Evaluation technique of kinetic parameters for irreversible charge transfer reactions from steady-state voltammograms at microdisk electrodes

An explicit approximate expression for half-wave potentials of irreversible steady-state current-voltage curves at a microdisk electrode was derived from the diffusion equation and the Butler-Volmer equation on the basis of the previous analytical method [K. Aoki, K. Tokuda, H. Matsuda, J. Electroanal. Chem. 235 (1987) 87]. The plot of the half-wave potential, E1/2 against ln(1− exp(−(E1/2−E0))F/RT) showed a linear relation with the slope of RT/αF, irrespective of the values of the kinetic parameters, where a is the radius of the electrode and α is the transfer coefficient. Values on the both axis in this plot are readily accessible from the voltammograms. The intercept gave the rate constant. Values of kinetic parameters obtained from the disk model were very close to those from the hemisphere model although there is big difference in current distribution on the two model electrodes.