Formation of Ag2S cages from polyhedral Ag2O nanocrystals and their electrochemical properties.

Ag2O nanocubes, rhombicuboctahedra, octahedra, and hexapods have been employed as templates for the generation of Ag2O-Ag2S core-shell structures through a rapid sulfidation process in a basic solution. Addition of an ammonia etching solution quickly removes the Ag2O cores, thereby resulting in the formation of Ag2S cages with morphologies that resemble the starting templates. The composition of the Ag2S shells and cages has been extensively determined by various analytical techniques including X-ray and electron diffraction and X-ray photoelectron spectroscopy. The Ag2S shells have a monoclinic crystal structure and are polycrystalline with some amorphous and porous regions. The nanocage formation process has been captured by transmission electron microscopy (TEM). Gap spaces are formed initially between the cores and the shells owing to uniform etching of the Ag2O cores on all of the faces. No linkages connecting the cores to the shells have been observed. Depending on the potential scanning ranges applied, four types of electrochemical redox behavior have been identified for the Ag2O and Ag2O-Ag2S cubes in a basic solution. The ability to easily fabricate thin sheets of Ag2S over different Ag2O surfaces should extend the applications of Ag2S nanostructures.