Understanding high photocatalytic activity of the TiO 2 high-pressure columbite phase by experiments and first-principles calculations

The clean production of hydrogen as a zero-emission fuel can be done using photocatalysis, with TiO 2 being one of the most promising photocatalysts. However, the activity of TiO 2 anatase and rutile phases is still limited. In this study, an oxygen-deficient high-pressure phase of TiO 2 , columbite, is stabilized by a high-pressure torsion method. The phase is utilized as an active photocatalyst for hydrogen production, and the mechanism of its high activity is examined using density functional theory (DFT). The activity of columbite appears to be experimentally higher than that of the anatase phase. DFT calculations revealed that columbite does not have a narrow electronic bandgap, but its optical bandgap and light absorbance are improved by oxygen vacancies more significantly compared to anatase. Moreover, the water adsorption energy is higher and the surface activation energy for water splitting on the (101) atomic plane of columbite is lower than that for the active planes of anatase. In conclusion, although columbite is not a low-bandgap semiconductor, its large light absorbance and high surface catalytic activity make it a promising candidate for photocatalytic reactions.