Nickel cobalt oxide (NiCo2O4) nanoagglomerates were effectively synthesized through a simplistic low-temperature co-precipitation technique. The obtained material was further calcined to enhance its morphological properties and reduce the size of its individual particle of agglomerates. The as-synthesized NiCo2O4 agglomerates were characterized through the employment of various techniques, which include scanning/transmission electron microscopies (SEM/TEM), X-ray diffraction, Raman spectroscopy and X-ray fluorescence spectroscopy (XRF), and thermogravimetric analysis (TGA). Electrochemical performances of the as-synthesized electrode materials evaluated in a three-electrode configuration could deliver an optimized specific capacity of 95.6 mA h g–1 at a 0.5 A g–1 specific current. A fabricated hybrid asymmetric supercapacitor (SC) composed of NiCo2O4 and the activated carbon obtained from cocoa pods (Cocoa AC-700) as the positive and negative electrodes (NiCo2O4//AC cocoa-700), respectively, delivered a specific capacity of around 168.7 mA h g–1 at 0.5 A g–1 and a corresponding specific energy and power of 47.7 W h kg–1 and 430.0 W kg–1, respectively. The SC exhibited a substantial cycling stability, resulting in a Coulombic efficiency of 97.2% with a related capacity retention of 96.6% recorded after a cycling test of over 11,000 cycles at 5 A g–1.

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This study has investigated the effect of the incorporation of graphene foam (GF) into the matrix of a ternary transition-metals hydroxide containing nickel, cobalt, and manganese for optimal electrochemical performances as electrodes for supercapacitors applications. An adopted simple, low-cost co-precipitation synthesis method involved the loading a mass of the ternary metal hydroxides (NiCoMn-TH) onto various GF mass loading so as to find ints effect on the electrochemical properties of the hydroxides. Microstructural and chemical composition of the various composite materials were investigated by employing scanning/transmission electron microscopy (SEM/TEM), x-ray diffraction (XRD), Raman spectroscopy, and N2 physisorption analysis among others. Electrochemical performances of the NiCoMn-TH/200 mg GF composite material evaluated in a three-electrode system using 1 M KOH solution revealed a maximum specific capacity around 178.6 mAh g−1 compared to 76.2 mAh g−1 recorded for the NiCoMn-TH pristine material at a specific current of 1 A g−1. The best mass loading of GF nanomaterial (200 mg GF), was then utilised as a positive electrode material for the design of a novel hybrid device. An assembled hybrid NiCoMn-TH/200 mg GF//CSDAC device utilizing the NiCoMn-TH/200 mg GF and activated carbon derived from the cocoa shell (CSDAC) as a positive and negative electrode, respectively, demonstrated a sustaining specific capacity of 23.4 mAh g−1 at a specific current of 0.5 A g−1. The device also yielded sustaining a specific energy and power of about 22.32 Wh kg−1 and 439.7 W kg−1, respectively. After a cycling test of over 15,000 cycles, the device could prove a coulombic efficiency of ~ 99.9% and a capacity retention of around 80% within a potential range of 0.0–1.6 V at a specific current of 3 A g−1. These results have demonstrated the prodigious electrochemical potentials of the as-synthesized material and its capability to be utilized as an electrode for supercapacitor applications.

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