Electron transfer kinetics current density

Therefore, three important electrode kinetic parameters—exchange current density electron transfer coefficient ( h). and electron transfer... 

The decreased contribution due to slow electron transfer kinetics for the microtubular electrode is also attributable to the higher underlying surface area of the tubular current collector. Because the surface area is higher, the effective current density for the microtubular TiS2 is less than for the thin film TiS2, which has a conventional planar current collector. The decreased contributions of film resistance and slow electron transfer kinetics also account for the higher peak current density of the microtubular electrodes (Fig. 27). 

At equilibrium (i.e., no current) there exist dynamic currents, measured in amps, at each electrode and are a fundamental characteristic of electrode behavior. The anode and cathode exchange current densities can be defined as the rate of oxidation and reduction respectively. The exchange current density is a measure of the electrode s ability to transfer electrons and occurs equally in both directions resulting in no net change in composition of the electrode.22 A large exchange current density represents an electrode with fast kinetics where there is a lot of simultaneous electron transfer. A small exchange current density has slow kinetics and the electron transfer rate is less. 

In the intermediate and late time regimes, the current density at a UME disk is intrinsically nonuniform because the edges of the electrode are more accessible geometrically to the diffusing electroreactant (17). This non-uniformity affects the interpretation of phenomena that depend on local current density, such as heterogeneous electron-transfer kinetics or the kinetics of second-order reactions involving electroactive species in the diffusion layer. 

Therefore, using RDE measurements, the kinetic parameters of electron-transfer kinetics such as the electron-transfer number (n) and coefficient a) and the exchange current density (/°) can be estimated. At the same time, the reactant transport parameters... 

In the above section, all the equations we derived are based on pure electron transfer kinetics. Unfortunately, in reality, mass transfer (e.g. hydrogen diffusion inside a porous fuel ceU CL) will have an effect on the overall reaction rate, and sometimes can become the rate-determining step. To address this mass transfer effect, we need to introduce another concept, called limiting diffusion current density, which can be expressed as in Eqns (1.35) and (1.36) [9] ... 

Figure 12.10 shows the CVs for methanol oxidation on a Pt/Ru catalyzed electrode at various temperatures. It can be seen that there is a significant increase in the current density with increasing temperature. From the data in this figure, the kinetic parameters of methanol oxidation can be estimated. For an electrochemical reaction controlled purely by electron transfer kinetics, if the reaction overpotential is large enough (>60mV), the Butler-Volmer equation can be simplified to the form of a Tafel equation, which is similar to Eqn (12.6) ... 

Voltammetry is a common electroanalytical technique for characterization of enzyme-modified electrodes. In cyclic voltammetry (CV), a potential window is scaimed in the forward and reverse directions while the resulting current is measured. This technique is useful for determining the reduction potential of the enzyme or coenzyme and for determining the overpotential for the system, which, in turn, corresponds to efficiency. Using this technique, detailed information about the catalytic cycle of the system can be determined including electron transfer kinetics, reaction mechanisms, current densities, and reduction potentials [6,7]. 

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