Elucidating the Degradation Mechanism at the Cathode-Interlayer Interfaces of Solid Oxide Fuel Cells

Abstract

Understanding degradation mechanism is essential in improving performance and long-term stability of solid oxide fuel cells. Model cells consisting of porous La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathodes were implemented on yttria-stabilized zirconia (YSZ) electrolytes with dense Gd-doped ceria (GDC) interlayers and tested in an open-circuit voltage condition at 800°C for 300 h in air to elucidate the degradation at the cathode-interlayer interfaces. The GDC films were prepared on poly-YSZ and single-crystal YSZ(100) electrolytes by pulsed laser deposition to generate dense and well-defined barrier microstructures namely granular polycrystalline (poly-GDC) and grain boundary-free single crystalline (sc-GDC) interlayers. Distinct features of the reaction phases at the cathode-interlayer interfaces were observed depending on the type of GDC interlayers. The severe SrZrO3 accumulation at the LSCF/poly-GDC interface caused the rapid cell performance degradation with the poly-GDC interlayers. Whereas, the SrZrO3 formation was suppressed successfully with the sc-GDC interlayers resulting in improved cell performance. However, the active reaction between cathode and interlayer results in the possible formation of GdFeO3 at the LSCF/sc-GDC interface and the CoO dissolution in sc-GDC interlayer appear to affect cell stability. Based on these results, plausible thermodynamic and kinetic considerations on interface chemistry and associated electrochemical behaviors were discussed.