Investigation of Mn/Co coated T441 alloy as SOFC interconnect by on-cell tests

T441 has been identified as the candidate for SOFC interconnect material because it is assumed that with the addition of Nb, Ti in T441, the formation of continuous silica sub-layer could be avoided or delayed due to Nb and Si rich secondary phase formation stabilizing silicon migration. Previously, electrodeposition Mn/Co alloys followed by oxidation has been proved as a simple and cost effective method to fabricate (Mn, Co)₃O₄ coatings. In this work, Mn/Co coated T441 interconnects were tested as the cathode current collector of solid oxide fuel cells. For comparison, uncoated and 500 h pre-oxidized T441 interconnects were tested as well. The cell with coated interconnect shows stable performance during total 850 h test, even after severe thermal cycles (heating rate 26.7 °C/min). The coating shows good adhesion with substrate and it can prevent Cr poisoning on SOFC cathode. While the cell with uncoated and pre-oxidized T441 interconnects degrade rapidly. XRD results show the coating peaks shifted from mainly Co₃O₄ with some little Mn before test to MnCo₂O₄ after test due to Mn diffusion from substrate. No Cr penetrated to the coating layer, as further proved by EDX linescan. The effect of laves phase on the Cr₂O₃ sub-layer formation and coating thickness was further discussed.