Synthesis Of MnO_x/C Nanocomposite Electrodes For Electrochemical Energy Storage

Abstract:With high power density, long-term cycle life and enhanced energy density, supercapacitors (SCs) have attracted increasing attention in recent years. The electrode materials of supercapacitors play a key role. Among many promising electrode materials, manganese oxides, characterized by high specific capacitance and their low-cost, abundance and environmentally friendly nature, have attracted significant interest as active electrode materials for SCs. A combination of MnOx and carbon materials may take advantage of both the excellent electrical conductivity and chemical stability of carbon and the high specific capacitance of MnOx. Different synthesis methods have been used to obtain MnOx/carobon composites in our study. The microstructures and morphologies, phases, BET surfaces and the pore-size distributions of the as-synthesized materials have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and BET analysis et. al. Furthermore, the SCs properties of these composites were also studied. The details are summarized as follows.A novel class of ultrathin MnO2nanoflakes with a petal-like nanostructure was obtained by a simple chemical co-precipitation process. The results show that the electrochemical properties of the as-synthesized composites have a direct relationship with the MnO2coating thickness and the BET surfaces:as the MnO2thichness increased, the composites’ BET surfaces increased, together with the specific capacitances. And when the concentration of KMnO4reached0.5M, the as-synthesized MnO2/CNTs obtained the best electrochemical properties:the specific capacitance of the composite electrode can reach450F/g at0.2A/g. And the electrode also exhibited excellent charge/discharge rate and good cycling stability, retaining over96%of its initial capacitance after1000cycles.A hierarchical nanostructures composed of carbon coated Mn3O4nanosheets on carbon nanotube back bones have been constructed by coating a polymer overlayer on the as-synthesized MnO2CNTs (MC), followed by heat treatment. When evaluated as a potential electrode material for SCs, the C/Mn3O4/CNTs (CMC) exhibited better rate capability than MC by virtue of their increasing electron conductivity.A novel solution combustion synthesis method was used to prepare3-D nanoporous hybrid structure, with carbon paper as the backbone and manganese oxide covered uniformly on the surface. Different morphologies of manganese oxide were obtained by tuning the ratio of the reactants. And the results show that the composite owned a continuous, uniform morphology when the ration was1:1. The hybrid structure shows excellent electrochemical performance, with a specific capacitance of201F/g at a current density of0.5A/g and good long-term cycle stability, with a retention of94%of the initial capacitance after1000cvcles.