A SERS investigation of the electrodeposition of Ag–Au alloys from free-cyanide solutions

Abstract

In this paper we investigated the electrodeposition of Ag-Au alloys from cyanide baths by in situ surface-enhanced Raman spectroscopy. The spectroelectrochemical investigation is complemented by electrochemical experiments (cyclic voltammetry and potentiostatic electrodeposition) and structural (X-ray diffraction), morphological (scanning electron microscopy) and compositional (energy dispersive spectroscopy) characterisation of the alloys. Electrochemical and spectroelectrochemical results on singlemetal electrodeposition baths of otherwise identical composition are reported for comparison. Single-phase deposits of composition ranging from 13% to 75% Au were obtained potentiostatically. The voltammetric behaviour was correlated to the vibrational characteristics of adsorbed ligands. Quantitative and qualitative differences in interfacial chemistry as a function of applied potential were assessed and explained on the basis of variations in the nature of cyanide-related surface species. The cyanide and metaladsorbate stretching bands have been analysed.

Potentiostatic versus galvanostatic electrodeposition of nanocrystalline Al–Mg alloy powders

“…3 and indicates its evolution into large smooth globules and eventually to rough globules. Similar observations were found in the electrodeposition of Co powders [11] and Ag-Au alloys [12] where disperse growing entities eventually coarsened at their tips and evolved into compact entities. Formation of the spherical diffusion zones was mentioned to be the reason for the realization of compact growth at later stages.…”

Evolution of Morphology and Microstructure in Electrodeposited Nanocrystalline Al–Mg Alloy Dendrites

“…The size of the globules increased along the length of the dendrites. Similar observations were found in the electrodeposition of Co powders [4] and Ag-Au alloys [10] where disperse growing entities eventually coarsened at their tips and evolved into compact entities. Formation of the spherical diffusion zones was mentioned to be the reason for the realization of compact growth at later stages.…”

“…For example, in the galvanostatic deposition of Au-Ag alloys, dendritic precursors were observed in the initial stages of deposition under mixed activation-diffusion controlled conditions. At higher potentials produced in the later stages of deposition, due to the onset of the spherical diffusion condition, poorly defined crystallites and globular morphologies were found [10]. In the case of the electrodeposition of Cu it has been shown that at relatively low current densities, deposits formed with protruded tips which eventually grew in the form of carrot-like structures under activation-controlled mechanisms [11].…”

Nanoporous Gold Electrodes and Their Applications in Analytical Chemistry

“…Au:Ag alloys in the form of a thin film, multilayer, a rod (e.g., wire), or in a suitable template can be made via electrodeposition [45][46][47][48][49]. In this case, Ag and Au cyanide salts [45][46][47] (or other salts in a thiosulfate solution [50]) are combined in a given ratio. Upon application of a sufficiently reductive potential to a working electrode immersed in this solution, the two salts can be electrodeposited together yielding the binary alloy.…”

“…Upon application of a sufficiently reductive potential to a working electrode immersed in this solution, the two salts can be electrodeposited together yielding the binary alloy. Au electrodeposition is kinetically favored, while Ag deposition is thermodynamically favored [45,47]. Films of varying Au:Ag atomic percent can be made by altering the deposition potential and/or solution composition [51].…”