Enhancing NO electroreduction on N/O co-coordinated single-atom catalysts via d-band center modulation

Abstract

Single-atom catalysts (SACs) have shown great potential in the nitric oxide reduction reaction (NORR), yet the role of their coordination environments in modulating activity remains elusive. Here, we systematically investigate NORR on a series of N/O co-coordinated SACs (M-NxO4-x, 1≤x ≤4) using density functional theory in combination with machine learning (ML). By leveraging a four-stage screening workflow, we identify three Cu-based SACs (Cu-N2O2α, Cu-N2O2β, and Cu-N3O1) with remarkably low limiting potentials of –0.13, –0.09, –0.17 V, respectively, outperforming most reported M-N4 catalysts. Notably, the Cu-N3O1 motif has recently been experimentally realized for efficient nitrate reduction (Angew. Chem. Int. Ed. 2025, e16401), lending support to the reliability of our theoretical predictions. Electronic-structure analyses further reveal that the incorporation of oxygen into the Cu coordination environment upshifts the Cu d-band center toward the Fermi level, which strengthens Cu–NO hybridization and facilitates NO adsorption and activation, thereby governing the enhanced NORR activity. Complementary ML analysis reveals that NO adsorption energetics are primarily governed by the metal valence electron count and oxygen coordination number. Overall, this work establishes a fundamental structure–activity framework for N/O co-coordinated SACs and offers design principles for efficient NO-to-NH3 electrocatalysts.