Defect Dipole-Piezopolarization Coupling Directs Charge Separation in CdS Photoanodes for Water Splitting

Conventional CdS-based photoanodes exhibit limited intrinsic polarization and severe carrier recombination, which hinder the full utilization of piezopolarization electric fields for charge separation in piezo-photoelectrocatalytic (piezo-PEC) water splitting, thus restricting their energy conversion efficiency. In this study, a doping-induced defect-dipole engineering strategy is proposed, in which La-doping leads to in-situ sulfur vacancy formation and thus a VS-Cd0.97La0.03S photoanode was successfully fabricated for piezo-PEC water splitting. The main principle behind this strategy is the construction of oriented La3+-VS dipoles, which are added in-phase with the natural electric field due to piezopolarization. Such a configuration significantly increases the strength of the built-in electric field and its alignment across space, creating highly efficient paths of carrier migration. Benefiting from this synergistic reinforcement, the VS-Cd0.97La0.03S photoanode shows excellent piezo-photoelectrocatalytic activity: it achieves a current density of 3.15 mA cm-2 at 1.23 V vs RHE, which is significantly higher than that of pristine CdS and other published analogues. The results of density functional theory calculations also confirm that the performance enhancement is a result of increased coupling between oriented defect dipoles and piezopolarization fields as well as improved orbital hybridization. Both these effects interact to regulate the built-in electric field and dynamic behavior of carriers. The present study establishes a design framework for the efficient control of carrier separation and transport in multi-field synergistic catalysis.