Atomic Edge Fe-N4 Active Sites on N-Doped Porous Carbon Nanosheets Derived from Zeolitic-Imidazolate Frameworks for High-Efficiency Oxygen Reduction

Defect and morphology engineering of metal-nitrogen codoped carbon (M-N/C) has been proven to be efficacious in promoting the oxygen reduction reaction (ORR) catalytic activity, yet the simultaneous construction of active sites with high intrinsic activity and efficient exposure is a challenge. Herein, an Fe-N/C catalyst consisting of edge Fe-N4 sites atomically dispersed on porous carbon nanosheets (e-Fe-N/CNS) is designed for high intrinsic catalytic active as well as efficient utilization. By combining an edge-doping process and an I2-etching effect, the edge Fe-N4 sites are constructed preferentially and the interior active sites are fully exposed. The edge Fe-N4 sites endow e-Fe-N/CNS with high intrinsic activity, which originated from the local electronic redistribution of the Fe-N4 configuration induced by the edge carbon, while the enriched porous nanosheet structure enhances the edge Fe-N4 sites utilization efficiency for high mass activity. The as-synthesized e-Fe-N/CNS exhibits a remarkable half-wave potential (E1/2, 0.90 VRHE) under alkaline conditions. This work provides a novel synthetic method for designing highly active defective sites in catalysts for energy conversion systems.