Perchloric acid functionalized nano-silica and protic ionic liquid based non-aqueous proton conductive polymer electrolytes

Abstract

Both protic ionic liquids (PILs) and superacids are known to be rich sources of protons and their good carrier as well. Herein, we report a novel approach in developing non-aqueous proton conductive nanocomposite electrolytes (PCNEs) by making composite of a PIL; diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]) and a superacid; perchloric acid (HClO4). Initially, HClO4 was immobilized on nano-silica powders; and then both ([dema][TfO]) and HClO4·SiO2 were incorporated into poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix. X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy suggest decrease in overall crystallinity of the composite membranes on addition of [dema][TfO]. Scanning electron microscopy (SEM) images show that microstructures such as spherulite structures and micropores on the membrane surface evolves with [dema][TfO] concentration. At 80 wt% of [dema][TfO], the density of pores appears on the membrane surface is maximum. The dc ionic conductivity is also observed to be increasing with [dema][TfO] concentration. The maximum conductivity of 0.02 mS cm−1 and 0.6 m Scm−1 are achieved at room temperature (30 °C) and 100 °C, respectively for 80 wt% of [dema][TfO]. This ionic conductivity variation is well correlated with the increase in pore density and decreasing crystallinity of the PCNE film.