Photocatalytic oxygen evolution reactivity at surface edges and corners of anatase TiO₂ nanoparticles revealed by coupled quantum mechanical and molecular mechanical simulations

Coupled quantum mechanical and molecular mechanical (QM/MM) method is applied to investigate the oxygen evolution reactions (OER) on a realistic 9.5-nm long anatase TiO₂ nanoparticle. The nanoparticle surface has easier electron and hole localization behavior on some of the corners and edges, compared to flat surfaces. As a result, OER reaction energy can be reduced by 0.1 - 0.5 eV at the corners and edges. However, since some of the structures with low reaction energies are also prone to form electron polarons, its high OER activity can be compromised due to electron-hole recombination. By considering both factors, the (101) facet and the edge between (101) and (011) facets are found to be the most active for OER, while the remaining corners and edges can be active for reduction reactions. Unlike early works where four-fold coordinated Ti_4c was attributed to the only reason for active corners and edges, this work shows that Madelung potential, surface relaxation can also be the cause of active surface.