Insights into the Effects of Chloride ions on Cyanide-Free Gold Electrodeposition

Abstract

It is very simple and convenient using the commercial chloroauric acid instead of sodium gold sulfite as the main salt in the Au(I) sulfite electrodeposition bath. In this paper, the effects of chloride ions on cyanide-free Au(I) electrodeposition in the gold sulfite bath are carefully investigated. Both UV-vis absorption spectroscopy and visual inspection reveal that chloride ions suppress the disproportionation reaction of Au(I) and improve the bath stability. Cyclic voltammetry indicates that chloride ions promote the cathodic reduction of Au(I). EC-SERS spectra elucidate that in the sodium sulfite solution, SO 3 2− ions firstly adsorb on the gold electrode, then experience a structural transformation (SO 3 2− → S 2 O 5 2−), and last electroreduce to) as the potential shifts negatively. In the gold sulfite electrolytes, the cathodic reduction of Au(I) and chloride ions hinder the reduction of S 2 O 5 2− ions. The gold coatings obtained from the gold sulfite electrolyte containing chloride ions present in fine and pure grains without chlorine and sulfur inclusion.

Suppressing Sulfite Dimerization at a Polarized Gold Electrode/Water Solution Interface for High-Quality Gold Electrodeposition

“…Therefore, sulfite is a suitable complexant for the cyanide-free electrodeposition of these metals. − For the oxidation process, sulfite is inherently unstable and commonly oxidized to sulfate (SO 3 2– → SO 4 2– ). , However, studies on the cathodic process of sulfite are very limited. In our previous work, we first reported that sulfite first experienced a dimerization to metabisulfite, then followed an electroreduction to thiosulfate (SO 3 2– → S 2 O 5 2– → S 2 O 3 2– ) with the potential shifted negatively at a gold electrode/water solution interface . The intricate electrochemical reactions led to the adsorption of S 2 O 5 2– and S 2 O 3 2– on the cathode.…”

“…In our previous work, we first reported that sulfite first experienced a dimerization to metabisulfite, then followed an electroreduction to thiosulfate (SO 3 2− → S 2 O 5 2− → S 2 O 3 2− ) with the potential shifted negatively at a gold electrode/water solution interface. 25 The intricate electrochemical reactions led to the adsorption of S 2 O 5 27 Therefore, the suppression of sulfite dimerization and its subsequent electroreduction can not only elaborate the reaction mechanism of sulfite at the solid/water interface but also provide a practical guidance for the metal electrodeposition.…”