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Pt-Ru fuel cell catalysts subjected to H2, CO, N2 and air atmosphere: An X-ray absorption study

Roth, C. and Benker, N. and Mazurek, M. and Scheiba, F. and Fuess, H. (2007):
Pt-Ru fuel cell catalysts subjected to H2, CO, N2 and air atmosphere: An X-ray absorption study.
In: Applied Catalysis A: General, Elsevier Science Publishing Company, p. 81, 319, ISSN 0926860X, [Online-Edition: http://dx.doi.org/10.1016/j.apcata.2006.11.018],
[Article]

Abstract

In situ X-ray absorption spectroscopy (XAS) measurements were carried out on commercial carbon-supported Pt, Ru and Pt-Ru alloy electrocatalysts as well as a Pt/Ru mixture electrocatalyst in a specifically designed reactor/furnace set-up at the Pt L3 and the Ru K edge. The catalysts were heated to 100 °C and subjected to different atmospheres – 5% H2/N2, 5% CO/N2, N2, air – of interest for fuel cell operation. X-ray absorption spectroscopy was used to follow changes in the catalyst structure, most importantly particle growth, oxidation, and (de-)alloying. Alloying is observed to be advantageous, as it decreases particle growth and oxidation tendency in the catalysts. Initially, all electrocatalysts contained large amounts of the respective oxides, as indicated by pronounced white-line intensities in the XANES spectra, whereas the catalysts were reduced to the metallic state upon exposure to hydrogen. In CO atmosphere, however, ruthenium oxides remain stable, depending on the Pt to Ru site distribution: it is assumed that Pt in contact with Ru acts as a “catalyst” for the reduction of ruthenium oxides and strengthens the Ru–CO bond favouring it over Ru-O (ligand effect). Consequently, the share of ruthenium oxides in the Pt-Ru alloy decreases in 5% CO/N2, whereas for the Pt/Ru mixture and the pure Ru it does not change significantly.

Item Type: Article
Erschienen: 2007
Creators: Roth, C. and Benker, N. and Mazurek, M. and Scheiba, F. and Fuess, H.
Title: Pt-Ru fuel cell catalysts subjected to H2, CO, N2 and air atmosphere: An X-ray absorption study
Language: English
Abstract:

In situ X-ray absorption spectroscopy (XAS) measurements were carried out on commercial carbon-supported Pt, Ru and Pt-Ru alloy electrocatalysts as well as a Pt/Ru mixture electrocatalyst in a specifically designed reactor/furnace set-up at the Pt L3 and the Ru K edge. The catalysts were heated to 100 °C and subjected to different atmospheres – 5% H2/N2, 5% CO/N2, N2, air – of interest for fuel cell operation. X-ray absorption spectroscopy was used to follow changes in the catalyst structure, most importantly particle growth, oxidation, and (de-)alloying. Alloying is observed to be advantageous, as it decreases particle growth and oxidation tendency in the catalysts. Initially, all electrocatalysts contained large amounts of the respective oxides, as indicated by pronounced white-line intensities in the XANES spectra, whereas the catalysts were reduced to the metallic state upon exposure to hydrogen. In CO atmosphere, however, ruthenium oxides remain stable, depending on the Pt to Ru site distribution: it is assumed that Pt in contact with Ru acts as a “catalyst” for the reduction of ruthenium oxides and strengthens the Ru–CO bond favouring it over Ru-O (ligand effect). Consequently, the share of ruthenium oxides in the Pt-Ru alloy decreases in 5% CO/N2, whereas for the Pt/Ru mixture and the pure Ru it does not change significantly.

Journal or Publication Title: Applied Catalysis A: General
Volume: 319
Publisher: Elsevier Science Publishing Company
Uncontrolled Keywords: Electrocatalysts, Fuel cell, Heat-treatment, In situ, Pt, Pt-Ru, X-ray absorption spectroscopy
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Erneuerbare Energien
11 Department of Materials and Earth Sciences > Material Science > Structure Research
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 20 Feb 2013 12:19
Official URL: http://dx.doi.org/10.1016/j.apcata.2006.11.018
Identification Number: doi:10.1016/j.apcata.2006.11.018
Funders: Financial support of the Deutsche Forschungsgemeinschaft is gratefully acknowledged.
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