▎ 摘　　要

Nitrogen-doped graphene materials provide the attractive potentials to replace the high-priced Pt and Pt based catalysts for oxygen reduction reaction (ORR) to accelerate the industrialization of fuel cells (FCs). Herein, the nitrogen-doped three-dimensional reduced graphene oxide (N-3DrGO) catalysts have been prepared by a facile hydrothermal method using the raw materials of GO, melamine and formaldehyde. The N contents in N-3DrGO products vary from 3.12 to 9.69 at.% which can be easily regulated by adjusting the feed mass ratios of GO and melamine. It is found that a higher content of N does not necessarily result in enhanced electrocatalytic activity. Rather, with the highest total percentage of graphitic N and pyridinic N (69.2%), superior solvent dispersibility, as well as a smaller interfacial and charge-transfer resistance, the N-3DrGO catalyst obtained by a mass ratio of 1:1.5 between GO and melamine presents the most excellent activity towards ORR. As a catalyst using in FCs for ORR, the obtained N-3 DrGO catalysts exhibit favorable electrocatalytic performance, excellent methanol tolerance and much enhanced durability compared with that of commercial Pt/C (20 wt%) catalyst in alkaline media. Furthermore, the above-mentioned approach is demonstrated to be a versatile method in fabricating N-3DrGO-based catalysts by introducing the foreign active atoms such as sulfur (S) to realize the N and S co-doping, which can further enhance the catalysts' ORR activity. (C) 2017 Elsevier B.V. All rights reserved.