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The Levich equation is written as: = where I L is the Levich current (A), n is the number of moles of electrons transferred in the half reaction (number), F is the Faraday constant (C/mol), A is the electrode area (cm 2), D is the diffusion coefficient (see Fick's law of diffusion) (cm 2 /s), ω is the angular rotation rate of the electrode (rad/s), ν is the kinematic viscosity (cm 2 /s), C ...
An RDE cannot be used to observe the behavior of the electrode reaction products, since they are continually swept away from the electrode. However, the rotating ring-disk electrode is well suited to investigate this further reactivity. The peak current in a cyclic voltammogram for an RDE is a plateau like region, governed by the Levich ...
The Koutecký–Levich equation models the measured electric current at an electrode from an electrochemical reaction in relation to the kinetic activity and the mass transport of reactants. A visualization of the Koutecký–Levich equation. The graph shows the measured current as a function of the mass transport current for given kinetic current.
The RRDE setup allows for many additional experiments well beyond the capacity of a RDE. For example, while one electrode conducts linear sweep voltammetry the other can be kept at a constant potential or also swept in a controlled manner. Step experiments with each electrode acting independently can be conducted.
A Levich constant (B) is often used in order to simplify the Levich equation. [1] Furthermore, B is readily extracted from rotating disk electrode experimental data. The B can be defined as: [ 2 ]
Marcus' formula shows a quadratic dependence of the Gibbs free energy of activation on the Gibbs free energy of reaction. It is general knowledge from the host of chemical experience that reactions usually are the faster the more negative is . In many cases even a linear free energy relation is found.
In electrochemistry, the Randles–Ševčík equation describes the effect of scan rate on the peak current (i p) for a cyclic voltammetry experiment. For simple redox events where the reaction is electrochemically reversible, and the products and reactants are both soluble, such as the ferrocene/ferrocenium couple, i p depends not only on the concentration and diffusional properties of the ...
The upper graph shows the current density as function of the overpotential η . The anodic and cathodic current densities are shown as j a and j c, respectively for α=α a =α c =0.5 and j 0 =1mAcm −2 (close to values for platinum and palladium).