Butler-Volmer theory

The ET reaction between aqueous oxidants and decamethylferrocene (DMFc), in both DCE and NB, has been studied over a wide range of conditions and shown to be a complex process [86]. The apparent potential-dependence of the ET rate constant was contrary to Butler-Volmer theory, when the interfacial potential drop at the ITIES was adjusted via the CIO4 concentration in the aqueous phase. The highest reaction rate was observed with the smallest concentration of CIO4 in the aqueous phase, which corresponded to the lowest driving force for the oxidation process. In contrast, the ET rate increased with driving force when this was adjusted via the redox potential of the aqueous oxidant. Moreover, a Butler-Volmer trend was found when TBA was used as the potential-determining ion, with an a value of 0.38 [86]. 

Therefore, unlike the empirical Butler-Volmer theory, in the Marcus formulation the heterogeneous electron transfer rate constant is sensitive to both the structure of the redox center and the solvent. 

Volmerian electrode reaction — This term has been used for electrode reactions in which the - charge transfer coefficient is constant. Reactions for which the latter is potential dependent were called non-volmerian. According to the - Marcus theory there is generally a potential dependence of the charge transfer coefficient, however that is usually very small. The terms Volmerian and non-volmerian refer to the classic Butler-Volmer theory (-> Butler-Volmer equation) where no potential dependence was assumed. See also -> Volmer. 

See Atkins (1995), Koryta (1991 1993) and Bard and Falkener (1980) for the Butler-Volmer theory and Tafel slopes. 

An alternative theory to the Butler-Volmer theory for electron transfer is provided by the Marcus-Hush theory (Marcus, 1968 Hush, 1968) which assumes a potential-dependent a. Since in most cases a is essentially independent of potential, use of the simpler Butler-Volmer equation is usually adequate. 

In a recent report, it was shown that the reaction of cytochrome c at indium oxide OTEs exhibits an electrochemical response consistent with Butler-Volmer theory when high-quality commercial samples of cytochrome c are further purified. The electrode reaction is quasi-reversible and the CV and DCVA results of th e experiments are shown in Figure 18. These data... 

This chemically modified electrode exhibits quasi-reversible rates of heterogeneous electron transfer for the reduction of cytochrome c as determined by single potential step chronoabsorptometry. However, reductive and oxidative experiments did not yield kinetic results in agreement with Butler-Volmer theory. 

Further models have been reported implementing elementary kinetic approaches based on the empirical Butler-Volmer theory to analyze the products of PFSA PEM degradation. ... 

If the mass transfer is presented by diffusion overpotential and the electron transfer is described using the Butler-Volmer theory, these two approaches can be combined... 

Felici has rightly brought attention to the importance of electrochemical processes in insulating liquids. However, it is rather surprising that his model, based on Butler-Volmer theory, can describe the electrical breakdown phenomenon in so wide a range of potentials. 

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