Effect of carbonate coverage on alloy corrosion in molten carbonate

Development of improved or new cell materials to achieve effective cost reduction and life extension is a central issue for fuel cell systems as they start to compete with state-of-the-art combustion systems. The results of corrosion measurements depend on the ratio of electrolyte volume to corroding surface area in the various three-phase contact geometries employed. A key factor is the gas access. When alloy samples are covered by a thin-film of carbonate under oxygen and CO2, the surface is totally oxidized within a few hours. The film-wetted allay forms a much more compact layer than the same alloy immersed in a deep layer of carbonate, due to the passive surface oxide layer formed under high oxygen activity. The corrosion layer thickness is thicker close to the bulk melt than at the top of the sample where it is only slightly covered by melt.