Electrochemical performance of solid oxide electrolysis cell electrodes under high-temperature coelectrolysis of steam and carbon dioxide

The SOEC electrodes during steam (H₂O) electrolysis, carbon dioxide (CO₂) electrolysis, and the coelectrolysis of H₂O/CO₂ are investigated. The electrochemical performance of nickel-yttria stabilised zirconia (Ni-YSZ), Ni-Gd_0.1Ce_0.9O_1.95 (Ni-GDC), and Ni/Ruthenium-GDC (Ni/Ru-GDC) hydrogen electrodes and La_0.8Sr_0.2MnO_3−δ-YSZ (LSM-YSZ), La_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (LSCF), and La_0.8Sr_0.2FeO_3−δ (LSF) oxygen electrodes are studied to assess the losses of each electrode relative to a reference electrode. The study is performed over a range of operating conditions, including varying the ratio of H₂O/H₂ and CO₂/CO (50/50 to 90/10), the operating temperature (550-800 °C), and the applied voltage. The activity of Ni-YSZ electrodes during H₂O electrolysis is significantly lower than that for H₂ oxidation. Comparable activity for operating between the SOEC and solid oxide fuel cell (SOFC) modes is observed for the Ni-GDC and Ni/Ru-GDC. The overpotential of H₂ electrodes during CO₂ reduction increases as the CO₂/CO ratio is increased from 50/50 to 90/10 and further increases when the electrode is exposed to a 100% CO₂ (800 °C), corresponding to the increase in the area specific resistance. The electrodes exhibit comparable performance during H₂O electrolysis and coelectrolysis, while the electrode performance is lower in the CO₂-electrolysis mode. The activity of all the O₂ electrodes as an SOFC cathode is higher than that as SOEC anodes. Among these O₂ electrodes, LSM-YSZ exhibits the nearest to symmetrical behaviour.