Studies On Application Of Metal-Organic Frameworks In Supercapacitors

The supercapacitor is a new type of electrochemical energy storage device which hasattracted considerable attention due to its high energy density, high power density, longcycle life and less pollution. Supercapacitors can provide higher power density thantraditional secondary batteries as well as much higher energy density than physicalcapacitors, which achieved much attention in many fields, such as mobiletelecommunication, information technology, consumer electronics, aerospace, militaryforce, and so on. Recently, studies on supercapacitors have been mainly focused on thepreparation of high performance electrode materials with both high power density andenergy density. According to the principle of energy-storage there are two types ofsupercapacitors: electric double-layer capacitor and faradaic pseudocapacitor. Electrodematerials mainly include carbon materials，metal oxides and conducting polymers (ECP).Metal-organic frameworks (MOF) has been considered as one of the most promisingmaterials for their extensive applications in many fields such as catalysis, hydrogen storage,ion exchange, sensor, medicine intermediate as well as optical materials. Comparing withtraditional porous materials, the flexible and various pore structures of MOFs have beenthe main reason for the particular attention. As a new type of porous material, MOFs notonly have high specific surface area but also contain active metal ions or clusters withintheir structures, which makes MOFs a promising candidate for electrode materials ofelectrochemical capacitors. However, studies on electrochemistry of MOFs, particularly ontheir application in electrochemical capacitors are rare at present and further research isneeded. In the present paper, a series of MOF materials containing cobalt, nickel and zincions were successfully synthesized via solvothermal method; Structural analysis werecarried out using single-crystal/powder XRD and N2adsorption-desorption studies; Electrochemical characterization were carried out using cyclic voltammetry, Galvanostaticcharge-discharge test, electrochemical impedance spectroscopy and cycle life test. Themain results and innovations are as follows:1. Cobalt-based MOF Co(bdc)(ted)0.5(bdc=1,4-benzenedicarboxylate; ted=triethylenediamine) with BET surface area of1244m2/g and3D pore size of7.3wasprepared using cobalt nitrate as metal precursor, terephthalic acid and triethylenediamine asorganic ligands via solvothermal method. Structural analysis and electrochemical test werecarried out; Influence of reaction temperature, reaction time and molar ratio of thereactants on the electrochemical performance of the electrode material was alsoinvestigated. The highest specific capacitance reached937F·g-1in6M KOH electrolyte atthe scan rate of5mv/s;2. Nickel-based MOF [Ni3(HCOO)6]·DMF with BET surface area of304m2/g and1D pore size of5.0was prepared using nickel nitrate as metal precursor, formic acid asorganic ligand via solvothermal method. Structural analysis and electrochemical test werecarried out; Influence of reaction condition on the electrochemical performance of theelectrode material was also investigated. The highest specific capacitance reached1217F·g-1in6M KOH electrolyte at the scan rate of5mv/s;3. Single crystal of zinc-based ionic metal-organic frameworks was prepared usingzinc nitrate as metal precursor and N,N`-diacetic acid imidazole as organic ligand viasolvothermal method. Single-crystal XRD was carried out to analyze the crystal structure;Electrochemical activities of the sample under different scan rates were studied andpromising capacitive performance under high scan rates was observed.