Impeding Thermal Atomization Enables Synthesizing Fe2N Cluster Liganded Single Fe-Atom Catalyst for Highly Efficient Oxygen Reduction Reaction

Anchoring a ligand, such as a functional group or a cluster, on the active metal center is an effective strategy for regulating the electronic structure of single-atom catalysts (SACs). Herein, we present a nitridation-induced-clustering strategy to produce not only SAC Fe-N4 in N-doped carbon nanorods, but also Fe2N cluster as a ligand anchored on the active Fe site (Fe2Nnc/Fe1-N-C). Unlike the conventional iron atomization process, the reactive nitridation process can generate thermodynamically stable Fe2N intermediates by nitriding the initially formed iron oxide, thereby impeding subsequent thermal atomization to fabricate Fe2Nnc/Fe1-N-C catalysts. Compared to the conventional SAC Fe1-N-C with Fe-N4 active sites, the Fe2Nnc/Fe1-N-C nanorods are more active for oxygen reduction reaction (ORR), yielding a record high half-wave potential of 0.957 V versus RHE in alkaline condition. The Fe2Nnc/Fe1-N-C nanorods can be utilized as air-cathode catalysts for Zn-air batteries with a charge-discharge gap of only similar to 0.658 V and outstanding cyclability up to 1000 h. Theoretical calculations show that the Fe2Nnc ligands indeed modified the electronic structures of Fe-N4 sites, leading to a lower adsorption energy for the ORR intermediate OH* and facilitating the desorption of OH* and thus higher activity for ORR.