Structure-engineering of core-shell ZnCo 2 O 4 @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 ZnCo 2 O 4 nanorod arrays as ZnCo 2 O 4 @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 ZnCo 2 O 4 @NiO is used as an electrode material in a supercapacitor as it provides a high specific surface area (134.79 m 2 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 ZnCo 2 O 4 @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 ZnCo 2 O 4 @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 ZnCo 2 O 4 @NiO architecture electrode is a promising functional material for energy storage devices.