Adsorption competition effects in the electrocatalytic reduction of organic halides on silver

A systematic study of {silver|inorg. and/or org. halide} interphases is described, based on cyclic voltammetric and impedance expts. carried out on polycryst. electrodes of high reproducibility (controlled by comparison with monocryst. ones), in H2O and in MeCN. The adsorption competition is brought into focus (i) between the 3 inorg. halides Cl-, Br-, and I-, with the possible interference of ions from the supporting electrolyte, and (ii) between org. and inorg. halides, esp. iodides. Actually adsorption competition proves to be a detg. factor in the electrocatalytic mechanism (a remarkable threshold effect being obsd. for the redn. potentials of org. bromides in correspondence with the limiting neg. potential for iodide anion adsorption). Vice versa, the variation of the redn. potentials of a given reacting mol. with the background electrolyte provides significant clues on the nature of the specifically adsorbed species