Preparation of Nitrogen-Doped Graphene and Its Electrocatalytic Activity for Oxygen Reduction Reaction

Nitrogen-doped graphene (NG) was prepared by chemical reduction of graphene oxide (GO) using dimethyl ketoxime (DMKO) as reducing and doping agents. The morphologies, structures, compositions, and electrocatalytic activities of the as-prepared materials were investigated using field-emission transmission electron microscopy (FETEM), ultraviolet-visible (UV-Vis) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), zeta potential and nanoparticle analyses, cyclic voltammetry (CV), and the rotating disk electrode (RDE) method. The results showed that GO sheets were effectively reduced by DMKO. NG samples with different nitrogen contents were obtained by adjusting the mass ratio of GO to DMKO; the nitrogen contents were in the range 4.40%-5.89% (atomic fraction). NG-1, obtained using a GO/DMKO mass ratio of 1:0.7, showed excellent electrocatalytic activity in the oxygen reduction reaction (ORR) in an O-2-saturated 0.1 mol.L-1 KOH solution. The peak current was 0.93 mA.cm(-2), and the number of electrons transferred per O-2 was 3.6; this was attributed to the increase in the number of ORR active sites in the presence of pyridinic-N. In addition, the electrocatalytic activity of NG was found to be dependent on the graphitic-N content, which determined the limiting current density, because of its higher electronic conductivity. The pyridinic-N content improved the onset potential, because of its lower overpotential for the ORR. NG therefore exhibited a high selectivity in the ORR, with good tolerance of methanol cross-over effects. It is therefore superior to commercial Pt/C catalysts.