Flower-Like Nickel-Cobalt Oxide Decorated Dopamine-Derived Carbon Nanocomposite for High Performance Supercapacitor Applications

The highly open space flower, coin, peony flower, and leaf-like nickel-cobalt oxide nanostructured materials with and without dopamine as a carbon source (D_1.5NiCo₂O₄, D_1.0NiCo₂O₄ (D-NiCo₂O₄), D_0.5NiCo₂O₄, and D_0.0NiCo₂O₄ (D- free NiCo₂O₄)) are prepared by a low temperature chemical synthesis method with improved electrical conductivity, providing the longtime electron pathway, and high surface area for high performance supercapacitors. The structure and morphology of the as-synthesized samples were characterized by X-ray diffraction pattern, X-ray photoelectron spectroscopy, scanning electron microscope, field emission-transmission electron microscope, and N₂ adsorption-desorption isotherms. Electrochemical properties of the electrodes were analyzed by cyclic voltammetry and galvanostatic charge-discharge methods. Notably, the as-synthesized flower-like D-NiCo₂O₄ nanocomposite exhibited a maximum specific capacitance of 667 F g^-1, which is superior to D- free NiCo₂O₄ viz. 202 F g^-1 at 5 A g^-1 with excellent cyclic stability of about 95% and 86% at 10 A g^-1 after 2000 charge-discharge cycles in 2.0 M KOH aqueous electrolyte solution for D-NiCo₂O₄, and D-free NiCo₂O₄, respectively. In addition, an asymmetric supercapacitor device is fabricated through D-NiCo₂O₄ as a positive electrode and biomass-derived AC as a negative electrode with the potential range of 0-1.5 V in PVA-KOH gel electrolyte solution. These results indicate that the as-prepared electrodes have high specific capacitance, excellent cycle stability, and good rate capability, which surpass several related metal oxide electrodes.