Visualizing the Effect of Partial Oxide Formation on Single Silver Nanoparticle Electrodissolution

Abstract

The impact of heterogeneous surface oxide formation on the electrochemical performance of single silver nanoparticles is explored using in situ superlocalization optical microscopy. Silver nanoparticles are well-known to form a natural oxide layer on their surface, but the effect of this oxide layer on electrochemical reactions is not well understood. Here we track the temporal and spatial dependence of electrodissolution of single silver nanoparticles in order to study the role of surface oxide layers on electrochemical reactions. Heterogeneity in electrodissolution kinetics is observed by following the time-dependent loss in scattering intensity from individual silver nanoparticles using dark-field scattering. Both fast and slow dissolution kinetics are observed, with the dominant pathway changing as a function of applied potential. To understand this, superlocalization imaging is employed to follow the spatial variance of the electrodissolution process and reveals that the silver nanoparticles undergo electrodissolution in either a spatially symmetric or asymmetric manner. We hypothesize that asymmetric dissolution events are due to heterogeneity in the exposed silver sites on the nanoparticle surface because of incomplete surface oxide formation. Polarization-resolved measurements support this hypothesis by revealing anisotropic dissolution of the nanoparticles over time. By tracking the electrodissolution behavior of silver nanoparticles in both the temporal and spatial domains, we provide an improved understanding of how heterogeneity in electrochemical reactions is impacted by nanoparticle surface properties.