Interface and grain boundary degradation in LSM-YSZ composite Solid Oxide Fuel Cell cathodes operated in humidified air

The interfaces between the different phases and the associated triple phase boundaries (TPBs) in solid oxide fuel cell (SOFC) cathodes are critical for the oxygen reduction reaction, and their degradation impacts SOFC performance and durability. This work examines nanostructure degradation of composite LSM/YSZ cathodes induced by electrochemical operation in humidified air. Three commercial button cells operated in humidified air for various durations at 800 degrees C exhibited more severe performance degradation than the cell operated in dry air. Microscopy imaging reveals nanostructure degradation within the cathode active layer, especially in the regions nearest to the electrolyte. Newly formed Mn-enriched nano-precipitates accompanied by nano-voids initiate at the original TPBs and propagate along the LSM/YSZ interface. The abundance of the nanoprecipitates at LSM/YSZ interfaces increases with operation time, and prolonged operation in humidified air further promotes the formation of the Mn-enriched precipitates along YSZ/YSZ grain boundaries. The formation mechanism of those precipitates and their influence on the cathode performance are discussed.