Solid oxide fuel cells (SOFCs) can be fueled with various gases, including carbon-containing compounds. High operating temperatures, exceeding 600 °C, and the presence of a porous, nickel-based SOFC anode, might lead to the formation of solid carbon particles from fuels such as carbon monoxide and other gases with hydrocarbon-based compounds. Carbon deposition on fuel electrode surfaces can cause irreversible damage to the cell, eventually destroying the electrode. Soot formation mechanisms are strictly related to electrochemical, kinetic, and thermodynamic conditions. In the current study, the effects of carbon deposition on the lifetime and performance of SOFCs were analyzed in-operando, both in single-cell and stack conditions. It was observed that anodic gas velocity has an impact on soot formation and deposition, thus it was also studied in depth. Single-anode-supported solid oxide fuel cells were fueled with gases delivered in such a way that the initial velocities in the anodic compartment ranged from 0.1 to 0.7 m/s. Both cell operation and post-mortem observations proved that the carbon deposition process accelerates at higher anodic gas velocity. Furthermore, single-cell results were verified in an SOFC stack operated in carbon-deposition regime by dry-coupling with a downdraft 150 kWth biomass gasifier.

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 La_0.6Sr_0.4Co_0.2Fe_0.8O₃ 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 $\tau \approx 0.5$ 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.