Dynamic Evolution and Reversibility of a Single Au₂₅ Nanocluster for the Oxygen Reduction Reaction

Ultrasmall metallic nanoclusters (NCs) protected by surface ligands represent the most promising catalytic materials; yet understanding the structure and catalytic activity of these NCs remains a challenge due to dynamic evolution of their active sites under reaction conditions. Herein, we employed a single-nanoparticle collision electrochemistry method for real-time monitoring of the dynamic electrocatalytic activity of a single fully ligand-protected Au₂₅(PPh₃)₁₀(SC₂H₄Ph)₅Cl₂²⁺ nanocluster (Au₂₅²⁺ NC) at a cavity carbon nanoelectrode toward the oxygen reduction reaction (ORR). Our experimental results and computational simulations indicated that the reversible depassivation and passivation of ligands on the surface of the Au₂₅²⁺ NC, combined with the dynamic conformation evolution of the Au₂₅⁹⁺ core, led to a characteristic current signal that involves "ON-OFF" switches and "ON" fluctuations during the ORR process of a single Au₂₅²⁺ NC. Our findings reinvent the new perception and comprehension of the structure-activity correlation of NCs at the atomic level.