固体氧化物燃料电池电极/电解质界面结构变化对电池电性能影响的研究

The electrical performance of solid oxide fuel cells (SOFC) is substantially confined by their internal resistances when operating at immediate and lower temperatures. Prior research has manifested that the contact resistance on the interface between the electrolyte and electrodes is the main restrictive factor to the elevation of cells electrical performance after the ohmic resistance, electrochemical polarization resistance and concentration resistance have been debased by the optimization of electrodes materials composition and electrolyte membraning. In view of this, we design to prepare a dense layer between the electrolyte and electrodes to reduce the interfacial contact resistance, for this type of structure evolution can turn the contact status between the electrolyte and electrodes from the point-to-plane fashion into plane-to-plane fashion. In addition, since both the contact resistance, the electrochemical polarization resistance and the concentration resistance also changes with the evolution of the contact status between the electrolyte and electrodes, the influence of interfacial structure changes on the latter two types of resistances also need to be investigated together with their resulting impact on cell electrical performance. For seeking a powerful research method, we combine the programming fitting of the AC impedance spectrum measurement data with voltammpograms measurement data to analysis the cells internal resistances. By using this method, it can be effectively separated the cell contact resistance from ohmic resistance, electrochemical polarization resistance and concentration resistance. On the basis of this, we can, therefore, research the functional principle between the structure evolution across the electrolyte and electrodes interface and the cells internal resistance together with cells electrical performance. Eventually, with the purpose of facilitating the commercialization and civil application of SOFC, we expect this research results can offer some scientific directions for the SOFC structure optimization and cell electrical performance elevation.

中低温下固体氧化物燃料电池内阻过大限制了其电性能提升。研究表明，通过对电极材料组成的优化和电解质的薄膜化将电池的欧姆电阻、电化学极化电阻和浓差极化电阻都降至一定程度以后，电极/电解质界面接触电阻就成为限制电池电性能提升的关键因素。本课题拟通过电极结构的优化，在电极和电解质之间形成一层致密层，从而将二者之间的接触由点-面接触变为面-面接触，以降低电池界面接触电阻。在此过程中研究电极/电解质界面接触状态变化对电池电化学极化电阻和浓差极化电阻的影响，并进一步阐明电极结构变化对电池电性能的影响。通过交流阻抗和伏安曲线的联合解析的方法，将电池的欧姆电阻、接触电阻、电化学极化电阻和浓差极化电阻相互分离，研究电池各内阻和电性能随电极/电解质界面结构的变化规律，探讨降低电池内阻的方法，为电池结构优化和电性能提升提供科学依据，以促进SOFC的商业化和民用化。

本项目以阳极支撑型Ni/YSZ||YSZ||LSCF-6428中温固体氧化物燃料电池(IT-SOFC)作为研究对象，重点研究电池欧姆电阻对电性能的影响。结果发现，在中温（550℃~650℃）范围内，欧姆电阻是制约电池电性能的主要因素，而接触电阻又构成了欧姆电阻的主要部分。接触电阻主要来自于阴极和电解质界面，阳极和电解质之间由于共烧结在一起，二者之间接触良好，其接触电阻不构成电池内阻的主要部分。. 电池的接触电阻可以通过伏安曲线和交流阻抗谱曲线联合解析得到。根据伏安曲线上峰值电流（峰值功率密度下对应的电流）处的斜率可以得到电池最小的总极化电阻。根据伏安曲线上的峰值电流和极限电流可以计算出峰值电流下电池的电化学极化电阻和浓差极化电阻，从而得到了电池的欧姆极化电阻。从对交流阻抗谱曲线的拟合可以得到电池的本体欧姆电阻。电池的欧姆极化电阻与本体欧姆电阻之差即为电池的接触电阻。. 通过球磨提高粉体的烧结活性，可以提高阴极层的致密度。结果发现，阴极层致密度提高以后虽然接触电阻明显下降，但电化学极化电阻明显上升了，这是由阴极中小颗粒团聚体的烧结导致活性位点数量减少引起的。采用双层阴极（内层为较为致密的阴极层，外层为疏松多孔层）可以有效地解决这个问题，但这两层阴极之间又会产生附加的接触电阻。采用双层阴极共烧结的方法可以大大降低这两层阴极之间的接触电阻。与柠檬酸盐法相比，熔盐法制备的粉体具有更高的烧结活性，球磨后的阴极粉体在800 ℃下就可以烧结在电解质表面形成一层致密层，从而将阴极和电解质的接触电阻降至最小，而致密层外面的与之共烧的功能层则起到提供电化学活性位和气体扩散通道的作用。. 总之，SOFC的极化电阻与阴极结构密切相关，致密的阴极内层提供阴极与电解质之间良好的接触，可以显著降低二者之间的接触电阻；与之共烧的疏松多孔外层提供电化学活性位和气体扩散通道以降低电化学极化电阻和浓差极化电阻。