Mechanistic control of a galvanic replacement reaction on cuprous oxide

Galvanic replacement (GR) reactions are a versatile approach to fabricating hierarchically structured functional nanomaterials for catalytic, plasmonic, and sensing applications. Most research efforts aim to identify chemical strategies to control the resultant morphology of GR deposition on metallic nanoparticle seeds. Recently, GR has become a method of interest for fabricating heterogeneous interfaces for these applications. Here, we study the chemical mechanism for the GR reaction of AuCl(4)(−) on Cu-based thin films. X-ray photoelectron spectroscopy and structural characterization show that, while the GR reaction proceeds through the direct dissolution of Cu and reduction of AuCl(4)(−) on Cu, the reaction on Cu(2)O results in the solid-state formation of CuO at the interface which passivates the interface from further Au deposition. As a result, the chemistry and morphology of Au deposited on Cu(2)O is limited by the rate of CuO dissolution in the background acidic electrolyte. To explain the observed differences between the GR reaction of AuCl(4)(−) on Cu and Cu(2)O interfaces, we propose a new mechanism for the GR reaction on Cu(2)O surfaces where disproportionation is the limiting intermediate reaction which can be mediated by AuCl(4)(−) concentration and by the photoelectrochemical generation of Cu nanoparticles throughout the bulk of the Cu(2)O. Consequently, the hierarchical structure of the GR deposition of Au can be chemically controlled on Cu(2)O films. More generally, this highlights how the details of the chemical kinetics at the reaction interface can be exploited to tailor the resulting nanostructure of metals deposited via GR reactions.