Understanding the Role of Potential and Cation Effect on Electrocatalytic CO₂ Reduction in All-Alkynyl-Protected Ag₁₅...

Atomically precise metal nanoclusters (NCs) have emerged as an intriguing class of model catalysts for electrochemical CO₂ reduction reactions (CO₂RR). However, the interplay between the interface environment (e.g., potential, cation concentration) and electron-proton transfer (ET/PT) kinetics─particularly in alkynyl-protected metal NCs─remains poorly understood. Here, we combined first-principles simulations and electrochemical experiments to investigate the role of potential and cation effect on CO₂RR performance in a prototype all-alkynyl-protected Ag₁₅(C≡C-CH₃)⁺ cluster. Our simulations revealed that the applied reduction potential triggers the elimination of the alkynyl ligand via sequentially breaking two π-type Ag-C bonds and one σ-type Ag-C bond to expose the catalytically active Ag sites, and the barrier of the Ag-C breakage monotonically decreases with the lowering in potential. Furthermore, we show that introducing the inner-sphere Na⁺ ions greatly enhances *CO₂ activation and promotes proton transfer to generate *COOH and *CO by forming the Na⁺-CO₂(*COOH) complexes, while the competitive hydrogen evolution reaction (HER) from water dissociation is greatly suppressed, thus dramatically improving the selectivity of CO₂ electroreduction. The electrochemical measurements further validated our predictions, where the CO Faradaic efficiency (FE_CO) and current density (j_CO) show a pronounced dependence on the Na⁺ concentration. At an optimal concentration of 0.1 M NaCl, FE_CO can reach up to ∼96%, demonstrating the crucial role of cations in promoting the CO₂RR. Our findings provide vital insights into the atomic-level reaction mechanism of the CO₂RR on alkynyl-protected Ag₁₅ NCs and highlight the important role of potential and electrolyte cation in governing the electron/proton transfer kinetics.