Evaluation of the kinetic parameters of the hydrogen oxidation reaction on nanostructured iridium electrodes in alkaline solution

Abstract

The kinetic study of the hydrogen oxidation reaction on a nanostructured iridium electrode was carried out in alkaline solution at different rotation rates. The electrode, prepared by sputtering on a glassy carbon substrate, was characterized by cyclic voltammetry, AFM and XPS techniques. Then, the experimental current density (j) vs. overpotential (η) curves were recorded in the range comprised between −0.015≤η /V≤0.30. The correlation of the resulting curves was carried out considering the Tafel-Heyrovsky-Volmer mechanism, with a Frumkin type isotherm for the adsorption of the reaction intermediate. The kinetic parameters (equilibrium reaction rates of the elementary steps and surface coverage of the adsorbed hydrogen) were evaluated. The results obtained indicate that, in the potential range evaluated, the reaction takes place mainly through the Tafel-Volmer route with a small contribution of the Heyrovsky-Volmer route. Finally, an explanation for the lower electrocatalytic activity observed in alkaline solutions with respect to that in acid solutions was proposed, on the basis of the movement restrictions of the hydroxyl ion inside the superficial water network to make possible the electron transference in the Volmer and Heyrovsky steps.