Electrode kinetics of oxygen reduction: A theoretical and experimental analysis of the rotating ring-disc electrode method

Abstract

The previous theoretical treatments of the rotating ring-disc electrode method to distinguish between the mechanisms of electroreduction of O 2 to H 2O with and without the formation of H 2O 2 as an intermediate, were examined. A new expression was derived for I d1/( I d1− I d) as a function of ω −1/2 (where I d1 is the disc limiting current, I d is the disc current and ω is the rotational speed of electrode) for five possible reaction models. This, along with the corresponding expressions for I d/ I r vs. ω −1/2 ( I r is the ring current), enables the calculations of the individual rate constants for the intermediate steps of O 2 reduction. The experimental data of I d and I r were obtained for O 2 reduction on platinum in 0.55 M H 2SO 4 at 25°C. By use of these experimental results in the present theoretical treatment, it is shown that: (1) the most applicable model over the entire potential region was the one suggested by Damjanovic, Genshaw and Bockris; (2) the models involving the adsorption/desorption of H 2O 2 were applicable only over a narrow region of potential; and (3) the models involving the chemical decomposition of H 2O 2 were inconsistent with the dependence of I d1/( I d1− I d) vs. ω −1/2.