Stable and Efficient Ir Nanoshells for Oxygen Reduction and Evolution Reactions

We report the characterization and applications of core-shellCu-Ir nanocatalysts for oxygen reduction reaction and oxygenevolution reaction. Core-shell Cu-Ir particles withtunable thickness of Ir can be oxidized to remove the Cu core andobtain Ir shells. The thickness of the Ir shells determines the stabilityand optimization of the precious metals. We showed with insitu scanning transmission electron microscopy the remarkablestability of the Ir shells at elevated temperatures under oxidativeand reductive environments. In situ scanning transmissionelectron microscopy and in situ X-ray absorptionspectroscopy also showed that traces of remaining copper could bedetected in the Ir shells. Electrochemical measurements for oxygenreduction and evolution reactions show promising activity and stabilitycompared to a commercial catalyst. Thin Ir shells, with high surfacearea per gram of Ir, were more active but less stable than thickershells. In contrast, thicker Ir shells were more stable and had excellentelectrochemical properties in aqueous and alkaline environments. Hence,Ir nanoshells appear as interesting candidates for reducing the costof catalysis while improving chemical performance in fuel cells.