[Show abstract][Hide abstract] ABSTRACT: Pd nanofilms were grown on Au(111) using the electrochemical form of atomic layer deposition (E-ALD). Deposits were formed by repeated cycles of surface-limited redox replacement (SLRR). Each cycle produced an atomic layer of Pd, allowing the reproducible formation of Pd nanofilms, with thicknesses proportional to the number of cycles performed. Pd deposits were formed with up to 30 cycles, in the present study, and used as a platform for studies of hydrogen sorption/desorption as a function of thickness. The SLRR cycle involved the initial formation of an atomic layer of Cu by underpotential deposition, followed by its galvanic exchange with PdCl42– ions at open circuit. The first three cycles were studied using in situ electrochemical scanning tunneling microscopy (EC-STM), which showed a consistent morphology from cycle to cycle and the monatomic steps indicative of layer-by-layer growth. Cyclic voltammetry was used to study the hydrogen sorption/desorption properties as a function of thickness in 0.1 M H2SO4. The results indicated that the underlying Au structure greatly influenced hydrogen adsorption, as did film thickness for deposits formed with fewer than five cycles. No hydrogen absorption occurred for the thinnest films, although it increased linearly for thicker films, producing an average H/Pd molar ratio of 0.6. Electrochemical annealing was shown to improve surface order, producing CVs that strongly resembled those characteristic of bulk Pd(111).
The Journal of Physical Chemistry C. 07/2013; 117(30):15728–15740.
[Show abstract][Hide abstract] ABSTRACT: Supported metallic nanoparticles have long been employed to catalyze a number of industrially-relevant chemical reactions. In many cases, metal addition has allowed one to increase the activity, selectivity and/or stability of single-metal catalysts. However, a detailed understanding of catalysis by metal nanoparticles, including nanoalloys, requires the use of model catalysts such as single-crystal surfaces and well-defined supported nanoparticles. In this chapter, after a brief presentation of its basic concepts, the structural aspects of heterogeneous catalysis by metals and alloys will be illustrated by several examples from (mainly) surface science. The so-called “size” and “alloying” effects, which have been classically described in terms of geometric and electronic effects, might have more subtle origins (morphology, support, etc.) and be interrelated. In turn, the structure of supported nanoparticles is highly sensitive to the reaction conditions, as illustrated by examples of adsorption-induced surface restructuring and segregation. In spite of this complexity, it will be shown that the recent advances in operando experimentation and computer simulation open the way to a “rational design” of bimetallic catalysts.
Nanoalloys: Synthesis, Structure and Properties, Springer edited by D. Alloyeau, C. Mottet, C. Ricolleau, 01/2012: chapter 11: pages pp. 369-404; Springer-Verlag., ISBN: 978-1-4471-4013-9
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