Specific adsorption of bromide and iodide anions from nonaqueous solutions on controlled-surface polycrystalline silver electrodes

A systematic study was performed on the specific adsorption of bromide and iodide anions on controlled-surface polycryst. Ag electrodes, from 3 org. solvents (acetonitrile (ACN), propylene carbonate (PC), and DMF), combining differential capacity and impedance expts. with a recently proposed indirect voltammetric method based on the monitoring of the neg. shift of the redn. peak potential of a probe org. halide mol. induced by progressive addns. of halide anions, resulting in increasing adsorption competition. Bromide and iodide ions are specifically adsorbed onto polycryst. Ag electrodes in the 3 org. solvents studied. The adsorption process, which is slow and it is characterized by a partial charge transfer and by a slow diffusion step, is modulated by the different coordination abilities of the solvents for the species involved in the adsorption. The 3 exptl. methods provide consistent results. In particular, the strength of halide adsorption increases in the halide sequence Br- < I-, and in the solvent sequence ACN < PC < DMF.