Protic ionic liquid-based gel polymer electrolyte: structural and ion transport studies and its application in proton battery

Abstract

Proton-conducting free standing gel polymer electrolyte (GPE) films containing protic ionic liquid, 1-butyl-3-methylimidazolium hydrogen sulphate, immobilized in blend of poly(vinylidenefluoride-co-hexafluoropropylene) and poly(vinylpyrrolidone) have been prepared by solution-cast technique. Films have been characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimetry (DSC), complex impedance spectroscopy, and cyclic voltammetry. Ionic conductivity of the semicrystalline and porous GPE films has been obtained as ~3.9 × 10−3 S cm−1 at room temperature. Protonic nature of conduction in the films has been established by performing cyclic voltammetry and complex impedance spectroscopy on the cells having both blocking (stainless steel) and both reversible electrodes (Zn + ZnSO4.7H2O). The electrochemical stability window of the films has been found as ~3.8 V. The highest conducting film has been used as a separator and proton conductor to fabricate a proton battery of configuration Zn + ZnSO4.7H2O |GPE film| PbO2 + V2O5. The battery shows an open circuit voltage of ~1.62 V. Energy density of the cell has been obtained as 35.2 W h kg−1 for low current drain. Rechargeability of the cell has been tested for ten cycles. The maximum discharge capacity of the cell has been obtained as ~2.50 mA h g−1 during the first discharge cycle.