Low-cost, high-density Mn–Co spinel coatings for stainless steel interconnect via efficient microwave heating

The high preparation cost and poor density of spinel coatings for stainless steel interconnect have always been puzzling conundrums for the solid oxide fuel cell stack developers. Herein, the microwave heating technology for fabricating Mn–Co spinel coating is developed to address these issues. We designed a device spontaneously providing reducing atmospheres and realized the low-cost, high-efficiency reduction of Mn–Co spinel via microwave heating. Dense coatings (MnO + Co) are formed on the steel surface at ∼1100 °C. The excellent density is related to the melting of Co particles induced by microwave selective heating. At initial, microwave heating is dominated by dipolar polarization, interfacial polarization, and natural resonance. After forming metallic Co, conductive loss and the lens effect further accelerate the reduction process. High-quality spinel coatings are formed during the subsequent oxidation at 800 °C, exhibiting an extremely low area-specific resistance increase rate.