Browsing by Author "Xaba, Nqobile"

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    Development of Anode Materials Using Electrochemical Atomic Layer Deposition (E-ALD) for Energy Applications
    (University of the Western Cape, 2018) Xaba, Nqobile; Khotseng, Lindiwe
    Nanomaterials have been found to undeniably possess superior properties than bulk structures across many fields of study including natural science, medicine, materials science, electronics etc. The study of nano-sized structures has the ability to address the current world crisis in energy demand and climate change. The development of materials that have various applications will allow for quick and cost effective solutions. Nanomaterials of Sn and Bi are the core of the electronic industry for their use in micro packaging components. These nanomaterials are also used as electrocatalysts in fuel cells and carbon dioxide conversion, and as electrodes for rechargeable sodium ion batteries. There are various methods used to make these nanostructures including solid state methods, hydrothermal methods, sputtering, and vacuum deposition techniques. These methods lack the ability to control the structure of material at an atomic level to fine tune the properties of the final product. This study aims to use E-ALD technique to synthesis thin films of Sn and Bi for various energy applications, and reports the use of E-ALD in battery applications for the first time. Thin films were synthesised by developing a deposition sequence and optimising this deposition sequence by varying deposition parameters. These parameters include deposition potential, and concentration of precursor solution. The thin films were characterised using cyclic voltammetry, linear sweep voltammetry, chronoamperometry for electrochemical activity. These were also characterised using scanning electron microscope for morphology, x-ray diffraction for crystal phases, energy dispersive spectroscopy for elemental mapping, and focused ion beam scanning electron microscope for thickness. The elemental content was analysed using electron probe micro analysis and inductively coupled plasma mass spectrometry. The electrochemical impedance charge and discharge profile were used for electrochemical battery tests.
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    Underpotential deposition of SnBi thin films for sodium ion batteries: The effect of deposition potential and Sn concentration
    (Elsevier, 2019) Xaba, Nqobile; Modibedi, Remegia M.; Khotseng, Lindiwe E.
    Bimetallic SnBi film was deposited on a Cu foil substrate via the electrochemical atomic layer deposition (E-ALD) technique. The deposition attainment of Sn and Bi were investigated using cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The deposition potential of Bi was varied in the underpotential deposition (UPD) region and the concentration of Sn was varied in the SnBi bimetallic material. The materials were characterised using field emission scanning electron microscopy coupled with energy dispersive spectroscopy (FE-SEM/EDS) for morphology and elemental distribution, focused ion beam scanning electron microscopy (FIBSEM) for thickness, X-ray diffraction (XRD) for crystallinity and inductively coupled plasma mass spectroscopy (ICP-MS) for composition measurements. Bi deposited at different UPD regions was structurally different. The deposits were crystalline SnBi materials containing Sn, Bi and other phases of Cu and Sn. Bi was concentrated on the surface, while Sn was distributed evenly across the film. The SnBi electrodes were tested as anode materials in Na-ion batteries using galvanostatic cycling (GC), CV and electrochemical impedance spectroscopy (EIS). Initial discharge capacities of 1900 mAh g 1 for SnBi (1:1) and 341 mAh g 1 for SnBi (3:1) electrodes at 38.5 mA g 1 were obtained, while the electrodes suffered capacity loss after 10 cycles.