Preliminary Study on the Performance of a Redox Capacitor with the use of Ionic Liquid-based Gel Polymer Electrolyte and Polypyrrole Electrodes

Redox capacitor, which is one type of supercapacitor, has been attracted tremendously as they show a satisfactory specific capacitance, good cycle ability, and good stability. The present study reveals a redox capacitor fabricated with an ionic liquid (IL) based gel polymer electrolyte (GPE). Electrodes of the redox capacitor were fabricated with the conducting polymer, polypyrrole (PPy). The composition of the GPE was polyvinylidenefluoride-co-hexafluoropropylene (PVdF-co-HFP) : 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (1E3MITF) : ZnTF. Characterization of redox capacitor was done by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charge-discharge (GCD) tests. The relaxation time constant (τ0) of the redox capacitor is about 31.57 s implying somewhat fast redox reactions. Initial single electrode specific capacitance (CSC) was 150.16 Fg-1 and at the 500th cycle, it was 40.03 Fg-1. The decrease of the CSC may be due to the formation of the passivation layer at the GPE / electrode interface resulting in degradation upon cycling. The GCD test resulted 48.40 Fg-1 of initial single electrode specific discharge capacitance (Csd) value. Upon 1000 cycles, it was reached 22.25 Fg-1. The decrease of Csd may be due to the degradation of the electrode and the IL-based GPE upon prolonged cycling.