The slow kinetics of the oxygen reduction reaction (ORR) is one of the key challenges in developing high performance energy devices, such as solid oxide fuel cells. Straining a film by growing on a lattice-mismatched substrate has been a conventional approach to enhance the ORR activity. However, due to the limited choice of electrolyte substrates to alter the degree of strain, a systematic study in various materials has been a challenge. Here, we explore the strain modulation of the ORR kinetics by growing epitaxial La0.6Sr0.4CoO3-δ (LSCO) films on yttria-stabilized zirconia substrates with the film thickness below and above the critical thickness for strain relaxation. Two orders of magnitude higher ORR kinetics is achieved in an ultrathin film with ∼0.8% tensile strain as compared to unstrained films. Time-of-flight secondary ion mass spectrometry depth profiling confirms that the Sr surface segregation is not responsible for the enhanced ORR in strained films. We attribute this enhancement of ORR kinetics to the increase in oxygen vacancy concentration in the tensile-strained LSCO film owing to the reduced activation barrier for oxygen surface exchange kinetics. Density functional theory calculations reveal an upshift of the oxygen 2p-band center relative to the Fermi level by tensile strain, indicating the origin of the enhanced ORR kinetics.
|Number of pages||8|
|Journal||Journal of Physical Chemistry C|
|State||Published - Nov 22 2017|
Bibliographical noteFunding Information:
This work was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences, Materials Science and Engineering Division (synthesis and structural characterization), and by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC, for the U.S. DOE (electrochemical characterization). The high-temperature XRD and SIMS measurements were conducted as a user project at the Center for Nanophase Materials Sciences, which is sponsored at ORNL by the Scientific User Facilities Division, U.S. DOE. Support for Ryan Jacobs and Dane Morgan for DFT calculations was provided by the National Science Foundation (NSF) Software Infrastructure for Sustained Innovation (SI2) Award No. 1148011. Computations in this work benefitted from the use of the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by NSF Grant OCI-1053575. We gratefully acknowledge helpful conversations with Professor Stu Adler.
© 2017 American Chemical Society.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Energy (all)
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films