Investigation of Manganese Cobalt Oxide (MCO) Coatings on Fuel Cell Interconnects

Abstract

Planar Solid Oxide Fuel Cells (SOFCs) are composed of repeating cathode-electrolyte-anode units separated by electrically conductive interconnects. With the reduction in fuel cell operating temperature to approximately 800°C, it has become possible to use chromium-based, ferritic stainless steel or Crofer for interconnects. These interconnects must survive the high temperature oxidizing and reducing environments while maintaining electrical conductivity. Unfortunately the formation of chromium oxide scale poisons the cell by significantly reducing cathodic activity. Chromium scale formation can be inhibited by applying an electrically conductive manganese cobalt oxide (MCO) spinel coating to the interconnect prior to its installation in the fuel cell. The most costeffective way to apply protective coatings to interconnects involves spray coating. To investigate the quality of the coatings and the coating adhesion, four-point bend experiments were undertaken at room temperature. Tensile cracking patterns on the convex surfaces of the bend specimens were used to determine the interfacial shear strengths of the coatings. SEM images of the cracked coating surfaces were processed to analyze the interface failure mechanisms, the crack spacing, and areas that spalled at higher strains. These investigations were able to show distinct differences between coatings formed with different processes parameters.