Study On New Supercapacitor Electrode Materials Based On Transition Metal Compounds

As a new class of energy storage and coversion devices,electrochemical capacitor（EC）has a series of advantages,such as high energy and power density,good rate performance and long time cycle life.Thus it has been widely applied in many fields.As the key component of EC,electrode material has great influence on the performance of EC.It’s an efficient way to improve capacitance performance by exploiting electrode material with low cost,high specific capacitance,excellent rate characteristics and long cycle life.In this thesis,cobalt oxide and cobalt sulfide nano materials were prepared by different methods based on metal organic frameworks（MOFs）.Their morphologies,structures and electrochemical capacitive behavior were investigated by various characterization techniques and electrochemical analysis methods.The main points of this thesis are summarized as follows:（1）Taking Co₃[Co（CN）₆]₂（Co-Co PBA）as template and precursor,mesoporous Co（OH）2 nanocubes have been synthesized via reacting Co-Co PBA with NaOH solution.The morphology and structure of the prepared Co（OH）2 nanocubes were examined by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）and micropore and chemisorption analyzer.Electrochemical properties were characterized by cyclic voltammetry（CV）,galvanostatic charge/discharge and electrochemical impedance spectroscopy（EIS）methods in 2 M KOH aqueous solution on a standard three-electrode system.The results show that the sample has an average particle size of 500 nm,and its specific surface area reaches 297 m2 g-1 and mainly shows mesoporous characteristic.The mesoporous Co（OH）2 nanocubes show high specific capacitance（420 F g-1 at 1 A g-1）and excellent rate performance（80.9%capacitance retention with the current density from 1 A g-1 to 10 A g-1）.Morever,the capacitance of the mesoporous Co（OH）2 nanocubes remain 82.4%after 5000 cycles even at a high current density of 10 A g-1,which shows its good long time cycle life.（2）Taking Co-Co PBA as precursor,porous CoS2 nanospheres have been prepared via hydrothermal and low-tempreture calcination methods.The morphology and structure of the as-prepared sample were investigated by SEM,TEM,XRD,micropore and chemisorption analyzer.Electrochemical properties were investigated by CV and galvanostatic charge/discharge methods.The results show that the porous CoS2 nanospheres have a specific surface area of 32.52 m2 g-1 and possess mesoporous characteristic.And it shows high specific capacitance（383 F g-1 at 1 A g-1）and excellent rate performance（87.7%capacitance retention with the current density from 1 A g-1 to 10 A g-1）in 2 M KOH aqueous solution.Morever,it shows excellent long-term cycle life（with 86.3%capacitance retention after 3000 cycles at a current density of 5 A g-1）.（3）Taking zeolite like organic frameworks/carbon nanotubes composite（ZIF-67/CNTs）as precusors,layer double metal hydroxide/CNTs（Co-Ni LDH/CNTs）was synthesized by acid-etching and co-precipitation,then the hierarchical NiCoO2/CNTs nano composites was prepared by the low-tempreture calcination process.The morphology and structure of the as-prepared sample was characterized by SEM,TEM and XRD.Electrochemical properties were characterized by CV,galvanostatic charge/discharge and EIS methods in 2 M KOH aqueous solution.The results show that,compared with NiCoO2,the NiCoO2/CNTs nano composites have comparative specific capacitance（460 F g-1 at 1 A g-1）and good rate performance（66.3%capacitance retention with the current density increasing from 1 A g-1 to 10 A g-1,higher than NiCoO2 electrode’s 52.9%）.Furthermore,the NiCoO2/CNTs nano composites electrode has more excellent long-term cycling stability than the NiCoO2 electrode,and the capacitance remains 89.9%of its initial value after 2500 cycles at the current density of 5 A g-1.