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 (D1.5NiCo2O4, D1.0NiCo2O4 (D-NiCo2O4), D0.5NiCo2O4, and D0.0NiCo2O4 (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.