Ti5O9 in TiO2 nanotube array activates the visible-light absorption properties significantly

In this study, one step hydrogen treatment (OSHT) method is first used for disposing the amorphous TiO2 nanotubes with nanowires formed on top (designed as TTW) to directly prepare the TiO2 containing Ti5O9 (designed as H-TTW(Ti5O9)), and also the method simplify the steps, shorter reaction time and lower cost. Through the first-principle calculations, we can conclude that the Ti5O9 is a narrow-gap material, the valence bands and conduction bands move down relative to that of TiO2 and generate new energy levels between the bands. These phenomena can be attributed to the existence of oxygen vacancies (VO). The H-TTW(Ti5O9) exhibits a larger absorption intensity of light in range of 350-800 nm, and a better photoelectrochemical (PEC) performance at 1.4 mA/cm2. Thus, the experimental results indicated that the existence of Ti5O9 in TiO2 is a highly promising material in activating various visible light functionalities and improving photoelectrochemical (PEC) performance.