2D Redox‐Active Covalent Organic Frameworks for Supercapacitors: Design, Synthesis, and Challenges

Abstract

the other hand, transition metal oxides, [8] conductive polymers, [9] and redox-active porous organic materials [10] are promising candidates as pseudocapacitive electrodes. These materials typically exhibit large capacities and high energy densities, resulting from the reversible faradic redox processes between the electrolytes and the redox-active electrodes.Covalent organic frameworks (COFs) are an emerging class of porous crystalline polymer networks connected by stable covalent linkages possessing unique characteristics, such as light weight, high porosity, diverse topologies, designable open channels, and functional tunability. [11] These advantages endow COFs with a wide range of applications in gas storage and separation, [12] catalysis, [13] drug delivery, [14] optoelectronics, [15] sensing, [16] etc. The open channels and designable structures based on various building blocks provide substantial possibilities for the construction of novel redox-active porous skeletons, where rapid mass transfer can be realized. Compared with other carbon (or metal)-based SC electrodes, crystalline redox-active COFs showcase unique physicochemical features, and thus featuring huge potentials for the construction of promising SC devices. First of all, redox-active COFs are crystalline polymers with extended and rigid skeletons connected by stable covalent bonds. Therefore, the rigid framework structures can be maintained under harsh conditions and exhibit superior electrochemical stability in various electrolytes.Secondly, ordered open channels of redox-active COFs facilitate the adsorption and migration of electrolyte ions. Thirdly, various redox-active moieties can be readily introduced into the COF skeletons and the density of active sites can be facilely controlled by the pore-wall engineering strategy. [17] Last but not least, 2D redox-active COFs can be easily grown as thin films at different interfaces, [18] which facilitate the integration of COFs into electric devices. Most reported redox-active COFs involve carbonyl-containing structures, N/S-rich moieties, free radical species, etc. The chemical stability is a mandatory requirement for 2D redox-active COF based SC electrodes, which is directly related to their eventual electrochemical performance. High crystallinity COFs were usually prepared by the highly thermodynamic reversible reactions, which might lead to the inferior stability of COFs. [19a] Nonetheless, many COF materials, such as CTFs and imine COFs, have been demonstrated with excellent chemical stability even under harsh conditions like strong acid/alkali solutions, which enables the application potentials under extreme conditions. Furthermore, many effective strategies have been developed to enhance the chemical stability Due to the tunable skeletons, variable pore environments, and predesignable structures, covalent organic frameworks (COFs) can be served as a versatile platform to tailor redox activities for efficient energy storage. Redox-active COFs with specific functional groups can not only...

Covalent organic frameworks: Design and applications in electrochemical energy storage devices

“…Current studies of COFs are mostly focused on 2D binary functional design and postprocesses for structural modifications. 31,41,42 Research efforts devoted toward various EES systems, though at different stages of development, often reveal recurring concepts and design principles applicable for other electrochemical processes as well. While COFs had been introduced in several comprehensive reviews 8,34,[43][44][45] as well as ones regarding specific EES systems, 31,32,41,46 few discussions were made to present the fundamental understanding of the working principles and design strategies of COFs in order to improve electrochemical performance for EES.…”

“…31,41,42 Research efforts devoted toward various EES systems, though at different stages of development, often reveal recurring concepts and design principles applicable for other electrochemical processes as well. While COFs had been introduced in several comprehensive reviews 8,34,[43][44][45] as well as ones regarding specific EES systems, 31,32,41,46 few discussions were made to present the fundamental understanding of the working principles and design strategies of COFs in order to improve electrochemical performance for EES. In this review, we will introduce the formation mechanism and synthesis methods of COF, and then present significant findings in EES applications through emphasizing the representative design approaches (Figure 1) utilized in each field and their underlying relationships with electrochemical performances.…”

Aqueous Organic Zinc-Ion Hybrid Supercapacitors Prepared by 3D Vertically Aligned Graphene-Polydopamine Composite Electrode

“…The construction and manufacture of electrochemical energy storage systems with high power and energy density, fast charge and discharge rates, and excellent cycle performance are of great importance to the rational use of energy [ 1 , 2 , 3 ]. Traditional energy storage devices mainly include batteries and supercapacitors, which are widely used in high energy density and high power ranges, respectively [ 4 ].…”

“…A few organic materials are being studied as electrode materials for supercapacitors, such as polyaniline (PANI) [ 12 , 13 ], polypyrrole (PPy) [ 14 , 15 ], poly(3,4-ethylenedioxythiophene) (PEDOT) [ 16 ], and quinone-based organics [ 3 , 17 ]. In recent years, the quinone-based organic of polydopamine (PDA), which contains a large amount of catechol and nitrogenous amino groups, has been widely studied as electrocatalysts and electrode materials for energy conversion and storage.…”

A Tröger’s Base-Derived Covalent Organic Polymer Containing Carbazole Units as a High-Performance Supercapacitor

“…Compared to traditional inorganic (silica, zeolite) and carbon porous materials, microporous organic polymers (POPs) have gained tremendous interest due to their unique properties such as permanent porosity, variable morphologies, high surface area, low density, easy functional modification, various synthetic strategies, and excellent thermal and chemical stability [ 21 , 22 , 23 ]. Recently, novel POPs have been reported, including covalent triazine frameworks (CTFs), covalent organic frameworks (COFs), polymers of intrinsic microporosity (PIMs), hyper-cross-linked polymers (HCPs), conjugated microporous polymers (CMPs), and porous aromatic frameworks (PAFs) [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. These unique features of POPs encouraged the use of POPs in several technological applications such as sensing, luminescence, catalysis, gas adsorption, energy storage, water splitting, and semiconducting devices [ 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 ].…”