Synergistic design and facile synthesis of zwitterionic vinylene-linked covalent organic frameworks for efficient photocatalytic hydrogen production

Two-dimensional covalent organic frameworks (2D-COFs) have emerged as promising photocatalysts for hydrogen evolution. Zwitterionic vinylene-linked COFs (ZVCOFs) integrate the stability and extended conjugation of vinylene linkages by charged ionic groups with strong dipole moments, which exhibit remarkable hydrophilicity, conductivity, and accelerated charge separation. However, the facile and scalable synthesis of high-performance ZVCOFs remains challenging. Here, we report a facile one-step hydrothermal synthesis of three ZVCOFs (BTT-ZVCOF, BDD-ZVCOF, and TTD-ZVCOF) that avoids organic solvents and conventional cumbersome freeze-pump-thaw operations while delivering high production. The as-synthesized ZVCOFs demonstrate outstanding hydrogen evolution across the entire visible-light spectrum. Notably, BDD-ZVCOF achieves a hydrogen evolution rate of 294.21 mmol g⁻¹ h⁻¹ with an apparent quantum yield of 29.43% at 500 nm. Combined experimental and theoretical analysis revealed that the introduction of planar thiophene units promotes exciton dissociation, while the synergistic effect between thiophene units and –SO₃⁻ groups generates robust built-in electric field that facilitates charge separation, and the negatively charged –SO₃⁻ groups lower the thermodynamic barrier for proton reduction, collectively contributing to the excellent photocatalytic performance of ZVCOFs. This work not only provides a facile, high-production route to ZVCOFs but also demonstrates a rational design strategy for achieving high-performance COF-based photocatalysts through built-in electric field engineering.