Anodic Displacement of Adsorbed H in Electrochemisorption of Organic Molecules at Platinum

Abstract

A new electrochemical adsorption effect is described in which chemisorption of organic substances such as thiourea, nitriles, benzene and dimethyl sulphide at Pt electrodes occurs by anodic displacement of previously adsorbed atomic H, if the adsorption is initiated at potentials less than 0.35 V against H2 electrode. Anodic adsorption transients are measured potentiostatically and the charges corresponding to quantities of H displaced can be quantitatively related to the blocking of the surface for H adsorption as determined in subsequent cyclic voltammetry experiments. The effects are shown to be quite different from previously described dissociative chemisorption effects at electrodes where anodic transients arise from electrochemical ionization of H atoms resulting from dissociation of the organic molecule itself. Applications of the effect to electrochemical hydrogenation processes are discussed for cases where cathodic component currents complicate the interpretation of the H displacement transients, c.g., with nitriles.