Insight into the adsorption and dissociation of water over different CuO(111) surfaces: The effect of surface structures

Abstract

Water adsorption and dissociation on solid surfaces play a key role in a variety of industrial processes, a detailed comprehension of this process and the effect of the surface structure will assist in developing the improved catalysts. In this study, the adsorption and dissociation of H2O on three different types of CuO(111) surfaces, including the stoichiometric, oxygen-vacancy and oxygen-rich surfaces, have been systematically investigated and compared using density functional theory methods. All possible initial configurations of H2O adsorbed on those surfaces with only one coverage have been identified. Our results show that the adsorption ability of H2O is substantially weaker than that of the dissociated species (HO, H and O). H2O chemisorbs at the CuSUB, Cu2 and CuSUB sites of the stoichiometric, oxygen-vacancy and oxygen-rich surfaces, respectively; subsequently, the chemisorption H2O dissociates into OH and H species. The dissociation mechanisms of chemisorption H2O and the single OH group leading to the final O and H species suggest that the dissociation of single OH species occurs at a higher barrier compared to the dissociation of OH in the presence of neighboring H atom (produced from the initial step of H2O dissociation), namely, the presence of H is in favor of OH dissociation, which agrees with the results of charge transfer. However, owing to the significantly high barrier of OH dissociation compared to the initial dissociation step of H2O, OH species is considered as the dominant product on those surfaces. Oxygen-rich surface is the most favorable for the initial dissociation of H2O both thermodynamically and kinetically than other two surfaces. The calculated vibrational frequencies for the adsorbed H2O and OH species on CuO(111) surfaces can be applied to guide the experimental research of surface vibrational spectroscopy. In addition, our results may provide a basis for the study of H2O interaction with other metal oxide surfaces.