▎ 摘　　要

Exploring high performance non-precious metal catalysts to substitute Pt for oxygen reduction reaction (ORR) has stimulated wide research interest recently, but it remains a great challenge. Herein, we report a single iron site confined in graphene catalyst via 4N atoms, forming flat FeN4 structure in the matrix of graphene. The optimized catalyst shows a high ORR activity, almost coming up to the activity of commercial 40% Pt/C catalyst, but a significantly higher stability and tolerance to SOx, NOx and methanol with respect to 40% Pt/C. This well-defined structure provides an ideal model to study the catalytic origin of iron-based catalysts. DFT calculations indicate that the high ORR activity origins from highly dispersed and high-density coordinatively unsaturated Fe centers, and the excellent stability origins from the unique confinement of the graphene matrix via 4N atoms. This reaction can proceed easily to H2O via a four electron transfer path way on the single iron site, which is further confirmed by the experiment. This experimental and theoretical study provides a further insight into the nature of the Fe/N/C catalyst and also introduces a reference for designing high efficient catalysts in electrocatalysis.