Solid oxide fuel cell reliability and performance modeling and fabrication by spray pyrolysis
SOFCs have the potential to meet the critical energy needs of our modern civilization and minimize the adverse environmental impacts from excessive energy consumption. They are highly efficient, clean and can run on a variety of fuel gases. However, wide adoption of SOFCs is currently hindered by cell durability, manufacturing cost, and lack of fundamental understanding on electrochemical performance of the cell. In order to evaluate the durability of SOFCs, a mathematical thermo-mechanical model was developed to provide the distribution of thermal stresses during thermal cycling, and predict the lifetime of a cell. In addition, an ultrasonic spray pyrolysis prototype fabrication setup, which has the ability to tailor the microstructure of the deposited film, was established as an economically practical fabrication method to deposit the electrode of SOFC. Then, the electrochemical performances of deposited cells with tailored microstructures were investigated in order to better understand the impact of fabrication process parameters on cell electrochemical performance using AC electrochemical impedance spectroscopy. Furthermore, a complete electrode polarization model of SOFCs has been developed and utilized to analyze the performance of homogenous and functionally graded anode with different particle size and porosity profiles. The thermo-mechanical model study showed thermal stresses were more concentrated near the free edge. As the porosity and the thickness of anode increased, the lifetime of the cell decreased. The precursor solution concentration and deposition temperature were found to be the most critical parameters that influenced the microstructure. By manipulating deposited microstructures, the Area Specific Resistance (ASR) of the deposited anode improved and the activation energy decreased. The developed thermo-mechanical model is one of the first attempts to understand cyclic failure behavior of multilayer SOFC through theoretical approach. Low polarization and activation energy makes the developed prototype fabrication setup a promising candidate for the fabrication of high performance SOFC electrode with tailored microstructure. The study of developing electrode polarization model experimentally and numerically demonstrated the potential of controlling the electrode microstructure of a SOFC to improve the cell's electrochemical performance. The work contributes to the understanding of cell performance in relation to graded microstructures.