A‐Site Engineering of Aurivillius Bi 4 Ti 3 O 12 for Enhanced Ferroelectric Polarization and Photocatalytic Overall Water Splitting

ABSTRACT Efficient suppression of photogenerated charge recombination remains a central challenge in photocatalytic water splitting. Bi 4 Ti 3 O 12 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 Bi 4 Ti 3 O 12 through lattice regularization. Specifically, Sm substitution suppresses localization disorder by attenuating the stereochemical activity of Bi 3+ 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 Bi 4 Ti 3 O 12 ‐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.