▎ 摘　　要

Nitrogen (N)-doped graphene (NG) sheets were prepared using (NH4)(2)CO3 and an aqueous dispersion of graphene oxide (GO) by an eco-friendly hydrothermal reaction. The in situ produced ammonia played an important role in the simultaneous nitrogen doping, the reduction and exfoliation of GO. The (NH4)(2)CO3/GO mass ratio and reaction temperature were varied to investigate the effects on the N doping level. The elemental analysis determined from the X-ray photoelectron spectroscopy showed that the nitrogen content of the NG was about 10.1 at.% and the oxygen content decreased significantly due to the hydrothermal reduction of GO. The electrochemical performances of the NG sheets increased with increasing doped N content. The highest specific capacitance of 295 F g(-1) at a current density of 5 A g(-1) and the highest specific surface area of 412 m(2) g(-1) were observed with the sample processed at 130 degrees C. The retention of the specific capacitance was maintained at similar to-89.8% after 5000 charge-discharge cycles. These results imply that NO sheets obtained by this simple eco-friendly approach are suitable for use in high performance energy storage electrode materials. (C) 2013 Elsevier Ltd. All rights reserved.