JP2001210337A - Solid polymer electrolyte membrane and a solid polymer electrolyte type fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a solid polymer electrolyte membrane and a solid polymer electrolyte type fuel cell which are inexpensive and has a high power generation performance. SOLUTION: In a homogeneous high polymer base material in a face, a solid polymer electrolyte membrane 2 in the membrane area which characterizes the introduction of an ion exchange group and a conjugate 10 of electrode 3a, 3b being with a catalyst with the solid polymer electrolyte membrane 2 are pinched and supported by a separator 4a, 4b to compose the solid polymer electrolyte type fuel cell.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a fuel cell.

[0002]

2. Description of the Related Art A fuel cell generally has a large number of cells stacked, and the cell has two electrodes (a fuel electrode and an air electrode).
Has a structure sandwiching the electrolyte.

At the fuel electrode, the following reaction occurs when hydrogen gas comes into contact with the catalyst.

[0004] _{^{2H 2 → 4H + + 4e -}} ········· (1) H + is a water migrate through the electrolyte to react with oxygen in the air reaching the air electrode catalyst.

[0005] 4H ⁺ + 4e ⁻ + O ₂ → 2H ₂ O (2) Power is generated by the reverse reaction of electrolysis using hydrogen and oxygen by the above-mentioned reaction, and clean power generation is performed without discharge other than water. It is drawing attention as a device.

[0006] In order to reduce air pollution as much as possible, measures against exhaust gas from automobiles have become important, and as one of the measures, electric vehicles have been used. However, due to problems such as charging facilities and mileage, they have become widespread. Not in. Vehicles using fuel cells are seen as the most promising clean vehicles.

[0007] Among the fuel cells, solid polymer electrolyte fuel cells are most promising for automobiles because they operate at low temperatures. The electrolyte of the solid polymer electrolyte fuel cell is a solid polymer electrolyte membrane.

Conventional solid polymer electrolyte membranes for fuel cells have used perfluorocarbon sulfonic acid.
The high cost of the solid polymer electrolyte membrane, which is a main component of the fuel cell, has been a major problem of the solid polymer electrolyte fuel cell. In order for fuel cells to be widely used, it is important to make solid polymer electrolyte membranes inexpensive.

In order to make the solid polymer electrolyte membrane inexpensive, it is manufactured by introducing an anionic group such as a sulfonic acid group using radiation graft polymerization into an inexpensive membrane-like polymer substrate such as inexpensive polyethylene or ETFE. Solid polymer electrolyte membranes have been considered.

As prior art 1, Japanese Patent Application Laid-Open No. 7-05017
No. 0 discloses a solid polymer electrolyte membrane in which a polyolefin is used as a membrane polymer substrate and a sulfonic acid group is introduced into the membrane polymer substrate.

As prior art 2, Japanese Patent Application Laid-Open No. 9-10232
No. 2 discloses a solid polymer electrolyte in which a copolymer of a fluorocarbon vinyl monomer and a hydrocarbon vinyl monomer is used as a film-like polymer substrate, and a sulfonic acid group is introduced into the film-like polymer substrate. A membrane is disclosed.

[0012]

However, in order to put the fuel cell to practical use, it is necessary to further improve the power generation performance of the fuel cell using the solid electrolyte polymer membrane of the prior art 1 and the prior art 2.

The present invention has solved the above-mentioned problems, and provides a solid polymer electrolyte membrane and a solid polymer electrolyte fuel cell which are inexpensive and have high power generation performance.

[0014]

Means for Solving the Problems In order to solve the above technical problems, the technical means (hereinafter referred to as the first technical means) taken in claim 1 of the present invention is homogeneous in a plane. A solid polymer electrolyte membrane characterized by introducing an ion exchange group into a simple membrane-like polymer base material.

The effects of the first technical means are as follows.

That is, since the obtained solid polymer electrolyte membrane is also homogeneous in the plane, the solid polymer electrolyte membrane has a uniform and large water absorption rate in the plane, and has high power generation performance and durability. An excellent fuel cell can be obtained.

In order to solve the above technical problem, the technical means (hereinafter referred to as second technical means) taken in claim 2 of the present invention is a mechanical means of the film-like polymer substrate. 2. The solid polymer electrolyte membrane according to claim 1, wherein the properties are uniform in the plane.

The effects of the second technical means are as follows.

That is, homogeneity of the mechanical properties means that there is no or low molecular orientation of the film-like polymer base material, and therefore a solid polymer electrolyte membrane having a high water absorption rate can be obtained.

In order to solve the above technical problem, the technical means (hereinafter referred to as the third technical means) taken in claim 3 of the present invention is that the film-like polymer substrate is made of fluorocarbon. 2. The solid polymer electrolyte membrane according to claim 1, which is a copolymer of a vinyl monomer and a hydrocarbon vinyl monomer.

The effects of the third technical means are as follows.

That is, by using the above-mentioned material as the membrane polymer substrate, a solid polymer electrolyte membrane which is inexpensive and has excellent mechanical strength can be obtained, and a fuel cell which is inexpensive and has excellent durability can be obtained. it can.

In order to solve the above-mentioned technical problem, a technical measure taken in claim 4 of the present invention (hereinafter referred to as a fourth technical measure) is that the anionic group is a styrene sulfonate. The solid polymer electrolyte membrane according to claim 1, wherein:

The effects of the fourth technical means are as follows.

That is, a solid polymer electrolyte membrane can be easily and inexpensively manufactured. Further, since the dissociation constant of styrene sulfonate is high, a solid polymer electrolyte membrane having low electric resistance can be manufactured.

In order to solve the above technical problems, the technical means (hereinafter referred to as fifth technical means) taken in claim 5 of the present invention is an electrode having a solid polymer electrolyte membrane and a catalyst. A solid polymer electrolyte fuel cell characterized in that the joined body is sandwiched between separators.

The effects of the fifth technical means are as follows.

That is, since a solid polymer electrolyte membrane which is inexpensive and has a high water absorption rate is used, a fuel cell which is inexpensive and has high power generation performance can be obtained.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to obtain a fuel cell having high power generation performance, a solid polymer electrolyte membrane having high and low electric resistance during power generation is required. The present inventor has conducted studies and studies on factors that determine the electric resistance of a solid polymer electrolyte membrane in which an ion exchange group has been introduced into a membrane-like polymer substrate, and reached the present invention.

The electric resistance of the solid polymer electrolyte membrane is determined by the water content in the membrane and the water content distribution in the film thickness direction. Among them, the water absorption rate of the solid polymer electrolyte membrane affects the electric resistance of the solid polymer electrolyte membrane during power generation,
As a factor that determines the water absorption rate, it has been found that the characteristics of the film-like polymer base material as a starting material for producing a solid polymer electrolyte membrane are important. That is, it has been discovered that the use of a film-like polymer base material that is non-oriented in the plane direction can improve the water absorption rate of the solid polymer electrolyte membrane, thereby improving the power generation performance of the fuel cell.

When the electrolyte is a solid polymer electrolyte membrane, a certain water content is required to maintain the performance of the electrolyte. In the power generation reaction of the fuel cells of the formulas (1) and (2), water also moves to the oxidant electrode side in the solid polymer electrolyte membrane with the movement of H ⁺ from the fuel electrode. For this reason, the water content of the solid polymer electrolyte membrane on the fuel electrode side decreases, so that the electric resistance of the solid polymer electrolyte membrane increases and the power generation performance decreases.

To prevent this, supply to the fuel electrode
The fuel gas is supplied with moisture. Solid polymer
If the water absorption rate of the degraded membrane is high,
Salary, H ⁺Stable water content even with water movement accompanying the movement of water
The amount can be maintained, and the power generation performance of the fuel cell can be improved.

The film-like polymer substrate is formed by a T-die method (a method in which a thin and flat sheet-like material extruded from a slit is formed while being strongly stretched in a cooling bath by a tension device) or an inflation method (a tubular extrusion method). Air is blown into the tube while it is allowed to cool to the optimal atmosphere, and it is formed so as to expand into a large cylinder. Then, it is squeezed between two rolls to form a flat sheet. To make a film by cutting with a knife).

The film-like polymer substrate produced by these methods is easily stretched in the film plane because the substrate is stretched during the production process, and has mechanical properties such as tensile strength in the direction perpendicular to the stretching direction. Breaking strength and elongation will be different.
For example, when the ratio of the tensile elongation at break in the stretching direction and the stretching perpendicular direction of the polymer substrate is smaller than 0.8, it means that the degree of the stretching orientation is large, and when this film-shaped polymer substrate was used, it was introduced. The compound having an ion exchange group is also oriented in the orientation direction of the substrate. Since the completed solid polymer electrolyte membrane has a dense molecular structure, it becomes a membrane that absorbs less water than a coarse membrane that is not oriented. For this reason, the water absorption rate of the solid polymer electrolyte membrane is reduced, resulting in a fuel cell with low power generation performance. On the other hand, by using a non-oriented membrane polymer substrate, the compound having an ion exchange group is also non-oriented, so that the water absorption rate of the solid polymer electrolyte membrane is improved and the power generation performance of the fuel cell is improved.

The orientation of molecules in the plane can be expressed by the fact that mechanical properties such as tensile strength at break and elongation are uniform in the in-plane direction of the film. That is, the most important in the film-like polymer substrate used is that mechanical properties such as tensile strength at break and elongation do not significantly differ in the in-plane direction of the film, for example, the maximum and minimum tensile elongation at break. The ratio is preferably 0.8 or more.

In the T-die method or the inflation method, in which the film is easily stretched and oriented in the film plane, the stretching orientation is suppressed by reducing the winding speed, and the ratio of the tensile elongation at break in the stretching direction to the stretching perpendicular direction becomes 0.8 or more. In this case, there is no particular limitation on the method for producing the film-like polymer substrate. In addition, a casting method (a method in which a liquid or viscous solution obtained by dissolving a material in a solvent is placed in a flat container and the solvent is evaporated under heating or under reduced pressure to form a film) and a pressing method (a temperature higher than the forming temperature of the material) (A method of forming a film by pressing with a heated flat plate).

Examples of the film-like polymer substrate used include polyolefins such as polyethylene and polypropylene, and halogenated polyolefins such as poly (ethylene-tetrafluoroethylene), poly (tetrafluoroethylene-hexafluoropropylene), and polyvinylidene fluoride. is there. These are much cheaper than perfluorocarbon sulfonic acid membranes. When used as a film-like polymer which is preferably a copolymer of a fluorocarbon vinyl monomer and a hydrocarbon vinyl monomer, a solid polymer electrolyte fuel cell which is inexpensive, has excellent durability, and has high performance can be obtained.

The thickness of the film-like polymer substrate is not particularly limited, but is preferably from 10 to 150 μm. When the thickness is less than 10 μm, the completed solid polymer electrolyte membrane is easily broken and loses durability. When the thickness is more than 150 μm, the electric resistance of the solid polymer electrolyte membrane increases and the power generation performance decreases.

There is no particular limitation on the method of introducing an ion-exchange group into the film-like polymer substrate, but after the graft chain is bonded to the polymer of the film-like polymer substrate, an anion group is bonded to the graft chain. And a method of bonding a graft chain having an anionic group to the polymer of the film-like polymer substrate. As a method of bonding a graft chain or a graft chain having an anionic group to a polymer of a film-like polymer substrate, a radiation graft polymerization method using an electron beam, γ-ray, or the like is excellent.

As the anionic group, there is a sulfonic acid group,
A sulfonic acid group can be introduced by bringing a vinyl compound having a sulfonic acid group, for example, styrene sulfonic acid, ethylene sulfonic acid, or the like, into contact with a polymer substrate irradiated with radiation. Further, for example, a method of introducing styrene into a polymer substrate and then introducing a sulfonic acid group by a sulfonation reaction may be used.

Hereinafter, a detailed description will be given based on embodiments.

Example 1 A 50 μm-thick poly (ethylene-tetrafluoroethylene) film produced by a T-die method was used as a film-like polymer substrate. The tensile elongation at break in the longitudinal and lateral directions in the film plane of the film was measured to be 0.85. The longitudinal and transverse directions in the film plane correspond to the stretching direction of the T-die method and the perpendicular direction thereof, and are the directions in which the difference in tensile elongation at break is maximized.

After irradiating the film with 20 kGy γ-rays in nitrogen at room temperature, it is immersed in a mixed solution of styrene monomer: divinylbenzene: xylene = 95: 5: 30 (volume ratio) at 60 ° C. for 2 hours. Thus, a styrene chain was grafted on poly (ethylene-tetrafluoroethylene). After drying, the film was immersed in a mixed solution of 30 parts by volume of chlorosulfonic acid and 100 parts by volume of 1,2-dichloroethane at 50 ° C. for 1 hour. After drying this film, 9
Dipped in deionized water at 0 ° C. for 1 hour. Further washing with fresh deionized water at 90 ° C. for 2 hours.

The physical properties (ion exchange capacity, saturated water content, water absorption rate) of the solid polymer electrolyte membrane thus obtained were measured. The ion exchange capacity was measured by a titration method. The saturated water content was determined by drying the solid polymer electrolyte membrane at 80 ° C. in a vacuum at a dry weight of 90 ° C. hot water for 2 hours.
After immersion as described above, it was determined from the difference between the measured saturated water contents. The water absorption rate was determined by measuring the water content when the dried film was immersed in deionized water at 25 ° C. for 5 seconds.

FIG. 1 is a sectional view of a solid polymer electrolyte fuel cell used for measuring the output characteristics of the fuel cell. This solid polymer electrolyte fuel cell 1 is composed of one cell (single cell). In general, a design is made such that a large number of such single cells are stacked to obtain an output according to the application.

The solid polymer electrolyte membrane 2 was sandwiched between the fuel electrode 3a and the oxidant electrode 3b and joined by hot pressing at 160 ° C. and a pressure of 8 MPa for 60 seconds. The assembly 10 was sandwiched between a separator 4 a having a fuel gas flow groove 5 a and a separator 4 b having an oxidizing gas flow groove 5 b and an O-ring 6, thereby producing a polymer electrolyte fuel cell 1. . The output characteristics of the fuel cell were evaluated by the output voltage at a current density of 0.7 A / cm ² while hydrogen was supplied to the fuel gas and air was supplied to the oxidizing gas at 0.2 MPa, and the cell temperature was maintained at 75 ° C. did.

Example 2 A solid polymer electrolyte membrane was obtained in the same manner as in Example 1 except that the tensile elongation at break in the longitudinal and transverse directions in the film plane of the film-like polymer substrate was 0.82. Was.
The membrane physical properties of the solid polymer electrolyte membrane thus obtained and the output characteristics of the fuel cell were evaluated in the same manner as in the examples.

Example 3 A poly (ethylene-tetrafluoroethylene) pellet was formed into a film having a thickness of 65 μm using a hot press controlled at 300 ° C. to obtain a film-like polymer substrate. The tensile elongation at break in the longitudinal and transverse directions in the film plane of the film-like polymer substrate was 0.99. A solid polymer electrolyte membrane was obtained in the same manner as in Example 1 using this film-like polymer base material. The membrane physical properties of the solid polymer electrolyte membrane thus obtained and the output characteristics of the fuel cell were evaluated in the same manner as in the examples.

Comparative Example A solid polymer electrolyte membrane was obtained in the same manner as in Example 1 except that the tensile elongation at break in the longitudinal and transverse directions in the film plane of the membrane polymer substrate was 0.72. . The membrane physical properties of the solid polymer electrolyte membrane thus obtained and the output characteristics of the fuel cell were evaluated in the same manner as in the examples.

(Evaluation Results) Table 1 shows the evaluation results of the membrane physical property values and the output characteristics of the fuel cell of Examples 1 to 3 and Comparative Example. The cell output voltages of the fuel cells of Examples 1 to 3 are higher than those of Comparative Examples. When the physical properties of the membranes of Examples 1 to 3 and Comparative Example were compared, no significant difference was observed in the ion exchange capacity and the saturated water content, but the water absorption rates were greatly different. The water absorption rates of the solid polymer electrolyte membranes of Examples 1 to 3 are about twice as large as those of Comparative Examples.

[0051]

[Table 1] The difference in the water absorption rate between Examples 1 to 3 and Comparative Example is due to the difference in the tensile breaking elongation ratio in the longitudinal and transverse directions in the film plane of the used film-like polymer base material. This is caused by the difference in the coarse density. As a result, membrane drying on the fuel electrode side, which occurs during operation of the fuel cell, can be prevented, so that the electric resistance of the solid polymer electrolyte membrane is reduced, and a fuel cell having large output characteristics can be obtained.

The solid polymer electrolyte membrane of the present invention can be used not only for a solid polymer electrolyte fuel cell but also for a salt electrolyte membrane for producing sodium hydroxide, hydrogen and chlorine from seawater.

[0053]

As described above, the present invention provides a solid polymer electrolyte membrane characterized in that an ion exchange group is introduced into an in-plane homogeneous film polymer base material and this solid polymer electrolyte membrane. A solid polymer electrolyte fuel cell characterized in that an assembly of an electrode having a catalyst and a catalyst is sandwiched between separators, so that it is inexpensive and has high power generation performance. Battery is made.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a solid polymer electrolyte fuel cell used for measuring output characteristics of a fuel cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Solid polymer electrolyte fuel cell 2 ... Solid polymer electrolyte membrane 3a ... Fuel electrode (electrode) 3b ... Oxidizer electrode (electrode) 4a, 4b ... Separator 10 ... Joint

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Claims (5)

[Claims] 1. A solid polymer electrolyte membrane wherein an ion-exchange group is introduced into an in-plane homogeneous film-like polymer base material. 2. The solid polymer electrolyte membrane according to claim 1, wherein the mechanical properties of the film-like polymer substrate are uniform in a plane. 3. The solid polymer electrolyte membrane according to claim 1, wherein the film-like polymer substrate is a copolymer of a fluorocarbon vinyl monomer and a hydrocarbon vinyl monomer. 4. The solid polymer electrolyte membrane according to claim 1, wherein the anion group is a styrene sulfonate. 5. A solid polymer electrolyte fuel cell characterized in that a joined body of a solid polymer electrolyte membrane and an electrode having a catalyst is sandwiched between separators.