Effect of Steam to Carbon Dioxide Ratio on the Performance of a Solid Oxide Cell for H2O/CO2 Co-Electrolysis

The mixture of H-2 and CO, the so-called syngas, is the value-added product of H2O and CO2 co-electrolysis and the feedstock for the production of value-added chemicals (mainly through Fischer-Tropsch). The H-2/CO ratio determines the process in which syngas will be utilized and the type of chemicals it will produce. In the present work, we investigate the effect of H2O/CO2 (steam/carbon dioxide, S/C) ratio of 0.5, 1 and 2 in the feed, on the electrochemical performance of an 8YSZ electrolyte-supported solid oxide cell and the H-2/CO ratio in the outlet, under co-electrolysis at 900 degrees C. The B-site iron doped lanthanum strontium chromite La-0.Sr-75(0).Cr-25(0).Fe-9(0).O-1(3-delta) (LSCF) is used as fuel electrode material while as oxygen electrode the state-of-the art LSM perovskite is employed. LSCF is a mixed ionic-electronic conductor (MIEC) operating both under a reducing and oxidizing atmosphere. The cell is electrochemically characterized under co-electrolysis conditions both in the presence and absence of hydrogen in the feed of the steam and carbon dioxide mixtures. The results indicate that under the same concentration of hydrogen and different S/C ratios, the same electrochemical performance with a maximum current density of approximately 400 mA cm(-2) is observed. However, increasing p(H-2) in the feed results in higher OCV, smaller iV slope and R-p values. Furthermore, the maximum current density obtained from the cell does not seem to be affected by whether H-2 is present or absent from the fuel electrode feed but has a significant effect on the H-2/CO ratio in the analyzed outlet stream. Moreover, the H-2/CO ratio seems to be identical under polarization at different current density values. Remarkably, the performance of the LSCF perovskite fuel electrode is not compromised by the exposure to oxidizing conditions, showcasing that this class of electrocatalysts retains their reactivity in oxidizing, reducing, and humid environments.