▎ 摘　　要

A series nGs with different electrocatalytic abilities toward oxygen reduction reaction (ORR) was prepared via a two-steps pyrolysis method by controlling the reaction temperature on the physical mixture of graphene oxideand urea. Transmission electron microscopy and scanning electron microscopy display nG with highly wrinkled and overlapping structures. X-ray photoelectron spectroscopy shows that nitrogen is successfully doped in graphene with the formation of pyridinic N, pyrrolic N and graphitic N, and the maximum nitrogen content is 6. 6% (molar fraction). Cyclic voltammogram and rotating disk electrode measurement show that nGs exhibit high electrocatalytic activity with an onset potential of 0. 1 V in an acid electrolyte. Moreover, the nGs catalyzed oxygen reduction revealed a favorable formation of water via a four-electron pathway and excellent stability over Pt/C catalyst. Furthermore, the nG obtained at 200 degrees C in the first pyrolysis step displays the best catalytic perfor-mance.