Charge neutralization process of mobile species developed during potentiodynamic conditions. Part 1: Theory

FERNANDO GARAY; CESAR A. BARBERO

JOURNAL OF ELECTROANALYTICAL CHEMISTRY

Elsevier

Año: 2008 vol. 624 p. 218 - 227

0022-0728

This is theoretical work in which a general expression for the diffusion and migration contribution of electroactive and non-electroactive species is provided. The model is employed to simulate concentration and concentration gradient profiles of electroactive and non-electroactive species, driven by an electrochemical process under potentiodynamic conditions. The effects of experimental parameters such as diffusion coefficients, charges of redox species and supporting electrolyte (SE) ions are examined and discussed. The curves included in this work are mostly related to systems where electroactive and non-electroactive species have different diffusion coefficients. The proposed model can explain extreme cases related to asymmetrical diffusion of involved species that are more difficult to understand, as well as simpler cases where all species would have similar diffusion coefficients. The data measurement related to concentration gradients would be more sensitive to determine concentration changes than those linearly related to concentration. If a given technique were applied to detect the concentration changes of a particular species, then this model could be used to estimate the profiles of the other species involved. Concentration gradients of electroactive and SE species are mostly interesting to describe profiles of in-situ techniques like probe beam deflection. Relatively low scan rates are considered to describe these profiles. This is because, the curves of (÷Cj/÷x)x‚0 are similar to the respective cyclic voltammogram and thus, it is possible to compare the position of anodic and cathodic peaks. However, this resemblance between (÷Cj/÷x)x‚0 and the response of current disappears when the probe-electrode distance or the potential scan rate is increased. A method for obtaining linear dependence between the square root of the forward potential peak of (÷Cj/÷x) and the distance Dx is provided. This method can be used to determine Dx by employing experimental data only.