Investigating the Properties of Expanded Graphite on CoO, NiO, and NiCo₂O₄ Electrodes for Supercapacitor Applications

Oxides of cobalt, nickel, and nickel cobalt (CoO/EG, NiO/EG, and NiCo₂O₄/EG) particles were fabricated using the microwave cum co-precipitation method and deposited by drop-casting. Expanded graphite was added during the synthesis because it possesses abundant surface area and trivial electrical resistance. The synergistic unification of existing elements and their composites with expanded graphite enhanced the performance, stability, and charge storage of the synthesized materials. The structures revealed in the x-ray diffractometer (XRD) plots confirm the nanocomposites as crystalline with a compact mesh-like dense morphology observed. Their elemental constituents were shown in the energy dispersive x-ray spectroscope (EDX) plots. Optical properties revealed a gradual drop in absorbance over longer wavelengths with energy band gap values within the 2.18 to 2.79 eV range. The highest specific capacitance values obtained at a scanning rate of 2 mV/s from the cyclic voltammograms were 309, 3916, and 3309 F/g for the CoO/EG, NiO/EG, and NiCo₂O₄/EG electrodes respectively. These results are obvious indications that the composites are better-performing electrodes than single transition metal oxides. Adding the expanded graphite was shown to enhance electrode performance. These electrodes are usefully applied in supercapacitors and energy storage systems.