Enhanced Generation of Reactive Oxygen Species via Piezoelectrics based on p–n Heterojunctions with Built-In Electric Field

Tuning the charge transfer processes through a built-in electric field is an effective way to accelerate the dynamics of electro- and photocatalytic reactions. However, the coupling of the built-in electric field of p-n heterojunctions and the microstrain-induced polarization on the impact of piezocatalysis has not been fully explored. Herein, we demonstrate the role of the built-in electric field of p-type BiOI/n-type BiVO₄ heterojunctions in enhancing their piezocatalytic behaviors. The highly crystalline p-n heterojunction is synthesized by using a coprecipitation method under ambient aqueous conditions. Under ultrasonic irradiation in water exposed to air, the p-n heterojunctions exhibit significantly higher production rates of reactive species (·OH, ·O₂^-, and ¹O₂) as compared to isolated BiVO₄ and BiOI. Also, the piezocatalytic rate of H₂O₂ production with the BiOI/BiVO₄ heterojunction reaches 480 μmol g^-1 h^-1, which is 1.6- and 12-fold higher than those of BiVO₄ and BiOI, respectively. Furthermore, the p-n heterojunction maintains a highly stable H₂O₂ production rate under ultrasonic irradiation for up to 5 h. The results from the experiments and equation-driven simulations of the strain and piezoelectric potential distributions indicate that the piezocatalytic reactivity of the p-n heterojunction resulted from the polarization intensity induced by periodic ultrasound, which is enhanced by the built-in electric field of the p-n heterojunctions. This study provides new insights into the design of piezocatalysts and opens up new prospects for applications in medicine, environmental remediation, and sonochemical sensors.