Deciphering the origin of high-order periodic and aperiodic cyclic voltammetric responses during oxidation processes on platinum

We report cyclic voltammograms of the hydrogen electrooxidation reaction on a rotating Pt ring electrode in diluted electrolytes that are either aperiodic or possess a period which is a multiple of the period of the cycling voltage. The complex voltammetric responses are experimentally studied in two electrolytes with different compositions of the base electrolyte (and thus different conductivity) as a function of the positive turning point of the applied voltage. The behavior can be rationalized in terms of the interaction between the inhibition of H-2 oxidation by Pt-oxides, the roughening of the electrode due to oxide reduction and its subsequent smoothing as well as a nonnegligible uncompensated voltage drop through the electrolyte. The proposed mechanism is translated into a mathematical model consisting of a set of four ordinary differential equations. The model indeed captures the main experimental findings. Since the principle ideas do not depend on the specific kinetics of the oxidation reaction under investigation, the mechanism should be operative in a variety of electrochemical systems. In particular, we suggest that it may underlie the complex cyclic voltammograms observed during many oxidation reactions of small organic molecules.