Preparation And Capacitance Characterization Of Manganese Dioxide Nanowire Monolithic Material

With the development of new energy resources and a fast-growing market for portable electronic devices and hybrid electric vehicles,there has been quick development in the field of new energy storage system.Supercapacitor attracts widespread attention,due to its high power density,long cycle life and environment friendly.As the core component,electrode material plays a decisive role on the supercapacitor energy type and performance.Metal oxide electrode occupies an important position in the electrode materials,due to its high theoretical specific capacitance and stable energy storage performance.In this thesis,we have chosen manganese dioxide as the research object.MnO₂ possesses many advantages,such as abundant resources,low cost and various stable valences.However,low specific surface area and poor electrical conductivity limit its application in supercapacitor.To improve the limits,the main content is as follows:1.Self-supported sponge MnO₂ nanotube monoliths?SMM?are synthesized via a hydrothermal method using commercial polyurethane foam as a sacrificial template.The SMM with its three-dimensional interconnected foam structure,macroporous channels,and mesoporous tube structure endow this novel material with a diversity of porous architectures and great promise for various applications involving sorbents,catalysts,ion exchange,and energy storage.As a proof of application,we have demonstrated that an SMM-based supercapacitor exhibits excellent capacitance behavior and rate capability.After 1000 cycles,there is almost no attenuation in the discharge specific capacitance.2.In order to improve electrical conductivity,on the basis of SMM synthesis in thepreviousstep,self-supportedspongeMnO₂nanowiremonoliths?SMM?/polyaniline?PANI?are fabricated by a simple oxidative template route,and SMM selected as the reactive template is prepared through a hydrothermal method using polyurethane foam as a sacrificial template.It is observed that uniform PANI shell is coated on the surface of MnO₂ nanowires,and the SMM/PANI still keeps the three-dimensional interconnected foam structure with hierarchical porous nanostructures.Cyclevoltammetry,galvanostaticcharge-dischargeand electrochemical impedance spectroscopy are used to characterizing the capacitive performance of SMM/PANI.It shows a high specific capacitance(343.7 F g^-1 at discharge current of 0.5 A g^-1),low charge transfer resistance(R_ct)(R_ct value of SMM/PANI?3.112??is lower than that of SMM?6.449??)and good electrochemical stability.3.Through the metal doping,further improve the charge transport properties of manganese dioxide nanowires.Nickel?cobalt?doped one-dimensional?1D?MnO₂nanowires array with different doping ratio are synthesized by simple hydrothermal method.The effects of Ni and Co with different doping ratio on morphology and structure of MnO₂ nanowires are studied systematically:With the changes of doping ratio?Ni and Co?,the grain diameter and BET surface area of MnO₂ are studied by peak width at half height of XRD diffraction peaks and Brunauer–Emmett–Teller?BET?method,respectively.Meanwhile,the electrochemical performance of Ni?Co?-doped MnO₂-based electrode is studied by three-electrode system.Optimal doping ratios of Ni and Co are both 1:0.01,and the specific capacitances increased by59.4%and 50%at the current intensity of 0.5A g^-1,respectively.