Metal organic frameworks (MOFs) are a type of crystalline porous material with a periodic network structure formed by connecting and bridging inorganic metal centers (metal ions or metal clusters) with organic ligands. Because MOFs have many properties such as porosity, large specific surface area, strong designability, multi-metal sites, etc., they have been extensively studied and used in the fields of gas storage, molecular separation, catalysis, and sustained drug release during the past 20 years.
Today, electrocatalytic technology plays an important role in the conversion of clean energy and contributes to the development of sustainable technologies in the future. Among them, single atom catalysts (SACs) based on MOF chemicals are emerging unconventional materials in electrochemical catalysis applications. It has unique electronic structure, quantum size effect and other advantages, and is expected to improve electrocatalytic activity, stability and selectivity in the field of clean energy conversion.
The redox pair of triiodide/iodide (I3-/I-) has the advantages of high safety and low cost, and its introduction into water-based rechargeable zinc-iodine (Zn-I2) batteries is a promising strategy. However, due to the uncontrolled shuttle effect of triiodide and adverse side reactions on the zinc anode, the service life of the Zn-I2 battery still needs to be improved. Studies have found that when MOF is used as an ion sieve membrane, it can simultaneously solve these problems of Zn-I2 batteries. The use of multifunctional MOF film suppresses the shuttle of I3- and related parasitic side reactions on the Zn negative electrode. At the same time, by adjusting the solvation structure of the electrolyte, the MOF channel can construct a unique electrolyte structure (more ions accumulate than in a saturated electrolyte). By improving both the iodine positive electrode and the Zn negative electrode, the Zn-I2 battery can achieve long service life (> 6000 cycles), high capacity retention (84.6%) and high reversibility (Coulomb efficiency: 99.65%).
Covalent Organic Frameworks (COFs) are two-dimensional or three-dimensional crystalline porous polymer materials formed by covalently connecting organic structural units. They have high thermal stability, large specific surface area, rich pores, and flexible molecular structure. Unlike Metal Organic Framework (MOFs), COFs can be completely composed of light elements such as carbon, hydrogen, nitrogen and oxygen, and do not contain heavier elements such as metals. Scientists can create COFs with different pore diameters and change the materials passing through them or the materials contained in these pores to achieve functional diversification. According to its spatial structure, COFs can be divided into two-dimensional and three-dimensional structures. In three-dimensional COFs, organic units are connected by covalent bonds to form a three-dimensional network structure. This three-dimensional structure material is widely used in catalysis, gas adsorption, which is similar to MOFs. However, in two-dimensional COFs, organic units are connected to two-dimensional atomic layers, and the atomic layers are further stacked through π-π interactions to form a layered structure. The entire framework structure is determined by intra-layer covalent bonds and is affected by non-covalent interlayers, so it has broad application prospects in the field of energy storage.
COF materials were first discovered in 2005 and have been extensively studied subsequently. COFs materials have the advantages of uniform pore size and easy modification. By introducing functional groups into monomers or COFs polymers, COFs materials can have many unique properties, and thus have great application potential in the fields of adsorption and catalysis. They can covalently integrate organic units into periodically arranged frameworks and aligned polygonal pores. Also, they are very promising for the design of functional materials.
