The research aims to explore the impact of sulphur on the Ni-based anodes used in solid oxide fuel cells (SOFCs). The work combines thermodynamic calculation, electrochemical measurements, anode microstructure analysis, and in-situ Raman techniques, to explore the interaction of hydrogen sulphide with nickel based anodes under SOFC operating conditions. Thermodynamic calculations have been made to predict the stability of SOFC·anode materials (Ni, Ceria, Zirconia) when exposed to hydrogen sulphide (H2S) in hydrogen/steam mixtures over a range of partial pressures of sulphur (pS2) and oxygen (p02) representative of fuel cell operating conditions. Measurements on a single fuel cells and anode half cells have been carried· out to study the effect of operating conditions (pH2S, pH2 • pH20, temperature) on the degree and nature of sulphur interaction with the anodes, correlating this with the thermodynamic predictions and microstructural analysis. Microstructural analysis used scanning electron microscopy on anode cermets, supported by work on Ni pellets, to explore anode surface structure alteration under the same test conditions as those used for electrochemical measurement. This allowed changes in anode microstructure induced by sulphur to be coupled to changes in anode electrochemical performance. Both ex-situ and in-situ Raman spectroscopy was also used to detect chemical species formed on the anode surface when exposed to sulphur. The work shows a correlation between electrochemical response and thermodynamic calculation. Nickel and ceria show differing behaviour depending on pH2S, pH2, pH20, or temperature. The impedance response of Ni anodes in hydrogen SUlphide atmospheres also shows a link with anode microstructure. Electrodes with relatively lower initial performance degraded at lower H2S concentrations than those with higher initial performance suggesting that the detrimental effect of sulphur on the anode is dominated by its interaction with three phase boundaries. Anode surface alteration induced by sulphur such as 'faceting' on Ni, and Ni agglomeration, was also observed and correlated with the impedance response. Raman spectroscopy offers promise as a probe to monitor surface electrolyte temperature as well as sulphur species on the nickel species.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:486595 |
| Date | January 2008 |
| Creators | Lohsoontorn, Pattaraporn |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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