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Structure and Chemical Composition of a Surfactant-Stabilized Pt3Sn Alloy Colloid

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Bönnemann,  Helmut
Research Group Bönnemann, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

Britz,  P.
Research Group Bönnemann, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Vogel,  Walter
Fritz Haber Institute, Max Planck Society;

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Citation

Bönnemann, H., Britz, P., & Vogel, W. (1998). Structure and Chemical Composition of a Surfactant-Stabilized Pt3Sn Alloy Colloid. Langmuir, 14(23), 6654-6657. doi:10.1021/la980459v.


Cite as: https://hdl.handle.net/21.11116/0000-0008-9CFD-C
Abstract
A tetraoctylammonium-stabilized PtSn colloid with nominal composition Pt3Sn has been prepared by coreduction of the metal salts. This colloid, which is used in the manufacture of anode catalysts for low-temperature polymer membrane fuel cells, was supported on silica and the structure studied by in situ X-ray diffraction and Debye function analysis. Results indicate that the supported colloid is best described as a highly disordered bimetallic fcc cluster with a particle size of ∼1.3 nm. From TEM images a slightly larger size of 1.5 ± 4 nm is derived. Point-resolved EDX (energy-dispersive X-ray spectroscopy) confirms the elemental ratio of 3:1 in the PtSn particles. However, the XRD simulation indicates some deviations from uniform alloy formation. On removal of the stabilizing tetraoctylammonium ligands by heating the samples in He to ∼200 °C, coalescence of neighboring particles occurs. The new alloy formed consists of a majority of cubic Pt0.81Sn0.19 particles, with average size 3.1 nm, and a minority phase of stoichiometric hexagonal PtSn, 4.4 nm in size. The former phase can be considered as a metastable supersaturated solid solution of Sn in Pt. The two phases are stable even on heating to 375 °C for 1.5 h in He.