Controlling chromium vaporization from interconnects with nickel coatings in solid oxide devices

Abstract

Vaporization of Cr-rich volatile species from interconnect materials is a major source of degradation that limits the lifetime of planar solid oxide devices (solid oxide fuel cells and solid oxide electrolysis cells) with metallic interconnects. Some metallic coatings (Ni, Co, and Cu) may significantly reduce the Cr release from interconnects and slow down the oxide scale growth on the steel substrate. To shed additional light upon the mechanisms of such protection and find a suitable coating material for ferritic stainless steel materials widely used for interconnects, we used a combination of first-principles calculations, thermodynamics, and diffusion modeling to investigate which factors determine the quality of the Ni metallic coatings. We found that Cr migration in Ni coatings is determined by a delicate combination of the nickel oxidation, Cr diffusion, and phase transformation processes. Although the formation of Cr2O3 is more exothermic than that of NiO, the kinetic rate of the chromia formation in the coating layer and its surface is significantly reduced by the low mobility of Cr in nickel oxide and in NiCr2O4 spinel. These results are in a good agreement with diffusion modeling for Cr diffusion through the Ni coating layer on the ferritic 441 steel substrate and available experimental data.