Insight of Reactive Sintering in Manganese Cobalt Spinel Oxide of Protective Layer for Solid Oxide Fuel Cell Metallic Interconnects

A dense protective layer has to be applied onto ferritic stainless steel metallic
interconnects for solid oxide fuel cell (SOFC) stacks to prevent a rapid performance degradation caused by chromia scale growth and chromium poisoning of the cathode. Manganese and cobalt spinel oxide (MCO) is known as an effective protective layer material owing to the high electrical conductivity and the thermal expansion coefficient matching that of the ceramic cell components. However, it appears difficult to prepare a dense MCO layer with wet chemical coating processes rather than dry coating methods such as physical vapour deposition and atmospheric thermal plasma spraying; a porous
coating limits durability of the stack; on the other hand, a wet coating process could reduce production cost. We introduced a reactive sintering process consisting of a reduction and subsequent oxidation step for MCO layers that are prepared by wet coating methods. As a result, the durability was enhanced by the improved coating density which suppressed the increase of area specific resistance and the chromium volatilisation. In this study, we have analysed detailed properties of the MCO coatings under reactive sintering conditions in order to understand how the sintering property is enhanced. Finally, we discuss a modified sintering process to prepare a dense MCO layer using a simple wet
chemical coating method and report on its performance as a protective coating for SOFC metallic interconnects.