Two-dimensional metal-organic framework and covalent-organic framework: synthesis and their energy-related applications

Two-dimensional (2D) metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) have recently emerged as a new class of crystalline materials with ultrahigh porosity and enormous surface area. These materials have attracted vast research interest due to their unique properties originating from ultrathin thickness, highly accessible active sites, and versatile structures. With many common features, MOFs and COFs also have distinct differences, both in synthetic and application aspects, as their building components are different. This review mainly focuses on the recent advances in the synthetic approaches of 2D MOFs and COFs and their applications in energy conversion reactions and storage devices. First, we discuss various strategies recently developed for the preparation of 2D MOFs and COFs by using self-assembly, template-directed method, surfactant-directed method, solid-supported growth, and decomposition, and the different considerations needed for desired 2D MOFs and COFs are compared. Secondly, energy-related applications of 2D MOFs and COFs are summarized with discussion on the structure-reactivity relationships. Finally, we give the insights into the challenges and outlook on the future research direction for 2D MOFs and COFs.