Preparation and characterization of proton-conducting CsHSO4–SiO2 nanocomposite electrolyte membranes

Microstructures and conductivity characteristics were investigated in proton-conducting CsHSO4–SiO2 composite electrolyte membranes prepared by CsHSO4 melt infiltration into porous SiO2 membranes with average pore sizes of 290 and 4 nm, respectively. XRD and TG-DTA analyses revealed that the pore-filled CsHSO4 proton-conducting phases in the nanocomposite electrolyte with the 290-nm SiO2 pores consisted of two crystallized CsHSO4 bulk phases and an amorphous CsHSO4 interface phase. For the electrolyte with 4-nm SiO2 pores, however, only the amorphous CsHSO4 interface phase dispersed with CsHSO4 crystallites was present in the nanocomposite. AC impedance measurements indicated that the proton-conducting characteristic of the nanocomposite with the 290-nm SiO2 membrane pores was similar to that of the pure CsHSO4 electrolyte, whereas the nanocomposite with 4-nm pores exhibited a high-temperature CsHSO4 proton-conducting characteristic across the entire testing temperature range, from nearly room temperature up to 200 °C, thus showing a significant enhancement in low-temperature conductivity vs. the pure CsHSO4 electrolyte—by two to three orders of magnitude. Moreover, the amorphous CsHSO4 interface phase in the nanocomposite with the 4-nm SiO2 pores was demonstrated to be stable even after having been kept at 40 °C for 1 week.