Composite membranes were prepared using supercritical carbon dioxide (scCO(2)) impregnation and polymerization procedures and were optimized as electrolytes by controlling the amount of divinylbenzene (DVB) for polymerization. These poly(vinylidene fluoride)/polystyrene sulfonic acid (PvdF/PSSA) membranes were characterized by various methods. The cross-sectional superficial morphology and structure of the PVdF/PSSA membranes were analyzed by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), FT-IR and small-angel X-ray scattering (SAXS). The ion exchange capacity (IEC), ion conductivity, methanol permeability and cell performance of PVdF/PSSA membranes were measured and compared with Nafion 115. As the concentration of added DVB increased, the ion conductivity and methanol permeability of the PVdF/PSSA membranes decreased. The PVdF/PSSA membrane containing 7.5 wt% DVB achieved 94% of the current density with Nafion 115. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.