Nanostructured manganese dioxides: Synthesis and properties as supercapacitor electrode materials

Low-cost layered manganese oxides with the rancieite structural type were prepared by reduction of KMnO4 or NaMnO4 in acidic aqueous medium, followed or not by successive proton- and alkali-ion-exchange reactions. Samples were characterized by X-ray diffraction, energy dispersive X-ray analysis, BET surface area measurements, thermal analyses and X-ray photoelectron spectroscopy. As a result of successive exchange steps, compounds with high surface area (reaching 200 m(2) g(-1)) can be obtained, and in the case of syntheses made with KMnO4, the alpha-MnO2 phase is formed. Capacitive properties of the synthesized materials were studied using potentiodynamic cycling in K2SO4. Correlations between the electrochemical and the physicochemical properties of the samples were investigated. The interesting conclusion is that the morphology and the size of the particles influence directly the capacitance, and that among the samples presenting the best morphology, the compounds derived from K-containing rancieite-type compounds (and containing alpha-MnO2) present a better cycleability. (C) 2008 Elsevier Ltd. All rights reserved.