Capacitive dominated charge storage in supermicropores of self-activated carbon electrodes for symmetric supercapacitors

Abstract

The present work demonstrates a systematic study of pore size and specific surface area (SSA) of biomass-derived carbon and the choice of electrolyte concentrations affecting charge-storage mechanism (surface controlled and diffusion controlled) and electrochemical behaviour. Porous nanocarbons derived from Caesalpinia Sappan pods were synthesized by pyrolysis at 400, 600, and 800 °C. Pyrolysis at 800 °C was found suitable for the self-activation mechanism which formed bimodal porous nanocarbons with a high SSA of 675 m2/g. A maximum specific capacitance of 261.8 F/g at 0.5 A/g in 5.0 M KOH was observed for electrode materials synthesized at 800 °C. The highlight of the study is the porous nanocarbon synthesized at 800 °C which was found to possess micropores of size 0.7–1.0 nm playing a pivotal role in enhancing capacitance. The effect of electrolyte concentration on capacitance and charge storage mechanisms was also analyzed. A diffusion-controlled self-discharge model is established for supercapacitor devices. The single cell can power a red LED for 15 min; exemplifying the sustainable strategy of the utilization of abundant bio-waste to efficient energy storage devices.