Electrochemically exfoliated covalent organic frameworks for improved photocatalytic hydrogen evolution

Abstract

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.