Experimental and DFT studies on spinel NiMn2O4 flower derived from bimetallic MOF as an efficient electrode for next-generation supercapacitor

Metal-organic frameworks (MOF) have recently emerged as an intriguing template for developing morphologi-cally pre-designed metal oxide nanostructures. MOFs offer excellent control over morphology, extremely high porosity and large surface area, which is highly beneficial for supercapacitor electrode applications. We report the synthesis of bimetallic MOF-derived Nickel Manganese oxide for an electrode in supercapacitor by an effi-cient solvothermal and subsequent calcination route. The physical characterization was carried out by X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA) and Bruner-Emmert-Teller (BET). We performed the cyclic voltammetry (CV), chronopotentiometry (CP), and electronic impedance spectroscopy (EIS) test in a 1 M KOH electrolyte to examine the electrochemical characteristics of the prepared samples. NiMn2O4 electrode material revealed high specific capacitance of 1387 F/g at 1 A/g current density and prominent cycle life (80% capacitance retention after 6500 cycles) and the porous structure of the material has a good BET surface area of 84.3 m2/g. Further, we performed spin-polarized ab-initio density functional theory calculations to study the structural, electronic, and magnetic properties of the spinel NiMn2O4 structure. Our calculated results are close to the experimentally determined structural parameters, and the enthalpy of formation confirms the thermodynamical stability of the spinel structure with Delta HF =-1.6 eV/atom. The orbital projected electronic structure is further investigated to understand the contribution of elements near the Fermi region, which paves the way for further understanding of the distribution of electrons at a particular energy interval of our system. The present findings will aid in fabricating the bimetallic MOF-derived metal oxide nanostructures for the next -generation supercapacitors.