| Supercapacitors,also known as electrochemical capacitors.are a new type of capacitor which has high specific capacitance,high energy density,long cycle life.Supercapacitors take the advantages of the capacitors and traditional batteries.It's considered to be able to replace the lithium-ion batteries.Supercapacitors are mainly composed of the electrode and electrolyte.The electrode is the core component of supercapacitors,which directly determine the electrochemical properties of supercapacitors.In this paper,pseudocapacitors electrode materials are mainly researched.In view of the current situation of transition metal oxides and carbon materials,a series of metal-organic frameworks precursors were synthesised.After annealing the transition metal oxides which had been modificated were obtained.The microstructures and the electrochemical properties were examined by transition electron microscopy,scanning electron microscopy,X-ray diffraction,thermo-gravimetric analysis,cyclic voltammetry,electrochemical impedance spectroscopy and chronopotentiometry.Specific contents and results are as follows:(1)Two nanoscale cobalt-organic frameworks(NMOFs)have been firstly prepared through a precipitation method(Co/imizadole-4,5-dicarboxylic acid as Co-Im and Co/pyridine-2,6-dicarboxylic acid as Co-Py).High temperature calcining of these Co-based NMOFs can result in Co3O4 electrodes(Co3O4-Im and Co3O4-Py).The sample were characterized by scanning electron microscopy,X-ray diffraction,thermogravimetric analysis,EDX spectrum,confirmed its structure just the same as Co3O4.The connection between the molecules of Co-Py is stronger than Co-Im.The thermal stability of Co-Im at high temperature is weak.The grain diameter of Co3O4-Im is more concentrated and smaller than Co3O4-Py.Series of electrochemical measurements showed that the as-prepared Co3O4-Im materials delivered a maximum specific capacitance of 233F/g when Co3O4-Py delivered 177 F/g at 0.2 A/g,Co3O4-Im delivered low charge-transfer resistance of 0.8 2 and good stability over 1500 cycles with the capacitance maintaining of 89.8%.Co3O4-Py delivered charge-transfer resistance of 1.22 ? and remained 73.7%of capacitance over 1500 cycles.As a result,Co/imidazole-4,5-dicarboxylic acid are more likely to form Co3O4,and have a better electrochemical performance.(2)The liquid phase coprecipitation method was used to synthesize the composite material of Ni-organic frameworks and multiwalled carbon nanotube with the help of the surfactant PSS(polystyrene sulfonic acid sodium).In the experiment,dmg and ATC-Na ware uesd as organic ligand to form the Ni-dmg-WMCNTs and Ni-ATC-WMCNTs.High temperature annealing calcining of these Ni-based NMOFs/WMCNTs can lead to the pseudocapative NiO/WMCNTs electrodes(NiO-1 and NiO-2).Then WCNTs-COOH was used instead of PSS to composite the NiO-3 and NiO-4.Sample characterized by TEM and XRD and confirmed that it is NiO.The carbon nanotube wall of NiO-1 was thickened obviously,and there were many NiO particles adhere to the surface.Kinds of electrochemical measurements indicated that the as prepared NiO-1 material could show a maximum specific capacitance of 195 F/g in the condition of 0.2 A/g,while NiO-2 and NiO-3 and NiO-4 were 131 F/g?132 F/g?73 F/g,respectively.In conclusion,WCNTs can dispersion well with the help of PSS.And the precusor Ni-dmg-WMCNTs have a better morphology and electrochemical performance.(3)On the basis of Ni-NMOFs,Cu2+ was added to the precursor with DI water and ethanol as solvent.High temperature annealing calcining of these precursor can result in NiO/CuO(as Cu-Ni-1 and Cu-Ni-2).The scanning electron microscopy graphic showed the microstructure of precursor had inform shape.The Cu-Ni-1 delivered a maximum specific capacitance of 133 F/g and Cu-Ni-2 delivered of 296 F/g at 0.2 A/g.There are a small amount of CuO in Cu-Ni-1,but Cu-Ni-2 formed a mixture of NiO and CuO.In this experiment,ethanol is more suitable as solvent to get better electrochemical properties of NiO. |
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