Designed Synthesis of Imine-Linked 2D Covalent Organic Frameworks with Enhanced Stability and Functionality

Covalent organic frameworks (COFs) linked by imine bonds have attracted significant attention, primarily due to the accessibility of monomers and the facile synthesis of highly crystalline materials. However, the reversible nature of imine bonds raises stability concerns for these materials in practical applications. Therefore, there is a pressing need for the development of imine-linked COFs that can combine high crystallinity, good stability, and functionality. Here, by adopting a two-in-one molecular design strategy, we designed an organic building block containing both acetal and amino connecting groups, featuring a pyridine functional site, and with side chains consisting of alkoxyl groups. Following a facile synthesis, these design elements were combined in a confined channel (0.85 nm), leading to two-dimensional (2D) COFs (COF-LIFM4 and COF-LIFM5) with good crystallinity and stability in both strong acid and base conditions. Moreover, COF-LIFM5 exhibited favorable CO₂ affinity and appropriate hydrophobicity, making it a promising modifier for improving mass transfer in the CO₂ reduction reaction (CO₂RR). As a result, Cu/COF-LIFM5 showcased an enhanced C₂₊ product selectivity in CO₂RR, with a Faradaic efficiency exceeding 80% at a current density of 500 mA cm^–2 in a flow cell.