| Yttria Stabilized Zirconia electrolyte used for Solid Oxide Fuel Cells and Solid Oxide Oxygen Pumps subjected to DC high current density develops micro-cracks which are the reasons for the change of the electrolyte fracture mode from transgranular to intergranular. To elucidate the mechanism of electrolyte damage, electrode and electrolyte supported fuel cells and oxygen pumps were fabricated.; Electrochemical cells were polarized under high current density, above 2.5 A/cm2, at 800, 900 and 1000°C. AC impedance characterization showed that cells started to deteriorate from the anode with electrolyte damage progressing toward cathode. Damage to the YSZ electrolyte depended on the anode materials with the highest deterioration rate for cells with SrTiO 3 anodes and the lowest rate for Ni/YSZ anodes.; TEM, SEM and optical microscopy showed pore formation at the grain boundaries, and dislocation activities in the grains and grain boundaries of the damaged electrolyte. In addition, computer simulation using Finite Element Analysis software ANSYS 5.7 was used to estimate stresses developed due to current application. Results from the computer simulations, microscopy analyses and electrochemical testing suggest that the mechanism of the YSZ electrolyte damage involves plasticity enhancement and stresses at the anode/electrolyte interface, caused by the high current densities. A detailed sequence of events leading to the electrolyte damage is proposed. |
