▎ 摘　　要

Designing and fabricating advanced oxygen reduction reaction (ORR) electrocatalysts is critical importance for the sake of promoting widespread application of fuel cells. In this work, we report that nitrogen-doped graphene (NG), synthesized via one-step pyrolysis of naturally available sugar in the presence of urea, can serve as metal-free ORR catalyst with excellent electrocatalytic activity, outstanding methanol crossover resistance as well as long-term operation stability in alkaline medium. The resultant NG1000 (annealed at 1000 degrees C) exhibits a high kinetic current density of 21.33 mA/cm(2) at -0.25 V (vs Ag/AgCI) in O-2-saturated 0.1 M KOH electrolyte, compared with 16.01 mA/cm(2) at -0.25 V for commercial 20 wt % Pt/C catalyst. Notably, the NG1000 possesses comparable ORR half-wave potential to Pt/C. The effects of pyrolysis temperature on the physical prosperity and ORR performance of NG are also investigated. The obtained results demonstrate that high activation temperature (1000 degrees C) results in low nitrogen doping level, high graphitization degree, enhanced electrical conductivity, and high surface area and pore volume, which make a synergetic contribution to enhancing the ORR performance for NG.