Textural and capacitive characteristics of MnO2 nanocrystals derived from a novel solid-reaction route

Nanostructured manganese dioxide (MnO2) materials were synthesized via a novel room-temperature solid-reaction route starting with Mn(OAc)(2)center dot 4H(2)O and (NH4)(2)C2O4 center dot H2O raw materials. In brief, the various MnO2 materials were obtained by air-calcination (oxidation decomposition) of the MnC2O4 precursor at different temperatures followed by acid-treatment in 2 M H2SO4 solution. The influence of calcination temperature on the structural characteristics and capacitive properties in 1 M LiOH electrolyte of the MnO2 materials were investigated by X-ray diffraction (XRD), infrared spectrum (IR), transmission electron microscope (TEM) and Brunauer-Emmett-Teller (BET) surface area analysis, cyclic voltammetry, ac impedance and galvanostatic charge/discharge electrochemical methods. Experimental results showed that calcination temperature has a significant influence on the textural and capacitive characteristics of the products. The MnO2 material obtained at the calcination temperature of 300 degrees C followed by acid-treatment belongs to nano-scale column-like (or needle-like) gamma,alpha-type MnO2 mischcrystals. While, the MnO2 materials obtained at the calcination temperatures of 400. 500, and 600 degrees C followed by acid-treatment, respectively, belong to gamma-type MnO2 with the morphology of aggregates of crystallites. The gamma,alpha-MnO2 derived from calcination temperature of 300 degrees C exhibited a initial specific capacitance lower than that of the gamma-MnO2 derived from the elevated temperatures, but presented a better high-rate charge/discharge cyclability. (c) 2008 Elsevier Ltd. All rights reserved.