Thermodynamic stabilities of SrCeO3 and BaCeO3 using a molten salt method and galvanic cells

• Published in: Journal of the Electrochemical Society Vol. 140; no. 4; pp. 1060 - 1065
• Main Authors: SRIKANTH GOPALAN, VIRKAR, A. V
• Format: Journal Article
• Language: English
• Published: Pennington, NJ Electrochemical Society 01.04.1993
• Subjects: Chemical thermodynamics; Chemistry; Exact sciences and technology; General and physical chemistry; Mixtures; Thermodynamic properties; Barium Cerium Oxides Mixed; Gibbs free energy; Cerium Strontium Oxides Mixed; Molten electrolyte; Thermodynamic stability; Heat of reaction; Experimental study; Thermodynamic properties; X ray diffraction; Inorganic compound; Molten salt
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/1.2056197

SrCeO3 and BaCeO3 are potential candidates as electrolytes in hydrogen concentrators and fuel cells in the temperature range of about 500 to about 1000 C. Their thermodynamic stabilities with respect to the individual oxides SrO and CeO2, and BaO and CeO2 in the anticipated application temperature regime have been studied via the molten salt method and galvanic cells. In the former, SrO and CeO2 or BaO and CeO2 were added in a 1:1 molar ratio to molten salt eutectics (NaOH-KOH or LiCl-KCl) at about 400 C and subsequently SrCeO3 and BaCeO3, formed by solid state synthesis at about 1100 C, were added. SrCeO3, added to molten LiCl-KCl eutectic, either transformed into SrCO3 and CeO2 or SrO and CeO2 depending upon whether the air circulated over the molten salt was ambient or was passed through soda lime and ascarite to remove CO2. In molten NaOH-KOH eutectic, SrCeO3 decomposed to form SrCO3 and CeO2 regardless of whether the circulated air was passed through soda lime. BaCeO3 decomposed to form BaCO3 and CeO2 in both eutectics in both ambient air and air passed through soda lime. This shows that, over the temperature range of investigation, both SrCeO3 and BaCeO3 are thermodynamically unstable. Galvanic cells with alkaline earth fluoride ion conductors were used to determine standard Gibbs free energies of the reactions SrCO3 + CeO2 to SrCeO3 + CO2 and BaCO3 + CeO2 to BaCeO3 + CO2. The results of these experiments were consistent with those of the molten salt method. 27 refs.