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Evaluation of the interfaces is critical for improved long-term stability and performance of solid oxide fuel cells (SOFC) under required operating conditions. In this work, cells consisting of LSCF-cathode|GDC-interlayer|8YSZ-electrolyte|Pt-anode were tested under open-circuit voltage (OCV) and cathodic polarization at a constant current of -0.3 A at 800°C for 300 h in air. Dense GDC films by pulsed laser deposition (PLD) were used as reaction barrier layers. The results showed that after cell tests, SrZrO3 formed at the LSCF/GDC interface in consequence of the fast Zr migration in the PLD-grown GDC interlayers. However, SrZrO3 formation and GDC microstructural feature differ between OCV and cathodic polarization. Under OCV, SrZrO3 laterally formed at the O2/LSCF/GDC triple phase boundary with GDC interlayer showing increased porosity near the YSZ electrolyte. Both of these led to a drastic increase in polarization resistance with time. Under cathodic polarization, localized transverse growth of SrZrO3 was observed, and an apparent pore elimination occurred in GDC. Cells also showed no performance degradation under cathodic polarization. Based on the above observation, a plausible cation diffusion behavior and oxygen transport is discussed. [ABSTRACT FROM AUTHOR]

The degradation of GDC interlayer is one of the key issues in the long-term stability of LSCF cathode-YSZ electrolyte based solid oxide fuel cells (SOFCs). Here we demonstrate that the cathode microstructure has a strong influence on the stability of GDC interlayer and cation diffusion behavior of LSCF/GDC/YSZ triplets. LSCF was prepared into two distinct morphologies: porous layers by screen-printing and dense layers by pulsed laser deposition (PLD). Dense GDC barriers by PLD were applied to both porous and dense LSCF cathodes. Interdiffusion and microstructural evolution were investigated at temperatures of 800°C to 1000°C in air. At 800°C, both cathodes showed no apparent formation of SrZrO3 at the GDC/YSZ interface. Instead, SrZrO3 formed at the LSCF/GDC interface, and was more evident for the porous LSCF annealed at 900°C. At 1000°C, severe cation interdiffusion at the LSCF/GDC interface became remarkable for the porous cathode, which exhibited rapid degradation of the GDC layer accompanied by the severe SrZrO3 formation; by contrast the dense cathode only showed localized SrZrO3 grains. The superior barrier stability of GDC in a dense cathode can be related to the air-tight interface which would minimize microstructural degradation occurring near the oxygen/LSCF/GDC triple phase boundary. [ABSTRACT FROM AUTHOR]

Performance degradation of SOFC cathodes has been partly attributed to sulfur dioxide (SO2), which is one of the major impurities naturally present in air. In this work, the sulfur poisoning behavior of (LaSr)(CoFe)O3 (LSCF) cathodes exposed to 1 ppm of SO2 in air was investigated as a function of time under various operation temperatures of 923 K, 973 K, and 1073 K. Severe performance degradation was observed at low temperatures of 923 K and 973 K. For these cases, only the polarization resistance (Rp) was increased, additionally no sulfur component was detected in the LSCF cathode. At 1073 K, both Rp and ohmic resistance (Rohmic) increased during the progress of degradation and SrSO4 was observed in cathode, especially near the LSCF/GDC interface. Plausible sulfur poisoning mechanisms were proposed based on the observed experimental phenomena. [ABSTRACT FROM AUTHOR]