【作者】 丁浩；

【导师】 孙海滨；

【作者基本信息】 山东理工大学 ， 材料科学与工程， 2021， 硕士

【摘要】 固体氧化物燃料电池（SOFCs）是一种清洁高效的电化学发电装置,可广泛应用于固定式电站、热电联供等领域。电解质是SOFCs的核心部件之一,其电学性能决定着电池性能的高低。在诸多电解质材料中,CeO₂/Ba CeO₃基复合电解质因兼具了CeO₂与Ba CeO₃基电解质的性能优势而备受关注。但是,该电解质的烧成温度高,容易引起界面扩散/反应、Ba元素挥发等问题,进而导致电学性能不理想。而且,电解质的晶界电导机制尚不明确。为了解决上述问题,本论文围绕CeO₂/Ba CeO₃基复合电解质的低温化烧结和晶界电导机制开展了一系列研究。主要研究内容如下:（1）添加烧结助剂是降低电解质烧成温度的一种有效途径。以固相法合成的Sm掺杂CeO₂（SDC）和Y、Zr共掺杂Ba CeO₃（BZCY）为原料,制备了SDC-BZCY复合电解质,研究了Fe₂O₃烧结助剂对烧结性能和电学性能的影响。结果表明:Fe₂O₃是一种良好的烧结助剂,可将SDC-BZCY复合电解质的烧成温度由1500℃降至1400℃;随着Fe₂O₃添加量的增加,电解质的电导率先增大后减小,当Fe₂O₃添加量为1.5 wt.%时,电导率达到最大值8.06×10^-3 S cm^-1（测试温度700℃）,显著优于未添加烧结助剂的同类电解质(1.78×10^-3 S cm^-1,700℃);所制备的电解质支撑型SOFCs在700℃的功率密度达到36 m W cm^-2。（2）提高粉体烧结活性是降低电解质烧成温度的另一种有效途径。采用燃烧法合成了高活性Bi、Sm共掺杂CeO₂/Ba CeO₃纳米粉体(Ce_0.8Sm_0.1Bi_0.1O_2-δ-Ba Ce_0.8Sm_0.1Bi_0.1O_3-δ,简写为Bi SDC-BCSBi),制备了Bi SDC-BCSBi复合电解质,研究了电解质的烧结性能和电学性能。结果表明:利用Bi元素的低熔点特性和纳米粉体的高活性,电解质的烧成温度可降低至1200℃,表现出优异的烧结性能;当Bi SDC和BCSBi的质量比为80:20时,电导率达到最大值,为2.80×10^-2 S cm^-1（测试温度600℃）;该电导率比未掺杂Bi元素的同类电解质高出6倍,这是因为Bi元素掺杂能够提高电解质的O-H和氧空位浓度;所制备的电解质支撑型SOFCs在600℃的功率密度达到397 m W cm^-2。（3）为了阐明晶界电导机制,分别采用传统烧结和两步烧结工艺制备了微米级（晶粒尺寸1～2μm）和超细晶粒（晶粒尺寸100～300 nm）Bi SDC-BCSBi复合电解质,通过交流阻抗测试、阻塞电极法、浓差电池设计等方法,研究了晶粒尺寸对电学性能的影响。结果表明:超细晶粒电解质的表观晶界电导率(2.83×10^-4 S cm^-1,350℃)比微米电解质高2个数量级,前者表现出了优异的“晶界效应”;“晶界效应”主要得益于晶界处O-H基、氧空位浓度的升高以及杂质的稀释。更多还原

【Abstract】 Solid oxide fuel cells（SOFCs）are one kind of clean and efficient electrochemical power generation devices,which can be widely used in fixed power stations,CHP（combined heat and power）and other fields.The electrolyte is one of the core components of SOFCs,and its electrical performance determines the performance of the cell.Among many electrolyte materials,CeO₂/Ba CeO₃ based composite electrolyte,which combines the advantages of CeO₂ and Ba CeO₃ electrolyte,has attracted much attention.However,the high sintering temperature of the electrolyte is likely to cause several problems such as interface diffusion/reaction and Ba element volatilization,leading to unsatisfactory electrical properties.Moreover,the grain boundary conductance mechanism of the electrolyte is still unclear.In order to solve the above problems,this work has carried out a series of studies on the low-temperature sintering and grain boundary conductance mechanism of CeO₂/Ba CeO₃-based composite electrolyte.The main research contents are as follows:（1）Adding sintering aids is an effective way to reduce the sintering temperature of the electrolyte.Sm2O₃ doped CeO₂（SDC）and Y2O₃,ZrO₂ co-doped Ba CeO₃（BZCY）synthesized by solid phase method were used as raw materials to prepare SDC-BZCY composite electrolyte.The effects of Fe2O₃ sintering aid on sintering performance and electrical properties of SDC-BZCY were studied.The results show that Fe2O₃ is an excellent sintering aid,which can reduce the sintering temperature of SDC-BZCY composite electrolyte from 1500℃to 1400℃.With the increase of Fe₂O₃ addition,the conductivity of the electrolyte increases firstly and then decreases.When the Fe2O₃ addition amount is1.5 wt.%,the conductivity reaches the maximum value of 8.06×10^-3 S cm^-1 at 700℃,which is significantly better than similar electrolyte without sintering aids(1.78×10^-3 S cm^-1,700℃).The prepared electrolyte-supported SOFCs has a power density of 36 m W cm^-2 at700℃.（2）Improving the powder sintering activity is another effective way to reduce the sintering temperature of the electrolyte.The high-activity Bi,Sm co-doped CeO₂/Ba CeO₃nanopowders（Ce0.8Sm0.1Bi0.1O₂-δ-Ba Ce0.8Sm0.1Bi0.1O₃-δ,named as Bi SDC-BCSBi）were synthesized by the combustion method.Bi SDC-BCSBi composite electrolyte pellets were prepared.The sintering performance and electrical properties of the electrolyte were studied.The results show that the sintering temperature of the electrolyte can be reduced to 1200℃by using the low melting point characteristics of Bi element and the high activity of nano powders,showing excellent sintering performance.When the mass ratio of Bi SDC and BCSBi is 80:20,the conductivity reaches the maximum value of 2.80×10^-2 S cm^-1 measured at 600℃,the conductivity is 6 times higher than that of similar electrolytes without Bi element.This is because Bi element doping can increase theO-H groups and oxygen vacancy concentration of the electrolyte.In addition,the power density of electrolyte-supported SOFCs reaches 397 m W cm^-2 at 600℃.（3）In order to clarify the mechanism of the grain boundary conduction,the micron-sized（grain size 1-2μm）and ultra-fine grained（grain size 100-300 nm）Bi SDC-BCSBi composite electrolyte were prepared by conventional sintering and two-step sintering process,respectively.The influence of grain size on electrical performance was studied by AC impedance test,blocking electrode method,concentration cell design and other methods.The results show that the apparent grain boundary conductivity of the ultra-fine grained electrolyte(2.83×10^-4 S cm^-1,350℃)is higher than that of the micron-sized electrolyte(6.39×10^-6 S cm^-1,350℃).The ultra-fine grained electrolyte exhibits excellent"grain boundary effect".The"grain boundary effect"is mainly due to the increase in the concentration ofO-H groups and oxygen vacancies at the grain boundary and the dilution of impurities.更多还原