Oxygen-rich microporous carbon derived from humic acid extracted from lignite for high-performance supercapacitors

Transforming lignite into functional carbon material with high value-added is a promising work. In this work, an oxygen -rich microporous carbon (OMC) was prepared by humic acid as a carbon precursor extracted from a lowrank lignite and catalytic assisted pyrolysis with potassium oxalate (K2C2O4) activator. Furthermore, OMC-2 demonstrates a higher specific capacitance (326 F g-1 at 0.5 A g-1) and energy density (15.9 Wh kg- 1 at 275 W kg - 1) than lignite -based microporous carbon (LMC) when utilized as electrode material for supercapacitors. The outstanding performance of OMC-2 is ascribed to its larger specific surface area (860 m2 g-1) and volume of micropores (0.4 cm3 g-1), coupled with the highest oxygen doping (14.46 %), which high micropore content produces a higher electric double -layer response, and the highest oxygen doping amount improves the hydrophilicity of the surface of carbon materials, enhance the diffusion kinetics, facilitates the mass transfer of electrons/ions, and furnishes partial pseudo capacitance. At a high current density of 10 A g-1, 6000 cycles were executed, and the capacitance retention of OMC-2 exceeded 69 %. This study proposes an effective way to solve the added value problem of lignite and creates a feasible carbon material for practical application.