The Effect of Ligand Field on Enhanced Electrocatalytic Performance of NO Reduction under Applied Potential

We employed density functional theory to investigate Co-N-4/Gra single-atom catalysts, focusing on the modification of axial ligand (X=-F, -CN and -C3H4N2) and examined the influence of ligand field and electric potential on eNORR. Our results demonstrate that Co-N-4[X]/Gra exhibit favorable thermodynamic adsorption (Delta G(*NO) < 0) and remarkable activation activity toward NO molecules. Co-N-4/Gra demonstrates a limiting potential of -0.13 V with the potential-determining step (PDS) of *NH3 -> * + NH3(g). Notably, under the introduction of ligands, Co-N-4[F]/Gra achieves the most favorable overpotential of -0.07 V, superior to most of NORR electrocatalysts, and meanwhile shows an exceptional selectivity of 99.99% for eNORR compared to competitive hydrogen evolution reaction. Under the solvent environment, Co-N-4/Gra features the triggering potentials of -0.33 V for a pH of 1, -0.71 V for a pH of 7, and -1.10 V vs RHE for a pH of 13, respectively. Additionally, the potential reduces the desorption energy and adsorption energy of NH3, facilitating the accessibility of the NH3 desorption step (PDS) and promoting NO reduction. Thus, under realistic conditions, the Co ion's active site displays variable valence electrons and forms a dynamic interplay with the ligand field effect, rendering a crucial effect on the adsorption of reaction species during the eNORR.