Defect-Induced Fermi Level Engineering in Z-Scheme Ov-ZnO/ZnS Heterojunctions for Enhanced Photocatalytic H2O2 Production

Abstract Photocatalytic synthesis of hydrogen peroxide (H2O2) 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 H2O2 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 (EF) of ZnO, significantly increasing the EF 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 H2O2 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 EF 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.