▎ 摘　　要

Nitrogen doping is considered to be a promising way to improve the performance of graphene-based supercapacitors. It is crucial to discuss that the role of nitrogen doping in regulating the electronic properties. Herein, we chose urea, NH3 center dot H2O and N2H4 center dot H2O as the nitrogen sources to modify the graphene based cobalt oxide composites to compare which nitrogen source made a great improvement on the supercapacitive performance of the composites. When the urea is used as the nitrogen source, the electrochemical performance was the best among the nitrogen-doped (N-doped) graphene based cobalt oxide composites (334.8 F g(-1) at a current density of 5 A g(-1) in 2 M KOH aqueous solution). Nitrogen doping worked as a modification to control the structure of graphene sheet and effectively improved the electrochemical performances. (C) 2017 Elsevier B. V. All rights reserved.