Durability testing of low temperature solid oxide cells is challenging as degradation phenomena related to microstructural changes like nickel-agglomeration are slow. In the present study, a nickel/gadolinia doped ceria (GDC) fuel electrode with a porous GDC-interlayer towards the zirconia electrolyte was investigated. The electrode, designed for operating temperatures of 600°C, was tested at an elevated temperature of 900°C for up to 1100 h to accelerate aging. Contrary to every expectation, the electrodes showed continuous improvement in electrochemical performance. Impedance spectroscopy, the distribution of relaxation times analysis, scanning electron microscope and transmission electron microscope were applied to correlate electrochemical and microstructural changes. Structural analysis showed a significant Ni agglomeration accompanied by a decrease in triple phase boundary density. Furthermore, a minor particle growth in the GDC-phase decreased the volume-specific double phase boundary GDC/pore. Considering these microstructural changes, the decrease in active reaction sites should have increased the polarization resistance, but a decrease of about 32% was observed. The discrepancy between polarization resistance improvement and microstructural degradation might be attributed to an activation of the GDC-surfaces in the electrode and the porous GDC-interlayer.

中文翻译：

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高温下镍-二氧化铈燃料电极的微观结构变化

低温固体氧化物电池的耐久性测试具有挑战性，因为与镍团聚等微观结构变化相关的降解现象很慢。在本研究中，研究了镍/氧化钆掺杂二氧化铈（GDC）燃料电极，其具有朝向氧化锆电解质的多孔GDC夹层。该电极设计工作温度为 600°C，在 900°C 的高温下进行了长达 1100 小时的测试，以加速老化。与所有人的预期相反，电极的电化学性能不断提高。应用阻抗谱、弛豫时间分布分析、扫描电子显微镜和透射电子显微镜来关联电化学和微观结构的变化。结构分析显示镍明显团聚，同时三相边界密度降低。此外，GDC 相中的小颗粒生长减少了体积特定的双相边界 GDC/孔。考虑到这些微观结构的变化，活性反应位点的减少应该会增加极化电阻，但观察到减少了约 32%。极化电阻改善和微观结构退化之间的差异可能归因于电极中 GDC 表面和多孔 GDC 夹层的活化。