Performance and Durability of a 10 layer SOE Stack operated under pressurized conditions

Kurzfassung

The major part of the prospective power supply system will be based on solar and wind energy. The associated intermittency of this energy supply requires flexible storage and usage options. Converting electrical into chemical energy could be an essential constituent in this challenge. One promising path is the solid oxide electrolysis cell (SOEC) technology which can largely contribute to hydrogen and hydrocarbon production as well as electric energy storage. SOECs offer a great potential for a highly efficient energy conversion due to their high operating temperature. The fast kinetics of electrochemical reactions lead to reduced electrochemical losses. Additionally, previous studies have shown that the performance of solid oxide cells can be significantly improved by operating at elevated pressure [1, 2]. A further reason for pressurization is the use of pressurized hydrogen or syngas in downstream processes for storage or fuel synthesis. Experimental results of a SOE stack operated under pressurized conditions in steam and co-electrolysis mode are presented. For a parameter study an overall number of five commercially available planar stacks consisting of 10 electrolyte supported cells were used. The stack was operated in a pressure range between 1.4 and 8 bar. Pressure influence on open-circuit voltage (OCV) and reachable power density was examined on the basis of current-voltage curves. Gas analysis was further used for determining the outlet gas composition of the stack in pressurized co-electrolysis tests. For quantifying and distinguishing between different pressure influenced electrochemical phenomena, impedance spectroscopy was carried out. Furthermore a degradation study of three different stacks over 1000 hours at 1.4, 4 and 8 bar with a reactant utilization of 70 % was performed in steam electrolysis mode. At the lowest pressure, a comparably low degradation rate of 0.7 %/kh was observed.