Light-induced migration of spin defects in TiO2 nanosystems and their contribution to the H2 evolution catalysis from water.

The photocatalytic activity for H 2 production from water, without presence of hole scavengers, of thermally reduced TiO 2 nanoparticles (H-500, H-700) and neat Anatase were followed  by in situ Continuous Wave Light induced EPR technique (CW-LEPR), in order to correlate the H 2 evolution rates with the electronic fingerprints of the photoexcited systems. Under UV irradiation, photoexcited electrons move from deep in the lattice towards surface exposed Ti sites. These photogenerated redo-ox sites mediate (e - + h + ) recombination and are the crucial electronic factor affecting catalysis. In the best performant system (H-500) we observe a synergic combination of mobile electrons, which dynamically create diverse types of Ti 3+ sites, including interstitial Ti 3+ , and formation of singly ionized electrons trapped in oxygen vacancies (V O · ). The interplay of these species feed successfully surface exposed Ti 4+ sites, which become a catalytically active, fast reacting Ti 4+ ↔Ti 3+ state that is key for the H 2 evolution process.

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