Relationship between interatomic electron transfer and photocatalytic activity of TiO2

We demonstrate the direct observation of interatomic electron excitation and transfer on single-crystal TiO2 (001) surface for water splitting by a synchronous illumination X-ray photoelectron spectroscopy (SI-XPS). The quantitative results clearly reveal that the initially absorbed water molecules on TiO2 surface promote the electron transfer between Ti and O atoms. However, when water molecule was dissociated into OH and H groups on Ti and O sites, respectively, the electron excitation and transfer ability have been gradually decreased and finally terminated, probably due to the reverse electron-attraction of OH group on Ti atoms. Amazingly, when Pt co-catalyst was deposited on TiO2, the electron excitation between Ti and O atoms have been significantly enhanced and no evident decrease has been observed during the entire water splitting process. In addition, the changes of Pt–O and Ti–O chemical bonds at the photocatalytic interfaces have been also detected. Furthermore, based on the above mechanism studies, the photocatalytic hydrogen production system for Pt/R-TiO2 (001) in KOH solution containing CH3OH was proposed, which exhibits a significant enhancement of hydrogen evolution rate (20.78 μmol h−1), which is nearly 2.5 times higher than that of traditional Pt/R-TiO2 (001) in CH3OH system (8.35 μmol h−1). The finding in this work may pave the way for developing other high-efficiency photocatalytic hydrogen production system over TiO2-based photocatalysts.