Publications

We use photo-electrons as a non-contact probe to measure local electrical potentials in a solid-oxide electrochemical cell. We characterize the cell in operando at near-ambient pressure using spatially-resolved X-ray photoemission spectroscopy. The overpotentials at the interfaces between the Ni and Pt electrodes and the yttria-stabilized zirconia (YSZ) electrolyte are directly measured. The method is validated using electrochemical impedance spectroscopy. Using the overpotentials, which characterize the cell’s inefficiencies, we compare without ambiguity the electro-catalytic efficiencies of Ni and Pt, finding that on Ni H2O splitting proceeds more rapidly than H2 oxidation, while on Pt, H2 oxidation proceeds more rapidly than H2O splitting. © the Owner Societies.

Single chamber electrochemical cells were fabricated by patterning working and counter electrodes of Ni and Pt on single-crystal Y2O 3-stabilized ZrO2. Cells were characterized in mixed atmospheres of H2 and H2O at ratios of 1:1 and 1:20 at nominally 923 K and 67 Pa total pressure. Potential sweep and impedance measurements were conducted simultaneously with ambient-pressure x-ray photoelectron spectroscopy (APXPS), which is a unique synchrotron-based probe designed for in-situ chemical characterization of surfaces using photoemission at gas pressures large enough to achieve realistic densities of faradic current. Electrochemically induced oxidation of Ni was observed under anodic polarization and could be reversed by applying a cathodic bias. The thin-film microstructure could also be manipulated electrochemically in that pores exposing underlying electrolyte would open through the Ni film after polarization. Application of APXPS to resolve fundamental details of high-temperature electrochemical process in-situ is discussed. ©The Electrochemical Society.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Atmospheric pressure chemical vapor deposition (APCVD) of tin oxide is a very important manufacturing technique used in the production of low-emissivity glass. It is also the primary method used to provide wear-resistant coatings on glass containers. The complexity of these systems, which involve chemical reactions in both the gas phase and on the deposition surface, as well as complex fluid dynamics, makes process optimization and design of new coating reactors a very difficult task. In 2001 the U.S. Dept. of Energy Industrial Technologies Program Glass Industry of the Future Team funded a project to address the need for more accurate data concerning the tin oxide APCVD process. This report presents a case study of on-line APCVD using organometallic precursors, which are the primary reactants used in industrial coating processes. Research staff at Sandia National Laboratories in Livermore, CA, and the PPG Industries Glass Technology Center in Pittsburgh, PA collaborated to produce this work. In this report, we describe a detailed investigation of the factors controlling the growth of tin oxide films. The report begins with a discussion of the basic elements of the deposition chemistry, including gas-phase thermochemistry of tin species and mechanisms of chemical reactions involved in the decomposition of tin precursors. These results provide the basis for experimental investigations in which tin oxide growth rates were measured as a function of all major process variables. The experiments focused on growth from monobutyltintrichloride (MBTC) since this is one of the two primary precursors used industrially. There are almost no reliable growth-rate data available for this precursor. Robust models describing the growth rate as a function of these variables are derived from modeling of these data. Finally, the results are used to conduct computational fluid dynamic simulations of both pilot- and full-scale coating reactors. As a result, general conclusions are reached concerning the factors affecting the growth rate in on-line APCVD reactors. In addition, a substantial body of data was generated that can be used to model many different industrial tin oxide coating processes. These data include the most extensive compilation of thermochemistry for gas-phase tin-containing species as well as kinetic expressions describing tin oxide growth rates over a wide range of temperatures, pressures, and reactant concentrations.

Abstract not provided.