Synthesis and Electrochemical Characterization of Silica-Manganese Oxide with a Core-shell Structure and Various Oxidation States

Abstract

Silica-manganese oxides with a core-shell structure were synthesized via precipitation of manganese oxides on the <TEX>$SiO_2$</TEX> core while varying the concentration of a precipitation agent. Elemental analysis, crystalline property investigation, and morphology observations using low- and high-resolution electron microscopes were applied to the synthesized silica-manganese oxides with the core-shell structure. As the concentration of the precipitating agent increased, the manganese oxide shells around the <TEX>$SiO_2$</TEX> core sequentially appeared as <TEX>$Mn_3O_4$</TEX> particles, <TEX>$Mn_2O_3+Mn_3O_4$</TEX> thin layers, and <TEX>${\alpha}-MnO_2$</TEX> urchin-like phases. The prepared samples were assembled as electrodes in a supercapacitor with 0.1 M <TEX>$Na_2SO_4$</TEX> electrolyte, and their electrochemical properties were examined using cyclic voltammetry and charge-discharge cycling. The maximum specific capacitance obtained was 197 F <TEX>$g^{-1}$</TEX> for the <TEX>$SiO_2-MnO_2$</TEX> electrode due to the higher electronic conductivity of the <TEX>$MnO_2$</TEX> shell compared to those of the <TEX>$Mn_2O_3$</TEX> and <TEX>$Mn_3O_4$</TEX> phases.