Ultra-thin Cage-based Covalent Organic Frameworks Nanosheets as Precursor for Pyrolysis-Free Oxygen Evolution Reaction Electrocatalyst

The ultra-thin Covalent Organic Frameworks (COFs) nanosheets are very appealing 2D material, but the mass production of ultra-thin COFs nanosheets remains a great challenge. Here, by using cage-like bicyclocalix[2]arene[2]triazines tri-aldehyde (BCTAL) as the building block, 2D COFs Cage-COF-1 was estimated to have a very weak interaction between adjacent layers (around 1/50 compare to that of graphite). As a result, 1.2 nm thick trilayer COFs nanosheets was facilely exfoliated from the pristine COFs with large lateral size and high thickness homogeneity. The Cage-COF-1 nanosheet is featured by the imine linkage, but it is catalytic inactive in oxygen evolution reaction (OER). After post-metalation with Co2+ under ambient condition, remarkable catalysis activity and stability was observed for Cage-COF-1-Ns/Co, which has lower overpotential (330 mV) and Tafel slope (56mV/dec) in catalytic OER compare to many other Co catalysts. This work has confirmed that weakening the interlaminar interaction is an effective strategy for the production of ultra-thin COFs nanosheets. Due to the fully exposed and accessible imine linkage, catalysis active metal site can be controllably produced via post-synthesis from nanosheets under very mild conditions.