Effect of the operating temperature on the degradation of solid oxide electrolysis cells

The present work aims to better understand the effect of operating temperature on the degradation of Solid Oxide Electrolysis Cells (SOECs). The studied SOECs consist of La0.6Sr0.4Co0.2Fe0.8O3-delta-Ce0.8Gd0.2O2-delta (LSCF-GDC) oxygen electrode, GDC diffusion barrier layer, Y0.16Zr0.84O1.92 (YSZ) electrolyte and Ni-YSZ hydrogen electrode. Durability tests are carried out at 750, 800 and 850 degrees C for 2000 h at -1 A cm-2, using 10/90 vol% H2/H2O and dry air at the hydrogen and oxygen electrodes, respectively. The electrochemical impedance spectra measured before and after ageing reveal a strong evolution related to the hydrogen electrode, while the change in the oxygen electrode contribution remains negligible. A set of advanced characterization techniques are employed to study the cell degradation. For the hydrogen electrode, a large Ni depletion is observed after ageing, which increases with the operating temperature. The analysis of the oxygen electrode shows an elemental interdiffusion between the LSCF-GDC/GDC/YSZ layers on the manufactured cells that seems to not evolve significantly upon operation. Moreover, the presence of SrZrO3 is not detected in the pristine cell and in the operated ones. Besides, only a limited LSCF decomposition is found in good agreement with the electrochemical characterizations. Hypotheses that could explain the good oxygen electrode stability are discussed.