3D marigold flowers of copper-nickel oxide composite materials as a positive electrode for high-performance hybrid supercapacitors

Despite their high specific capacitances, metal oxide-based electrodes still do not meet the commercial standard for cycling stability owing to their inherent poor electronic conductivity and morphological structural changes during charging and discharging. A superior specific capacitance, accompanied with long-term cycling durability, is pivotal for supercapacitor application. In this research article, different precursor volume ratios of copper-nickel solution were used for the construction of binder-free 3D marigold flower-like copper-nickel oxide (3D-MCuNi oxide) electrodes via a hydrothermal method. XPS, EDAX, and TEM studies reveal that the increased amount of O-vacancies in the marigold flowers of the copper-nickel oxide composite is caused by a significant number of imperfections in the structure and might enhance their electrical conductivity. The marigold flower-like morphological structure exhibits electrode-electrolyte ions with significantly high hydrophilicity and better electrochemical diffusion performance. The optimized volume ratio of Cu : Ni = 1 : 1 for 3D-MCuNi oxide composite nanomaterials demonstrates an excellent specific capacitance of 2387.15 F g⁻¹ at a current density of 0.6 mA cm⁻² and 93% cycling capacitive retention performance up to 10 000 cycles. Additionally, a flexible hybrid supercapacitor device (HSD) was assembled using reduced graphene oxide (rGO) and 3D-MCuNi oxide as the negative and positive electrode, respectively, which revealed excellent electrochemical charge storage performance with a high energy density of 120.9 W h kg⁻¹, power density of 34.82 kW kg⁻¹, and superior cycling stability of 87% retention. Thus, the 3D-MCuNi oxide composite potential materials are more attractive for charge storage supercapacitor applications.