Unraveling Pathways of Photocatalytic Oxygen Evolution on Fluorinated Anatase TiO2

Recentexperiments reported that the efficiency of the oxygen evolutionreaction (OER) was greatly improved in fluorinated TiO2 by forming the surface hydrogen bonds, but the mechanism remainsambiguous. Herein, we systematically investigated dual OER pathwayson the fluorinated anatase TiO2(101) surface by using thefirst-principles calculations. The dual H-bonding water is significantlyactivated by trapping a first hole in the system and facilitates itsproton transfer in pathway I. The inactive Ti-coordinated water alsotransfers a proton to a bridge O2- ion with a similarbarrier and simultaneously traps the first hole in pathway II. Both center dot OH radicals separately transfer a proton to the F- ion and bridge O2- ion very quickly and trap thesecond hole to produce the center dot O radical. Consequently, the center dot Oradical directly couples with the bridge O2- ionswith a high barrier of about 0.72 eV to produce the flat peroxo dimer(O-2 (2-)) in pathway I. The Ti-coordinated center dot O radical undergoes two steps of the proton transfer and O-Ocoupling with both high barriers of about 0.75 eV to produce the obliqueO(2) (2-) species in pathway II. Finally,the O-2 (2-) spontaneously and successivelytraps the third and fourth holes to quickly form the oxygen molecule.Additionally, the fluorine atoms are further demonstrated to acceleratethe proton transfer and the O-O coupling steps by comparingthe pathways on the fluorinated and pure TiO2 surfaces.These results may provide new insights into the OER mechanism in fluorinatedTiO(2) and roles of the dopant in improving OER efficiencyof the TiO2 photocatalysts.

Automated summary

Recent experiments have shown that the efficiency of the oxygen evolution reaction (OER) can be greatly improved in fluorinated TiO2 by forming surface hydrogen bonds, but the mechanism is not yet clear. In this study, dual OER pathways on the fluorinated anatase TiO2(101) surface were investigated using first-principles calculations. It was found that dual H-bonding water molecules play a significant role in facilitating proton transfer and hole trapping in both pathways.