Ligand-induced changes in the electrocatalytic activity of atomically precise Au₂₅ nanoclusters

Atomically precise gold nanoclusters have shown great promise as model electrocatalysts in pivotal electrocatalytic processes such as the hydrogen evolution reaction (HER) and carbon dioxide reduction reaction (CO₂RR). Although the influence of ligands on the electronic properties of these nanoclusters is well acknowledged, the ligand effects on their electrocatalytic performances have been rarely explored. Herein, using [Au₂₅(SR)₁₈]^- nanoclusters as a prototype model, we demonstrated the importance of ligand hydrophilicity versus hydrophobicity in modulating the interface dynamics and electrocatalytic performance. Our first-principles calculations revealed that Au₂₅ protected by hydrophilic -SCH₂COOH ligands exhibits faster kinetics in stripping the thiolate ligand and better HER activity due to enhanced proton transfer facilitated by boosted interface hydrogen bonding. Conversely, Au₂₅ protected by hydrophobic -SCH₂CH₃ ligands demonstrates enhanced CO₂RR performance by minimizing water interference to stabilize the key *COOH intermediate and lower the barrier for CO formation. Experimental validation using synthesized hydrophilic and hydrophobic ligand-protected Au₂₅ nanoclusters (NCs), such as [Au₂₅(MPA)₁₈]^- (MPA = mercaptopropionic acid), [Au₂₅(MHA)₁₈]^- (MHA = 6-mercaptohexanoic acid), and [Au₂₅(SC₆H₁₃)₁₈]^-, confirms these findings, where the hydrophilic ligand-protected Au₂₅ NCs exhibit better activity and stability in the HER, while the hydrophobic ligand-protected Au₂₅ NCs achieve higher faradaic efficiency and current density in the CO₂RR. The mechanistic insights in this study provide valuable guidance for the rational design of surface microenvironments in efficient nanocatalysts for sustainable energy applications.