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

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 (Fe₂N_nc/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 Fe₂N_nc/Fe₁-N-C catalysts. Compared to the conventional SAC Fe₁-N-C with Fe-N₄ active sites, the Fe₂N_nc/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 Fe₂N_nc/Fe₁-N-C nanorods can be utilized as air-cathode catalysts for Zn-air batteries with a charge-discharge gap of only ∼0.658 V and outstanding cyclability up to 1000 h. Theoretical calculations show that the Fe₂N_nc 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.