Electrodeposition and isothermal aging of Co and Mn layers on stainless steel for interconnectors: Initial stages of spinel phase formation

• Electrodeposited Co and Mn layers were annealed to obtain an oxide coating.
• Structural and chemical analysis of early stages of transformation is reported.
• Spinel phase formation was achieved in both oxidizing and neutral atmosphere.
• Co and Mn diffusion and counter-diffusion was tracked up to 1 h exposure.
• No Cr from the stainless steel substrate was detected in the coating.

Electrodeposited Co and Mn spinel phase oxides for application as coatings for metallic interconnectors in Solid Oxide Fuel Cells were prepared. The study aims at understanding the initial stages of transformation of the metallic layers into the spinel phase. Co and Mn metallic layers were sequentially deposited over AISI 430 stainless steel substrate from acidic sulfate solutions and annealed in oxidizing and inert atmospheres between 600 °C and 800 °C. The coatings obtained showed a thickness above 20 μm. After 1 h of isothermal aging the coatings were composed of layers of un-reacted metallic elements and Mn based oxides. The spinel phase was studied by XRD and revealed Mn based tetragonal structure Mn3O4 with Co in solid solution and a non-determined Co/Mn ratio. According to EDS measurements this ratio should vary with depth. Full conversion was not obtained at these time frames with the presence other Mn oxides (MnO and Mn2O3). In inert atmosphere, the allotropic Mn transformation from α to β phase was detected. No outward diffusion of Cr was detected, due to the short exposure times.