Water Adsorption and Dissociation at Metal-Supported Ceria Thin Films: Thickness and Interface-Proximity Effects Studied with DFT plus U Calculations

The chemistry of several catalytic processes can be controlled by tuning metaloxide interfaces, as demonstrated by fundamental studies on inverse model catalysts. We investigate the effects of the metaloxide interface on the surface reactivity of ceria (CeO2) thin films supported by a copper metal surface. Our density functional theory (DFT+U) calculations reveal that the interface has impact on the surface water adsorption and dissociation when the thickness of the ceria film is below approximate to 9 angstrom. On thinner films, the energetics of adsorption and dissociation display a significant variation, which arises from a combination of thickness and interface-proximity effects, and which we rationalize in terms of charge-density response at the adsorbate-oxide and oxide-metal interfaces. The adsorption energy is maximized for film thicknesses of 5.5 angstrom (corresponding to two OCeO trilayers), while thinner films affect primarily the relative stability between molecular, semidissociated, and dissociated water adsorption. These results provide useful insights into the effect of low-dimensional ceria species in Cu/CeO2 catalysts.