Facile route to achieve hierarchical hollow MnO2 nanostructures

Abstract

Hierarchical hollow nanostructured MnO2 has been fabricated using polyaniline spheres as reactive templates. The reaction between KMnO4 and polyaniline leads to the reduction of KMnO4 into Mn2+ ions that are further oxidized by excessive KMnO4 into MnO2 layers. Meanwhile, the polyaniline cores are over-oxidized and diffuse into the solution to form the cavity. The ratio of the KMnO4 and polyaniline plays an important role in achieving the hollow structure via establishing a reasonable diffusion/reaction rate equilibrium. Owing to the unique nanostructure, the MnO2 electrode exhibits a specific capacitance of 308Fg−1 at a current density of 0.2Ag−1 and maintains 91% capacitance value after 3000 cycles at a current density of 2Ag−1. An asymmetric supercapacitor assembled by the hollow MnO2 and activated carbon presents energy densities of 20.93∼7.23W h kg−1 under the power densities of 180∼9000Wkg−1 and 24% capacitance fading is detected after 2000 cycles at a current density of 4Ag−1.