Comparative Studies of the Electrochemical Behavior of Silver Electrode in Chloride, Bromide and Iodide Aqueous Solutions

Comparative studies of the electrochemical behaviour of Ag in aqueous NaCl, NaBr and NaI solutions of various concentrations ranging from 0.1 M to 1.0 M have been made by means of cyclic voltammetry and chronoamperometry techniques, complemented with SEM observation. The cyclic voltammograms of Ag in the three halide solutions are nearly similar and characterized by the occurrence of a broad anodic peak (AI) corresponding to the electroformation of AgX film (X- = Cl-, Br-, I-) and a sharp cathodic peak (CI) corresponding to the electroreduction of AgX to Ag. The peak current density of peak AI decreases in the order I- > Br- > Cl-. The electroformation of AgX is found to be limited by the diffusion of X- ions from the bulk of the solution to the electrode surface. The apparent activation energies required for the electroformation of AgX films and its electroreduction were calculated from Arrhenius plots. It was found that, the activation energies decrease in the order: Cl- > Br- > I-. Potentiostatic current/time transients show that the instantaneous and steady-state current densities increase by increasing either the anodic step potential (Es,a), solution concentration, or temperature. SEM examination for AgX films indicates that, the AgI film is highly porous and associated with large microcracks as compared to AgBr and AgCl films.