Dynamic Collision Oxidation Behaviors of Ag Nanoparticles on Au Nano-Disk Electrodes and Nanopore Electrodes

The dynamic collision behaviors of single nano particles (NPs) using nano-sized electrodes in a confined space are highly desirable to be explored for revealing the intrinsic reaction mechanism that is masked in ensemble-averaged measurements. Herein, we illustrate the collision phenomena of silver NPs (Ag NPs) with different agglomeration degrees by using a gold nanodisk electrode (NDE) and a nanopore electrode (NPE). The dynamic collision behaviors of electro-oxidation of the Ag NPs at the single particle level and aggregation state were investigated on the gold NDE and NPE. The results show that the collision/ oxidation events of single Ag NPs on the NDE usually lead to diffusion of NPs into the solution after the collision; thus, the degree of oxidation is low. On NPEs, the Ag NPs can hardly escape from the pore, so it shows more multi-peak phenomena and a higher oxidation charge. However, the oxidation collision of the aggregates of Ag NPs exhibits higher peak currents, longer relaxation times, and more obvious shoulder peaks on the Au NDEs and NPEs; the single collision event usually consists of a series of 1-10 discrete "sub-events" within an interval of approximately 5 ms. Compared with a single Ag NP collision, the aggregates of Ag NPs will disperse into smaller or even individual NPs after the first few collisions and then stochastic collisions will occur repeatedly. These findings can help us deeply understand the dynamic oxidation process of metal NPs and will benefit the applications in fundamental electrochemistry, electrocatalysis, and energy-related research.