Electrochemically Deposited NiO And MnO₂ Films With Excellent Electrochemical Capacitive Behavior

In this thesis, the newest development in research of supercapacitors and the electrode materials of supercapacitor devices have been reviewed. Nickel oxide and manganese dioxide have advantages of low cost, abundant resources and good electrochemical performances, the nickel oxide films and manganese dioxide films are prepared by a facile electrodepositon method using 3D network-like nickel foam as substrate, and are directly as electrode materials for supercapacitors. The relationships between electrochemical deposition conditions and electrochemical performances have been systemically studied through a variety of electrochemical measurements and material characterization of test method. The main studies are as follows:1.Three-dimensional network-like NiO films are prepared on nickel foam by the negative electrodeposition. Structures, morphologies, pore size distributions and pore volumes of the films have been systemically explored, and the effect of deposition conditions on the morphologies and the electrochemical capacitance characteristics has also been studied. Structure characterizations indicate that a network-like structure with low crystallinity for the NiO films is obtained. The as-prepared NiO films possess a narrow mesoporous distribution at around 8¹1 nm and have a surface area of 142 m²/g. The unique microstructure is responsible for the good electrochemical capacitance performance, which creates the fast electrochemical accessibility of the electrolyte and OH– ions to the bulk of the NiO phase, providing an important morphological basis for the high specific capacitance. The deposition potential and the deposition mass of NiO films are examined and found to have a significant effect on the specific capacitance and surface morphology of the deposited films. A maximum specific capacitance of 1361 F/g is obtained for the 0.83 mg network-like NiO films at the deposited potential of -0.7 V.2.MnO₂ films grown on nickel foam with a desirable 3D structure are investigated as electrochemical pseudocapacitor materials for potential energy storage applications. The effect of structures and technical parameters on electrochemical characteristics of MnO₂ is studied using orthogonal test and single factor experiment. The optimum technical parameters in anode deposition method are that the deposition potential was 0.5 V, the electrolyte concentration of Mn(CH3COO)2 was 0.25 mol/L, the specification of nickel foam was 420 g/m². The specific capacitance of MnO₂ electrodeprepared in this condition is up to 664 F/g at a discharge current density of 5.5 A/g, which is higher than that of most reported corresponding materials.3.Nanostructuredε-manganese dioxide films are deposited directly on three-dimensional nickel foam from 0.25 M Mn(CH3COO)2 by means of the potentiostatic method (PSM) and potentiodynamic method (PDM). The prepared MnO₂ films are characterized by X-ray diffraction and scanning electron microscopy. The electrochemical properties of MnO₂ films are investigated by cyclic voltammetry, charge/discharge tests, and alternating current impedance spectroscopy. The results show that the PSM-MnO₂ films exhibit higher specific capacitance and better high-rate discharge ability, which are more promising for applications in supercapacitor than PDM-MnO₂ films.