A new deep hole-trapping site for water splitting on the rutile TiO2(110) surface

Abstract

The mechanism of the water photooxidation reaction on the rutile TiO₂(110) surface has been extensively discussed but still remains highly controversial. By ab initio many-body Green's function theory, we discover a new deep hole-trapping site 2Ti_6c–O_br–O–Ti_5c which should be the key intermediate regulating the reaction. This site releases an O₂ molecule after capturing two holes, producing a bridging oxygen vacancy simultaneously. Accompanied by a huge Stokes shift, electron–hole recombination at this site emits light around 1.5 eV. These two phenomena can solve the long-standing mysteries of surface roughening and photoluminescence at 810 nm observed experimentally. We find that introducing Ti vacancies into rutile to turn it into a p-type conductor can make H₂O dissociate directly at bridging oxygen, so that photooxidation efficiency may be elevated substantially.