N/S dual-doped graphene with high defect density for enhanced supercapacitor properties

Abstract

N/S dual-doped graphene was prepared by one-pot process using graphene oxide as raw material and thiourea and urea as reduction-dopants. The field emission scanning electron microscopy (FESEM), X-ray powder diffraction (XRD), Raman spectroscopy (Raman), nuclear magnetic resonance (NMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and other means were used to characterize the microstructure and morphology of the samples. The electrochemical properties of the samples were tested by cyclic voltammetry, electrochemical alternating impedance and constant current charge-discharge techniques, and compared with graphene and nitrogen-doped graphene. Results show that the defect density of graphene can be increased more effectively by N/S dual doping than by nitrogen doping, and the contents of doped nitrogen and sulfur have a significant effect on the morphology and performance of the samples. The specific surface area of the best sample reaches 275.8 m2 g−1, and its conductivity is 477.6 S m−1. When the window voltage is −1.2-0 V, the best sample shows superior specific capacitance of 386.5 F g−1 and a high energy density of 69.6 Wh kg−1 at a scan rate of 10 mV s−1. At the current density of 10 A g−1, after 5000 constant current charge/discharge cycles, the specific capacitance retention rate is 94.5%, showing excellent cyclic stability.