Impregnating hygroscopic nanoparticles, typically silica in Nafion membrane has received intense interest in high-temperature PEMFCs application due to increased water retention ability, proton conductivity and Mechanical stability. However, typical Nafion/silica membranes may suffer from potential durability degradation because of the instability of inorganic-organic electrostatic interface under humidifying conditions. Here, we investigate microstructural evolutions of this membrane and the subsequent performance. Aggregation and dissolving of silica nanoparticles and membrane fractures are observed under humidifying and RH cycling tests, thus leading to a significant decay of proton conductivities from similar to 0.095 S cm(-1) to similar to 0.055 S cm(-1) after 720 h of RH cycles. Simultaneously, H-2 crossover soars to nearly 40 times larger than the initial. Inorganic-organic interfaces are recognized to be crucial in the stability and performance of this type of composite membrane. The insight into the degradation process will provide meaningful reference for optimizing composite membranes and designing competent candidates for high-temperature PEMFCs operation. (c) 2013 Elsevier B.V. All rights reserved.