Atomic Scale Structure and Reduction of Cerium Oxide at the Interface with Platinum

A detailed atomic scale description of the interfaces between cerium oxide and metals is necessary for a clear understanding of interfacial interactions, and it may open the way to the optimization of the properties of the combined material in view of its applications. In this study the interface between cerium oxide epitaxial films and the (111) surface of platinum is studied by aberration‐corrected scanning transmission electron microscopy and by ab initio density functional theory calculations. Local modifications of the registry between the cerium oxide and platinum lattices and the occurrence of nanometric platinum islands at the interface are detected by high‐angle annular dark field imaging. Moreover, the preferential adsorption sites of Ce and O atoms at the interface are determined by a comparison of the images acquired in annular bright‐field mode and the results of density functional theory calculations. The presence of a non‐negligible concentration of Ce3+ ions at the interface is detected by electron energy loss spectroscopy and it is rationalized in terms of interfacial charge transfer as evidenced by the calculations. This work provides an insight into the atomic and electronic structure of the technologically relevant CeO2/Pt interface and it helps to clarify the properties of the combined material. A significant reduction of cerium ions in cerium dioxide at the interface with platinum is ascribed to charge transfer from the metal. The effect is understood through an accurate determination of the epitaxy and of the absorption geometry of cerium oxide on platinum, obtained by comparing transmission electron micro­scopy analysis and density functional theory calculations.