Processes of adsorption/desorption of iodide anions and cadmium cations onto/from Ag(111)

Abstract

In this work, the adsorption/desorption processes of iodide anions and cadmium cations in the presence of iodide anions onto/from Ag(111) were investigated. It was shown that both processes were complex, characterized by several peaks on the cyclic voltammograms (CVs). By PeakFit analysis of the recorded CVs and subsequent fitting of the obtained peaks by the Frumkin adsorption isotherm, the interaction parameter (f) and the Gibbs energy of adsorption (?G?ads) for each adsorbed phase were determined. In the case of iodide adsorption, four peaks were characterized by negative values of f, indicating attractive lateral interaction between the adsorbed anions, while two of them possessed value of f < -4, indicating phase transition processes. The adsorption/desorption processes of cadmium cations (underpotential deposition - UPD of cadmium) in the presence of iodide anions was characterized by two main peaks, each of them being composed of two or three peaks with negative values of f. By the analysis of charge vs. potential dependences obtained either from the CVs or current transients on potentiostatic pulses, it was concluded that adsorbed iodide anions did not undergo desorption during the process of Cd UPD, but became replaced by Cd ad-atoms and remained adsorbed on top of a Cd layer and/or in between Cd the ad-atoms.