Kinetic study of formic acid oxidation on Ti/IrO2 electrodes prepared using the spin coating deposition technique

In the first part of this paper, IrO₂ electrodes produced by thermal decomposition of H₂IrCl₆ precursor were manufactured using the spin coating deposition technique, where centrifugal forces spread the precursor solution with simultaneous evaporation of the solvent on the rotating Ti substrate. It was found using this technique, that it is possible to obtain thin and uniform IrO₂ coatings with controlled loadings. The influence of the concentration of iridium salt in the precursor solution (c₀) as well as the influence of the rotation speed at which the substrate spins (ω) on the IrO₂ loading have been studied using voltammetric charge measurements. From these results, a simple relation has been proposed for the estimation of the IrO₂ loading for a given c₀ and ω.In the second part of this paper and from measurements performed using different IrO₂ loadings and formic acid concentrations, the kinetic parameters of the oxidation of formic acid have been quantitatively determined using a model that involves the redox couple IrO₃/IrO₂ as mediator of this reaction. Furthermore, using the kinetic parameters obtained together with the Nernst equation and the I-V curves of the supporting electrolyte (1 M HClO₄), theoretical I-V curves could be constructed for different concentrations of formic acid and different IrO₂ loadings.