Theoretical study of interfacial electron transfer from reduced anatase TiO2(101) to adsorbed O2.

We study the electron transfer from a reduced TiO2 surface to an approaching O2 molecule using periodic hybrid density functional calculations. We find that the formation of an adsorbed superoxo species, *O2(-), via the reaction O2(gas) + e(-) → *O2(-), is barrierless, whereas the transfer of another electron to transform the superoxo into an adsorbed peroxide, i.e. *O2(-) + e(-) → *O2(2-), is nonadiabatic and has a barrier of 0.3 eV. The origin of this nonadiabaticity is attributed to the instability of an intermediate where the second electron is localized at the superoxo adsorption site. These results can explain the experimental finding that O2 is not an efficient electron scavenger in photocatalysis.