Piezoelectric polarization assisted WO3/CdS photoanode improved carrier separation efficiency via CdS phase regulation

The key factor for efficient photoelectrochemical (PEC) water splitting is to design a semiconductor as photoanode with high carrier separation. Piezoelectric polarization is a considerable method to improve the carriers separation efficiency via providing a powerful built-in electric field. Herein, we synthesized WO3/CdS type II heterojunction and firstly explored the influence of CdS phase transition from sphalerite β-CdS to wurtzite α-CdS on piezoelectric polarization for WO3/CdS. Benefited from the asymmetric structure of α-CdS, fluctuation swings can be seen in the LSV curves of WO3/α-CdS due to piezoelectric polarization under ultrasound. The photocurrent density of WO3/α-CdS are enhanced with the increase of ultrasound frequency and the maximum of 2.13 mA/cm2 at 1.23 V vs. RHE, which is 1.61 times before ultrasound. The outstanding PEC performances of WO3/α-CdS under ultrasonic conditions are contributed to carrier separation driven by enhancing internal electric field between heterojunction, the built-in electric field inside the α-CdS and ballast carriers participating in water splitting reaction. This work provides a promising strategy for improving carrier separation efficiency in photoelectrodes via piezoelectric polarization.