Determination of Electrochemical Kinetic Parameters of Irreversible Redox Couples That Do Not Obey Conventional Butler–Volmer and Marcus–Hush Kinetic Models

Cyclic voltammetry is routinely applied for the kinetic analysis of irreversible redox couples in two distinct manners: (i) by utilizing digital simulations that adhere to either the conventional Butler-Volmer (cB-V) or conventional Marcus-Hush (cM-H) kinetic models or (ii) by employing characteristic analytical equations. Recent studies demonstrated that these traditional models are inadequate for the kinetic parametrization of redox couples exhibiting significant peak potential differences and adhere to a modified B-V (mB-V) model, wherein the condition of α + β = 1 is relaxed. Consequently, a simulation program has been developed using Python, and the existing equations have been revised to accommodate the mB-V model and are verified employing digital simulations. The accurate kinetic parameters obtained using the modified method for the Fe³⁺/Fe²⁺ couple are α = 0.38 ± 0.00, β = 0.38 ± 0.00, <i>E</i>_f⁰ = 0.47 ± 0.00 V, and <i>k</i>⁰ = (4.9 ± 0.2) × 10^-5 cm/s. For the [UO₂(CO₃)₃]^4-/[UO₂(CO₃)₃]^5- couple, the parameters are α = 0.27 ± 0.00, β = 0.26 ± 0.00, <i>E</i>_f⁰ = -0.70 ± 0.00 V, and <i>k</i>⁰ = (3.2 ± 0.4) × 10^-6 cm/s. It is strongly recommended to determine whether α + β = 1 or α + β ≠ 1 and subsequently apply the corresponding analytical equations to achieve accurate kinetic parametrization of irreversible couples.