Phase evolution of electrodeposited manganese oxide for supercapacitor applications

Energy is of paramount importance in our everyday lives and energy storage technologies are needed to solve the global energy problems largely. In this work, manganese oxide (Mn_xO_y) films were electrodeposited chronoamperometrically on stainless steel (ss) and fluorine doped tin oxide (FTO) substrates at different step potentials. The effect of the deposition potential and temperature treatment on the phase and supercapacitive properties of the Mn_xO_y were studied. At a step potential of less than 1.2 V no deposition was achieved while at 1.2 V, the as deposited oxide showed a bit of amorphousness with vestiges of Mn(OH)₂ as evident from the x-ray diffraction (XRD) studies. At higher potentials (1.4 and 1.6 V), the as-deposited oxide appeared as the MnO₂ phase. However, higher temperature treatment (600 °C) of all the deposits obtained at the various potentials resulted to Mn₂O₃ phase. The scanning electron microscopy (SEM) of the films showed that the as-deposited and the 400 °C annealed electrodes are porous while they become more compact and cemented at 600 °C. The obtained bandgap energies ranged from 1.26–2.65 eV for the films deposited at differing potentials and heat treatments. The electrochemical analysis shows the highest specific capacitance of 455 F g⁻¹ for the 1.2 V@400 °C electrode while the Mn₂O₃ electrodes are more stable. The electrodes exhibited good potentials for supercapacitor application.