An environment-friendly strategy to prepare oxygen-nitrogen-sulfur doped mesopore-dominant porous carbons for symmetric supercapacitors

We report an environment-friendly method of particular mesopore-dominant oxygen-nitrogen-sulfur co-doped porous carbons from biomass-derived carbon materials (BCMs) using methylene blue (MB) as self-doping media for high performance supercapacitors. The as-prepared BCMs possess a high specific surface area of 1734.58 m2/g, large pore volume of 1.80 cm3/g, high oxygen (8.08 %), nitrogen (3.13 %) contents, and ultra -strong MB adsorption capacity (1337.83 mg/g). This unique architecture provides ion shuttle back and forth pore size to enhance double layer capacitance, and rapid diffusion of electrolyte ions. Besides, after adsorption with methylene blue, N/S elements (4.22/1.17 wt%) co-doped into BSMs led to multiple synergistic effects, improve surface wettability and supply additional pseudo-capacitance. The as-obtained co-doped BCMs exhibited the highest specific capacitance of 208 F/g at 1 A/g in a three-electrode system, and the symmetric supercapacitor showed superior cycling stability with high retention of 100 % at 5 A/g over 20,000 cycles. The symmetric supercapacitor showed a high energy density of 6.89 Wh/kg at a power density of 5272.23 W/kg in a 1 M Et4NBF4/PC electrolyte. The high energy density and high power density of as-obtained carbon materials can approach commercial porous carbon YP-50, demonstrating the good potential for practical application. Overall, this study is valuable for the multifunctional applications of BCMs in dye wastewater treatment and capacitive energy storage, and builds a bridge to the future between environment and capacitive energy storage.