Few layer graphene nanosheets from kinnow peel waste for high-performance supercapacitors: A comparative study with three different electrolytes

Utilization of carbonaceous waste into energy storage applications not only solves the problem of waste management but also promotes the circular economy. Any carbonaceous material with a high surface area and sheet-like nanostructure facilitates fast-ion transport due to which it can act as a suitable candidate for the electrode material in Supercapacitors. This work reports the preparation of few-layer graphene nanosheets from fruit waste: kinnow peel waste (KPW) for the first time, via two-step pyrolysis with activation using KCl as the activating agent followed by probe sonication. The confirmation of few-layer graphene (FLG) nanosheets from KPW was done with the help of RAMAN, XRD, FT-IR, SEM, and TEM. The high surface area with the presence of both the meso and micropores in synthesized FLG nanosheets was confirmed with the help of BET. The KPW-derived few-layer graphene (KPW-FLG) nanosheets were further investigated for high-performance supercapacitors by fabricating three different supercapacitor devices (SCs); SC-1, SC-2, and SC-3 corresponded to 6 M KOH, 1 M H<inf>2</inf>SO<inf>4</inf> and 1 M H<inf>3</inf>PO<inf>4</inf> respectively. The ideal and reversible capacitive behavior of the fabricated SC devices was analyzed with the help of Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) techniques. The SC-2 displayed the highest gravimetric specific capacitance (C<inf>s</inf>) value of 642 F/g at a scan rate of 5 mV/s in a 1 M H<inf>2</inf>SO<inf>4</inf> electrolyte with the highest energy density of 48.9 Wh/Kg and better power density of 629.5 W/Kg. Our study revealed that the KPW-FLG can be used as the potential candidate for electrode material in fabricating the high-performance supercapacitor which showed the best results in capacitance, charge-discharge, cyclic stability, and energy density with 1 M H<inf>2</inf>SO<inf>4</inf> electrolyte.