High-temperature behavior of CsH2PO4 and CsH2PO4–SiO2 composites

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 °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 °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 ∼ 41–520 m2/g) with pH ∼ 7 exhibit the low proton conductivity at T > 220 °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.