Engineering the Morphology and Crystal Phase of 3 D Hierarchical TiO 2 with Excellent Photochemical and Photoelectrochemical Solar Water Splitting

Owing to their unique characteristics, hierarchical TiO 2 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 2 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 2 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 2 (AR‐2) results in excellent photocatalytic H 2 generation activity of 5753 μmol g −1 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 2 (R‐1) composed of nanorods shows enhanced photocatalytic activity compared with pure anatase and pure rutile TiO 2 nanoparticles, and this demonstrates the role of morphology. The best‐performing mixed‐phase 3 D TiO 2 shows excellent durability up to 25 h and is shown to produce 3522 μmol g −1 of H 2 under natural sunlight, which highlights its potential for long‐term application.