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Title: The synthesis and evaluation of proton conducting electrolytes for high temperature steam electrolysers
Author: Stuart, Paul Anthony
ISNI:       0000 0004 2682 2889
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2010
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Proton conducting ceramics based on acceptor doped perovskites are the subject of investigation as candidate electrolyte materials for Solid Oxide Electrolyser Cells (SOECs). Specifically, BaCe0.9Y0.1O3-[delta](BCY10) and BaZr0.9Y0.1O3-[delta](BZY10) were investigated. Samples with greater than 95% of the maximum theoretical density were successfully prepared using a BCY10 commercial powder. It was found that when small additions of ZnO were added to a BZY10 commercial powder, a density of greater than 95% of the theoretical maximum was achievable whereas without ZnO addition, the maximum achievable density was 85%. BCY10 was found to have a total conductivity approximately one order of magnitude greater than Zndoped BZY10 over the entire temperature range studied. Spray pyrolysis and sol-gel methods were used successfully to prepare single phase pure BZY10 powders. The sintering behaviours of the powders produced by spray pyrolysis were found to alter significantly with changes in powder processing parameters. BCY10 and Zn-doped BZY10 cells were tested in electrolysis and fuel cell modes and the effects of varying operating conditions on cell performances were studied. At 750oC, the Area Specific Resistances (ASR) of a BCY10 cell in electrolysis mode was found to be lower when the anode compartment was humidified to [approximately equal]83% than to[approximately equal]3%. Below this temperature, ASR values were greater when using increased humidity levels. It was concluded that a degree of oxide ion conduction may be beneficial to the operation of proton conducting electrolysers. Post-test, BCY10 cell cross-sections were imaged using scanning electron microscopy and analysed using Energy Dispersive X-ray (EDX) spectroscopy. Significant erosion of grain boundaries regions close the electrode-electrolyte interfaces was observed and EDX spectroscopy results suggested the formation of a secondary phase in these regions, possibly Y:CeO2. Had testing continued over an extended period of time it is probable that BCY10 cells would have undergone mechanical failure.
Supervisor: Skinner, Stephen Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral