Impact of Sweep Gas on the Degradation of an La_0.6Sr_0.4Co_0.8Fe_0.8O₃ Anode in a Solid Oxide Electrolysis Cell

Abstract

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 × 4 cm2) were tested under a constant current (−0.25 A/cm2) in the electrolysis mode while supplying the cathode side with 70% H2O–30% H2 mixtures at 800 °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 Ω cm2 compared to relatively stable values of 0.15–0.2 Ω cm2 for N2), 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 N2 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 N2, namely the presence of a slow process at τ≈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.

Keywords

• solid oxide electrolysis cell
• anode
• degradation
• DRT
• steam electrolysis