Oxygen Electrocatalysis on Epitaxial La_0.6Sr_0.4CoO_3-δPerovskite Thin Films for Solid Oxide Fuel Cells

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 0.6 Sr 0.4 CoO 3- δ (LSC60-40 113 ) 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 LSC60-40 113 thin films were found to have similar surface oxygen exchange coefficients to LSC60-40 113 bulk, surface coverage of (001)-oriented (La 0.5 Sr 0.5 ) 2 CoO 4± δ (LSC 214 ) on the LSC60-40 113 thin films led to significant enhancement in the surface oxygen kinetics up to ∼3 orders of magnitude. Interestingly, LSC 214 -decorated LSC60-40 113 films have comparable surface exchange kinetics (∼1·10 −5 cm·s −1 at 550°C) to similarly prepared LSC 214 -decorated La 0.8 Sr 0.2 CoO 3- δ films. Such high surface oxygen kinetics are among the most active SOFC cathode materials reported to date.