Solar Hydrogen Production by Plasmonic Au–TiO₂ Catalysts: Impact of Synthesis Protocol and TiO₂ Phase on Charge Transfer Efficiency and H₂ Evolution Rates

Abstract

The activity of plasmonic Au–TiO2 catalysts for solar hydrogen production from H2O/MeOH mixtures was found to depend strongly on the support phase (anatase, rutile, brookite, or composites thereof) as well as on specific structural properties caused by the method of Au deposition (sol-immobilization, photodeposition, or deposition–precipitation). Structural and electronic rationale have been identified for this behavior. Using a combination of spectroscopic in situ techniques (EPR, XANES, and UV–vis spectroscopy), the formation of plasmonic Au particles from precursor species was monitored, and the charge-carrier separation and stabilization under photocatalytic conditions was explored in relation to H2 evolution rates. By in situ EPR spectroscopy, it was directly shown that abundant surface vacancies and surface OH groups enhance the stabilization of separated electrons and holes, whereas the enrichment of Ti3+ in the support lattice hampers an efficient electron transport. Under the given experimental conditions, these properties were most efficiently generated by depositing gold particles on anatase/rutile composites using the deposition–precipitation technique.