Defect-Induced Fermi Level Engineering in Z-Scheme Ov-ZnO/ZnS Heterojunctions for Enhanced Photocatalytic H ₂ O ₂ Production

Photocatalytic synthesis of hydrogen peroxide (H 2 O 2 ) from water and oxygen represents a sustainable alternative to the industrial anthraquinone process for solar-to-chemical energy conversion. However, the efficiency of Z-scheme heterojunctions is often limited by a weak internal electric field (IEF), which hinders effective charge carrier separation. Herein, we demonstrate a defect-engineering strategy to modulate the interfacial energetics of a Z-scheme Ov-ZnO/ZnS (ZZO) heterojunction, enabling H 2 O 2 production in pure water via simultaneous two-electron water oxidation (WOR) and oxygen reduction (ORR) pathways. Experimental investigations and theoretical calculations reveal that the introduction of oxygen vacancies (Ov) elevates the Fermi level (E F ) of ZnO, significantly increasing the E F disparity at the interface and creating an enhanced IEF. The strengthened IEF enables rapid spatial charge separation, effectively suppressing recombination and prolonging electron lifetimes. In pure water, the optimized ZZO-2 exhibits an H 2 O 2 generation rate of 1.11 mmol·g –1 ·h –1 . This represents a 4.27-fold increase relative to pristine Ov-ZnO and a 3.01-fold increase relative to the ZnO/ZnS heterojunction. This work establishes defect-induced E F engineering as a generalizable strategy to boost IEF-driven charge dynamics, providing a blueprint for the design of high-efficiency Z-scheme photocatalysts for solar-to-chemical conversion.