Interface-Engineered CuO x /TiO ₂ Hollow Spheres Regulate Charge-Carrier Pathways via a Built-In p–n Junction for Bifunctional Photoelectrochemical Applications

Multifunctional photoelectrochemical systems that combine solar energy conversion and chemical sensing are gaining interest, but their performance is often limited by poor interfacial charge separation and uncontrolled charge-carrier pathways. Herein, CuOx modified TiO₂ hollow spheres (CuOx/TiO₂ HSs) were engineered to construct a built-in p-n heterojunction that actively regulates interfacial charge transfer. Combined characterization and DFT calculations indicate that the successful construction of the p-n heterojunction enables efficient separation of photogenerated electrons and holes. This not only allows electrons to migrate to the TiO₂ surface enhancing the hydrogen evolution reaction rate, but also directs holes to the CuOx surface, where they participating in oxidation reactions to improve sensing performance. Consequently, the optimized CuOx/TiO₂ HSs achieve a hydrogen evolution rate of 1.43 mmol g⁻¹ h⁻¹ under simulated sunlight with excellent cycling stability (88% retention after 16 h). In addition, the material exhibits a wide linear range of 60-12,000 μM and a low detection limit of 3.37 μM for glucose sensing. This work provides an experimental approach for the design of p-n TiO₂ heterojunctions.