High temperature water electrolysis with solid oxide electrolysis cells (SOECs) is a promising method for hydrogen production. In order to study the performance and degradation behavior of cells with different cell components in electrolysis mode, a four-cell stack was assembled that used JULICH's F10 design with two types of air electrodes based on La0.6Sr0.4CoO3-delta (LSC) and La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF). A PVD-prepared GDC layer was applied to LSCF cells while a screen-printing GDC layer was used in the LSC cells. The performance of the stack was first characterized with IV-curve measurements in both SOFC and SOEC modes within the temperature range of 700-800 degrees C. The durability of the stack was investigated by conducting a long-term stationary electrolysis operation with a constant current density of -0.5 Acm(-2) and steam conversion rate of 50% at 800 degrees C. Electrochemical Impedance Spectroscopy (EIS) was used to study the electrochemical performance of the stack, as well as the degradation behavior during long-term electrolysis operation. The method "Distribution of Relaxation Times" (DRT) was applied for the further analysis of the EIS data, and the DRT results have successfully supported the stack degradation analysis. (C) 2017 Elsevier Ltd. All rights reserved.