AVS 59th Annual International Symposium and Exhibition
    In Situ Microscopy and Spectroscopy Focus Topic Tuesday Sessions
       Session IS+AS+SS+EN-TuM

Paper IS+AS+SS+EN-TuM5
Epitaxial Strontium Substituted Lanthanum Cobalt Oxides Investigated using In Situ Ambient Pressure X-ray Photoelectron Spectroscopy Near Operating Conditions Under Applied Potentials

Tuesday, October 30, 2012, 9:20 am, Room 007

Session: In Situ Spectroscopic Studies of Catalysis and Gas-Solid Reactions
Presenter: E. Crumlin, Massachusetts Institute of Tech.
Authors: E. Crumlin, Massachusetts Institute of Tech.
E. Mutoro, Massachusetts Institute of Tech.
Z. Liu, Lawrence Berkeley National Lab
M.D. Biegalski, Oak Ridge National Lab
W.T. Hong, Massachusetts Institute of Tech.
H.M. Christen, Oak Ridge National Lab
H. Bluhm, Lawrence Berkeley National Lab
Y. Shao-Horn, Massachusetts Institute of Tech.
Correspondent: Click to Email
Operating conditions for solid oxide fuel cell (SOFC) are typically at high temperatures (~500 – 1000 °C) and ambient pressures (~1 atm). We have to understand how the physical and chemical properties of SOFC materials, particularly the cathode which is responsible for a majority of the fuel cells area specific resistance, change under operating conditions. Such data can provide insights into the mechanism of the oxygen reduction reaction (ORR) which may lead to material development strategies to improve the cathode performance. However, these operating conditions are far away from conventional characterization techniques that are often applied at room temperature or even in ultrahigh vacuum (UHV). Our recent work using in situ ambient pressure X-ray photoelectron spectroscopy (APXPS) has shown that (001) oriented epitaxial films of La0.8Sr0.2CoO3–δ (LSC113) can exhibit Sr enrichment in the near-surface perovskite lattice structure (“lattice”) as temperatures were raised from 220 °C to 520 °C in a p(O2) of 1×10-3 atm. In contrast under the same conditions, a bulk pellet of LSC demonstrated no changes in Sr content within the “lattice” region. The Sr enrichment is believed to play a key role in the observed one order of magnitude enhancement in ORR activity (as measured by the surface exchange coefficient, kq) of the (001) epitaxial films relative to bulk LSC113. In this work, we continue the previous investigations of the chemical properties of (001) epitaxial LSC113 as a function of temperature cycling between 220 °C and 520 °C at a p(O2) of 1×10–3 atm. Additionally, the comparison of LSC113­, (La0.5Sr0.5)2CoO4±δ (LSC214), and LSC214-decorated LSC113 (LSC113/214) at p(O2) of 1×10–3 atm as a function of temperature and under applied cathodic potentials will be presented in order to provide insights into the physical origin responsible for the observed ~3 orders of magnitude ORR activity enhancement of LSC113/214 relative to (001) epitaxial LSC113.