Built-in electric field in triazine-based COF and bimetallic sulfide S-scheme heterojunctions for efficient photocatalytic hydrogen production

Abstract

Covalent organic frameworks have shown remarkable potential in the field of photocatalysis. However, their photocatalytic activity toward the hydrogen evolution reaction is frequently constrained by the rapid recombination of photogenerated electron–hole pairs. To overcome this fundamental limitation, in this study, a CuNi₂S₄/PaTp-COF S-scheme heterojunction structure was successfully synthesized using an in situ growth method. This heterostructure facilitates the separation and directional migration of photogenerated electrons and holes—rather than excitons—via an interfacial internal electric field intrinsic to the S-scheme configuration, thereby substantially improving the hydrogen evolution rate. In optimal conditions, the CuNi₂S₄/PaTp-COF S-scheme heterojunction achieved a hydrogen evolution of 934.7 µmol, with an apparent quantum yield of 4.03% at 500 nm. To gain a deeper understanding of the catalytic mechanism of this heterojunction, this research comprehensively employed X-ray photoelectron spectroscopy analysis and density functional theory calculations. The results elucidated the S-scheme charge transfer pathway and further enhanced the comprehension of charge separation kinetics. This study not only demonstrates the multiple advantages and application prospects of COFs in photocatalytic hydrogen evolution but also provides new perspectives and inspirations for the future development and design of materials.