Scandia-zirconia electrolytes for intermediate temperature solid oxide fuel cell operation

Conductivity of several compositions in the scandia-zirconia system (Sc2O3 content between 7.0 and 11.0 mol%) has been investigated as a function of t emperature and time at the nominal solid oxide fuel cell operating temperat ure of 850 degreesC. For comparison, the stability of electrolyte compositi ons was also studied at 1000 degreesC by monitoring conductivity as a funct ion of time. All compositions showed conductivity degradation as a function of time both at 850 and 1000 degreesC, however, it was much lower in compo sitions containing Sc2O3 between 9.0 and 11.0 mol% especially at 1000 degre esC. The maximum conductivity was observed for materials with compositions close to 9 mol% Sc2O3-ZrO2. The 10.0 and 11.0 mol% Sc2O3-ZrO2 compositions showed the presence of a rhombohedral-phase (Sc2Zr7O17, the beta-phase) at room temperature. Hysteresis loops were observed in the conductivity-temper ature plots around 500-600 degreesC due to the transformation of the low co nducting beta-phase to high conductivity cubic-phase on heating and the rev erse on cooling. The contribution of grain boundary impedance in as-sintere d and annealed specimens was relatively small for all specimens studied. (C ) 2000 Elsevier Science B.V. All rights reserved.