Phosphonic acid functionalized aminopropyl triethoxysilane–PVA composite material: organic–inorganic hybrid proton-exchange membranes in aqueous media

Abstract

Poly(vinyl alcohol)–silica composite proton-exchange membranes were prepared by a sol–gel process in acidic conditions using aminopropyltriethoxysilane as an inorganic precursor and functionalized with phosphonic acid. Phosphorylation of the membranes was confirmed by Fourier transform infrared (FTIR) spectroscopy and ion-exchange capacity (IEC) studies. These membranes were extensively characterized for their thermal and mechanical stabilities, physicochemical and electrochemical properties using thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), water uptake studies, proton conductivity and methanol permeability measurements. The silica content in the membrane matrix and the time allowed for the phosphorylation were optimized as functions of the membrane properties. It was observed that the PVA–silica composite acts as an excellent methanol barrier possessing good hydrophilicity and proton conductivity. Moreover, from estimation of the selectivity parameter among all the synthesized membranes, 50% silica composition and 3 h of phosphorylation resulted in the best proton-exchange membrane, which exhibited about 20% more suitability in comparison to Nafion 117 membrane for direct methanol fuel cell applications.