AVS 50th International Symposium
    Electrochemistry and Fluid Solid Interfaces Tuesday Sessions
       Session EC+SS-TuM

Paper EC+SS-TuM6
Ultrahigh Vacuum Studies of Static and Dynamic Solid Oxide Electrocatalysts by Field Ionization and Spectroscopic Techniques

Tuesday, November 4, 2003, 10:00 am, Room 326

Session: Water at Interfaces I: Structure and Electrochemistry
Presenter: R.A. Manghani, University of Washington
Authors: R.A. Manghani, University of Washington
V.K. Medvedev, University of Washington
E.M. Stuve, University of Washington
Correspondent: Click to Email
Understanding solid oxide fuel cell reactions and electrochemical promotion of catalysts requires a complete description of the three-phase boundary (catalyst/electrolyte/fluid) under both static and dynamic (that is, reacting) conditions. We have undertaken two approaches to examine solid oxide electrocatalytic surfaces under well-defined, ultrahigh vacuum (UHV) conditions. The first method uses field ionization and field emission methods to probe the static properties of the three-phase boundary. A platinum field emitter tip of radius 35 nm was studied in a highly oxidized state and in the form of a Pt/ceria supported catalyst. Subsurface oxygen, which has been implicated in the NEMCA effect, was prepared on the platinum tip by oxygen ion sputtering at high temperature. Local work function measurements were performed by field emission microscopy to examine the oxide surface with and without chemisorbed oxygen. Pt/ceria surfaces were prepared by coating the Pt tip with a ceria adlayer and then evaporating platinum onto the ceria coating. The reactions of hydrocarbons (methane and butane) and water were examined on the Pt/ceria substrates by field ionization microscopy and mass spectrometry (time-of-flight and Wien filter modes). The second method uses a full solid oxide fuel cell (SOFC) operating in an ultrahigh vacuum system. The UHV-SOFC permits study of solid oxide anodes for direct oxidation of hydrocarbons such as methane and butane. The anode consists of a ceria coated YSZ pellet (5 mm diameter), which has a sealed tube on the cathode side to deliver oxygen at approximately 1 mbar. The anode side was studied by x-ray photoelectron spectroscopy, Auger electron spectroscopy, and quadrupole mass spectrometry while being exposed to the hydrocarbon reactant. The UHV-SOFC thus allows surface analysis of a dynamic electrocatalyst surface. This work is supported by the Office of Naval Research.