Natural polymers as sustainable precursors for scalable production of N/SOx doped carbon material enabling high-performance supercapacitors

Natural polymers-based carbon electrodes have gained significant research attention for next-generation portable supercapacitors. Herein, present an environmentally benign and novel approach for the synthesis of N/S-O_x carbon material derived from natural polymers on gram scale. By capitalizing the synergistic effect of sulfonated lignin and amino-containing chitosan, this methodology produces a straightforward, low-budget, and scalable process. The incorporation of sulfonate motifs from lignin contributes to the formation of C-SO_x moieties and multi-porous architecture with a high surface area. Simultaneously, amino groups in chitosan induce nitrogen doping, enhancing conductivity, and wettability. The resulting N/SO_x carbon material exhibits a micro/meso-porous architecture, facilitating electrolyte diffusion, and demonstrating improved rate capability and pseudocapacitance via Faradaic redox reactions. The N/SO_x carbon material showcases notable capacitance (392 F g⁻¹ at 1 Ag⁻¹) as compared with the reported carbon materials form biomass and outstanding cyclic stability (94.8% retention after 5000 cycles). By optimizing various chitosan mass ratios, the most effective N/SO_x carbon material SNACM = S/N-doped activated carbon material (SNACM-2) was produced using a lignin: chitosan sample ratio of 1:2 for symmetric supercapacitors. Furthermore, the quasi-solid-state symmetric supercapacitors based on SNACM-2 exhibit an excellent specific capacitance of 142 F g⁻¹ at 1 A g⁻¹, coupled with outstanding flexibility. The SNACM-2 demonstrates a high-energy density of 9.8 W h kg⁻¹ at a power density of 0.5 kW kg⁻¹. This study presents a successful strategy for transforming low-valued, eco-friendly natural polymers into renewable, high-performance carbon materials for supercapacitors.