Detailed examination of the conduction processes in solid oxides identified as potentially beneficial materials for use as electrolytes in solid oxide fuel cells (SOFC's), is of tremendous interest. The current study focuses on materials that are of potential interest in forming the electrolyte layer of a SOFC, or as gas sensors or separation membranes. Currently, the most common electrolyte material used in SOFC applications is yttria stabilized zirconia (YSZ). To achieve reasonable levels of conduction through this material, high operating temperatures ≥ 800°C are required. However, devices containing materials which demonstrate reasonable conduction at slightly lower temperatures (≈ 600°C) could potentially be constructed from a wider range of materials i.e. stainless steel. Given the unique and sensitive ability NMR has to examine the subtle dynamic aspects of a system on a localized level, we have undertaken to use this technique to answer some difficult questions regarding several complex ionically conducting solid oxide materials. First, a uniquely constructed, column-containing system of the formula Bi26Mo10O69 was studied because it is compositionally related to materials which have been found to be highly conducting, but has a very unusual structure. This material demonstrated unexpected levels of ionic motion at a tremendously wide range of temperatures. Next, the oxide conduction aspects of the parent as well as lanthanum and gallium doped forms of barium indium oxide (Ba2In2O5) were examined in depth. While NMR spectra have previously been acquired of the end member of this material, a re-examination at higher field strengths revealed new structural information. Lanthanum and gallium doped analogs were examined by 17O and 71Ga NMR for the first time. Finally, proton conduction in hydrated analogs of barium indium oxide (Ba2In 2O5·H2O) was examined by variable temperature NMR. Proton conducting hydrates of oxide materials are very useful as electrolytes in intermediate temperature solid oxide fuel cells (ITSOFC). Proton spectra have previously been acquired for this system at room temperature, however, no interpretation as to the structural or dynamic implications of these spectra have yet been undertaken until the current study.
|Advisor:||Grey, Clare P., Parise, John B.|
|School:||State University of New York at Stony Brook|
|School Location:||United States -- New York|
|Source:||DAI-B 70/05, Dissertation Abstracts International|
|Keywords:||Electrolytes, Fuel cells, Ion conduction, Solid oxides|
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