Synthesis of NiMn2O4 and its ordered structure for supercapacitor electrode

Abstract

In recent years, the search for efficient and sustainable energy storage systems has intensified, with supercapacitors emerging as a promising solution due to their high power and energy density, rapid charge/discharge capabilities, and long cycle life. Commercial supercapacitor utilizes high surface area carbon as an electrode to store charges. But, these types of devices lack the high energy density. electrode. Ideal supercapacitor electrode materials should have a higher surface area, good electrical conductivity, optimum porosity, and excellent chemical and thermal stability. On the other hand, different transition metal oxides and few conducting polymer-based (PVA, PANI conducting polymer) polymers electrodes can store charges via fast and reversible faradic reaction with suitable electrolytes and demonstrate very high energy density. Different transition metal oxides like RuO2, MnO2, NiO, CuO, etc. fall under the category which store charges via faradaic mechanism. However, these metal oxides demonstrate very poor conductivity in regards to electronic conduction, which results in an increase of overall internal resistance of the electrode and thus hampering the overall power delivery. In order to address the issues of conductivity, researchers have tried to form composite with two metal oxides. Binary metal oxides typically demonstrate better electrochemical performance compared to the single metal oxides due to synergistic effects between two metal components. Bimetal oxides can better withstand repeated charge-discharge cycles without significant degradation, ensuring longevity of the device. Furthermore, the morphology of electrode materials has huge influence on the above parameters thus plays a significant role in electrochemical performance. So far, NiMn2O4 nanoparticles prepared by the sol–gel method and drop cast onto Ni-foam showed a specific capacitance of 854.7 F/g at 5 mV/s in 2 M aqueous KOH electrolyte. Spinel NiMn2O4 synthesized through microwave-assisted co-precipitation method followed by calcination at 500°C showed a specific capacitance increasing from 290.56 F/g to 751.57 F/g as the KOH electrolyte concentration was increased from 1 M to 6 M at a scan rate of 5 mV/s. We have synthesized an SDS-assisted bimetal oxide of Ni of Mn, NiMn2O4 via hydrothermal method. Which was annealed at 400OC and then specific capacitance was measured using a 3-electrode system, which gives 3088.8 F/g in 0.5 M Na2SO4 as electrolyte at 2 mV/s scan rate. Electrospining techniques is a very slow yield process for mass production. We used a rather simple device Rotary Jet Spin (RJ-Spin) which has the same mechanism as candy floss machine. We separately annealed PVA fiber obtained from RJ-spin and annealed at 800OC within vacuum, the FTIR of this annealed fiber confirmed the rGO phase. NiMn2O4/C (using PVA) fiber fabricated using RJ-spin setup. The obtained fiber was annealed at 900OC in vacuum chamber and XRD result compared of both confirms the presence of NiMn2O4 particle at obtained PVA fiber as matrix. The obtained fiber had high moister affinity and sublimate most weight percentage during annealing.