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

Four mixed ionic-electronic conducting (MIEC) perovskite-related oxides were studied as potential H+-SOFC cathode materials: La0.6Sr0.4Fe0.8Co0.2O3-delta, Ba0.5Sr0.5Co0.8Fe0.2O3-delta, PrBaCo2O5+delta and Pr2NiO4+delta. Their hydration properties were measured by TGA: Ba0.5Sr0.5Co0.8Fe0.2O3-delta shows the largest water uptake. Their electrochemical performances were characterized using BaCe0.9Y0.1O3-delta as electrolyte; polarization resistances as low as 0.5 Omega cm(2) were found at 600 degrees C, for PrBaCo2O5+delta and Pr2NiO4+delta. The rate determining steps of the oxygen reduction reaction were determined on the basis of electrochemical studies performed as a function of pH(2)O, in air. Proton transfer and water release appear to be the rate determining steps for Ba0.5Sr0.5Co0.8Fe0.2O3-delta, PrBaCo2O5+delta and Pr2NiO4+delta. No rate determining step involving proton was found for La0.6Sr0.4Fe0.8Co0.2O3-delta. On the basis of this study, one can suggest that Ba0.5Sr0.5Co0.8Fe0.2O3-delta, PrBaCo2O5+delta and Pr2NiO4+delta show some protonic conduction as well as oxide diffusivity and can be labeled Triple Conducting (e-/O2-/H+) Oxides, so-called TCO. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.101205jes] All rights reserved.