Modifying the second coordination spheres of Fe active sites for electrocatalytic nitric oxide reduction in realistic electrochemical environment

The first and second coordination spheres in the coordination microenvironment may regulate the electronic structure of single-metal atoms supported on carbon matrix, which in turn modulates the catalyst's catalytic activity. Simulating the kinetic process of electrocatalytic nitric oxide reduction reaction (NORR) by the theoretical modeling of electrochemical microenvironments helps understand the theoretical structure–activity relationship and guides a more rational design of electrocatalysts. In this study, density functional theory calculations combined with a constant-potential/hybrid-solvent model and microkinetic modeling are employed to study NORR mechanism on the carbon-based FeN4, FeN4-O and FeN4-B catalysts with different electronegativity atoms in the second coordination spheres under −1.00 ∼ 0.40 V vs. RHE. The free energy changes of all elementary reactions for NORR on the catalysts reveal that the optimal pathways for NORR on FeN4 produce both ammonia and hydroxylamine, proceeding through the reaction intermediates *NHOH. Within −1.00 ∼ -0.37 V vs. RHE, the kinetic barriers of the rate-determining steps for NORR increase sequentially on FeN4, FeN4-O, and FeN4-B, corresponding to the sequentially decreasing reaction rate constants. At −6.00 mA∙cm−2, the electrode potential for ammonia production on FeN4 catalyst is the lowest among the catalysts at −0.70 V vs. RHE, indicating it has higher electrocatalytic activity.