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

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 hydrogen-related species to yield adsorbed CH2=NH and CH3-NH2. Similarly, in Ag(I) baths, Ag-CN¯ reacts to polycyanogens. No reactivity of Cu-CN¯ was found, under otherwise identical conditions. Our conclusions are supported also by dedicated DFT molecular computations.