X-ray photoelectron spectroscopy of TiO2 and other titanate electrodes and various standard Titanium oxide materials: Surface compositional changes of the TiO2 electrode during photoelectrolysis

Surface compositional changes were observed for TiO₂ single crystal electrodes used for photoelectrolysis of water. Surface stoichiometries of several types of TiO₂, SrTiO₃ and BaTiO₃ electrodes were characterized by XPS and compared with a variety of titanium, titanium oxide and titanium hydride standard materials. Reduction of the electrode surface in a hydrogen atmosphere results in an oxygen deficient surface composition. Photoelectrolysis at current densities of $\text{10–15}\text{mA}\text{cm}{}^2$ for periods up to 8 h appears to return the electrode surface to a nearly stoichiometric oxygen-to-metal ratio. Reduction of the titanium oxide surfaces was also observed by exposure to an argon ion beam. Analysis of the electrode surface by a combination of XPS and ion-sputter profiling was still possible by simultaneous analysis of standard materials.