Supercritical fluid processing of nitric acid treated nitrogen doped graphene with enhanced electrochemical supercapacitance

Supercritical fluid processing of nitrogen (N) doped graphene and nitric acid treated N-doped graphene is demonstrated using urea as the nitrogen source. The qualitative and quantitative information concerning doped nitrogen in the graphene sheets were investigated using X-ray diffraction, elemental analysis, Fourier transform infrared, Raman and X-ray photoelectron spectroscopic analysis. The surface morphology and physical nature of the samples are demonstrated using scanning electron and transmission electron microscopic analysis. The electrochemical performance of prepared electrode materials was characterized using cyclic voltammetry and galvanostatic charge-discharge analysis in a conventional three-electrode system. Nitric acid treated N-doped graphene prepared using supercritical fluid processing shows an enhanced specific capacitance of 261 F g(-1) at a current density of 0.5 A g(-1). In addition, it shows 126% capacitance retention after 1000 cycles of charge-discharge and it is stable up to 3000 cycles at a current density of 5 A g(-1).