Spinel oxide protective coatings for solid oxide fuel cell interconnects

Abstract

Metallic interconnects in solid oxide fuel cells are dependent on protective coatings to ensure adequate application lifetime. Of the many coatings investigated, spinel composition coatings display the most promising results. Currently, these coatings are deposited by expensive powder based methods. In contrast, spray pyrolysis is a deposition technique that is regarded as both simple and cost-effective. Thus it appears as an attractive alternative, but has until recently been given little attention.In this work, spinel manganese cobalt oxide (MnCo2O4) coatings deposited by spray pyrolysis has been studied. The influence of substrate surface roughness was evaluated and it was found that substrates with a higher degree of surface finish yielded the best coatings with respect to microstructure.Furthermore, the layer-by-layer approach was employed in order to produce thicker coatings. This proved successful as stable multilayer coatings with increased thickness were obtained, although the desired thickness value of 10 µm was not reached in this work. Various heat treatments were conducted in order to elucidate their effect on the coating density, crack evolution and overall coating microstructure. Findings show that longer heat treatments at elevated temperatures resulted in denser coatings. However, the heating temperature must be kept on a reasonable level where phase pure MnCo2O4 is maintained. For heat treatment in air, 800 °C is close to the maximum temperature limit that can be used. For heat treatment in argon, a temperature of 1100 °C proved to exceed the phase stability region of pure MnCo2O4. A subsequent heat treatment at lower temperature proved futile to recover a phase pure coating.