Synthesis of Nitrogen-Doped Molybdenum Sulphide and Molybdenum Sulphide/Oxide Nanocomposite As Active Materials for Supercapacitor Electrode

Abstract

The layered transition metal dichalcogenide molybdenum disulphide (MoS2) is an excellent electrode material due to the presence of pseudocapacitance and electric double layer capacitance. However, low rate performance and capacity fading restrict its application in supercapacitor field. The doping and composite formation can tackle these problems easily. The nitrogen doping can increase the electrical conductivity of MoS2, which eventually enhances the supercapacitor performance while the formation of oxide and sulphide nanocomposite may increase the pseudocapacitance of the MoS2 materials. Thus, here we report the synthesis of nitrogen-doped MoS2 and MoO2/MoO3/MoS2 nanocomposite for application in supercapacitor electrode. The nitrogen doped molybdenum sulphide and molybdenum sulphide/oxide nanocomposite were synthesised using hydrothermally synthesised MoS2 and urea as a nitrogen precursor in a tube furnace. The structural, as well as morphological characterisation, were done to confirm the synthesis of three-dimensional flowerlike MoS2 (Hexagonal) and nitrogen doped MoO2/MoO3/MoS2 nanocomposite using various spectroscopic and microscopic techniques. The X-ray diffraction (XRD) and selected area electron diffraction (SAED) pattern confirm the formation of mixed oxide and sulphide phases during the nitrogen doping process. The X-ray photoelectron spectroscopy (XPS) confirmed the nitrogen doping of the MoS2 nanostructures. Field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) were used to study surface morphology of synthesised MoS2 and nitrogen doped MoO2/MoO3/MoS2 nanocomposite. The FESEM and TEM show the flower-like morphology for sulphides and rod/plate-like structure for oxide phase of the nanocomposite. The electrochemical analysis were done to study the supercapacitor behaviour of synthesised materials. The electrochemical impedance measurements display increment in conductivity of MoS2 nanomaterials due to nitrogen doping. The highest specific capacitance observed for 1:1 (MoS2: Urea) weight ratio. The nitrogen doped MoS2 with mixed oxide and sulphide phases (MoO2/MoO3/MoS2) showed the nearly four times enhancement in specific capacitance (~129 F/g at 2A/g) than pristine hydrothermally synthesised MoS2 (~34 F/g at 2A/g). Overall, nitrogen doped MoO2/MoO3/MoS2 composite materials can likely to be used for application in supercapacitors. Figure 1