Synthesis and supercapacitor performance studies of N-doped graphene materials using o-phenylenediamine as the double-N precursor

N-doped graphene (NG) materials have been prepared through a one-step solvothermal reaction by using o-phenylenediamine as a double-N precursor. N-doping and reduction of graphene oxide (GO) are both achieved simultaneously during the solvothermal reaction. The results of scanning electron microscopy and high resolution transmission electron microscopy measurements indicate that NG is highly crumpled. And the N-doping is confirmed by elemental analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, Fourier transformed infrared spectroscopy and ultraviolet–visible spectroscopy. The doping level of nitrogen reaches up to 7.7 atom% and the types in NG are benzimidazole-N and phenazine-N. The NG materials exhibit excellent electrochemical performance for symmetric supercapacitors with a high specific capacitance of 301 F g⁻¹ at a current density of 0.1 A g⁻¹ in 6 M KOH electrolyte, which is remarkably higher than the solvothermal products of pristine GO (210 F g⁻¹ at 0.1 A g⁻¹). The NG materials also exhibit superior cycling stability (97.1% retention) and coulombic efficiency (99.2%) after 4000 cycles, due to the high content of nitrogen atoms, unique types of nitrogen and improved electronic conductivity.