A SERS investigation of the electrodeposition of Au in a phosphate solution

The spectroelectrochemical behaviour of cyanide and phosphate ions adsorbed on a Au electrode during electrodeposition and corrosion in a KAu(CN)2 phosphate bath was studied by in situ SERS (Surface Enhanced Raman Spectroscopy) and cyclic voltammetry. SERS spectra exhibiting features corresponding to CN− and PO4− vibrations were recorded under potentiostatic control in an interval from − 1600 to + 1500 mV vs. Ag/AgCl. Surface CN− species are the dominating ones under both cathodic and anodic polarisations. As far as the phosphate vibrations are concerned, bands related to PO4− are visible in both cathodic and anodic conditions. A fluorescence background was evident in the potential range − 1300 ÷ + 1300 mV. At cathodic potentials phosphate ion adsorption on electrode surface prevails over cyanide for potentials more cathodic than − 1000 mV. At − 700 mV a discontinuity is noticed in the Stark tuning of CN−, probably due to a change of Au(CN)2− adsorption mechanism. At anodic potentials bands due to cyanide oxidation could be observed.