可逆固体氧化物电池中混合导体氧电极的活化-去活化现象及偏析抑制

Oxygen electrode is the key component of reversible solid oxide cells (RSOC), and the surface chemistry at high temperature plays a critical role in determining the electrode activity and stability of electrodes. The activation-deactivation behaviors of oxygen electrodes are mainly focused on (La,Sr)MnO3 based electronic conductors which is closely related with Sr surface segregation, while the current reports on mixed conductive electrodes are rare. We recently found that layered GdBaCo2O5+ (GBCO) mixed conductors show obvious segregation phenomena, which deserves further study. In this project, we choose GBCO as model electrodes and aim to study the following unsolved issues. 1) The effects of surface segregations under cathodic-anodic polarizations on electrode activity, surface composition, microstructure and its reversibility.2) The segregation difference among different orientation of GBCO electrodes, the re-dissolving of segregation to the host lattice and the effect of segregation on oxygen reactions. 3) Through two ways of surface F- anion diffusing into oxygen vacancy and high valent Nb5+,Hf4+ substitution of Co3+/Co4+ to decrease the concentration of surface oxygen vacancy, and thus suppressing the surface segregation, improving the activity and durability. With this project, the relationship of working environment- surface chemistry- electrode activity will be clarified, the understanding of cation segregations in mixed conductors and its effect on activation-deactivation behavior will be deepened. The finding of effective ways for segregation suppression will surely provide favorable support for the development of highly active and durable oxygen electrodes of RSOC.

氧电极是可逆固体氧化物电池(RSOC)的关键部件，而极化条件下电极表面化学演变是影响电极活性和稳定性的重要因素。目前表面偏析引起的电极活化-去活化研究主要集中在传统电子导电型(La,Sr)MnO3体系，而关于混合导体的报道较少。最近申请人在混合导体GdBaCo2O5+d (GBCO)中发现明显偏析现象，值得深入研究。本项目计划以GBCO为模型材料，针对以下问题进行研究：1）阴极-阳极极化下表面偏析对表面组分、微结构和电极活性的影响以及可逆性，2）不同晶面偏析差异、对氧电极反应影响及理论解释；3）通过氟离子进入表面氧空位和高价Nb5+、Hf4+替代表面Co离子两种途径来减小表面氧空位浓度，进而抑制偏析。希望通过实验和理论研究建立混合导体的工作环境-表面化学-电极活性内在关联，加深对偏析规律和电极活化-去活化现象的理解，探索偏析抑制新途径，为开发高性能、高稳定性的RSOC氧电极提供有益参考。

可逆固体氧化物电池(RSOC)是一种高效、清洁的能量转化装置，而氧电极则是关键部件之一，其极化条件下电极表面化学演变是影响电极活性和稳定性的重要因素。本项目双钙钛矿结构GdBaCo2O5+d等电极为模型材料，针对以下问题进行了研究并取得进展。1）系统研究了双钙钛矿氧电极的表面偏析与Cr沉积的规律和内在关联，BaO偏析与Cr的反应活性大于Co,生成物为BaCrO4和CoCr2O4尖晶石；2)系统考察了电极极化以及水蒸气对双钙钛矿氧电极表面偏析的影响，大电流阳极极化处理对电极微结构影响更大且电极衰退更快，水蒸气会促进阳离子偏析；3)通过理性成分设计，氧空位调控和A/B位中高熵策略有效抑制表面偏析并显著提高稳定性。中高熵氧电极具有优异的电极活性，电极表面的阳离子偏析程度大大减小，电极耐Cr和耐CO2中毒能力显著提高。本研究加深了对双钙钛矿基氧电极材料高温性质的理解，对RSOC及相关研究起到了很好的促进作用。在本项目资助下共发表SCI论文12篇，培养博士2人，硕士5人。