Preparation and Characterization of Proton Conductive Phosphosilicate Membranes Based on Inorganic-Organic Hybrid Materials

A series of proton conductive inorganic-organic hybrid membranes doped with phosphoric acid ( H₃PO₄ ) and/or triethylphosphate (PO(OEt) ₃ ) have been prepared by sol-gel process with 3-glycidoxypropyltrimethoxysilane (GPTMS), 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS) as precursors. High proton conductivity of 3.0 × 10⁻³ S/cm with composition of 50TEOS-30GPTMS-20APTES-50 H₃PO₄ was obtained at 120 ∘C under 50% relative humidity. Thermal stability of membrane was significantly enhanced by the presence of SiO ₂ framework up to 250 ∘C . XRD revealed that the gels are amorphous. IR spectra showed a good complexation of H₃PO₄ in the matrix. The conductivity under 75% relative humidity was significantly improved by addition of APTES due to the increase in concentration of defected site in hybrid matrix. The effect of PO(OEt) ₃ , humidifying time, and heat-treatment were also investigated. PO(OEt) ₃ had no improvement on conductivity and conductivity increased with humidifying time, however, decreased with heating temperature.