The long-term stability of anode cermets for solid oxide fuel cells (SOFC) was studied for the composites NiO/scandia stabilized zironia (ScSZ) and NiO/scandia-alumina stabilized zirconia (SASZ). Heat treatment at 800 °C over 600 h resulted in gradual conductivity degradation for the NiO/ScSZ composites, while no significant changes were found for the NiO/SASZ composites. The conductivity drop was caused by an aggregation of Ni in the cermet matrix at high temperatures, and the addition of alumina to the cermet matrix protected the Ni segregation and improved the long-term stability. The effect of the alumina was examined using a sintered model anode of the NiO/ScSZ system. Although the initial conductivity decreased with increasing alumina content, an anode with an alumina content of 3 mol% showed no conductivity degradation during heating over 600 h. The initial conductivity drop was caused by a NiAl2O4 spinel formed during the initial sintering process. The spinel phase was reduced at 800 °C and transformed slowly into metastable NiAl10O16, which contributed to the long-term stability of the alumina composite anode cermets.
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