层状双钙钛矿型中温SOFC阴极表面元素偏析的机理及其抑制方法研究

The layered double perovskites LnBaCo2O5+δ (Ln = rare earth elements) have great potential as cathode materials for intermediate temperature solid oxide fuel cell (SOFC). However, the stability problem, especially the performance degradation caused by element segregation, has always restricted their large-scale application. At present, there are few reports about the element segregation mechanism of these cathodes. In view of this scientific problem, we intend to take LaBaCo2O5+δ and its Sr and Ca doped thin film materials as the research objects. Combining experiments with theoretical calculations, we study (1) the evolution of chemical composition and microstructure of cathode surface under the interaction of external factors (temperature, oxygen partial pressure, polarization current, etc.) and internal factors (elastic strain, electrostatic interaction, etc.); (2) the correlation of different external factors and their corresponding internal factors; (3) the qualitative/quantitative relationship between external/internal factors and element segregation; (4) the effect of element segregation on electrochemical catalytic performance of cathodes as well as its mechanism. Through above research work, on one hand, the mechanism of element segregation on the cathode surface and its effect on the cathode performance degradation will be revealed, which will enrich the basic theory of SOFC cathode. On the other hand, efficient methods to suppress the element segregation will be proposed, which will provide new ideas for the design of novel cathode materials in the future.

层状双钙钛矿型化合物LnBaCo2O5+δ（Ln为稀土元素）作为中温固体氧化物燃料电池（SOFC）阴极材料潜力巨大。但其稳定性问题，尤其是元素偏析导致的性能衰减，始终制约其大规模应用。目前，该类阴极表面元素偏析机理的研究国内外鲜有报道。针对该科学问题，本项目拟以LaBaCo2O5+δ及其Sr和Ca掺杂的薄膜材料为研究对象，实验和理论计算相结合，研究：①外因（温度、氧分压和极化电流等）和内因（弹性应变、静电相互作用等）交互作用下阴极表面化学组分和微观结构的演变规律；②不同外因和与之对应内因之间的关联性；③各外因/内因与元素偏析之间的定性/定量关系；④元素偏析对阴极电化学催化性能的影响规律及机制。通过上述研究，一方面揭示该类阴极表面元素偏析的微观机理及其对性能衰减的影响机制，丰富和完善SOFC阴极基础理论；另一方面提出抑制元素偏析的有效方法，为未来新型高稳定性SOFC阴极材料的设计提供新思路。

固体氧化物燃料电池（SOFC）是一种全固态的能量转换装置，可直接将储存在燃料和氧化剂中的化学能高效、环境友好地转化成电能，被公认为21世纪的绿色能源技术。在微观层面上揭示SOFC阴极材料表面元素偏析的机理，提出抑制偏析的有效方法，从根本上解决由于元素偏析导致的性能衰减，对于SOFC的发展应用具有重要的意义。本项目围绕双钙钛矿型SOFC阴极表面元素的偏析及其对SOFC性能的影响开展了大量的实验，取得了如下成果：（1）温度越高，LBCO电极表面元素的偏析程度越大，由此导致其电化学性能衰减迅速；（2）低氧分压下，LBCO电极表面元素偏析程度越大，由此导致其电化学性能衰减迅速；（3）阳极极化电流处理促进LBCO电极表面元素偏析，而阴极极化电流处理可以抑制电极表面元素的偏析；（4）高浓度CO2气氛下，LBCO电极材料表面更易发生元素的表面偏析，从而不利于其电化学催化。（5）A位离子尺寸匹配性越好，越有利于抑制双钙钛矿型SOFC阴极材料表面的元素偏析。（６）A位引入阳离子缺位，有利于改善电极材料表面元素偏析，提升电化学催化性能。本项目的研究，对于未来高稳定性SOFC阴极材料的研发具有重要意义。