Sulfur Vacancy Modulation‐Induced Electronic Rearrangement in S‐Scheme BaTiO 3 @ZnIn 2 S 4 Heterojunctions: Toward Synergistic Piezo‐Photocatalytic H 2 O 2 Evolution

High‐yield photocatalytic H 2 O 2 production in sacrificial agent‐free pure water constitutes a critical bottleneck requiring urgent advances in energy catalysis. Although ZnIn 2 S 4 (ZIS) exhibits favourable visible light absorption, it is plagued by severe bulk charge carrier recombination and scarce accessible surface‐active sites. In this work, step‐scheme (S‐scheme) BaTiO 3 @ZnIn 2 S 4 (BTO@ZIS‐V S ) heterostructures bearing surface S vacancies (V S ) are synthesised via thermal reduction, which achieve synergistic modulation of bulk heterojunction construction and surface vacancy engineering for the first time. The piezo‐photocoupled pathways governing H 2 O 2 evolution and organic pollutant degradation originating from the dual structural configurations are thoroughly elucidated. The optimised BTO@ZIS‐V S ‐2 sample achieves a photocatalytic H 2 O 2 evolution rate of 23.87 mM g −1 h −1 , and this catalytic activity is further boosted 2.31 times with the assistance of piezoelectric field stimulation. The outstanding catalytic improvement stems from ultrafast interfacial charge transfer (1.01 ps) across the S‐scheme interface, which effectively suppresses unfavourable carrier recombination. Furthermore, introduced V S imperfections break the local lattice symmetry of ZIS to enhance piezoelectric performance; meanwhile, these vacancies trigger the formation of intrinsic in–Zn directional local electric fields and create coordinatively unsaturated Zn active centres. The present research develops a promising avenue to overcome interfacial electron transfer drawbacks in piezo‐photocatalytic systems and improves the economical recycling of wastewater resources.