First-principles study of H intercalation in rutile TiO2 -: art. no. 165421

The geometry of hydrogen intercalation sites in rutile TiO2 has been studied using first principles calculations. A new intercalation site is predicted which is consistent with all current experimental data. The apparent contradiction between spectroscopic, diffraction and magnetic resonance data are resolved by taking into account the strong local distortions of the structure induced by localization of donated charge. In particular the predicted OH vibrational frequency is in excellent agreement with that measured. A similar local geometry is predicted in the presence of 3+ counter ions but with a preferential site occupancy which is consistent with the local symmetry implied by spectroscopic measurements of aluminium substituted titania. The local distortions of the structure are shown to result in preferential ordering of the hydrogen ions in layers over a wide range of intercalation concentrations and the consequences of this ordering for electrochemical insertion of hydrogen are discussed.