Ba0.5Gd0.8La0.7Co2O6−δ Infiltrated BaZr0.8Y0.2O3-δ Composite Oxygen Electrodes for Protonic Ceramic Electrolysis Cells

Abstract

Protonic ceramic electrolysis cells (PCECs) are drawing attention for hydrogen production due to their high efficiency and flexibility, as well as high purity of the produced hydrogen at intermediate temperatures (400-600 ℃). However, one of the major challenges for further improvement of PCECs performance has been the low reaction kinetics at the oxygen electrodes which can lead to high polarization resistances (Rp). In this study, a mixed proton-electronic conducting (MPEC) Ba0.5Gd0.8La0.7Co2O6− δ (BGLC) and proton-conducting BaZr0.8Y0.2O3- δ (BZY20) composite oxygen electrode material was prepared by infiltration and studied as symmetric cells (BGLC-BZY20//BZY20//BGLC-BZY20). The oxygen electrode operating conditions (temperature, oxygen and steam partial pressures) were systematically varied in order to identify and characterize the different electrochemical processes that take place in the oxygen electrode under realistic operation conditions. Two obvious electrode reaction processes were observed in the impedance spectra; the middle frequency one is tentatively ascribed to a charge transfer process and the low frequency one clearly involves oxygen surface exchange reactions. In addition, the results confirm the infiltrated cells exhibit significantly decreased polarization resistance (Rp) and enhanced long-term durability. The polarization resistances increase with pH2O and decrease with pO2. The Rp for infiltrated BZY20 electrodes are 0.44, 1.17 and 2.87 Ω cm2 in 3 % humidified synthetic air (21% O2/79% N2) at 600, 550 and 500 ℃ respectively. In addition, the electrode demonstrated good stability with no detectable degradation within 400 h durability test in 10% humidified synthetic air at 600 ℃. Overall, we conclude that the BGLC infiltrated BZY20 is a promising oxygen electrode material for PCECs operated at intermediate temperatures.