Enhancement in performance of supercapacitor using eucalyptus leaves derived activated carbon electrode with CH3COONa and HQ electrolytes: A step towards environment benign supercapacitor

Abstract

Abstract The present work specifies capacitive characteristics of supercapacitors built from electrodes derived from biomass (viz., Eucalyptus leaves) and environment-friendly electrolytes. Activated carbon is derived from eucalyptus leaves and used as electrodes. The electrolytes used are environment benign electrolyte sodium acetate (1 M CH3COONa) (free from harmful F- and S- compounds) and CH3COONa added hydroquinone (HQ-redox additive). A chemical activation approach (ZnCl2–KOH) was adopted to synthesize the activated charcoal. Further, it was characterized using BET, XRD, RAMAN, SEM, and FTIR techniques. The specific BET surface area of activated charcoal is found to be 2639 m2 g−1. The performance characteristics of the supercapacitor cells were characterized by cyclic-voltammetry, charge-discharge, and electrochemical impedance spectroscopy techniques. It was observed that the supercapacitor cell utilizing pristine electrolyte CH3COONa shows a specific capacitance of 213 F g−1 and a corresponding energy density of 16.2 WhKg−1 at a specific current of 0.75 A g−1. Interestingly, the values of specific capacitance and energy density increased more than 3-fold to 702 F g−1 and 47.2 WhKg−1 respectively when the electrolyte consisting of redox additives (hydro-quinone) HQ in sodium acetate solution was used. A possible reason for such a behaviour is the Faradic redox reaction between the HQ/Q redox couple. The obtained results were compared for different electrolyte systems 1 M Na2SO4 (with and without HQ) for the same electrode. It was observed that supercapacitor cells fabricated by utilizing CH3COONa based electrolyte system exhibit better capacitive performance. The optimized supercapacitor cells were also tested in a harsh environment by varying the temperature from 25 °C to 60 °C and it shows improvement in capacitive performance with increase in temperature. Cyclic stability of supercapacitor cells was also tested for up to 10,000 cycles and it shows appealing results by offering capacitive retention of more than 122% for the optimized capacitor cell.