This work describes the preparation of hybrid membranes using octaphenyl polyhedral oligomeric silsesquioxane Ph8Si8O12 (POSS), either partially sulfonated (30%) or non-sulfonated as a filler and Nafion as polymer matrix. The membranes have been evaluated in terms of thermal stability (TGA, DSC), water uptake and ex situ in-plane proton conductivity. Morphology has been investigated using SEM and AFM. The hybrid membranes were electrochemically characterized into single cells in order to determine in situ through-plane proton conductivity, hydrogen crossover and cell performance. The analysis was made at 80 degrees C cell temperature, atmospheric pressure and different levels of relative humidity. The results showed the potential applicability of these membrane materials as electrolytes in PEMFC at medium/low humidity conditions. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.