Surface Charge Modulation in Covalent Organic Frameworks for Controlled Pt‐Photodeposition and Enhanced Photocatalytic Hydrogen Evolution

Covalent organic frameworks (COFs) represent a new class of organic photocatalysts for the hydrogen evolution reaction (HER). While the influence of COF structural and optoelectronic properties on HER is well-studied, the role of surface charge in optimizing interfacial interactions with reactants remains underexplored. In this study, it is demonstrated that converting imine to amide linkages in a thiophene-based COF allows for altering surface charge through different protonation behaviors of the linkages. Zeta potential measurements reveal that the amide-linked COF, due to its lower basicity, is deprotonated and negatively charged in the presence of ascorbic acid, while the imine-linked COF is protonated and positively charged. This electrostatic contrast drives the photoreduction of [PtCl₆]²⁻ to Pt, with the imine-linked COF yielding uniformly distributed small Pt particles (1-2 nm), whereas the amide-linked COF forms larger Pt particles (up to 100 nm). The amide-linked COF, acting as an antenna that facilitates interdomain electron transport along COF agglomerates, promotes both Pt growth and subsequent proton reduction demonstrating a 300% increase in photocatalytic HER rate compared to its imine form. This work introduces surface charge modulation as a novel tool for controlling photocatalytic processes in COF-based systems expanding the COF functionality in photocatalysis.