Size-dependent electrochemical oxidation of silver nanoparticles

Here we quantify the electrochemical oxidation of Ag nanoparticles (NPs) as a function of size by electrostatically attaching Ag NPs synthesized by seed-mediated growth in the presence of citrate (diameter = 8 to 50 nm) to amine-functionalized indium-tin oxide coated glass electrodes (Glass/ITO), obtaining a linear sweep voltammogram from 0.1 V, where Ag(0) is stable, up to 1.0 V, and observing the peak potential (E(p)) for oxidation of Ag(0) to Ag(+). Electrostatic attachment to the organic linker presumably removes direct interactions between Ag and ITO and allows control over the total Ag coverage by altering the soaking time. This is important as both metal-electrode interactions and overall Ag coverage can affect E(p). E(p) shifts positive from an average of 275 to 382 mV as the Ag NP diameter increases for a constant Ag coverage and under conditions of planar diffusion, suggesting a shift in E(p) due to a thermodynamic shift in E(0) for the Ag/Ag(+) redox couple with size. The negative shift in E(p) with decreasing Ag NP radius follows the general trend predicted by theory and agrees with previous qualitative experimental observations. A better understanding of metal nanostructure oxidation is crucial considering their potential use in many different applications and the importance of metal corrosion processes at the nanoscale.