Multi-orbital engineering of single-atom catalysts: unlocking high-efficiency nitrate reduction†

Abstract

Single-atom catalysts (SACs) doped with heteroatoms have shown great promise for the electrocatalytic nitrate reduction reaction (NO₃RR), yet the underlying mechanisms linking doping configurations to catalytic activity are not well understood. In this study, we apply density functional theory (DFT) calculations to systematically investigate the structural, energetic, and electronic properties of 52 two-dimensional TM–N₃X nanosheets, focusing on their electrocatalytic behavior in the NO₃RR. Our results reveal that doping with O, P, S, and B atoms alters system stability, with P, S, and B doping resulting in reduced or comparable adsorption energies compared to the N₄ coordination, while O doping strengthens adsorption. Crucially, we identify that symmetry breaking induced by heteroatom doping significantly contributes to lowering the formation barriers of key intermediates. Additionally, we establish linear correlations between key thermodynamic descriptors-ΔG_*NO3, ΔG_MAX, ΔG(*NOH → *N), the d-band center, and limiting potentials, which provide a deeper mechanistic understanding of electrocatalytic activity. Our analysis further highlights the significant influence of multi-orbital splitting energy (d_SE) and the magnetic moment of the active site on the bonding and anti-bonding states of intermediates, thereby modulating adsorption behavior. By elucidating the critical role of heteroatom-induced symmetry breaking, this work offers valuable insights into how coordination microenvironments affect electrocatalytic reaction mechanisms and paves the way for the rational design of similar more efficient NO₃RR electrocatalysts.