Synthesis of 3D nitrogen-doped graphene quantum dots and reduced graphene oxide composites by a hydrothermal method for supercapacitors anodes

This work reports a feasible method to fabricate a simple chemical functionalization of graphene oxide (GO) electrode. The hydrothermal synthesis of nitrogen-doped graphene quantum dots modified reduced graphene oxide (NGDQs/rGO-2) using ammonium citrate and graphene oxide (GO) as raw materials. Ammonium citrate effectively acts as a nitrogen dopant cum reducing agent for graphene which remarkably enhances its electrochemical properties. Diffraction of X-rays (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS) were employed to characterize the structure and properties of the (NGDQs/rGO-2), and the NGDQs/rGO-2 was used as the electrode to test the electrochemical performance. According to the electrochemical test results, when the molar ratio of NGDQs to rGO is 1:2, the specific capacitance can reach 357 F/g at a current density of 1 A/g; after 1000 cycles, the capacitance retention rate is 82%. For comparison, under the same current density condition, the specific capacitance of the rGO electrode is only 74 F/g. By assembling a symmetrical supercapacitor for double electrode test, the specific capacitance can reach 237 F/g at a low current density of 0.5 A/g. As the current density increases, the capacitance decreases slightly. When the current density is 1 A/g, the specific capacitance is 113 A/g. Thus, the synthesized NGDQs/rGO-2 using this simple, cost-effective, environment friendly method could be a potential candidate for high performance energy-storage applications.