  Catalysis is indispensable to chemical processes and relevant to many aspects
of modern life. Owing to the intriguing electronic structures and good ionic
properties, multivalent transition metal oxides have attracted attention as key
catalysts for various energy and environmental applications. Here, we
demonstrate that brownmillerite strontium cobaltite (SrCoO2.5) can be a good
cathode material for sold oxide fuel cells and rechargeable batteries due to
the open oxygen frameworks. When the orientation of oxygen vacancy channels
(OVCs) is properly controlled, one can drastically increase the surface oxygen
exchange rate approximately up to two orders of magnitude. The improved oxygen
reduction kinetics is attributed to a substantial decrease in the thermal
activation energy. Importantly, the strong enhancement of crystallographic
orientation-dependent oxygen reduction reaction required the creation of
neither structural disorders nor chemical doping. Thus, our epitaxial approach
can pave a novel pathway to providing precise interpretation of oxygen
reduction reactions and to developing oxide-based energy materials.
