Rational design of hierarchical FeCo₂O₄ nanosheets@NiO nanowhiskers core-shell heterostructure as binder-free electrodes for efficient pseudocapacitors

Hierarchical core-shell nanoarchitectures have triggered significant technological and scientific interests because of their remarkable versatility in nanoscale electronics and energy storage systems. Meanwhile, designing and fabricating the heterostructure electrode materials by employing effective interface modification could acquire prominent electrochemical performance for supercapacitors. In this study, we reported that FeCo₂O₄ nanosheets were first synthesized on Ni foam, and then the novel microstructure of NiO nanowhiskers was covered on FeCo₂O₄ by surface modification. The FeCo₂O₄ NSs@NiO NWs composite with hierarchical and core-shell structure presented ultrahigh specific capacitance of 4746.2 F g⁻¹ at the current density of 1 A g⁻¹, and the remarkable capacitance retention was 88.9% after 8000 cycles at 5 A g⁻¹. Meanwhile, the asymmetric supercapacitors (FeCo₂O₄ NSs@NiO NWs//AC) exhibited excellent energy density of 60.6 Wh kg⁻¹ and remarkable power density of 30 kW kg⁻¹, which could efficiently light up 23 red LED (1.8 V). The device also displayed prominent cyclic stability with 130.8% capacitance retention after 8000 cycles at a current density of 5 A g⁻¹. This work presented a new method to accomplish a controllable synthesis of hierarchical core-shell heterostructure as electrode materials for high-performance electrochemical energy storage.