Microstructural Evolution of Solid Oxide Fuel Cell: Modeling and Optimization

The solid oxide fuel cell (SOFC) with up to 60 % energy efficiency and a life expectancy of 40,000 hours has emerged as an ideal candidate to meet the energy challenges of the modern world. However, the commercialization of SOFC is hindered due to its high operating temperature, high manufacturing cost, and lack of structural reliability. Previous studies have investigated the development of functionally graded electrodes to improve SOFCs performance; however, further investigation needs to be done on the cell-level optimization for functionally graded electrodes. In addition, the performance of functionally graded SOFCs is influenced by the SOFC microstructural evolution at elevated operating temperature. Microstructural evolution cause performance degradation and crack formation at elevated operating temperate. It is generally believed that microstructural evolution caused by the coarsening of Ni particles of Ni-yttria stabilized Zirconia (YSZ) in the anode of a SOFC, which leads to the performance degradation and crack formation. Ni particle coarsening is believed to be controlled by the interface diffusion due to the minimization of total free energy of the anode system. High operating temperature of SOFC leads to the enhanced interface diffusion of Ni particle. In this work, a multi-scale electrode polarization model of SOFCs has been expanded and developed into a cell-level model using various nonlinear particle size and porosity graded microstructures. The cell-level SOFCs model has been utilized to reveal the complex relationship among the transport phenomena, which include the transports of electron, ion, and gas molecules through the electrode. The performance of functionally graded electrodes has been investigated to understand the effects of tailored electrode microstructures on cell power output, as well as microstructural evolution using diffuse-interface theory as well as phase-field method. The developed microstructural evolution framework is capable of exploring the quantitative effect of Ni particle coarsening by tracking the effective properties (e.g., particle size, particle size ratio, TPB area) on the performance of SOFC. The TPB is found to be affected by microstructural evolution and the accumulation of pores is discovered to be responsible for crack formation. The work advances the understanding of the cell performance with graded microstructures and the effect of microstructural evolution on the performance of SOFC