Surface Chemistry of La0.99Sr0.01NbO4-d and Its Implication for Proton Conduction.
Surface Chemistry of La0.99Sr0.01NbO4-d and Its Implication for Proton Conduction.
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DOI：
10.1021/acsami.7b04856
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发表时间：
2017-08
影响因子：
9.5
通讯作者：
Cheng Li;S. Pramana;N. Ni;J. Kilner;S. Skinner
中科院分区：
文献类型：
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作者：
Cheng Li;S. Pramana;N. Ni;J. Kilner;S. Skinner
受主掺杂的 LaNbO4 是一种有前途的质子传导燃料电池（PCFC）应用电解质材料。由于电荷转移过程控制器件性能，受主掺杂 LaNbO4 的最外表面将在确定电池的整体性能方面发挥重要作用。然而，表面成分的表征很差，并且对其对质子交换过程的影响的了解还很初级。在这项工作中，使用 LEIS 和 SIMS 对 1 原子％ Sr 掺杂的 LaNbO4（La0.99Sr0.01NbO4-d，表示为 LSNO）质子导体的表面化学进行了表征。使用同位素交换技术研究了表面层对质子传输的影响。结果表明，将样品在 1000 °C 的静态空气中退火 10 小时后，会形成约 6-7 nm 厚的富 Sr 但缺 La 的表面层。发现偏析开始于 600 至 800 °C 之间，并在 10 小时退火后形成平衡表面层。由于 Sr 在 LaNbO4 中的溶解度较低，因此提出了一种相分离机制来解释观察到的偏析行为。结论是表面层阻碍了水的结合过程，导致 D216O 湿交换过程后同位素分数减少，突出了表面化学对质子交换过程的影响。
Acceptor-doped LaNbO4 is a promising electrolyte material for proton-conducting fuel cell (PCFC) applications. As charge transfer processes govern device performance, the outermost surface of acceptor-doped LaNbO4 will play an important role in determining the overall cell performance. However, the surface composition is poorly characterized, and the understanding of its impact on the proton exchange process is rudimentary. In this work, the surface chemistry of 1 atom % Sr-doped LaNbO4 (La0.99Sr0.01NbO4-d, denoted as LSNO) proton conductor is characterized using LEIS and SIMS. The implication of a surface layer on proton transport is studied using the isotopic exchange technique. It has shown that a Sr-enriched but La-deficient surface layer of about 6-7 nm thick forms after annealing the sample under static air at 1000 °C for 10 h. The onset of segregation is found to be between 600 and 800 °C, and an equilibrium surface layer forms after 10 h annealing. A phase separation mechanism, due to the low solubility of Sr in LaNbO4, has been proposed to explain the observed segregation behavior. The surface layer was concluded to impede the water incorporation process, leading to a reduced isotopic fraction after the D216O wet exchange process, highlighting the impact of surface chemistry on the proton exchange process.