(Invited) Characterization of Thermally and Cathodic Polarization Induced LSM Electrode/YSZ Electrolyte Interface of Solid Oxide Fuel Cells By Combined FIB-STEM Techniques

Abstract

In high temperature solid oxide fuel cells (SOFCs), electrode/electrolyte interfaces play an ultimate role in the electrocatalytic activity and durability of the cells. In this study, thermally and electrochemically induced electrode/electrolyte interfaces were investigated on pre-sintered and in situ assembled La0.8Sr0.2MnO3 (LSM) electrode on Y2O3-ZrO2 (YSZ) electrolyte, using focus ion beam and high resolution scanning transmission electron microscopy (FIB-STEM). The results indicate that thermally induced interface is characterized by convex contact rings with depth of 100-400 nm and diameter in agreement with the particle size of pre-sintered LSM electrodes, while the cathodic polarization induced interfaces on in situ assembled electrodes are characterized by particle-shaped contact marks (20-50 nm in diameter). The results show that the electrochemical activity of the cathodic polarization induced electrode/electrolyte interface is comparable to the thermally induced one for the O2 reduction reaction under SOFC operation conditions. The FIB-STEM analysis clearly shows that along the rim of the contact rings of pre-sintered LSM electrode, there is formation of a thin layer of La and Sr on the YSZ electrolyte surface, while Mn diffuses into YSZ and the distribution of Mn inside YSZ electrolyte follows closely the profile of the contact rings. The preliminary results provide direct evidences that Mn cation inter-diffusion plays a critical role in the formation of LSM/YSZ interface of SOFCs.