Supercritical fluid processing of N-doped graphene and its application in high energy symmetric supercapacitor

A simple one-pot methodology is developed for the synthesis of nitrogen doped graphene via supercritical fluid (SCF) processing using glycine as a nitrogen precursor. The presence of various N-containing functional groups was determined by FT-IR and the amount of N-doping in the graphene was found to be 4.5 wt% using the elemental analysis and X-ray photoelectron spectroscopy. The electrochemical capacitance measurements are performed using cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The nitrogen doped graphene exhibited enhanced capacitive performance with a maximum specific capacitance of 270 F/g at 0.5 A/g current density with high specific capacitance retention of 90% over 10,000 cycles at 10 A/g current density. The fabricated symmetric supercapacitor cell showed a high energy density of 4.1 and 36 Wh/kg in aqueous and ionic liquid electrolyte, respectively. The high energy density obtained in ionic liquid is promising for their potential application in electrochemical energy system.