A Ca and Fe Co-Doped Layered Perovskite as Stable Air Electrode in Solid Oxide Electrolyzer Cells under High-Current Electrolysis

•SmBa0.75Ca0.25CoFeO5 + δ layered perovskite was employed as air electrode in SOEC.•SBCCF air electrode performed better in electrolyzer mode than in fuel cell mode.•Electrolysis test was conducted under 1 A cm−2 at 800 °C for 216 h.•During the last 120 h of electrolysis test, RP of SBCCF remained at 0.52 Ω cm2.•SBCCF as air electrode realized stable operation under high-current electrolysis.

In this study, the electrochemical performance and the stability of Ca and Fe co-doped SmBaCo2O5+δ, SmBa0.75Ca0.25CoFeO5+δ (SBCCF), layered perovskite is examined as the air electrode for solid oxide electrolyzer cells (SOECs). In a half-cell with three-electrode configuration, the initial polarization resistance, RP, of GDC|SBCCF is 0.16 Ω cm2 at 800 °C. Under an anodic bias of 200 mV, RP decreases to 0.03 Ω cm2 ; however, under cathodic bias of 200 mV, RP increases to 0.18 Ω cm2, indicating that SBCCF is more active towards oxygen evolution reaction than oxygen reduction reaction. During the electrolysis test under 1 A cm−2 at 800 °C for 216 h, RP of GDC|SBCCF increases to 0.52 Ω cm2 in the first 96 h and remains at 0.52 Ω cm2 for the remaining 120 h. In contrast, RP of GDC|LSCF increases with a rate of 0.08 Ω cm2/100 h at the same time. This result demonstrates that SBCCF is a promising candidate as air electrode in SOECs for stable operation under high electrolysis current, which is critical to achieve high hydrogen production rate and to lower the cost of the system. Effective methods for the improvement of the performance of SBCCF will be developed in future studies.