ReaxFF Reactive Force Field Study of the Dissociation of Water on Titania Surfaces

We studied the adsorption and dissociation of water at 300 K on the following TiO2 surfaces: anatase (101), (100), (112), (001), and rutile (110) at various water coverages, using a recently developed ReaxFF reactive force field. The molecular and dissociative adsorption configurations predicted by ReaxFF for various water coverages agree with previous theoretical studies and experiment. ReaxFF predicts a complex distribution of water on these surfaces depending on an intricate balance between the spacing of the adsorption sites (under-coordinated Ti and O surface atoms), water-surface interactions, and water-water interactions. Using molecular dynamics simulations to quantify water dissociation over the TiO2 surfaces at various water coverages, we find that the extent of water dissociation predicted by the ReaxFF reactive force field is in general agreement with previous density-functional theory studies and experiments. We demonstrate a correlation between the extent of water dissociation on different TiO2 surfaces and the strength of hydrogen bonding between adsorbed water molecules and water outside the adsorbed layer, as evidenced by the red shift of the O-H vibrational stretching mode of adsorbed water.