Creep Behavior Analysis for a Bilayer Functional Graded Electrolyte Supported High Temperature Ceramic Fuel Cells

Ceramic fuel cell, such as solid oxide fuel cell (SOFC), usually has three functional layers with one dense electrolyte in the middle and two porous electrodes on each side of it, which operates around 1000°C. Recent research activities in SOFC tend to lower the operation temperature to the range of 700°C-800°C due to improvement in mechanical properties, and reduction in costs. However, the state-of-the-art electrolyte yttria-stabilized zirconia (YSZ) under this reduced temperature produces relatively poor ionic conductivity. Ceria-based electrolyte is an excellent candidate in electrical properties under intermediate temperature range, even though it shows a lattice expansion by cerium reduction at the very low oxygen partial pressure occurring at the anode side. Hence, a bilayer yttria doped ceria (YDC) with thin YSZ protection at anode side is designed to maximize the ionic conductivity. However, this lattice expansion of cerium results in an internal stress under this SOFC consideration. In this paper, oxygen partial pressure dependent creep behavior of an edge crack at the bi-material interface (YSZ:YDC) is studied numerically. The steady state C* path independent integral is obtained from ABAQUS code. Bi-material and homogeneous cases are discussed under extensive creep. Finally, fracture analysis of an edge crack at the bilayer electrolyte is also investigated for homogeneous bilayer materials.