Effects of applied current density and thermal cycling on the degradation of a solid oxide fuel cell cathode

Abstract

Effects of applied current density and thermal cycles on the durability of a solid oxide fuel cell (SOFC) cathode have been studied. SOFC half-cells with and without a gadolinium-doped ceria (GDC) interlayer were fabricated and tested for 1000 h at 900 °C under various current densities and thermal cycles. Performance degradation of the half-cells was assessed by increment of the area specific resistance (ASR). Initially, the ASR of the half-cells without the GDC interlayer decreased for around 150 h due to cathode activation and thereafter increased. A rapid increase in the ASR was observed at higher applied current density, which is attributed to delamination of the electrolyte/cathode interface due to the formation of Sr zirconates, and microstructural change in the cathode. However, these adverse effects were prevented by the GDC interlayer. The half-cells with the GDC interlayer exhibited a smaller degradation rate as compared to that without the GDC interlayer. During the thermal cycling test, ASR values of all GDC interlayer thickness cells increased with an increasing number of thermal cycles. The thermally cycled cell with a GDC interlayer thickness of 3.4 μm showed a lower degradation rate due to the dense GDC interlayer, which resulted in less interfacial resistance and prevented elemental diffusion towards the electrolyte. However, the half-cells with GDC interlayer thickness of 2.4 and 4.5 μm showed a higher increase in the ASR due to relatively higher Sr diffusion and delamination of the cathode/GDC interlayer interface, respectively.