Significantly enhanced cocatalyst-free H2 evolution from defect-engineered Brown TiO2

TiO2 is the extensively investigated materials for various photocatalytic reforming and water splitting. Superior stability towards photo-corrosion, appropriate band energy levels driving most photocatalytic reactions, and lowcost production are promising features of TiO2. However, a primary limitation with TiO2 is that it only absorbs ultraviolet light constituting less than 5% of the solar spectrum. In this work, we use a facile, low temperature, vacuum-free, and solution-route synthesis approach to rationally induce oxygen vacancy/Ti3+ defects to reduce the bandgap of TiO2 to 2.0 eV (3.2 eV for pristine white TiO2) to form brown TiO2 with enhanced visible-light absorption. The mechanism of defect formation is systematically deduced from the detailed investigation through Raman spectroscopy, spin-sensitive technique, high-resolution microscopy, and surface analysis. The brown TiO2 yielded 8.1 mmol h(-1)g(cat)(-1) H-2 evolution without any cocatalyst under natural sunlight, which is a factor two higher than pristine (white) TiO2. To the best of our knowledge, the observed H-2 evolution rate is the highest reported value under natural sunlight for any TiO2-based photocatalyst. This work demonstrates the applicability of brown TiO2 to fabricate large-area photocatalyst panels for the cost-effective production of solar H-2.

Automated summary

TiO2 is extensively studied for its photocatalytic properties, but its limitation in absorbing visible light is addressed in this study through the induction of defects to reduce bandgap. The brown TiO2 synthesized showed enhanced visible-light absorption and significantly improved H-2 evolution efficiency under natural sunlight, demonstrating its potential for cost-effective solar H-2 production.