Thermal treated 3D graphene materials are developed as a highly efficient metal-free electrocatalyst toward oxygen reduction reaction (ORR). Electrochemical analysis reveals that the as-prepared sample shows comparable catalytic activity, better tolerance to methanol crossover effect as well as higher stability than those of commercial Pt/C. For the first time, we find that C=O bonds on 3D graphene display a vital role in catalytic kinetics toward ORR, of which the C=O bonds might influence the adsorption type between oxygen molecule and catalytic active sites on graphene surface. Meanwhile, the unique porous structure of 3D graphene materials are able to trap oxygen molecules, contributing to decrease in diffusion resistance while enhance electrolyte-electrode accessibility for fast mass transport. This work offers a highly efficient metal-free ORR catalyst obtained by a universal approach, and the prepared 3D graphene materials could be further utilized in other energy conversion/storage fields. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.