Waste biomass-derived N, S-codoped porous carbon flakes for high energy density asymmetric supercapacitors

Production of affordable energy devices requires the fabrication of cheap electrode materials with high energy and power densities and long cycle stability. Carbon materials retrieved from waste biomass in sugar mills have attracted considerable attention because of their low-cost and environmental benefits. But their low capacitance and poor rate-capability still remain serious issues. Herein, activated N, S-codoped porous carbon (NS-WSB-AC) was synthesized via simultaneous in-situ and gas-phase heteroatom doping, carbonization, and KOH + CO₂ activation processes, where waste sugarcane bagasse (WSB) as a carbon source, hydrazine as a nitrogen source and H₂S gas as a sulfur source were used. As-prepared NS-WSB-AC exhibited a high specific surface area of 2455.6 m²/g, a large mesoporosity of 0.4784 cm³/g, and a substantial heteroatom content (19.45 atom%). Because of these features, the NS-WSB-AC achieved a high specific capacitance of 405.67 F/g at 0.2 A/g with remarkable rate-performance (72.7 % at 5 A/g) in a 6 M KOH electrolyte. However, the NS-WSB-AC demonstrated outstanding cycling stability (98.7 % capacitance retention after 10000 cycles) in a 1 M Na₂SO₄ electrolyte. The NS-WSB-AC//WSB-AC ASC device with KOH electrolyte exhibited a superior energy density of 54.73 Wh kg⁻¹ at a power density of 207.8 W kg⁻¹ when compared to the Na₂SO₄-based device.