Effect of Size, Coverage, and Dispersity on the Potential-Controlled Ostwald Ripening of Metal Nanoparticles

Here, we describe the size-dependent, electrochemically controlled Ostwald ripening of 1.6, 4, and 15 nm-diameter Au nanoparticles (NPs) attached to (3-aminopropyl)triethoxysilane (APTES)-modified glass/indium-tin-oxide electrodes. Holding the Au NP-coated electrodes at a constant negative potential of the dissolution potential in a bromide-containing electrolyte led to electrochemical Ostwald ripening of the different-sized Au NPs. The relative increase in the diameter of the NPs (D_final/D_initial) during electrochemical Ostwald ripening increases with decreasing NP size, increasing applied potential, increasing NP population size dispersity, and increasing NP coverage on the electrodes. Monitoring the average size of the Au NPs as a function of time at a controlled potential allows the measurement of the Ostwald ripening rate. Anodic stripping voltammetry and electrochemical determination of the surface area-to-volume ratio provide fast and convenient size analysis for many different samples and conditions, with consistent sizes from scanning electron microscopy images for some samples. It is important to better understand electrochemical Ostwald ripening, especially under potential control, since it is a major process that occurs during the synthesis of metal NPs and leads to detrimental size instability during electrochemical applications.