【作者】 王靖；

【导师】 邓长生；

【作者基本信息】 清华大学 ， 材料科学与工程， 2013， 博士

【摘要】 根据平板式高温固体氧化物电解池对阳极材料性能的要求，分别对La_0.8Sr_0.2MnO₃（LSM）和La_0.8Sr_0.2FeO₃（LSF）两种体系的四种阳极材料进行研究，采用了X射线衍射谱（XRD）、扫描电镜（SEM）、透射电镜（TEM）、电化学阻抗谱（EIS）、X射线光电子能谱（XPS）等分析测试手段，从材料的成分和微观形貌入手，分析了在温度、氧分压和极化电流作用下，阳极的电化学性能变化。首先选取xLSM-（100-x）YSZ（0<x<60wt%）复相材料体系，深入研究了该体系随着LSM掺入量的变化，直流电导率转变机制、LSM与YSZ两相的三维连通模型、以及电化学特性的变化规律。结果表明，当x从10增加到30时，该体系的导电机制由离子导电向电子导电转变。当x=20，电导率激活能最大。根据实验结果，提出了该复相材料的三维连通模型，并发现LSM有效电导率与其体积分数的关系符合改进的Koh-fortini关系，该公式的模拟结果与实验测量数据基本吻合。对于多孔LSM-YSZ复合阳极，随着氧分压的增加，极化电阻大幅度减小，但随着孔隙率的增加，阻抗谱中低频弧的半径明显减小。通过微分阻抗谱分析，发现只有中频弧和低频弧与氧分压有关。随着孔隙率的增加，扩散过程的弛豫时间在缩短。而对于多孔LSF电极，随着孔隙率的增加，阳极极化电流对阻抗谱低频部分影响越来越明显，极化电阻随着极化时间延长而增加。采取离子注入法将LSM纳米颗粒引入LSF电极骨架，可以使具有催化活性的纳米颗粒均匀地分布在LSF电极表面，起到修饰效果。其极化电阻在800oC时为0.27·cm²，比单相的LSF和LSM低。进一步采用非水基LSM前驱体溶液包覆LSF电极，制备出芯壳结构电极。研究发现，0.010mol·L^-1前驱体溶液所制备的芯壳结构电极，在800oC时其极化电阻约为0.30·cm²；并且在1A·cm-2阳极电流下极化处理20h后，极化电阻增加幅度比LSM-YSZ复合电极小近7倍，表明具有一定的抗阳极极化的潜力。针对经过LSF纳米颗粒修饰的LSF电极，建立了该电极结构的三相界面模型。基于电荷传输和质量传递机制，该模型中将三相界面的长度作为分析阳极浓差过电势的一个因素。模拟结果表明，纳米颗粒修饰后的电极的三相界面长度比传统方法制备的LSM-YSZ复合电极大5⁸个数量级；而浓差过电势随着三相界面长度、氧分压、孔隙率、孔径四个因素的增加而减小，随着阳极厚度的增加而增加。更多还原

【Abstract】 In order to meet the requirements of planar solid oxide electrolysis cells （SOEC）,four kinds of anode materials with different compositions based on La_0.8Sr_0.2MnO₃（LSM） and La_0.8Sr_0.2FeO₃（LSF） were prepared. Their compositions, microstructuresand properties have been investigated by X-ray Diffraction （XRD）, Scanning ElectronMicroscopy （SEM）, Transmission Electron Microscopy （TEM） methods, as well asElectrochemical Impedance Spectroscopy （EIS） and X-ray Photoelectron Spectroscopy（XPS）. Also, the effects of temperature, oxygen partial pressure （pO₂） and polarizationcurrent on the electrochemical properties of the anodes were systematically discussed.A system of xLSM-（100-x）YSZ （0<x<60wt%） composite materials has beenstudied with regard to its direct current （DC） conductivity transition, connectivity andelectrochemical behaviors. The experimental results demonstrated that the DCconductivity decreases with increasing x, and increases above x=20. As a result oftemperature dependent DC conductivity, a corresponding peak of the activation energyof the DC conductivity was observed at approximately x=20. The DC conductivitytransition from ionic to electronic was found to take place in the range of10<x<30.Based on the results, a simple model schematically showing the three dimensionalconnectivity of the two phases was constructed with variation in x. Furthermore, thecorrelation between the effective conductivity of LSM and its volume fraction wasconsistent with the modified Koh-Fortini equation in the LSM-rich range （x>40）. Thepredicated fittings were comparable with the experimental measurements.The polarization resistance （R_p） of the LSM/YSZ porous composite anodesdecreased with the increase of pO₂and the radius of low frequency arcs in EISdecreased greatly with the increase of the porosity. In addition, the differential analysisof impedance spectra （DIS） indicated only the intermediate and low frequencies arcs arestrongly affected by pO₂. Meanwhile, with the increase of the porosity, thepositions of the peaks in DIS shifted to higher frequency, indicating that therelaxation-time of diffusion was shortened. For the porous LSF electrodes, theinfluence of anodic polarization current on the low frequency arcs became moreand more obvious with the increase of the porosity. Furthermore, the R_pvaluesof the LSF porous electrodes always increase with the increase of anodic polarization time.La_0.8Sr_0.2FeO₃electrodes modified with La_0.8Sr_0.2MnO₃nanoparticles （LSF/LSM）were prepared by infiltration method. The catalytically active LSM phase could beuniformly distributed. The R_pvalue of the LSF/LSM electrode was0.27·cm²at themeasuring temperature of800oC. This value was much lower than those of pure LSFand LSM electrodes. Additionally, LSF@LSM （core@shell） electrodes were preparedvia the infiltration of LSM non-aqueous-solution. The results showed that the bestperformance of the electrodes with core-shell structure was obtained at theconcentration of0.010mol L^-1for precursor solution. The R_pvalue of the electrodereached0.3·cm²at800oC. Moreover, the R_pvariation of the LSF@LSM anode wasseven times less than that of the conventional LSM-YSZ anode after anodic polarizationcurrent of1A cm-2for20h. This clearly demonstrated the LSF@LSM materials will bea promising anode with anti-polarization characteristic.A triple phase boundary （TPB） model derived from the LSF anode modified with alot of LSM nanoparticles was presented. Based on charge transfer and mass transfermechanisms, the TPB length was considered as an important factor for the calculationof concentration overpotential of the anode in SOEC. The results showed that the TPBlength in the LSF/LSM anodes was5to8orders of magnitude higher than that in theconventional composite electrodes. Moreover, the concentration overpotential decreasedwith the increase of the TPB length, oxygen partial pressure, porosity, pore radius.However, it increased with the increase of the thickness of diffusion layer in the anodeof SOEC.更多还原