Internal Precipitation of Molecular Oxygen and Electromechanical Failure of Zirconia Solid Electrolytes

The phenomenon of electromechanical failure of zirconia has been examined. It is shown that spatial variation of electronic conductivity in a predominantly oxygen ion conductor can lead to internal precipitation of molecular oxygen and its pressurization. Internal pressures high enough to crack zirconia can develop if the electronic conductivity is higher on the oxygen exit side. The calculations demonstrate that the kinetics of pressurization are very sensitive to the relative magnitudes of the electronic and the ionic conductivities. Oxygen was electrolyzed at 800°C through zirconia solid electrolytes with lanthanum strontium manganate (LSM) electrodes under an applied dc potential of 1.0 V. Spalling of the solid electrolytes was observed. Composite disk electrolytes were fabricated such that part of the disk contained TiO 2 as a dopant which was added to enhance the electronic conductivity. The electrolytes exhibited severe cracking and pitting when the TiO 2 ‐doped region was on the oxygen exit side. No degradation occurred when the TiO 2 ‐doped region was on the oxygen entry side. Implications regarding the use of mixed conductors as dense electrodes in electrochemical systems are discussed.