Preparation of N and O doped coal tar pitch based porous carbon for supercapacitor electrode

Abstract

Coal tar pitch (CTP) is mainly composed of a mixture of polycyclic aromatic hydrocarbons, is almost hydrophobic, and has a low heteroatom content, which limits its surface function. During carbonization, it is prone to condensation and difficult to form pore structures, resulting in poor electrochemical performance for carbon electrode materials. Herein, nitrogen (N) and oxygen (O) doped hierarchical porous carbon (C-ANOCTP) was prepared by HNO3 oxidation and KOH activation using CTP as carbon precursor. The oxidation of HNO3 remarkably increases the hydrophilic functional groups containing N and O on the surface of CTP, improves the hydrophilicity of CTP surface, facilitates the activation process of KOH, promotes the development of carbon material pore structure and the generation of active sites, as well as the formation of defect structures. The specific surface area of C-ANOCTP obtained is 1130 m2/g, with O content of 10.29 at% and N content of 2.37 at%. The specific capacitance of C-ANOCTP in a three-electrode system with 6 M KOH electrolyte is as high as 410.51 F/g at 0.5 A/g. A symmetric supercapacitor is assembled in a 6 M KOH electrolyte using C-ANOCTP as electrode. When the power density is 25 W/kg, the energy density is 10.24 Wh/kg. After 10,000 cycles, the capacitance retention rate is still 90.03% and the coulomb efficiency is 100%. The high N and O content of porous carbon is prepared by simple HNO3 oxidation synergistic KOH activation and low temperature carbonization, which shows excellent electrochemical properties in supercapacitors, making CTP an ideal candidate material for high energy density supercapacitors.