▎ 摘　　要

Graphitic carbon materials have shown great potential for use as high-performance catalysts for electrochemical reactions and devices. In this work, we developed a simple and versatile method for synthesis of porous N-doped graphene layers (NGS) by high-temperature treatment of chitosan film deposited on the graphitic carbon nitride (g-C3N4) nanosheets. In the sandwiched chitosan/g-C3N4/chitosan structure, the g-C3N4 nanosheet served as a substrate for chitosan film. The pyrolysis of this substrate, g-C3N4 nanosheet, prevented the severe agglomeration of as-carbonized chitosan sheets and resulted the porous structure. The BET surface area, micropore volume, nitrogen content and graphitic level of result sample highly depended on the heat-treatment temperature. The NGS synthesized at 1000 degrees C (NGS-1000) exhibited an ultrahigh specific surface area (1183 m(2) g( 1)) and high nitrogen content (4.12%). Importantly, NGS-1000 exhibited a higher limiting current density (5.8 mA cm( 2)) and a greater stability than the commercial Pt/C electrocatalyst in alkaline media for oxygen reduction reaction (ORR). Such excellent electrocatalytic performance can be explained by a balanced combination of appropriate nitrogen doping level, the degree of graphitization, porous structure, and high specific surface area. (C) 2018 Elsevier Ltd. All rights reserved.