The design and development of low-cost and highly efficient electrocatalysts for nitrogen reduction reaction is crucial for NH3 synthesis. Herein, by means of comprehensive density functional theory (DFT) calculations and thermodynamic analysis, the catalytic mechanisms of N-2 to NH3 conversion on single Fe atom embedded in single vacancy and N-doped graphene are systematically investigated. Significantly, the magnetic moment of Fe atom varies with the coordination of neighboring N atom. An approximately linear scaling is found between the adsorption energy of N atom (Delta E-N*) and Fe magnetic moment. The increased magnetic moment of Fe atom can strengthen the Delta E-N*, and promote the charge transfer between the N-2 molecule and substrates, resulting in a substantially lower overpotential for N-2 electroreduction. Our results highlight an important role of Fe magnetism in N-2 activation, which offers a novel strategy for inspiring the rational design of highly efficient carbon-based materials for N-2 fixation and conversion. (c) 2018 Elsevier Ltd. All rights reserved.