Time-Resolved Detection of Surface Oxide Formation at Individual Gold Nanoparticles: Role in Electrocatalysis and New Approach for Sizing by Electrochemical Impacts.

Nanoparticle (NP) impacts on electrode surfaces has become an important method for analyzing the properties and activity of individual NPs, by either (i) electrocatalytic reactions or (ii) volumetric (dissolution) analyses. Using Au NPs as an exemplar system, this contribution shows that it is possible to detect surface oxide formation at individual NPs, which can occur on a rapid time scale (few μs). The charge associated with this "surface oxidation method" can be used for sizing (with results that are comparable to TEM) despite charges of only fC being measured. This platform further allows the role of surface oxides in electrocatalysis to be elucidated, with the time scale of oxide formation being controllable (i.e., "tunable") via the applied potential, as illustrated through studies of borohydride and hydrazine electro-oxidation. Finally, all of these studies are carried out on an oxide-covered Au substrate, which can be prepared and regenerated straightforwardly on an Au electrode, through the applied potential.