Performance and Stability of Solid Oxide Cell Stacks in CO2-Electrolysis Mode

Abstract

Compared to low-temperature electrolysis techniques, solid oxide cell (SOC) technology has attracted growing interest in Power-to-X scenarios based on renewable energy due to its high efficiency, reversibility, and the possibility of simultaneously converting CO2 and H2O into syngas, a chemical precursor for synthetic fuels or intermediates such as methanol. Furthermore, SOCs can also be operated in CO2 electrolysis mode in order to produce pure CO, which is in great demand in the chemical and steel industries. Based on previous experience with fuel cell, steam,- and co-electrolysis operation, the electrochemical performance and durability of planar fuel electrode-supported SOC stacks are investigated with a focus on CO2 electrolysis. Their current-voltage characteristics and electrochemical impedance have been measured in both CO2 and co-electrolysis modes. The main aim of these investigations was to gain insights into the electrochemical processes and limitations of the currently used electrodes during CO2 electrolysis, and to understand the general degradation mechanisms of cells under different conditions. Using state-of-the-art cells, the stack can be operated at 800°C with a current density of -1000 mA cm-2 below cell voltages of 1.4 V in a CO2/CO (1:1) mixture. Based on the findings thus far, some promising approaches with respect to the optimization of fuel electrode microstructures and reaction kinetics to increase the performance and durability of the cells under CO2 electrolysis operation are discussed.