Preparation Of Molybdenum Disulfide Nanocomposites And Their Electrochemical Performance

Since nanomaterials possess special structures and a series of fantastic physical and chemical properties, they have got wide applications in various kinds of fields, including biosensor, photocatalysis or electrocatalysis, material engineering, biomedicine, energy storage and conversion and environmental protection, and have shown their unique advantages.As a typical layered transition metal sulfide, molybdenum disulfide (MoS2) has a similar layered structure with graphite, in which the atoms within the layer are held together by strong covalent forces (S-Mo-S) while van der Waals interaction enables stacking of the layers. In recent years, nanostructured MoS2 has attracted increasing attention because of their exceptional physical, chemical, optical and mechanical properties and great potential in many applications, including lithium ion batteries (LIBs), transistors, topological insulators and catalyst for hydrogen evolution reaction (HER).In this thesis, three kinds of MoS2 nanocomposites were prepared via liquid exfoliation, two-step electrodeposition and self-assembly approaches, and their applications in the fields of electrocatalysts for HER, electrochemical sensors, and anode materials for LIBs were also studied and discussed. The content of this thesis mainly consists of three parts:In the first part, an efficient electrocatalyst for hydrogen evolution has been developed based on liquid exfoliation of bulk MoS2 powder via a direct dispersion and ultrasonication method. Transmission electron microscopy and atomic force microscopy measurements show that the exfoliated MoS2 consists of two-dimensional nanosheets. The exfoliated MoS2 nanosheets modified glass carbon electrodes (E-MoS2/GCE) with various loadings are fabricated via a drop-casting method. The electrocatalytic activity of E-MoS2/GCEs toward hydrogen evolution reaction is examined using linear sweep voltammetry. It is shown that the E-MoS2/GCE with an electrode loading of 48 μg cm-2 exhibits high catalytic activity for hydrogen evolution with a low overpotential (120 mV) and a high current density (6.36 mA cm-2, at η= 200 mV). The increased catalytic activity of exfoliated M0S2 is attributed to an improved conductivity compared to the bulk MoS2 powder. Therefore, this study provides a new approach for a cheap and efficient HER catalyst, which can be easily prepared and is promising for large-scale production.In the second part, an efficient nonenzymatic glucose sensor based on Ni(OH)2/MoSx nanocomposite modified glassy carbon electrode (Ni(OH)2/MoSx-GCE) has been fabricated via a twe-step electrodeposition approach and its electrochemical performance has been studied by cyclic voltammetry and chronoamperometry. Scanning electron microscopy images reveal that the Ni(OH)2 nanoparticles are uniformly deposited on the film with diameter of 100±20 nm. Cyclic voltammetry and chronoamperometry indicate that Ni(OH)2/MoSx-GCE displays a remarkably electrocatalytic activity toward nonenzymatic oxidation of glucose. Response is linear in 10～1300 μM concentration range (R2=0.9987), the detection limit is very low (5.8 μM), response is rapid (<2 s), and selectivity over ascorbic acid, dopamine, uric acid, fructose and galactose is very good. Therefore, the Ni(OH)2/MoSx nanocomposite can be potentially used as a feasible electrochemical sensor for the determination of glucose. In addition, this study provides a new approach for the development of MoSx film as a promising support material for various applications in synergistic catalysis.In the third part, MoS2/multiwall carbon nanotubes (MWCNTs) nanocomposites have been prepared through a self-assembly method and their characterization and application as an anode in lithium-ion batteries have also been studied. Zeta potential measurements show that polyethyleneimine (PEI) coated MWCNTs contain positive charges and polyvinylpyrrolidone (PVP) stabilized MoS2 nanosheets contain negative charges. Through a self-assembly process driven by electrostatic interactions, MoS2/MWCNTs nanocomposites are prepared in various weigth ratios (3:1,1:1 and 1:3). The electrochemical tests show that the MoS2/MWCNTs nanocomposites exhibit good lithium-ion storage performance with large specific capacity, good cycling stability and enhanced rate performance over pristine MoS2 and MWCNTs. Such enhanced performance has been attributed to the synergistic effects of MoS2 and MWCNTs.