Hydration Properties and Rate Determining Steps of the Oxygen Reduction Reaction of Perovskite-Related Oxides as H+-SOFC Cathodes

• Published in: Journal of the Electrochemical Society Vol. 159; no. 6; pp. B683 - B694
• Main Authors: Grimaud, A., Mauvy, F., Bassat, J. M., Fourcade, S., Rocheron, L., Marrony, M., Grenier, J. C.
• Format: Journal Article
• Language: English
• Published: The Electrochemical Society, Inc 01.01.2012; Electrochemical Society
• Subjects: Chemical Sciences; Material chemistry; Perovskite; Chemical reactions; Oxides; SOFC; Cathodes
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/2.101205jes

Four mixed ionic-electronic conducting (MIEC) perovskite-related oxides were studied as potential H+-SOFC cathode materials: La0.6Sr0.4Fe0.8Co0.2O3−δ, Ba0.5Sr0.5Co0.8Fe0.2O3−δ, PrBaCo2O5+δ and Pr2NiO4+δ. Their hydration properties were measured by TGA: Ba0.5Sr0.5Co0.8Fe0.2O3−δ shows the largest water uptake. Their electrochemical performances were characterized using BaCe0.9Y0.1O3−δ as electrolyte; polarization resistances as low as 0.5 Ω cm2 were found at 600°C, for PrBaCo2O5+δ and Pr2NiO4+δ. The rate determining steps of the oxygen reduction reaction were determined on the basis of electrochemical studies performed as a function of pH2O, in air. Proton transfer and water release appear to be the rate determining steps for Ba0.5Sr0.5Co0.8Fe0.2O3−δ, PrBaCo2O5+δ and Pr2NiO4+δ. No rate determining step involving proton was found for La0.6Sr0.4Fe0.8Co0.2O3−δ. On the basis of this study, one can suggest that Ba0.5Sr0.5Co0.8Fe0.2O3−δ, PrBaCo2O5+δ and Pr2NiO4+δ show some protonic conduction as well as oxide diffusivity and can be labeled Triple Conducting (e-/O2−/H+) Oxides, so-called TCO.