Electrochemically exfoliated covalent organic frameworks for improved photocatalytic hydrogen evolution

Covalent organic frameworks (COFs) have recently shown great prospects for their photocatalytic applications in solar-to-hydrogen conversion. Nevertheless, most of the COFs were synthesized as crystalline bulk powders, impeding the exposure of surface catalytically active sites. Developing a noninvasive and expedient route to exfoliate COFs in liquids still remains a great challenge. Herein, two typical 1,3,5-tri(thiophen-2-yl)benzene (TTB)-based COFs (one possesses non-donor-acceptor constitution, denoted as TTB-PB, while the other possesses donor-acceptor constitution, denoted as TTB-PT) were synthesized via Schiff-base condensation reactions. Subsequently, these bulk COFs were exfoliated via a facile electrochemical strategy in aqueous systems. The obtained exfoliated COFs can not only facilitate photo-triggered exciton dissociation but also afford more accessible active sites and enhanced hydrophilicity. Consequently, the exfoliated COFs exhibited much higher photocatalytic capabilities for H2 evolution from water in sharp contrast to their unexfoliated precursors. It is to be noted that the exfoliated donor-acceptor COFs achieved a maximum H2 evolution rate of 27.24 mmol h-1 g-1, which is superior to that of the exfoliated non-donor-acceptor COF (i.e., 9.86 mmol h-1 g-1), and also ranks at the top of the state-of-the-art thiophen-based COF photocatalysts in the literature. This work enriches the fabrication approach of COF exfoliation. Furthermore, utilizing the synergetic strategy of aqueous electrochemical exfoliation and suitable molecular design, TTB-based COFs demonstrate promising photocatalytic activity. Thiophen-based covalent organic frameworks were exfoliated via a facile and noninvasive electrochemical strategy for improved photocatalytic hydrogen evolution.