Impact of Sweep Gas on the Degradation of an La0.6Sr0.4Co0.8Fe0.8O3 Anode in a Solid Oxide Electrolysis Cell

The degradation of solid oxide electrolysis (SOE) cells with different anode sweep gases was studied in 1000 h-long measurements in order to investigate the impact of sweep gas composition on cell performance. Cathode-supported electrolysis cells with an La0.6Sr0.4Co0.2Fe0.8O3 air electrode (active area of 4 x 4 cm(2)) were tested under a constant current (-0.25 A/cm(2)) in the electrolysis mode while supplying the cathode side with 70% H2O-30% H-2 mixtures at 800 degrees C and using oxygen, nitrogen, and steam as sweep gases. It was demonstrated that the degradation of the anode in steam conditions resulted in more than a 2-fold increase in both, polarization and ohmic resistance (from 0.20-0.25 to 0.6-0.65 Omega cm(2) compared to relatively stable values of 0.15-0.2 Omega cm(2) for N-2), as a consequence of the phase decomposition. Strontium played an important role in steam-induced degradation, migrating from the volume of the electrode layer to the surface of the electrolyte. As a result, the Sr-enriched layer demonstrated susceptibility to Cr poisoning. The cell purged with N-2 demonstrated enhanced performance, while the use of oxygen led to degradation originating from the well-described delamination process. DRT analysis demonstrated some similarity of the spectra for steam and N-2, namely the presence of a slow process at tau approximate to 0.5 s, which might be associated with hindered oxygen transport due to point defect association in the perovskite structure. The results of this study showed that Sr-containing materials likely cannot be used as an SOE anode in high humidity conditions.