Kinetic bottlenecks

As the scan rate v increases, an additional kinetic bottleneck is introduced. Because the electrons move slowly through the electrode, there is a perceptible time lag between the potential at the voltage source (generally a potentiostat) and that at the electrode solution interface. Since all potentials experience this lag , the peaks are shifted to more extreme potentials, thus giving the CV a stretched appearance. 

Ozawa was perhaps the first author who tried to determine whether the anode or cathode acts as the kinetic bottleneck in a full lithium ion cell, although the purpose at the time was not intended for low-temperature considerations. In interpreting the... 

The removal of kinetic bottlenecks by removing regulation and/or by amplifying the genes that code for the rate-limiting enzymes. Alternatively, the WT enzymes may be replaced by mutated or heterologous ones with a different control architecture. 

Zhong DK, Gamelin DR (2010) Photoelectrochemical water oxidation by cobalt catalyst ( Co-Pi )/a-Fe203 composite photoanodes oxygen evolution and resolution of a kinetic bottleneck. J Am Chem Soc 132 4202-4207... 

We close this discussion with the note that water splitting is not the only reaction of interest in solar energy conversion and environmental remediation. Splitting of CO2 (to a fuel product such as methanol or methane) constitutes a value-added approach to combating the accumulation of this greenhouse gas molecule [24]. However the kinetic bottlenecks to CO2 splitting pose steep... 

Most electrochemical and photoelectrochemical systems produce only the two-electron reduction products of CO and formate, the products of two-electron reductions, evidencing once again the kinetic bottleneck associated wth multielectron and multiproton processes. As in the oxidation of water, efforts have been directed towards the development of transition-metal based electrocatalysts with multiple metal centres to facilitate charge accumulation in highly reduced intermediates and allow multiredox processes to occur. " " ... 

Kinetic studies of reactions will not, generally, tell us absolutely what the reaction mechanism is, but they may well tell us what it is not. Compare the two reactions of Figure 8.9. The kinetics of the substitution of bromomethane are second order, while those for tert-butyl bromide are first order. This tells us immediately that the two reactions do not proceed by the same mechanism. In the reaction of tert-butyl bromide, the hydroxyl ion must be involved somewhere, because it is there in the product, but it is not involved in the RDS. Thus, we must conclude that there are at least two steps in this process we are measuring only the rate of the RDS, the kinetic bottleneck. The mechanism proposed is a two-step process, where the RDS is the heterolytic cleavage of the C-Br bond to give a carbocation, which then reacts rapidly with the hydroxyl ion (Figure 8.10). Note that mechanisms may be consistent with experimental data, but such data do not prove ... 

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