| Supercapacitor is a new type of green energy storage device between traditional capacitors and secondary batteries.It is widely used in many fields.Electrode material is the most critical factor determining the energy storage effect of supercapacitor.The electrode material is modified by noble metal-Metal oxide which has attracted much attention due to its excellent energy storage effect,but the high cost restrictits widespread utilization.Therefore,the development of efficient and inexpensive electrode material becomes a research focus that needs to be solved urgently in the field of supercapacitor.POM-based metal-organic framework crystal materials combine the advantages of POM and metal-organic framework materials,whichexert low cost and high stability.POM-based metal-organic framework crystal materials reveal great potential as a kind of negative electrode material for supercapacitor to replace noble metal compounds.However,research in this area has just begun.This work is based on Keggin-type POMsintroducing transition metal ions(Cu,Ni,Co)and nitrogen-containing organic ligands 4-amino-triazole(4-atrz)and 1,2-Di(pyridin-4-yl)ethene(BPE).Eleven kinds of Keggin POMs-based crystal materials(compounds 1-11)with novel structures,regular shapes and good stabilityare obtained byhydrothermal synthesis.The supercapacitor properties of POM-based crystal materials are studied by cyclic voltammetry(CV),galvanostatic charge/discharge(GCD)and electrochemical impedance spectroscopy(EIS).The pathsfor improving the superelectric properties of these electrode materials are investigated.The main contents are as follows:1.Based on the classic Keggin-type POMs,three unreported POMs-based supramolecular crystal materials has been designed and synthesized by adding nitrogen-containing organic ligand BPE and mineralizer,which are:(?)The results of single crystal X-ray diffraction show that compounds 1-3 are 3D supramolecular structures that connected by hydrogen bondswith the same connection mode.The specific capacitance values are 75 F g-1?49.3 F g-1and 137.5F g-1at a current density of 2A g-1.And,after 1000 cycles of GCD,the capacitance retention rates are 62.4%,77.0%,and 37.8%,respectively.2.When selecting keggin-type classic POMs as the basic unit and Cu as the transition metal,three 3D POMs-based crystal materials that connected by covalent bonds have been designed and synthesized by adding organic ligand 4-atrz:(?)The compounds 4-6 have 3D structures and have the same connection mold.The specific capacitance values of compounds 4-6 are 231.7 F g-1?147.5 F g-1 and232.5 F g-1,respectively.The specific capacitance values remain 88.2%,95.3% and98.8% after 1000 cycles of GCD.3.When choosing Keggin-type classic POMs as the basic unit,five novel 3D POM-based crystal materials could be prepare by modulating the metal nodes and adding organic ligand 4-atrz:(?)The specific capacitance values of compounds 7-11 are 150.8F g-1,236.3 F g-1,291.6 F g-1,275.2 F g-1and 212.7 F g-1at the current density of 1A g-1.After 1000 cycles of GCD,the capacitance retention rates are 93.76%,85.94%,83.33%,76.92% and 58.84%,respectively.In compounds 1-11,although compounds 1-3 have 3D supramolecular structure connected by hydrogen bonds,their capacitance value and stability are not satisfactory.In contrast,compounds 4-6 have 3D network structure connected by covalent bonds,and the capacitance value and stability are improved.Further,by introducing nickel and cobalt ions with outstanding electrochemical performance,the 3D close-packed structure has been constructed and crystalline materials 7-11 with the superior supercapacitor performance have been obtained.The specific capacitance of the electrode materials are effectively improvedby adjusting the type of metals and the spatial structure of the compounds. |
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