One-step molten salt carbonization of tobacco stem for capacitive carbon

High-performance carbon materials for supercapacitors were prepared by a one-step molten salt carbonization of tobacco stem in molten carbonate. Physicochemical properties of the as-prepared carbon materials were studied by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and nitrogen adsorption/desorption isotherms, as well as electrochemical properties were measured by tests of cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy. All of the carbon materials possess hierarchically porous structure with rich self-doping of oxygen for introducing pseudocapacitance and high specific surface area for providing sufficient active sites, and exhibit ideal capacitive behavior with high performance which is comparable to that of commercial activated carbon material. Carbon material obtained by molten salt carbonization for 2 h delivers specific capacitance of 225.3 F/g at 0.2 A/g, energy density of 31.2 Wh/kg at 0.2 A/g and power density of 989.5 W/kg at 2 A/g besides acceptable rate capacity and long-term cyclic stability using a three-electrode configuration in 1 mol/L H 2 SO 4 aqueous solution. Moreover, it possesses specific capacitance of 143.5 F/g at 0.2 A/g, energy density of 5.0 Wh/kg at 0.2 A/g and power density of 491.3 W/kg at 2 A/g besides excellent rate capacity using a symmetrical two-electrode configuration in 6 mol/L KOH aqueous solution. The dependence of the capacitive performance on hierarchically porous structure is also discussed.