Defect dipole alignment mediated by poling for simultaneous optimization of piezoelectricity and carrier concentration in piezocatalysts

Piezoelectric materials with high piezoelectric coefficients often exhibit low carrier concentrations, which hinders the generation of free charges for piezocatalytic processes. To address this, defect engineering has emerged as a promising approach to adjust the electronic structure and enhance the carrier concentration of piezocatalytic materials. However, the introduction of defects can negatively affect the piezoelectric performance by increasing charge screening and reducing domain wall mobility. In this work, we demonstrate that a high carrier concentration can be achieved without compromising the piezoelectric properties, by applying an external electric field to enhance polarization and rearrange oxygen defect dipoles. This poling process significantly improves both piezoelectric and piezocatalytic properties. Specifically, the effective piezoelectric coefficient of a polarised, oxygen-deficient Bi₂WO_6-x material increased from d^*₃₃ ~ 4.79 pm V^‒1 to d^*₃₃ ~ 39.89 pm V^‒1. Moreover, its carrier concentration remained high, approaching N_d ~ 7.39×10²⁰cm^‒3, when subjected to ultrasonic vibrations. As a result of the high piezoelectric activity and carrier concentration, the piezocatalytic hydrogen production efficiency (per unit power) attained ~3.49 μmol g⁻¹ h⁻¹ W⁻¹. This work enables the design of efficient and energy-saving piezocatalytic materials, providing a significant step forward for hydrogen production via piezocatalytic water splitting.