Preparation And Electrochemical Performance Of MnO₂-Polyaniline Nanocomposites

As a kind of chemical energy storage device, supercapacitors featuring high power density, high specific energy and excellent long-term cyclability have received great interest for many potential applications. In supercapacitors, active materials are the most crucial factor governing the electrochemical performance. Generally, the electrode materials of supercapacitors are of three types, carbon materials, conducting polymers and transition metal oxides. Each of them has its own advantages and disadvantages. Therefore, binary or ternary composites have been synthesized and investigated for use in supercapacitors as a way of obtaining materials with a combined and balanced merit of the three kind materials.In the present work, MnO2nanorod electrode materials for supercapacitor were prepared by a liquid refluxing method, inwhich K2Cr2O7was added into the reactants for controllable synthsis of MnO2nanorods. The influence of K2Cr2O7on structure and electrochemical properties of MnO2was studied. XRD and SEM results show that the morphology of the products gradually changed from γ-MnO2nanospheres to α-MnO2nanorods with the increase of Cr amount. The electrochemical results demonstrate that the electrical conductivity of MnO2was improved by Cr doping. This is interpreted that the nanorod structure of the α-MnO2greatly enhances specific surface area and particle dispersion, which reduce the internal resistance by close contact between the electrode materials and electrolyte. When the content of Cr is10%, the sample shows the best electrochemical performance. A specific capacitance of147.3F/g is obtained for the MnO2electrode at a current density of0.1A/g, suggesting that MnO2nanorod is a promising material for supercapacitors.In order to improve the specific capacitance of MnO2nanorods, the polyaniline-MnO2nanorods(PANI-MNW) composites were synthesized by in situ chemical oxidative polymerization of aniline monomer in a suspension of MnO2nanorods. The factors such as oxidants of aniline, amount of oxidant, the ratios of aniline/MnO2and reaction time were optimized to synthesize the PANI-MNW composites with excellent performance. Structural characterization shows that the porosity of PANI-MnO2nanocomposites is much higher than that of α-MnO2nanorods. Electrochemical characterization shows that at the current density of0.1A/g, the PANI-MNW-10owns the highest specific capacitance, ca.384F/g. However, PANI-MNW-5shows the highest specific capacitance when the current density is higher than 1A/g. And its specific capacitance still remains230F/g at a current density of2A/g, suggesting that PANI-MNW-5has good power characteristics. The composite also has a good cyclic performance and coulomb efficiency. The improved properties are mainly attributed to the composite structure wherein high porosity was produced between MnO2nanorods and PANI during the process of fabricating PANI-MNW nanocompositcs.