Subtle structure matters: the vicinity of surface Ti_5c cations alters the photooxidation behaviors of anatase and rutile TiO₂ under aqueous environments

While the structure–function relationship is frequently referred in heterogeneous catalysis, the concept falls short of applications in photocatalysis owing to its complicated processes. Here, we take the photocatalytic oxygen evolution reaction (OER) as a case study and demonstrate the significance of subtle surface structures in altering the photooxidation functions of anatase and rutile TiO₂ under aqueous environments. On the basis of our recent progresses in developing a solution simulation method and clarifying the photocatalytic OER process at rutile TiO₂ (Nat. Catal.2018, 1, 291–299), we successfully identified a complete OER mechanism at the water/anatase-TiO₂(101) interface with an explicit involvement of photoholes/radicals and lattice oxygens. Kinetic analysis further revealed the leading reaction pathway varying with the concentration of surface-reaching photoholes (Ch+), as well as the most efficient way to boost the OER via enriching the Ch+ rather than lowering the reaction barriers (of water dissociation or O/O coupling). Anatase TiO₂(101) generally shows poorer OER activity relative to the rutile TiO₂(110) but much higher surface coverage of Ot– radicals under experimental conditions, rationalizing its good activity for photodegradation of organics. Such varied catalytic functions were found to be simply decided by the distance between two vicinal under-coordinated Ti cations on the surface that promotes or prohibits the key step of O/O coupling. These results not only provide essential understandings on the structure–function principles governing the photooxidation behaviors but also offer strategies to achieve efficient catalysis via matching proper surface structures with targeted reaction characteristics.