JPH11273696A - Solid polymer electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid polymer electrolyte fuel cell which, although being low in internal resistance, has sufficient generating performance, without adversely affecting electrode reactions, by having a high water content, and using a water-repellent polymer electrolyte film for its surface. SOLUTION: This fuel cell comprises a solid polymer electrolyte film having ion exchangeability and a positive electrode and a negative electrode which are placed in contact with both sides thereof. In this case, the surface of the solid polymer electrolyte film has a water-repellent solid polymer electrolyte film formed by the crosslinked structure of styrene and divinyl benzene, the water repellency angle of the surface of the solid polymer electrolyte film being 85 deg. or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art Solid polymer electrolyte fuel cells are expected to be applied to automobiles and the like as small and lightweight power sources using hydrogen and oxygen as oxidants. Such a battery is composed of a solid polymer electrolyte membrane having ion exchange ability, and a positive electrode and a negative electrode arranged in contact with both sides thereof. Fuel hydrogen is electrochemically oxidized at the negative electrode to generate protons and electrons. This proton moves to the positive electrode to which oxygen is supplied in the polymer electrolyte membrane. On the other hand, the electrons generated at the negative electrode pass through the load connected to the battery and flow to the positive electrode, where protons, oxygen, and electrons react to generate water at the positive electrode.

As described above, a solid polymer electrolyte fuel cell has been studied as a power source for automobiles because of its low-temperature operability, small size and high power density. Perfluorocarbon polymer membrane having a sulfonic acid group (trade name;
Nafion, Dupont Co., Ltd., trade name; Aciplex, Asahi Kasei Corporation) and the like are used. However, it cannot be said that it is still sufficient in terms of increasing the output of the fuel cell. In addition, they are very expensive and hinder practical use.

[0004] Therefore, research and development of an inexpensive and high-performance polymer ion exchange membrane that substitutes for a perfluorocarbon polymer membrane has been promoted. By radiation graft polymerization, E
TFE (ethylene-tetrafluoroethylene copolymer)
The ion exchange membrane produced by introducing styrene into the film and then sulfonating it is possible in principle to lower the electrical resistance compared to the perfluorocarbon polymer membrane,
Since further cost reduction is possible, the characteristics of fuel cells using the same have been evaluated. In general, it is effective to reduce the internal resistance to improve the performance of the fuel cell. Therefore, it is considered that it is advantageous to increase the ion exchange capacity of the polymer ion exchange membrane as the electrolyte. According to the radiation graft polymerization method, it is possible to easily produce a low electric resistance film, but in this case, the film surface becomes extremely hydrophilic, which adversely affects the electrode reaction and lowers the internal resistance. Nevertheless, there may be a problem that sufficient power generation performance cannot be obtained, and this is remarkable when the water repellency of the electrode is low.

[0005]

Therefore, the present invention has a high water content and a water-repellent polymer electrolyte membrane on the surface so that the electrode reaction is not adversely affected and the internal resistance is low. Regardless, the present invention provides a solid polymer electrolyte fuel cell having sufficient power generation performance.

[0006]

Means for Solving the Problems In order to solve the above technical problems, the technical means taken in claim 1 of the present invention is to contact a solid polymer electrolyte membrane having ion exchange ability with both sides thereof. In a solid polymer electrolyte fuel cell comprising a positive electrode and a negative electrode arranged, the surface of the solid polymer electrolyte membrane is provided with a solid polymer electrolyte membrane having water repellency due to a crosslinked structure of styrene and divinylbenzene. Is a solid polymer electrolyte fuel cell.

According to a second aspect of the present invention, there is provided a technique for solving the above technical problem, wherein a water repellent angle of a surface of the solid polymer electrolyte membrane is 85 ° or more. A solid polymer electrolyte fuel cell according to claim 1.

When the water repellent angle is less than 85 °, the voltage sharply drops, and a solid polymer electrolyte fuel cell having sufficient power generation performance cannot be obtained.

According to a third aspect of the present invention, there is provided a solid polymer electrolyte membrane comprising a copolymer of a fluorocarbon vinyl monomer and a hydrocarbon vinyl monomer. 2. The solid polymer electrolyte fuel cell according to claim 1, wherein the cation exchange membrane comprises a hydrocarbon-based side chain having a sulfonic acid group and a main chain formed by:

[0010] In order to solve the above technical problems, the technical measures taken in claim 4 of the present invention are as follows.

[0011]

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Wherein R 1 is a fluorine atom or a fluoroalkyl group having 1 to 3 carbon atoms, R 2 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, m is an integer of 1 or more, and n is an integer of 1 or more. Wherein the side chain is

[0013]

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Wherein R 3, R 4 and R 5 are each a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, s is an integer of 1 or more, and t is 0 or an integer of 1 or more. The solid polymer electrolyte fuel cell according to claim 3, wherein:

According to a fifth aspect of the present invention, in order to solve the above technical problem, the main chain is an ethylene-tetrafluoroethylene copolymer. Is a solid polymer electrolyte fuel cell.

According to a sixth aspect of the present invention, there is provided a technical solution for solving the above-mentioned technical problems, wherein the side chain is a styrene sulfonic acid polymer. It is a molecular electrolyte fuel cell.

In order to solve the above-mentioned technical problems, a technical measure taken in claim 7 of the present invention is that a main chain formed of a copolymer of a fluorocarbon vinyl monomer and a hydrocarbon vinyl monomer has γ. Irradiating with a beam or an electron beam, forming a styrene graft copolymer on the surface, contacting with divinylbenzene, sulfonating with a chlorosulfonic acid mixture, and treating the surface with chlorosulfonic acid alone. A solid polymer electrolyte fuel cell comprising a solid polymer electrolyte membrane produced from a step of forming a bridge of divinylbenzene and a step of hydrolyzing.

## EQU1 ##

[0019]

The present invention has a high water content and has a water-repellent polymer electrolyte membrane on the surface, so that it does not adversely affect the electrode reaction and has sufficient power generation performance despite its low internal resistance. And a solid polymer electrolyte fuel cell having the same. In other words, the solid polymer electrolyte fuel cell of the present invention is configured so that the water repellency of the ion exchange membrane surface in contact with the electrode catalyst is high, and the ion conductivity inside the ion exchange membrane is large. Battery operation is stabilized and output performance is improved.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described.
explain.

In order to uniformly sulfonate the inside of the ETFE-styrene graft film, chlorosulfonic acid as a sulfonating agent is stable against the ETFE-styrene graft film and swells the ETFE-styrene graft film. It is carried out by dissolving in a solvent capable of being brought into contact therewith. Depending on the concentration of chlorosulfonic acid and the reaction temperature, the degree of crosslinking of the styrene benzene ring via SO2, which is a side reaction of the sulfonation reaction, has a great effect.

For example, when chlorosulfonic acid having a high concentration of 5 to 80% by weight is used, cross-linking greatly proceeds, the water content of the obtained ion exchange membrane is reduced, the water repellency of the surface is increased, and The resistance also increases.

Conversely, when chlorosulfonic acid having a low concentration of 0.5 to 2% by weight is used, the water content is high, the surface is hydrophilic and the electric resistance is low.

In order to operate the fuel cell satisfactorily, it is important to immediately remove water generated at the positive electrode from the catalyst layer as vapor. However, when the surface of the polymer ion exchange membrane is hydrophilic, The generated water is more likely to remain as a liquid in the catalyst layer, and as a result, diffusion of oxygen or air supplied to the positive electrode is hindered, and performance is reduced.
On the other hand, inside the polymer ion exchange membrane, it is desirable that the capacity of the ion exchange membrane be as high as possible so that the electric resistance of the entire fuel cell becomes small, and also from the viewpoint of the stability of cell operation, a large amount of water is contained. It is desirable that this acts as a buffer.

Next, the solid polymer electrolyte fuel cell of the present invention will be described in more detail based on examples. Note that the present invention is not limited to the embodiment.

(Example) After irradiating an ethylene-tetrafluoroethylene copolymer film (film thickness: 50 μm) with gamma rays at a dose of 20 kGy in the air at room temperature, styrene from which oxygen was sufficiently removed by nitrogen bubbling was added to 60 gms. After contacting the mixture at 3 ° C. for 3 hours to uniformly graft the styrene to the inside, the film was immediately separated from styrene and contacted with divinylbenzene at 60 ° C. for 1 minute.

The washed and dried film was contacted with a mixed solution of 5 parts by weight of chlorosulfonic acid and 60 parts by weight of dichloroethane at room temperature in a nitrogen atmosphere for 1 hour to carry out a sulfonation reaction.

Next, by treating with water at 90 ° C. for 1 hour, hydrolysis was performed to obtain an ion exchange membrane. Table 1 shows the results.

(Comparative Example) In the above operation, a sample was prepared in which styrene and divinylbenzene were not crosslinked. All other operations were the same as in the example. Table 1 shows the results of the comparative example.

As shown in Table 1, the sample of the example had a contact angle of 89.3 ° and almost completely repelled water.
The sample of the comparative example had a contact angle of 70.1 °, and the surface was wet.

As is clear from the contact angle data in Table 1, the surface condition of each sample is significantly different, and the sample of the example has water repellency and the sample of the comparative example is hydrophilic. It was clear.

The gas diffusion electrode used to compare the power generation performance of the fuel cells of the sample of the example and the comparative example was a mixture of Teflon dispersion (40% by weight of platinum), a commercially available Nafion solution and isopropanol on commercially available carbon paper. It was prepared by coating so as to have a platinum amount of 0.35 mg / cm2. Using the gas diffusion electrode as a positive electrode and a negative electrode, samples of Examples and Comparative Examples were joined by hot pressing to form a fuel cell, and a hydrogen pressure of 2.5 atm (utilization rate 80%) and an air pressure of 2.5 atm ( Utilization rate 40%),
At a battery temperature of 80 ° C., V (voltage) -I (current density) characteristics were measured and compared.

As shown in FIG. 1, in the sample of the embodiment, the battery operates well even in the high current density region, but in the sample of the comparative example, the voltage suddenly decreases from the current density per 0.7 A / cm 2. The decline was seen. In general, this phenomenon is caused by the accumulation of generated water in the gas diffusion layer, that is, so-called flooding. Therefore, an attempt was made to adjust the humidification amount on the air electrode side and not perform humidification, but no improvement in performance was observed.

[0034]

The present invention has the following effects.

That is, the present invention has a high water content, and the surface is made of a water-repellent polymer electrolyte membrane, so that the electrode reaction is not adversely affected and sufficient power generation is achieved despite low internal resistance. An object of the present invention is to provide a solid polymer electrolyte fuel cell having high performance.

[0036]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a graph showing VI characteristics of an example of the present invention and a comparative example.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mitsuaki Kato 2-1-1 Asahi-cho, Kariya-shi, Aichi Prefecture Aisin Seiki Co., Ltd.

Claims (7)

[Claims] 1. A solid polymer electrolyte fuel cell comprising a solid polymer electrolyte membrane having an ion exchange ability and a positive electrode and a negative electrode arranged in contact with both sides thereof, wherein the surface of the solid polymer electrolyte membrane is A solid polymer electrolyte fuel cell comprising a solid polymer electrolyte membrane having water repellency due to a crosslinked structure of styrene and divinylbenzene. 2. The solid polymer electrolyte fuel cell according to claim 1, wherein the water repellent angle on the surface of the solid polymer electrolyte membrane is 85 ° or more. 3. The cation exchange membrane according to claim 1, wherein said solid polymer electrolyte membrane comprises a main chain formed of a copolymer of a fluorocarbon vinyl monomer and a hydrocarbon vinyl monomer and a hydrocarbon side chain having a sulfonic acid group. 2. The solid polymer electrolyte fuel cell according to claim 1, wherein the fuel cell is a membrane. 4. The method according to claim 1, wherein the main chain is (In the formula 1, R1 is a fluorine atom or a fluoroalkyl group having 1 to 3 carbon atoms, R2 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, m is an integer of 1 or more, and n is an integer of 1 or more.) Wherein the side chain is Wherein R3, R4 and R5 are each a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, s is an integer of 1 or more, and t is 0 or an integer of 1 or more. The solid polymer electrolyte fuel cell according to claim 3. 5. The solid polymer electrolyte fuel cell according to claim 4, wherein said main chain is an ethylene-tetrafluoroethylene copolymer. 6. The solid polymer electrolyte fuel cell according to claim 4, wherein the side chain is a styrene sulfonic acid polymer. 7. The main chain formed of a copolymer of a fluorocarbon vinyl monomer and a hydrocarbon vinyl monomer has γ
Irradiating with a beam or an electron beam, forming a styrene graft copolymer on the surface, contacting with divinylbenzene, sulfonating with a chlorosulfonic acid mixture, and treating the surface with chlorosulfonic acid alone. A solid polymer electrolyte fuel cell comprising a solid polymer electrolyte membrane produced from a step of forming a bridge of divinylbenzene and a step of hydrolyzing.