The effect of pre-oxidation treatments on the oxidation tolerance of Ni-yttria-stabilized zirconia anodes in solid oxide fuel cells

When a Ni-YSZ (yttria-stabilized zirconia) anode-supported solid oxide fuel cell (SOFC) is exposed to air at high temperatures, the outcome can be catastrophic cell degradation (primarily YSZ electrolyte cracking), resulting from the 70% volume expansion of Ni as it forms NiO. Earlier work showed that the damage is less severe under conditions when no gradient in the NiO content into the Ni-YSZ support layer was allowed to develop during the oxidation process (e.g., oxidation at 600 degrees C). This was correlated with qualitative scanning electron microscopy observations, showing that NiO particles are ejected out of the Ni-YSZ/air surface. In the present work, XPS analysis confirmed the enrichment of NiO at the outer anode surface, suggesting that it may be possible to pre-oxidize the Ni-YSZ support layer at 600 degrees C to force some NiO out onto the anode surface and thus enhance cell oxidation tolerance. It is shown here that, following pre-oxidation at 600 degrees C, the amount of Ni oxidation tolerated prior to electrolyte cracking at 600 degrees C increased from 75% to 80%. For oxidation at 800 degrees C, following pre-oxidation at 600 degrees C, electrolyte cracking was less severe, but cracks still appeared before 50% of the Ni in the anode was oxidized. (C) 2014 Elsevier B.V. All rights reserved.