Three-dimensional nitrogen-doped graphene hydrogels prepared via hydrothermal synthesis as high-performance supercapacitor materials

Three-dimensional nitrogen-doped graphene hydrogel (3D NG) samples are successfully synthesized via a hydrothermal method. The synthesized 3D NG exhibits excellent mechanical properties, including the support of approximately 1165 g with three NG cylinders. The morphology, structure, component and electrochemical performance of the NG samples are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscope, X-ray photoelectron spectroscopy, thermogravimetric analysis, N2 adsorption-desorption, cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy, respectively. X-ray photoelectron spectroscopy indicates that N is present in the graphene as pyrrolic N, pyridinic N and quaternary/graphitic N, with pyrrolic N being the predominant species in all of the samples. The electrochemical results demonstrate that the 3D NG with a nitrogen content of 7.7 wt% shows excellent capacitive behavior (387.2 F g(-1) at 1 A g(-1)) in 6 M KOH. In addition, the specific capacitance value of this sample remains at approximately 90.5% of the maximum value (298.5 F g(-1) at 5 A g(-1)) after 5500 cycles. The main reason for the excellent electrochemical behavior is the incorporation of the pyrrolic and pyridinic N in the graphene, enhancing the pseudocapacitance of this material. It indicates that the 3D NG can be used as an electrode material for high-performance supercapacitors. (C) 2016 Elsevier Ltd. All rights reserved.