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.