Synthesis and Characterization of the Co-electrolessly Deposited Metallic Interconnect for Solid Oxide Fuel Cell

Abstract

For this paper, we investigated the area specific resistance (ASR) of commercially available ferritic stainless steels with different chemical compositions for use as solid oxide fuel cells (SOFC) interconnect. After 430h of oxidation, the STS446M alloy demonstrated excellent oxidation resistance and low ASR, of approximately 40 <TEX>$m{\Omega}cm^2$</TEX>, of the thermally grown oxide scale, compared to those of other stainless steels. The reason for the low ASR is that the contact resistance between the Pt paste and the oxide scale is reduced due to the plate-like shape of the <TEX>$Cr_2O_3$</TEX>(s). However, the acceptable ASR level is considered to be below 100 <TEX>$m{\Omega}cm^2$</TEX> after 40,000 h of use. To further improve the electrical conductivity of the thermally grown oxide on stainless steels, the Co layer was deposited on the stainless steel by means of an electroless deposition method; it was then thermally oxidized to obtain the <TEX>$Co_3O_4$</TEX> layer, which is a highly conductive layer. With the increase of the Co coating thickness, the ASR value decreased. For Co deposited STS444 with 2 <TEX>${\mu}m$</TEX>hickness, the measured ASR at <TEX>$800^{\circ}$</TEX> after 300 h oxidation is around 10 <TEX>$m{\Omega}cm^2$</TEX>, which is lower than that of the STS446M, which alloy has a lower ASR value than that of the non-coated STS. The reason for this improved high temperature conductivity seems to be that the Mn is efficiently diffused into the coating layer, which diffusion formed the highly conductive (Mn,Co)<TEX>$_3O_4$</TEX> spinel phases and the thickness of the <TEX>$Cr_2O_3$</TEX>(S), which is the rate controlling layer of the electrical conductivity in the SOFC environment and is very thin