Voltammetric and in situ FTIRS study on CN− and Au(CN)−x complexes at the polycrystalline gold surface in citrate medium

The adsorption and reactivity of citrate anions, cyanide anions, and the Au(I) and Au(III) cyanocomplexes (KAu(CN)2 and KAu(CN)4, respectively) on gold polycrystalline electrodes have been investigated by means of cyclic voltammetry and in situ FTIR spectroscopy in pH 7 sodium citrate medium. It was found that citrate anion adsorbs reversibly through the carboxylate groups from 0.4 V (RHE) on bare gold surfaces. However, the onset of this adsorption process is shifted by 600 mV in the positive direction when adsorbed cyanide species are present at the electrode surface. The Au(I) cyanocomplex produces a film on the gold electrode that inhibits the oxidation of both citrate anions and the gold surface. The reduction of the Au(III) cyanocomplex gives rise to the formation of the Au(I) cyanocomplex at potentials less negative than those required for gold deposition. Upon reduction, both cyanocomplexes release adsorbed cyanide on the gold electrode, which can be subsequently oxidized to cyanate at higher potentials.