MIGRATIONAL EFFECTS ON 2ND WAVES OF EE MECHANISMS UNDER STEADY-STATE OR QUASI-STEADY-STATE REGIMES

An analytical theory is developed to predict the current plateaus at second waves of EE mechanisms when the rate constant of the reproportionation reaction is extremely large and migration contributes to the transport of molecules because of a reduced concentration of the supporting electrolyte. By comparison to those we previously developed for single waves, the present analytical solutions establish that the effect of migration at the second wave may be considerably magnified with respect to the effect on the first wave even when the diffusion coefficients of all species are equal. Moreover, the current plateaus of second waves differ significantly from those that would be evaluated upon considering a direct reduction or oxidation of the substrate without involvement of the reproportionation reaction. This difference arises because this reaction segregates the diffusion layer into two adjacent regions with extremely different compositions. The theory is tested on the two cases (z = 0, n = 1, dicyano(fluoren-9-ylidene)methane; z = 2, n = 1, methylviologen dication) which are predicted to give the largest effects. The results are found to be in remarkable agreement with the experimental measurements.