Preparation And Electrochemical Performance Of Nickel/Carbon Composites And Modified MnO₂

As supercapacitor electrode material, RuO2has high capacity and good electrochemical performance. For its high cost, the application of supercapacitor is extremely restricted. In view of rich resource and extremely similar capacitance to noble metals such as RuO2, MnO2is the cheapest metal oxides to replace RuO2. In this thesis, nickel/carbon composites and Fe-modified MnO2were characterized by XRD and SEM, their electrochemical performance was also investigated. The main results are as follows:Nickel/carbon composites with large capacity and good electrochemical reversibility were prepared by heat treatment of the composite precursors at the temperature of600°C. Graphite peak occurred at25.5°, and became more and more intense with the increase of temperature. The Ni particles with good dispersion have the sizes of0.5~2μm. With increasing the amount of K2CO3, the specific capacitance of the composites increased first and then decreased. In the case of using0.5g of K2CO3, the prepared sample showed the largest inductive current-voltage curve and scanning area, suggesting the highest specific capacitance. In the process of constant current charging and discharging, the specific capacitance showed the trend of decrease with the increase of current density. The capacitance of electrode can reach to90F/g at the current density of0.5A/g. The use of carboxymethyl cellulose could make the composite precursor well dispersed, which is helpful to improve the electrochemical capacity and stability.Nanostructured manganese dioxide (MnO2) was synthesized using a simple co-precipitation method wherein potassium permanganate and tetrahydrate manganese chloride were used as precursors. Certain amount of FeCL3-6H2O was introduced during the preparation process for the modification of MnO2. The structure and morphology of MNO2were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The capacitive behaviors of MnO2were studied by cyclic voltammetry (CV) and galvanostatic charge-diacharge in1mol/L KOH electrolyte. The results showed that the addition of FeCl3-6H2O significantly influenced the structure and morphology of MnO2. With increasing the molar ratio of Fe to Mn, MnO2changed from y-phase into layered structure. And the morphology of MnO2changed from flake into sphere whose diameter is about100nm. Significant enhancement of electrochemical performance was observed for the Fe-modified MnO2. The MnO2which was obtained with5%(the molar ratio of Fe to Mn) FeCl3-6H2O showed the specific capacitance of279F/g at a current density of1A/g.Ammonium ferrous sulphate was also used to modify MnO2through the liquid precipitation reaction. With increasing the amount of ammonium ferrous sulphate, XRD and SEM results showed that the crystal changed from y-MnO2into a-MnO2. And the morphology changed from the mixed structure of sheets and nanorods into nanorods, the average particle size is about75nm, length is0.8~2μm. Electrochemical tests showed that the specific capacitance increased first and then decreased along with the reaction time. When the amount is10%and the reaction time is1h, the specific capacitance still could reach to247F/g at a current density of1A/g.