Theoretical investigation of N and O coordination effects on the bifunctional oxygen electrocatalytic activity of Co-based single-atom catalysts†

Single-atom catalysts (SACs) have garnered considerable attention due to their outstanding electrocatalytic performance in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Their key advantage lies in the ability to significantly activate the intrinsic activity of the central metal atom through fine-tuning of the coordination environment. In this study, density functional theory calculations were employed to systematically investigate a series of graphene-based cobalt SACs. By modulating the N/O coordination environment around the Co atom, the stability and bifunctional electrocatalytic performance of these catalysts were evaluated. The results show that CoN₃O exhibits excellent bifunctional catalytic activity (η^ORR = 0.44 V, η^OER = 0.37 V). Furthermore, a correlation between the adsorption free energies of intermediates and the O–Co bond length (d_O–Co) was identified: the adsorption free energies of *OOH and *OH show a positive correlation with d_O–Co, while that of *O is independent of d_O–Co. Projected density of states and charge density difference analyses reveal that strong hybridization between Co 3d and O 2p orbitals, along with significant charge transfer, enhances the coupling between active sites and reactants, thereby improving catalytic activity. This study highlights the crucial role of coordination environment and electronic structure in tuning the performance of SACs.