Study of cerium species in molten Li2CO3-Na2CO3 in the conditions used in molten carbonate fuel cells. Part I: Thermodynamic, chemical and surface properties

The chemical and surface behaviour of cerium oxide, a candidate material fo r MCFC applications is analysed in Li2CO3-Na2CO3 carbonate eutectic in redu cing (H-2:CO2:H2O:CO) and oxidizing (O-2:CO2) atmospheres. The electrochemi cal stability domains of cerium species are established at different temper ature on the basis of thermochemical calculations. CeO2 is the stable speci es whatever the acidity level in both the anode and cathode conditions; nev ertheless, a partial solubility of Ce2O3 in CeO2 can be predicted. The solu bility of cerium and cerium oxide samples, determined by absorption spectro photometry, is about 5 x 10(-4) mol kg(-1) in cathodic conditions and 3 x 1 0(-4) mol kg(-1) in anodic conditions. X-ray diffraction (XRD) confirmed th e presence of CeO2 at the surface of the samples. Incorporation of sodium s pecies in the CeO2 lattice is likely; the presence of Ce(III) in long endur ance tests was detected by X-ray photoelectron spectroscopy (XPS).