A SERS Investigation of Cyanide Adsorption and Reactivity during the Electrodeposition of Gold, Silver and Copper from Aqueous Cyanocomplexes Solutions

TL;DR

This study uses SERS to investigate how cyanide adsorbs and reacts during the electrodeposition of gold, silver, and copper from cyanocomplex solutions, revealing metal-dependent reactivity and reaction pathways.

Contribution

It provides new insights into cyanide reactivity on electrode surfaces during metal deposition, supported by experimental SERS data and DFT calculations.

Findings

Au-CN reacts with Au-H, forming adsorbed amines.

Ag-CN reacts with Ag-H, producing polycyanogens.

Cu-CN shows no reactivity under tested conditions.

Abstract

In this paper we report on the reactivity of adsorbed cyanide deriving from ligand release during metal electrodeposition from cyanocomplex solutions of Au(I), Au(III), Ag(I) and Cu(I) in H2O and D2O. When CN is adsorbed at cathodic potentials in excess of the HER threshold, metal-dependent reactivity can be detected by SERS. Finite surface coverages with adsorbed CN at such cathodic potentials can be obtained only if CN is delivered directly to the cathode surface as by decomplexing of the cyanocomplexes of the metals undergoing cathodic reduction. In Au(I) and Au(III) baths, Au-CN reacts with Au-H and is hydrogenated to adsorbed CH2=NH and CH3-NH2. In Ag(I) baths, Ag-CN reacts with Ag-H giving rise to polycyanogens. No reactivity of Cu-CN was found, under otherwise identical conditions. Our conclusions are supported also by dedicated DFT molecular computations.