Preparation and characterization of hybrid membranes based on Nafion® using partially sulfonated inorganic fillers

This work reports the preparation and characterization of inorganic hybrid membranes cast from solutions of perflouorinated sulfocationic ionomers (Nafion® 117) containing 10 wt % dispersed inorganic fillers. Silica gel, SBA-15 and sepiolite, all of them partially functionalized with sulfonic acid groups, were used as fillers. Fillers slightly reduce the water uptake without altering the ion-exchange capacity of the membrane composites. FTIR and DMTA analysis techniques suggest that filler-polymer matrix interactions are stronger with sepiolite than with the other fillers. The fillers used enhance the mechanical properties of the membranes, but they negatively affect the thermal stability of the composites. The permeability coefficient of oxygen in Nafion® and Nafion®-sepolite membranes is similar, and it is slightly lower in the others. The conductivity of the hybrid membranes equilibrated with water, measured at 80° C by impedance spectroscopy, is 4.0, 6.0 and 6.3 S/m for the hybrid membranes containing functionalized Silica gel, SBA-15 and Sepiolite fillers, respectively, somewhat lower than that found for the Nafion® 117 membrane, 5.9 S/m, measured in the same conditions.