Reversible Decomposition of Secondary Phases in BaO Infiltrated LSM Electrodes—Polarization Effects

In operando Raman spectroscopy is used to study ceramic La_0.85Sr_0.15MnO_{3± δ} electrodes infiltrated with BaO. The aim of this work is to clarify why BaO infiltration reduces the polarization resistance in oxygen containing atmospheres. Prior to the in operando experiments, ex situ X-ray diffraction and Raman spectroscopy reveal the formation of a secondary phase, Ba₃Mn₂O₈, on the electrode. During the in operando Raman investigation of the BaO-infiltrated La_0.85Sr_0.15MnO_{3± δ} electrodes, experiments are performed at 300 and 500 °C with oxygen partial pressure 0.1 atm and with −1 or +1 V applied potential. A changing electrode surface is observed during operation as the Ba₃Mn₂O₈ secondary phase decomposes and manganese oxide accumulates on the electrode surface during cathodic polarization. The observed changes are reversible. These results suggest that the formation of Ba₃Mn₂O₈ is responsible for the reduced polarization resistance observed at open circuit voltage (OCV) in an oxygen containing atmosphere. Furthermore, the results illustrate the dramatic differences between the electrode surface composition at OCV and during cathodic polarization. Overall, the results highlight the dynamic interactions between minor secondary phases and applied potential, a general effect that may be important for the high-performance frequently observed with ceramic electrodes prepared by infiltration.