Characterization of cashew nut shell–derived biochar via O2-CO2 gasification for supercapacitor applications

Biochar derived from biomass waste has emerged as a promising sustainable electrode material for electrochemical energy storage applications. In this study, cashew nutshell-derived biochar was synthesized through an O 2 –CO 2 gasification process using a single-step self-sustainable reactor operating at approximately 1000 °C. The CO 2 -assisted thermochemical conversion promoted intrinsic activation and generated a mesoporous carbon structure with a specific surface area of approximately 45 m 2 /g. Despite the relatively low surface area and absence of chemical activation, the obtained biochar exhibited favorable electrochemical performance. In a three-electrode configuration using 6 M KOH electrolyte, the electrode delivered a high specific capacitance of 382 F/g at 1 A/g, indicating efficient charge storage behavior. A symmetric two-electrode device demonstrated with a low internal resistance of 2 Ω gives a specific capacitance of 58 F/g at 1 A/g, with a maximum energy density of 15.6 Wh/kg and a power density of 3500 W/kg. Furthermore, the device exhibited excellent cycling durability, retaining 105.8% of its initial capacitance after 5000 charge–discharge cycles. The enhanced electrochemical performance is attributed to the synergistic contribution of accessible mesopores, defect-rich carbon structure, and improved ion transport characteristics induced by the O 2 –CO 2 gasification environment. The present work demonstrates that O 2 –CO 2 gasification provides a simple, scalable, and sustainable route for producing biomass-derived carbon electrodes without additional chemical activation, offering significant potential for cost-effective and environmentally benign supercapacitor applications.