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

• Transform lignite into high added-value HA-based oxygen-rich microporous carbon electrode material. • OMC-2 exhibits a micropore-specific surface area of 860 m2 g−1 (S mic /S BET = 98 %). • OMC-2 electrode displays the fastest reaction kinetics due to its high oxygen functional group content. • The specific capacitance of OMC-2 measured at 0.5 A g−1 is 326 F g−1. • High energy density of 15.9 Wh kg−1 (at 275 W kg−1) in the symmetric supercapacitor. 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 low-rank lignite and catalytic assisted pyrolysis with potassium oxalate (K 2 C 2 O 4) 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. [ABSTRACT FROM AUTHOR]