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 for MCFC applications is analysed in Li2CO3-Na2CO3 carbonate eutectic in reducing (H-2:CO2:H2O:CO) and oxidizing (O-2:CO2) atmospheres. The electrochemical stability domains of cerium species are established at different temperature on the basis of thermochemical calculations. CeO2 is the stable species whatever the acidity level in both the anode and cathode conditions; nevertheless, a partial solubility of Ce2O3 in CeO2 can be predicted. The solubility of cerium and cerium oxide samples, determined by absorption spectrophotometry, is about 5 x 10(-4) mol kg(-1) in cathodic conditions and 3 x 10(-4) mol kg(-1) in anodic conditions. X-ray diffraction (XRD) confirmed the presence of CeO2 at the surface of the samples. Incorporation of sodium species in the CeO2 lattice is likely; the presence of Ce(III) in long endurance tests was detected by X-ray photoelectron spectroscopy (XPS).