▎ 摘　　要

Nitrogen-containing graphene is a promising candidate for oxygen reduction reaction (ORR) in fuel cells. However, there are still some challenges in further application and modification of N-graphene and in understanding the roles of various nitrogen states on electrocatalysis. Herein, we design a simple and effective solvothermal method to synthesize amino-functionalized graphene (AG) from graphite oxide (GO) only in the presence of ammonia solution. Having a significant amount of amino species with the total nitrogen content of up to 10.6% (atom%), the resultant product can act as an efficient metal-free catalyst, exhibiting enhanced electrocatalytic properties for ORR. Furthermore, a combination of X-ray photoelectron spectroscopy (XPS) and electrochemical measurements was used to investigate the roles of various nitrogen states in ORR, and the contribution of amino group has been demonstrated for the first time. Our experiments show that the graphitic- and amino-type of nitrogen components determine the onset potential and electron transfer number, while the total content of graphitic and pyridinic nitrogen atoms is the key factor to enhance the current density in the electrocatalytic activity for ORR. This work could lead to economical synthesis of AG as efficient ORR electrocatalyst in fuel cells, and help to understand the catalytic mechanism of various nitrogen states towards ORR. (C) 2012 Elsevier Ltd. All rights reserved.