Hierarchical core-shell structure of NiCo₂O₄ nanosheets@HfC nanowires networks for high performance flexible solid-state hybrid supercapacitor

Rationally constructing the electrode with the hierarchical structure, different components, and the flexibility is a promising approach to further improve the electrochemical properties and meet the demand for flexible electronic devices. In this paper, for the first time, hafnium carbide nanowires (HfC_NWs) networks, with the metrics of large specific surface area, excellent conductivity, and chemical/physical stability, are served as nanoscale conductive skeletons on carbon cloth (CC) for supporting the porous NiCo₂O₄ nanosheets (NSs). Benefiting from the structural advantages, the as-formed free-standing core-shell NiCo₂O_4NSs@HfC_NWs/CC exhibits a high specific capacitance of 2102 F g⁻¹ at a current density of 1 A g⁻¹, good rate capability (85% capacitance retention at 20 A g⁻¹) and outstanding cycling stability (98% capacitance retention after 5000 cycles at 10 A g⁻¹). Additionally, assembled with the NiCo₂O_4NSs@HfC_NWs/CC and activated carbon (AC)/CC, the flexible solid-state hybrid supercapacitor displays a high energy density of 53 Wh kg⁻¹ at a power density of 800 W kg⁻¹ and excellent performance stability with good flexibility. More impressively, our work could not only further widen the application of HfC_NWs, but also put forward the new thinking of rational construction of high-performance flexible supercapacitors.