Mechanism of Nitrogen Coordination Modulation of Fe_Nx@BP System Catalysts on the Activity of Oxygen Reduction Reaction

In the face of the increasing demand for sustainable energy, the development of economical and environmentally friendly energy conversion technologies has become an inevitable trend. Oxygen reduction reaction (ORR) is a fundamental process in novel energy storage and conversion systems such as fuel cells and metal–air batteries, determining the overall performance and durability of the system. At present, single-atom Fe–N–C electrocatalysts have become a strong contender for platinum-based catalysts in the ORR field due to their stability, excellent activity, and cost-effectiveness. Nevertheless, the source of the ORR reactivity of Fe–N–C catalysts is unknown, which hinders the development of Fe–N–C catalysts. In this investigation, we systematically explored the great potential of two-dimensional single-atom catalysts (SACs): the biphenylene-based iron–nitrogen system (Fe_Nx@BP, x = 1–3) for ORR studies by means of density functional theory calculations. Among all of the proposed configurations, Fe_N3@BP (three N atoms occupying a dyadic coordination site of a single Fe atom) has the best oxygen reduction activity and selectivity, with an overpotential of only 0.591 V. The coordination atom N effectively modulated the charge distribution of the iron-doped biphenylene. The electron transfer between the metal monatomic Fe in the single active sites and the oxygen-containing intermediates is promoted, which ultimately improves the monatomic ORR catalytic ability of the Fe_Nx@BP system. This study provides a theoretical guidance for the further development of highly efficient and environmentally friendly carbon-based SAC catalysts through nitrogen atom coordination design and promotes the development and practical application of two-dimensional biphenylene materials in SACs.