Formation Pathways of Porous Alloy Nanoparticles through Selective Chemical and Electrochemical Etching.

Porous alloy nanomaterials are important for applications in catalysis, sensing, and actuation. Chemical and electrochemical etching are two methods to form porous nanostructures by dealloying bimetallic nanoparticles (NPs). However, it is not clear how the NPs evolve during these etching processes. Insight into the morphological and compositional transformations of the NPs during the etching is critical to understanding the nanoscale details of the dealloying process. Here, using in situ liquid phase transmission electron microscopy, the structural evolution of individual AuAg alloy NPs is tracked during both chemical and electrochemical etching of their Ag component. The observations show that the electrochemical etching produces NPs with more uniform pore sizes than the chemical etching and enables tuning the NPs porosity by modulating the electrochemical potential. The results show that at the initial stages of both etching methods, Au-rich passivation layer forms on the surface of the NPs, which is critical in preserving the NP's porous shell as pores form underneath this layer during the etching. These findings describing the selective etching and dealloying of AuAg NPs provide a critical insight needed to control the morphology and composition of porous multimetallic NPs, and paves the way for synthesizing nanomaterials with tailored chemical and physical properties for various applications.