Protective coating based on manganese–copper oxide for solid oxide fuel cell interconnects: Plasma spray coating and performance evaluation

Abstract

A solid oxide fuel cell (SOFC) stack requires metallic interconnects to electrically connect unit cells, while preventing fuel from mixing with oxidant. During SOFC operations, chromia scales continue to grow on the interconnect surfaces, resulting in a considerable increase of interfacial resistance, and at the same time, gaseous Cr species released from the chromia scales degrades the cathode performance. To address these problems, in this study, protective Mn2CuO4 coatings are fabricated on metallic interconnects (Crofer 22 APU) via a plasma spray (PS) process. The PS technique involves direct spray deposition of molten Mn2CuO4 onto the interconnect substrate and leads to the formation of high-density Mn2CuO4 coatings without the need for post-heat-treatment. The thickness, morphology, and porosity of the PS-Mn2CuO4 coating are found to depend on the processing parameters, including plasma arc power, gas flow rate, and substrate temperature. The PS-Mn2CuO4 coating fabricated with optimized parameters is completely impermeable to gases and has high adhesion strength on the interconnect substrate. Furthermore, no resistive chromia scales are formed at the coating/substrate interface during the PS process. As a result, the PS-Mn2CuO4-coated interconnects show a very low area-specific resistance below 10 mΩ cm2 at 800 °C in air and excellent stability during both continuous operation and repeated thermal cycling. This work suggests that an appropriate combination of the material and coating process provides a highly effective protective layer for SOFC interconnects.