Degradation mechanisms in La₀.₈Sr₀.₂CoO₃ as oxygen electrode bond layer in solid oxide electrolytic cells (SOECs)

[摘要] (cont.) We hypothesize that the long-range transport of Sr, Co, and Cr cations can be caused by two primary mechanisms: 1) Driven by Cr-related thermodynamics, where the Crcontaning species (i.e. at the vicinity of the interconnect) could thermodynamically favor the presence of select cations (i.e. Sr and Co) at the region interfacing the interconnect. 2) Driven by the electronic or oxygen ion current. To test these hypotheses and to isolate the governing mechanism, we simulated controlled electrochemical conditions on reference cells having ASM electrodes coated with LSC, on both sides of SSZ electrolyte, without any Cr-containing layers on the LSC bond layer. The reference cells degraded even in the absence of Cr. AES results showed that the microstructure and surface composition of the reference cells stayed stable and uniform upon the electrochemical treatment, in spite of the degradation. Thus, this thesis concludes that the Cr-related thermodynamics could be the dominant mechanism driving the uneven dissociation and segregation of cations in LSC as observed in the stack cells. As a mechanism for Cr-deposition in the LSC bond layer, we suggest that a thermodynamically-favored reaction between the La-enriched phase (at the surface of the LSC grains) and the volatile Cr-species (Cr0₃ and CrO₂(OH)) is responsible for the formation of poorly-conducting secondary phases. This interaction is likely to be limited by the presence of the segregated La-O-species which can serve as a nucleation agent for this reaction.

[发布机构] Massachusetts Institute of Technology