Effect of Gd-Doped Ceria Interlayer Microstructure on the Interdiffusion Behavior Between La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ Cathodes and Yttria-Stabilized Zirconia Electrolytes

Formation of secondary phases at the interface between cathode and electrolyte is one of the issues affecting the long-term stability of solid oxide fuel cells. La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) perovskite cathode is known to react with yttria-stabilized zirconia (YSZ) forming SrZrO₃ at the interface. To reduce secondary phase formation, a barrier layer such as Gd-doped ceria (GDC) is inserted between LSCF and YSZ. However, the stability of the interlayer may be directly affected by the microstructure and cation diffusion through GDC. In this work, the microstructure of the reaction barrier layer is controlled by growing the GDC thin films on polycrystalline and single crystal YSZ (100) electrolytes using pulsed laser deposition technique. Electrochemical impedance spectroscopy and microstructural analyses were performed on LSCF|GDC|YSZ|Pt cells with different GDC interlayers under an open-circuit condition at 800ºC for 300 h in air. It is observed that SrZrO₃ formed at the LSCF/GDC interface of cells with polycrystalline GDC interlayers resulting in a rapid increase in area-specific resistance (ASR) with time. In the case of GDC on YSZ(100), the LSCF/GDC interface showed no SrZrO₃. Instead, a significant interdiffusion between LSCF cathode and GDC interlayer occurred. The active diffusion of Gd into LSCF and possible formation of perovskite phases at the LSCF/GDC interface may have contributed to slow increase in the ASR with time. Microstructural changes and type of secondary phase formation at the LSCF/GDC interface give rise to a different rate of increase in ASR and is shown to be directly related to the microstructure of GDC interlayer.