Thermal, mechanical, and electrical properties of LSCo/mullite composite contact materials for solid oxide fuel cells

Abstract

Lanthanum strontium cobaltite (LSCo) is considered as a good candidate cathode contact material for solid oxide fuel cells, due to high electrical conductivity. However, LSCo has a very large coefficient of thermal expansion (CTE) than the cells and metallic interconnects. As a result, poor mechanical stability is expected during thermal cycling. To minimize the CTE mismatch, we investigate a composite approach involving mixing LSCo with an inert material of low CTE, such as mullite at volume fractions from 0.1 to 0.4. Composite's CTE shows a decreasing trend with increasing mullite volume fractions and is consistent with model predictions. X‐ray powder diffraction analysis of sintered LSCo/mullite composites exhibits no presence of other phases for samples aged for 500 hours at 800°C, indicating chemical compatibility. Electrical conductivity by a 4‐pt method shows a decreasing trend with increasing mullite content. Contact strength of as‐sintered and thermally cycled samples show that only the composite with 0.4 volume fraction has a measurable strength; the other composites have no strength. Overall, the composite approach is demonstrated in the LSCo/mullite system to lower the CTE and hence achieve thermal cycle stability. The addition of the inert phase to the LSCo matrix, however, also reduces the electrical conductivity.

Mullite-Based Ceramics from Mining Waste: A Review

“…Mullite coatings have been used successfully as environmental barrier coatings for the protection against oxidizing agents, reducing agents or aggressive chemicals at high temperatures [53,54]. Besides ceramic or metallic surfaces, mullite composites, including composites prepared with mullite matrix or mullite fiber, find important applications as components in turbine engines, high-performance furnaces or heat shields for space vehicles [55][56][57]. Mullite is a mineral not very abundant in nature since high temperature and low pressure conditions are required for its formation.…”