Abstract
In this work, a novel carbon nanotubes (CNTs)/NiCo2S4 composite for high performance supercapacitors was prepared via a simple chemical bath deposition combined with a post-anion exchange reaction. The morphologies and phase structures of the composites were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS) and low-temperature sorption of nitrogen (BET). The electro-chemical tests revealed that the CNT/NiCo2S4 composite exhibited high electrochemical performance, because the CNTs were used as a conductive network for the NiCo2S4 hexagonal nanoplates. Compared with pure NiCo2S4 and the mechanically mixed CNTs/NiCo2S4 composite, the CNTs/NiCo2S4 composite electrode material exhibited excellent supercapacitive performance, such as a high specific capacitance up to 1537 F/g (discharge current density of 1 A/g) and an outstanding rate capability of 78.1% retention as the discharge current density increased to 100 A/g. It is therefore expected to be a promising alternative material in the area of energy storage.
Highlights
Supercapacitors have attracted considerable attentions because of their fast recharge capability, higher power density, and long cycling lifespan, all of which make them an essential power source for various energy storage applications[1,2,3]
Park et al.9. determined that the replacement of oxygen (O) with sulphur (S) creates a more flexible structure because the electronegativity of Sis lower than that of oxygen (O), which prevents the disintegration of the structure by the elongation between the layers followed by the enchancement of the electron transport efficiency in the structure
An efficient way to overcome the above problems is to prepare a hybrid composite with highly conductive materials, such as nanoporous carbons, carbon nanotubes (CNTs), and graphene sheets[12,13,14,15]
Summary
The following materials were used: polyvinylpyrrolidone (PVP, K-30) (Aladdin Industrial Corporation), Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Na2S·9H2O, urea and ammonium hydroxide (Sinopharm chemical reagent Co., Ltd.), and CNTs (Shenzhen Nanotech Port Co., Ltd.). The CNTs/NiCo2S4 composite was prepared according to the following steps: 1) 40 mg of CNTs were dispersed in 30 ml of PVP aqueous solution (10 mg/ml) under ultrasonic dispersion and stirring; 2) 4 mmol of Co(NO3)2·6H2O and 2 mmol of Ni(NO3)2·6H2O were dissolved in 30 ml of deionized water under stirring; 3) The above solutions were mixed together and stirred for 1 hour; 4) 0.9 g of urea and 1 ml of ammonium hydroxide were added to the above mixture; 5) After stirring for 3 hours, the precipitate was collected and washed with deionized water several times and dried at 60 °C for 4 hours; 6) the obtained precursor was dispersed in 64 ml of 0.1 M Na2S aqueous solution, stirred for 10 minutes, and the suspension was transferred into an 80 ml Teflon-lined stainless-steel autoclave; 7) The autoclave was heated at 160 °C for 12 hours and cooled to room temperature naturally; 8) The as-obtained black precipitate was collected and washed with deionized water several times and dried at 60 °C for 4 hours in vacuum. Electrochemical impedance spectroscopy (EIS) measurements were collected in the frequency range of 0.1–100,000 Hz by applying an AC voltage with 5 mV perturbation
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