Hydrothermal Synthesis and Pseudocapacitance Properties of MnO2 Nanostructures

Abstract

The effect of varying the hydrothermal time to synthesize manganese oxide (MnO₂) nanostructures was investigated along with their influence on structural, morphological, compositional, and electrochemical properties in supercapacitor electrode materials. XRD and TEM studies showed that the MnO₂ prepared in shorter hydrothermal dwell time was a mixture of amorphous and nanocrystalline particles, and there was an evolution of crystallinity of the nanostructures as the dwell time increased from 1 to 18 h. Interestingly, SEM, TEM, and HRTEM revealed a variety of structures ranging from nanostructured surface with a distinct platelike morphology to nanorods depending upon the hydrothermal reaction time employed during the preparation of the manganese oxide: increasing the amount of individual nanorods in the materials prepared with longer hydrothermal reaction time. The surface area of the synthesized nanomaterials varied from 100 to 150 m²/g. Electrochemical properties were evaluated using cyclic voltammetry (CV) and galvanostatic charge−discharge studies, and the capacitance values were in the range 72−168 F/g depending upon synthesis conditions. The formation mechanism of the nanorods and their impact on the specific capacitance were discussed in detail.