The conductivity and its ageing behaviour was determined for zirconia co-doped with 10mol% of Sc2O3 and 1 mol% CeO2 in different partial pressures of oxygen at 600C. After 3000 h, samples kept in air, in a humidified mixture of H2/N2 and in humidified H2 exhibited loss in the ionic conductivity of 9, 19 and 25%, respectively. The conductivity degradation rates after the first 1000h were 1.5%/1000h in air and 4.3%/1000h in humidified H2. For all atmospheres, after 3000 h at 600C the conductivity value remained above 10 mS/cm, the minimum value required for viable solid oxide fuel cells. On ageing in reducing conditions, the colour on the surface of the sample changed from white to dark orange, indicating the reduction of Ce4+ cations, which also explains the higher degradation rate in reducing conditions, than in air. The colour gradient within the sample indicated the progress of the reduction front. The core/shell model was applied on the aged reduced sample, and the conductivity of the reduced region was estimated to be 27% lower than the un-aged sample. The conductivity behaviour upon re-oxidation was also investigated in air at 600C. The conductivity recovers significantly in the first 500 h, thereafter increasing linearly with time. After 2000 h of re-oxidation in air, the gain in conductivity was 3.7% compared to the as-aged sample.

Ionic Conductivity Ageing Investigation of 1Ce10ScSZ in Different Partial Pressures of Oxygen. S.Omar, A.Belda, A.Escardino, N.Bonanos: Solid State Ionics, 2011, 184[1], 2-5