The recently proposed multi-frequency electrochemical Faradaic spectroscopy (MEFS) technique was investigated for a quasireversible electrode reaction of a dissolved redox couple under the influence of changing molar fractions and varying diffusion coefficient ratio of the species of the studied redox couple through simulation and experimentation. The frequency-normalized net current in MEFS exhibits a quasi-reversible maximum (QRM), a feature that is sensitive to the standard rate constant. The position of the maximum is independent of the molar fractions and remains unchanged for non-identical diffusion coefficients until the ratio ρ = D Red / D Ox > 0.6. Under certain conditions the maximum vanishes – which could be used as a qualitative indicator of the composition of the system in terms of molar factions of redox species. Based on experimental evidences, the QRM emerges at low SW frequencies, thus being free of undesirable artefacts related to the charging current and uncompensated resistance. Based on a large pool of theoretical data, a semi-empirical equation was derived linking the critical frequency of the QRM with the standard rate constant of the studied electrode reaction. • Multi-frequency analysis with qualitative insight to the system's redox state. • Kinetic analysis unaffected by molar fractions and unequal diffusion coefficients. • New equation for reliable estimation of k s without de novo simulation for every case. • Guidance for multi-frequency electrochemical faradaic spectroscopy in potentiostats.
Glaubitz et al. (Fri,) studied this question.
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