CO₂ and steam electrolysis using a microtubular solid oxide cell

Abstract Nickel-yttria stabilized zirconia (Ni-YSZ) supported tubes were fabricated by plastic extrusion molding (PEM). YSZ was used as the electrolyte and LSM-YSZ (lanthanum-strontium doped manganite) as the oxygen electrode. Both layers were deposited by dip coating and were then sintered at 1500 °C and 1150 °C, respectively. Coelectrolysis experiments were performed in these cells at 850 °C, using different fuel gas conditions varying the amount of steam, carbon dioxide, nitrogen and hydrogen. Area specific resistance (ASR) values ranged from 0.47 Ωcm², when rich steam and CO₂ flows are used, to 1.74 Ωcm², when a diluted composition is used. Gas chromatography was used to examine the amount of H₂ and CO in the output gas. The obtained results are consistent with the equilibrium of the water gas shift reaction. For all the different analysed conditions, faradaic efficiency was found to be close to 100%. This experiment confirmed that there is no electronic conduction taking place through the YSZ electrolyte. The threshold for electronic conduction in the diluted feeding conditions (Poor H₂O and CO₂) for these particular YSZ-based cell was found at voltages of about 1.65 V.