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

Abstract

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.