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–Gd0.1Ce0.9O1.95 (Ni–GDC), and Ni/Ruthenium–GDC (Ni/Ru–GDC) hydrogen electrodes and La0.8Sr0.2MnO3−δ–YSZ (LSM–YSZ), La0.6Sr0.4Co0.8Fe0.2O3−δ (LSCF), and La0.8Sr0.2FeO3−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.