Electronic Structure Modulation of Fe-N4-C for Oxygen Evolution Reaction via Transition Metal Dopants and Axial Ligands

The popular single-atom catalyst (SAC) Fe-N4 isgenerallybelieved to be an excellent oxygen reduction reaction (ORR) electrocatalyst,which is less active in the oxygen evolution reaction (OER). Herein,FeM-N6 configuration catalysts (M = Fe, Co, Ni, Cu, Ag, andAu) were constructed for the oxygen evolution reaction by embeddingM dopants on Fe-N4 systems based on the density functionaltheory. The electronic structure analysis reveals that the Fe-Mmetal interactions play dominant roles in regulating the d orbitaldistributions of Fe sites, which in turn alter the catalytic OER performance.Subsequent thermodynamic results indicate that the potential-determiningstep (PDS) for all catalysts is the formation of OOH*, which exhibitsa tendency of decreased overpotentials with enhanced metal interactions.Apart from these, the effects of axial ligands on the OER activityof the catalysts in practical conditions were considered. Generally,most of the axial ligands are found to be thermodynamically favorablefor the OER process. Interestingly, a competitive relationship ofthe electrons from the d orbital of Fe sites was found between theaxial ligand and the adsorbed intermediate species during the reaction,which raises the energy barrier for OH* to O* conversion and can evenalter the PDS in certain cases. The present work sheds new light onthe design of future high-performance OER catalysts.