Impact of Air Moisture and Operating Mode on the Degradation of Solid Oxide Cells

To study the impact of humid air on the solid oxide cell durability, long-term tests of 1000 h were performed in dry air condition and with a water content of 3% and 8% at 800 °C and +/-1 A.cm −2 . The cell was made of a La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3− δ -Ce 0.8 Gd 0.2 O 2− δ (LSCF-GDC) oxygen electrode, a GDC diffusion barrier layer, an Y 0.16 Zr 0.84 O 1.92 (YSZ) electrolyte, and a Ni-YSZ hydrogen electrode. In electrolysis mode, the degradation rate increased with increasing water content in the air. In addition, the degradation rate was higher under electrolysis current than in fuel cell mode. At the highest level of humidity in electrolysis mode, the addition of water in the air affected the series and polarisation resistances in the impedance spectra. In this case, conversely to the dry condition, the post-test characterizations revealed that the Ni migration was promoted at the cell outlet. Moreover, the LSCF decomposition was aggravated by the humid condition especially in electrolysis mode at the cell inlet. In this zone, it leads to the formation of a quasi-dense SrO phase at the top of the current collecting layer. Such insulating layer could induce a current redistribution in the cell explaining the higher Ni migration at the cell outlet.