▎ 摘　　要

The development of efficient oxygen reduction reaction (ORR) catalysts is essential for the commercialization of fuel cells. Graphene can significantly improve the ORR performance of platinum-based catalysts, but the fundamental mechanism of such a promotional effect is unclear. Herein, the reaction processes of the ORR on graphene supported PtFe nanoalloys have been investigated using in situ enhanced Raman spectroscopy through the fabrication of graphene-isolated satellite nanostructures. The *OOH and *OH intermediates are identified and confirmed using isotopic substitution during the ORR on PtFe with or without graphene, respectively. Density functional theory (DFT) calculations and X-ray photoelectron spectroscopy further demonstrate such a difference result from the electronic effect of graphene. The graphene electronic effect promotes the formation of *OOH and the further conversion of *OH to the final product water, thus leading to the improved ORR performance of PtFe supported on graphene. This work sheds light on the molecular mechanism of the promotional role of graphene on the ORR and provides theoretical guidance for the rational design of ORR catalysts.