【作者】 李世萍；

【导师】 罗孟飞；

【作者基本信息】 浙江师范大学 ， 物理化学， 2009， 硕士

【摘要】 固体氧化物燃料电池（SOFC）是一种高效、清洁的能源转换装置。该领域的研究趋向是追求操作温度中温化,以克服传统高温SOFC（操作温度约1000℃左右）的种种技术和材料问题,并进一步提高性能和降低制造成本。实现中温化主要有两条途径:一是寻找在中温时具有高的氧离子电导率的新型电解质,主要集中在具有立方萤石结构的掺杂CeO₂材料上:另一种是将电解质薄膜化。迄今,大量文献报道了关于掺杂CeO₂基电解质的研究,然而就其理论解释仍然存在很多不足之处。本论文立足于掺杂CeO₂基电解质的研究,试图从电解质的掺杂离子浓度、制备方法、化学组成、氧空位浓度和形貌等多角度考察影响电解质电导性能的因素。主要工作成果归纳如下:1、掺杂离子浓度对CeO₂基电解质电导性能的影响采用溶胶-凝胶法合成Ce_1-xSm_xO_<sub>2-δ（x=0,0.1,0.2）系列固体电解质。通过XRD、Raman、SEM和交流阻抗技术系统研究掺杂离子浓度对电解质导电性能的影响。研究结果表明,Ce_0.9Sm_0.1O_2-δ和Ce_0.8Sm_0.2O_2-δ电解质的相对密度和晶粒大小都十分接近。较多Sm³⁺的掺入能促使样品形成更多的氧空位,更有利于O^2-的传递,从而使得Ce_0.8Sm_0.2O_2-δ的电导性能高于Ce_0.9Sm_0.1O_2-δ样品。2、不同热处理方法对CeO₂基电解质电导性能的影响采用两种不同热处理的柠檬酸溶胶-凝胶法制备Ce_0.8Sm_0.2O_2-δ电解质。结果显示在N₂热处理制备样品的过程中,由于碳包裹在前躯体的周围阻碍了粒子的增长,因而通过这种热处理方法能制备出粒子大小在10 nm以内的样品。同时这些超细纳米粒子在烧结初期能形成较大的成核晶粒,最后形成高致密度和较大晶粒的电解质。研究结果表明即使在相同氧空位浓度条件下,通过N₂热处理制备的电解质由于其高致密度和大晶粒使得其电导性能得到了极大的提高。3、双掺杂对CeO₂基电解质电导性能的影响采用柠檬酸溶胶-凝胶法制备Ce_0.8Sm_0.1Nd_0.1O_2-δ、Ce_0.8Sm_0.2O_2-δ和Ce_0.8Sm_0.2O_2-δ电解质。运用XRD、SEM、原位Raman和交流阻抗技术来考察双掺杂对电解质导电性能的影响。SEM结果显示Ce_0.8Sm_0.2O_2-δ和Ce_0.8Sm_0.1Nd_0.1O_2-δ电解质的晶粒大于Ce_0.8Sm_0.2O_2-δ的晶粒。原位Raman结果表明,双掺杂样品Ce_0.8Sm_0.1Nd_0.1O_2-δ的氧空位浓度最高,Ce_0.8Sm_0.2O_2-δ的氧空位浓度其次,Ce_0.8Sm_0.2O_2-δ的最少。样品的电导性能不仅与形貌有关而且也与氧空位浓度有着密切的关系。Ce_0.8Sm_0.1Nd_0.1O_2-δ电解质由于具有大晶粒和高氧空位浓度从而表现出较好的电导性能。4、助烧结剂对CeO₂基电解质的性能影响采用溶胶-凝胶法制备了掺杂Co₃O₄的Ce_0.8Sm_0.2O_2-δ粉末,考察了少量Co₃O₄掺杂对电解质烧结性能和电导性能的影响。结果发现,通过少量Co₃O₄掺杂的电解质,其烧结活性明显提高,同时在1200℃就可烧结致密,比未掺杂的Ce_0.8Sm_0.2O_2-δ电解质烧结温度降低300℃左右。同时Ce_0.8Sm_0.1Co_0.1O_2-δ的电导性能也得到了明显的提高。更多还原

【Abstract】 Solid oxide fuel cell （SOFC） is a highly efficient and clean energy conversion device. The research interest is to lower the operating temperature to intermediate range, in order to overcome the problem of technique and materials for the traditional high temperature SOFC （operated at about 1000℃）, and further improve the performance and reduce the manufacturing cost. There are two main methods to realize the intermediate temperature SOFC. The first one is to develop some new electrolyte materials with high oxygen ionic conductivity at intermediate temperature, the potential candidates are doped ceria. The second one is to reduce the thickness of electrolyte membrance. So far, large amount of papers reported the research of doped ceria, but detailed investigation is still necessary. The current study investigated the influence of content of doped ion, synthesis, chemical composition, content of oxygen vacancies and morphology on the electrical conductivity of the doped ceria electrolytes. The main contents are as follows:1. Effect of the content of doped ion on the electrical properties of CeO₂A series of Ce_1-xSm_xO_<sub>2-δ （x= 0, 0.1 and 0.2） solid electrolytes were prepared by a citrate sol-gel method. Influence of content, density, grain size and concentration of oxygen vacancies on their electrical properties were investigated by X-ray diffraction （XRD）, Raman spectroscopy, SEM and AC impedance spectroscopy. The XRD results confirmed the formation of Ce_1-xSm_xO_<sub>2-δ solid solution with uniform particle sizes. The Raman spectroscopic results show that a higher substitution of Sm into the ceria lattice could enhance the formation of oxygen vacancies. Under the same doped ion, grain size and density, the improvement of oxygen vacancies was beneficial to the migration of O^2-, which resulted in a higher electrical conductivity obtained on the Ce_1-xSm_xO_<sub>2-δ compared to that of the Ce_0.9Sm_0.1O_2-δ. 2. Effect of thermal treatment conditions on the electrical properties of CeO₂Ce_0.8Sm_0.2O_2-δ electrolytes were prepared by sol-gel methods with different thermal treatment conditions. It was found the particle size of the powders thermally treated in N₂ could be controlled less than 10 nm, due to the fact that carbons that enwrapped the precursors could inhibit their crystallization. At the same time, the nano-sized precursors could form larger nuclei at the initial stage of sintering, resulting in the formation of electrolyte with higher density and larger grain size. At the same consent of oxygen vacancies, the enhancement of electrical properties for the electrolyte was correlated to its microstructure obtained by the N₂ thermal treatment.3. Effect of co-doped on the electrical properties of CeO₂Ce_0.8Sm_0.2O_2-δ,Ce_0.8Sm_0.2O_2-δ and Ce_0.8Sm_0.1Nd_0.1O_2-δ samples were prepared by a citrate sol-gel method. Effects of microstructures and oxygen vacancies of the samples on their electrical properties were investigated by X-ray diffraction （XRD）, scanning electron microscope （SEM）, in situ Raman spectroscopy and AC impedance spectroscopy. SEM results indicated that larger grains were formed on the Ce_0.8Sm_0.2O_2-δ and Ce_0.8Sm_0.1Nd_0.1O_2-δ electrolytes compared to that on the Ce_0.8Sm_0.2O_2-δ. In situ Raman spectra suggested that the concentration of oxygen vacancies of the Ce_0.8Sm_0.1Nd_0.1O_2-δ sample was the highest while that of Ce_0.8Sm_0.2O_2-δ was the lowest. It was found that the difference in the electrical conductivity for these electrolytes was closely related to the microstructure and oxygen vacancies of the samples. The highest electrical conductivity obtained on the Ce_0.8Sm_0.1Nd_0.1O_2-δ sample was ascribed to its larger grain size and higher concentration of oxygen vacancies.4. Effect of sintering promoters on the electrical properties of CeO₂Ce_0.8Sm_0.2O_2-δ powder with Co₃O₄ was synthesized by a sol-gel method, and theeffect of Co₃O₄ addition on the sintering and conductivity properties was investigated. The results indicated that after being doped with small quantities of Co₃O₄, the sintering ability increased and densification was reached at 1200℃which was about 300℃lower than that of the Ce_0.8Sm_0.2O_2-δ. In the meantime, the electrical conducitivity of Ce_0.8Sm_0.1Co_0.1O_2-δ was improved compared with the Ce_0.8Sm_0.2O_2-δ.更多还原