 3 Copolymer of polyetherimide (product name: Ultem 5001 by GE Plastics Japan)
58 g of 1,1,2,2-tetrachloroethane 790 m
After dissolving in (l), 310 g of (chloromethoxy) methane,
3.5 g of anhydrous tin chloride was added, and a chloromethylation reaction was performed at 110 ° C. for 4 hours. Next, the reaction product was precipitated with 4 liters of methanol, and the reaction product was washed to obtain 56 g of a chloromethylated copolymer (hereinafter, referred to as copolymer c). The introduction rate of chloromethyl groups in the copolymer c was about 1.9 per repeating unit. When all the chloromethyl groups were aminated with trimethylamine, the ion exchange capacity was 2.4 meq / g dry. It was a resin.

The copolymer c was dissolved in 90 g of 1,1,2,2-tetrachloroethane to prepare a 10% by weight solution.
While stirring this solution at 0 ° C, 10 ml of a 1 mol / liter solution of trimethylamine in N, N-dimethylformamide was slowly dropped, and 2 g of 2-methoxyethanol was added. 78 ml of a solution having an ion exchange capacity of 0.9 meq / g was obtained.

The solution thus obtained was heated at 60.degree.
The film was cast in a short time to obtain a film having a thickness of 50 μm. Next, the above film was treated with 1 mol / liter of N, N, N ', N'-
It was immersed in a methanol solution of tetramethyl-1,3-diaminopropane at 50 ° C. for 4 hours to obtain a crosslinked anion exchange membrane. The ion exchange capacity of the obtained anion exchange membrane was 2.6 meq / g dry resin.

Example 4 50 g of a polysulfone copolymer (Amoco product name: Udel P-1700) was added to 1,1,
After dissolving in 520 ml of 2,2-tetrachloroethane,
235 g of (chloromethoxy) methane, anhydrous tin chloride
5 g was added, and a chloromethylation reaction was performed at a temperature of 50 ° C. for 0.5 hour while purging with nitrogen. Next, the reaction product was precipitated with 4 liters of methanol, and the reaction product was washed to obtain 53 g of a chloromethylated copolymer (hereinafter, referred to as copolymer d). The introduction rate of chloromethyl groups in the copolymer d was about 0.9 per repeating unit. When all the chloromethyl groups were aminated with trimethylamine, the ion exchange capacity was 1.7 meq / mol.
g resin.

15 g of the copolymer d was dissolved in 85 g of N, N-dimethylformamide to prepare a 15% by weight solution. While stirring this solution at 0 ° C., 14 ml of a 1 mol / liter solution of trimethylamine in N, N-dimethylformamide was slowly added dropwise, and 2 g of 2-methoxyethanol was added to give an ion exchange capacity of 0.9 mm. 120 ml of a solution with an equivalent weight / g were obtained.

The solution thus obtained was heated at 60.degree.
The film was cast in a short time to obtain a film having a thickness of 50 μm. Next, the above film was treated with 1 mol / liter of N, N, N ', N'-
It was immersed in a methanol solution of tetramethyl-1,2-diaminoethane at 50 ° C. for 4 hours to obtain a crosslinked anion exchange membrane. The ion exchange capacity of the obtained anion exchange membrane was 1.8 meq / g dry resin.

Example 5 (Comparative Example) (chloromethyl) styrene 80 g, divinylbenzene 20 g, nitrile rubber 5
g was stirred and mixed, and the woven fabric was impregnated with a monomer syrup solution to which benzoyl peroxide as a polymerization initiator was added, and then polymerized at 70 ° C. for 6 hours and at 90 ° C. for 3 hours. Then, it was immersed in a 1 mol / liter methanol solution of trimethylamine at 60 ° C. for 16 hours to obtain a 60 μm-thick anion exchange membrane made of a copolymer having a strong base type anion exchange group. The ion exchange capacity of the obtained anion exchange membrane was 2.0 meq / g.

Example 6 (Comparative Example) As an electrolyte, a perfluorocarbon sulfonic acid type ion exchange membrane (Dupont product name: Nafion 117) was used.

[Evaluation] As the electrolyte, the anion exchange membranes prepared in Examples 1 to 5 were used. An anion exchange resin obtained by aminating a chloromethylated product of a copolymer of an aromatic polyether sulfone and an aromatic polythioether sulfone is prepared, and a platinum-ruthenium alloy catalyst is dispersed and coated with the anion exchange resin. An electrode was prepared and used as a methanol electrode. The effective area of the gas diffusion electrode of the methanol electrode was 10 cm ² , and the amount of platinum in the gas diffusion electrode was 2 mg / cm ² per apparent surface area. Also,
A gas diffusion electrode in which a platinum catalyst was dispersed and coated with the above-mentioned anion exchange resin was prepared and used as an air electrode. The electrode effective area of the gas diffusion electrode of the air electrode was 10 cm ² , and the amount of platinum in the gas diffusion electrode was 1 mg / cm ² per apparent surface area.

The above-mentioned anion exchange membrane was hot-pressed,
The methanol electrode and the air electrode were joined to form an electrode-membrane assembly. In addition, except that the cation exchange membrane of Example 6 was used as the electrolyte, and the catalyst used for the methanol electrode and the air electrode was coated with a cation exchange resin having the same composition as Nafion 117, the same procedure as in the above-mentioned method was repeated. And an electrode-membrane assembly was prepared.

A fuel cell was assembled by sandwiching the obtained joined bodies between a pair of ribbed separators. Air as an oxidizing gas is supplied to the fuel cell through a humidifier maintained at 130 ° C.
A gaseous aqueous solution of methanol is gasified through a vaporization chamber maintained at 140 ° C. and supplied to the fuel cell.
A power generation test was performed at a cell temperature of 130 ° C. Table 1 shows the output voltage at a current density of 100 mA / cm ² .

[0049]

[Table 1]

[0050]

According to the present invention, it is possible to reduce the amount of cross leak of methanol in the ion exchange membrane as the electrolyte,
The output voltage of the methanol fuel cell can be improved.

Claims (5)

[Claims] 1. A solid polymer electrolyte type methanol fuel cell comprising a methanol electrode joined to one surface of an ion exchange membrane which is a solid polymer electrolyte and an air electrode joined to the other surface. The exchange membrane is -X-Ar-Y- (X
And Y are each independently -O- or -S-. Ar is a group represented by Formula 1, Formula 2 or Formula 3. A polymer electrolyte type methanol fuel cell comprising a polymer having an anion exchange group introduced into a polymer having a repeating unit represented by the formula (1). Embedded image However, in Formulas 1, 2, and 3, W is a single bond,-
O -, - S-, or -CR ⁶ R ⁷ - (alkyl R ⁶ and R ⁷ each independently represent a hydrogen atom or 1 to 6 carbon atoms.). R ¹ , R ² , R ³ , R ⁴ and R ⁵ are each independently an alkyl group having 1 to 8 carbon atoms. a is an integer of 0-3. b
+ C is an integer of 0 to 7. d + e is an integer of 0-5. 2. An ion exchange membrane having an ion exchange capacity of 0.5.
The solid polymer electrolyte type methanol fuel cell according to claim 1, wherein the amount of the dry resin is 8 to 4.5 meq / g dry resin. 3. The solid polymer electrolyte type methanol fuel cell according to claim 1, wherein the polymer having the anion exchange group introduced therein has a crosslinked structure. 4. The solid polymer electrolyte type methanol according to claim 1, wherein the polymer having the anion exchange group introduced therein is cross-linked by a polyamine compound having two or more amino groups in one molecule. Fuel cell. 5. The solid polymer electrolyte type methanol fuel according to claim 1, wherein the ion exchange membrane comprises a polymer obtained by introducing an anion exchange group into the polymer represented by the formula (4). battery. Embedded image However, in Formula 4, X and Y are each independently -O
-Or -S-. Ar is a group represented by Formula 1, Formula 2 or Formula 3. Z is -SO ₂ -, - O- or -S-. R ⁸ , R ⁹ ,
R ¹⁰ and R ¹¹ are each independently an alkyl group having 1 to 8 carbon atoms. f, g, h, and i are each independently an integer of 0 to 4.
m and n are each independently an integer of 2 to 200. m / n is 0.1-100.