Polymer electrolyte membrane having excellent durability

Abstract

A polymer electrolyte membrane for a polymer electrolyte fuel cell, that overcomes disadvantages of the conventional polymer ion-exchange membranes including fluorine-based polymer electrolyte membranes and can maintain cell characteristics even in use over a long period of time (e.g., several thousand hours). The polymer electrolyte membrane comprises a fluorine polymer substrate having grafted thereon monomers having sulfone groups as a cation-exchange group, wherein a main chain of the graft chain comprises a hydrocarbon or a partially fluorinated hydrocarbon, and sulfone groups or substituents having sulfone groups are bonded as a side chain, and wherein in element compositional ratio by ESCA, at least one surface of the polymer electrolyte membrane has O/S value of 5.0 or higher, and a surface element proportion of S is 0.4-5.0%.

Dependencies are inferred from the claim text.