【作者】 李健；

【导师】 程继贵；

【作者基本信息】 合肥工业大学 ， 材料学， 2009， 硕士

【摘要】 固体氧化物燃料电池(SOFC)由于具有能量转化率高,无污染,安全等优点而受到广泛的关注。为使SOFC从实验室走进我们的日常生活之中,操作温度中低温化是必经之路。Sm2O3掺杂CeO2 (Ce0.8Sm0.2O1.9)就是一种在中低温范围内性能出色的电解质材料,在800℃以下离子电导率比YSZ高一个数量级以上。因此Ni/Ce0.8Sm0.2O1.9 (简称Ni/SDC)被认为是一种很有潜力的SOFC的阳极材料。目前阳极材料的制备普遍采用固相法、水热合成法、共沉淀法和溶胶-凝胶法等。这些方法都存在一定的不足之处,近年来,随着低温合成技术的不断发展,研究人员探索将溶胶一凝胶法和自蔓延高温合成技术(SHS)结合在一起,同时兼顾溶胶一凝胶法和SHS的优点,制备高烧结活性、组分分散均匀的粉体,开发出了一种新型的化学合成方法--柠檬酸燃烧法。柠檬酸燃烧法制备NiO/Ce0.8Sm0.2O1.9 (简称NiO/SDC)粉体可以减少晶界电阻,并最终得到泡沫状,疏松表面活性大的纳米粉体。但是由于纳米颗粒粒度小、比表面积大、表面能大,处于能量不稳定状态,因而很容易凝并、团聚形成二次粒子,使粒子粒径变大,失去纳米颗粒所具备的特性,给NiO/SDC纳米粉体的制备和燃料电池性能带来负面影响。本课题采用改进的柠檬酸燃烧法解决NiO/SDC纳米粉体团聚问题,对实现无团聚纳米粉体制备具有积极的意义。本文讨论了前驱体溶液中柠檬酸与金属阳离子摩尔比(MRCM)大小对制备出的NiO/SDC粉体粒度和团聚状态影响:前驱体溶液中标志柠檬酸含量的MRCM分别取1.0、1.5和2.0,XRD结果显示MRCM=1.0时晶粒尺寸最小,NiO为7.1nm, SDC为5.04nm。MRCM=1.15时制备的NiO/SDC粉体,由DTA-TG结果可知360℃时干凝胶分解基本结束。XRD的结果表明点燃后没有出现Sm2O3的衍射峰,说明Sm3+已进入CeO2晶格形成固溶体。粉体点燃后的比表面积最大,达到29.508 m2/g,800℃焙烧后粉体比表面积为6.298 m2/g,随着焙烧温度上升粉末比表面积下降,这是由焙烧温度升高晶粒长大造成的。由TEM显示粉体呈规则球型,但是晶粒相互之间的团聚现象比较严重,这是因为晶粒尺寸小、表面活性高,容易发生团聚。采用柠檬酸燃烧法制备了Ni/SDC金属陶瓷,并对其结构、形貌、烧结性能和电导率等进行研究:还原后的Ni/SDC金属陶瓷孔隙率集中在20%至50%之间,满足燃料气体和产物水的扩散。由烧结收缩率曲线和热膨胀系数显示在不影响阳极性能的前提下,含NiO(wt%)45%-55%的NiO/SDC与SDC粉体共烧结时具有较好的匹配性能。Ni/SDC金属陶瓷电导率随Ni含量增加、测试温度下降而上升,烧结温度降低而下降。论文还通过向前驱体溶液中添加分散剂解决NiO/SDC粉体团聚现象,对不同分散机理的分散剂解聚效果进行比较:粒度分析结果表明在前驱体溶液中添加分散剂制备的NiO/SDC粉体团聚状况有了明显的改善,二次团聚被抑制。添加非离子型分散剂聚乙二醇6000的NiO/SDC粉体具有最好的分散效果,磷酸三乙酯和聚乙烯醇124次之。添加聚乙二醇6000的NiO/SDC粉体具有最小的体积平均粒径1.758μm,最大的比表面积6.44m2/g和最小的表面积平均粒径0.932μm。更多还原

【Abstract】 Great attention has been paid on Solid Oxide Fuel Cell(SOFC) for the advantages of high efficiency,clean, and safety.The low operating temperature of reaction is the key to bring SOFC into our dailylife.The Sm2O3 doped CeO2 (Ce0.8Sm0.2O1.9) system is the electrolyte with excellent performance at intermediate-to-low temperature.It exhibits 10 times oxide ion conductivity higher than yttria stabilized zirconia(YSZ) under 800℃. Therefore, Ni/Ce0.8Sm0.2O1.9 (Ni/SDC) is a potential material for the anode of the SOFC.The anode are usually synthesized by solid-state reaction ,co-precipitation and sol-gel methods.These methods have some deficiency.In recent years, with the development of lower-temperature synthetic technique, the scientists searching for a way to unite the sol-gel and self propagation high temperature synthesis(SHS) to prepare high sintering activity、dispersed powders and keep both of their merits developed a new chemosynthesis---citric acid-nitrate combustion method.NiO/Ce0.8Sm0.2O1.9(NiO/SDC) which were synthesized by citric acid-nitrate combustion method can reduce the resistance of crystal boundry and get nanocrystalline with high activity and porosity. However,because of the little particle size, high specific area ,high surface energy and instability , the Nano-powders agglomerate into second particle easily whose particle size growing up. Then Nano-powders losing their characteristic impact the synthesis of NiO/SDC and the performance of SOFC.This task adopts improved citric acid-nitrate combustion method to solve agglomeration of NiO/SDC which has positive meaning on non-agglomerate nano-powders.Study is made about the effects of different molar ratios of citric acid to metal ions(MRCM) on the particle size and agglomeration of NiO/SDC powders in this thesis.The value of MRCM adopted 1.0、1.5 and 2.0, respectively. The XRD data indicate that the powders have smallest crystallite size than the others’when the MRCM=1.0. The crystallite size of NiO is 7.1nm, SDC is 5.04nm. NiO/SDC powders were synthesized when MRCM=1.15, DTA -TG results show that the decomposition process of dried gel can be nearly finished below 360℃. XRD shows there hasn’t the peak of Sm2O3 in ignited powders.The Sm3+ had joined in fluorite structure of CeO2 .The specific surface area of ignited powders is biggest, achieved 29.508 m2/g,the powders calcined at 800℃is 6.298 m2/g .Because of crystallite grow up with increasing calcination temperature,the specific surface area of powders decreased. Because of the little particle size and high surface activity ,it can be seen clearly from TEM that the powders are nearly ideal spherical in shape and exhibit a narrow distribution in sizes .Ni/SDC cermet were synthesized by citric acid-nitrate combustion method. The structure, morphology ,sinter performance and conductivity had been observed: The reduced Ni/SDC metal cermets with porosity of about 20-50% can satisfy the diffusion of fuel gas and water.According to sintered shrinkage curves and technical thermal expansion coefficientsγ,NiO/SDC with NiO content from 45 to 55 wet.% has matched well with SDC electrolyte in the thermal expansion. The conductivities increase accordingly with Ni content and calcination temperature ,but decrease with testing temperature.Using different dispersants in the precursors to solve the agglomeration of NiO/SDC powders,and compared their effects in this thesis: Particulate properties shows that NiO/SDC powders prepared with dispersants in the precursors have obvious effects on reduction of agglomeration,the second agglomeration is inhibited.The NiO/SDC powders prepared with PEG6000 in the precursors have the best dispersion effects. Triethyl phosphate and polyvinyl alcohol 124 take the second place. The NiO/SDC powders prepared with PEG6000 have the least average particle size, maximal surface area and least surface area average particle size,the values are 1.758μm, 6.44m2/g and 0.932μm respectively.更多还原