Development of high-efficiency atomic transition metal catalysts for oxygen electrode reactions is attractive for regenerative energy conversion and storage technologies. Here we report a facile approach to fabricate an atomic iron- and nitrogen-codoped graphene catalyst with high content of iron (up to 1.5 wt%). The atomic iron-based catalyst on glassy carbon electrodes displays low overpotential (194 mV and 275 mV) reported at 10 mA cm(-2) in 1.0 M KOH and 0.1 M KOH solutions for the oxygen evolution reaction (OER), respectively. In addition, the atomic iron-based composite electrocatalyst exhibits a high half-wave potential of 0.90 V vs. RHE for the oxygen reduction reaction (ORR) in 0.1 M KOH, and a combined ORR and OER potential gap of 0.605 V. Structural characterization and theoretical calculations demonstrate that the efficient active sites for OER and ORR should be FeN4-moiety embedded into the graphene, on which the overpotential-determining step is the O-O coupling step. (C) 2019 Elsevier Inc. All rights reserved.