Durability of a Segmented-in-Series Tubular SOFC with a (Ce_,Sm)O₂Cathode Interlayer: Influence of Operating Conditions

Abstract

The influence of operating temperature and fuel/air utilization on long-term chemical stability and cell performance degradation is comprehensively investigated and reported for a segmented-in-series tubular solid oxide fuel cell (SOFC), with a (La 0.5 Sr 0.25 Ca 0.25 )MnO 3 (LSCM) cathode and a (Ce 0.8 Sm 0.2 )O 2 (SDC) cathode interlayer, under development for large-scale power plants combined with SOFCs. During three kinds of durability tests for 5000 hours, the average degradation rates of the cell-stacks were around zero, well meeting a tolerant cell voltage degradation rate target of 0.25% per 1000 hours, corresponding to the 10% cell voltage degradation for 40,000 hours. The electrochemical performance was stable at high operating temperature, although the porosity of the SDC cathode-interlayer decreased due to Mn and Ca diffusion from the LSCM cathode. On the other hand, the cell voltage noticeably decreased at lower operating temperature, below 800 • C. Detailed observation of the microstructure and elemental distribution after durability testing revealed that a dense layer formed between the LSCM cathode and the SDC interlayer at low temperature, consisting of La, Ca, and Mn. The degradation in cell performance is attributed to the formation of this dense layer, preventing oxygen supply to the electrode reaction sites.

Towards Comprehensive Description of Stack Durability/Reliability Behavior

“…The most curious and important phenomena in cathodes were observed in the LaMnO 3 ‐based cathodes in the segment‐in‐series cells by MPHS 65; with decreasing temperature, the dense layer was formed between the doped ceria and the cathode, leading to increasing cathode degradation 65. This is a kind of sintering of LaMnO 3 ‐based cathodes.…”

Micro-Tubular Solid Oxide Fuel Cells with One Closed-End Fabricated Via Dip-Coating and Co-Firing

“…Tubular SOFCs can be divided into two configurations (35,37): (i) open-end type configuration or the conventional tubular cells, and (ii) one closed-end type configuration. The one closed-end configuration is preferred for practical applications because it enables saving the complex sealing process or simplifying the membrane reactors design (38).…”

“…During high temperature operations, the tubular cells with two open ends can be cracked by thermal stresses resulting from two fixed ends (35). Additionally, the one closed-end tubular cells enable obtaining a uniform temperature distribution in cell stacks owing to the co-flow configuration (37,39). The closed-end structure can be adopted for direct carbon fuel cells (DCFC) (40), and the continuous supply of solid fuel for one closed-end cells is relatively easy (41).…”