On the kinetics of photoelectrocatalytic water splitting on nanocrystalline TiO2 films

► Partial electrochemical reduction enhances TiO2 photoelectrocatalytic activity. ► This is attributed to the formation of defect states within the bandgap. ► Bandgap states at different energy levels induce two voltage dependent kinetic regions. ► Adsorbed water splitting proceeds through the photo activation of 'wet electron' state. ► Oxygen evolution is observed with selectivity ≤10% at the saturation current.