Understanding high photocatalytic activity of the TiO2 high-pressure columbite phase by experiments and first-principles calculations

TL;DR

This study demonstrates that the high-pressure columbite phase of TiO2 exhibits superior photocatalytic activity for hydrogen production due to enhanced light absorption and surface activity, as shown by experiments and first-principles calculations.

Contribution

It introduces a stabilized high-pressure columbite TiO2 phase as a new, highly active photocatalyst for hydrogen evolution, supported by experimental and theoretical analysis.

Findings

Columbite TiO2 shows higher photocatalytic activity than anatase.

Oxygen vacancies improve optical absorption in columbite.

Lower water splitting activation energy on columbite's surface.

Abstract

The clean production of hydrogen as a zero-emission fuel can be done using photocatalysis, with TiO2 being one of the most promising photocatalysts. However, the activity of TiO2 anatase and rutile phases is still limited. In this study, an oxygen-deficient high-pressure phase of TiO2, 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.