Investigation on the phase stability of yttria-stabilized zirconia electrolytes for high-temperature electrochemical application

For the Fundamental studies on the phase stability of YSZ, we tried to approach the detailed influences of practical conditions through various hypotheses. The phase stability of cubic and tetragonal yttria-stabilized zirconia (YSZ) was studied in the specific electrochemical conditions of current loading and molten salt flux. The degradation of electrochemical performance in the cubic phase occurred more easily than in the tetragonal phase because of yttrium elution in the lattice. The fully stabilized cubic phase showed high electrical performance as an oxide ion-conducting electrolyte, but phase decomposition occurred more easily under applied currents or chemical loading conditions than for the partially stabilized tetragonal phase. When YSZ reacted with a molten salt fluoride flux in solid oxide membrane (SOM) processing, which is used for direct metal reduction, and hightemperature electrolysis in the molten salt, the electrical conductivity of cubic YSZ was decreased by similar to 37%, while that of tetragonal YSZ showed no change. Our findings have important implications for the use of YSZ as an oxygen conductor in various electrochemical devices.