Insight Into Oxygen-Vacancy Regulation on Piezocatalytic Activity of (Bi <sub>1/2</sub>Na <sub>1/2</sub>)TiO <sub>3</sub> Crystallites: Experiments and First-Principles Calculations

Oxygen vacancy (OV) is one of the most common defects in piezoelectric materials, and the concentration of OV can dramatically influence the performance of piezoelectric materials. It is of great scientific significance to clarify the effect of OV on the piezocatalytic performance. Here, eco-friendly piezoelectric (Bi1/2Na1/2)TiO3 (BNT) crystallites with various OV concentrations are employed to explore the role of OV in piezocatalysis. Experimental and theoretical results comprehensively elucidate that the OV plays a double-edged-sword role in regulatin g the piezocatalytic performance. It reveals that increasing the concentration of OV enhances the adsorption of O2 and H2O molecules onto the surface of BNT crystallite and improves the charge concentration in BNT, which helps charges transport from BNT to O2 and H2O molecules, contributing to the generation of active radicals for boosting the piezocatalytic performance. However, the increase of OV weakens the piezoelectric property, which is adverse to charge transfer and thus decreases active oxygen species, suppressing the piezocatalytic activity. This work not only theoretically clarifies the regulation mechanism of OV engineering on piezocatalytic performance, but also experimentally provides an effective method to improve piezocatalytic activity by OV engineering.