Effect of Petroleum Coke Expanding by HNO3 on the Performance of Supercapacitor Based on the Activated Carbon

Petroleum coke (PC) was expanded by using KMnO4 as oxidant and HNO3 as intercalator so as to decrease the amount of KOH needed for the successive activation. The expanded PC (EPC) was activated at KOH / coke mass ratio of 3:1, 4:1 and 5:1. The products were denoted as EAC-3, EAC-4 and EAC-5, respectively. As a comparison, PC was also activated at the same KOH / coke mass ratio. The products were denoted as AC-3, AC-4 and AC-5, respectively. Thermogravimetry (TG), XRD, I-2 adsorption, N-2 adsorption, cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were used to investigate the influence of expanding treatment on the structure and performance of the PCs and ACs. The research revealed that expanding treatment increased the interplanar distance of PC microcrystalline from 0.344 nm to 0.359 nm and decreased the microcrystalline thickness from 2.34 nm to 1.61 nm. The specific surface areas of EAC-3 and AC-5 were 3325 and 3291 m(2)/g, respectively. The average pore size of EAC-3 was 2.16 nm, which was 0.08 nm larger than that of AC-5. At a scan rate of 0.5 mV/s, EAC-3 and AC-5 achieved a specific gravimetric capacitance of 448 and 429 F/g, respectively. Supercapacitor based on EAC-3 possessed lower resistance and better power performance.