Surface screening effects by specifically adsorbed halide anions in the electrocatalytic reduction of a model organic halide at mono- and polycrystalline silver in acetonitrile

The silver surface screening effects by specifically adsorbed halide anions in the electrocatalytic reduction of a model organic bromide (acetobromoglucose) have been studied by cyclic voltammetry on controlled mono- and polycrystalline silver surfaces in acetonitrile+0.1 M tetraethylammonium perchlorate medium as a function of the concentration cX of added TEAX (X=Cl, Br, or I, TEA, tetraethylammonium). The reduction peak potentials, Ep, are regularly shifted in the negative direction with increasing cX, typically tending to an asymptotic value for cX≈0.1 M. Several literature models describing adsorption/desorption equilibria have been applied to justify the above experimental Ep versus cX trends (being logarithmic in the iodide cases) for the three halides and the four silver surfaces tested.