Thermodynamics of dissociated water motifs at oxide-bulk water interfaces: The TiO2 anatase (0 0 1) case

Highlights: • The surface free energy of (2×3) and (2×4) water induced reconstructions (WIR) of TiO₂ anatase (0 0 1) surfaces in bulk water is calculated by ab-initio molecular dynamics. • In bulk water the stability hierarchy of the WIR TiO₂ anatase (0 0 1) surface depends on the temperature. • At room temperature the experimental surface periodicity is recovered on a WIR basis and explains the inertness of this surface for water splitting. Water on metal oxides interfaces generate a variety of ordered motifs that depend on the structural properties of the exposed solid surfaces. Here we emphasize the importance of considering the thermodynamic state of the surrounding liquid to find the interface structures in real systems. In particular, using ab initio molecular dynamics, we have studied the thermodynamic behavior of the water induced reconstructed (WIR) anatase (0 0 1) surface under full hydration. The long standing issue of the reconstruction symmetry in this facet of the anatase, that is the TiO₂ stable phase at the nanoscale, is addressed showing that the stable state for a WIR surface in vacuum and in bulk water are different, the latter depending on the thermodynamic state of the system. Thermally activated surface phase transitions between (2×4) and (2×3) symmetries are lead by the surface relaxation caused by the molecular adsorption and release phenomena at the interface. Our approach enables the validation to aqueous environment of surface-confined water structures derived in vacuum, emphasizing the role of the thermodynamics conditions for characterizing solid-liquid interfaces especially for nano sized systems.