The investigation of disordered phases in nanocomposite proton electrolytes based on MeHSO 4 (Me=Rb, Cs, K)

Abstract

Properties of alkali metal hydrogensulphate MeHSO 4 (Me=Cs, Rb, K) in (1− x)MeHSO 4– xA (A=Al 2O 3, TiO 2, SiO 2; x=0–0.9) nanocomposite solid electrolytes were studied by X-ray powder diffraction, differential scanning calorimetry methods and conductivity measurements. The conductivity of the composites was shown to exceed that of the individual salts by more than 1–3.5 orders of magnitude and to depend on composition. The conductivity and thermal stability of (1− x)CsHSO 4– xA composites increase in the order Al 2O 3<TiO 2<SiO 2. The properties of composites (1− x)MeHSO 4– xSiO 2 depend markedly on the grain and pore size of silica. The optimum SiO 2 pore size was in the range 35–100 Å, where the highest composite conductivity was observed. For these composites, the enthalpies of CsHSO 4 and RbHSO 4 phase transitions and melting decreased considerably and the thermal stability increased. The ionic component became amorphous. Analysis of calorimetric data indicated the presence of two crystalline phases with different temperatures of phase transition and melting in the composites with silica of pore size 170 Å. The MeHSO 4 state changed slightly when the SiO 2 pore size was 1000 Å. In the systems with pore size of 14 Å, both crystalline and amorphous salts were observed.