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 (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-50H 3PO4 was obtained at 120 °C under 50% relative humidity. Thermal stability of membrane was significantly enhanced by the presence of SiO2 framework up to 250 °C. XRD revealed that the gels are amorphous. IR spectra showed a good complexation of H 3PO4 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.