Title: 2D Covalent Organic Frameworks for Energy Applications
Covalent Organic Frameworks are a class of porous, crystalline materials constructed from highly symmetric organic building blocks via dynamic bond formation chemistry. The building blocks can be bridged via a multitude of different bond types. Although interest in three dimensional COFs is high and the number of examples is growing, layered two dimensional (2D) covalent-organic frameworks are the predominantly reported class of COFs. Commonly, through the ordered stacking of the 2D layers, frameworks with 1D channels are obtained. Due to their layer stacked nature, there is a growing interest in their delamination, since they can be viewed as porous analogues of more traditional 2D materials like graphene or hexagonal boron nitride. The targeted delamination of such frameworks is still challenging, but solvent-assisted delamination methods offer a facile way to achieve few layer 2D dimensional COFs.
Within the first part of this presentation recent progress in the preparation of side chain modified COFs and their solvent assisted delamination will be presented. The COFs under discussion are prepared from pyrene-based tetratopic amines, linked via imine bridges with terephthalic aldehydes functionalized with alkoxy side chains in 2,5-position. The nature of the attached side chain (chain lengths, branched vs linear) and the solvent during ultrasonic treatment have a crucial impact on the delamination. It was possible to exfoliate the prepared COFs into nanosheets as thin as 1.5 nanometers (4-5 layers). Furthermore, when long side chains are attached, the materials form stable dispersions, which were used to integrate the COFs into membranes used as separators in Lithium Ion batteries.
The second part of the presentation the focus will lay on the preparation of COFs that are suitable electrode materials for Lithium Organosulfide and Lithium Organoselenide batteries. For this, redox active moieties used in Lithium Sulfur/Selenium Batteries are combined in parallel within one framework with redox moieties typically used in COFs for Lithium Ion battery, and by clever choice of the electrolyte the potential window can be enhanced to address the sulfur/selenium rich moieties as well as the N/O rich moieties in parallel, enhancing the overall capacity.