High-performance solid state asymmetric supercapacitor based on electrochemically decorated 3D network-like Co3O4 architecture on NiO nanoworms

Highlights: • A thin layer of NiO nanoworms (NiONWs) were grown on anodized Ni foil. • Co₃O₄ nanosheets were electrodeposited on a-NF/NiONWs electrode. • NiO nanoworms play a substantial role on the morphology of deposited Co₃O₄ nanosheets. • A solid state a-NF/NiONWs/Co₃O₄//RGO/NF asymmetric supercapacitor was fabricated. The unique 3D network-like cobalt oxide architecture was electrochemically deposited on nickel oxide nanoworms (NiONWs) with nickel foil (NF) substrate. After the anodic polarization of NF and its activation, a very thin film of NiO nanoworms with the average diameter of 30 nm and the length of 100 nm was successfully grown on anodized Ni foil (a-NF) by using a facile hydrothermal method under the mild conditions including a saturated alkaline solution of Ni²⁺ at 65 °C to prepare a-NF/NiONWs. Then, 3D network-like Co₃O₄ nanosheets with the average thickness of 25 nm were directly electrodeposited on a-NF/NiONWs by using cyclic voltammetry under the optimized experimental conditions. The morphologies and detailed geometrical structures of the electrodes were conducted by FE-SEM. The fabricated a-NF/NiONWs/Co₃O₄ electrode provides a high areal specific capacitance of 1320 mF cm^-2 at a current density of 4 mA cm⁻² and high mass specific capacitance of 2000 F g⁻¹ at the current density of 6 A g⁻¹. By using a-NF/NiONWs/Co₃O₄ as a positive electrode and reduced graphene oxide-deposited NF (RGO/NF) as a negative electrode, a solid-state asymmetric a-NF/NiONWs/Co₃O₄//RGO/NF supercapacitor was assembled and it exhibited a high specific capacitance of 471.4 mF cm^-2 at a current density of 3 mA cm⁻². The fabricated solid-state supercapacitor also showed good rate capacity and long-term cycling performance of 2000 cycles.