Mesoporous composites made of silica and α-zirconium phosphate (SiO2·xZrP) were synthesized from mixtures of delaminated ZrP dispersions and tetrapropylammonium oligosilicate solutions. The surface area of the composites attained a maximum of 700m2/g for x-values of about 0.02. The average pore diameter was equal to about 40Å for x-values ranging from 0.05 to 0.35. In order to increase proton conductivity at low relative humidities, SiO2·xZrP·yH3PO4 composites were characterized by performing 29Si and 31P magic-angle scanning nuclear magnetic resonance and conductivity measurements. At 100C and 6% relative humidity, the conductivity of the composites, with H3PO4 loadings of 80% of the pore volume, rose from 5 x 10-4 to 2 x 10-2S/cm for as x decreased from 0.35 to 0.05; due to a concomitant increase in pore volume. For a composite with x = 0.18, the dependence of the conductivity upon H3PO4 loading was also investigated for different temperatures and relative humidity values. A combined increase in humidity, temperature and H3PO4 loading resulted in an increase in conductivity from 10-7S/cm (y = 0.09, T = 25C, 0% relative humidity) to 4 x 10-2S/cm (y = 0.61, T = 100C, 30% relative humidity).

Silica–Zirconium Phosphate–Phosphoric Acid Composites - Preparation, Proton Conductivity and Use in Gas Sensors. P.Armento, M.Casciola, M.Pica, F.Marmottini, R.Palombari, F.Ziarelli: Solid State Ionics, 2004, 166[1-2], 19-25