Single-Atom Engineering of Atomically Precise Ag-Cu Alloy Nanoclusters Enables Site-Gated Pathway Switching in CO₂...

Atomically precise metal nanoclusters (NCs) provide a molecular platform for single-atom-level manipulation and unraveling structure-property relationships. Herein, we realize site-resolved single-atom engineering on an Ag-Cu alloy NC platform, allowing for the precise decoupling of surface atomic identity as an independent structural variable. Starting from Ag₂₆Cu₁₇(SR)₃₀(PPh₃)₇ (Ag₂₆Cu₁₇, SR = SPh-p-CF₃), three surface-exposed Ag atoms are sequentially replaced by Cu through a controlled metal-exchange reaction, generating an isostructural series of Ag₂₅Cu₁₈, Ag₂₄Cu₁₉, and Ag₂₃Cu₂₀ NCs. Electrospray ionization mass spectrometry enables in situ tracking of the single-atom substitution process, while single-crystal X-ray diffraction confirms complete retention of the cluster framework and ligand environment. Using CO₂ electroreduction as a structure-sensitive probe, progressive Cu substitution at the three equivalent surface gate sites triggers a reaction pathway switch from CO-selective reduction on Ag₂₆Cu₁₇ to dominant deep-reduction on Ag₂₃Cu₂₀, through modulating *CO stabilization and the *CO → *CHO energy barrier. Specifically, the faradaic efficiency (FE) for CO decreases from 90.42% to 13.46%, whereas the total FE for deep reduction products increases from 2.67% to 73.00%, with CH₄ as the major product (FE_CH4 = 53.98%). Consequently, this work establishes Ag-Cu NCs as a robust platform for single-atom engineering and atomic-scale structure-property analysis.