Kinetics analysis of oxygen vacancies in TiO2 solar water reduction: Revealing effects and eliminating disadvantages

Abstract

A consensus is yet to be reached on the effects of oxygen vacancy (VO) on the performance of TiO2 for photocatalytic water splitting as contrasting viewpoints have been presented in the latest researches. Herein, a comprehensive set of spectroelectrochemical methods are deployed to clearly reveal the advantages and disadvantages of VO on the performance of TiO2. The results indicate that surface VO improves the photocatalytic activity while bulk VO has a negative effect on the water reduction performance of TiO2. Intensity-modulated photocurrent spectroscopy (IMPS) and UV–vis spectroscopy provide compelling evidence that the improvement of H2 evolution can be attributed to the presence of defect level, while the low interface charge transfer efficiency caused by surface VO limits the further improvement of photocatalytical H2 evolution, which can be alleviated by an organic hole transport coating. The density functional theory (DFT) and surface photovoltaic (SPV) analyses confirm that the built-in field between TiO2 and hole molecules is the reason for the interface charge transfer efficiency improvement. Our findings provide a comprehensive understanding of VO in TiO2 by carrier behavior analysis and a scheme to further promote the photocatalytic performance.