Remarkable Capacity Retention of Nanostructured Manganese Oxide upon Cycling as an Electrode Material for Supercapacitor

Abstract

Electrochemical capacity retention of nearly X-ray amorphous nanostructured manganese oxide (nanoMnO 2 ) synthesized by mixing directly KMnO 4 with ethylene glycol under ambient conditions for supercapacitor studies is enhanced significantly. Although X-ray diffraction (XRD) pattern of nanoMnO 2 shows poor crystallinity, it is found that by Mn K-edge X-ray absorption near edge structure (XANES) measurement that the nanoMnO 2 obtained is locally arranged in a δ-MnO 2 -type layered structure composed of edge-shared network of MnO 6 octahedra. Field emission scanning electron microscopy and XANES measurements show that nanoMnO 2 contains nearly spherical shaped morphology with δ-MnO 2 structure, and 1D nanorods of α-MnO 2 type structure (powder XRD) in the annealed (600 °C) sample. Volumetric nitrogen adsorption−desorption isotherms, inductively coupled plasma analysis, and thermal analysis are carried out to obtain physicochemical properties such as surface area (230 m 2 g −1 ), porosity of nanoMnO 2 (secondary mesopores of diameter 14.5 nm), water content, composition, etc., which lead to the promising electrochemical properties as an electrode for supercapacitor. The nanoMnO 2 shows a very high stability even after 1200 cycles with capacity retention of about 250 F g −1 .