Abstract
In this study, the combustion method was utilized to synthesize ZnMn2O4 (ZMO) metal oxide doped with Cu, Ni, and Co at varying concentrations of (1, 3, and 5 wt%) to investigate the stability of the material, cycle life, and electrochemical performance in battery-type supercapacitors. The crystal structure of the synthesized metal oxide material was analyzed using X-ray diffraction (XRD). The crystallite sizes and strains induced in the crystal lattice of Cu, Ni, and Co-doped were calculated from ZMO with a size of 39.78 nm – to a size of the dopant of ZMO: Ni as lower size 34.71 nm. The surface morphology of the metal oxide material was examined using Scanning Electron Microscopy (SEM), showing a diamond-like irregular shape with nanoparticles. The elemental composition of the metal oxide material was determined using Energy Dispersive X-ray Spectroscopy (EDS). FT-IR was used to investigate the functional group of the metal oxide material. Electrochemical properties of the material were investigated using Cyclic Voltammetry(CV), Galvanostatic Charge–Discharge(GCD), and Electrochemical Impedance Spectroscopy(EIS). The XRD results showed that doping ZMO with Cu, Ni, and Co did not change the structure; a single phase was identified, except in the concentration of Co with 5 wt% where new peaks were observed due to ammonium nitrate. The surface morphology of the metal oxide revealed a diamond-like structure with a catalyst present on top of those diamond shapes with nanoparticles. FT-IR showed the functional elements group of the material with common metal oxide values ranging from 478.35 – 609.51 cm-1. The electrochemical analysis was prepared by using the three-electrode methods, working (active material), Counter (Platinum), and reference (Ag/Agcl) electrode in 2 M KOH electrolytes. The electrodes were prepared by the ratio of 80 wt%:10 wt%:10 wt% under a potential window of 0 - 0.6 V. CV revealed that all the curves display a similar behavior of pseudo capacitance. ZMO doped with Cu 3 wt% showed an excellent performance with CV having the maximum specific capacitance of 88.24 Fg-1 at 5 mVs-1 scan rate. The material further shows GCD's highest specific capacitance value of 299.50 Fg-1 at the lowest current density of 2 Ag-1. Additionally, cycle stability revealed capacity retention of 105 % for 1000 cycles at 2 Ag-1, which suggests that incorporating ZMO with Cu 3 wt% is great for supercapacitor applications. Incorporating ZMO with Ni revealed that CV has greater specific capacitance at 3 wt% at the value of 34.49 Fg-1 at a lower scan rate of 5 mVs-1. GCD curve displays the highest value of charge and discharge specific capacitance at 275.45 Fg-1 for 3
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wt% of Ni. Furthermore, cycle stability showed capacity retention of 90% after 1000 cycle numbers at 3 Ag-1 with the highest charge value and discharge-specific capacitance at 275.45 Fg-1 for 3wt% of Ni, with a coulombic efficiency of 97%. EIS showed excellent performance of ZMO with 3wt% displays a steeper vertical behaviour. ZMO doped with Co revealed that the CV curve has a significant specific capacitance of ZMO: CO 1 wt% with a value of 45.85 Fg-1 at 5 mVs-1. ZMO: Co 3 wt% displays a GCD curve with the maximum value of charge and discharge specific capacitance at 1376.06 Fg-1 at a current density of 3 Ag-1. Furthermore, displaying cycle stability showed capacity retention of 98% for 1000 cycle numbers at current density 5 Ag-1 with a coulombic efficiency of 96%. The results of this study show that ZMO doped with Cu, Ni, and Co is a potential electrode for the supercapacitor battery application.