Preparation And Capacitance Performance Of Mn/C Composite

Manganese dioxide（MnO₂） has become one of the promising alterativecandidates for the electrode materials of supercapacitors， because of its idealpseudocapacitance behavior， natural abundance， low cost and environmentalfriendness. However， the practical application of MnO₂as supercapacitor has beenlimited by. the low electronic conductivity and poor cycling peformance Whereas，thecarbon-based material has benefits of high effective specific surface area and goodelectronic conductivity. A combination of MnO₂and canbon may take advantage ofboth the excellent electrical conductivity and chemical stability of carbon and the highspecific capacitance of MnO₂.Based on the inxestigation of literatures，the objective of this study is to explorethe influencing factors of the electrochemical performances of Mn/C-based materialin supercapacitor. The physical and chemical properties of composites werecharacterized by X-ray diffraction （XRD），X-ray photoelectron spectroscopy （XPS），scanning electron microscopy （SEM） etc．MnO₂/MCNTs composites were synthesized by ultrasonic method and liquidprecipitation，and the electrochemical properties of the composite were researchedwith the different molar of C/Mn．When the initial molar ratio of C/Mn was1.2:1，MnO₂/MCNTs composites has the optimal capacitor performance and exhibited moreexcellent electrochemical properties than that of pure MnO₂.Liquid precipitation was adopted to investigate the influence of diameter andlength of MWNTs on their electrochemical performance. The results showed that thediameter and length of the MWNTs affected the electrochemical properties.Compared with the pure MnO₂electrode, MnO₂/MCNTs composite has relativelyhigh lining and outer specific capacitance and the inner and outer specific capacitanceof MnO₂/MCNTs composite electrode was210.00F·g^-1and162.86F·g^-1. The cyclelife test indicates that the composite has a good cycle stability.Mn₃O₄/RGO composites were successfully prepared by a liquid phasehydrothermal reaction with manganese sulfate solution as the precursor. The resultsshow that the Mn₃O₄particles grow on the surface of graphene. After90cycles ofcyclic voltammetry test, the specific capacitance of the electrod was132.4F·g^-1.However, Mn₃O₄/RGO composite is not suitable for high charge and dischargebecause of poor rate performance. MnO₂/Graphene composites were prepared by the the liquid phase hydrothermalreaction with the potassium permanganate solution as the precursor. The results showthat when the hydrothermal reaction time was6h，the starting molar ratio of C/Mnwas1:1and reaction temperature was150℃, caterpillar-like nanoflaky MnO₂areuniformly coated on the surface of graphene. Electrochemical tests show that thespecific capacitance of MnO₂/graphene was194.8F·g^-1at the scan rate of5mV·s-1.The cycle life test indicates that the composite has an ideal cycle stability.Additionally，in comparison with the capacitance of MnO₂/GN，MnO₂/HRG andMnO₂/RGO composite at the same reaction conditions, MnO₂/RGO composite has thegood capacitor performance.