Effect of Fe3+ on the synthesis and electrochemical performance of nanostructured MnO2

Different MnO2 nanostructures were synthesized in stoichiometric KMnO4/MnSO4 aqueous solutions in the absence/presence of Fe3+ at temperature ranging from 30 °C to 180 °C. The phase structures, morphologies and electrochemical properties of the as-prepared MnO2 products were investigated using X-ray powder diffraction, scanning electron microscope, N2 physical adsorption and cyclic voltammetry techniques. The results showed that the presence of Fe3+ addition had a significant effect on the phase structural evolution, morphological features and electrochemical properties of the MnO2 products. Fe3+ was found to greatly prevent the epitaxial growth and crystallization of MnO2 nucleus, which in turn influenced textual characteristics. The electrochemical performance of the nanostructured MnO2 products had a complex relationship with the phase structures, specific surface area as well as pore characteristics. MnO2 prepared in the presence of Fe3+ (KMF-MnO2) showed relatively higher specific capacitance compared to that of MnO2 prepared in the absence of Fe3+ (KM-MnO2). Maximum capacitance of 214 F g−1 was obtained for KMF-MnO2 prepared at 30 °C at a scan rate of 2 mV s−1 in 0.1 M Na2SO4 electrolyte.