Surface Aspects of Hydrogen Photogeneration on Titanium Oxides

Strontium titanate and titanium dioxide have received considerable attention as materials for photoanodes and photocatalysts in the dissociation of water (1,2,3), and in other photoassisted reactions. Knowledge of how the surface composition and electronic structure of these materials change under illumination when in contact with gases or liquid electrolytes is essential if detailed understanding of the mechanisms of semiconductor photochemistry is to be achieved. Although these wide bandgap oxides do not exhibit gross photocorrosion under most reaction conditions (2) and would appear less susceptable to possible Fermi-level pinning than many semiconductors with smaller bandgaps (4), more subtle surface chemical effects have been documented. Evidence for photocorrosion (5,6,7), surface-state mediation of electron and hole transfer to electrolyte species (8,9), and the dependence of quantum efficiencies on surface preparation techniques (10), indicate important roles for surface species on wide bandgap materials. Most detailed studies of water photodissociation on SrTiO3 and TiO2 have