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.