Structure–Property Relation of Mechanochemically Synthesized β ‐Ketoenamine‐Linked COFs in Photocatalytic Hydrogen Evolution

ABSTRACT

Covalent organic frameworks (COFs) are promising photocatalysts for solar‐driven hydrogen evolution due to their tunable structures and intrinsic porosity. In this work, a series of Tp–Pa ‐based COFs bearing different electron‐withdrawing groups was synthesized via a scalable mechanochemical route to examine the impact of framework functionalization on their structural, electronic, and photocatalytic properties. Spectroscopic analyses (solid‐state ^{1 3} C CP‐MAS NMR and FT‐IR) confirmed the formation of β ‐ketoenamine linkages, while PXRD revealed higher crystallinity for pristine Tp–Pa compared to its functionalized analogues. Electrochemical studies indicated n‐type semiconducting behavior, with pristine Tp–Pa exhibiting more efficient charge separation and lower charge‐transfer resistance. Under visible‐light irradiation, Tp–Pa showed the highest hydrogen evolution rate (25,717 µmol g ^{− 1} h ^{− 1} ), whereas functionalized derivatives displayed reduced activity, with Tp–Pa–NO ₂ being nearly inactive. Notably, Tp–Pa also demonstrated excellent performance in simulated seawater (33,331 µmol g ^{− 1} h ^{− 1} ). These findings highlight the critical role of functionalization and synthesis strategy in governing crystallinity, charge transport, and photocatalytic efficiency, offering design guidelines for scalable COF‐based hydrogen evolution systems.