High electrochemical performance of spinel Mn3O4 over Co3O4 nanocrystals

Abstract

Manganese and Cobalt oxide (Mn3O4 and Co3O4) nanocrystals are prepared via a simple and low cost combustion synthesis. The structural studies using XRD, Raman Spectroscopy and Fourier Transform Infrared Spectroscopy reveal that, the formation of Mn3O4 in tetragonal structure with I41/amd (141) space group and Co3O4 in cubic structure with Fd3m (227) space group. The average crystallite size of nanocrystals are estimated using Debye Scherrer formula and found to be 14 and 22 nm for Mn3O4 and Co3O4, respectively. The SEM images of as-prepared Mn3O4 and Co3O4 nanocrystals show the irregular shape of grains and uniform spherical grains with an average grain size of 100 and 120 nm. The binding energy peaks of Manganese, Cobalt and Oxygen from EDS and XPS spectra show the chemical purity of the samples. The optical band gap of Mn3O4 and Co3O4 nanocrystals are 2.93 and 2.50 eV respectively. The magnetic properties of Mn3O4 and Co3O4 nanocrystals prove a strong ferromagnetic nature at 5 K temperature. The electrochemical investigations of the samples demonstrate that the Mn3O4 nanocrystals exhibited a high specific capacitance of 417 F g−1 at a current density of 0.5 A g−1 with almost 100% coloumbic efficiency after 600 cycles and good cyclic stability up to 10,000 cycles. The poor electrochemical behavior of spinel Co3O4 proves that Mn3O4 nanocrystals are good electrodes for electrochemical capacitors due to greater mass transport of electrolyte ions into the Mn3O4 electrode.