In-situ growth of sea urchin-like NiCo2S4 on crab-shell carbon for high-performance supercapacitors and capacitive deionization

Supercapacitors as one of the new energy storage devices have attracted much attention from researchers. The design and preparation of new electrode materials with high conductivity and energy density has become a frontier and key issue in the research of supercapacitor performance improvement. In addition, flow capacitor deionization (FCDI) relying on the working principle of supercapacitors is a promising technology for desalination and has received crucial attention. NiCo 2 S 4 (NCS) is a promising pseudocapacitive material with high electrical conductivity and ideal stability. In this study, sea urchin-like NiCo 2 S 4 electrode materials (CC@NCS) grown in situ on crab shell carbon (CC) were prepared by a simple molten salt-assisted hydrothermal two-step method. The composite successfully combined the properties of CC and NiCo 2 S 4 . The prepared material exhibited excellent electrochemical properties and energy storage performance. In the three-electrode system, the specific capacitance is up to 692.4 F/g at a current density of 0.5 A/g. Asymmetric supercapacitors assembled with CC as the negative electrode, CC@NCS as the positive electrode, and 3 M KOH as the electrolyte obtained high specific capacitance (0.5 A/g, 163.6 F/g) and high energy density (305.16 W/kg, 8.18 Wh/kg). The device also showed excellent cycling performance in the long cycle test (88.65 % retention after 5000 cycles). In addition, the FCDI device with this material as the flow electrode achieved a final conductivity of 15.16 μS/cm by electrosorption of a 1000 mg/L NaCl solution at a constant pressure of 1.2 V for 60 min along with an impressive average salt removal rate (0.0621 mg/cm 2 ·min −1 ) and charge efficiency value (90.79 %), and a low energy consumption value (0.02 kWh/mol). What's more, it also exhibited excellent desalination properties. This indicates that the composite is a promising active material for energy storage and desalination.