Hydrodynamic Voltammetry at a Rocking Disc Electrode: Theory versus Experiment.

Rocking disc electrode voltammetry (RoDE) is introduced as an experimentally convenient and versatile alternative to rotating disc voltammetry. A 1.6 mm diameter disc electrode is employed with an overall rocking angle of θ = 90 degree applied over a frequency range of 0.83 Hz to 25 Hz. For a set of known aqueous redox systems (the oxidation of Fe(CN) 6 4− in 1 M KCl , the reduction of Ru(NH 3 ) 6 3+ in 0.1 M KCl , the oxidation of hydroquinone in 0.1 M pH 7 phosphate buffer, the oxidation of I − in 0.125 M H 2 SO 4 , and the reduction of H + in 1 M KCl) the mass transport controlled limiting current I lim is demonstrated to follow in good approximation the Levich-type expression I lim = 0.111   n F A c D 2 / 3 v − 1 / 6 Θ f with n , the number of electrons transferred per molecule diffusing to the electrode surface, F , the Faraday constant, A , the geometric area, c , the concentration of the active redox species, D , the diffusion coefficient, v , the kinematic viscosity, θ is the overall rocking angle in degree, and f , the rocking rate in Hz. Quantitative theory is developed based on a two-dimensional (2D) axisymmetric laminar flow model accounting for the conservation of mass, momentum and species along with the kinematic analysis of a “four-bar mechanism” to obtain the rocking motion. [ABSTRACT FROM AUTHOR]