Quantitative electrochemical contributions of cell, air electrode contact, and hydrogen electrode contact in the solid-oxide electrolysis cell (SOEC) stack are investigated with an H2O/H-2 ratio of 90/10 and at 750 degrees C. Ohmic resistances of cell, hydrogen electrode contact, and air electrode contact are 63.6%, 4.8%, and 30.9%, respectively, of those of the stack under OCV condition. Moreover, their polarization resistances account for 93%, 2.6%, and 3.5% of those of the stack, respectively. When the stack is operated at a constant electrolysis current density of 0.8 A cm(-2) for 384 h, voltage degradations of cell, hydrogen electrode contact, and air electrode contact are 71.5%, 8.9% and 19.6%, respectively, of the total voltage degradation of the stack. Variation in stack resistance is highly attributed to the increase in cell ohmic resistance caused by air-electrode delamination from the GDC (Ce0.9Gd0.1O1.95). However, the applied voltage of the stack is more sensitive to the cell polarization resistance caused by Ni-particle agglomeration in hydrogen electrode, which may be the major factor affecting SOEC stack degradation. Copyright (c) 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.