Functional Materials for Energy

Orienting oxygen defects for enhanced oxygen reduction kinetics

Schematics of SrCoO2.5 epitaxial films with the oxygen vacancy channels parallel to the film surface (left, low ORR activity) and terminating at the surface (right, high ORR activity), achieved by epitaxial growth onto differently oriented substrates.

Functional oxygen defects are shown to result in a two orders of magnitude improvement of the catalytic oxygen reduction kinetics in epitaxial SrCoO2.5 films. This discovery will impact our understanding of the fundamental properties in multivalent transition metal oxides and provides technological insights into developing new strategies for advanced energy materials and systems.

The oxygen reduction reaction (ORR) is one of the critical rate-limiting processes in many applications, including catalytic converters, oxygen-separation membranes, solid oxide fuel cells (SOFC), and batteries. Yet, a systematic understanding of the complex functional coupling between the catalytic reactions and surface states in transition metal oxides has not been achieved due to the lack of oriented single crystalline materials. Here, improved ORR kinetics are obtained in brownmillerite SrCoO2.5 films if the oxygen vacancy channels are oriented such that they reach the surface, rather than running parallel to it. This demonstrates that controlling the orientation of catalytically functional defects in cathode materials is a useful design strategy in the development of new materials for advanced energy technologies.

H. Jeen, Z. Bi, W. S. Choi, M. F. Chisholm, C. A. Bridges, M. P. Paranthaman, and H. N. Lee, “Orienting oxygen vacancies for fast catalytic reaction,” Advanced Materials DOI: 10.1002/adma.201302919.

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