Conductivity optimization of La_0.3Sr_0.7TiO₃/La_0.8Sr_0.2MnO₃ bilayer interconnects via interfacial oxygen partial...

Although the design of bilayer interconnects in solid oxide fuel cells (SOFCs) has attracted attention, the regulation mechanism of the bilayer interconnect system on the electrical transport properties remains unclear. In this study, La_0.3Sr_0.7TiO₃ (LST) and La_0.8Sr_0.2MnO₃ (LSM) were used as bilayer interconnect materials. The interfacial oxygen partial pressure was tuned by systematically adjusting the LST/LSM thickness ratio, and the conduction mechanism of the bilayer interconnect was interpreted. LSM acted as an oxygen barrier. A thickness of about 5 µm appeared to be necessary to effectively block oxygen. The thickness of LSM influenced the baseline level of the interfacial oxygen partial pressure, while the thickness of LST protected the Ti³⁺ charge carriers by regulating the oxygen ion transport distance, thereby determining the actual level of conductivity. The results suggest that increasing LSM thickness or decreasing LST thickness reduced the interfacial oxygen partial pressure. At a fixed total thickness, a relatively high conductivity can be obtained when the LSM layer was slightly thinner than the LST layer. The regulation mechanism of bilayer interconnect thickness on electrical conductivity is as follows: the thicknesses of LSM and LST jointly affect the interfacial oxygen partial pressure, which in turn modulates the O^2- content and Ti³⁺ carrier concentration within the LST layer and ultimately influences the electrical conductivity of the bilayer interconnect. The optimized bilayer interconnect was applied to a 5-cell flat-tubular segmented-in-series SOFC (FT-SIS-SOFC), which contributed to an approximately 40% increase in output power density compared to the non-optimized counterpart. This study may contribute to understanding the thickness ratio-conductivity relationship in LST/LSM bilayer interconnects and offers a potential theoretical basis and practical guidance for the rational design of high-performance SOFC interconnects.