Influence of post-treatments on the contact resistance of plasma-sprayed La_0.8Sr_0.2MnO₃ coating on SOFC metallic interconnector

Lowering the cell operation temperature to the intermediate temperature range of 600-700 °C allows the use of cheaper and more conductive metallic interconnect materials instead of ceramics. Stainless steel is considered to be one of the most promising candidate materials owing to its adaptable thermal expansion coefficient and low price. However, its lifetime is limited owing to the insulating oxide scale which forms on the steel surface and the degradation of the cathode performance due to the vaporization of the chromia-containing oxide scale. In order to reduce the degradation of the cell performance, an effective protective layer needs to be developed. To this end, in this study, an LSM (La_0.8Sr_0.2MnO₃) coating was deposited by the plasma spraying method. The solid-state reaction method was used to synthesize the LSM powders prior to the plasma spraying. Uniform and dense coatings of LSM were deposited on stainless steel by plasma spraying. The post surface treatment with plasma and thermal annealing was found to improve the crystallinity and porosity of the coating itself, but increased the contact resistance. The variation of the stoichiometry, degree of crystallinity and nature of the interface were investigated, in an attempt to explain the conductivity behavior of the plasma-sprayed LSM coating after post-treatment.