Supercapacitor performance of porous nickel cobaltite nanosheets

In this work, nickel cobaltite (NiCo₂O₄) nanosheets with a porous structure were fabricated on nickel foam as a working electrode for supercapacitor applications. The nanosheets were fabricated by electrochemical deposition of nickel-cobalt hydroxide on the nickel foam substrate at ambient temperature in a three-electrode cell followed by annealing at 300 °C to transform the coating into a porous NiCo₂O₄ nanosheet. Field emission scanning electron microscopy and transmission electron microscopy revealed a three-dimensional mesoporous structure, which facilitates ion transport and electronic conduction for fast redox reactions. For one cycle, the NiCo₂O₄ electrodeposited nickel foam has a high specific capacitance (1734.9 F g^-1) at a current density (CD) of 2 A g^-1. The electrode capacitance decreased by only approximately 12.7% after 3500 cycles at a CD of 30 A g^-1. Moreover, a solid-state asymmetric supercapacitor (ASC) was built utilising the NiCo₂O₄ nanosheets, carbon nanotubes, and a polyvinyl alcohol-potassium hydroxide gel as the anode, cathode, and solid-state electrolyte, respectively. The ASC displayed great electrochemical properties with a 42.25 W h kg^-1 energy density at a power density of 298.79 W kg^-1.