In the present study, a novel composite methanol-blocking polymer electrolyte membrane was prepared by anchoring water-soluble phosphotungstic acid (HPW) in bulk phase of Nation through interactions between HPW and Cs(+) ions. Results of morphology and elemental mapping analysis indicated that this composite membrane had a dense structure with uniformly distributed Cs-HPW clusters. The composite membrane exhibited a rather low methanol diffusion coefficient (P, 0.97 x 10(-6) cm(2) s(-1)) and also the comparable conductivity (sigma, 3.6 x 10(-2) S cm(-1)) contrast with pristine Nafion (sigma, 5.1 x 10(-2) S cm(-1)). The selective factor (sigma/P) of the composite membrane was six times higher than that of pristine Nation. Single cell performance results showed that the maximum power density increased by 26% over the cell performance of pristine Nation under the same conditions. (C) 2010 Elsevier B.V. All rights reserved.