Currently, enormous attention is being paid to the difficult design and synthesis of hierarchical nanosheet structures for high-performance supercapacitors. In the present study, we have explored electrochemically synthesized nanostructures of free standing NiCo₂O₄@NiCo₂O₄ composite electrode interconnected hierarchical nanoplates, and NiCo₂O₄ connected hierarchical nanowires were directly grown on a high conductivity Ni foam substrate as an electrode for supercapacitor applications through a cost effective and simple chemical bath deposition method. The electrochemical properties were investigated via cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy studies. This optimized NiCo₂O₄@NiCo₂O₄ nanoplate electrode delivered a remarkable specific capacitance of 2800 F g⁻¹ at a current density of 35 A g⁻¹, which is higher than that of the NiCo₂O₄ nanowire electrode (1200 F g⁻¹ at 35 A g⁻¹) in 3 M KOH aqueous solution, with good electrochemical and superior cycling life properties because of its higher conductivity, broad surface area and the mesopores on its walls. The NiCo₂O₄@NiCo₂O₄ nanoplate composite electrode is directly grown on the high conductivity Ni foam substrate with NiCo₂O₄ nanowires to support efficient electrocatalytic oxidation reactions. The mesoporous features of the NiCo₂O₄@NiCo₂O₄ nanoplate electrode enhance the properties through fast electron/ion transfer and enhance the utilization of the electrode material and large number of electroactive sites. All these results indicate that the NiCo₂O₄@NiCo₂O₄ nanoplate composite electrode would be a promising positive electrode material for flexible electrochemical capacitors.

Schematic of the synthesis of the honeycomb with a folded silk-like NF@NiMoO₄@NiCo₂O₄ nanostructure, honeycomb-like NF@NiMoO₄ structure and nanoplate-like NF@NiCo₂O₄ structure on nickel foam (NF).

Supercapacitors have become a popular form of energy-storage device in the current energy and environmental landscape, and their performance is heavily reliant on the electrode materials used. Carbon-based electrodes are highly desirable due to their low cost and their abundance in various forms, as well as their ability to easily alter conductivity and surface area. Many studies have been conducted to enhance the performance of carbon-based supercapacitors by utilizing various carbon compounds, including pure carbon nanotubes and multistage carbon nanostructures as electrodes. These studies have examined the characteristics and potential applications of numerous pure carbon nanostructures and scrutinized the use of a wide variety of carbon nanomaterials, such as AC, CNTs, GR, CNCs, and others, to improve capacitance. Ultimately, this study provides a roadmap for producing high-quality supercapacitors using carbon-based electrodes.

Schematic representation of the synthesis of nanoplate-like NiCo ₂ O ₄ structure on nickel foam (NF).

Schematic representation of the synthesis of MoNiO₄ flower-like nanostructures.