Light-Induced Migration of Spin Defects in TiO₂ Nanosystems and their Contribution to the H₂ Evolution Catalysis from...

The photocatalytic activity for H₂ production from water, without presence of hole scavengers, of thermally reduced TiO₂ nanoparticles (H-500, H-700) and neat anatase were followed by in-situ continuous-wave light-induced electron paramagnetic resonance technique (CW-LEPR), in order to correlate the H₂ evolution rates with the electronic fingerprints of the photoexcited systems. Under UV irradiation, photoexcited electrons moved from the deep lattice towards the superficially exposed Ti sites. These photogenerated redox sites mediated (e^- +h⁺ ) recombination and were the crucial electronic factor affecting catalysis. In the best-performant system (H-500), a synergic combination of mobile electrons was observed, which dynamically created diverse types of Ti³⁺ sites, including interstitial Ti³⁺ , and singly ionized electrons trapped in oxygen vacancies (V_O ^. ). The interplay of these species fed successfully surface exposed Ti⁴⁺ sites, which became a catalytically active, fast reacting Ti⁴⁺ ⇄Ti³⁺ state that was key for the H₂ evolution process.