Polymer electrolyte fuel cell, electrolyte material therefore and method for its production

Abstract

An electrolyte material for a polymer electrolyte fuel cell, which is made of a copolymer comprising repeating units based on CF2═CFCF2OCF2CF2SO3H and repeating units based on tetrafluoroethylene and which has an ion exchange capacity of from 0.9 to 1.5 (meq / g dry resin). This electrolyte material has ion conductivity and durability equal to conventional electrolyte material, is easy to synthesize, has a softening point higher than electrolyte material heretofore widely used for application to fuel cells and is suitable for operation of a polymer electrolyte fuel cell at a temperature higher than the conventional material.

Description

DESCRIPTION TECHNICAL FIELD The present invention relates to an electrolyte material for a polymer electrolyte fuel cell, and a polymer electrolyte fuel cell. BACKGROUND ART As an electrolyte material to be used as a polymer electrolyte membrane or a proton conductive polymer to be incorporated in a catalyst layer of an electrode constituting a polymer electrolyte fuel cell, it has been common to employ a polymer obtained by hydrolyzing a copolymer of tetrafluoroethylene (hereinafter referred to as “TFE”) with a perfluorovinyl ether of the formula (A), followed by treatment for conversion to an acid-form to convert —SO2F groups to —SO3H groups. In the formula (A), Y is a fluorine atom or a trifluoromethyl group, m is an integer of from 0 to 3, n is an integer of from 1 to 12, and p is 0 or 1, provided that (m+p)>0. CF2═CF(OCF2CFY)mOp(CF2)nSO2F  (A) Among such polymers, particularly preferably employed is one obtained by converting a polymer obtainable by copolymerization of TF...

AI Technical Summary

Benefits of technology

The present invention has been made in view of the problems which the above-mentioned prior art has had, and it is an object of the present invention to provide an electrolyte material for a polymer electrolyte fuel cell which is easy to synthesize and which has an ion conductivity and durability equal to the above-mentioned conventional electrolyte materials, and to provide a polymer electrolyte fuel cell constituted by using such a material.

The present inventor has conducted an extensive research to accomplish the above object and as a result, has found it possible to obtain a polymer having a practically sufficient ion exchange capacity and a sufficient molecular weight and having a higher content of the monomer (2) than U.S. Pat. No. 4,273,729 or Journal of Applied Polymer Science, Vol. 47, 735-741 (1993), by improving the polymerization conditions. Further, it has been found that a TFE / monomer (2) copolymer prepared by adjusting the ion exchange capacity within a prescribed range, has sufficient ion conductivity and durability at the same time, and thus, the present invention has been accomplished.

The electrolyte material for a polymer electrolyte fuel cell of the present invention can be prepared without using hexafluoropropylene oxide as a raw material, whereby as compared with the above-mentioned conventional electrolyte material, the production cost can be substantially reduced. Further, the electrolyte material for a polymer electrolyte fuel cell of the present invention has excellent ion conductivity and durability equal to the conventional electrolyte material, since its ion exchange capacity (hereinafter referred to as AR) is from 0.9 to 1.5 (meq / g dry resin) (hereinafter referred to simply as meq / g).

Problems solved by technology

However, although the above-mentioned conventional copolymer was excellent in such properties as an ion conductivity to accomplish a high cell output power and durability to make a long term operation possible, it had a problem that the production cost was high, and it could not be produced at low costs.

However, the polymer synthesized for brine electrolysis in an Example (UTILITY EXAMPLE Q) of this patent publication, has an ion exchange capacity of 0.85 (meq / g dry resin) (equivalent weight: 1180), and thus, the ion exchange capacity is inadequate for a fuel cell, whereby it has a problem that the resistance is practically too high.

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