Electronic Confinement Induced Single Atom Functionality in Hydroxylamine Synthesis Unveiled by Constant Potential Simulation.

Electrochemical nitric oxide (NO) reduction offers a sustainable route for hydroxylamine (NH2OH) synthesis. Single-atom catalysts (SACs), featuring isolated metal centers and weaker adsorbate binding than extended metals, are widely regarded as ideal NH2OH-selective catalysts. However, the recent observation of NH2OH production on highly reactive metals challenges this conventional viewpoint and indicates that SACs are not indispensable in hydroxylamine electrosynthesis. Here, we establish a unified picture in which electronic confinement induces single-atom functionality that underlies NH2OH selectivity. Specifically, our constant-potential simulations identify the competition between *HNO and *NOH formation as a key determinant of NH2OH versus NH3 selectivity, with preferential *HNO formation directing the reaction toward NH2OH production. Grand canonical Monte Carlo simulations further reveal that highly reactive metals undergo operando surface restructuring, generating isolated metal centers that acquire single-atom functionality and preferentially stabilize *HNO. Electronic structure analysis uncovers a unified origin of *HNO preference: heteroatom coordination induces strong orbital hybridization, narrowing the metal d-band and localizing the electronic states of the isolated metal centers. This electronic confinement enables balanced *HNO-metal interactions while preserving the intramolecular N─O bond, thereby stabilizing *HNO and promoting NH2OH selectivity. These findings establish electronic confinement as a promising and general design principle for developing NH2OH-selective electrocatalysts beyond predefined SACs.