Localized Oxygen Enrichment in a Covalent Organic Framework–ZnIn 2 S 4 S-Scheme Heterojunction Enables Spatially Confined Oxygen Reduction and Boosts Photocatalytic H 2 O 2 Selectivity

Hydrogen peroxide is essential for green synthesis, disinfection, and energy storage, but its production remains reliant on the energy-intensive anthraquinone process, prompting the need for sustainable photocatalytic alternatives. A key challenge in artificial H 2 O 2 photosynthesis is achieving high selectivity in the two-electron oxygen reduction reaction while enhancing the reactant transport and charge separation efficiency. Herein, we design a S-scheme heterojunction integrating a sp 2 carbon-conjugated covalent organic framework (CC-COF) and ZnIn 2 S 4 (ZIS) that enables localized oxygen enrichment and spatially confined oxygen reduction reaction sites, favoring selective H 2 O 2 production. The CC-COF structure provides accessible oxygen adsorption sites, while ZIS nanosheets facilitate hydrophilic transport pathways and efficient charge separation. As a result, the heterojunction achieves a H 2 O 2 production rate of 53.6 μmol g –1 min –1 with a high selectivity of ∼70%. This work provides a rational design strategy for optimizing reactant transport and charge flow in H 2 O 2 photosynthesis, contributing to the development of sustainable solar-driven H 2 O 2 production.