Palladium-based carbon and ceria nanocomposites as electrocatalysts for fuel cell applications

Ogada, Jimoo Joretta
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The electrooxidation of alcohol in alkaline media is vital for the development of alkaline direct alcohol fuel cells (ADAFCs). This research investigated and compared the electrocatalytic properties of different alternatives of palladium catalysts supported on carbon black (CB) and onion-like carbon (OLC), and their CeO2 added counterparts - Pd/CB, Pd/OLC, Pd-CeO2/CB and Pd CeO2/OLC - towards ethanol oxidation. All the nanocatalysts were characterized by powder x-ray diffraction (PXRD), thermogravimetric analysis (TGA), Raman spectroscopy, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), x-ray absorption spectroscopy (XAS) and x-ray photoelectron spectroscopy (XPS). The addition of CeO2 significantly enhanced anodic performance as compared to carbon-only-based support for palladium. Half-cell reactions were studied, and Pd-CeO2/OLC was observed to be the best of the four nanomaterials for EtOH oxidation reaction in terms of current densities (highest current density), smaller peak-to-peak separation (faster electron transport), higher jf/jb value (less poisoning from products of the intermediate reaction) and the lowest resistance to current flow as seen in the EIS results. The Pd nanocatalysts were explored for hydrogen oxidation and oxygen reduction in alkaline environment. Pd-CeO2/OLC showed the best behaviour towards both experiments, evidenced by higher current density. The addition of CeO2 to the electrocatalysts enhances their performances toward the alkaline HOR and ORR. For ORR, the catalysts containing OLC showed better electrocatalysis
A dissertation submitted in fulfilment of the requirements for the degree of Master of Science to the Faculty of Science, School of Physics, University of the Witwatersrand, Johannesburg, 2021