Characteristics of the surface states produced on titanate photoanodes by mechanical polishing

Investigations using repetitive triangular potential sweeps and X-ray photo electron spectroscopy reveal that stable, surface-bound peroxotitanium species are produced without illumination on mechanically polished n-type SrTiO 3, SrTi 3O 7, BaTiO 3, BaTi 4O 9 and TiO 2 polycrystalline photoelectrodes in alkaline media, under anodic polarization. Formation of peroxotitanium species is related to the chemical reactivity of the surface regions that incorporate the mechanically-induced crystalline defects, according to the scheme: 2 OH s − = ( O 2 2−) s + 2 H + + 2 e − . Bulk flaws present the mechanically damaged surface region allow a quasi-isoenergetic transfer of electrons from the conduction band at the bulk to empty surface states (peroxo species). At much more anodic potential [ V appl ≳ 0.45 V ( SCE) ], the Fermi level is pushed below the surface states and the electrons are transferred from ss to the CB via bulk flaws, leading to the underpotential evolution of oxygen: ( O 2 2−) s = O 2 + 2 e − .