Facile chemical synthesis of nitrogen-doped graphene sheets and their electrochemical capacitance

To improve the electrochemical performance of graphene materials, nitrogen-doped graphene sheets (NGS) were simultaneously reduced and functionalized with nitrogen (N) doping from graphene oxide (GO) by a simple process using 1 wt.% ammonia water solution as the reducing agent, nitrogen precursor and solvent. The NGS were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy-energy dispersive spectroscopy microanalysis, and differential scanning calorimetry. The thermal stability of NGS was much higher than that of GO. The N content in NGS was 4.4 at.% and a maximum specific capacitance up to 233.3 F g^-1 was obtained at 0.5 A g^-1. At 0.02 V s^-1, the NGS exhibited a specific capacitance of 140.3 F g^-1, which was over 8 times that of GO and nearly 2 times that of graphene without N-doping. These results revealed that N-doping of functional graphene provide remarkable improvements on the electrochemical capacitive performance of graphene materials. The NGS also showed high cycle stability of capacitive performance.