Synthesis of N/O/S Co-doped activated carbon from thiamethoxam-modified peanut shell for solid-state asymmetric supercapacitor with superior energy and power densities

Multi-element heteroatom doping is more effective than single-element doping for improving the supercapacitor performance of biomass-derived carbon. However, identifying suitable dopant sources and efficient synthesis routes remains challenging. In this study, N/O/S co-doped waste peanut shell-derived carbon (PSAC) was synthesized through carbonization, in-situ thiamethoxam doping, and CO 2 activation. Spectroscopic and microscopic characterizations revealed that the N/O/S co-doped activated carbon (N/O/S-PSAC) possessed a compact morphology with an irregular porous surface, uniformly distributed heteroatoms, and hierarchical porosity. The mass ratio of thiamethoxam to the peanut shell precursor was systematically optimized to tune the mass density, surface porosity, and dopant content of N/O/S-PSAC. The optimized N/O/S-PSAC-5 exhibited enhanced charge-storage performance, delivering gravimetric and volumetric capacitances of 337.96 F g −1 and 380.88 F cm −3 , respectively, at 0.2 A g −1 . The electrode also demonstrated excellent cycling stability in 6 M KOH, retaining 98.32% of its initial capacitance after 10,000 cycles. An asymmetric solid-state supercapacitor constructed using the developed electrodes and a copolymer-based gel electrolyte achieved an energy density of 40.97 Wh kg −1 at 2000 W kg −1 , together with 97.4% capacitance retention after 10,000 cycles and remarkable voltage retention during self-discharge. This study demonstrates the potential of waste peanut shell-derived N/O/S co-doped carbon as a green, renewable, and cost-effective electrode material for high-performance supercapacitors.