Direct growth of AC@NiCo2S4 composite on nickel foam as binder-free electrodes for supercapacitors

In this study, folded nanotubes were directly grown on Ni foam by two-step hydrothermal method to form activated carbon (AC) and NiCo2S4 composite material with a unique structure like nano-urchin. In addition, the morphology and structure can be controlled by the time of hydrothermal reaction. The resulting samples were characterized by means of XRD, XPS, EDS and SEM. The electrochemical test results show that compared with the 6 h and 24 h hydrothermal composites, the 12 h hydrothermal composites (AC@NiCo2S4-2) form a complete folded nanotube structure, provide a large number of reactive sites, and show better electrochemical properties. And compared with the capacitance of NiCo2S4 (456.14 C g-1), the AC@NiCo2S4-2 exhibited a high specific capacitance of 653.9 C g-1 at a current density of 1 A g-1. In addition, after combination with AC, AC@NiCo2S4 has better electrochemical performance and cycle stability, the capacitance retention rate at 10 A g-1 is 62.84 % of 1 A g-1, and can still maintain 84.96 % of the initial capacitance after 3000 cycles. Moreover, the fabricated hybrid supercapacitor (HSC) based on AC@NiCo2S4-2 and AC electrodes achieved a high energy density of 29.75 Wh kg-1 at the power density of 700 W kg-1 and still maintain the energy density of 16.86 Wh kg-1 at the high power density of 7000 W kg-1.

Automated summary

Folded nanotubes were grown directly on Ni foam using a two-step hydrothermal method to form activated carbon (AC) and NiCo2S4 composite material with a unique nano-urchin structure. The morphology and structure could be controlled by the duration of the hydrothermal reaction. Characterization of the samples was done using XRD, XPS, EDS, and SEM. The electrochemical tests showed that the 12-hour hydrothermal composites (AC@NiCo2S4-2) had a complete folded nanotube structure, a large number of reactive sites, and better electrochemical properties compared to the 6-hour and 24-hour composites. The AC@NiCo2S4-2 also exhibited a high specific capacitance of 653.9 C g-1 at a current density of 1 A g-1, compared to the capacitance of NiCo2S4 (456.14 C g-1). Furthermore, the AC@NiCo2S4-2 showed improved electrochemical performance and cycle stability after combining with AC, with a capacitance retention rate of 62.84% at 10 A g-1 compared to 1 A g-1 and retaining 84.96% of the initial capacitance after 3000 cycles. Additionally, the hybrid supercapacitor (HSC) based on AC@NiCo2S4-2 and AC electrodes achieved a high energy density of 29.75 Wh kg-1 at a power density of 700 W kg-1 and maintained an energy density of 16.86 Wh kg-1 at a high power density of 7000 W kg-1.