Electrochemical Cleaning Stability and Oxygen Reduction Reaction Activity of 1-2 nm Dendrimer-Encapsulated Au Nanoparticles

Here we show that just three electrochemical scans to modest positive potentials result in substantial growth of 1–2 nm Au dendrimer-encapsulated nanoparticles (DENs). We examined two sizes of Au DENs, denoted as G6-NH₂(Au₁₄₇) and G6-NH₂(Au₅₅), where G6-NH₂ represents a sixth-generation, amine-terminated, poly(amidoamine) dendrimer and the subscripts, 147 and 55, represent the average number of atoms in each size of DENs. Ex situ transmission electron microscopy (TEM) and in situ X-ray absorption spectroscopy (XAS) results indicate that G6-NH₂(Au₅₅) DENs grow to the same size as the G6-NH₂(Au₁₄₇) DENs following these scans. Importantly, this growth occurs prior to the onset of detectable faradaic Au oxidation or reduction current. The observed growth in the size of the DENs directly correlates to changes in the electrocatalytic ORR activity. The key point is that after just three positive scans the G6-NH₂(Au₁₄₇) and G6-NH₂(Au₅₅) DENs are essentially indistinguishable in terms of both physical and electrocatalytic properties.