Recent Progress of Advanced Conductive Metal–Organic Frameworks: Precise Synthesis, Electrochemical Energy Storage Applications, and Future Challenges

Abstract

inherent disadvantage of unstable output, which means electrochemical energy storage and conversion devices are essential for storing and utilizing these energies at any time. [6] Supercapacitors (SCs), lithium-ion batteries (LIBs), lithium-sulfur (Li-S) batteries, and electrochemical water splitting can efficiently convert electricity into chemical energy for storage and thus have received extensive attention. [7] The performance of the energy storage devices mainly depends on the electrode materials and the performance of energy conversion devices mainly depends on catalysts. Therefore, the development of high-performance electrode materials and electrocatalysts is crucial.Metal-organic frameworks (MOFs), also known as porous coordination polymers, are a new type of porous crystalline material. [8] Obtained by bridging metal ions or clusters and organic ligands via well-defined coordination bonds, MOFs possess unique structures with ultrahigh specific surface area, tunable composition, adjustable pore structure, and abundant exposed active sites, exhibiting significant potential for applications in gas storage and separation, catalysis, sensing, and energy storage. [9,10] The regular open pore structures of MOFs enable them to effectively contact electrolytes and alleviate volume expansion during charging and discharging when serving as electrodes. Besides, the abundant exposed active sites and the ultrahigh specific surface area of MOFs can meet the performance requirements of electrocatalysts for water splitting and electrode materials for SCs and LIBs, the plentiful polar sites and the complex pore structure of MOFs can effectively adsorb polysulfides as sulfur host. [11,12] Therefore, in recent years, great efforts have been devoted to the use MOFs as electrode materials for supercapacitors, anode materials for LIBs, sulfur hosts for Li-S batteries, and electrocatalysts for water splitting.The pristine MOFs possess numerous electrochemically active sites, which are almost fully accessible due to the regular pore structures. However, MOFs are usually composed of metal ions and redox-inactive organic ligands, lack free charge carriers, and charge transport paths, and thus are mostly electrically insulating, meaning that only the part in contact with current collectors or conductive additives can gain electrons to participate in the reaction, resulting in low utilization of Metal-organic frameworks (MOFs) with diverse composition, tunable structure, and unique physicochemical properties have emerged as promising materials in various fields. The tunable pore structure, abundant active sites, and ultrahigh specific surface area can facilitate mass transport and provide outstanding capacity, making MOFs an ideal active material for electrochemical energy storage and conversion. However, the poor electrical conductivity of pristine MOFs severely limits their applications in electrochemistry. Developing conductive MOFs has proved to be an effective solution to this problem. This review focuses on the design and syn...

2D Metal–Organic Frameworks as Competent Electrocatalysts for Water Splitting

“…Hydro/solvothermal synthesis is a liquid-phase chemical reaction in a sealed pressure vessel with water or other solvents under certain conditions. [120] Controlling the reaction conditions, such as the solvent, temperature, and volume, can adjust the morphology and crystal structure of conductive MOFs. Interface-assisted synthetic routes, including liquid-liquid, liquid-solid, and gas-liquid interfacial approaches.…”

Self-supporting metal–organic framework-based hydrogen and oxygen electrocatalysts

“…The hydro/solvothermal method is one of the most common preparation methods for self-supporting MOFs with high crystallinity and various morphologies in an autoclave over a wide temperature range (100–200 °C). 50 Surface oxygen groups and defects on the surface of conductive substrates favor MOF's nucleation and conformal growth, which facilitates the uniform deposition and solid bonding of MOFs on conductive substrates. Yang et al reported self-supporting Co/Zn-based ZIF (ZIF = zeolitic imidazolate framework) nanosheets on Ni foam (NF) through a facile hydrothermal method (Fig.…”

Microporous Organic Network: Superhydrophobic Coating to Protect Metal–Organic Frameworks from Hydrolytic Degradation

“…Metal–organic frameworks (MOFs), an emerging type of crystalline porous material, are coordination networks assembled from organic ligands and metal joints. − Owing to their excellent characteristics, such as large specific surface area, excellent thermal durability, and tunable structure and topology, , MOFs have been increasingly employed in applications such as pollutant elimination, , separation, − catalysis, − energy storage, , and adsorption. , However, because water molecules can gradually replace organic ligands through ligand exchange or hydrolysis, some MOFs become unstable in the presence of humidity. , Manipulating wettability to prepare hydrophobic MOFs is a feasible way to prevent water-sensitive MOFs from decomposing in high humidity, which can significantly broaden the application scope of MOFs. − …”