Interactions of Water with the (111) and (100) Surfaces of Ceria

This density functional theory study compares water adsorption on the ceria (111) and (100) surfaces. In the absence of water, the (111) surface is more stable than the polar (100) surface, but at higher water coverages the (100) surface is favored due to the formation of a highly stable “square ice” layer on top of the fully hydroxylated surface. At ceria (111), an amorphous ice layer is favored that consists predominantly of molecularly adsorbed water. This change in the water–surface interactions stems from the different surface terminations: the lower coordination numbers of ions at the (100) surface lead to higher water adsorption energies and a preference toward dissociative adsorption. Furthermore, the distance between neighboring surface oxygen ions (274 pm) is very close to the O–O distance in bulk ice, which facilitates the growth of a well-ordered ice layer. At the (111) surface, the distance between neighboring surface oxygen ions is significantly larger (388 pm), which hampers water–water interactions in the surface layer.