Oxygen‐Incorporation‐Engineered Interfacial Water Modulation on Single‐Atom Cu Sites for Enhanced Dilute Nitrate Electroreduction

Abstract The efficiency of nitrate reduction reaction (NO 3 RR) is highly dependent on the complex interfacial microenvironment, where the triumvirate of alkali metal cations, water network, and NO 3 − adsorption dynamics collectively dictate reaction activity and selectivity. However, how the structural engineering of catalyst governing the interfacial microenvironment is still unclear, yet critical for the construction of efficient catalytic system. In this work, we develop a series of oxygen‐engineered Cu–NCO x SACs featuring asymmetric Cu─N 3 O 1 active site with tunable oxygen‐containing functional groups that enable highly efficient NO 3 RR in dilute nitrate concentrations (100 ppm NO 3 − –N). Experimental and theoretical results show that the introduction of Cu─O coordination results in the pronounced electron‐deficient Cu site, which is beneficial for NO 3 − adsorption and activation. Meanwhile, the electron‐rich nucleophilic oxygen functionalities specifically O = C─O and C = O can efficiently trap Na⁺‐hydrated water (Na⁺–H 2 O) being close to the electrode through electrostatic interactions. The NO 3 RR performance follows a distinct volcano relationship with interfacial Na⁺–H 2 O concentration due to the enhanced HER with large localized *H enrichment. As a result, the Cu–NCO M electrocatalyst possessing optimal oxygen incorporation exhibits an exceptional NH 3 Faradaic efficiency (FE NH3 ) of 96.7% with an outstanding NH 3 yield rate of 10.5 mol h −1 g Cu −1 . This research provides an effective O‐incorporation strategy to boost NO 3 RR performance in dilute NO 3 − aqueous solution by precisely controlling the interfacial water structure around asymmetric Cu SACs centers.