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

Abstract

The SOEC electrodes during steam (H 2 O) electrolysis, carbon dioxide (CO 2 ) electrolysis, and the coelectrolysis of H 2 O/CO 2 are investigated. The electrochemical performance of nickel-yttria stabilised zirconia (Ni-YSZ), Ni-Gd 0.1 Ce 0.9 O 1.95 (Ni-GDC), and Ni/Ruthenium-GDC (Ni/Ru-GDC) hydrogen electrodes and La 0.8 Sr 0.2 MnO 3-δ - YSZ (LSM-YSZ), La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3-δ (LSCF), and La 0.8 Sr 0.2 FeO 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 H 2 O/H 2 and CO 2 /CO (50/50 to 90/10), the operating temperature (550-800 °C), and the applied voltage. The activity of Ni-YSZ electrodes during H 2 O electrolysis is significantly lower than that for H 2 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 H 2 electrodes during CO 2 reduction increases as the CO 2 /CO ratio is increased from 50/50 to 90/10 and further increases when the electrode is exposed to a 100% CO 2 (800 °C), corresponding to the increase in the area specific resistance. The electrodes exhibit comparable performance during H 2 O electrolysis and coelectrolysis, while the electrode performance is lower in the CO 2 -electrolysis mode. The activity of all the O 2 electrodes as an SOFC cathode is higher than that as SOEC anodes. Among these O 2 electrodes, LSM-YSZ exhibits the nearest to symmetrical behaviour. © 2010 Elsevier B.V. All rights reserved.