复合稀土电解质、电极晶界和界面微结构与电性能及在中温固体氧化物燃料电池中的应用研究

As one of the most promising energy conversion devices, solid oxide fuel cells (SOFCs) with high efficiency, low pollutant and fuel flexibility have received a great attention in the past 20 years . To date, considerable efforts are focusing on reducing the operating temperatures of SOFCs to an intermediate range of 500-800 _C in order to prolong life time and to reduce the cost of SOFCs .Ceria-based solid solutions have been acknowledged to be the most promising electrolyte for intermediate temperature SOFC (IT-SOFC)since their ionic conductivity is higher than yttria stabilized zirconia at the intermediate temperature range . It is generally accepted that Gd- or Sm-doped ceria exhibits the highest conductivity due to the small association enthalpy between dopant cation and oxygen vacancy in the fluorite lattice .Acceptor-doped CeO2（DCO） is present in the form of polycrystals,so the grain boundaries often have a significant influence on the overall properties. In the low temperature regime, the specific grain-boundary conductivity is known to be 2-3 orders lower than the bulk conductivity .The grain boundary is a crucial part of the microstructure. The grain boundary has a blocking effect to the ionic transport across the electrolyte . Studies of grain-boundary behavior are essential to the design of ceramic materials and to the control and optimization of their performance. To a large extent, the blocking behavior of grain boundaries is attributed to the presence of thin siliceous films . The presence of SiO2 impurity is ubiquitous in precursor materials. The SiO2 contamination can also be introduced from furnace refractories during high temperature sintering. Therefore, it is difficult to eliminate the negative effect of grain boundaries to the total conductivity. As a result, attempts have been made to reduce the grain boundaries effect. At elevated temperature and low oxygen partial pressures Ce4+ in DCO tends to be partly reduced to Ce3+ and this results in some electronic conductivity. Electronic conductivity in electrolyte will lead to a reduction of the open-circuit voltage (OCV) and thus to an energy loss . A composition electrolytes DCO-TMOS(TMOS:transition metal oxide) may overcome these barriers. In this study, we fabricate the composite electrolytes with DCO-TMOS,studies well have been carried out on the effect of TMOS addition on the densification, microstructure and electrical properties of DCO-TMOS .To our knowledge, there is no report on the performances of SOFC with this kind of composite electrolytes. In this studies, we well give the correspondence of the grain-boundary conductivities with dopant concentrations and strcture of DCO-TMOS composite electrolytes.Electrolyte-supported solid oxide fuel cells fabricated with these composite electrolytes well be studied.

中低温固体氧化物燃料电池（SOFC）有良好的应用前景。SOFC中的化学能直接转换成电能的效率主要决定于固体电解质、电极的性能。项目以复合材料可设计理论为依据，应用第二项粒子效应，以双稀土中温电解质（DCO）为基体材料复合过渡族金属氧化物（TMOs），考虑晶界存在本征的空间电荷效应和杂质阻塞效应两种因素对晶界阻塞作用的影响，建立晶界电导与晶粒电导、空间电荷势及杂质阻塞项之间的方程关系，分析调控晶界、界面电导，提高电解质在中温区的离子导电性，发挥双稀土电解质在中温区离子导电率高的优势，克服双稀土电解质在还原气氛下的电子导电及机械强度差的弱点。研究DCO-TMOs复合电解质中物理性能的巨非线性增强效应的规律，提高电解质和电极晶界、界面电性能，应用于SOFC的研制中，系统研究电池的电化学特性，探索复合稀土中温电解质、电极物质体系及微观结构与性能的内在规律。为SOFC早日实用化提供科学数据。

中低温固体氧化物燃料电池（SOFC）有良好的应用前景。SOFC中的化学能直接转换成电能的效率主要决定于固体电解质、电极的性能。项目以复合材料可设计理论为依据，应用第二项粒子效应，以双稀土中温电解质（DCO）为基体材料复合过渡族金属氧化物（TMOs），考虑晶界存在本征的空间电荷效应和杂质阻塞效应两种因素对晶界阻塞作用的影响，建立晶界电导与晶粒电导、空间电荷势及杂质阻塞项之间的方程关系，分析调控晶界、界面电导，提高电解质在中温区的离子导电性，发挥双稀土电解质在中温区离子导电率高的优势，克服双稀土电解质在还原气氛下的电子导电及机械强度差的弱点。研究表明，电解质样品晶界电导性能取决于晶粒电导率、晶界处的硅杂质、空间电荷势和平均晶粒尺寸。同时考虑上述影响晶界电导率的因素，计算得到电解质的表观单位晶界电导率，研究少量NiO的加入对样品杂质阻塞效应和空间电荷势的影响。发现DCO 复合NiO（SDCN）可减小杂质阻塞效应，提高表观单位晶界电导率，并不改变空间电荷势。NiO可以限制电解质中的含硅杂质向电解质/电极界面处的扩散。以SDCN为电解质的对称电极电池的电极界面极化电阻小于以SDC为电解质的对称电极电池的电极界面极化电阻。复合NiO对DCO电解质晶界SiO2具有“束缚”作用，使阳极与电解质界面电阻、阴极与电解质界面电阻都减小，电池欧姆内阻降低、输出功率非常明显的增大。. 合成Ba0.8Sr0.2Co0.7Fe0.2Nb0.1O3-δ（BSCFN）-Ce0.85Sm0.15O1.925(SDC)复合阴极。实验结果表明，在BSCFN中复合SDC明显提高了电极的性能，掺入质量分数为30%SDC时复合电极的性能最好（BSCFN-30SDC）。复合SDC降低了BSCFN的热膨胀系数，提高了阴极与电解质的热匹配性。研究电极的反应动力学过程,电极的极化电阻随氧分压的变化。结果表明，氧分压大于0.05atm时氧离子和氧空位结合生成晶格氧过程为限速步骤，氧分压小于0.05atm时氧的解离吸附和扩散过程为限速步骤。复合SDC后阴极反应步骤由三步变为两步，提高了反应速率，电极的界面极化阻抗降低。BSCFN-30SDC为阴极的单电池的输出功率密度明显提高。