▎ 摘　　要

Electrochemical oxygen reduction is key to many clean and sustainable energy technologies, including proton exchange membrane fuel cells and metal-air batteries. However, the high activation barriers in the oxygen reduction reaction often make it the bottleneck of energy conversion processes; thus, highperformance oxygen reduction electrocatalysts are desired. At present, the best commercially available oxygen reduction catalyst is based on the precious metal Pt. However, it suffers from resource scarcity and unsatisfactory operational stability, hindering its widespread and large-scale application in clean and sustainable technologies. Nitrogen-doped graphene has excellent electrocatalytic properties for oxygen reduction. In this paper, a scalable method to prepare nitrogen-doped graphene with high quality was introduced, in which the graphene oxide prepared by high-gravity technology and urea was reacted under hydrothermal conditions. Accompanying the hydrothermal reaction, graphene oxide reduction and nitrogen doping were accomplished at the same time. The effect of the content of nitrogen on the performance of nitrogen-doped graphene was investigated. When the mass ratio (graphene oxide/urea) was 1:400, the nitrogen-doped graphene had the best oxygen reduction performance. Compared with the undoped samples, the initial reduction voltage of the nitrogen-doped samples distinctly shifted 45 mV to the right. When the voltage was 1.0 V, the electron transfer number was 4.1, indicating good oxygen reduction activity. The preparation method is feasible, simple, and can be easily scaled up. (C) 2017 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.