The Effects of Operating Conditions on the Performance of a Solid Oxide Steam Electrolyser: A Model-Based Study

To support the development of hydrogen production by high temperature electrolysis using solid oxide electrolysis cells (SOECs), the effects of operating conditions on the performance of the SOECs were investigated using a one-dimensional model of a cathode-supported planar SOEC stack. Among all the operating parameters, temperature is the most influential factor on the performance of an SOEC, in terms of both cell voltage and operation mode (i.e. endothermic, thermoneutral and exothermic). Current density is another influential factor, in terms of both cell voltage and operation mode. For the conditions used in this study it is recommended that the SOEC be operated at 1,073 K and with an average current density of 10,000 A m(-2), as this results in the stack operating at almost constant temperature along the cell length. Both the steam molar fraction at the inlet and the steam utilisation factor have little influence on the cell voltage of the SOEC but their influence on the temperature distribution cannot be neglected. Changes in the operating parameters of the SOEC can result in a transition between endothermic and exothermic operation modes, calling for careful temperature control. The introduction of air into the anode stream appears to be a promising approach to ensure small temperature variations along the cell.