1. Center for Functional Nanomaterials Seminar

    ""Surface chemistry of model solid oxide electrochemical cells studied in-situ by synchrotron based photoemission microscopy and spectroscopy""

    Presented by Kaveh Adib, Science and Technology Division, Corning Incorporated

    Monday, March 11, 2013, 10 am
    CFN, Bldg 735, Conference Room B

    Hosted by: Peter Sutter

    Despite its ability to measure surface composition, oxidation state and speciation, the use of X-ray photoelectron spectroscopy (XPS) in investigating surface reactions is extremely limited due its ultrahigh vacuum (UHV) limitations. In this talk I will present a series of applications of XPS both in UHV settings and in near ambient conditions. As a UHV tool, XPS is a materials surface characterization tool with limited applicability to practical surface reaction studies. The bulk of the talk will be devoted to synchrotron based XPS and scanning photoemission microscopy (SPEM) studies of the surface compositions of model electrochemical systems containing a cathode, primarily LaxSr1- xMnO3 (LSM), and yttrium-stabilized zirconia (YSZ) electrolyte under various oxygen pumping conditions at approximately 650°C. SPEM in the vicinity of the LSM/YSZ interface indicates depletion of Mn atoms from the LSM surface and their accumulation on the YSZ surface with increasing cathodic bias. XPS indicates that the accumulation of Mn on the YSZ is accompanied by reduction in the oxidation state of Mn. Within a wide range of applied voltage these changes are reversible. XPS of oxygen core levels also indicates that under cathodic bias, during which oxygen is incorporated from the surrounding gas into the cathode and pumped through the electrolyte, an additional oxygen species is present on the surface of LSM. Preliminary results of application of these studies to electrochemical promotion of catalysis in near ambient conditions will also be presented.