Covalent organic frameworks based nanomaterials: Design, synthesis, and current status for supercapacitor applications: A review

Abstracts Covalent organic frameworks (COFs) are emerging crystalline porous materials linked via covalent bonding possessing flexible molecular design and synthetic strategies have been widely investigated and technologically essential materials due to their unique advantages of large surface area and porosity, high modifiable, conjugated structures and sufficient building blocks, low density, and high chemical stability. The success of linking atoms in two and three dimensions to construct extended framework structures moved the chemistry of COFs beyond the structures to methodologies, highlighting prospective applications' possibility. Covalent bonds connect atoms to form molecules and then further link these molecules to giant covalent structures. More specifically, noticeable capacitive response and promising capacitance availability have driven huge attention for efficient energy storage systems. Particular emphasis has been given to correlating their capacitive behavior with varying morphology obtained via various synthetic procedures. However, the most significant stumbling block to their widespread application in electrochemical energy storage systems is the low electrical conductivity and poor electrochemical performance (low specific capacitance) of pristine COFs based materials. The performance of pristine COFs-based materials can be improved by introducing redox-active groups into the skeleton of COFs, morphology control, hydrogen bonding, constructing hybrid systems with conducting polymers, carbon materials, chalcogenides, metal oxides, etc., to fabricate binary/ternary/quaternary nanocomposites with superior features for advanced energy storage applications, have also been outlined. Therefore, numerous efforts have been exerted to exploit the advantages and remedying the disadvantages. In this review paper, firstly, a background overview of COFs is provided, comprised of a brief introduction, merits, and demerits of COFs for supercapacitors are summarized in detail. Afterward, recent advancements of COFs (pristine and composites) design features are emphasized with a discussion about the principles and strategies involved. In the end, challenges remaining in this type of materials for real applications are outlined for supercapacitors.