Nitrogen-doped coal-based porous carbon and reduced graphene oxide composites for high-performance symmetrical supercapacitors†

Abstract

Supercapacitors, bridging traditional capacitors with fuel cell and battery technologies, demand advanced electrode materials to enhance energy storage performance. This study focuses on the synthesis of nitrogen-doped coal-based porous carbon/reduced graphene oxide (rGO) composites using low-cost, abundant low-rank lignite as a precursor. The hybrid material, activated by KOH and nitrogen-doped via urea, achieves specific capacitances of 207 F g⁻¹ and 145.2 F g⁻¹ in three- and two-electrode systems, respectively, at 1 A g⁻¹ after thermal treatment at 800 °C. The assembled symmetrical supercapacitor exhibits a high energy density of 20.2 W h kg⁻¹ at a power density of 999.8 W kg⁻¹ at 1 A g⁻¹, with nearly 100% capacitance retention and a coulombic efficiency over 10 000 cycles. The synergistic effects from coal-based porous carbon and rGO provides a high specific surface area, optimal pore size distribution, and a suitable carbon microcrystalline structure, collectively promoting ion transport and charge storage. This work provides not only advanced high-performance supercapacitor design, but also evidence for the sustainable utilization of low-grade coal resources in clean energy technologies.