Intermediate-temperature composite proton electrolyte CsH5(PO4)2/SiO2: Transport properties versus oxide characteristic

Composite solid electrolytes (1 − x)CsH5(PO4)2/xSiO2 (x = 0–0.75) based on silica with different specific surface areas have been studied by the complex impedance, DSC, and X-ray diffraction methods. The proton conductivity of composites is shown to depend on the silica's specific surface area: the higher the specific surface area the stronger influence on the transport properties of composites. The maximal composite conductivity was 2.3 mS∙cm− 1 at T = 140 °C, which exceeded the conductivity of pure CsH5(PO4)2 by more than one order of magnitude. The drastic changes in the transport properties of composites are governed by the salt dispersion and/or amorphisation, which are confirmed by the changes in thermodynamic parameters. An H2/air fuel cell based on CsH5(PO4)2/SiO2 demonstrates a maximum power density of 8 mW/cm2 at U = 0.3 V and a current density up to 80 mA/cm2 at a short circuit.