Computational insights into fused heterocyclic-based 2D COFs for photocatalytic hydrogen evolution

Hydrogen production via photocatalytic water splitting offers a promising route for converting solar energy into clean fuel. Two-dimensional covalent organic frameworks (2D COFs) incorporating fused heterocycles feature broad-spectrum light absorption and facilitate efficient charge migration through extended π-conjugation, enabling efficient separation of photogenerated electron-hole pairs. Leveraging these advantages, nine fused heterocyclic-based 2D COFs were designed and evaluated for their potential in solar-driven hydrogen evolution. HSE06 calculations reveal that the introduction of fused heterocyclic units significantly enhances intramolecular charge transfer. All proposed 2D COFs possess suitable band structures to drive water reduction under visible light, with the bandgap ranging from 1.44 to 2.32 eV. Such reduced bandgaps broaden the light-harvesting range and are conducive to improving solar-to-hydrogen (STH) efficiency. Notably, CHF-DTBT exhibits the widest light absorption spectrum, with its absorption edge extending to 910 nm, and achieves a theoretical energy STH efficiency of 40.50%. This study demonstrates the strong potential of fused heterocyclic-based 2D COFs for photocatalytic hydrogen generation and provides valuable insight into the design strategies for high-performance photocatalysts.