Structure-Property Engineering in Ag₂₃ Nanoclusters for Electrocatalytic Nitrate Reduction

Electrocatalytic nitrate reduction reaction (NO₃RR) provides a sustainable pathway for ambient ammonia synthesis; however, achieving concurrent high activity, high selectivity and appropriate stability of catalysts remains a substantial challenge. Here we report the synthesis and structure-property engineering of a class of atomically precise silver nanoclusters via geometric tuning and copper substitution. Compared with the parent nanocluster Ag₂₃(PET)₁₈(PPh₃)₈ (abbreviated as Ag₂₃-1), a Cu-substituted Ag₁₉Cu₄(SCH₂PhCl)₁₈(PPh₃)₄ nanocluster (i.e., Ag₁₉Cu₄) modulates the electronic structure and catalytic active sites, giving rise to an improved Faradaic efficiency (FE ∼71%) upon NO₃RR electrocatalysis but with irreversible alteration of the metal oxidation states. Intriguingly, a geometry-tuned [Ag₂₃(SAdm)₁₂]³⁺ cluster (Ag₂₃-2) exhibits enhanced stability due to its superatomic eight-electron shell structure (1S²|1P⁶||) and delivers an NH₃ yield of ∼6.5 mg_NH3·h^-1·mg^-1 _cat at -0.9 V, outperforming the parent Ag₂₃-1 and comparable with the Ag₁₉Cu₄ NCs. Density functional theory (DFT) calculations indicate that the reaction proceeds via a stepwise hydrogenation pathway, with the *NO₂-to-*NO conversion serving as the rate-determining step, where the energy barriers can be efficiently lowered by the Ag₁₉Cu₄ NCs. This work illustrates that structural engineering constitutes an effective strategy for tailoring activity, selectivity, and stability in atomically precise nanocluster catalysts.