Localized Oxygen Enrichment in a Covalent Organic Framework–ZnIn2S4 S-Scheme Heterojunction Enables Spatially Confined Oxygen Reduction and Boosts Photocatalytic H2O2 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 H2O2 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 sp2 carbon-conjugated covalent organic framework (CC-COF) and ZnIn2S4 (ZIS) that enables localized oxygen enrichment and spatially confined oxygen reduction reaction sites, favoring selective H2O2 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 H2O2 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 H2O2 photosynthesis, contributing to the development of sustainable solar-driven H2O2 production.