Phase Transformation of YSZ Electrolyte in Anode-Supported SOFCs

The addition of nickel oxide (NiO) to 8 mol% yttria-stabilized zirconia (8YSZ) accelerates the phase transformation from cubic phase to tetragonal phase when exposed to a reducing atmosphere at relatively high temperatures such as 900 ℃, resulting in the degradation of oxide ion conductivity.In this study, NiO-related phase transformation of 8YSZ electrolyte is investigated for anode-supported cells (ASCs). 8YSZ electrolyte co-sintered with NiO-YSZ anode at high temperatures exhibited NiO dissolution into the 8YSZ electrolyte during the sintering process and the amount of dissolved NiO increased with increased sintering temperatures. After reducing the cells at 900 ℃, phase transformation is observed in the 8YSZ electrolyte and resulted in a decrease of the oxide ion diffusion coefficient ( D* ). On the other hand, no phase transformation is observed for the cells reduced at 700 ℃for 5 hours.