Oxygen Electrocatalysis by [Au₂₅(SR)₁₈]: Charge, Doping, and Ligand Removal Effect

Abstract

Considering the promising prospects of Au25(SR)18q and its alloy clusters in numerous fundamental catalysis research studies derived from their well-defined structures, developing a deep understanding of the structure–property correlation becomes significantly urgent. Herein, we explored a prototype [Au25(SR)18]q cluster, monoatom-doped bimetallic [MAu24(SR)18]q clusters (M = Pt, Pd, Ag, Cu, Hg, or Cd), and their singly deligated M-exposure and S-exposure systems as electrocatalysts toward O2 reduction reaction (ORR) at the acidic medium. Theoretical simulations reveal that the fully ligand-protected clusters prefer H2O2 formation through the two-electron (2e–) mechanism, whereas the dethiolated clusters prefer to proceed via the four-electron (4e–) pathway for H2O production. Among them, a single Hg substitution at the staple site, namely, fully ligated [HgAu24(SCH3)18]0–O and dethiolated [HgAu24(SCH3)17]0–O with an exterior −SCH3 removal has great potential to realize high-efficiency 2e– and 4e– ORR, with an ultralow overpotential of 0.08 and 0.43 V, respectively. The correlation between adsorption of oxygenated intermediates and Bader charge as well as active metal d-band center sheds light on the underlying origin of selectivity and activity. Besides, the analysis of projected density of states suggests that monoatom doping has a mild modification to the s-bands of Au, but the removal of the −SR ligand can obviously amend the electronic structure of Au-s states. Particularly, in contrast to the strong d-electron effect in Au25q and other doped MAu24q clusters, the s-electron effect from the staple-doped Hg atom shows great promise in optimizing the intermediate adsorption and functions as a distinguished electrocatalyst for O2 reduction. These insights provide useful guidelines for the design of high-efficiency metal nanocluster electrocatalysts by implementing late-transition metal or p-block metal with a strong s- or p-electron effect to achieve superior ORR activity.