Effect of cobalt doping on the electrochemical performance of trimanganese tetraoxide.

Nanostructured transition metal oxides (TMO) are potential materials widely explored by researchers for energy storage applications. In this study, spinel trimanganese tetraoxide (Mn3O4) and cobalt doped trimanganese tetraoxide (Co-Mn3O4) was synthesized by using a simple solvent assisted hydrothermal route. Pure Mn3O4 and Co-Mn3O4 nanomaterials were characterized by an x-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), UV-diffuse reflectance spectroscopy (UV-DRS), field emission scanning electron microscope (FESEM), and high resolution transmission electron microscope (HRTEM). XRD analysis revealed the body centered tetragonal spinel structure of Mn3O4 and Co-Mn3O4 with a space group as l41/amd (141) and an approximate crystallite size of 45-33 nm. The presence of an Mn-O bond vibration was confirmed using FTIR and the band gap properties were analyzed through UV-DRS. Surface morphology and average grain size were examined using FESEM and HRTEM micrographs as nanosquares and nanospheres with diameter 126 nm and 118 nm, respectively. Electrochemical properties of Mn3O4 and Co-Mn3O4 were evaluated using cyclic voltammograms, charge-discharge curves, and electrochemical impedance spectra (EIS). Pure Mn3O4 showed a specific capacitance of 971 F g-1 at 0.1 A g-1 current density while Co-Mn3O4 achieved relatively higher specific capacitance of 1852 F g-1 at the same current density. It is observed that the increased specific capacitance of Co-Mn3O4 mainly arises from the doping effect. Electrochemical analysis shows that the Co doped Mn3O4 nanomaterials can be a promising electrode material for supercapacitor.