Green synthesis of S/P dual-heteroatom-doped walnut shell-based porous carbon for supercapacitor electrode materials

This study develops an environmentally friendly method to create S/P dual-doped porous carbon (WSC-SP-800) from walnut shells for supercapacitor electrodes. Compared with the raw carbon materials, WSC-SP-800 exhibits higher specific surface area, richer microporous and mesoporous structures, as well as superior electrochemical performance. The specific surface area rises from 1533.40 m 2  g −1 to 3061.96 m 2  g −1 , and the capacitance increases from 156 F g −1 to 417 F g −1 at a current density of 0.5 A g −1 . Additionally, WSC-SP-800 maintains a capacitance of 270 F g −1 even at a high current density of 10 A g −1 . When assembled into a symmetric supercapacitor, it achieves an energy density of 13.15 Wh kg −1 at a power density of 250 W kg −1 and retains 100 % of its capacity after 5000 cycles. This work not only achieves cost-effective, high-performance energy storage with environmentally benign characteristics but also establishes a novel paradigm for the valorization of biowaste through heteroatom engineering, providing a sustainable pathway for supercapacitor development.