Patent ID: 8557472

Claim:
A proton-conducting polymer membrane, comprising: a polymer membrane comprising a polybenzimidazole compound having a sulfonic acid group and/or a phosphonic acid group; and vinylphosphonic acid contained in the polymer membrane; wherein the mass of the vinylphosphonic acid contained in the polymer membrane is between 0.1 and 10 times the mass of the polybenzimidazole compound, and wherein said polybenzimidazole compound comprises a component that contains a sulfonic acid group and/or a phosphonic acid group and is represented by Structural Formula (1): wherein n represents an integer of 1 to 4, R 1 represents a tetravalent aromatic linking unit capable of forming an imidazole ring, R 2 represents a bivalent aromatic linking unit, and Z represents a sulfonic acid group and/or a phosphonic acid group.