The effect of Zr-doping on the interaction of water molecules with the ceria (111) surface

Abstract

The interaction of water molecules with the Zr-doped ceria (111) surface is investigated by using the DFT + U method. For the stoichiometric Zr-doped ceria (111) surface, a water molecule can be adsorbed not only through a one-H-bond configuration with its O* (oxygen of water) binding to a surface Ce ion, but also preferably through a nearly dissociated configuration with its O* binding to a surface Zr ion, at variance with that on the pure ceria (111) surface, where only a one-H-bond configuration is observed. While Zr-doping enhances the interaction of water with the unreduced CeO 2(111), it reduces the tendency of water dissociation on the reduced ceria. On the first kind Ce 0.75Zr 0.25O 2 − x (111) surface (V I, with a surface oxygen vacancy not neighboring a Zr dopant), water molecules prefer to dissociate around the Ce sites with the formation of the O*–Ce bond. On the second kind Ce 0.75Zr 0.25O 2 − x (111) surface (V II, with a surface oxygen vacancy neighboring a Zr dopant, which has a much higher formation probability than V I), the tendency of water dissociation (although preferred) is reduced compared with those on the CeO 2 − x (111) and the first kind Ce 0.75Zr 0.25O 2 − x (111). Additionally, the electronic interaction of water and the Zr-doped ceria (111) surface or the reduced Zr-doped ceria (111) surface is mainly from the interaction of the O*–Ce bond and the H b–O bond because the charge affinity of Ce ions is stronger than that of Zr ions. Although the O* fills the vacancy site when a water molecule dissociates on the Ce 0.75Zr 0.25O 2 − x (111), it does not oxidize the surface.