Directional Construction\nof Low-Coordination Fe–N<sub>3</sub> Coupled with Intrinsic\nCarbon Defects for High-Efficiency\nOxygen Reduction

Regulating the coordination environment of Fe–N<sub><i>x</i></sub> sites is an efficient but challenging approach\nfor\npromoting the intrinsic catalytic activity of single-atom Fe/N-codoped\ncarbon (Fe–N–C) toward the oxygen reduction reaction\n(ORR). Herein, low-coordination Fe–N<sub>3</sub> sites coupled\nwith carbon vacancies (Fe–N<sub>3</sub>/C<sub>V</sub>) are\ndirectionally constructed in Fe–N–C via pyrolysis of\na metal–organic framework (MOF) precursor with N<sub>3</sub>–Zn–O–Fe moieties, which are delicately prefabricated\nby chemically anchoring Fe<sup>3+</sup> onto a H<sub>2</sub>O-etching\ninduced linker-missing Zn–N<sub>3</sub> site in the MOF precursor.\nThe optimized Fe–N–C with the Fe–N<sub>3</sub>/C<sub>V</sub> sites displays a high ORR half-wave potential of 0.92\nV (vs RHE), which is attributed to the optimized electronic structure\nand binding strengths of the active Fe center toward the ORR intermediates\nstemming from the synergy of the asymmetric configuration of Fe–N<sub>3</sub> as well as the adjacent carbon vacancies. This work could\nbe enlightening for the design and construction of high-activity coupling\nsites in metal and nitrogen-codoped carbon catalysts.