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Nanostrukturen und Grenzflächen Poster: Do., 13:00–15:30 D-P284
Anomalous small-angle X-ray scattering investigation of Ru-Se catalysts
supported on carbon
Sylvio Haas 1 , Armin Hoell 1 , Gerald Zehl 1 , Sebastian Fichter 1
1 Hahn-Meitner-Institut Berlin, D-14109 Berlin
Carbon supported catalysts for use in fuel-cells based on ruthenium and selenium have
been prepared at the Hahn-Meitner-Institut in the department solar energy research
SE5. They are already tested to be promising catalysts. The aim behind this elements
instead of the platinum is expense factor and the deposit of the materials. Another
advantage of ruthenium and selenium is the possibility to use them in direct methanol
fuel cells (DMFC). Platnium is not useable in this case.
By studying the electrochemical behaviour and comparing it to the atomic structure
analysed by using EXAFS, XANES, TEM and XRD, many open questions remain [1,2].
One of the main open question is the real nanostructure, which is up to now unclear.
Particularly the selenium is important because the catalytic efficiency depends strongly
on the content of the selenium and also most probably on its bonds to ruthenium and
carbon. Up to now it is clear that most ruthenium form spherical particals with a
diameters of about 1nm to 8 nm dispersed on the surface of the black pearls (carbon).
Catalysts supported on porous materials like black perls (carbon) are a three phase
system (support, voids and metal). The use of synchrotron radiation allows to seperate
the scattering of the support from the one of the metal by taking advantage of the socalled
anomalous or resonant behavior of the atomic scattering amplitude of an element
near its absorption edge [3, 4].
A complete set of samples have been measured at the SAXS instrument (7T-WLS-
SAXS) at BESSY in Berlin. This means that we measured the final catalysts contains
ruthenium, selenium and the support (carbon). We also measured the carbon support
only and carbon samples which contains ruthenium only or selenium only on the support.
To seperate the scattering of the metals from the strong scattering of the porous
carbon particle, which have a diameter of about 50nm (internal surface ∼ 1800 m 2 /
g BET), combined measurments with X-ray energies near the Ru-K and Se-K X-ray
absorption edges have been performed. The ASAXS measurement should help to localize
the selenium which could mainly perform a shell surrounding the ruthenium or
distributed somewhere in the samples.
[1] M. Bron, P. Bogdanoff, S.Fichter, H.Tributsch; J. Electroanal. Chem. 578 (2005)
339 [2] M. Bron, P.Bogdanoff, S. Fichter, I. Dorbandt, M. Hilgendorff, H. Schulenburg,
H. Tributsch; J. Electroanal. Chem. 500 (2001) 510 [3] H. Brumberger, D. Hagrman,
J. Goodisman, K.D. Finkelstein; J. App. Cryst. 38 (2005) 147 [4] H. Brumberger, D.
Hagrman, J. Goodisman, K.D. Finkelstein; J. App. Cryst. 38 (2005) 324