Effects of Potassium-Based Activating Agents on the Biochar Derived from Coconut Tree Husk for Enhancing the Surface Area and Supercapacitor Performance

The growing demands for environmental and energy sustainability drive the development of energy storage devices with high energy and power densities and, consequently, potential electrode materials. The conversion of biomass waste into sustainable electrode materials has attracted much attention in the scientific community for energy storage applications. In this work, porous carbon is derived from the agricultural biowaste of the coconut tree (Cocos nucifera) husk. This biowaste is activated through a chemical activation method using different activating agents, such as K2CO3, KOH, KMnO4, KCl, KBr, and KI. Among the samples, biomass-derived carbon activated using the KMnO4 activating agent (AC3) delivers a high specific surface area of 2333.4 m2 g–1 with a pore volume of 2.625 cm3 g–1, which results in excellent electrochemical performance, with a gravimetric capacitance of 560 F g–1 at 2 A g–1 current density in 2 M KOH electrolyte solution. To demonstrate the real-time application, symmetric aqueous (KOH) and gel [poly(vinyl alcohol)-PVA/KOH] electrolyte devices are fabricated using the AC3@graphite sheet as positive and negative electrodes. The fabricated symmetric gel electrolyte device achieves a high gravimetric capacitance of 276 F g–1 at the current density of 2 A g–1. The above device manifests an energy density of 38.3 Wh kg–1 at a power density of 1 kW kg–1. Besides, the cycle stability retains 98% even after 5000 cycles at 10 A g–1 current density. These superior electrochemical outcomes suggest that this AC3@graphite sheet electrode will have potential in electric double-layer supercapacitors.