Metal and covalent organic frameworks (MOFs and COFs): A comprehensive overview of their synthesis, characterization and enhanced supercapacitor performance

Abstract

The introduction of renewable energy sources (i.e., sunlight, wind, waves, etc.) into the energy grid is limited by its intermittency, amongst other disadvantages. This has led to the investigation of energy storage devices to close the gap and store excess energy. Supercapacitors (SCs) have been observed as excellent energy storage candidates, considering their long cycling, high power density, and minimal safety concerns. However, its low energy density limits SC application in real life. Recently, crystalline porous materials (CPMs) such as Metal and Covalent Organic Frameworks (MOFs and COFs) have sparked great interest in the design and engineering of electrode materials for energy storage systems (i.e., SCs and batteries) as a result of their intrinsic structural features that include rapid ion transport, ultrahigh and tunable porosity, large surface areas that offer maximized electroactive sites (derived from distinct selections of organic linkers), and rich redox metal centers (in the case of MOFs). These materials have shown a massive impact on the electrochemical performances of the devices, as pristine (MOFs and COFs) and also upon composite formations with other nanostructured materials such as graphene, carbon nanotubes (CNTs), metal oxides, conducting polymers, etc. This electrochemical performance is perceived to be highly dependent on MOFs and COFs structural architecture (i.e., 1D – 3D) and morphology (i.e., micro- or nanostructure), which are determined by the design and synthesis of these electrode materials and their composites. This review aims to demonstrate the outstanding findings from the literature on the use of MOFs and COFs as robust electrode materials with distinct structural features arising from carefully selected synthetic routes, organic linkers and metal centers (in the case of MOFs) for improved electrochemical performance in SCs. The review also briefly explores the literature evaluations on the role of theoretical modelling and statistical analysis in order to relate the electrochemical performance to the structural features of the electrode materials in SCs. • Crystalline porous materials have sparked great interest in the design of electrode materials for energy storage systems • Detailed comparative synthesis methods of MOFs and COFs and their electrochemical performance in supercapacitors are provided • Synthetic routes, organic linkers and metal centers in MOFs and COFs are pivotal for improved supercapacitor performance