掺杂改性Sr2MgMoO6双钙钛矿型SOFC阳极材料的电导率和催化活性增强机理研究

Double perovskite Sr2MgMoO6 as an anode of solid oxide fuel cells (SOFCs) has been attracted great attentions in recent years. However, it shows low electronical conductivity and poor electrocatalytic activity, which limit its practical application. In this project, A-site donor doping is adopted to increase the electronic conductivity, meanwhile doping transition metal with 3d empty orbit at Mg-site is introduced to increase the ionic conductivity and catalytic activity of SMMO-based materials. In order to further improve the electrochemical performance, template is introduced to prepare electrode with three-dimensional ordered mesoporous structure to increase the specific surface area and fabricate the electrode pores, resulting in the improvement of the electrochemical performance. The nanoelectrocatalyst GDC is loaded on the SMMO base by using ultrasonication combined with ion-impregnation method. Therefore, the three-phase interface is increased, which enhances the electrochemical performance of the electrode. The effects of the doping elements on the electric conductivity, catalytic performance, chemical stability, chemical compatibility and thermal expansion with electrolyte are investigated. The influence of specific surface area, porosity and the tortuousity on the electrode performance is also studied. The impact of grain size and distribution of the GDC on the electrode performance is analyzed, and the mathematical model is established about the relation of the length of the three-phase interface and the growth of the GDC grains. This study can provide a theoretical basis for the development of double perovskite based anode with high performance.

双钙钛矿结构的Sr2MgMoO6是近年来固体氧化物燃料电池阳极材料的研究热点。但其电导率和催化活性偏低，这将限制该类材料的应用。本项目拟针对这两个问题展开研究。采用A、B位共掺杂以期同时提高材料的电子电导、离子电导率。为了进一步提高SMMO阳极材料的电化学性能，采用模板法制备三维有序介孔结构的SMMO阳极，提高阳极材料的比表面积，改善电极的孔结构，提高其催化性能，降低极化电阻。通过超声辅助真空浸渍法在阳极基体中低温负载GDC纳微电催化剂，增加三相反应界面，提高电极的电化学性能。系统分析掺杂元素对SMMO电导率，催化性能、化学稳定性、与电解质的化学相容性和热膨胀匹配性等性能的影响。研究阳极材料比表面积，阳极骨架的孔隙率和曲折度对电极性能的影响。研究GDC粒径和分散度对电极性能的影响并给出三相线长度随GDC颗粒生长变化的数学模型。本研究可望为设计新型高性能双钙钛矿型阳极材料提供一定的理论指导。

Sr2MgMoO6-δ(SMMO)双钙钛矿型阳极材料具有良好的抗氧化还原循环能力，并且有好的抗碳沉积和硫中毒能力。但是该材料的电子电导率比较低，且催化活性的好坏还存在着很大的争议，这些都将影响其实际阳极工作特性。本项目针对这些问题展开了系列研究。采用柠檬酸低温燃烧法制备掺杂的SMMO阳极材料。研究表明，在A位掺杂La可以大幅提高材料的电子电导率，并且降低了阳极材料的极化电阻，提高了电池的功率密度。通过在B位进行Al、Co、Ni的掺杂，提高了SMMO阳极材料的电子、离子电导率和电池的功率密度。掺杂的SMMO和电解质La0.8Sr0.2Ga0.8Mg0.2O3-δ(LSGM)、Gd0.2Ce0.8O2-δ (GDC)都具有良好的化学相容性，但与电解质YSZ会发生反应。一般来说含Co材料的热膨胀系数较大，但热膨胀测试表明，Co掺杂略微提高SMMO材料的热膨胀系数，Sr2Mg0.3Co0.7MoO6在50-1300 °C温度范围内的平均热膨胀系数为13.9×10-6 K-1，比未掺杂的SMMO (12.9×10-6 K-1) 略大一些，与电解质LSGM的热膨胀系数很接近。制备了不同比例的Sr2Mg0.3Co0.7MoO6-δ/GDC复合阳极材料。研究表明，通过GDC的引入，提高了电极材料的氧离子电导率，改善了电极反应速度，当Sr2Mg0.3Co0.7MoO6与GDC质量比为4:1时，电池性能最佳。本项目研究开发出的结构稳定、抗碳沉积和硫中毒能力强的新型双钙钛矿型阳极材料对于SOFC的商业化具有重要的意义。