Localized Oxygen Enrichment in a Covalent Organic Framework-ZnIn₂S₄ S-Scheme Heterojunction Enables Spatially Confined Oxygen Reduction and Boosts Photocatalytic H₂O₂ Selectivity.

Abstract

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.