Enhanced charge separation of CuS and CdS quantum-dot-cosensitized porous TiO₂-based photoanodes for photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting using high-performance catalysts shows considerable promise in generating environment-friendly hydrogen energy. Its practical applications, however, suffer from several shortcomings, such as low photocurrent density, large onset-voltage value, and poor durability. In this study, CuS and CdS quantum-dot-cosensitized porous TiO₂-based PEC catalysts (CuS-CT) have been successfully synthesized via in situ sulfuration of CuO and CdO coexisting inside a porous TiO₂ monolith by a hydrothermal method. Compared to porous TiO₂, CuS-sensitized porous TiO₂ (CuS-TiO₂), and CdS-sensitized porous TiO₂ (CdS-TiO₂) in terms of PEC performance, the CuS-CT photoanode exhibited a significantly high anodic photocurrent for water splitting under simulated sunlight radiation. The photocurrent produced by the optimized sample of 7% CuS-5% CdS-TiO₂ (7% CuS-CT) was nearly 2.7 times higher than that of pure porous TiO₂ at 1.0 V versus a reversible hydrogen electrode (RHE). Porous TiO₂ possesses large surface areas that can drive fast electrolyte transport and afford more surface reaction active sites. On the other hand, CuS and CdS quantum dots not only broaden the visible light absorption range, but also improve photoinduced electron-hole separation efficiency. The co-sensitized multi-nanostructures photoanodes lead to a remarkable and promising application in PEC water splitting reactions.