Mixed metal chalcogenide shell with carbon interlayer wrapped 3D NiCo₂O₄ nanowire array: A hierarchical self-supported electrode for high-performance supercapacitors

The expansion of effective mass transportation and elevated electrochemical active sites are cogent strategies for designing hierarchical transition metal-based heterostructures electrodes in high-performance supercapacitors (SC). In this study, we fabricated a self-supported three-dimensional NiCoO@NC@NiCoMnSe core-shell nanowire array (NWA) on Ni foam via a two-step hydrothermal process followed by vapor phase selenification. Fabricated multivalent heterostructured core-shell NWA electrode exhibited a high areal capacity of 0.761 mA h cm⁻² (2.73 C cm⁻²) at 2 mA cm⁻² with cyclic stability of 83.1% after 5000 cycles at 30 mA cm⁻². An assembled HSC device with NiCoO@NC@NiCoMnSe as a positive electrode and activated carbon (AC) as a negative electrode exhibited a high volumetric energy density of 3.87 mWh cm⁻³ at a volumetric power density of 20.17 mW cm⁻³ and further retained an energy density of 2.64 Wh cm⁻³ at a power density of 201.5 W cm⁻³. The HSC exhibited high-capacity retention of 98.2% after 10 000 cycles at 6 mA cm⁻², evidence of the high durability of the rich redox-active heterostructured electrode. A thin carbon nanowall between the core and shell interface enriched the mass electron transfer, reduced the impedance, and promoted its structural durability, resulting in the heterostructure's superior electrochemical performance.