Preparation And Capacitance Performance Of Graphene/MnO₂Matrix Composite

Supercapacitors, also called electrochemical capacitors, are a newelectrochemical energy storage system, which fill the gap between the traditional solidstate capacitors and the batteries. Generally, supercapacitors can be classified into twocategories on the basis of their energy storage mechanism, namely, electric doublelayer capacitors and pseudocapacitors. Electrode materials are one of the main factorsthat influence the supercapacitors performance.Manganese dioxide(MnO2) is considered one of the most promisingpseudocapacitive materials for high performance supercapacitors due to its low cost,natural abundance, environmental benighity and high theoretical capacitance.However, MnO2electrodes often suffer from poor electronic and ionic conductivities,intensive surface morphology, which greatly limits their practical application. Perfectgraphene is a flat hexagonal lattice, every carbon atom is sp2hybridization andcontributes a remaining p orbital electron to form the big π-π bond, the electrons onthe π-π bond can move and give graphene great mechanical stability and electronicconductivity. Polyaniline (PANI) is a kind of conductive polymers with highconductivity, good flexibility, and a large number of benzene rings, Polyaniline(PANI) also have capacitance characteristics.Thus adding Polyaniline tographene/MnO2, namely preparation of graphen/PANI/MnO2ternary composites hasbecome a new research direction.In this paper, we prepared Graphene/MnO2binary composite by liquidcoprecipitation, and prepared the graphene/PANI/MnO2ternary composite materialsby the two-step method,and prepared3D-Graphene/MnO2by hydrothermalself-assembly method.The physical and chemical properties of composites werecharacterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM)etc, the capacitance performance of composites is studied by cyclic voltammograms(CV) and AC impedance testing (EIS).Graphene/MnO2binary composites were synthesized by liquidcoprecipitation, and the electrochemical properties of the composites with differentmass ratio of C/Mn. were studied When the initial mass ratio of Graphene/MnO2was 1:5, Graphene/MnO2composite has the maximum specific capacitance.Graphene/PANI/MnO2ternary composites were successfully prepared byin-situ polymerization and the following liquid coprecipitation method. The effect ofdifferent mass PANI on the Graphene/PANI/MnO2ternary composites is alsoconsidered. The results show that addition of suitable amount of PANI has certaineffect on composites’ electrochemical performance and surface morphology. Whenthe initial feeding of aniline is50ul, the inner and outer specific capacitance ofGraphene/PANI/MnO2composite were256.4F/g,175F/g, respectivly.π-π conjugate method and the following liquid phase coprecipitation wasadopted to prepare Graphene/PANI/MnO2composite,and to investigate the influenceof different amount of PANI on Graphene/PANI/MnO2composite. SEM and XRDresults show that the addition of suitable amount of PANI could effectively improveMnO2dispersion, reduce its size and increase the porosity; Cyclic voltammogramsand AC impedance test results were as follows, when the amount of PANI was5mg,the ternary composite had higher specific capacitance value(240F/g,0.5M Na2SO4aselectrolyte, sweep speed of5mv/s, the inner and outer specific capacitance were333.3F/g、205F/g), and the cycle stability was very good,with the specific capacitance onlyreducing to92.7%of the original value after a3000–cycle.3D-Graphene was successfully prepared by hydrothermal self-assemblymethod, and then was reacted with potassium permanganate to get the3D-Graphene/MnO2composites.The results show that the time of hydrothermal hascertain effect on the composites.