Effect of the Electrochemical Active Site on Thermal Stress in Solid Oxide Fuel Cells

A 3D model is developed by coupling the equations for momentum, gas-phase species, heat, electron and ion transport to analyze cell polarization, current density and temperature in solid oxide fuel cells (SOFCs). The increase of active sites is beneficial to improve efficiency of electrochemical reactions, but it can be also detrimental to SOFCs' stability as it will induce changes in strength and distribution of the thermal stresses. The variation of thermal stresses is systematically studied by grading the active site along the main flow direction. The results indicate that the first principle stress increases with the active site at the interface of electrolyte and electrode, but the shear stress mainly appears in the vicinity of gas inlets, which both suffer from a dramatic change when the active site is enhanced from the initial state to 1.5 times. Moreover, the electrolyte is subjected to large contrary tensile stresses, and the first principle stress is responsible for crack possibly occurring to the electrolyte. We also confirm that the sharp fluctuation of stress caused by the active sites can be relieved through adjusting thickness of the anode active layer.