Ligand-induced Changes in the Electrocatalytic Activity of Atomically Precise Au₂₅ Nanoclusters

Abstract

Atomically precise gold nanoclusters have shown great promise as model elctrocatalysts in pivotal electrocatalytic processes such as hydrogen evolution reaction (HER) and carbon dioxide reduction reaction (CO2RR). Although the influence of ligands on the electronic properties of these nanoclusters are well acknowledged, the ligand effects on their electrocatalytic performances have been rarely explored. Herein, using [Au25(SR)18]- nanocluster as the prototype model, we demonstrated the importance of ligand hydrophilicity versus hydrophobicity in modulating the interface dynamics and electrocatalytic performance. Our first-principle computations revealed that Au25 protected by hydrophilic -SCH2COOH ligands dictates faster kinetics in stripping the thiolate ligand and exhibits 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 HER, while the hydrophobic ligand-protected Au25 NCs achieve higher Faradaic efficiency and current density in CO2RR. The mechanistic insights in this study provide valuable guidance for the rational design of surface microenvironment in efficient nanocatalysts for sustainable energy applications.