Interface and Grain Boundary Degradation of Cathode from Commercial Cells Induced By Electrochemical Operation in Humidified Air

Abstract

Electrode performance degradation is a major obstacle for the development of SOFC technologies. Among different causes of electrode performance degradation, variation of operating gas environment could impact durability of SOFCs and lead to degradation. For the cathode, certain degree of humidity is always present in ambient air. It has been consistently reported that the degradation rate is accelerated when the cell is operated in the humidified air. This work presents nanostructure analyses of operated commercial SOFCs with either LSM/YSZ cathode or with mixed conducting LSCF/SDC cathode exposed to humidified air. For the cell with LSM/YSZ cathode, three commercial button cells were operated in humidified air for various time at 800 °C. Microscopy work reveals nanostructure degradation occurred within the cathode active layer, and it is most pronounced in the region next to the electrolyte. Newly grown Mn-rich nano-precipitates accompanied with nano-voids and cracking propagate at the LSM/YSZ interface. Additionally, prolonged operation in humidified air promotes the formation of the Mn-enriched precipitates at the YSZ/YSZ grain boundaries. By contrast, for the cell with LSCF/SDC cathode, upon long term operation of 2600 hours, Co and Fe enriched Spinel nano-grains were found accumulated at the original pore region of the cathode. The formation mechanism of Mn-enriched nano-precipitates and Co-enriched nanograins for the LSM/YSZ and LSCF/SDC cathode are discussed.