Leaf-like integrated hierarchical NiCo2O4 nanorods@Ni-Co-LDH nanosheets electrodes for high-rate asymmetric supercapacitors

In order to diminish charge transfer resistance and improve rapid reversible redox reactions of super-capacitors, leaf-like hierarchical NiCo2O4 nanorods@Ni-Co-layered double hydroxide nanosheets (NCO@NiCo-LDH) core/shell nanostructure was synthesized by two-step oxalic acid-assisted and metal organic framework (MOF)-derived method. Firstly, NCO nanorods as a core structure were synthesized in the presence of oxalic acid as an oxidizing agent. Then, Ni-Co-LDH as a shell structure was prepared by MOFbased synthesis. As-prepared hybrid core/shell NCO@Ni-Co-LDH electrodes displayed the highest capacitance (2370 F g(-1) under 1 Ag-1), exceptional rate-capability (78.2% at 30 A g(-1)) and a remarkable lifespan of 86.4% after successive 5000 charge/discharge performance. These extraordinary electrochemical properties are ascribed to the synergistic effects of NCO nanorods and Ni-Co-LDH nanosheets in a single core/shell structured framework, providing more accessible electroactive sites for rapid redox reactions with superior mechanical stability for longer cycle during charge-discharge cycles. Furthermore, an asymmetric NCO@NiCo-LDH//N-doped graphene hydrogel (NGH) supercapacitor delivered excellent energy density (50.71 Wh kg(-1)), high power density (773.54 W kg(-1)), and remarkable cyclic lifespan (89% after 5000 cycles under 5 A g(-1)). (C) 2021 Elsevier B.V. All rights reserved.