Piezoelectric Field‐Mediated Charge Transport Regulation in SrTiO ₃ /BiFeO ₃ Composites for Boosted Piezophotocatalytic Overall Water Splitting

Photocatalytic overall water splitting is a promising solar‐to‐chemical energy conversion strategy for storable hydrogen production. However, its efficiency is severely limited by the rapid recombination of photogenerated electron–hole pairs, among which charge separation remains the core bottleneck. Although the piezoelectric effect promotes charge separation, its rational use to solve band mismatch in composite photocatalysts remains underexplored. Herein, SrTiO 3 /BiFeO 3 composites with tight interfacial contact were prepared by ultrasonic‐assisted calcination. Under light alone, SrTiO 3 photogenerated carriers tend to transfer to BiFeO 3 , but its improper band positions reduce redox ability and limit water splitting performance. Innovatively, ultrasonic vibration generates a strong piezoelectric field in BiFeO 3 that regulates charge transport of the composite photocatalyst, suppressing detrimental carrier migration from SrTiO 3 to BiFeO 3 and enhancing electron–hole separation in SrTiO 3 . As a result, the optimal SrTiO 3 /BiFeO 3 ‐2% composite exhibits H 2 and O 2 evolution rates of 56.5 and 26.6 μmol•h −1 , respectively, under simultaneous light and ultrasonic irradiation—approximately 1.81 times higher than those achieved under pure photocatalysis. This work develops a distinct strategy to overcome band alignment bottlenecks, providing a new paradigm for coupling polarized materials with semiconductors to construct high‐efficiency piezophotocatalytic systems for overall water splitting.