Two-Dimensional Carbon-Rich Conjugated Frameworks for Electrochemical Energy Applications

Abstract

Following a 15-year-long investigation on graphene, two-dimensional (2D) carbon-rich conjugated frameworks (CCFs) have attracted growing research interest as a new generation of multi­functional materials. Typical 2D CCFs include 2D π-conjugated polymers (also classified as 2D π-conjugated covalent organic frameworks) and 2D π-conjugated metal–organic frameworks, which are characterized by layer-stacked periodic frameworks with high in-plane π-conjugation. These unique structures endow 2D CCFs with regular porosities, large specific surface areas, and superior chemical stability. In addition, 2D CCFs exhibit certain notable properties (e.g., excellent electronic conductivity, designable topologies, and defined catalytic/redox-active sites), which have motivated increasing efforts to explore 2D CCFs for electrochemical energy applications. In this Perspective, the structural features and synthetic principles of 2D CCFs are briefly introduced. Moreover, we discuss recent achievements in 2D CCFs designed for various electrochemical energy conversion (electrocatalysis) and storage (supercapacitors and batteries) applications. Particular emphasis is placed on analyzing the precise structural regulation of 2D CCFs. Finally, we provide an outlook about the future development of synthetic 2D CCFs for electrochemical applications, which concerns novel monomer design, chemical methodology/strategy establishment, and a roadmap toward practical applications.

Chemical Conversion and Locking of the Imine Linkage: Enhancing the Functionality of Covalent Organic Frameworks

“…[16] Additionally, a great deal of attention is currently paid to 2D pconjugated COFs as they appear ideal for applications in electronic and electrochemical energy devices. [17] Indeed, theoretical studies predict semiconducting properties with highly tuneable band gaps and strict correlation between topology and electronic properties in these materials. [18] Nevertheless, even when (photo)electroactive units, such as porphyrins, pyrenes, thiophenes, and phthalocyanines are embedded into the COF structure, 2D imine COFs exhibit limited in-plane p-conjugation due to the inherent polarization of the C=N connection.…”

2D framework materials for energy applications

“…Rapid improvements in their synthesis and properties are made, and growing interest towards energy related applications is observed. 39 Evidently, many potential applications make good use of the enhanced diffusion pathways created by the downsizing along one dimension of the crystal structures and the resulting improved access to catalytic or redox active sites, which are important features for ion storage in supercapacitors or for faster redox reactions in batteries and during electrocatalysis. Further, novel optical properties arise through the formation of 2D arrays of fluorophores and the tuning of the materials bandgap through nanosizing.…”

Two-dimensional conjugated metal–organic frameworks (2D c-MOFs): chemistry and function for MOFtronics

“…195 Benefiting from the intrinsically conductive and porous properties, 2D c-MOFs have shown excellent performance in metal-ion batteries and supercapacitors, which could function as the power sources for the above mentioned MOFtronics. [197][198][199][200][201] 6.5.1 Metal-ion batteries. Benzene-based 2D c-MOFs with dense redox active sites have been widely utilized as active cathode materials for lithium/sodium-ion batteries (Fig.…”