In-situ Fe-doped MnCo spinel coatings on Crofer 22 APU and AISI 441 interconnects: microstructural, electrical and oxidation properties

Manganese cobaltite-based spinel coatings have been reported to effectively limit oxidation and Cr-evaporation from ferritic stainless steel interconnects in solid oxide cell stacks. Currently, the possibility to improve the coating performance by transition metals doping of the spinel is of great interest; however, doped Mn-Co spinels are usually synthetized before the coating deposition. In this work, Fe-doped Mn-Co spinel coatings are obtained by a singlestep electrophoretic co-deposition of Mn1.5Co1.5O4 and Fe2O3; a co-deposition mechanism is proposed and discussed. The efficacy of obtained Fe-doped Mn-Co spinels coatings deposited on both Crofer 22 APU and AISI 441 steel is evaluated through a study of the oxidation kinetics and area specific resistance at 750 °C up to 3200 h. Fe-doped coatings show great stability during aging, considerably decreasing the oxidation rate of the substrates. In particular, Fe-modified coating leads to a reduction of ASR of coated interconnects, despite the poorer conductivity of the Fe-doped Mn-Co spinel compared to the undoped Mn-Co. A detailed SEM and TEM post mortem analysis reveals the development of different oxide scale and reaction layers depending on both the coatings and the substrates; oxidation mechanisms for Fe-doped Mn-Co spinel coated Crofer 22 APU and AISI 441 are reviewed and discussed.