Discovery of Fe₂P-Type Ti(Zr/Hf)₂O₆ Photocatalysts toward Water Splitting

We report the discovery of Fe₂P-type TiO₂-based photocatalysts, TiZr₂O₆ and TiHf₂O₆, through first-principle calculations. Appearing as the solid solutions of TiO₂ and Zr(Hf)O₂ at 150 GPa, Ti (Zr/Hf)₂O₆ unit cells are constructed by replacing two Ti atoms with Zr or Hf atoms in the pure Fe₂P-type TiO₂ lattice. The two compounds are mechanically and dynamically stable at ambient conditions. The electronic structure calculations predict direct bandgaps of 2.29 and 2.65 eV for TiZr₂O₆ and TiHf₂O₆, respectively. Significant evidence in the electronic properties prove both TiZr₂O₆ and TiHf₂O₆ to be attractive photocatalysts in the visible light region, but TiZr₂O₆ is more promising in the application of hydrogen generation by water splitting. Thus, instead of element doping, we narrow the bandgap of TiO₂ by developing intrinsic stable semiconductors from scratch. The rational design in this work of predicting high-pressure phases and stabilizing them open a way for prompting photoelectrochemical activities of photocatalysts.