Spatial Decoupling of Adsorption and Transformation Sites on Ag‐Cu Dual‐Single‐Atom Catalysts for Highly Selective Photocatalytic Nitrate‐to‐Ammonia Reduction

Photocatalytic nitrate (NO₃ ^-) reduction to ammonia (NH₃) presents a sustainable solution for simultaneous NH₃ synthesis and wastewater remediation. However, achieving high selectivity is challenging, plagued by sluggish kinetics and parasitic side reactions. In this study, we rationally design a synergistic Ag-Cu dual-atom catalyst on g-C₃N₄ (AgCu-CN) that embodies a spatially decoupled tandem scheme. We demonstrate that the oxophilic Cu₁ site serve as Lewis acid centers to efficiently capture and activate NO₃ ^-, before the crucial *NO intermediate is shuttled to adjacent Ag₁ site, which is intrinsically inert toward the hydrogen evolution reaction, act as dedicated hydrogenation center for rapid and deep *NO reduction. This atomic-level synergy manifests in a state-of-the-art performance, with AgCu-CN delivering an impressive 98% NH₃ selectivity and a production rate of 630.5 µmol h^-1 g^-1 under visible light. In situ spectroscopic studies and theoretical calculations corroborate the tandem mechanism and the critical role of the Ag-Cu dual sites in steering reaction selectivity. This study establishes a powerful tandem catalytic design principle to manage the selectivity challenges in complex multi-proton/electron reactions.