Degradation of Solid Oxide Electrolysis Cells Operating Galvanostatically at Different Temperatures: Emphasis on the 900°C Regime

Optimizing the operating temperature of a steam electrolysis unit is essential for its design and efficiency. This study investigates the impact of operating temperature on the galvanostatic operation of solid oxide electrolysis cells. Initial electrochemical characterization is performed at four temperatures, followed by durability testing at -1 A cm^-2. Two additional durability tests are conducted at 920°C and considerably higher current densities. Electrochemical impedance spectroscopy data analysis indicates that increasing the temperature from 750°C to 920°C improves the single cell's initial performance and durability. This enhancement is mainly due to reduced degradation of the Ni-YSZ fuel electrode, with ohmic and fuel electrode resistance degradation rates decreasing by factors of 80 and 5, respectively. Post-mortem microstructure analysis reveals loss of percolating Ni and increased porosity close to the Ni-YSZ fuel electrode/8YSZ electrolyte interface, with no Ni migration toward this interface neither below nor above 900°C. Thermodynamic calculations indicate that Si impurities significantly contribute to the degradation of the Ni-YSZ fuel electrode. However, in this study the overpotentials developed during the durability tests at 850°C and 920°C are insufficient to destabilize the Ni/YSZ interface or promote the diffusion of impurities into Ni grains.