Density Functional Theory calculations are employed in the investigation of the ethanol oxidation reaction (EOR) at the anode of Direct Ethanol Fuel Cells (DEFC), with a view to mechanistic understanding of the reaction pathways, determination of the factors governing the onset potential of activity and selectivity towards C02, and ultimately the design of an optimal electrocatalyst in these regards. The lowest energy pathway of ethanol decomposition on platinum is identified and it is found that the reaction kinetics do not significantly vary with catalyst morphology. The aqueous medium is found to somewhat facilitate all reaction pathways. Surface hydroxyl is found to oxidise ethanol to acetaldehyde. Surface atomic oxygen is found to selectively oxidise adsorbed carbon monoxide to carbon dioxide. The onset potentials of surface hydroxyl and atomic oxygen on platinum are calculated to be in good agreement with experimental data. It is determined that onset potentials of < 0.1 V vs. SHE will result in inactive hydroxyls, while an onset potential of < 0.2 V results in inactive surface atomic oxygen, providing a target for catalyst optimisation. Onset of EOR is found to occur at potentials between 0.4 V and 0.5 V earlier on a range of platinum tin catalysts than on platinum, and Pt3Sn is found to be kinetically the best example of such a catalyst These findings are in good agreement with experimental observations. The addition of rhodium to platinum is found to result in a hydroxyl onset potential below the 0.1 V threshold for activity, and the near-optimal onset potential of surface atomic oxygen, resulting in excellent selectivity towards C02. However, the stability of the hydroxyl species delays the formation of atomic oxygen and so delays the onset of ethanol oxidation activity to an unacceptably high degree. This effect is believed to be general to metallic systems.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:678702 |
| Date | January 2014 |
| Creators | Kavanagh, R. J. |
| Publisher | Queen's University Belfast |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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