Corrosion of a Cobalt coated Metallic Interconnect exposed to Solid Oxide Fuel Cell Conditions

摘要

Solid oxide fuel cells (SOFC) can produce electricity with a high efficiency by electrochemicalconversion of the chemical energy in a fuel into electrical energy. A majorchallenge of SOFC technology is to develop a suitable interconnect material. Promisingcandidate materials are ferritic stainless steels.The interconnects are subjected to a very corrosive environment as they are exposedto high temperatures (700-850 °C) with reducing conditions on one side andoxidizing on the other. Well-known corrosion mechanisms for the cathode side arehigh temperature oxidation and chromium evaporation. Corrosion of the anode sidehas received much less attention and is not as understood.Here the corrosion of cobalt coated ferritic steel Crofer 22 APU exposed to realSOFC conditions for 2800 hours has been investigated. The steel was in contact witha nickel anode and a lanthanum strontium manganite (LSM) cathode. Characterizationwas done with SEM and EDS.The oxide scales on the cathode side of the interconnect consisted of an outerlayer of cobalt, manganese and iron oxides and an inner layer of chromium oxide.A large amount of nickel had diffused from the anode into the steel which maycause a transformation of the ferrite structure into austenite. This is of concern becausethermal stresses and poor oxidation is a potential consequence. A considerableamount of chromium carbides and nitrides were present in the bulk steel.The results indicates a cobalt coating is effective on the cathode side of the interconnectbut another solution is required on the anode side to prevent interconnect/anode interactions.