Stabilization of the (C2H5)4NHSO4 High-Temperature Phase in New Silica-Based Nanocomposite Systems.

Abstract

In this study, the electrotransport, thermal and structural properties of composite solid electrolytes based on (C2H5)4NHSO4 plastic phase and silica (1 - x)Et4NHSO4-xSiO2, where x = 0.3-0.9) were investigated for the first time. The composites were prepared by mechanical mixing of silica (300 m2/g, Rpore = 70Å) and salt with subsequent heating at temperatures near the Et4NHSO4 melting point. Heterogeneous doping is shown to change markedly the thermodynamic and structural parameters of the salt. It is important that, with an increase in the proportion of silica in the composites, the high-temperature disordered I41/acd phase is stabilized at room temperature, as this determines the properties of the system. Et4NHSO4 amorphization was also observed in the nanocomposites, with an increase in the matrix contents. The enthalpies of the endoeffects of salt melting and phase transitions (160 °C) changed more significantly than the Et4NHSO4 contents in the composites and completely disappeared at x = 0.9. The dependence of proton conductivity on the mole fraction reached a maximum at x = 0.8, which was three or four orders of magnitude higher than the value for pure Et4NHSO4, depending on the composition and the temperature. The maximum conductivity values were close to those for complete pore filling. The conductivity of the 0.2Et4NHSO4-0.8SiO2 composite reached 7 ∗ 10-3 S/cm at 220 °C and 10-4 S/cm at 110 °C.