Noble-Metal Nanotubes Prepared via a Galvanic Replacement Reaction Between Cu Nanowires and Aqueous HAuCl4, H2PtCl6, or Na2PdCl4

The galvanic replacement reaction between Ag nanostructures and aqueous HAuCl4 solution has been widely studied for the purpose of generating noble-metal nanostructures with hollow interiors. Here we explore the galvanic replacement reaction between Cu nanowires and HAuCl4, H2PtCl6, or Na2PdCl4, which also generates hollow metal nanostructures. Compared to the galvanic replacement reaction using Ag nanowires in boiling water, the reaction involving Cu nanowires is relatively mild and can be conducted at room temperature since the reduction potential of Cu2+/Cu is much lower than that of Ag+/Ag. Moreover, the Cu nanowires are inexpensive to prepare, making this approach more practical for large-scale production. In this study, we use electron microscopy to characterize the morphological evolution and final structure of the Au, Pt, and Pd nanotubes. We find that the final structure retains the initial circular morphology of the Cu nanowires and that the surface of the nanotubes is decorated with 20-nm (for Au) or 2-nm pores (for Pt and Pd). Using energy dispersive X-ray spectroscopy (EDX), we find that we can obtain pure Au nanotubes when a stoichiometric amount of HAuCl4 is reacted with the Cu nanowires. We also evaluate the electrocatalytic activity of the Pt nanotubes for formic acid oxidation.