Electromicrogravimmetric Study of the Effect of Cl – Anions on Thallium Underpotential Deposition Onto Gold

Abstract. The effect of chloride adsorption on underpotential deposi-tion of thallium onto gold electrode was studied using cyclic voltam-metry coupled with microgravimetry. The results obtained suggest the existence of two potential regions with different processes occur-ring during Tl UPD in the presence of anions. In the first zone, at low coverage, there are two simultaneously occurring processes: desorp-tion of all chloride atoms, which are adsorbed on the gold substrate prior to the onset of Tl UPD, and thallium adsorption on the energeti-cally most favorable sites (grain boundaries, steps, etc) present on the electrode surface. During these processes a strong interaction among thallium atoms is induced by the presence of chloride atoms on the adjacent sites. This strong interaction generates sharper current peaks in the voltammogram, associated with the above processes, and their displacement towards cathodic potentials proportional to the anion concentration. However, in the second potential zone at high cover