Allowance for Force Constant Changes in the Theory of Electron Transfer at the Metal-Redox Electrolyte Interface

1995 ◽  
Vol 48 (11) ◽  
pp. 1853 ◽  
Author(s):  
D Matthews

The Gurney-Gerischer-Marcus (GGM) model for electron transfer1 is used to investigate the effects of force constant changes between initial and final states for electron transfer at the interface between a metal and a redox electrolyte. The effects on the symmetry factor, β, and on the determination of the redox electrolyte distribution of states are investigated and compared to the predictions of the GGM model using no change in force constant. Comparisons are also made between the Marcus2,3 and GGM models. The GGM model with non-identical parabolas for the potential energy-nuclear configuration diagrams is used to numerically calculate the distribution of states in the redox electrolyte from which data the rate constant distribution for reduction is obtained from the overlap between occupied states of the metal and the unoccupied states of the redox electrolyte. Numerical integration of the rate constant distribution gives the rate constant which is calculated as a function of the electrode potential. The calculated Tafel plots are found to be non-linear but do not go through a maximum. The Marcus and GGM models predict markedly different dependences of the symmetry factor on potential. Differentiation of the calculated rate constant with respect to potential gives the distribution of states for the redox electrolyte except for a small deviation which is due to the weak dependence on energy of the distribution of states in the metal. Anomalous results reported in the literature are shown to be qualitatively consistent with a difference in force constant between initial and final states for electron transfer.


1995 ◽  
Vol 48 (11) ◽  
pp. 1843 ◽  
Author(s):  
D Matthews

The Gurney-Gerischer-Marcus (GGM) model is used to investigate the potential and temperature dependence of the rate constant for electron transfer at the interface between a metal and a redox electrolyte. In this model electron transfer is described in terms of nuclear configuration-potential energy diagrams, electronic configuration-potential energy diagrams, state distribution functions and rate constant distribution functions. The model of identical parabolas, which leads to Gaussian electron distribution functions, g(E), for the redox electrolyte, is used for the nuclear configuration diagrams. The rate constant distribution, k(E), is obtained from the overlap between occupied and unoccupied state distribution functions of the metal and redox electrolyte. Integration of k(E) over the vertical transition (Franck-Condon) energies, E, gives the rate constant, k, which is calculated as a function of the electrode potential and temperature for various values of the reorganization energy, λ. Differentiation of k with respect to potential returns g(E) for the redox electrolyte except for a small deviation which is due to the weak dependence on energy of the distribution of states in the metal. For high λ the variation of symmetry factor with potential is small and the Tafel plots do not show a significant decrease in rate at high overpotentials. For small λ the Tafel plots are strongly curved but do not go through a maximum at high overpotential; the Tafel plots tend to a limiting value with only a small decrease in rate constant at high overpotential. This result is reflected in the temperature dependence of the rate constant and in the dependence of the Arrhenius activation energy, Ea, on potential; Ea does not increase at high overpotentials. These results are due to the weak dependence on energy of the distribution function for a metal compared to a redox electrolyte and emphasize the advantages of using distribution functions to describe the kinetics of electron transfer.



1981 ◽  
Vol 12 (48) ◽  
Author(s):  
V. M. ZASKUL'NIKOV ◽  
V. L. VYAZOVKIN ◽  
B. V. BOL'SHAKOV ◽  
V. A. TOLKATCHEV


2017 ◽  
Vol 26 (10) ◽  
pp. 1464-1489 ◽  
Author(s):  
Y. Zhang ◽  
P. Forssén ◽  
T. Fornstedt ◽  
M. Gulliksson ◽  
X. Dai


1994 ◽  
Vol 47 (12) ◽  
pp. 2171 ◽  
Author(s):  
D Matthews

The theory of electron transfer at the metal- redox electrolyte interface is described by starting with the work of Gurney and incorporating that of Gerischer and Marcus. This GGM model brings together diverse approaches to the description of electron transfer at electrodes. The electron transfer is described in terms of nuclear configuration potential energy diagrams, electronic configuration potential energy diagrams, electron distribution functions and rate distribution functions. The distinction between microscopic energies and macroscopic (thermodynamic) energies is made and the concept of the Fermi level of the redox electrolyte is clarified. The model of identical parabolas is used for the nuclear configuration diagrams and this is shown to lead to Gaussian electron distribution functions for the redox electrolyte. The rate distribution is obtained from the overlap between occupied and unoccupied states of the metal and redox electrolyte. Integration of the rate distribution gives the rate which is calculated as a function of the electrode potential for various values of the reorganization energy λ. It is shown that the variation of symmetry factor β is small for high λ and that the Tafel plots do not show significant decrease in rate at high overpotentials in the anomalous or inversion region. The Tafel plots for charge transfer (mass transfer is assumed to be fast at all potentials) tend to a limiting value with only a small decrease at high overpotential. This contrasts with the prediction based on nuclear configuration potential energy curves and is attributed to the fact that the overlap is between a Gaussian and a Fermi function rather than between two Gaussians, the latter being the case for homogeneous reactions.



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Vol 13 (8) ◽  
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