Ba_0.5Gd_0.8La_0.7Co₂O_6-δ Infiltrated BaZr_0.8Y_0.2O_3-δ Composite Oxygen Electrodes for Protonic Ceramic Cells

In this study, a composite oxygen electrode is prepared by infiltrating a protonic-electronic conducting material, Ba_0.5Gd_0.8La_0.7Co₂O_6-δ (BGLC) into a proton-conducting BaZr_0.8Y_0.2O_3-δ (BZY20) backbone. The composite oxygen electrode is studied in a symmetrical cell configuration (BGLC-BZY20//BZY20//BGLC-BZY20). The electrode and cell performance are characterized via electrochemical impedance spectroscopy (EIS) with varying the operating conditions, including temperatures, oxygen, and steam partial pressures, with the purpose to identify and characterize the different electrochemical processes taking place in the oxygen electrode. Three electrode reaction processes are observed in the impedance spectra, which are tentatively assigned to i) diffusion of adsorbed oxygen/proton migration/hydroxyl formation, ii) oxygen reduction, and iii) charge transfer, going from the low- to high-frequency range. The BGLC-BZY20 electrode developed in this work shows a low polarization resistance of 0.22, 0.58, and 1.43 Ω cm² per single electrode in 3% humidified synthetic air (21% O₂/79% N₂) at 600 °C, 550 °C, and 500 °C, respectively. During long-term measurement, the cell shows no degradation in the first 350 h but degrades afterward possibly due to insufficient material stability.