Kinetic and optical relaxation studies of adsorbed intermediates in some electrochemical reactions

Abstract

In certain electrocatalytic reactions, co-adsorption of more than one electroactive intermediate may arise. The charge under the overall potentiodynamic current-potential profile for the adsorbed species may not then be used to evaluate coverage by the species. A method is proposed for resolution of processes involving more than one electrochemisorbed species when the electroactivity of, e.g., two species arises over a common potential range. The method is based on the different kinetic relaxation response of “reversibly” electrosorbed species from that for more “irreversibly” electrosorbed species. Applications to the case of reduction of adsorbed nitriles at Pt enables a two-stage mechanism to be formulated and in the reduction of benzene the charges for co-adsorption of H and benzene reduction can be distinguished. In the initial stages of Pt surface oxidation, the method enables the reversibly electrosorbed OH species to be distinguished from more irreversibly reactive rearranged surface oxide.

The behaviour of chemisorbed CH₃CN and the oxide film on Pt below a monolayer have also been investigated by a.c. modulated reflectance over a range of a.c. frequencies and wavelengths of light.