High-temperature behavior of CsH2PO4 and CsH2PO4–SiO2 composites

• Published in: Solid state ionics 2007-04, Vol.178 (7-10), p.729-734
• Main Authors: PONOMAREVA, V, SHUTOVA, E
• Format: Article
• Language: English
• ISSN: 0167-2738
• DOI: 10.1016/j.ssi.2007.02.035

We report a comparative study of transport and thermodynamic properties of CsH2PO4 and (1-x)CsH2PO4/xSiO2 composite electrolytes (x=0.2-0.7) based on various types of silica. The role of acidic centers of silica surface for chemical and thermal stability of CsH2PO4 in composites at 200-230 deg C has been shown. Silica modified by small amounts of CsHSO4 and H3PO4 has been obtained. Heterogeneous doping by modified silica causes a significant increase of the low temperature conductivity of CsH2PO4 due to disordered state of salt. The composite systems with modified silica exhibit high proton conductivity, 10-3-10-2 S/cm at 130-250 deg C and have higher thermal stability at lower water vapor partial pressures comparing with the pure salt. Contrary to the former, composites based on highly dispersed SiO2 (Ssp 41-520m2/g) with pH 7 exhibit the low proton conductivity at T > 220 deg C due to strong interface interaction and Cs2H2P2O7 formation. The phase composition of the systems which depends on x has been determined. The investigations have been carried out by means of X-ray diffraction, differential scanning calorimetry, IR and complex impedance spectroscopy at different atmosphere humidity.