Oxygen Electrocatalysis on Epitaxial La[subscript 0.6]Sr[subscript 0.4]CoO[subscript 3-δ] Perovskite Thin Films for Solid Oxide Fuel Cells

Abstract

Hetero-structured interfaces of oxides, which can exhibit reactivity characteristics remarkably different from bulk oxides, are interesting systems to explore in search of highly active fuel cell catalysts for oxygen electrocatalysis. (001)-oriented La[subscript 0.6]Sr[subscript 0.4]CoO[subscript 3-δ] (LSC60-40[subscript 113]) thin films having thicknesses from tens to hundreds of nanometers were grown epitaxially on (001)-oriented yttria-stabilized zirconia (YSZ). Atomic force microscopy showed that all the film surfaces were of high quality with average surface roughness approximately one nanometer. The surface oxygen exchange kinetics of these films were determined by electrochemical impedance spectroscopy. While (001)-oriented LSC60-40[subscript 113] thin films were found to have similar surface oxygen exchange coefficients to LSC60-40[subscript 113] bulk, surface coverage of (001)-oriented (La[subscript 0.5]Sr[subscript 0.5)2]CoO[subscript 4±δ] (LSC[subscript 214]) on the LSC60-40[subscript 113] thin films led to significant enhancement in the surface oxygen kinetics up to ∼3 orders of magnitude. Interestingly, LSC[subscript 214]-decorated LSC60-40[subscript 113] films have comparable surface exchange kinetics (∼1·10[superscript −5] cm·s[superscript −1] at 550°C) to similarly prepared LSC[subscript 214]-decorated La[subscript 0.8]Sr[subscript 0.2]CoO[3subscript -δ] films. Such high surface oxygen kinetics are among the most active SOFC cathode materials reported to date.