Axial Coordination of Iron Single-Atom Catalysts on Defective Graphene for Electrocatalytic Conversion of Nitric Oxide to Hydroxylamine: A Theoretical Investigation

With the rapid development of modern society and the chemical industry, the demand for hydroxylamine (NH₂OH) has expanded significantly across diverse fields. However, its conventional synthesis remains challenged by severe pollution and intensive resource consumption. Building upon the experimentally realized Fe@N₄ structure, we propose a ligand coordination strategy to module the electronic structure of iron single-atom catalysts via 15 axial ligands (-F, -Cl, -Br, -I, -N, -O, -OH, -OOH, -CH, -CH₂, -CH₃, -NH₂, -SH, -CN, -SCH₃), aiming to enhance the electrocatalytic reduction of nitric oxide (NO) to NH₂OH. Among these, 13 catalysts effectively suppress hydrogen evolution reactions and the generation of undesired byproducts such as NH₃ and N₂O/N₂. Notably, the -CH₂ ligand significantly alters the local electronic environment of the active site, enabling the activation of NO molecules through an electronic "accept-donate" mechanism. This modulation enhances both the activity and selectivity for NO reduction, ultimately leading to a spontaneous, exothermic conversion of NO to NH₂OH. This work theoretically proposes a strategy whereby axial coordination can enhance the catalytic reactivity of single-atom catalysts.