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 supercapacitors, leaf-like hierarchical NiCo₂O₄ nanorods@Ni-Co-layered double hydroxide nanosheets (NCO@Ni-Co-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 MOF-based synthesis. As-prepared hybrid core/shell NCO@Ni-Co-LDH electrodes displayed the highest capacitance (2370 F g⁻¹ under 1 A g⁻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@Ni-Co-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).