First-principles study on unidirectional proton transfer on anatase TiO 2 (101) surface induced by external electric fields.

The electric field (EF) effect on hydrogen or proton transfer (PT) via hydroxyl groups on an anatase TiO 2 (101) surface is examined using first-principles density functional theory and the modern theory of polarization. This study focuses on unidirectional surface PT caused by external EFs at various orientations toward the surface. The preferred PT pathway can change depending on the magnitude and direction of the EF. Detailed analysis reveals that the variation in the energy profile with the EF is significantly different from that determined by the classical electric work of an EF carrying a point charge. The EF effect on the energy profile of the PT is governed by the rearrangement of the chemical bond network at the interface between the water molecules and the surface.