The Partial Charge Transfer Coefficient of Lorenz and Salie

The Partial Charge Transfer Coefficient of Lorenz and Salie 

In their pioneering work on pet, Lorenz and Salie1 adopted a kinetic approach, suggested by their initial experimental research on the Tl-amalgam/Tf ion electrode reaction. In this system, pet is assumed to involve an adsorbed intermediate, while the reactant Ox and the final product Red are both present in the bulk of their respective phases. This led these authors to work out a general reaction scheme in which one or more adsorbed intermediates are interposed between Ox and Red. 

Confining ourselves to the reaction scheme of Eq. (1), in which the intermediate S2+x exists only in the adsorbed state, Lorenz s approach10 starts from the expression for the adsorption current density j, which is given by doiJdt. By expressing aM as the sum of the two extrathermodynamic contributions of Eq. (9), we get  

Considering that the free charge density qM is a function of both Fs and E, we can write  

Lorenz refers to f as the macroscopic pet coefficient and regards it as experimentally accessible. C M can be measured by the extrapolated value of the differential capacity C at infinite frequency, when the surface concentration rs is frozen, i.e., when it cannot keep up with the ac signal. Since, however, the partial charge associated with chemisorption does follow the ac signal, this is only true if A can be regarded as potential independent. It can be readily seen that l in Eq. (31) is the opposite of the electrosorption valency l. In fact, replacing from Eq. (9) into Eq. (2) yields  

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