Porous carbon from verbena straw with self-doped O/N and its high-performance aqueous and flexible all-solid-state supercapacitors

This study presents a novel approach for preparing a porous carbon electrode material from waste biomass with significant advantages, such as low-priced, simple synthesis process, environmental sustainability, and outstanding electrochemical performance, making it highly relevant in the area of energy storage for supercapacitors (SCs). Verbena straw with a loose hollow structure is selected as the precursor, the proposed K2CO3/NaCl synergistic preparation route successfully yields a highly efficient porous activated carbon electrode material (VSC-800) with a high surface area of 2055 m2 g−1, plentiful pores (1.262 cm3 g−1), and enriched oxygen and nitrogen self-doping. Impressively, VSC-800 exhibits outstanding specific capacitance of 438 F g−1 at 0.5 A g−1. Furthermore, a high specific capacitance of 362.3 F g−1 is achieved by flexible all-solid-state symmetric SCs utilizing a PVA/KOH gel electrolyte at 0.5 A g−1, resulting in an impressive energy density of 21.3 Wh kg−1. This work provides a feasible approach for the environmentally friendly utilization of waste biomass materials and emphasizes the immense promise of utilizing waste biomass-derived porous carbon in creating flexible all-solid-state SCs with exceptional performance.