Abstract

Porous graphitic carbon nanosheets (MNC-x) with well-developed porosity and appropriate heteroatom doping are prepared by directly carbonizing sodium lignosulfonate in inert atmosphere. Interestingly, MNC-900 prepared at 900 °C shows sharp increases in specific surface area, carbon to oxygen atom ratio, graphitization degree and electrical conductivity compared with MNC-800 prepared at 800 °C, which are mainly attributed to the quinonyl decomposition accompanied by formation of graphitic carbons. The high oxygen content (20.1 at. %) and mesopore ratio (71.0%) of MNC-800, large specific surface area (1400 cm3 g−1) and superior conductivity (2208 S m−1) of MNC-900 make them suitable for supercapacitor electrodes in aqueous and organic electrolytes, respectively. Specifically, MNC-800 electrode shows large specific capacitance (196 F g−1 at 0.25 A g−1), superior rate capability (170 F g−1 at 20 A g−1) and outstanding cycling stability (96% capacitance retention after 10,000 cycles) in symmetrical supercapacitor using 3 M KOH electrolyte. For MNC-900 based symmetrical supercapacitor with 1 M (C2H5)4NBF4/PC electrolyte, an impressive energy density of 30.2 Wh kg−1 at a power density of 309.8 W kg−1 is achieved, which remains 15.2 Wh kg−1 even at 9.9 kW kg−1.

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