Tailoring energy bands and internal polarization in ZnIn2S4 for synergistic enhancement of carrier separation and high-performance Piezo-PEC water splitting

Abstract

ZnIn₂S₄ 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 ZnIn₂S₄: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 ZnIn₂S₄ 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 ZnS₄/InS₄ 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 Piezo-PEC catalytic system optimization.