Designing the Optimal Cr-Doped TiO ₂ Photocatalyst for Solar-Driven Hydrogen Production: A Comprehensive DFT Study

We present a comprehensive DFT study of the structural, magnetic, optical absorption, electronic, water redox properties, and thermodynamic stability of Cr-doped bulk anatase TiO2 for solar-driven photocatalytic hydrogen production. Calculations employed a modified hybrid PBE0 functional (15% HF + 85% PBE exchange), providing accurate electronic structure predictions. A wide range of Cr doping configurations, including substitutional and interstitial geometries with various spatial distributions such as isolated, separated, gathered, dissociated, and clustered dopant arrangements (not previously reported), are systematically explored. Among all investigated systems, the ferromagnetic TiO(2+3x)Cr2x emerged as the most promising candidate for visible-light-driven photocatalytic water splitting. Its structure corresponds to interstitial Cr2O3 species, with one O atom bridging two neighboring Cr3+ ions in distorted octahedral sites. This material can be thermodynamically stabilized under standard and O-rich growth conditions using Cr-containing precursors with a weak reducing character. Its optical absorption spectrum exhibits visible-light-responsive bands beyond 700 nm, originating from hybridized Cr 3d-Ti 3d-O 2p states, promoting hole mobility and suppressing electron–hole recombination. These findings provide valuable atomic-scale insights for the rational design of clustered Cr-doped TiO2 photocatalysts for efficient solar-driven hydrogen production.