Structure and energetics of water adsorbed at TiO2 anatase (101) and (001) surfaces

We present density functional calculations of H2O interacting with the (101) and (001)surfaces of TiO2 anatase at various coverages theta. On the (101) surface, nondissociative molecular adsorption at fivefold coordinated Ti sites is favored at both low and monolayer coverage. On the (001) surface, for theta less than or equal to 0.5, H2O is adsorbed dissociatively, with an adsorption energy Delta H-H,H-OH similar to 1.6 eV. At theta = 1, H2O can be adsorbed molecularly (Delta H-H2O = 0.82 eV/molecule), but a state with half of the H2O adsorbed dissociatively and the other half H bonded in a "second layer" is energetically more favorable. These results are discussed in the context of the available experimental information.