A Study On Preparation And Properties Of Manganese Dioxide Nanomaterial For Supercapacitor

In recent years, supercapacitors have attracted intense attention for hybrid electric vehicles and portable electronic device, due to their high power density, long cycle life, and extremely fast charging/discharging times. MnO2 have received great attention, and considered the most promising transition metal oxides for the next generation of supercapacitors, due to its high theoretical specific capacitance of 1370 F g-1, low cost, environmental compatibility and natural abundance. In this paper, a series of manganese oxide nanomaterials were synthesized using a facile hydrothermal method for supercapacitor electrode.MnO2 are characterized by XRD, SEM, BET, cyclic voltammetry, the galvanostatical charge/discharge and electrochemical impedance spectroscopy for its composition, structure/morphology, specific surface area and capacitive properties. The main research contents are summarized as follows:1. Branched α-MnO2 multipod nanostructures are synthesized using a facile hydrothermal method without surfactants or templates. For KMnO4-MnSO4 reaction system, The formation of α-MnO2 with different morphologies, including branched multipods and nanorods with controllable length, is achieved by controlling the starting concentration of reactants. The effect of reactant concentration and reaction time on the crystal structure and morphology of the product have been studied. The electrochemical properties of as-synthesized branched α-MnO2 Multipods are also studied by cyclic voltammetry (CV), galvanostatic charge/discharge. The branched α-MnO2 multipods electrode shows a high specific capacitance of 182 F g-1 at the current density of 2 A g-1, with a good rate capability and an excellent cycling stability.2. α-MnO2 supported on graphite substrate is synthesized by mixing KMnO4 with MnSO4 under hydrothermal condition. The results show that α-MnO2 deposited homogeneously on the graphite substrate with nanorod structures. The well interconnected α-MnO2 nanorods could facililate the diffusion of the electrolyte into MnO2, provide fast electron transport channels and shorten the transport path of ion and electron. The electrochemical performances indicated that the film exhibits good rate capability and excellent cycling stability with no more than 2% capacitance loss after 2000 cycles at the current density of 2 A g-1, and the specific capacitance (SC) value is 229 F g-1 at the current density of 1 A g-1.3. Nanowired α-MnO2 material supported on carbon fiber paper (α-MnO2/CFP) is synthesized using a facile hydrothermal method for supercapacitor electrode. The highly conductive CFP network as current collectors could serve as ideal electron pathways for the fast charge-discharge reactions. A synergy effect of the conducting matrix of CFP and the α-MnO2 nanowire network could facilitate the mechanical strain associated with ion diffusion into the electrode relaxation during cycling. The porous α-MnO2 material electrode shows a high specific capacitance of 251 F g-1 at the current density of 1 A g-1, and also exhibits a good rate capability and an excellent cycling stability. It is testified that even after 3000 cycles, the capacitance retention of the porous α-MnO2 CFP material electrode can still maintain over 98.9% of the capacitance at the high current density of 4 A g-1, demonstrating its excellent cycling stability.4. The δ-MnO2 and Cu-doped δ-MnO2 grown on Ni foams are synthesized by a simple hydrothermal method for supercapacitor electrode application. The effects of various doping concentrations on structure, surface morphology and electrochemical properties of the δ-MnO2 films were studied elaborately. Copper addition can vary the self-assembly of δ-MnO2 nanosheets, inducing the formation of flower-like structure. The morphology and electrochemical performance of the formed δ-MnO2 electrodes can be controlled by simply tuning the copper doping concentration. The 2 at% Cu-doped δ-MnO2 film obtains the maximum specific capacitance as high as 296 F g-at 1 A g-1, which is 80% higher than that of the pure δ-MnO2 film. Furthermore, it also shows a better cyclic stability than undoped δ-MnO2 film.