Improving Nitric\nOxide Reduction Reaction Activity\nof TMN<sub>4</sub>–C Model Catalysts by Axial Atom Coordination

In comparison with the conventional four-nitrogen coordinated\ntransition\nmetal (TMN<sub>4</sub>), we clarify that the electrochemical nitric\noxide reduction reaction (NORR) activity can be significantly improved\nby axially coordinating nonmetal atoms (O, F, Cl) over the metal sites.\nIn light of an electron-withdrawing effect, the axial fifth ligand\ndisrupts the electron distribution symmetry and regulates the local\nelectronic structure of the metal active center. It subsequently moderates\nthe TM–NO interaction and thus enhances the activity. In particular,\nMnN<sub>4</sub>O–C, FeN<sub>4</sub>O–C, CoN<sub>4</sub>O–C, and CoN<sub>4</sub>F–C are identified as promising\nNORR catalysts with ultralow limiting potential (<i>U</i><sub>L</sub>) of −0.07, −0.07, −0.07, and −0.05\nV, respectively. In addition, the axial atom can also passivate the\ncompeting hydrogen evolution reaction (HER), increasing the selectivity\ntoward NH<sub>3</sub> formation. It therefore can be concluded that\nthe present work affirms a novel strategy for the rational design\nof advanced electrocatalysts, highlighting the significance of optimal\nmetal–ligand match and the coordination microenvironment tuning\nof the active centers.