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Abstract
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Layered double hydroxides (LDHs) of transition metals have attained significant attention for supercapacitor applications due to their excellent charge storage, low internal resistance, and superior electrochemical stability. Here, a nanocomposite of reduced graphene oxide/nickel cobalt layered double hydroxide (rGO/NiCo LDH) on the surface of nickel foam (NF) containing hierarchical nickel cobalt copper transition metal oxides (TMOs) is prepared through two-step processes of electrochemical and coprecipitation methods. The TMOs/rGO/NiCo LDH nanocomposite is characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman, X-ray energy-dispersive (EDS), and X-ray photoelectron (XPS) spectroscopies as well as by transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), elemental mapping analysis, nitrogen adsorption/desorption, and contact angle measurements. The supercapacitive behavior of the electrodes has been investigated through cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) measurements, and electrochemical impedance spectroscopy (EIS). The study has shown that the synergetic effect and the electrochemical properties have considerably improved when the layered double hydroxides are synthesized in the presence of rGO. The TMOs/rGO/NiCo LDH nanocomposite exhibits an excellent specific capacitance of 2763 F g–1 at a current density of 1 A g–1 and a stability of 85% after 3000 GCD cycles at a current density of 24 A g–1. Also, a TMOs/rGO/NiCo LDH//rGO asymmetric supercapacitor device is constructed with an aqueous KOH electrolyte, which shows a capacitance of 244 F g–1 at a current density of 1 A g–1. The device attains the highest energy density of 34 Wh kg–1 and power density of 2500 W kg–1, with an excellent cycling stability of 100% after 3000 GCD cycles at a current density of 10 A g–1.
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