Organic-inorganic hybrid membrane: Thermally stable cation-exchange membrane prepared by the sol-gel method

Organic-inorganic hybrid membranes based on poly(vinyl alcohol)-SiO2 were prepared under acidic and basic conditions, in which sulfonic acid groups were introduced at the inorganic segment. These membranes were extensively characterized for their morphology, intermolecular interactions, thermal and mechanical stability, and physicochemical properties using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and water uptake studies. Schematic models for acid-catalyzed linear weakly polymeric clusters and for base-catalyzed highly branched polymeric clusters were proposed. A higher ion-exchange capacity, perm-selectivity, and conductivity for the acid-catalyzed hybrid membranes than for the base-catalyzed membranes with the same composition indicated that the former route is suitable for the preparation of ion-exchange membranes. The electrochemical properties of the membrane and the equivalent pore radius were found to be highly dependent on Si content in the membrane phase. It was concluded that a definite compromise between the silica content and the membrane ion-exchange properties is required in order to have an organic-inorganic hybrid cation-exchange membrane. Furthermore, the physicochemical and electrochemical properties of these membranes were comparable to those of Nafion membrane, which suggests that they may be suitable for fuel cell and chlor-alkali applications as a substitute for Nafion membrane.