Polarization-Enhanced direct Z-scheme ZnO-WO3-x nanorod arrays for efficient piezoelectric-photoelectrochemical Water splitting.

• Direct Z-scheme ZnO-WO 3- x was constructed by in-situ solvothermal treatment. • Suitable band structure and Fermi level drive the formation of Z-scheme structure. • Stirring leads to piezoelectric polarization of ZnO, and enhances Z-scheme effect. • Zn-W-5 shows very high piezoelectric-photoelectrochemical activities. Photosynthesis with Z-scheme charge transfer has been recognized as an efficient pathway to achieve solar-energy conversion. Herein, the all-solid-state direct Z-scheme ZnO-WO 3-x nanorod arrays were synthesized by in-situ solvothermal treatment for highly piezoelectric (PE)-photoelectrochemical (PEC) water splitting. The chemical bonding between WO 3-x and ZnO via W-O-Zn and the inherent band structures/Fermi levels drive the formation of direct Z-scheme charge-transfer pathway. Importantly, the optimized structure (Zn-W-5) shows higher PEC activities with high photocurrent density of 2.39 mA/cm2 at 1.23 V vs. RHE, which is 2.13 times higher than pure ZnO. Surprisingly, the obvious PE polarization of ZnO increases its Fermi level toward conduction band and significantly enhances Z-scheme effect between ZnO and WO 3-x. Especially, the best sample (Zn-W-5-1000 rpm) shows a photocurrent of 3.38 mA/cm2 at 1.23 V vs. RHE, which is 3.02 times higher than pure ZnO. This work provides a facile PE polarization approach for enhancement of Z-scheme charge-transfer process. [ABSTRACT FROM AUTHOR]