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

Abstract

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.