Biowaste-derived honeycomb-like hierarchical porous activated carbon from justicia adhatoda stem for high-capacity flexible supercapacitors

Activated carbon synthesized from bio-waste sources as a reliable option for developing efficient electrodes for electrochemical energy storage applications, owing to its natural abundance and clean, sustainable nature, positioning it as a viable alternative to fossil fuels. This work reports the synthesis of a 3D honeycomb-structured porous activated carbon (AC) derived from the Justicia Adathoda (JUAD) through carbonization process, followed by KOH activation. Benefiting from the optimal activation temperature of 700 °C, the JUAD-derived AC exhibits a well-developed three-dimensional honeycomb-like porous architecture with remarkably enhanced electrochemical response of the material. JUAD-700-derived activated carbon exhibits a specific capacitance of 430.97 F g⁻¹ at a current density of 0.5 A g⁻¹ and retains 99% of its capacitance even over 9000 GCD cycles. Further, a symmetric flexible device assembled through JUAD-700 electrodes (SJC-700) delivers a specific capacitance of 184 F g⁻¹ at a current density of 0.5 A g⁻¹, along with an impressive energy density of 83.14 Wh kg⁻¹ and a power density of 16.2 kW kg⁻¹. Notably, SJC-700 maintains 81.5% of its capacitance later 8000 charge-discharge cycles, along coulombic efficiency of 97.7%, highlighting its excellent cycling stability. The overall results clearly indicate that JUAD-700-derived activated carbon is a promising and economical material for use in supercapacitors (SCs), being an excellent bio-derived source of carbon waste.