Modification of Surface Oxide Layer of Fe-Cr-Al Alloy with Coating Materials for SOFC Applications

We investigated the treatment of Fe-Cr-Al alloy for application in solid oxide fuel cells (SOFCs). The electrical resistance of the Al₂O₃-based surface oxide layer on the alloy decreased and was stable when La_0.6Sr_0.4Co_0.2Fe_0.8O₃(LSCF), La_0.8Sr_0.2MnO₃(LSM), LaNi_0.6Fe_0.4O₃(LNF), or Pr_0.8Sr_0.2MnO₃(PrSM) were first coated on the alloy and heat treated at 700 °C in air. The activation energy, calculated from the resistance, also suggested that the surface oxide became more conductive with treatment. The surface oxide layer after treatment had a microstructure of columns growing outward in the same direction, containing small amounts of elements such as Sr, Ni, Fe, La, Mn, and Pr. The microstructure consists of polycrystalline γ-Al₂O₃and small amounts of Al compounds with these elements. In the case of the LNF coating, the formation of NiAl₂O₄was observed_.The enhanced electrical conductivity may have resulted from the arrangement of the columnar structure, along with the electronic conduction path generated by the reaction of γ-Al₂O₃with these elements.