Bimetallic Clusters by Underpotential Deposition on Layered Au Nanoparticle Films

Characterization of Pt@Cu core@shell dendrimer-encapsulated nanoparticles synthesized by Cu underpotential deposition

Dendrimer-encapsulated nanoparticles (DENs) containing averages of 55, 147, and 225 Pt atoms immobilized on glassy carbon electrodes served as the electroactive surface for the underpotential deposition (UPD) of a Cu monolayer. This results in formation of core@shell (Pt@Cu) DENs. Evidence for this conclusion comes from cyclic voltammetry, which shows that the Pt core DENs catalyze the hydrogen evolution reaction before Cu UPD, but that after Cu UPD this reaction is inhibited. Results obtained by in situ electrochemical X-ray absorption spectroscopy (XAS) confirm this finding.

Sieving behaviour of nanoscopic pores by hydrated ions

In this study, for the first time, the anion dependency of Ag-deposition on self-assembled monolayers (SAMs) with alkyl chains long enough to meet the densely packed and well-organized surface is reported. Irrespective of pH, types of terminal groups of the SAMs, and the convective mass transfer condition, SAM structures show the "sieving behaviour" to the Ag deposition by the composition of the electrolytes.

Electrochemical Characterization of Polyelectrolyte/Gold Nanoparticle Multilayers Self-Assembled on Gold Electrodes

Polyelectrolyte/gold nanoparticle multilayers composed of poly(l-lysine) (pLys) and mercaptosuccinic acid (MSA) stabilized gold nanoparticles (Au NPs) were built up using the electrostatic layer-by-layer self-assembly technique upon a gold electrode modified with a first layer of MSA. The assemblies were characterized using UV-vis absorption spectroscopy, cyclic and square-wave voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy. Charge transport through the multilayer was studied experimentally as well as theoretically by using two different redox pairs [Fe(CN)(6)](3-/4-) and [Ru(NH(3))(6)](3+/2+). This paper reports a large sensitivity to the charge of the outermost layer for the permeability of these assemblies to the probe ions. With the former redox pair, dramatic changes in the impedance response were obtained for thin multilayers each time a new layer was deposited. In the latter case, the multilayer behaves as a conductor exhibiting a strikingly lower impedance response, the electric current being enhanced as more layers are added for Au NP terminated multilayers. These results are interpreted quite satisfactorily by means of a capillary membrane model that encompasses the wide variety of behaviors observed. It is concluded that nonlinear slow diffusion through defects (pinholes) in the multilayer is the governing mechanism for the [Fe(CN)(6)](3-/4-) species, whereas electron transfer through the Au NPs is the dominant mechanism in the case of the [Ru(NH(3))(6)](3+/2+) pair.

Designed Nanostructured Pt Film for Electrocatalytic Activities by Underpotential Deposition Combined Chemical Replacement Techniques

Multiple-deposited Pt overlayer modified Pt nanoparticle (MD-Pt overlayer/PtNPs) films were deliberately constructed on glassy carbon electrodes through alternately multiple underpotential deposition (UPD) of Ag followed redox replacement reaction by Pt (II) cations. The linear and regular growth of the films characterized by cyclic voltammetry was observed. Atomic force spectroscopy (AFM) provides the surface morphology of the nanostructured Pt films. Rotating disk electrode (RDE) voltammetry and rotating ring-disk electrode (RRDE) voltammetry demonstrate that the MD-Pt overlayer/PtNPs films can catalyze an almost four-electron reduction of O(2) to H(2)O in air-saturated 0.1 M H(2)SO(4). Thus-prepared Pt films behave as novel nanostructured electrocatalysts for dioxygen reduction and hydrogen evolution reaction (HER) with enhanced electrocatalytic activities, in terms of both reduction peak potential and peak current, when compared to that of the bulk polycrystalline Pt electrode. Additionally, it is noted that after multiple replacement cycles, the electrocatalytic activities improved remarkably, although the increased amount of Pt is very low in comparison to that of pre-modified PtNPs due to the intrinsic feature of the UPD-redox replacement technique. In other words, the electrocatalytic activities could be improved markedly without using very much Pt by the technique of tailoring the catalytic surface. These features may provide an interesting way to produce Pt catalysts with a reliable catalytic performance as well as a reduction in cost.