Two-dimensional covalent organic framework nanosheets: Synthesis and energy-related applications

Two-dimensional (2D) covalent organic framework nanosheets (CONs) are attracting increasing research attention because of their unique properties derived from their ultrathin thickness, high surface-to-volume atomic ratio, and extremely large surface area. 2D CONs can provide high transport pathways for charge carriers (e.g., electrons, holes and ions) through either the conjugated skeletons or the open channels. Therefore, they have shown great potential in energy related applications. In this review, we firstly introduce the recent developments and characteristics of 2D CONs by focusing on the two typical synthetic methods, i.e., top-down and bottom-up methods. Then, the energy-related applications in energy storage and conversion of 2D CONs are summarized. Finally, we give our personal views on the challenges and perspectives for the future research of 2D CONs and their composites.