JPH05174856A - Methanol isolating membrane having ion exchange function - Google Patents

Abstract

PURPOSE:To provide a methanol isolating membrane to be used for a methanol fuel cell, which has ion exchange function and methanol isolation properties as well. CONSTITUTION:Macro molecule composition containing polystyrene sulfonic acid and polyvinyl alcohol is casted over a carrier such as porous polypropylene and the like so as to be polymerized by thermal cross linking. And a methanol electrode 14 and an air electrode 15 are disposed at both the sides of an obtained methanol isolating membrane 11 via electrolytic solution 13, so that a methanol fuel cell can thereby be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a methanol barrier membrane having an ion exchange capacity capable of preventing methanol fuel from permeating from a methanol electrode to an air electrode in a methanol fuel cell.

[0002]

2. Description of the Related Art Conventionally, there has been proposed a fuel cell using an ion exchange membrane as an electrolyte and methanol as a fuel. The ion exchange membrane used in this fuel cell includes, for example, —SO ₃ H composed of a perfluorinated sulfonic acid polymer called Nafion 117 (registered trademark of DuPont).
An ion exchanger having a group is used as an electrolyte, sandwiched by electrodes from both sides of this Nafion membrane, a methanol chamber is provided on one side of the electrode, and a methanol fuel cell is provided with an air chamber on the other side. To do.

The charge carrier of this methanol fuel cell is the hydrated proton H ⁺ .xH ₂ O, and the hydrated proton generated at the cathode passes through the electrolyte and reaches the sulfonic acid group SO ₃ ^{− in} Nafion in the anode. By doing so, a current is generated in the external circuit connected between the cathode and the anode.

[0004]

However, the fuel cell using the ion exchange membrane as the electrolyte and methanol as the fuel has been proposed in the prior art, in which methanol permeates the ion exchange membrane and reaches the air electrode in a short time. After reaching, the methanol reacted at the air electrode and the methanol was directly oxidized, which was the same result as the generation of the methanol electrode in the air electrode. As a result, the air electrode potential has dropped and the output performance of the fuel cell has declined.

In order to minimize the influence of such methanol permeation, the distance between the air electrode and the methanol electrode is 10 m.
m or more to reduce the effect of methanol permeation,
Attempts have also been made to reduce the concentration of the aqueous methanol solution of the fuel, but doing so has the drawback that the size of the cell stack becomes considerably large. It was also considered to arrange a blocking membrane for preventing the permeation of methanol between the methanol electrode and the air electrode, but no one having an ion-exchange ability even if it can prevent the permeation of methanol has been conventionally found. It could not be used as a fuel cell.

In addition, the previously proposed Nafion 1
When a fuel cell including 17 (registered trademark of DuPont) and an electrode assembly is used, Nafion 117, which is an ion exchange membrane, swells gradually and is separated from the electrode and cannot be used as a fuel cell. It was Therefore, the present invention is an ion exchange membrane used in a fuel cell using methanol as a fuel, while preventing methanol on the methanol electrode side from penetrating the electrolyte and reaching the air electrode,
It is an object of the present invention to provide a new ion exchange membrane having excellent ion exchange ability. A further object of the present invention is to provide a novel ion exchange membrane that can be used as a small-sized methanol fuel cell as a whole and is free from fear of separation from the electrode.

[0007]

In order to solve the above-mentioned problems, the present invention is to cast a polymer composition containing polystyrene sulfonic acid and polyvinyl alcohol on a porous support and thermally crosslink it. It is a methanol blocking membrane having ion exchange ability, which is obtained by polymerization by.

A method for producing a methanol barrier membrane having an ion exchange capacity for a methanol fuel cell of the present invention will be described below. The purified polyvinyl alcohol and polystyrene sulfonic acid are dissolved in an aqueous ethanol solution. In this case, the reason for dissolving in the aqueous ethanol solution is to adjust the surface tension of the solution and to extend the polymer chain. The weight ratio of polystyrene sulfonic acid and polyvinyl alcohol is 1/1 to 1
/ 3 is preferred. Next, the dissolved polyvinyl alcohol-polystyrene sulfonic acid-ethanol aqueous solution is cast on the porous support to sufficiently impregnate the inside of the porous support. In order to sufficiently permeate the inside of the pores, the surface tension of the casting liquid is impregnated inside the pores by changing the mixing ratio of ethanol. As described above, the reason for impregnating the inside is to make the support film well compatible with water because the film generally used as the support film has water repellency. Resins such as polypropylene, polyethylene, and polyfluorinated ethylene are used for this porous support, and the porous support can be applied to a wide range of pore sizes from micron order to millimeter order.

The thus cast material is dried for a whole day and night to remove water and ethanol in the casting film. By performing such gentle drying, generation of bubbles in the film can be prevented. next,
100 to 150 ° C. for 1 to 48 hours, more preferably
Heat treatment is performed at 110 to 140 ° C. for 1 to 24 hours. This heat treatment causes a crosslinking reaction of the ion exchange membrane. This cross-linking reaction proceeds at a high temperature for a longer time, and the finished film becomes a hard and dense film. This membrane is used as a methanol barrier membrane for a methanol fuel cell.

To apply the methanol barrier membrane of the present invention to a methanol fuel cell, for example, the methanol fuel cell shown in the conceptual diagrams of FIGS. 4 and 5 can be used. In FIG. 4, a methanol electrode 14 and an air electrode 15 are arranged on both sides of a methanol barrier membrane 11 having ion exchange capacity according to the present invention.
The methanol fuel cell is shown by filling the electrolytic solution 13 between the methanol barrier film 11 and both electrodes.

A gas diffusion electrode is generally used as the methanol electrode 14 or the air electrode 15. This gas diffusion electrode is, for example, one in which carbon particles carrying a catalyst are solidified with PTFE to form a porous electrode. When such an electrode material is used, the methanol barrier film 11 having ion exchange capacity of the present invention is not flexible like the conventional Nafion 117 (registered trademark of DuPont) membrane, and therefore the methanol electrode 14 or the air electrode 15 is used. Even if the methanol barrier film 11 having ion exchange capacity according to the present invention is bonded to the Nafion 11
Unlike the 7 (registered trademark of DuPont) membrane, the interface between the electrode and the electrolyte does not have a three-dimensional structure. Therefore, since the ion exchange is not sufficiently performed in such an electrode-electrolyte arrangement, in the present invention, the electrolytic solution 13 is filled between the methanol blocking film 11 and both electrodes as described above.

FIG. 5 shows still another example of a methanol fuel cell using the methanol barrier membrane 11 having the ion exchange ability of the present invention. This methanol fuel cell supplies an anolyte 16 composed of a mixed aqueous solution of methanol-sulfuric acid to one side of a methanol barrier membrane 11, and arranges a methanol electrode 14 in the anolite 16 while electrolyzing the other side of the methanol barrier membrane 11. By arranging the air electrode 15 via the liquid 13, a methanol fuel cell is obtained.

The methanol barrier membrane 11 having ion exchange capacity according to the present invention is not limited to the above-mentioned methanol fuel cell, but a hydrazine fuel cell using hydrazine as a fuel, which has been a permeation problem in the same manner as methanol. You can apply it to.

[0014]

Example 1 Preparation of polystyrene sulfonic acid: sodium polystyrene sulfonate (POLLY NaSS 50: trade name,
To remove sodium bromide contained as an impurity in (Tosoh), by adding acetone (special grade reagent manufactured by Wako Pure Chemical Industries) to sodium polystyrenesulfonate to precipitate sodium polystyrenesulfonate, and collecting the precipitate, Sodium bromide contained in the filtrate was removed.
The purpose of removing this sodium bromide is that Br ⁻ ions adversely affect the crosslinking by the heat treatment to be performed later.
The polystyrene sulfonic acid obtained by precipitation was washed several times with acetone. Next, the washed polystyrene sulfonic acid was dissolved in pure water, and sodium ions were exchanged for hydrogen ions using an ion exchange resin. The ion-exchanged polystyrene sulfonic acid aqueous solution was dried to precipitate as a solid. In this way, the molecular weight of 10
More than 10,000 polystyrene sulfonic acids were obtained.

Preparation of polyvinyl alcohol: polyvinyl alcohol (Kuraray Poval PVA-120: trade name,
Kuraray's saponification degree of 98 to 99 mol% was dissolved in pure water, and methanol (Wako Pure Chemical Industries, Ltd. special grade reagent) was added for precipitation. The precipitated polyvinyl alcohol was washed several times with methanol. Next, this polyvinyl alcohol was dried to remove methanol. Thus the molecular weight 1,
700 or more polyvinyl alcohol was obtained.

Production of methanol barrier membrane having ion exchange ability: The purified polyvinyl alcohol and polystyrene sulfonic acid obtained as described above were dissolved in an aqueous ethanol solution. The dissolved polyvinyl alcohol-polystyrene sulfonic acid-ethanol aqueous solution was applied to a thickness of 25 μm.
m, opening ratio 45%, opening diameter 0.25 × 0.075 μm polypropylene film-shaped support (Celguard: trade name, manufactured by Daicel Industries), casting film thickness 150 μ
Casting was done so that it would be m. The ethanol and water contained in the casting film were removed by drying the casting film for 24 hours. The dried casting film was heat-treated at 120 ° C. for 24 hours for crosslinking.

The crosslinked casting film was immersed in a 1N-sodium hydroxide aqueous solution for 24 hours. By this alkali treatment, unreacted polyvinyl alcohol and polystyrene sulfonic acid are removed. Then, a casting film during the ion-exchange groups in the alkali treatment is -SO ₃ ^- N
Since it was a ⁺ , it was immersed in a 1N-hydrochloric acid aqueous solution for 24 hours in order to convert this ion-exchange group from Na ⁺ type to H ⁻ type. The thus-prepared methanol barrier membrane 11 having an ion exchange capacity was stored in pure water.

Next, the methanol permeation test of the methanol barrier membrane 11 having the ion exchange capacity of the present invention was conducted as follows. FIG. 1 shows a flow chart of the methanol permeation amount measuring apparatus. Reference numeral 1 denotes a container containing an aqueous methanol solution, which is placed at a high position to keep the water level constant. Reference numeral 2 denotes a measuring cell 2 for measuring the methanol permeability, which is arranged at a position lower than the container 1 containing the aqueous methanol solution. 3 is a trap for cooling and condensing the nitrogen gas, methanol and water discharged from the measurement cell 2, and 4 is an integrating flow meter for measuring the integrated amount of the discharged nitrogen gas.

FIG. 2 shows an enlarged view of the measuring cell 2 shown in FIG. 11 is the methanol barrier film of the present invention. The methanol blocking film 11 has a 1 mm mesh FEP mesh 12 made of fluorinated ethylene-propylene copolymer on both sides thereof.
It is sandwiched with 1, 122 and incorporated in the measuring cell 2. On one side of the measuring cell 2, an inlet 5 for receiving methanol and water and an outlet 6 for discharging the received methanol and water are provided, and the methanol and water introduced into the measuring cell 2 through the inlet 5 are provided. Is passed through the FEP net 121, which is in contact with one side of the methanol blocking film 11, and is discharged to the outlet 6.

On the other hand, the other side of the measuring cell 2 has an inlet 7 for receiving nitrogen gas and an outlet 8 for discharging nitrogen gas, methanol and water. Entrance 7
The nitrogen gas introduced from the exhaust gas passes through the FEP network 122 and is discharged from the outlet 8. However, in the FEP network 122 on the way, together with methanol and water that have permeated from the methanol blocking film 11, the nitrogen gas is discharged from the outlet 8. Is discharged.

The apparatus shown in FIGS. 1 and 2 was used to measure the amount of methanol permeation between the methanol barrier membrane 11 of the present invention and the conventional Nafion 117 (registered trademark of DuPont) membrane. FIG. 3 is a graph showing the relationship between the amount of methanol permeation and the concentration of aqueous methanol solution. PASS in the figure
A-PVA shows the methanol barrier film 11 of the first embodiment.

From this graph, it can be seen that the methanol barrier film 11 of the present invention is excellent in its methanol barrier performance when the aqueous methanol solution having a methanol aqueous solution concentration of less than 50% by weight is used. Next, the ion exchange capacity of the methanol barrier film 11 having the ion exchange capacity of the present invention was examined. The ion exchange capacity of the methanol blocking membrane 11 is
Since it can be evaluated by measuring the electrical resistance of the methanol blocking film 11, the electrical resistance of the methanol blocking film 11 obtained by the above method was measured by the four-terminal measuring method.
As a result, it was 0.68 Ω · cm ² . For comparison, the Nafion 117 (registered trademark of DuPont) membrane was measured under the same conditions to obtain 1.52 Ω · cm ² . Therefore, it is understood that the methanol barrier film 11 of the present invention has excellent ion exchange ability.

[0023]

INDUSTRIAL APPLICABILITY Since the methanol barrier membrane of the present invention is excellent in methanol barrier performance and ion exchange property as an ion exchange membrane, it can be used as an electrolyte for preventing permeation of methanol in a methanol fuel cell. .. Further, the present invention can be a small-sized methanol fuel cell as a whole.

[Brief description of drawings]

FIG. 1 shows a flow chart of a methanol permeation amount measuring device.

2 shows an enlarged view of the measuring cell 2 shown in FIG.

FIG. 3 is a graph showing the relationship between the amount of permeated methanol and the concentration of aqueous methanol solution.

FIG. 4 is a conceptual diagram of a methanol fuel cell using the methanol barrier film of the present invention.

FIG. 5 shows a conceptual diagram of another methanol fuel cell using the methanol barrier membrane of the present invention.

[Explanation of symbols]

 1 Container 2 Measuring Cell 3 Trap 4 Integrating Flowmeter 5,7 Inlet 6,8 Outlet 11 Methanol Blocking Membrane 12 FEP Network 13 Electrolyte 14 Methanol Electrode 15 Air Electrode 16 Anolite

Claims (1)

[Claims] 1. A methanol barrier having ion-exchange ability, which is obtained by casting a polymer composition containing polystyrene sulfonic acid and polyvinyl alcohol on a porous support and polymerizing by thermal crosslinking. film.