Engineering the Morphology and Crystal Phase of 3 D Hierarchical TiO with Excellent Photochemical and Photoelectrochemical Solar Water Splitting.

Owing to their unique characteristics, hierarchical TiO nanostructures have several advantages in solar-fuel production. In this work, a single-step approach has been developed to control both the crystal phase and morphology of TiO with 3 D urchin-like structure via a surfactant-free solvothermal route. The growth of 3 D hierarchical structure with phase-engineered band alignment, the role of the H O/HCl ratio, and fine-tuning of the reaction parameters are investigated systematically. An optimum ratio of anatase (41 %) to rutile (59 %) in the mixed-phase TiO (AR-2) results in excellent photocatalytic H generation activity of 5753 μmol g after 5 h of irradiation with apparent quantum yields of 20.9 % at 366 nm and 4.5 % at 420 nm. The superior performance of AR-2, attributed to efficient separation of charge carriers through the phase junction, is apparent from the transient photocurrent response and photoluminescence studies. The 3 D urchin-like pure rutile TiO (R-1) composed of nanorods shows enhanced photocatalytic activity compared with pure anatase and pure rutile TiO nanoparticles, and this demonstrates the role of morphology. The best-performing mixed-phase 3 D TiO shows excellent durability up to 25 h and is shown to produce 3522 μmol g of H under natural sunlight, which highlights its potential for long-term application.