A novel multifunctional catalyst CsxH3-xPW12O40/CeO2 was prepared to mitigate the free radical attack to membranes in fuel cell environment. CsxH3-xPW12O40/CeO2 nanoparticles synthesized by solution-based hydrothermal method and two-step impregnation method were dispersed Uniformly into the Nafion (R) resin, and then the composite membrane was prepared using solution-cast method. The particles prepared were characterized by X-ray powder diffraction (XRD), TEM and FT-IR to evaluate the crystallite size, distribution of the nanopaticles and the crystal structure. The membrane degradation was investigated via ex Situ Fenton test and in situ open Circuit voltage (OCV) accelerated test. In the durability tests, the fluoride emission rate (FER) reduced nearly one order of magnitude by adding CsxH3-xPW12O40/CeO2 nanoparticles into the Nafion membrane, suggesting that CsxH3-xPW12O40/CeO2 catalyst has a promising application to greatly improve the proton exchange membrane (PEM) durability. (c) 2009 Elsevier B.V. All rights reserved.