Utilization of Waste Rice Husk to Derive Graphitic Carbon Nanosheets as Novel Electrode Materials for the Fabrication of Symmetric Supercapacitor

The biomass-derived carbon-based electrode materials have gained huge attention due to their cost-effective preparation. Therefore, this study proposed the derivation of hierarchical carbon nanosheets from rice husks via carbonization and activation in KOH at different temperatures (600, 700, 800, and 900 °C). The inactivated carbon material exhibits the lowest surface area of 69 m2g− 1 and becomes the largest (1985 m2g− 1) at an activation temperature of 900 °C. The increasing activation temperature enhances the structural ordering and partial stacking of graphene layers. The ID/IG ratio decreases from 0.94 to 0.24 with increasing the activation temperature from 600 to 900 °C, which reflects the etching of the amorphous carbon. At maximum activation temperature (900 °C), the carbon materials progressively exfoliated into few-layer graphene-based nanosheets, offering high surface area. The intensity ratios of sp2/sp3 hybridized carbon is increased (2.95–9.14) with increasing temperature, thereby indicating increasing graphitization. The maximum specific capacitance of 914 Fg− 1 at a current density of 0.75 Ag− 1 is calculated for the sample activated at 900 °C. The sample activated at 900 °C is demonstrates cyclic stability of 96% after 10,000 cycles and charge transfer resistance of 0.062 ohms. The assembled symmetric supercapacitive device displays a specific capacitance of 214 F/g at 0.5 A/g, capacitance retention of 95.23% for 10,000 cycles, and minimum power of 532 W/kg at maximum energy density of 29 Wh/kg.