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Formation of apatite oxynitrides by the reaction between apatite-type oxide ion conductors, La8+xSr2-x(Si/Ge)6O26+x/2, and ammonia

Orera, A and Headspith, D and Apperley, D.C. and Francesconi, M.G. and Slater, P.R. (2009) Formation of apatite oxynitrides by the reaction between apatite-type oxide ion conductors, La8+xSr2-x(Si/Ge)6O26+x/2, and ammonia. Journal of Solid State Chemistry, 182. pp. 3294-3298.

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URL of Published Version: http://www.sciencedirect.com/science/article/pii/S0022459609004642

Identification Number/DOI: 10.1016/j.ssc.2009.09.029

Following growing interest in the use of ammonia as a fuel in Solid Oxide Fuel Cells (SOFCs), we have investigated the possible reaction between the apatite silicate/germanate electrolytes, La8+xSr2-x(Si/Ge)6O26+x/2, and NH3 gas. We examine how the composition of the apatite phase affects the reaction with ammonia. For the silicate series, the results showed a small degree of N incorporation at 600○C, while at higher temperatures (800○C), substantial N incorporation was observed. For the germanate series, partial decomposition was observed after heating in ammonia at 800○C, while at the lower temperature (600○C), significant N incorporation was observed. For both series, the N content in the resulting apatite oxynitride was shown to increase with increasing interstitial oxide ion content (x) in the starting oxide. The results suggest that the driving force for the nitridation process is to remove the interstitial anion content, such that for the silicates the total anion (O+N) content in the oxynitrides approximates to 26.0, the value for an anion stoichiometric apatite. For the germanates, lower total anion contents are observed in some cases, consistent with the ability of the germanates to accommodate anion vacancies. The removal of the mobile interstitial oxide ions on nitridation suggests problems with the use of apatite-type electrolytes in SOFCs utilising NH3 at elevated temperatures.

Type of Work:Article
Date:02 October 2009 (Publication)
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Chemistry
Keywords:apatite, solid oxide fuel cell, electrolyte, ammonia
Subjects:QD Chemistry
Institution:University of Birmingham
Copyright Holders:Elsevier
ID Code:779
Refereed:YES
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