Surface Oxygen Engineering Catalytic Pore Tailoring of Coal-Based Needle Coke toward Capacitive Porous Carbon

Coal-based needle coke (CNC) is an ideal carbon precursor for capacitive materials due to its layered graphitic structure and high electrical conductivity. However, the pore-rich engineering and graphitic structural inheriting of CNC-derived carbon during the conventional activation process present challenges. Herein, a surface oxygen engineering catalytic pore tailoring strategy is developed to manipulate the porous structures of CNC-derived porous carbon. This synthesis uses air oxidation to form oxygen-rich microregions on the CNC surface, which can effectively tear the graphite protective shell, accelerate the bonding of KOH with oxygen groups, and catalyze the etching reaction between potassium compounds and carbon atoms. Thanks to the low activation temperature of 600 °C and alkali-to-carbon ratio of 1:1, the obtained porous carbon (PC) inherits the long-range graphitic structure from CNC, and its specific surface areas can be adjusted from 182.6 to 855.4 m2 g–1 by adjusting the oxidation temperature, which is far more than that of PC (7.6 m2 g–1) derived from CNC direct activation. The optimized PC shows a high specific capacitance of 308.3 F g–1 at 0.5 A g–1 and a capacitive retention of 212.2 F g–1 at 20 A g–1 with a capacitive retention of 68.8%. The assembled supercapacitor delivers an energy density of 8.12 Wh kg–1 at a power density of 50.0 W kg–1 and ultralong cycle stability with capacitance retention of 99% and Coulombic efficiency of 100% after 50,000 cycles. This study validates the feasibility of pore tailoring by surface oxygen engineering catalysis in soft carbon for enhancing capacitance.