CoMn2O4 and Cu0.5Co0.5Mn2O4 spinels as efficient protective coating layers on SUS430 for SOFC interconnect

Abstract

In this study, CoMn2O4 and Cu0.5Co0.5Mn2O4 spinels are examined as protective coatings for chromium diffusion in metallic interconnect of solid oxide fuel cell. Both spinels are prepared by co-precipitation technique in order to obtain high temperature conducting spinels. The spinels obtained after 4 h of calcinations in air at 500 °C exhibit tetragonal crystal structure with average grain size between 90 and 100 nm. Cu0.5Co0.5Mn2O4 spinel exhibits superior electrical conductivity over CoMn2O4 and both display NTCR (negative temperature co-efficient of resistance) behavior illustrating their use as a protective layer on interconnects for fuel cells operating at higher temperatures. Doctor-blade employed spinel coating over SUS430 alloy exhibits good adhesion between protective spinel layer and metallic alloy. Cross section micrographs reveal presence of nanosized and highly dense grains capable to resist the outflow of chromium ions present in SUS430. Mass gain and diffusion rate constant (Kp) was high for CoMn2O4 coated SUS430 illustrating Cu0.5Co0.5Mn2O4 spinel as a better protective coating layer for interconnect application. Chromium outflow is restricted and the same is evident from all cross-section micrographs of spinel coated SUS430 specimens subjected for oxidation up to 1000 h. Estimated thickness of Cr2O3 layer was ∼15 nm for CoMn2O4 whereas Cu0.5Co0.5Mn2O4 coated SUS430 specimen had ∼12.5 μm thickness at the SUS430/spinel interface demonstrating superior resistance to chromium outflow. The area specific resistance was lowest for Cu0.5Co0.5Mn2O4 coated specimen (between 14 mΩcm2 – 15 mΩcm2) followed by CoMn2O4 coated specimen reiterating Cu0.5Co0.5Mn2O4 as efficient protective coating material for SUS430 SOFC interconnect.