Mechanism of O2 Production from Water Splitting: Nature of Charge Carriers in Nitrogen Doped Nanocrystalline TiO2 Films and Factors Limiting O2 Production

The low efficiency of the extensively investigatedvisible light photocatalyst N-TiO2 has been widely assumed to be determined by the dynamics of the charge carriers. The nature of the photoelectrons and photoholes produced on the nanostructured (nc) N-TiO2 film has been systematically investigated in this work by the use of time-resolved absorption spectroscopy. Here the fingerprints of the two distinct photohole populations on nc-N-TiO2 films are reported and the reaction between these photoholes and water has been examined. The origin of the low efficiency of the visible-driven material for water oxidation was explored and rapid electron hole decay following visible excitation is believed to be a key factor. Pt deposition on nc-N-TiO2 resulted in an 80% enhancement of the quantum yield for O2 production under UV light. Finally, it has been summarized that the oxygen production on the nc-N-TiO2 film requires photoholes with lifetimes of ∼0.4s.