Fabricating covalent organic framework/CdS S-scheme heterojunctions for improved solar hydrogen generation

The fabrication of S-scheme heterojunctions has received considerable attention as an effective approach to promote the separation and migration of photoexcited electron/hole pairs and retain strong redox abilities. Herein, an imine-based porous covalent organic framework (COF-LZU1) is integrated with controllably fabricated CdS hollow cubes, resulting in the formation of an S-scheme heterojunction. When the COF content reaches 1.5 wt%, the COF/CdS heterostructure (1.5%COF/CdS) achieves the highest hydrogen generation rate of 8670 μmol·h–1·g–1, which is approximately 2.1 times higher than that of pure CdS. The apparent quantum efficiency (AQE) of 1.5%COF/CdS is approximately 8.9% at 420 nm. Further systematic analysis shows that the intimate contact interface and suitable energy band structures between CdS and COF can induce the formation of an internal electric field at the heterojunction interface, which can effectively drive the spatial separation of photoexcited charge carriers and simultaneously maintain a strong redox ability, thus enhancing the photocatalytic H2 evolution performance.