Lewis Acid-Based Pair Enable Charge-Reactant Synergy in Sulfur-Vacancy-Engineered Bi19Br3S27– x /Covalent Organic Framework S-Scheme Heterojunctions for Photocatalytic H2O2 Production

Abstract S-scheme heterojunctions achieve efficient spatial charge separation via the built-in electric field. However, atomic-level precision in regulating interfacial charge transport and reactant activation remains a significant challenge. Herein, we introduce sulfur vacancies (SVs) into a Bi19Br3S27 S-scheme heterojunction to develop an effective strategy that combines interface engineering with interfacial Lewis acid–base chemistry. The SVs serve dual functions: on the one hand, they shorten adjacent Bi–O bonds, enhancing structural stability. On the other hand, they generate Lewis acid sites that facilitate O2 adsorption. Notably, Lewis acids are capable of coupling with Lewis bases within the COF structure, thereby facilitating Lewis acid–base-mediated interfacial charge transfer. Pyridine adsorption infrared spectroscopy directly confirms the emergence of strong Lewis acid sites following the introduction of SVs. Femtosecond transient absorption, in situ XPS, and Kelvin probe force microscopy collectively reveal the characteristic S-scheme charge-transfer pathway. Furthermore, density functional theory calculations indicate that Lewis acid sites optimize the O2 adsorption configuration. Structural and electronic-state analyses demonstrate that the formation of interfacial Lewis acid–base pairs effectively lowers the charge-transport potential barrier, thereby drastically boosting photocatalytic performance. This work pioneers the integration of Lewis acid–base chemistry into S-scheme heterojunction design, achieving end-to-end regulation from bulk charge separation to surface O2 activation.