A-Site Engineering of Aurivillius Bi4Ti3O12 for Enhanced Ferroelectric Polarization and Photocatalytic Overall Water Splitting.

Efficient suppression of photogenerated charge recombination remains a central challenge in photocatalytic water splitting. Bi4Ti3O12 is a promising ferroelectric semiconductor for overall water splitting, yet its quantum efficiency is fundamentally constrained by weak polarization and sluggish carrier dynamics. Herein, we demonstrate that isovalent A-site substitution provides an effective route to amplify the intrisinc polarization of Bi4Ti3O12 through lattice regularization. Specifically, Sm substitution suppresses localization disorder by attenuating the stereochemical activity of Bi3+ lone pairs, thereby reducing excessive octahedral tilting and enabling more coherent dipole alignment. The resulting enhanced ferroelectric polarization field markedly facilitates charge separation and carrier migration. In addition, post-synthetic acid treatment tailors the surface termination and suppresses the self-corrosion typically associated with bismuth-based photocatalysts. Upon cocatalyst loading, the optimized Bi4Ti3O12-Sm photocatalyst achieves an efficient overall water splitting with an apparent quantum efficiency of 10.5% at 365 nm. This work establishes structural regularization as a viable design principle for enhancing ferroelectric polarization and advancing high-performance photocatalytic systems.