The Study On Metal Oxide Materials For Supercapcitor Electrode With High Specific Capacitance

In this thesis,we have reviewed the newest development in research of electrode material of supercapacitor devices,prepared relevant electrode materials and explored their applications in the kind of devices in detail.The microstructures and morphologies of these materials were investigated by TGA,XRD,SEM,TEM and BET measurements.The electrochemical performance has been evaluated by galvanostatic charge-discharge,cyclic voltammetry(CV)and electrochemical impedance spectra (EIS).The charge-storage capability of the electrodes materials has been discussed mostly.The main content is the following:Cobalt hydroxide was successfully synthesized by a facile chemical precipitation reaction between CoCl₂·6H₂O and NH₃·H₂O.The CO₃O₄ nano-flakes materials with less crystallization were obtained by calcining Co(OH)₂ precursor at different temperatures.The effect of material morphologies,discharging mechanism,discharging current and annealing temperatures on the electrochemical capacitance characteristics has also been systemically explored.Structure characterizations indicate that a flower-like structure with low crystallinity for the cobalt hydroxide and cobalt oxide samples was obtained.The as-prepared Co(OH)₂ possesses a narrow mesoporous distribution at around 4-40 nm and has a surface area of 77.22 m²/g. Preliminary electrochemical studies were carried out using cyclic voltammetry, chronopotentiometry technology and ac impedance spectroscopy,respectively.A maximum specific capacitance of 368 F/ g could be achieved in 2 M aqueous KOH with the potential range from -0.2 to 0.4 V(vs.SCE)in a half-cell setup configuration for the Co(OH)₂ electrode,suggesting its potential application in electrochemical capacitors.As the annealing temperature increase,the specific capacitance of the Co₃O₄ samples increase at lower temperature with a peak at 250℃,on further heating the specific capacitance decrease,and the maximum specific capacitance of 615 F/g could be achieved for the Co₃O₄ material at a discharging current of 5mA.Nickel hydroxide was successfully synthesized by a facile chemical precipitation reaction between NiCl₂·6H₂O and NH₃·H₂O.The NiO nano-flakes materials with less crystallization were obtained by calcining Ni(OH)₂ precursor at different temperatures. The effect of discharging current and annealing temperatures on the electrochemical capacitance characteristics has also been systemically explored.Structure characterizations indicate that a flower-like structure with low crystallinity for the cobalt hydroxide and cobalt oxide samples was obtained.A maximum specific capacitance of 2055 F/g could be achieved in 2 M aqueous KOH with the potential range from 0 to 0.4 V(vs.SCE)in a half-cell setup configuration for the Ni(OH)₂ electrode,suggesting its potential application in electrochemical capacitors.As the annealing temperature increase,the specific capacitance of the material decrease,the specific capacitance of the NiO material obtained at 250℃is 942 F/g.As discharge current increases,the large voltage drop is produced,and finally the capacitance decreases.Finally,the Co(OH)₂/USY and Ni(OH)₂/USY composite were synthesized by a liquid-precipitated method,which used the super-stable Y zeolite as the template,and we hven applied these materials in the supercapacitor fields.The microstructures and morphologies and electrochemical characteristic of these materials were systemically investigated.The results have shown that the compound has a loosely packed microstructure in the nanometer scale.The special microstructure can accommodate the electroactive species not only on the surface but also in the solid bulk,which is very helpful for making full use of the electroactive sites to take place the faradic reaction,and contributed to the increase of the specific capacitance of the material. The composite of Co(OH)₂/USY(60 wt%loading Co(OH)₂)shows the specific capacitance of 514.6F/g,or 857.6F/g after correcting for the weight percentage of the Co(OH)₂ phase.The composite of Ni(OH)₂/USY(50 wt%loading Ni(OH)₂)shows the specific capacitance of 1580.4F/g,or 3160.7F/g after correcting for the weight percentage of the Co(OH)₂ phase.