Abstract
The expression of the faradaic impedance is calculated in the case of a quasi-reversible system O+ ne agR under the following conditions: (a) both the oxidized and the reduced forms are strongly adsorbed; (b) the adsorption rate is large, and does not control the kinetics of the system; (c) the adsorption of both O and R obeys a Frumkin type isotherm (interactions between the adsorbed molecules are considered). The results are compared to those obtained previously in the case of a Langmuir isotherm. The cotangent of the phase angle φ is still proportional to ω/ k s ( k s=rate constant of the electrochemical reaction), so that φ still tends towards 90° when ω/ k s→0, but the slope of the straight line obtained is a complicated function of the superficial concentration and of the interaction coefficients. The height of the a.c. wave is no longer proportional to the bulk concentration of the reactant, to τ 7/6 (τ=drop time) and to h −1/2 ( h=height of the mercury reservoir). When ω/ k s→0, the shape of the a.c. wave is identical to that of the linear sweep voltammogram.
Published Version
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