Tailoring Energy Bands and Internal Polarization in ZnIn 2 S 4 for Synergistic Enhancement of Carrier Separation and High-Performance Piezo-PEC Water Splitting

Abstract

ZnIn 2 S 4 is a promising photoelectrocatalytic material, but its water-splitting performance is limited by weak light absorption and insufficient polar regulation. Thus, this study proposes a Cu-Fe co-doping strategy for ZnIn 2 S 4 : Cu is introduced into Zn sites (A sites) to form band gap intermediate energy levels facilitating electron transitions; Fe is incorporated into In sites (B sites) to significantly affect internal polar structures, with both synergistically optimizing catalytic activity. Results show co-doping modulates the band gap (2.49→2.36 eV) and enhances piezoelectric response via polar structure reconstruction. Under piezoelectric excitation, the Cu-Fe co-doped ZnIn 2 S 4 photoanode achieves 0.664 mA/cm 2 at 1.23 V RHE , a 42% improvement over unmodified samples (without ultrasonication). Experiments and DFT confirm Cu/Fe substitution in ZnS 4 /InS 4 tetrahedra alters polar structures. Ultrasonic assistance enhances dipole electric field intensity, and the generated piezoelectric polarization field effectively suppresses photogenerated electron-hole recombination. Meanwhile, co-doping-induced band gap narrowing constructs rapid carrier transport channels and reduces electron transition barriers. The study innovatively achieves directional carrier migration and efficient separation via synergistic coupling of ultrasound-induced polarization and photogenerated fields, integrating triple optimization (energy band engineering, internal polar regulation, piezoelectric polarization). This provides new insights into macroscopic polarization mechanisms of piezoelectric materials and establishes a theoretical framework for