Tafel electrical potential difference

The proportionality of n kf) to the applied potential difference (also called Tafel behavior) was observed back in 1975 by Gavach et al and has been corroborated ever since by many groups (e.g.. Ref. 53, 54, 56, 57). The results of Shao and Girault, illustrated in Fig. 7, show beyond any doubts that a Butler-Volmer relationship (as described by Eq. (10)) accounts very well for the experimental data. In the case of the metal-electrolyte solution interface, such an equation is rationalized by the fact that the applied potential difference, A, the driving force for the electron transfer reaction, is located at the interface and that the variation of the activation energy with A is a fraction of the variation of the electrical driving force. 

In cathodic area, the Tafel slope in the presence of DDTC is bigger than that in the absence of DDTC, and the cathodic curves imder the conditions of different DDTC concentration are almost parallel and their Tafel slopes only change a little. These demonstrate that the chemisorption of DDTC on the surface of jamesonite electrode also inhibits the cathodic reaction, but the chemisorption amoimt of DDTC is a little and almost not affected by the DDTC concentration due to their negatively electric properties of DDTC anion and the electrode surface. This reveals that there is a little DDTC chemisorption on the mineral even if the potential is lower (i.e., negative potential). 

Deviation of 60 mV/decade can be seen in Table 5.3 under different conditions. In addition to the potential distribution in the two double layers, there are two other possible causes for the deviations. The first is possible potential drops in other parts of the electrical circuit, e.g., in the electrolyte and semiconductor. The second possibility is the change of effective surface area due to the formation of a porous silicon layer during the course of i-V curve measurement. In addition, if the reaction is controlled by a process involving the Helmholtz layer, the apparent Tafel slope may be smaller than the 60 mV/decade as would be expected from the formula, B = kTI23anq, because the effective dissolution valence n is not a constant with respect to potential but varies from 2 to 3 in the exponential region. 

The difference between the potential of the electrode when electric current flows through it and its equilibrium potential is called overvoltage and is given by the Tafel equation ... 

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