Fundamental studies about the interaction of water with perfect, oxygen-vacancy and pre-covered oxygen Cu2O(1 1 1) surfaces: Thermochemistry, barrier, product

Abstract

The adsorption and dissociation of H2O on three types of Cu2O(111) surfaces, including perfect, oxygen-vacancy and pre-covered oxygen surfaces have been systematically investigated using periodic density functional slab model calculations. Different kinds of possible modes of H2O adsorbed on those surfaces are identified. Our results first show that the bonding of dissociated species (HO, H and O) for H2O is substantially stronger than that of H2O on Cu2O(111) surface. Then, on perfect surface, H2O mainly exist in the form of molecular adsorption, in which CuCUS site is chemisorption, OSUF site is physisorption with a weak hydrogen bond. On oxygen-vacancy surface, dissociative adsorption of H2O occurs predominantly, suggesting that oxygen-vacancy exhibits a strong catalytic activity toward H2O dissociation; meanwhile, a small quantity of chemisorption H2O adsorbed at CuCUS site also exists. On pre-covered oxygen surface, H2O is typical of physisorption due to a hydrogen bond interaction between H of adsorbed H2O and pre-covered oxygen. Further, the dissociation mechanisms of molecular adsorption H2O, OH from dissociative adsorption H2O, as well as single OH group on different surfaces, leading to the final products H and O atoms, give out the thermochemistry, barrier of each elementary reaction, which indicates that OH species is energetically the most stable product on those surfaces. Pre-covered oxygen on Cu2O(111) surface can act as a promoter to facilitate the first dehydrogenation of molecular adsorption H2O leading to OH species, which is more favorable both thermodynamically and kinetically than that of molecular adsorption H2O on other two surfaces. Finally, the vibrational frequencies for the adsorbed H2O and OH species on Cu2O(111) surfaces can be applied to guide surface vibrational spectroscopy in experiment. Our calculation may be a worthwhile theoretical example for the interaction of H2O with other metal oxide surface.