Hierarchical 1D nanofiber-2D nanosheet-shaped self-standing membranes for high-performance supercapacitors

Abstract

Coaxial electrospinning technology is a simple, effective method to prepare core–shell structured nanofibers with a large specific surface area, good electrical conductivity and excellent flexibility, which are considerably investigated as electrode materials for supercapacitors. Herein, we report a hierarchical structure of NiCo₂S₄ nanosheets aligned on a double capillary carbon nanofiber (NiCo₂S₄@DCCNF) to make a self-standing electrode by using the combination of coaxial electrospinning technology and a hydrothermal process. The mass loading of NiCo₂S₄ on the nanofibers was 34.33 wt%. Taking advantage of the highly conductive, porous structure of the DCCNF and open framework of the three-dimensional nanoarchitecture of NiCo₂S₄ nanosheets, such a unique 1D nanofiber-2D nanosheet-shaped hierarchical structure is capable of increasing the accessible surface area for active sites, shortening the ion diffusion length and decreasing the ion diffusion resistance. Therefore, the hybrid electrode exhibits high specific capacitance (1275 F g⁻¹/1474 F g⁻¹ at 5 mV s⁻¹/1 A g⁻¹) and excellent rate capability (85%/82% at 50 mV s⁻¹/50 A g⁻¹) in 3 M KOH electrolyte. Moreover, flexible all-solid-state supercapacitors based on NiCo₂S₄@DCCNF with PVA/KOH gel electrolyte deliver a high capacitance of 166 F g⁻¹ and remarkable electrochemical stability, with a maximum energy density of 55.6 W h kg⁻¹ at a power density of 1061 W kg⁻¹. The scalable coaxially electrospun materials with superior performance may pave the way to wearable electronics.