Directional Construction of Low-Coordination Fe–N₃ Coupled with Intrinsic Carbon Defects for High-Efficiency Oxygen Reduction

Regulating the coordination environment of Fe-N_<i>x</i> sites is an efficient but challenging approach for promoting the intrinsic catalytic activity of single-atom Fe/N-codoped carbon (Fe-N-C) toward the oxygen reduction reaction (ORR). Herein, low-coordination Fe-N₃ sites coupled with carbon vacancies (Fe-N₃/C_V) are directionally constructed in Fe-N-C via pyrolysis of a metal-organic framework (MOF) precursor with N₃-Zn-O-Fe moieties, which are delicately prefabricated by chemically anchoring Fe³⁺ onto a H₂O-etching induced linker-missing Zn-N₃ site in the MOF precursor. The optimized Fe-N-C with the Fe-N₃/C_V sites displays a high ORR half-wave potential of 0.92 V (vs RHE), which is attributed to the optimized electronic structure and binding strengths of the active Fe center toward the ORR intermediates stemming from the synergy of the asymmetric configuration of Fe-N₃ as well as the adjacent carbon vacancies. This work could be enlightening for the design and construction of high-activity coupling sites in metal and nitrogen-codoped carbon catalysts.