稀土镓酸盐中离子传导机制的研究与新型固体电解质设计

Solid oxide fuel cell, as a new generation energy source with the characters of high efficiency, low pollution and long-term development, is a hopeful energy-conversion device that will be the substitution of fossil fuel based power plant， engine, etc. Current solid electrolytes can not fulfil the requirement for application. Developing novel solid electrolyte with high performance demands deep understanding of the mechanism of ion transport in lattice. However, most reports focus on the influence of lattice structure on the conductivity of solid electrolyte, and no comprehensive theory exists at the present time. In this proposal, lattice structure and susceptibility are both considered for the design of novel solid electrolytes. Rare earth gallates, which are the most hopeful for application, is selected for investigation. The lattice structure and susceptibility are tuned by doping rare earth ions with small radius and s2 ions, respectively. Doping rare earth ions with small radius can increase the orthorhombic-rhombohedral transition temperature higher than the operating temperature, hinder hole conduction at low oxygen partial pressure, lower activation energy, making it more competitive in the middle and low temperatures. The introdution of s2 ions can lower the barrier for oxygen vacancy immigration, hence increase the conductivity. By summarizing the effects of the two factors, solid electrolytes with higher performance than LaGaO3-based materials are expected to be found, which will be operated at middle and low temperature range.

作为高效、低污染、可持续发展的新一代能源，固体氧化物燃料电池是有望在未来替代热电厂、燃油发动机等的能量转换装置。现有的固体电解质还不能满足其实用化的要求。发展高性能的固体电解质，需要深刻理解离子在晶格中迁移机制。目前尚缺少一个完善的理论描述，多数报道局限于讨论晶格结构对电导率的影响。针对这一情况，本研究将兼顾晶格结构和晶格离子极化率两个方面。选择最具发展潜力的稀土镓酸盐电解质为研究对象，利用小半径稀土掺杂改变晶格结构，利用高极化率的s2离子掺杂来调节极化率。小半径稀土的引入将提高正交-菱方相变到工作温度以上、降低高氧压下的空穴导电，并能降低导电活化能，使其在中低温范围内的电导率更具竞争力。在晶格中引入s2离子会降低离子扩散的势垒，从而提高电导率。系统总结这两个因素对电导率影响的规律性，以期找到可替代掺杂LaGaO3、工作于中低温区的、性能优良的固体电解质。

利用高温和高压手段，成功合成了B位Mg单掺杂、A位稀土和B位Mg双掺杂的稀土镓酸盐电解质。然后对以上样品和Sr/Mg双掺杂LaGaO3进行过渡金属Co掺杂改性。结果表明，A位的最佳离子半径约为1.19 Å，介于La3+和Pr3+之间。La0.3Pr0.7Ga0.835Mg0.15Co0.015O3和PrGa0.86Mg0.1Co0.04O3两种材料的性能优越。其中PrGa0.86Mg0.1Co0.04O3在700℃和600℃时电导率分别为0.1 Scm-1和0.07 Scm-1，与La0.8Sr0.2Ga0.8Mg0.2-xCoxO3体系相当，而且在工作温区不存在结构相变；以La0.3Pr0.7Ga0.835Mg0.15Co0.015O3为电解质材料的电池在600℃的短路电流密度达到161 mAcm-2，最大输出功率密度为38.7 mWcm-2，使得这两种材料在中低温下具有竞争力。根据结构数据提出了稀土镓酸盐电解质中的氧离子传输模型，即需同时考虑氧离子通道的尺寸和长度，这些因素决定了离子传导的活化能。这个模型对固体电解质的设计是有帮助的。