Electrochemical Cycling of Polycrystalline Silver Nanoparticles Produces Single-Crystal Silver Nanocrystals

Electrochemically driven phase transformations in redox-active nanoparticles (NPs) are important in a number of areas, including batteries and sensors. We use high-resolution electron microscopy in conjunction with ex situ electrochemical experiments on TEM grids to study the oxidative conversion of polycrystalline silver NPs to amorphous silver oxide nanoparticles and their reductive conversion back to single-crystal silver nanocrystals (NCs). Results show that during oxidation nucleation occurs uniformly at the NP surface, producing a Ag@Ag2O core@shell structure during growth. The images reveal polycrystalline Ag cores and amorphous Ag2O shells for these structures. Electron microscopy also showed that the electrochemical reduction of Ag2O NPs can produce single-crystal Ag nanocrystals, suggesting that point nucleation at the NP–electrode interface during reduction enables a growth mechanism favoring the formation of single-crystal nanoparticles.