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

Abstract

A series of proton conductive inorganic-organic hybrid membranes doped with phosphoric acid (<TEX>$H_3PO_4$</TEX>) and/or triethylphosphate (PO(OEt)<TEX>$_3$</TEX>) 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 <TEX>${\times}$</TEX> <TEX>$10^{-3}$</TEX> S/cm with composition of 50TEOS-30GPTMS-20APTES-50<TEX>$H_3PO_4$</TEX> was obtained at 120 <TEX>${^{\circ}C}$</TEX> under 50% relative humidity. Thermal stability of membrane was significantly enhanced by the presence of SiO<TEX>$_2$</TEX> framework up to 250 <TEX>${^{\circ}C}$</TEX>. XRD revealed that the gels are amorphous. IR spectra showed a good complexation of <TEX>$H_3PO_4$</TEX> 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)<TEX>$_3$</TEX>, humidifying time, and heat-treatment were also investigated. PO(OEt)<TEX>$_3$</TEX> had no improvement on conductivity and conductivity increased with humidifying time, however, decreased with heating temperature.