Enhanced diffusion barrier layers for avoiding degradation in SOFCs aged for 14000 h during 2 years

Abstract

Electrolyte-cathode interfaces are critical regions of solid oxide fuel cells where important degradation phenomena are localized due to cation interdiffusion and reactivity. State-of-the-art barrier layers deposited by screen-printing are not fully blocking, resulting in the formation of insulating phases such as SrZrO3. This article is the continuation of a previous work where a dense gadolinium doped ceria (CGO) barrier layer deposited by pulsed laser deposition (PLD) was optimized and deposited on large-area cells (80 cm2) (Morales et al., 2018) [1]. Those cells, together with reference cells made with CGO screen-printed barrier layers were operated in the same stack for 14000 h during two years. In this work, advanced post-mortem characterisation of the cells is presented showing important microstructural differences between the two types of cell. Operated reference cells present formation of SrZrO3 and cathode demixing, as observed in previous works. Moreover, the generation of a fracture parallel to the barrier layer inside the electrolyte is reported, which is compatible with the coalescence of Kirkendall voids formed at the diffusion front of the Gd/Ce cations into the electrolyte. In contrast, the PLD barrier layer remains stable, avoids the formation of insulating phases and prevents the formation of the mentioned fracture.