Article pubs.acs.org/JPCC
In Situ Ambient Pressure X‑ray Photoelectron Spectroscopy of Cobalt Perovskite Surfaces under Cathodic Polarization at High Temperatures Ethan J. Crumlin,†,⊥ Eva Mutoro,†,# Wesley T. Hong,† Michael D. Biegalski,‡ Hans M. Christen,‡ Zhi Liu,§ Hendrik Bluhm,∥ and Yang Shao-Horn*,† †
Electrochemical Energy Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States ‡ Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States § Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States ∥ Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States S Supporting Information *
ABSTRACT: Heterostructured oxide interfaces have demonstrated enhanced oxygen reduction reaction rates at elevated temperatures (∼500−800 °C); however, the physical origin underlying this enhancement is not well understood. By using synchrotron-based in situ ambient pressure X-ray photoelectron spectroscopy (APXPS), we focus on understanding the surface electronic structure, elemental composition, and chemical nature of epitaxial La0.8Sr0.2CoO3−δ (LSC113), (La0.5Sr0.5)2CoO4±δ (LSC214), and LSC214decorated LSC113 (LSC113/214) thin films as a function of applied electrical potentials (0 to −800 mV) at 520 °C and p(O2) of 1 × 10−3 atm. Shifts in the top of the valence band binding energy and changes in the Sr 3d and O 1s spectral components under applied bias reveal key differences among the film chemistries, most notably in the degree of Sr segregation to the surface and quantity of active oxygen sites in the perovskite termination layer. These differences help to identify important factors governing the enhanced activity of oxygen electrocatalysis observed for the LSC113/214 heterostructured surface.
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INTRODUCTION
possesses a synchrotron high-intensity X-ray source coupled with a differentially pumped electrostatic lens system that is capable of conducting ambient pressure (
