Consolidated nanomaterials synthesized using nickel micro-wires and carbon nanotubes
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Nano-devices are the next step in the application of nanomaterials in modern technology. One area of research that is receiving an increased amount of attention globally is the fabrication of new nano-devices for applications in hydrogen energy technologies. The current work focuses on the synthesis and characterization of nano-devices with potential application in alkaline electrolysis and secondary polymer lithium ion batteries. Previous work with Nickel micro-wires demonstrated the potential to use these nanomaterials as electrodes in alkaline electrolysis. Carbon nanotubes have been shown to posse excellent electrochemical properties. A new direction in research is explored by combining nickel micro-wires with CNT, a new consolidated composite carbon nanocomposite can be realized and the characterization of such a novel composite was the focus of this thesis. Novel composite carbon nanomaterials were synthesized using an electrochemical template technique and a hydrocarbon pyrolysis step. The first step involved the deposition of nickel within the pores of ion track etched Polyethylene terephthalate (PET) membrane; with pore diameters of 1μ, 0.4μ and 0.2 μ. Electrochemical deposition of nickel was carried out galvanostatically in a nickel hard bath between 35-40°C, and using a deposition current density of 75 mAcm2. Carbon nanotubes were then deposited directly onto the surface of the nickel micro-wires via a chemical vapour deposition (CVD) technique using liquid petroleum gas (LPG) as the carbon source. CVD was done at a temperature of 800°C and the deposition time was 5 minutes. The morphology and structural studies of these novel composite nanomaterials were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Electrochemical investigations were done using Cyclic Voltammetry (CV), Chronoamperometry (CA) and Electrochemical Impedance Spectroscopy (EIS). After removal of the template, before CNT CVD growth, SEM images revealed free standing arrays of nickel micro-wires, and after CNT growth via CVD the SEM micrographs showed that the morphology of the Ni micro-wires was moderately altered by the CVD process. From the XRD results it was shown that the crystallinity of the Nimicro-wires was persevered after the CVD process. The XRD of the nickel micro-wires with CNT grown directly on the surface revealed the characteristic CNT peak at 2θ =24.60. Cyclic Voltammetry (CV) was performed on the consolidated composite nanomaterial in an alkaline solution. The CV revealed that the novel composite carbon nanomaterial was the most active for hydrogen evolution when compared to unmodified Ni micro-wires and a flat nickel electrode. This was attributed to the increase in electrochemical accessible surface area. Electrochemical impedance spectroscopy (EIS) showed that the novel composite carbon nanomaterial had a much higher capacitance than the nickel micro-wires, a flat nickel electrode, a flat nickel substrate modified with CNT, and a graphite electrode. When a similar comparison was done using a commercially available anode for lithium ion battery applications, the novel consolidated composite carbon nanomaterial had double the capacitance of the commercial anode. The consolidated composite carbon nanomaterial was modified by depositing Pt on to the surface of the CNT via electroless deposition. The presence of Pt was determined by Energy dispersive spectrometry and the electrocatalytic activity of the Pt modified consolidated composite carbon nanomaterial was significantly improved. The work presented in this thesis provides a new and unique direction in the synthesis and application of novel consolidated carbon nanomaterials through true synergistic effect between nickel micro-wires and CNT. The exploration of the characteristics of the system and the ability to functionalize the CNT with different moieties allows for a wide range of application in energy conversion devices.