Patent ID: 6926984

Claim:
A membrane electrode assembly comprising a pair of electrodes, and a polymer electrolyte membrane sandwiched by both electrodes, said polymer electrolyte membrane being obtained by subjecting an ion-conducting, aromatic polymer membrane to a hot-water treatment, said ion-conducting, aromatic polymer membrane having a maximum water absorption in a range of 80-300 weight % based on its dry weight before said hot-water treatment, wherein said ion-conducting, aromatic polymer membrane is a sulfonated polyarylene membrane, wherein said sulfonated polyarylene membrane is subjected to a hot-water treatment by immersion in hot water at 80-95° C. for 0.5-5 hours by itself or in the form of a membrane electrode assembly, wherein said sulfonated polyarylene is a sulfonated arylene copolymer obtained by introducing a sulfonic group into a side chain of a copolymer comprising 30-95 mol % of a first aromatic monomer unit represented by the following chemical formula (1): wherein Ar is an aryl group, and X is a bivalent electron-attractive group selected from the group consisting of —CO—, —CONH—, —(CF 2 ) p — wherein p is an integer of 1-10, —C(CF 3 ) 2 —, —COO—, —SO— and —SO 2 —, and 70-5 mol % of a second aromatic monomer unit represented by the following chemical formula (2): wherein X is the same as in the chemical formula (1) and may be the same as or different from each other, and a is an integer of 0-3.