Experimental Analysis of the Co-Electrolysis Operation under Pressurized Conditions with a 10 Layer SOC Stack
Marc Riedel, Marc P. Heddrich, K. Andreas Friedrich
Abstract
This study examines the performance of a solid oxide cell (SOC) stack during co-electrolysis of CO 2 and H 2 O at elevated pressures up to 8 bar. Steady-state and dynamically recorded U ( i )-curves were performed in order to evaluate the performance over a wide temperature range and to quantify the area specific resistance ( ASR ) at different pressure levels. Furthermore, the outlet gas composition at various current densities was analyzed and compared with the thermodynamic equilibrium. The open circuit voltage ( OCV ) was found to increase with higher pressure due to well known thermodynamic relations. An increase of the limiting current density at elevated pressure was not observed for the investigated stack with electrolyte supported cells. The ASR of the stack was found to decrease slightly with higher pressure. It revealed an increase of the cell resistance with lower H/C ratios in the feed at lower temperatures, whereas the performance of the co-electrolysis was very similar to steam electrolysis for temperatures above 820 °C. Within an impedance study for steam, co- and CO 2 electrolysis operation it was shown that pure CO 2 electrolysis exhibits a higher pressure sensitivity compared to pure steam or co-electrolysis due to significantly increased activation and diffusion resistances.