Siebenhofer Matthäus, Riedl Christoph, Nenning Andreas, Artner Werner, Rameshan Christoph, Opitz Alexander Karl, Fleig Jürgen, Kubicek Markus
Institute of Chemical Technologies and Analytics, TU Wien Vienna Austria
Centre for Electrochemistry and Surface Technology, CEST Wr. Neustadt Austria.
J Mater Chem A Mater. 2023 Feb 13;11(24):12827-12836. doi: 10.1039/d2ta09362f. eCollection 2023 Jun 20.
Minimizing the overpotential at the air electrode of solid oxide fuel cells (SOFC) is one of the key challenges regarding a broad applicability of this technology. Next to novel materials and geometry optimization, surface modification is a promising and flexible method to alter the oxygen exchange kinetics at SOFC cathode surfaces. Despite extensive research, the mechanism behind the effect of surface decorations is still under debate. Moreover, for Sr decoration, previous studies yielded conflicting results, reporting either a beneficial or a detrimental impact on the oxygen exchange kinetics. In this contribution, impedance spectroscopy during pulsed laser deposition was used to investigate the effect of Sr containing decorations under different deposition conditions. Depending on deposition temperature and interactions with the gas phase, opposing effects of Sr decoration were found. In combination with near-ambient pressure X-ray photoelectron spectroscopy and non-ambient X-ray diffractometry, it was possible to trace this phenomenon back to different chemical environments of the surface Sr. At high temperatures, Sr is deposited as SrO, which can have a beneficial effect on the oxygen exchange kinetics. At low temperatures, SrCO adsorbates are formed from trace amounts of CO in the measurement atmosphere, causing a decrease of the oxygen exchange rate. These results are in excellent agreement with the concept of surface acidity as a descriptor for the effect of surface decorations, providing further insight into the oxygen exchange kinetics on SOFC cathode surfaces and its degradation. In addition, this study shows that Sr segregation itself initially does not lead to performance degradation but that segregated SrO readily reacts with acidic compounds, reducing the catalytic capability of mixed conducting oxides.
将固体氧化物燃料电池（SOFC）空气电极上的过电位降至最低，是该技术广泛应用面临的关键挑战之一。除了新型材料和几何结构优化外，表面改性是一种很有前景且灵活的方法，可改变SOFC阴极表面的氧交换动力学。尽管进行了广泛研究，但表面修饰效果背后的机制仍存在争议。此外，对于Sr修饰，先前的研究结果相互矛盾，报道了其对氧交换动力学的有益或有害影响。在本论文中，利用脉冲激光沉积过程中的阻抗谱研究了不同沉积条件下含Sr修饰的影响。根据沉积温度和与气相的相互作用，发现了Sr修饰的相反效果。结合近常压X射线光电子能谱和非常压X射线衍射，有可能将这种现象追溯到表面Sr的不同化学环境。在高温下，Sr以SrO的形式沉积，这对氧交换动力学可能有有益影响。在低温下，测量气氛中痕量的CO会形成SrCO吸附物，导致氧交换速率降低。这些结果与表面酸度概念作为表面修饰效果描述符的观点高度一致，为深入了解SOFC阴极表面的氧交换动力学及其降解提供了进一步的依据。此外，本研究表明，Sr偏析本身最初不会导致性能下降，但偏析的SrO很容易与酸性化合物反应，降低混合导电氧化物的催化能力。
