First-Principles Study of the Water Adsorption on Anatase(101) as a Function of the Coverage

An understanding of the interaction of water with the anatase(101) surface is crucial for developing strategies to improve the efficiency of the photocatalytic reaction involved in solar water splitting. Despite a number of previous investigations, it is still not clear if water preferentially adsorbs in its molecular or dissociated form on anatase(101). With the aim of shedding some light on this controversial issue, we report the results of periodic screened-exchange density functional theory calculations of the dissociative, molecular, and mixed adsorption modes on the anatase(101) surface at various coverages. Our calculations support the suggestion that surface-adsorbed OH groups are present, which has been made on the basis of recently measured X-ray photoelectron spectroscopy, temperature-programmed desorption, and scanning tunneling microscopy data. It is also shown that the relative stability of water adsorption on anatase(101), at different configurations, can be understood in terms of a simple model based on the number and nature of the hydrogen bonds formed as well as the adsorbate-induced atomic displacements in the surface layers. These general conclusions are found to be insensitive to the specific choice of approximation for electronic exchange and correlation within the density functional theory. The simple model of water–anatase interactions presented here may be of wider validity in determining the geometry of water–oxide interfaces.