▎ 摘　　要

In this work, a simple method by using ammonia at a relatively low temperature (90 degrees C) to prepare nitrogen-doped graphene hydrogel (N-GH) is demonstrated. Ammonia is not only a nitrogen source but also a modification to the 3D structure of graphene hydrogel. The structure and morphology characterization of the materials was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. The resulting N-GH has a high atomic percentage of N up to 13.44%. It has been found that the supercapacitor performance of the resulting N-GH could be significantly improved. At the constant current density of 1 A g(-1), the specific capacitance was estimated as 217.8 F g(-1). Even at the constant current density of 200 A g(-1), the electrode still has a specific capacitance of 189.8 F g(-1). The material also has a retention rate of 95.8% of its initial capacitance after 1000 cycles at a current density of 20 A g(-1). Moreover, the N-GH has excellent electrochemical stability and a good performance for the rate property even at an ultrafast charge/discharge rate; thus, they may have potential applications as ultrafast supercapacitors.