Observing Electrochemical Dealloying by Single-Nanoparticle Collision

We report direct observation of electrochemical and thermal dealloying processes of individual metal alloy nanoparticles (NPs). Electrochemical dealloying of single Ag-Hg alloy NPs was achieved in a basic solution (e.g., pH 13) by oxidizing Hg under controlled potentials. Ag can also be oxidized during single-particle collision. However, it requires elevated potentials. The strong basic environment promoted the formation of metal oxides during collision leading to a unique core-shell type nanostructure which was further confirmed by transmission electron microscopy (TEM). In thermal dealloying, Hg was evaporated due to the use of a high-energy electron beam and the process was imaged in situ inside a TEM. Both electrochemical and thermal dealloying processes resulted in the transformation of an amorphous NP to a more stable Ag-Hg alloy nanocrystal. This work demonstrates that NP collision can be a useful tool to study dealloying processes of various nanomaterials at a single-particle level.