Study On The Effect Of Capacitance Of Nano MnO₂ By Ion-doping And Nano Conductive Polymer Hybridization

Supercapacitor has emerged as one of the most attractive electrochemical storage systems with unique characteristics featuring high power delivery and long-term cycling stability.Manganese oxides?MnO₂?have particularly received increasing attention owing to their high specific capacitance,low cost,natural abundance,and environmental benignity.MnO₂ with ?-MnO₂,?-MnO₂,?-MnO₂ and ?-MnO₂ were prepared by hydrothermal method.The effects of reaction temperature and reaction time on the crystal structure and surface morphology of MnO₂ were investigated,and the electrochemical performances of the resultants were measured.The experimental results show that: the electrochemical performances of nano ?-MnO₂ were the best.Based on that the ?-MnO₂ was modified by ion-doping and nano conductive polymer hybridization.The specific research contents and the main results are as follows:1.In this chapter,KMnO4 was used as the raw material,the reaction of ?-MnO₂ and ?-MnO₂ was carried out at 100 ° C,140 ° C and 180 ° C for 1 h,3 h,6 h and 12 h under acidic conditions,respectively.Through the characterization of the obtained samples and the electrochemical performance test,the experimental results show that: with the increase of reaction temperature and the extension of reaction time,firstly,the obtained MnO₂ formed the surface smooth spherical ?-MnO₂,gradually growed into flower spherical ?-MnO₂ composed of nanoneedles,and finally nanosheets crimped into nano-tubular ?-MnO₂.In this process,MnO₂ is converted from a 2D layer to a [2×2] tunnel structure.The color of the experimental samples was also changed from black to dark brown.It indicates that the reaction temperature and reaction time are important factors affecting the crystal structure and morphology of MnO₂.And the specific capacitance obtained at a reaction temperature of 100 °C and a reaction time of 1 h is as high as 196.8 F g-1.With the reaction temperature and reaction time increasing,the specific capacitance of the resulting sample gradually decreases The highest specific capacitances of ?-MnO₂ and ?-MnO₂ are 117.2 F g-1 and 37.6 F g-1,respectively..In summary,the electrochemical performance of ?-MnO₂ is better than that of other ?-MnO₂.2.On the basis of the study of the third chapter,?-MnO₂ was chosen as the object of metal ions doping.The KMnO4 and Ni foam?NF?as raw materials,Co²⁺,Bi³⁺ and Fe³⁺ doped-MnO₂/NF complexwas synthesized by simple hydrothermal method.The specific capacitances of MnO₂/NF doped with 2at.% Co²⁺,2at.% Bi³⁺,and 4at.% Fe³⁺ at 2 mV s-1 are 506.8 F g-1,365.6 F g-1,and 376.1 F g-1,respectively.Thoses are much higher than that of undoped MnO₂/NF with 198.5 F g-1.Its impedance performance has also been greatly improved.3.Nano PANI with sea cucumber-like nano-rod-shaped was prepared by ice bath method using aniline monomer as the reducing agent and ammonium persulfate as oxidant.The KMnO4 as the oxidant,the ?-MnO₂ nanosheets growed on the surface of the nano PANI substrate by in situ growth method,then the ?-MnO₂@PANI nanocomposites was obtained.Through the characterization of the electrode material and the test of electrochemical performances,the experimental results show that: PANI exhibited good reduction performance to KMnO4,so that nano-scale ?-MnO₂ was supported on the surface of PANI nanorods.?-MnO₂@PANI nanocomposites have a specific capacitance of 524.2 F g-1 at a current density of 0.5 A g-1,which is much larger than that of pure PANI and ?-MnO₂.In turn,as the PANI was grown on the surface of ?-MnO₂,the specific capacitance of PANI@?-MnO₂ was only 261.8 F g-1,and the impedance performance was not improved.