JPH1079257A - Ion exchange membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain lowering of membrane strength and improve output by sandwiching by a first polymer membrane a second polymer membrane having its ion exchange greater than of the first membrane. SOLUTION: An ion exchange membrane 1 is a first polymer membrane 1a having a predetermined ion exchange quantity, and a second polymer membrane 1b having its ion exchange quantity greater than the first film is sandwich. With such a structure, an internal side has its higher ion exchange quantity than a surface side (electrode side), that is, the electrode side ion exchange quantity is restrained less than the internal side, therefore, on the electrode side, swelling due to humidifying is reduced, membrane strength is prevented from being lowered, and a function as a barrier membrane can be maintained. On the other hand, on the internal side, sufficient water content quantity can be kept, and a high output capacity can be given. The ion exchange quantity is preferably 0.8 to 1.2mg equivalence (dry equivalence) in a membrane 1a and preferably 1.2 to 2.4mg equivalence (dry equivalence) in a membrane 1b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion exchange membrane, and is particularly effective when applied to an electrolyte of a solid polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art A solid polymer electrolyte fuel cell has an ion exchange membrane (solid polymer electrolyte) for transferring protons between a negative electrode and a positive electrode, and hydrogen as a fuel gas is supplied to the negative electrode. On the other hand, when the oxidant gas, oxygen or air, is supplied to the positive electrode, the following reactions occur in the negative electrode and the positive electrode.

[0003]

## STR1 ## _{^{2H 2 → 4H + + 4e -}} ··· anode _{^{O 2 + 4H + + 4e -}} → 2H 2 O ··· positive

That is, in the negative electrode, hydrogen is dissociated into protons and electrons, and the protons flow to the positive electrode through the ion exchange membrane, and the electrons flow to the positive electrode through an external load circuit. Oxygen reacts with the protons and the electrons to produce water. In this reaction, the electrons flow through the circuit to generate electric energy.

[0005] Such an ion exchange membrane is required to have a low electric resistance, a fast movement of moisture, a high water retention rate, a gas permeability capable of supplying hydrogen and oxygen, and the like. Also required are chemical stability and physical strength. Therefore, polystyrene sulfonate, polyvinyl sulfonate, perfluorosulfonate, or the like having cation exchange properties is applied to such an ion exchange membrane. Among them, perfluorosulfonate is currently mainly used because it is particularly stable chemically (for example, Nafion (trade name) manufactured by DuPont).

[0006]

In the above-mentioned ion exchange membrane, improvement in output performance has been studied in view of a demand for higher performance of a fuel cell. Therefore, in a fluorine-based ion-exchange membrane such as perfluorosulfonate as described above, since the sulfonic acid groups in the side chains have ion conductivity, the sulfonic acid groups in the side chains are increased to increase the proton conductivity. It has been considered that the output performance is improved by increasing the value. However, when an ion exchange membrane having a large number of side chain sulfonic acid groups is applied to a fuel cell, the swelling due to humidification is large, and the membrane strength is reduced. Will be.

Further, since the above-mentioned ion exchange membrane cannot exhibit high proton conductivity unless it is in a wet state, the wet state is maintained by the moisture of the humidified fuel gas. . When the ion exchange membrane is humidified in this manner, moisture tends to be insufficient on the inner side and excessive on the electrode side, so that it is not possible to immediately respond to a change in load of the fuel cell, and it is difficult to quickly start up. Was.

In view of the above, the present invention provides an ion exchange membrane capable of improving the output while increasing the water content inside while suppressing the decrease in membrane strength due to swelling due to humidification. It was aimed at.

[0009]

In order to solve the above-mentioned problems, an ion exchange membrane according to the present invention comprises a first polymer membrane having a predetermined ion exchange capacity and a larger ion exchange membrane than the first polymer membrane. It is characterized by being sandwiched by a second polymer film having a capacity.

In the above-mentioned ion exchange membrane, the ion exchange capacity of the first polymer membrane is not less than 0.8 meq. The exchange capacity is 1.2 to 2.4 meq / g dry weight.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an ion exchange membrane according to the present invention will be described with reference to FIG. FIG. 1 is a schematic structural diagram.

In FIG. 1, 1 is an ion exchange membrane, 1a is a first polymer membrane, and 1b is a second polymer membrane. As shown in FIG. 1, the ion exchange membrane 1 sandwiches a second polymer membrane 1b having a larger ion exchange capacity than the first polymer membrane 1a with a first polymer membrane 1a having a predetermined ion exchange capacity. It is.

According to such an ion exchange membrane 1, the ion exchange capacity is higher on the inner side than on the front side (electrode side). In other words, the ion exchange capacity on the electrode side is smaller than that on the inner side. Therefore, on the electrode side, swelling due to humidification can be suppressed to prevent a decrease in membrane strength, and the function as a diaphragm can be maintained, while on the inner side, a sufficient water content can be maintained and high Output capability can be demonstrated.

The ion exchange membrane 1 as described above can be manufactured as follows. After reacting a chain sultone having acid fluoride with hexafluoropropene oxide, a functional group monomer is synthesized by thermal decomposition and olefination, and tetrafluoroethylene, hexafluoropropene, chlorotrifluoroethylene, etc. A starting polymer can be obtained by copolymerizing such a fluorine-based olefin with the above functional group monomer.

The molecular weight of the raw material polymer is not particularly limited, but is preferably about 10,000 to 100,000. Because, when the molecular weight is smaller than 10,000, the strength becomes insufficient when formed into a film,
If the molecular weight is larger than 100,000, it becomes difficult to heat and melt during molding.

The raw material polymer obtained as described above is formed into a film by an extrusion molding method, a casting method of dissolving about 1 to 10% by weight in a solvent, uniformly applying the solution on a plate with a roller, and then drying. By subjecting this to various post-treatments such as hydrolysis, the above-mentioned polymer film is obtained. In addition, the thickness of the film is about 1 to 200 μm.

The ion exchange capacity of the polymer membrane can be adjusted by changing the input amounts of the functional group monomer and the fluoroolefin. The ion exchange capacity of the polymer membrane is preferably 0.8 to 2.4 milliequivalents per gram of dry weight (hereinafter, expressed in numerical values per gram of dry weight unless otherwise specified). When the ion exchange capacity is smaller than 0.8 meq, the proton conductivity is too small, and when the ion exchange capacity is larger than 2.4 meq, it becomes difficult to produce a polymer membrane. Because.

Among the polymer membranes manufactured as described above, the one having the smaller ion exchange capacity sandwiches the one having the larger ion exchange capacity, that is, the first polymer membrane 1a sandwiches the second polymer membrane 1b. About 200-300 ° C, about 100-200
By pressing under the condition of kg / cm ² , the above-described ion exchange membrane 1 can be obtained. Here, it is preferable that the upper limit of the ion exchange capacity of the first polymer membrane 1a is less than 1.2 meq, and the lower limit of the ion exchange capacity of the second polymer membrane 1b is 1.2 meq or more. . This is because if the ion exchange capacity is less than 1.2 meq, the required strength (200 kg / cm ² or more in tensile strength) can be obtained, and if the ion exchange capacity is 1.2 meq or more. This is because a sufficient water content can be maintained and the output capability can be improved.

[0019]

EXAMPLES In order to confirm the effects of the ion exchange membrane according to the present invention, the following comparative experiments were conducted.

[Production of raw material polymer] <Raw material polymer A> A monomer having a functional group (CF ₂ ＣＦCF)
_{OCF 2 CF (CF 3) OCF} 2 CF 2 SO 2 F) 10
g of ammonium perfluorooctanoate (C ₇ F ₁₅ COONH ₄ )
g, and emulsified. Then, the mixture was put into a stainless steel autoclave (internal volume: 300 ml), 0.2 g of ammonium peroxodisulfate ((NH ₄ ) ₂ S ₄ O ₆ ) was added, and tetrafluoroethylene gas (CF ₂ = CF) was added. ₂ ) 10k
By blowing to gf / cm ² and reacting for 8 hours, a starting polymer A was obtained.

<Raw material polymer B> The raw material polymer B was synthesized in the same manner as the above-mentioned raw material polymer A except that the blowing pressure of the tetrafluoroethylene gas was changed to 7.5 kgf / cm ² in gauge pressure. Obtained.

<Raw Material Polymer C> A raw material polymer C was obtained by synthesizing in the same manner as the above-mentioned raw material polymer A, except that the blowing pressure of the tetrafluoroethylene gas was changed to a gauge pressure of 5 kgf / cm ² . .

<Raw Material Polymer D> The raw material polymer D was synthesized in the same manner as the above-mentioned raw material polymer A except that the blowing pressure of the tetrafluoroethylene gas was changed to a gauge pressure of 2.5 kgf / cm ^2. Obtained.

[Production of polymer film] <Polymer film A> The raw material polymer A is dissolved in isopropanol, coated on a smooth glass plate and dried to form a film. After hydrolysis in sodium oxide solution for 8 hours,
A proton type polymer membrane A was produced in a 5 wt% sulfuric acid solution for 8 hours. This polymer membrane A had a thickness of 45 μm, an ion exchange capacity of 0.92 meq, and a water content of 25 wt%.

<Polymer Membrane B> A proton-type polymer membrane B was produced using the starting polymer B in the same manner as in the polymer membrane A. This polymer film B has a thickness of 53 μm,
1.18 meq ion exchange capacity, 30wt% water content
Met.

<Polymer Membrane C> A proton-type polymer membrane C was produced using the starting polymer C in the same manner as in the polymer membrane A. This polymer film C has a thickness of 46 μm,
1.67 meq ion exchange capacity, 38wt% water content
Met.

<Polymer Membrane D> A proton-type polymer membrane D was produced using the starting polymer D in the same manner as the polymer membrane A. This polymer film C has a thickness of 50 μm,
2.35 meq ion exchange capacity, 45wt% water content
Met.

[Manufacture of Ion Exchange Membrane] <Ion Exchange Membrane α> An ion exchange membrane α was obtained by sandwiching the polymer membrane D with the polymer membrane B and heating and pressing. That is, the ion exchange membrane α is obtained by applying the polymer membrane B to the first polymer membrane and applying the polymer membrane D to the second polymer membrane. This ion exchange membrane α had a thickness of 130 μm.

<Ion Exchange Membrane β> The polymer membrane D is sandwiched between the polymer membranes A, and is heated and pressed to obtain the ion exchange membrane β.
I got In other words, the ion exchange membrane β is obtained by applying the polymer membrane A to the first polymer membrane and applying the polymer membrane D to the second polymer membrane. The thickness of the ion exchange membrane β was 135 μm.

<Ion-exchange membrane γ> The polymer membrane A is sandwiched between the polymer membranes A, and is heated and pressed to obtain the ion-exchange membrane γ.
I got That is, the ion exchange membrane γ is obtained by applying the polymer membrane A to the first polymer membrane and applying the polymer membrane C to the second polymer membrane. This ion exchange membrane γ had a thickness of 135 μm.

<Ion Exchange Membrane δ> An ion exchange membrane δ is formed by sandwiching the polymer membrane D between the polymer membranes A and hot pressing.
I got That is, the ion exchange membrane δ is obtained by applying the polymer membrane A to the first polymer membrane and applying the polymer membrane D to the second polymer membrane. This ion exchange membrane δ had a thickness of 125 μm.

<Ion exchange membrane ε> A commercially available ion exchange membrane (Nafion 117 manufactured by DuPont) was used as it was. This ion exchange membrane ε had a thickness of 175 μm, an ion exchange capacity of 0.9 meq, and a water content of 27 wt%.

[Measurement of ion-exchange capacity] Each of the above-mentioned ion-exchange membranes α to ε was completely left in a 1N hydrochloric acid at 80 ° C. for 8 hours to be completely protonated, and then sufficiently washed with a 0.1N sodium hydroxide solution. After leaving for 24 hours in the solution, the ion-exchange membranes α to ε are taken out of the solution, and the amount of sodium hydroxide in the solution is titrated with 0.1 N hydrochloric acid, whereby the ion-exchange membranes α to ε The capacity was measured. Table 1 shows the results.

[0034]

[Table 1]

As can be seen from Table 1, the ion exchange membranes α to
δ indicates an ion exchange capacity larger than that of the ion exchange membrane ε.

[Measurement of Water Content] Each of the above ion exchange membranes α to
Cut a sample of 2cm x 2cm from ε,
After vacuum drying at 100 ° C. for 8 hours, the weight X is measured.
Next, these samples were boiled in deionized water at 100 ° C. for 1 hour and then immersed in deionized water at 25 ° C. for 30 minutes. The samples were taken out, and the water adhering to the surface was wiped off to measure the weight Y. . From the weights X and Y thus determined, the water content was calculated based on the following equation (1). Table 2 shows the results.

[0037]

W (%) = {(Y−X) / X} × 100 (1) where W is a water content.

[0038]

[Table 2]

As can be seen from Table 2, the ion exchange membranes α to
δ showed a higher water content than the ion exchange membrane ε.

[Measurement of Power Generation Characteristics] Each ion exchange membrane α
~ Ε sandwiched between the positive and negative electrodes, 200 ° C, 50kg / c
Press bonding was performed under the conditions of m ² , and a single cell of a fuel cell as shown in FIG. 2 was manufactured using this. In FIG. 2, reference numeral 2 denotes a negative electrode, and 3 denotes a positive electrode. The negative electrode 2 and the positive electrode 3 are each manufactured by adding a polymer compound to fine carbon powder supporting a platinum catalyst. The amount of the platinum catalyst was 0.5 m
g / cm ² . Humidified hydrogen was supplied to the negative electrode side of such a fuel cell, air was supplied to the positive electrode side, and the voltage-current characteristics were measured at a cell temperature of 40 ° C. The result is shown in FIG.

As can be seen from FIG. 3, the ion exchange membranes α to
δ showed more excellent power generation characteristics than the ion exchange membrane ε.

[0042]

According to the ion exchange membrane of the present invention, the output can be improved while suppressing the swelling due to humidification. Therefore, the decrease in membrane strength is suppressed, and the function as a diaphragm is prevented from being reduced. The performance of the fuel cell can be improved. Further, since the water content on the internal side can be increased, it is possible to immediately respond to a change in the load of the fuel cell and start up quickly.

[Brief description of the drawings]

FIG. 1 is a schematic structural diagram of an embodiment of an ion exchange membrane according to the present invention.

FIG. 2 is a schematic configuration diagram of a fuel cell used in a confirmation test.

FIG. 3 is a graph showing voltage-current characteristics of a fuel cell to which each ion exchange membrane is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ion exchange membrane 1a First polymer membrane 1b Second polymer membrane 2 Negative electrode 3 Positive electrode

Claims (2)

[Claims] 1. An ion exchange membrane comprising a first polymer membrane having a predetermined ion exchange capacity and a second polymer membrane having an ion exchange capacity larger than the first polymer membrane. 2. The ion exchange capacity of the first polymer membrane is at least 0.8 meq / g and less than 1.2 meq / g dry weight, and the ion exchange capacity of the second polymer membrane is dry weight. The ion exchange membrane according to claim 1, wherein the amount is 1.2 to 2.4 meq / g.