Direct electrodeposition of mercury onto gold nanorods on an ITO substrate, without reducing agents, is reported. The growth of single gold amalgam nanoalloy particles and subsequent stripping was monitored in real-time monitoring by plasmonic effects and single-nanoparticle dark-field spectroelectrochemistry techniques. Time-dependent scattering spectral information conferred insight into the growth and stripping mechanism of a single nanoalloy particle. Four critical stages were observed: First, rapid deposition of Hg atoms onto Au nanorods; second, slow diffusion of Hg atoms into Au nanorods; third, prompt stripping of Hg atoms from Au nanorods; fourth, moderate diffusion from the inner core of Au nanorods. Under high Hg(2+) concentrations, homogeneous spherical gold amalgam nanoalloys were obtained. These results demonstrate that the morphology and composition of individual gold amalgam nanoalloys can be precisely regulated electrochemically. Moreover, gold amalgam nanoalloys with intriguing optical properties, such as modulated plasmonic lifetimes and quality factor Q, could be obtained. This may offer opportunities to extend applications in photovoltaic energy conversion and chemical sensing.

Real-Time Plasmonic Monitoring of Single Gold Amalgam Nanoalloy Electrochemical Formation and Stripping.

Electrochemical studies of the UPD of mercury on Au(111) electrodes have been carried out in sulfuric acid and in perchloric acid alone as well as in the presence of sulfate and chloride anions and in acetate/acetic acid buffer with emphasis on the processes taking place in the presence of (bi)sulfate anions. These voltammetric studies have been compared to recent in-situ AFM, STM, and surface X-ray scattering studies in an effort to correlate voltammetric features with surface structures and their transitions. The different processes taking place during mercury UPD on A(111) in sulfuric acid can be summarized as follows:  (i) At potentials higher than the first mercury UPD peak, there exists an ordered (bi)sulfate adlayer. The onset of mercury deposition triggers an order/disorder transition that gives rise to the first set of UPD peaks; C1/A1. (ii) Mercury deposition is governed mainly by mercury−gold interactions. As monolayer deposition reaches completion a disorder/order transition takes place giving...

Underpotential Deposition of Mercury on Au(111): Electrochemical Studies and Comparison with Structural Investigations

Partial charge transfer and adsorption at metal electrodes. The underpotential deposition of Hg(I), Tl(I), Bi(III) and Cu(II) on polycrystalline gold electrodes

We report on an in situ surface X-ray diffraction study of the underpotential deposition (UPD) of mercury on Au(111). We have observed three UPD phases present at potentials prior to bulk mercury deposition. These phases consist of two well-ordered intermediate states and what appears to be either a fully discharged two-dimensional liquid Hg layer or a monolayer of an amorphous Hg-Au alloy. Both ordered intermediate phases have hexagonal structures with lattice vectors that are rotated 30{degree} from those of the Au(111) substrate. The first phase (phase I), present at a potential of +0.68 V, was only observed on fresh flame-annealed Au(111) electrodes and appears to be an open incommensurate structure with a lattice constant of 3.86 {+-} 0.03 A. This phase appears to be metastable since it changes to a second ordered phase (phase II) after a certain time. The second phase has a more compact lattice with a = 3.34 {+-} 0.01 A and appears to be a commensurate 2x2 structure with 2/3 of the Hg atoms at threefold hollow sites and 1/3 on atop sites. Similar to the first one, this phase is also metastable and can be transformed to a final, fully discharged, state of a two-dimensionalmore » liquid Hg layer or an amorphous Hg-Au alloy. The entire Hg UPD process, from Hg{sup 2+} to the fully discharged metallic Hg layer, agrees well with a multistep mechanism based on previous electrochemical kinetic studies on polycrystalline Au electrodes. 31 refs., 10 figs., 2 tabs.« less

G. Salié

Papers

Partial charge transfer in the underpotential deposition of metals: Part II. mercury deposition on polycrystalline gold electrodes