Solid-Solution Alloy Nanoparticles of the Immiscible Iridium-Copper System with a Wide Composition Range for Enhanced Electrocatalytic Applications.

For the first time, we synthesize solid-solution alloy nanoparticles of Ir and Cu with a size of ca. 2 nm, despite Ir and Cu being immiscible in the bulk up to their melting over the whole composition range. We performed a systematic characterization on the nature of the Ir Cu solid-solution alloys using powder X-ray diffraction, scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The results showed that the Ir Cu alloys had a face-centered-cubic structure; charge transfer from Cu to Ir occurred in the alloy nanoparticles, as the core-level Ir 4f peaks shifted to lower energy region with the increase in Cu content. Furthermore, we observed that the alloying of Ir with Cu enhanced both the electrocatalytic oxygen evolution and oxygen reduction reactions. The enhanced activities could be attributed to the electronic interaction between Ir and Cu arising from the alloying effect at atomic-level.