• Energy Research
• chemical sciences close

The present chain of five papers considers the concept of solar-to-chemical energy conversion using TiO2-based semiconductors. The series reports the effect of chromium on the key performance-related properties of polycrystalline TiO2 (rutile), including electronic structure, photocatalytic activity, intrinsic defect disorder, electrochemical coupling and surface versus bulk properties. In this work, we show that the effect of chromium on photocatalytic performance of TiO2 depends on its elemental content and the related defect disorder that is determined by oxygen activity in the oxide lattice. At high oxygen activity, chromium leads to enhanced photocatalytic performance only for dilute solid solutions (up to 0.04–0.043 at.% Cr). Higher chromium content results in a decrease of photocatalytic activity below that for pure TiO2, despite the observed substantial decrease of the band gap. The photocatalytic performance of Cr-doped TiO2 annealed in reducing conditions is low within the entire studied range of compositions. The obtained results led to derivation of a theoretical model representing the mechanism of the light-induced reactivity of TiO2 with water and the related charge transfer. The photocatalytic performance is considered in terms of a competitive effect of several key performance-related properties. The performance is predominantly influenced by the concentration of titanium vacancies acting as reactive surface sites related to anodic charge transfer.