Dynamic Evolution and Reversibility of a Single Au 25 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 Au 25 (PPh 3 ) 10 (SC 2 H 4 Ph) 5 Cl 2 2+ nanocluster (Au 25 2+ 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 Au 25 2+ NC, combined with the dynamic conformation evolution of the Au 25 9+ core, led to a characteristic current signal that involves "ON-OFF" switches and "ON" fluctuations during the ORR process of a single Au 25 2+ NC. Our findings reinvent the new perception and comprehension of the structure-activity correlation of NCs at the atomic level.