Publications Search Results

Now showing 1 - 2 of 2
  • Publication
    Electrooxidation of ethanol on Pt. An in situ and time-resolved XANES study
    ( 2012)
    Melke, Julia
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    Schoekel, Alexander
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    Gerteisen, Dietmar
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    Dixon, Ditty
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    Ettingshausen, F.
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    Roth, C.
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    Ramaker, David E.
    The ethanol oxidation reaction is studied using X-ray absorption spectroscopy during chronoamperometric cell operation with a carbon-supported Pt catalyst. The analysis of the XANES region of the Pt L 3 edge by the -technique allows the coverage of the Pt surface with OH-, n-fold O-, and C-species to be determined. The current-voltage characteristics and the coverage is modeled by means of a multistep reaction mechanism based on a modified Butler-Volmer approach that additionally includes adsorbate-adsorbate lateral interactions. The model is validated against experimental current and surface coverage data over time. With the model, the importance of acetaldehyde formation via initial C -H vs O-H bond cleavage is examined, the latter dominating at higher potentials on vacant sites remaining in the oxygen coverage coming from water activation.
  • Publication
    The use of in situ X-ray absorption spectroscopy in applied fuel cell research
    ( 2010)
    Croze, V.
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    Ettingshausen, F.
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    Melke, Julia
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    Söhn, M.
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    Stürmer, D.
    ;
    Roth, C.
    For a detailed understanding and systematic optimization of fuel cell systems, in situ studies are an indispensable tool, as they provide information on the catalyst structure in different operation conditions. X-ray absorption spectroscopy (XAS) is in particular suitable for operando investigations, since it does not require ultra high vacuum conditions or long-range order in the sample. Furthermore, it provides in situ information on oxidation state, adsorbed species and catalyst structure, and thus complements ex situ information, e.g. from X-ray diffraction (structure), X-ray photoelectron spectroscopy (oxidation state) and FTIR (adsorbates) nicely. In a spectroelectrochemistry experiment, XAS can be combined with different electrochemical techniques in order to satisfy different needs and scientific aims. Spectra of both a Pt-Ru anode catalyst and a Pt-Co cathode catalyst were recorded at different potentials, while measuring the current-potential characteristics of a single cell. So-called half-cell measurements, where the former fuel cell cathode was used with hydrogen as the reference electrode, were performed in water and ethanol to obtain a more detailed mechanistic insight into the ethanol electrooxidation. From a more industrial point of view, different catalysts were tested with a fast potential cycling protocol simulating rapid load changes in a vehicle.