Preparation And Properties Of Carbon Nanotube Based Supercapacitor Electrode Materials

Supercapacitors?SCs?are a new type of energy storage devices that bridge the gap between batteries and traditional capacitors.SCs have a series of merits including high power density,high energy density and good cycle life.Moreover,SCs can be used for wastewater purification and seawater desalination due to their outstanding capacity in adsorbing ions.In this thesis,using carbon nanotubes?CNTs?as the target material,by loading metal sulfides on the surface of CNTs and structure engineering,SCs with increased specific capacity were obtained.NiCo₂S₄,which has high specific energy but poor conductivity,was loaded onto CNTs using the heat treated SiO₂@CNTs as a sacrificial template through a two-step hydrothermal method.The resulting NiCo₂S₄@CNTs exhibit good rate performance as high-performance supercapacitor electrode.Scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray diffraction?XRD?,Raman spectroscopy?Raman?,X-ray photoelectron spectroscopy?XPS?and nitrogen adsorption desorption testing were used to characterize the morphology and structure of NiCo₂S₄@CNTs.The results show that the heat treatment temperature of SiO₂@CNTs is a key factor affecting the microstructure and capacitance of NiCo₂S₄@CNTs.When the heat treatment temperature is 800°C,the NiCo₂S₄@CNTs has good electrochemical performance.At the current density of 1 A·g^-1,the capacitance value is as high as 1947.5 F·g^-1,which can also retain 87%at a large current density of 5 A·g^-1(compared to the current density of 1 A·g^-1).At 1 A·g^-1,the NiCo₂S₄@CNTs has a capacity retention rate of up to 75%after 2000 cycles.Carbon nanotube is an excellent electrode material for capacitive deionization?CDI?,due to its excellent electronic conductivity and outstanding chemical/physical stability.A free-standing CNT film was fabricated by floating-catalyst chemical vapor deposition and used as a binder-free electrode for CDI.By simply adjusting the pyrrole content in the precursor,the morphology of the resulted CNT film can be tuned to meet the requirements of CDI.In the presence of 2 wt.%pyrrole,the CNTs film with a mesoporous structure exhibited a large specific surface area of 198 m²·g^-1 and an increased electric double layer capacity,which is more than 2 times as large as the pristine CNTs film.The electrosorption capacity for NaCl of the CNTs film electrode has been greatly improved to 11.39 mg·g^-1,showing a good potential for the large-scale practical CDI.