Impact of Ni on Accelerated Degradation of 8.5 Mol% Y₂O₃-Doped Zirconia

Abstract

This study focuses on the investigation of the influence of dissolved nickel on the accelerated degradation of the ionic conductivity of 8YDZ (8.5 mol% Y 2 O 3 -doped zirconia) under reducing atmosphere. In comparison to pure 8YDZ, the degradation of Ni-containing 8YDZ proceeds 50 times faster and is completed after 100 h at 950 o C. The impact of Ni-incorporation into 8YDZ on microstructure and chemistry was studied by light microscopy (LM) and transmission electron microscopy (TEM). After thermal treatment under reducing atmosphere, a characteristic colour change of 8YDZ is observed by LM that is attributed to the in-diffusion (> 50 µm) of Ni into the 8YDZ substrate. TEM dark-field imaging reveals the coarsening of nanoscaled precipitates of the metastable t''-YDZ in cubic 8YDZ which is correlated with the degradation of the ionic conductivity. Since the decomposition rate of 8YDZ is determined by the mobility of Y and Zr, the dissolved Ni must have a strong impact thereon. An explanation based on the reduction of dissolved Ni under reducing operation conditions is proposed. It is based on the strain field which is expected to arise in the vicinity of the Ni-atoms after reduction.

Enhancement of Performance and Sulfur Tolerance of Ceria-Based Fuel Electrodes in Low Temperature SOFC

“…This can be allocated to the additional Ni-contact layer which was applied on top of the Ni/GDC10 fuel electrode of sample B resulting in an improved current collection. Additionally, it is also well known that nickel diffuses from the electrode into the YSZ electrolyte during sintering and decreases the ionic conductivity of YSZ [52][53][54] resulting in an increased ohmic resistance. This could be the case for sample A as the Ni/GDC10 is directly applied on the YSZ.…”

“…The reason for this is not clear. Nickel diffusion into the YSZ, decreases the ionic conductivity [52][53][54] usually at much higher temperatures during the sintering process.…”

Impedance analysis of electrolyte processes in a solid oxide cell

“…Well known examples are insulating zirconate interlayers formed between (La,Sr)(Co,Fe)O 3 (LSCF) air electrodes and zirconia-based electrolytes [1][2][3][4][5] or the interdiffusion of Ni from the fuel electrode into zirconia electrolytes [6][7][8][9][10]. To avoid them, interdiffusion barrier layers are implemented [1,2,5,11] resulting in complex multilayered electrolytes.…”

“…Thus, morphology and sintering conditions of the ceria layer have to be optimized to prevent zirconate formation but simultaneously avoid severe interdiffusion. At the fuel electrode, the interdiffusion of NiO into an 8YSZ-electrolyte during sintering [7,8] and the subsequent reduction of NiO to metallic Ni during operation leads to an irreversible decrease in electrolyte conductivity [6,8]. The reason for this conductivity loss is a phase transformation from cubic to tetragonal [6,[8][9][10].…”

“…At the fuel electrode, the interdiffusion of NiO into an 8YSZ-electrolyte during sintering [7,8] and the subsequent reduction of NiO to metallic Ni during operation leads to an irreversible decrease in electrolyte conductivity [6,8]. The reason for this conductivity loss is a phase transformation from cubic to tetragonal [6,[8][9][10]. The phase of YSZ is strongly dependent on the yttrium amount in the zirconia oxide.…”