The role of surface morphology on the electrocatalytic reduction of organic halides on mono- and polycrystalline silver

The electrocatalytic reduction of organic halides on silver, assumed to hinge on an attenuated radical intermediate R⋯X⋯Ag, is a reaction of great applicative interest that also provides an example of organic electrocatalytic process particularly convenient for a mechanistic study. The complexity of the problem requires to analyze separately the roles of the many actors involved. The present work focuses on the role of the silver surface morphology, contrasting the reactivity of a series of model halides in systematic CV experiments on (1 1 1), (1 1 0), and (1 0 0) silver monocrystals and on controlled polycrystalline silver surfaces of increasing roughness, in acetonitrile+tetraethylammonium perchlorate medium. The reduction potentials of the alkyl, glycosyl, and benzyl derivatives appear significantly shifted in the positive direction with increasing surface roughness (for polycrystals) or atomic densities and/or surface faceting (for monocrystals) by an extent linked with the molecular structure of the organic halide to be reduced. The addition of strongly specifically adsorbed iodide anions, resulting in surface screening, also results in a leveling effect of the catalytic properties of the different surfaces tested.