Structure-engineering of core-shell ZnCo₂O₄@NiO composites for high-performance asymmetric supercapacitors

The implementation of a structure-designed strategy to construct hierarchical architectures of multicomponent metal oxide-based electrode materials for energy storage devices is in the limelight. Herein, we report NiO nanoflakes impregnated on ZnCo₂O₄ nanorod arrays as ZnCo₂O₄@NiO core-shell structures on a flexible stainless-steel mesh substrate, fabricated by a simple, cost-effective and environmentally friendly reflux condensation method. The core-shell structure of ZnCo₂O₄@NiO is used as an electrode material in a supercapacitor as it provides a high specific surface area (134.79 m² g^-1) offering high electroactive sites for a redox reaction, reduces the electron and ion diffusion path, and promotes an efficient contact between the electroactive material and electrolyte. The binder-free ZnCo₂O₄@NiO electrode delivers a high specific capacitance of 882 F g^-1 at 4 mA cm^-2 current density and exhibits remarkable cycling stability (∼85% initial capacitance retention after 5000 charge-discharge cycles at 10 mA cm^-2). The asymmetric supercapacitor device ZnCo₂O₄@NiO//rGO delivered a maximum energy density of 46.66 W h kg^-1 at a power density of 800 W kg^-1. The device exhibited 90.20% capacitance retention after 4000 cycles. These results indicate that the ZnCo₂O₄@NiO architecture electrode is a promising functional material for energy storage devices.