Anodic Oxidation of Ethylene Glycol on Platinum: a Mechanistic Study

Abstract

Anodic oxidation of ethylene glycol (EG) has been examined on platinum in 1 N H2SO4 by means of potentiostatic and potentiodynamic techniques. Experimental results consist of steady-state, potential-current relationships, reaction order derivatives, inhibition inflections, potentiodynamic profiles, and product analysis. Reaction mechanism has been proposed by combining these results with the previous information on the adsorption of EG on platinum, and on the pH effects in the anodic oxidation of EG. An analysis of these data has been presented in terms of kinetics under both Langmuir and Temkin conditions of electrode coverage. Inhibition inflections have been interpreted in terms of the kinetic theory of passivation effects proposed by Gilroy and Conway. It has been suggested that a chemical step of the type Pt.EG + Pt.OH → Pt.R + H2O + Pt is the likely rate-determining-step (r.d.s.). The data indicate that quasi-equilibria prior to the r.d.s. are probably different in the ascending and descending direction of potentials (on the potential–current curves), owing to the presence of different extents of oxygenated (Pt.OH or Pt.O) adsorbed species and the associated effects of coverage on kinetics.