Stable and Efficient Ir Nanoshells for Oxygen Reduction and Evolution Reactions

We report the characterization and applications of core-shell Cu-Ir nanocatalysts for oxygen reduction reaction and oxygen evolution reaction. Core-shell Cu-Ir particles with tunable thickness of Ir can be oxidized to remove the Cu core and obtain Ir shells. The thickness of the Ir shells determines the stability and optimization of the precious metals. We showed with in situ scanning transmission electron microscopy the remarkable stability of the Ir shells at elevated temperatures under oxidative and reductive environments. In situ scanning transmission electron microscopy and in situ X-ray absorption spectroscopy also showed that traces of remaining copper could be detected in the Ir shells. Electrochemical measurements for oxygen reduction and evolution reactions show promising activity and stability compared to a commercial catalyst. Thin Ir shells, with high surface area per gram of Ir, were more active but less stable than thicker shells. In contrast, thicker Ir shells were more stable and had excellent electrochemical properties in aqueous and alkaline environments. Hence, Ir nanoshells appear as interesting candidates for reducing the cost of catalysis while improving chemical performance in fuel cells.