Evaluation of electroplated Co-Cu metallic coatings for intermediate-temperature solid oxide fuel cells

Abstract

Co-Cu alloys have been co-deposited onto 430 ferritic stainless steels via electroplating with a citrate solution. At the initial oxidation stage, a three-layer scale composed of a thin CuO outer layer, a thick (Cu,Fe,Cr)-doped Co3O4 middle layer and a (Cu,Fe)-doped (Co,Cr)3O4 inner layer was formed on the coated steel. With extended oxidation, the (Co,Cr)3O4 inner layer has been transformed into a Cr-rich oxide inner layer. An obvious outward diffusion of Fe appeared, leading to the formation of an (Cu,Cr,Mn)-doped (Co,Fe)3O4 interaction zone between the Co3O4-based spinel and the chromia oxides. The Co-Cu coating effectively blocked the outward migration of Cr from the substrate. No Cr element could be found in the coupled La0·8Sr0·2MnO3 (LSM) plate of the coated sample after oxidized at 800 °C in air for 500 h. The highly conductive coating with a structure of CuO/Co-based spinels significantly decreased the growth of the Cr-rich oxide scale, and thus a much lower scale area specific resistance (ASR). The electrical properties and the oxidation mechanism of the coated substrates were discussed.