【作者】 朱晓东；

【导师】 孙克宁；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2007， 博士

【摘要】 本研究采用非水基流延法制备大面积镓酸镧(La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-δ简称LSGM)电解质支撑体,并对与之相匹配的新型高性能电极的材料制备、组织结构和各方面性能特别是电化学性能进行详细系统的研究,为大功率电池堆的组装打下坚实的基础。对固相反应法合成LSGM粉体的制备工艺进行优化,确定了LSGM粉体的最佳煅烧制度为:900℃预烧24 h,1300℃煅烧36 h,得到粉体平均粒径为3.04μm。随后通过沉降试验和粘度测试,确定了LSGM的流延浆料组成:粉料—LSGM 80 g,溶剂—丁酮/乙醇36 mL/24 mL,分散剂—三乙醇胺2 mL,粘结剂—聚乙烯缩丁醛6.4 g,塑性剂—聚乙二醇/邻苯二甲酸二乙酯3.2 g/4 mL。用此浆料流延出的素坯经过1500℃烧结6 h后,制备出宏观平整均匀、大小为10 cm×10 cm的大面积LSGM电解质,相对密度和显气孔率分别可以达到96.0%和0.38%,与玻璃陶瓷密封胶BCAS551的热膨胀匹配性良好,保证了工作温度范围内电池结构的稳定性。电化学阻抗谱分析表明LSGM电解质低温区电导率主要取决于晶界电导,而在高温区电导率主要取决于晶粒电导。低温下由于缺陷缔合的存在,电导率激活能较高为0.91 eV,随着温度升高到600℃解缔合之后,在高温下的激活能较低为0.62 eV。利用NiO-La_0.45Ce_0.55O_2-δ（LDC）阳极/LDC阻挡层/LSGM电解质这一阳极半电池中La3+离子的等活度策略,设计并验证了LDC作为NiO-LDC新型阳极和LSGM电解质之间的阻挡层,来抑制阳极与电解质间的界面反应。采用草酸共沉淀法制备出分布范围较窄平均粒径为1.36μm的LDC粉体。通过对浆料粘结剂、丝网印刷和烧结工艺的系统研究,采用丝网印刷法成功制备出一层厚约10μm、表面致密且与电解质结合紧密的LDC阻挡层薄膜。该薄膜与电解质和阳极间化学相容性和热膨胀匹配性良好,并改善了阳极与电解质之间的热膨胀匹配性,抑制了阳极/电解质界面固相反应的发生,在还原气氛下的混合离子电导促进了阳极/电解质界面的电荷转移过程。采用共沉淀法合成了在分子级水平上混合均匀的NiO-LDC阳极复合粉体,制备了新型NiO-LDC复合阳极。发现NiO的含量决定了阳极的导电机制,当NiO的含量>25mass%时金属Ni在阳极中形成连通的网络结构所导致的“逾渗相变”是造成导电机制发生变化的微观机制,其中NiO含量为60mass%的阳极电导率高达2260 S·cm^-1,催化性能较好,在极化电流密度接近200 mA·cm^-2时,过电位为0.1V。通过对SrCo_0.8Fe_0.2O_3-δ（SCF）粉体合成工艺、阴极烧结工艺、LDC与SCF和LSGM的热膨胀匹配性和化学相容性的系统研究,制备了SCF-LDC复合阴极,研究表明LDC的加入可以有效改善阴极材料的热膨胀性能,增大阴极的三相反应界面,内层中LDC含量为50mass%的SCF50双层复合阴极的电化学性能最好,800℃时在0.1 V过电位的极化电流密度达到了1.102 A·cm^-2,极化电阻为0.1480 ?·cm2,优于单层复合阴极中最佳的SCF60阴极。在此基础上,提出并制备了SCF-LDC三层复合阴极,优化结构为SCF含量在三层阴极中由内至外分别为50mass%、70mass %和10mass %。复合阴极中LDC的加入,不仅大大改善了阴极与电解质间的结合和SCF阴极的热膨胀性能,而且增加了三相界面和阴极的总的比表面积,使三层复合阴极在800℃过电位为0.1 V时,极化电流密度达到了1.32 A·cm^-2。通过电化学阻抗谱系统地研究了复合阴极的电化学性能,提出了SCF-LDC三层复合阴极的反应机理:氧的扩散和解离吸附—氧原子在三相界面处发生电化学还原—氧离子由三相界面处向阴极与电解质界面的传输,认为氧的扩散和解离吸附过程成为速度控制步骤。研究了电池各元件的热膨胀匹配性,组装了电池,并对SCF-LDC三层复合阴极组装的电池进行了放电性能测试,在800℃时开路电压为1.073 V,电池的最大功率密度为0.33 W·cm^-2。更多还原

【Abstract】 This study prepared the lanthanum gallate, La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-δ（LSGM） electrolyte base of a large area with non-aqueous solvent tape-casting and conducted a sysmtematic investigation on the preparation technology, microstructure and electrochemical performance of the high performance electrodes, which layed a consolidate foundation for the assembly of the SOFC stacks.The preparation conditions of the LSGM powders by a solid state reaction method were investigated and the optimum sintering procedure was decided. The average size of LSGM powders was 3.04μm as obtained by being sintered at 900℃for 24 h and at 1300℃for 36 h. Then, the best slurry composition, which was decided by precipitation and viscocity tests, contained 80 g LSGM powders, 36 mL/24 mL butanone/ethanol as the solvent, 2 ml triethanolamine as the dipersant and 6.4 g polyvinyl butyral as the binder and 3.2 g polyethylene glycol/4 mL diethyl phthalate as the plasticizer.The smooth and homogeneous LSGM electrolyte base of 10 cm×10 cm in size was obtained by non-water solvent tape-casting and sintering the green tape at 1500℃for 6 h. The thus prepared LSGM electrolyte base possessed a relative density of 96%, a porosity of 0.38% and good thermal compatiblitty with the BCAS551 glass-ceramic sealing materials, which ensured the structural stability of the cell within the operating temperature. Electrochemical impedance spectrum test revealed that the conductivity of the LSGM electrolyte was primarily controlled by conductivity of the grain boundary at the low temperatures and the conductivity of the grain at the high temperatures. The conductivity activation energy was 0.91eV at low temperatures, which was higher than the conductivity activation energy of 0.62 eV at the temperature above 600℃.Moreover, the strategy of La³⁺ isoactivity in the anodic half cell of NiO-LDC anode/LDC interlayer/LSGM electrolyte was utilized to design and to evaluate the effectiveness of LDC as the buffer layer to restrain the reaction between the anode and the electrolyte. The LDC powders of 1.36μm with a narrow diameter distribution were prepared by oxalic acid coprecipitation method. A thin and dense LDC barrier layer of 10μm, which adhered strongly to the electrolyte, was successfully prepared by screen-printing method based on the systematic study of the slurry composition, screen-printing conditions and sintering procedure. The thus prepared barrier layer improved the chemical and thermal compatibility between the anode and the electrolyte, hampered the reation between the anode and the electrolyte, and facilitated the charge transfer process in the reducing atomophere.Furthermore, the anodic NiO-LDC composite powders mixed at the molecular level, which were later used to prepare the new NiO-LDC composite anode, were synthesized by the coprecipitation method. The conducting mechanism of the anode material depended on the NiO content strongly and the conductivity of the anode was 2260 S·cm^-1 with 60% NiO content. The anode with 60mass% NiO content possessed the best polarization performance, which was 200 mA·cm^-2 at the overpertantial of 0.1 V.SCF-LDC composite cathodes were prepared by the systemic investigation on the synthesis conditions of SrCo_0.8Fe_0.2O_3-δ （SCF） powders, sintering procedure of cathodes, thermal expansion and chemical compatibility of LDC, SCF and LSGM. It was found that the thermal expansion characteristic of the cathode was improved and triple-phane-boundaries were increased. Electrochemical performance of the double-layer SCF-LDC composite cathode with the interior layer doped 50mass% LDC was the best, which showed the polarization current density of 1.102 mA·cm^-2 at 800℃under the 0.1V overpotential and polarization resistance of 0.1480 ?·cm2. These properties were better than those of SCF60 cathode which was optimized in the monolayer composite cathode. The triple- layer SCF-LDC composite cathode with the respective SCF content of 50mass%、70mass% and 100mass% from the interior to the exterior layers was put forward and prepared, which not only improved the thermal compatibility between the cathode and the electrolyte, but also increased the three-phase boundaries and the total specific surface area. The triple-layer composite cathode had a current density of 1.32 A·cm^-2 under the 0.1 V overpotential. The electrochemical performance of the triple-layer composite cathode was studied by EIS and the reaction mechanism of the cathode was proposed. The results showed that cathode reaction process were composed of the diffusion, desorption and dissociation of oxygen, the electrochemical reduction of oxygen atoms at three-phane-boundaries and the diffusion of oxygen ions from three-phane- boundaries to the interface of cathode and electrolyte. The rate determining step was the diffusion, desorption and dissociation of oxygen.Finally, the thermal compatibility between all the components of the cell was studied and the cell assembled with the triple-layer SCF-LDC composite cathode has a maximum power density of 0.33 W·cm^-2 and an OCV of 1.073 V at 800℃.更多还原