Proton-conductive membranes doped with orthophosphoric acid based on inorganic-organic hybrid materials

A series of proton-conductive inorganic-organic hybrid membranes doped with phosphoric acid (H3PO4) have been prepared by the sol-gel process with 3-glycidoxypropyltrimethoxysilane (GPTMS), 3-aminopropyltriethoxysilane (APTES), and tetraethoxysilane (TEOS) as precursors. High proton conductivity of 3.0 x 10(-3) S/cm with a composition of 50TEOS-30GPTMS-20APTES-50H(3)PO(4) was obtained at 120 degrees C under 50% relative humidity (RH). The differential thermal analysis curve showed that thermal stability of membrane is significantly enhanced by the presence of an SiO2 framework up to 250 degrees C. X-ray ray diffraction revealed that the gels were amorphous. Infrared spectra showed a good complexation of H3PO4 in the matrix. The porous hybrid membrane, characterized by scanning electron microscopy, shows humidity-dependent conduction, and the conductivity under 75% relative humidity was significantly improved by addition of APTES due to the increase in the concentration of the defective site in the hybrid matrix.