Photoluminescence (PL) spectroscopy of intra-bandgap trap states is used to investigate the mechanism of photocatalytic water oxidation in pristine and hydrogen-treated rutile TiO2 nanowires. H-treated nanowires were previously shown to be superior to pristine nanowires for the photoelectrochemical evolution of oxygen from water, owing to more efficient charge separation and carrier transport. The present work examines the near-IR PL of rutile nanowires under applied electrochemical potential in order to address the possible influence of hydrogen treatment on electron or hole traps and their role in water oxidation. It is concluded that the near-IR PL of rutile nanowires, identical to that of bulk and conventional nanocrystalline rutile, arises from the radiative recombination of trapped electrons with valence band holes, and that valence band holes, rather than trapped holes, are more likely responsible for water oxidation. The shape and intensity of the near-IR PL is found to be invariant to H-treatment and thus does not arise from traps introduced by annealing in H2, such as oxygen vacancies. Instead, H-treatment influences carrier transport and the recombination processes which compete with reductants for hole consumption. The role of contacting solvent, water versus wet acetonitrile, is shown to exert a strong influence on whether deep traps are occupied isoenergetically (from the potentiostat) or inelastically (by photogenerated electrons in the conduction band).

Spectroelectrochemical photoluminescence of reactive trap states in H-treated rutile TiO2 nanowires

253rd National Meeting (2017)

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