Oxygen-Incorporation-Engineered Interfacial Water Modulation on Single-Atom Cu Sites for Enhanced Dilute Nitrate...

The efficiency of nitrate reduction reaction (NO₃RR) is highly dependent on the complex interfacial microenvironment, where the triumvirate of alkali metal cations, water network, and NO₃ ^- 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─N₃O₁ active site with tunable oxygen-containing functional groups that enable highly efficient NO₃RR in dilute nitrate concentrations (100 ppm NO₃ ^--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 NO₃ ^- adsorption and activation. Meanwhile, the electron-rich nucleophilic oxygen functionalities specifically O = C─O and C = O can efficiently trap Na⁺-hydrated water (Na⁺-H₂O) being close to the electrode through electrostatic interactions. The NO₃RR performance follows a distinct volcano relationship with interfacial Na⁺-H₂O 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 NH₃ Faradaic efficiency (FE_NH3) of 96.7% with an outstanding NH₃ yield rate of 10.5 mol h^-1 g_Cu ^-1. This research provides an effective O-incorporation strategy to boost NO₃RR performance in dilute NO₃ ^- aqueous solution by precisely controlling the interfacial water structure around asymmetric Cu SACs centers.