Theoretical Explanation of the Photogenerated Carrier Separation at the Surface Junction

Abstract For photocatalytic reactions, the fabrication of surface junction has been proven to be an effective method to increase the photogenerated carrier (excited electrons and photogenerated holes) separation efficiency. However, the carrier separation mechanism has not been studied in detail. In this work, density functional theory has been employed to study the photogenerated carrier‐separation mechanism based on an interfacial model consisting of TiO 2 (1 0 1) and (0 0 1) facets. Both excited electrons and photogenerated holes preferentially locate on the (0 0 1) facets rather than the (1 0 1) facets. However, the high conduction‐band energy level of the interface inhibits the electron interfacial migration. In contrast to the exited‐electrons migration process, the suitable valence‐band energy of interface permits the hole interfacial migration from the (1 0 1) to the (0 0 1) facets. The electrons easily recombine with the holes on the (0 0 1) facets owing to the holes overflow effect. Excited electrons and holes would fill the (1 0 1) facets and (0 0 1) facets, respectively. Based on such interfacial energy band properties, we propose a new photocatalytic material design concept, named “selective migration” structure, which can promote the photogenerated carrier separation and offer more strongly reductive electrons for the photoreduction reaction or more strongly oxidative holes for the photooxidation reaction. These results are expected to provide a deeper understanding of the surface junction and a guide for designing new photocatalysts.