First author: Yang Yiwen
Corresponding authors: Prof. Yifa Chen, Prof. Yaqian Lan
Author Affilications:South China Normal University
【Full text at a glance】
Porous crystalline conjugated macrocyclic materials (CMMs) have broad application prospects in the field of energy storage due to their planar macrocyclic conjugated π electronic system, high porosity, tunable structure/function and efficient charge transport capabilities. In this review, the authors summarize the synthesis methods, structural properties, and applications of porous crystalline CMMs in energy storage fields such as lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, potassium-ion batteries, Li-CO2 batteries, Li-O2 batteries, zinc-air batteries, supercapacitors, and triboelectric nanogenerators, and discuss the challenges and opportunities of porous crystalline CMMs. This review can provide ideas for the development of advanced energy storage materials based on porous crystalline CMMs.
【Background】
Porous crystalline conjugated macrocyclic materials (CMMs) are a class of porous crystalline materials that integrate conjugated macrocyclic units into MOFs/COFs. Their extended π-π conjugated structure gives them high conductivity, charge transfer mobility, and excellent electrochemical stability compared to other amorphous macrocyclic compounds, which is beneficial for energy storage applications. The application of porous crystalline CMMs in the field of energy storage can be traced back to 2015, and one of the porous crystalline CMMs was originally applied to lithium-sulfur batteries. Since then, tremendous progress has been made in the field of related energy storage, and many jobs have been reported.
Figure 1. Time development table of porous crystalline CMMs applied to energy storage.
Porous crystalline CMMs have shown the following advantages in the field of energy storage: 1) the active interface and internal channels of their porous structure can accelerate the transfer of multiple electrons, reactants and intermediates; 2) Its high specific surface area promotes the formation of solid-liquid or solid-gas interface between porous crystalline CMMs and the guest, which is conducive to electrolyte penetration and rapid transfer of metal ions. 3) Modifiable metal sites confer rapid redox capabilities in their structures to meet the needs of intermediate capture and catalytic conversion in energy storage devices; 4) Low density and abundant active sites can improve the energy density and coulombic efficiency of energy devices, making functional devices lightweight and portable. 5) The stable skeleton with high electrochemical stability makes it highly stable in acidic, alkaline and redox environments.
Figure 2. Energy storage applications of porous crystalline CMMs.
In this review, the authors provide an overview of the latest developments in the field of energy storage of porous crystalline CMMs, including their design, synthesis methods, properties, and energy applications (Figure 2).
【Content Description】
1. Characteristics and design synthesis of porous crystalline CMMs
Porous crystalline CMMs for various energy storage applications can be boiled down to two parts: 1) conjugated ligands containing various functional groups (i.e., amides, aldehydes, imides, nitro, carboxyl, cyano, sulfhydryl, and hydroxyl groups) have been reported to yield different kinds of porous crystalline CMMs by solvothermal or ionic thermal synthesis methods; 2) The introduction of additional functional groups by the co-ligand will also have an impact on the application of porous crystalline CMMs in the field of energy storage. Table 1 summarizes the reported organic ligands.
Table 1. Different connection styles and ligands for porous crystalline CMMs for energy storage devices.
2. Energy storage applications of porous crystalline CMMs
The advantage of porous crystalline CMMs in the field of energy storage lies in their unique structural features, such as conjugated macroring frameworks, tunable pore structures, and abundant designable functional sites, making them highly potential candidates in this field. Based on the above excellent properties, porous crystalline CMMs have been used in various energy storage applications, such as lithium-ion, potassium-ion, sodium-ion, lithium-sulfur, zinc-air, lithium-oxygen batteries, lithium-carbon dioxide batteries, supercapacitors and triboelectric nanogenerators.
3. Outlook
Porous crystalline CMMs can tweak the pore structure, which is conducive to the storage and diffusion of metal ions. At the same time, they have high chemical stability and good resistance to volume changes caused by charging or discharging. However, the application of porous crystalline CMMs in the field of energy storage still faces severe challenges: (1) synthesis problems: the structural rigidity of the conjugated unit makes it relatively difficult to prepare porous crystalline CMMs, and it is difficult to obtain high-crystallinity structures; (2) Stability problem: the coordination metal center of macrocyclic molecule will face the problem of detachment under strong acid or strong alkali conditions; (3) The contradiction between conductivity and crystallinity: there is a balance between crystal structure and conductivity; (4) High cost: the synthesis process of conjugated macrocyclic ligands is complex and relatively harsh, which limits its large-scale production; (5) Limited application forms: most of them are mainly in powder form, and only a small number of processing examples are reported.
Therefore, the further application of porous crystalline CMMs needs to pay more attention to some important issues: 1) for synthesis problems, it may be necessary to explore green sustainable media with high solubility to macrocyclic ligands, such as ionic liquids or supercritical CO2 (SC CO2); 2) For stability issues, it is necessary to design more stable conjugated macrocyclic MOFs (i.e., zirconium-based, aluminum-based and titanium-based MOFs) and COFs with stronger connection methods (oxazole, hydrazone, sp3 and sp2 connections) or hybridization with other protective materials; 3) To solve the contradiction between conductivity and crystallinity, the nanomorphology of porous crystalline CMMs (nanosheets, nanofibers and nanotubes) can be regulated; 4) For the high cost and large-scale production of conjugated macrocyclic ligands, green and inexpensive synthesis techniques or one-pot synthesis strategies from ligand precursors (Por, Pc, Phen) to porous crystalline CMMs are necessary; 5) For limited application forms, explore more advanced application forms (membranes, fibers, foams) to meet the needs of specific scenarios of different energy storage applications.
【Summary】
In this review, the authors summarize important advances in porous crystalline CMMs in various energy storage applications. Firstly, the structure of porous crystalline CMMs was summarized and discussed in detail. After that, the different applications of porous crystalline CMMs in the field of energy storage were introduced. Finally, the current challenges and opportunities they face in energy storage applications are proposed. The authors hope that this review will stimulate more scientists' interest in the application of porous crystalline CMMs in the field of energy storage.
Yang, Y., Yao, X., Xuan, Z., Chen, X., Zhang, Y., Huang, T., Shi, M., Chen. Y. & Lan, Y.-Q. Porous crystalline conjugated macrocyclic materials and their energy storage applications, Materials Horizons. 2024.
https://doi.org/10.1039/D4MH00313F
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