Abstract
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-N(4) in N-doped carbon nanorods, but also Fe(2)N cluster as a ligand anchored on the active Fe site (Fe(2)N(nc)/Fe(1)-N-C). Unlike the conventional iron atomization process, the reactive nitridation process can generate thermodynamically stable Fe(2)N intermediates by nitriding the initially formed iron oxide, thereby impeding subsequent thermal atomization to fabricate Fe(2)N(nc)/Fe(1)-N-C catalysts. Compared to the conventional SAC Fe(1)-N-C with Fe-N(4) active sites, the Fe(2)N(nc)/Fe(1)-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 Fe(2)N(nc)/Fe(1)-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 Fe(2)N(nc) ligands indeed modified the electronic structures of Fe-N(4) sites, leading to a lower adsorption energy for the ORR intermediate OH* and facilitating the desorption of OH* and thus higher activity for ORR.