TiO₂/CdS/PDA Ternary Heterojunction Photoanode for Enhancing Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is a promising pathway for solar-to-fuel conversion. The success in PEC water splitting lies in developing efficient and stable photoanodes. Herein, we develop a TiO₂/CdS/PDA ternary heterojunction photoanode for PEC water splitting via chemical bath deposition and oxidative self-polymerization. It is revealed that the π-π* stacking conjugated structure of PDA enhances light absorption and offers efficient pathways for charge transfer. More importantly, the introduction of PDA enables the formation of the type-II multilevel band alignment, which accelerates interfacial charge transfer and prolongs the lifetime of photoexcited carriers. Moreover, the PDA layer can function as an effective antiphotocorrosion barrier to protect CdS. As a result, the optimized TiO₂/CdS/PDA-60 photoanode delivers a photocurrent density of 4.57 mA/cm² at 1.23 V vs RHE with excellent stability, representing a 3.5-fold enhancement compared to the pristine TiO₂ photoanode. This study provides a new strategy for designing efficient and durable photoanodes for PEC water splitting.