Formation of apatite oxynitrides by the reaction between apatite-type oxide ion conductors, La8+xSr2−x(Si/Ge)6O26+x/2, and ammonia |
| |
Authors: | A. Orera D.C. Apperley P.R. Slater |
| |
Affiliation: | a School of Chemistry, University of Birmingham, Birmingham B15 2TT, UK b Department of Chemistry, The University of Hull, Cottingham Road, Hull, UK c Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK |
| |
Abstract: | 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/2) 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. |
| |
Keywords: | Apatite Ammonia Solid oxide fuel cell |
本文献已被 ScienceDirect 等数据库收录! |
|