Achieving Controllable CoTiO₃-Encapsulated TiO₂ Heterostructures for Enhanced Photoelectrochemical Water Splitting

High light absorption capability and excellent charge carrier kinetics play a key role in determining the improved photoelectrochemical (PEC) performance. Here, to extend the photoresponse of TiO2 to the visible-light range, we encapsulated narrow band gap CoTiO3 on the surface of TiO2 nanowire arrays (NWAs) to form a core–shell heterostructure. The CoTiO3 shell thickness can be controlled by the hydrothermal reaction time. The TiO2/CoTiO3 NWAs with 9.7 nm of CoTiO3 shell thickness had the highest Jph (0.95 mA/cm2 at 1.23 V versus RHE) and largest carrier concentration (1.53 × 1021 cm–3), indicating about 30% and 346% increase compared to bare TiO2 NWAs, respectively. The results indicate that the improved photoresponse of TiO2 NWAs can be attributed to the broadened light absorption, effective separation of the photogenerated electron–hole pairs, and fast interfacial charge carrier transfer achieved over a TiO2/CoTiO3 core–shell heterostructure.