Publication
556
J. Phys.
Chem. B., 106 (36), 9387 -9395, 2002
DOI: 10.1021/jp0258006 S1089-5647(02)05800-5 |
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Effect of the Electrode Continuum of States
in Adiabatic and Nonadiabatic Outer-Sphere
and Dissociative Electron Transfers. Use of
Cyclic Voltammetry for Investigating Nonlinear
Activation-Driving Force Laws
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Jean-Michel
Savéant
Contribution from the Laboratoire
d'Electrochimie Moléculaire de l'Université Denis
Diderot (Paris 7), UMR CNRS 7591, 2 place Jussieu,
75251 Paris Cedex 05, France
The impact of taking into account the multiplicity of electrode electronic
states on the kinetics of outer-sphere and dissociative electron transfers
is discussed under the approximation that the electronic coupling energy
and the density of states are not strongly dependent on the energy of
the electronic states with emphasis on practical consequences. It is
shown that, in most cases of practical interest, the activation-driving
force laws may be derived from the classical Marcus-Hush quadratic relationship
by application of a simple and small correction. Under the same approximation,
the passage from adiabatic to fully nonadiabatic behaviors can be estimated
as a function of the electronic coupling energy, showing that the reaching
of complete adiabaticity requires rather modest values of this factor.
In the same pragmatic vein, we discuss how cyclic voltammetry can be
used to derive nonlinear kinetic laws from experimental data. It is often
believed that the extraction of kinetic information from the cyclic voltammetric
raw data requires that the form of the kinetic law be known a priori,
consequently causing a preference for potential-step or impedance techniques
where this question does not arise. It will be shown that simple treatments
of the raw data, both in the case where the reactants are attached to
the electrode surface or free to move in the solution, can be used to
circumvent this apparent difficulty making cyclic voltammetry a tool
as efficient as the above-mentioned techniques for this purp |
