Acid-functionalized silica-Nafion composite membranes with high proton conductivity

A series of new Nafion based composite membranes have been prepared via a in-situ sol-gel reaction of 3-(trihydroxylsilyl)propane-1-sulfonic acid and solution casting method. The morphological structure, ion-exchange capacity, water uptake, proton conductivity and methanol permeability of the resulting composite membranes have been extensively investigated as functions of the content of sulfopropylated polysilsesquioxane filler, temperature and relative humidity. Unlike the conventional Nafion/silica composites, the prepared membranes exhibit an increased water uptake and associated enhancement in proton conductivity compared to unmodified Nafion. In particular, considerably high proton conductivities at 80 and 120 °C under 30% relative humidity have been demonstrated in the composite membranes, which are over two times greater than Nafion. Apart from a remarkable improvement in proton conductivity, the composite membranes display lower methanol permeability in comparison with plain Nafion.