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

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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.