Jahn–Teller Distortion of MnO 6 Octahedra Enhances Piezoelectric Polarization and Lattice Oxygen Activation of BaTiO 3 for Efficient Piezo‐PEC Water Splitting

Piezo‐photoelectrochemical (Piezo‐PEC) water splitting enables efficient solar conversion, yet its practical implementation is limited by an insufficient piezoelectric polarization field and sluggish water‐splitting kinetics. Herein, we firstly propose a Jahn–Teller effect‐driven strategy to regulate the local B‐site octahedral structure of perovskite BaTiO 3 for efficient Piezo‐PEC water splitting. By introducing Mn 3+ ions with asymmetric e g orbital occupancy (t 2g 3 e g 1 ), a local MnO 6 octahedral coordination environment is constructed and pronounced Jahn–Teller distortion is induced. Experimental characterizations and density functional theory (DFT) calculations reveal that the Jahn–Teller distortion drives the cooperative displacement of Ti and O atoms and enhances crystal non‐centrosymmetry, thereby generating a stronger piezoelectric polarization field under mechanical stress. Meanwhile, the introduction of Mn 3+ strengthens Ti─O bond covalency, thereby activating lattice oxygen species and promoting the water‐splitting pathway from the conventional adsorbate evolution mechanism (AEM) toward the lattice oxygen mechanism (LOM), thus accelerating reaction kinetics. Under coupled ultrasonic vibration and illumination, the optimized BTMO‐6 photoanode delivers a high photocurrent density of 2.18 mA cm −2 at 1.23 V RHE and exhibits a piezoelectric coefficient (d 33 ) of 52.3 pm V −1 . This work reveals that Jahn–Teller distortion simultaneously enhances piezo‐polarization and tunes reaction pathways, offering new insights for robust Piezo‐PEC water‐splitting systems.