Oxygen self-doped hierarchical porous carbons derived from coal liquefaction residue for high-performance supercapacitors in organic and ionic liquid-based electrolytes

Rational design of electrodes from suitable materials is vital for developing supercapacitors . Herein, oxygen self-doped hierarchical porous carbons (OHPCs) are prepared by a two-step heat treatment using coal liquefaction residues (CLR) and potassium hydroxide (KOH) as raw material and activation agent, respectively. The oxygen-containing functional group undergoes a redox reaction during the energy storage process to increase the pseudocapacitance when OHPC is used as electrode material for supercapacitor . Density functional theory (DFT) calculations show that the doping oxygen species in carbon enhances the adsorption to the electrolyte and provides a fast electron transfer pathway. The OHPC-600 (obtained at 600ºC) presents high specific capacitance of 457 F g −1 at 0.5 A g −1 , superior rate capability with capacitance of 261 F g −1 at 50 A g −1 . The assembled symmetric supercapacitors also exhibit outstanding cycling life with 93% retention over 10000 cycles at 4 A g −1 Moreover, when the aqueous electrolyte is replaced by an organic electrolyte or ionic liquid , this device delivers a remarkable energy density of 35.2 Wh kg −1 and 46.5 Wh kg −1 at a power density of 10000 W kg −1 , respectively. This study provides a reference for the prepare of novel carbon-based electrode materials and the effective exploitation of coal resources for energy storage.