N-doped hierarchically porous carbon from lignite-derived residue for high-performance supercapacitor

Lignite-derived residue with cross-linked aromatic structure and heteroatom groups is an alternative and low-cost precursor for porous carbon. Herein, N-doped hierarchically porous carbon (NDHPC) was prepared by KOH activation from lignite-derived residue using ZnO as the template and dicyandiamide as the nitrogen source. The optimal NDHPC presents hierarchically porous stacked layered structure with high specific surface area (2648.18 m²/g) and contains abundant O/N functional groups, making it promising candidate as the electrode material. Introducing nitrogen can provide more pseudocapacitors and meanwhile improve the wettability of the NDHPC, thus enhancing electrochemical performance. The optimal NDHPC exhibits a high specific capacitance of 336 F g⁻¹ at the current density of 0.5 A g⁻¹ with good rate performance. Additionally, the assembled NDHPC symmetrical supercapacitor presents outstanding cycle stability with 96.2 % capacitance retention and possesses energy density of 7.85 Wh kg⁻¹ at power density of 250 W kg⁻¹. This study offers an effective and low-cost approach to fully utilize the organic matter in coal-derived residue for preparing supercapacitor electrode materials.