Poly(vinyl)alcohol/1-butyl-3-methylimidazolium hydrogen sulfate solid polymer electrolyte: Structural and electrical studies

Proton conducting polymer electrolyte membranes consisting of poly(vinyl)alcohol and 1-butyl-3-methylimidazolium hydrogen sulfate ionic liquid are prepared by solution cast technique. The membranes are found to be free-standing and mechanically stable for the 40, 60 and 80 wt.% concentration of ionic liquid. The membranes have been characterized by X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, complex impedance spectroscopy and cyclic voltammetry. The crystallinity and melting point of the membranes are found to decrease with increasing concentration of ionic liquid. The membrane with 80 wt.% ionic liquid has been found to be completely amorphous. The highest ionic conductivity has been found to be ~ 10− 3 S cm− 1 at room temperature for the membrane with 80 wt.% ionic liquid. The variation of ionic conductivity with temperature follows Arrhenius type behavior in the temperature range of 40-130 °C. The membranes show protonic conduction as established by cyclic voltammetry and complex impedance spectroscopic studies. The electrochemical window of the membranes has been found to be ~ 3.4 V.