Electronic Theses and Dissertations (Masters)

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    Synthesis of platinum-based electrocatalysts using nitrogen doped onion-like carbon and WS2 composites as the support for electrooxidation of ethanol in direct alcohol fuel cells
    (University of the Witwatersrand, Johannesburg, 2024-10) Bila, Laercia Rose; Gqoba, Siziwe; Maubane-Nkadimeng, Manoko S.
    The study reports on the synthesis of onion-like carbons (OLCs)/tungsten disulfide (WS2) composites as catalyst support for direct alcohol fuel cells (DAFC). OLCs were synthesized using waste engine oil over a flame pyrolysis (FP) method. The pristine OLCs (p-OLCs) were functionalized and purified using nitric acid (HNO3). The functionalized OLCs (F-OLCs) were further doped with nitrogen using melamine to increase the electronic properties of the OLCs. WS2 was synthesized using the colloidal method and oleylamine was used as the capping agent. Pt/p-OLCs, Pt/F-OLCs, and Pt/N-OLCs were synthesized using a reflux method where ethylene glycol was the reducing agent. Finally, WS2/N-OLCs were synthesized using the colloidal method and then Pt was dispersed on WS2/N-OLCs to form Pt/WS2/N-OLCs. High-resolution transmission electron microscopy showed the presence of onion-like rings in the OLCs and the quasi-spherical morphology, while a flower-like morphology was observed for WS2. Powder X-ray diffraction revealed that the synthesized WS2 had traces of WO3 due to the oxidation of WS2 which introduces WO3 impurities. Energy Dispersive X-ray Spectroscopy revealed that the OLCs derived from waste engine oil present some impurities that were attributed to the motor wear as well as the fuel. When Pt was loaded onto the WS2/N OLCs composite, the WS2 lost its original nanoflower morphology, which was attributed to the presence ethylene glycol used as a reducing agent. X-ray photon spectroscopy confirmed the successful synthesis of the Pt electrocatalysts. Cyclic voltammetry was used to determine the oxidation of ethanol and the current density of the synthesized electrocatalysts. Interestingly, the Pt/p-OLCs electrocatalyst had a higher current density compared to Pt/F-OLCs and Pt/N-OLCs. This was attributed to metal impurities found in p-OLCs, which were reduced during the purification process. The Pt/WS2/N-OLCs electrocatalyst showed higher current density compared to Pt/WS2 but this was low compared to Pt/N-OLCs. The data reveals that the addition WS2 shows a co-catalyst behaviour, rather than a support.