Reaction Pathway of Photocatalytic Water Splitting on Two-Dimensional TiO2 Nanosheets

Using density functional theory and many-body Green's function theory, we examine the mechanism of the water splitting reaction photocatalyzed by two-dimensional TiO2 nanosheets, which has gained attention recently in the TiO2 community. We reveal the barriers and the hole-transfer pathway in the reaction. Compared with its bulk isomer phases, such as the rutile TiO2, the advantage of the TiO2 nanosheet in this reaction is that the key reaction intermediate Ti-OH has good hole-trapping capacity, which is extremely beneficial for the oxidation half-reaction. However, the poor stability of Ti-OH relative to its precursor is a negative factor for the reaction on the TiO2 nanosheet and might have a huge effect on the photocatalytic efficiency of the nanosheet. We find that introducing Ti vacancies into the nanosheet to convert the TiO2 material into a p-type semiconductor can make bridging oxygen atoms become favorable active sites for water splitting and hence may be an effective way to increase the photocatalytic efficiency.