Structure of the Voltammograms of the Platinum-Black Electrodes: Derivative Voltammetry and Data Fitting Analysis

Voltammograms of Pt-black electrodes were recorded in aerated 1 M HClO4 solution, at T = 298 K, for three different upper values of the oxidation potential, Emax = 1.6 V, 1.44 V and 1.39 V. Numerical differentiation of the raw data enhanced details which hardly were visible in the original voltammograms. The derivative of the anodic current resided in well defined peaks attributed to two peaks-like electrode reactions (potential range 0.6 V–1.0 V) and a smooth reaction generating the anodic current plateau, at potential higher than 1 V. The derivative of the cathodic peaks revealed that the cathodic current results from two reactions occurring simultaneously, but with different rates: the reduction of the adsorbed - OH* followed by that of the adsorbed–O*. The data fitting analysis was performed with the empirical kinetic equations based upon the sigmoid-like functions. The analysis confirmed the results found on the derivative voltammograms and enabled to compute the individual component of the anodic and cathodic branches. Complementary mass measurements with the electrochemical quartz crystal microbalance (EQCM) confirmed that both the oxidation and the reduction processes on the Pt-black electrodes consist of a complex succession of overlapping reactions associated with both the adsorbed - OH* and - O* species.