The Role of Atomic Ensembles in the Reactivity of Bimetallic Electrocatalysts

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Science  07 Sep 2001:
Vol. 293, Issue 5536, pp. 1811-1814
DOI: 10.1126/science.1061696

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Bimetallic electrodes are used in a number of electrochemical processes, but the role of particular arrangements of surface metal atoms (ensembles) has not been studied directly. We have evaluated the electrochemical/catalytic properties of defined atomic ensembles in atomically flat PdAu(111) electrodes with variable surface stoichiometry that were prepared by controlled electrodeposition on Au(111). These properties are derived from infrared spectroscopic and voltammetric data obtained for electrode surfaces for which the concentration and distribution of the respective metal atoms are determined in situ by atomic resolution scanning tunneling microscopy with chemical contrast. Palladium monomers are identified as the smallest ensemble (“critical ensemble”) for carbon monoxide adsorption and oxidation, whereas hydrogen adsorption requires at least palladium dimers.

  • * Present address: Laboratoire de Physique des Liquides et Electrochimie (CNRS UPR-15), Université P & M Curie, 4 Place Jussieu, F–75005 Paris, France.

  • Permanent address: Laboratoire de Physique de la Matière Condensée, CNRS–Ecole Polytechnique, F-91128 Palaiseau, France.

  • To whom correspondence should be addressed. E-mail: olaf.magnussen{at} (O.M.M.); juergen.behm{at} (R.J.B.)

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