Theoretical Study on Photocatalytic Reduction of CO₂ on Anatase/Rutile Mixed-Phase TiO₂

The construction of anatase/rutile heterojunctions in TiO₂ is an effective way of improving the CO₂ photoreduction activity. Yet, the origin of the superior photocatalytic performance is still unclear. To solve this issue, the band edges between anatase and rutile phases were theoretically determined based on the three-phase atomic model of (112)_A/II/(101)_R, and simultaneously the CO₂ reduction processes were meticulously investigated. Our calculations show that photogenerated holes can move readily from anatase to rutile via the thin intermediated II phase, while photoelectrons flowing in the opposite direction may be impeded due to the electron trapping sites at the II phase. However, the large potential drop across the anatase/rutile interface and the strong built-in electric field can provide an effective driving force for photoelectrons' migration to anatase. In addition, the II phase can better enhance the solar light utilization of (112)_A/(100)_II, including a wide light response range and an intensive optical absorption coefficient. Meanwhile, the mixed-phase TiO₂ possesses negligible hydrogenation energy (CO₂ to COOH*) and lower rate-limiting energy (HCOOH* to HCO*), which greatly facilitate CH₃OH generation. The efficient charge separation, strengthened light absorption, and facile CO₂ reduction successfully demonstrate that the anatase/rutile mixed-phase TiO₂ is an efficient photocatalyst utilized for CO₂ conversion.