Influence electron transfer kinetics

Influence of the Kinetics of Electron Transfer on the Faradaic Current The rate of mass transport is one factor influencing the current in a voltammetric experiment. The ease with which electrons are transferred between the electrode and the reactants and products in solution also affects the current. When electron transfer kinetics are fast, the redox reaction is at equilibrium, and the concentrations of reactants and products at the electrode are those specified by the Nernst equation. Such systems are considered electrochemically reversible. In other systems, when electron transfer kinetics are sufficiently slow, the concentration of reactants and products at the electrode surface, and thus the current, differ from that predicted by the Nernst equation. In this case the system is electrochemically irreversible. 

N.D. Popovich, S.S. Wong, S. Ufer, V. Sakhrani, and D. Paine, Electron-transfer kinetics at ITO films — influence of oxygen plasma, J. Electrochem. Soc., 150 H255-H259, 2003. 

The next section is devoted to the influence of the electron transfer kinetics on the electrochemical responses for both attached and free-moving... 

We now remove the assumption that electron transfer is fast and discuss the influence of the follow-up reaction on the electron transfer kinetics. The simplest case is when the follow-up reaction is fast so as to stay unconditionally at equilibrium. The concentrations at the electrode surface may thus be expressed as... 

In biological systems, electron transfer kinetics are determined by many factors of different physical origin. This is especially true in the case of a bimolecular reaction, since the rate expression then involves the formation constant Kf of the transient bimolecular complex as well as the rate of the intracomplex transfer [4]. The elucidation of the factors that influence the value of Kf in redox reactions between two proteins, or between a protein and organic or inorganic complexes, has been the subject of many experimental studies, and some of them are presented in this volume. The complexation step is essential in ensuring specific recognition between physiological partners. However, it is not considered in the present chapter, which deals with the intramolecular or intracomplex steps which are the direct concern of electron transfer theories. 

The STM has also been used to follow the evolution of surface-confined reactions such as the oxidation of adsorbed sulfide to form adsorbed Sg and iodide to polyiodide [275,288,289]. The substrate exerts a strong influence on the dimensions and ordering of the adsorbed molecules, particularly the formation of the first monolayer. In a similar manner, studies of the impact of different adlayer structures on the electron transfer kinetics of various soluble redox species have been initiated [290]. 

Morris studied the aqueous solution voltammetric behavior of some uranyl coordination complexes to learn how changes in the ligand environment influence the redox potentials and heterogeneous electron-transfer kinetic parameters for the single-electron transfer... 

Ohmic error is not obvious in data on the Ni(II)/Ni(I) couple for this molecule (Table 23.3B), since a systematic decrease in the determined values of ks/D1/2 is not found. With a ks value of 0.025 cm/s, this couple has AEp values that are much larger than those of the Ni(III)/Ni(II) couple, and errors of, for example, 10 mV are small when compared to the inherent AEp arising from sluggish electron transfer kinetics. In this system, the slow electron transfer kinetics probably arise from molecular structure changes concomitant with the Ni(II)/Ni(I) electron transfer. A good discussion of the influence of ohmic errors on determination of kj values in various nonaqueous media is available [13]. 

Micelles and microemulsions have been explored as membrane mimetic systems since they possess charged microscopic interfaces which act as barriers to the charge recombination process (Fendler et al., 1980 Hurst et al., 1983). Namely, the influence of the location of the sensitizer on photoinduced electron transfer kinetics and on charge separation between photolytic products in reversed micelles has been studied (Pileni etal., 1985). 

Duo, I., Levy-Clement, C., Fujishima, A. and ComnineUis, Ch. (2004) Electron transfer kinetics on boron-doped diamond Part 1 Influence of anodic treatment. J. Appl. Electrochem. 34,935-943. 

We have investigated the influence of amide bonds upon electron-transfer kinetics in well-organized assemblies of alkanethiolates possessing buried amide groups within the chain [49, 129, 130]. Electron-transfer data obtained for a ferrocene-... 

In this section, we will treat the one-step, one-electron reaction O + R using the general (quasireversible) i-E characteristic. In contrast with the reversible cases just examined, the interfacial electron-transfer kinetics in the systems considered here are not so fast as to be transparent. Thus kinetic parameters such as kf, and a influence the responses to potential steps and, as a consequence, can often be evaluated from those responses. The focus in this section is on ways to determine such kinetic information from step experiments, including sampled-current voltammetry. As in the treatment of reversible cases, the discussion will be developed first for early transients, then it will be redeveloped for the steady-state. 

Fomeli, A., Palomares, E., Torres, T., and Durrant, J.R. (2009) Ru(II)-phthalocyanine sensitized solar cells the influence of co-adsorbents upon interfadal electron transfer kinetics. 

Smalley, I, L. Geng, A. Chen, S. Feldberg, N. Lewis, and G. Cali (2003). An indirect laser-induced temperature jump study of the influence of redox couple adsorption on heterogeneous electron transfer kinetics. Journal of Electroanalytical Chemistry 549, 13-24. 

The one-electron electroreduction of hexacyanoferrate(III) to hexacyanoferrate(Il) (or ferricyanide to ferrocyanide) is a classic example of a quasi-reversible process. Despite being initially regarded as an outer-sphere adiabatic charge-transfer process [44], the electrode kinetics of the [Fe(CN)6] transformation exhibits a pronounced dependence on the properties of the electrode, and reproducible results can be achieved only when the working electrode surface is reproducibly pretreated and cleaned, either by polishing or electrochemically [47,48]. Metal electrodes provide notably faster heterogeneous electron transfer kinetics of [Fe(CN)6] as compared to carbon surfaces, possibly due to differences in the density of electronic states (DOS) for these materials, which can impose a notable influence on the rate of adiabatic charge transfer [49]. 

Electrochemical reactions are heterogeneous in nature with the reaction kinetics being controlled by the properties of the electrode-electrolyte interface and the concentration of reactant available at this interface. Therefore, the physical, chemical, and electronic properties of the electrode surface are of paramount importance. Several factors will influence the electron-transfer kinetics for a redox system (i) type of electrode material, (ii) surface cleanliness, (iii) surface microstructure, (iv) surface chemistry, and (v) electronic properties (e.g., charge carrier mobility and concentration, which can be potential dependent for some semiconducting electrodes). Of course, if the solid is not a good electrical conductor (low charge carrier mobility and/or carrier concentration), then the current flow will be limited and the material will have drawbacks for electrochemical measurements. With the exception... 

With regard to its electronic properties, no studies are available that clearly demonstrate that electron transfer through such a supramolecular assembly is possible. Solid-state electrochemical studies on the crystalline material are not available at the present time. The closest to supramolecular electrochemistry are studies of ordered two-dimensional peptide arrays on gold. For some Fc-peptide cystamines, self-assembled monolayers of Fc-peptide cystamines were prepared that allow the quantification of the electron transfer kinetics by electrochemical techniques. Similar to the supramolecular assemblies, H-bonding plays an important role. At the present time (2003), only a few systems were studied and offer a rather complex picture of the ET properties. Additional experimental work is required to obtain definite results on the influence of the peptide primary and secondary structure on ET kinetics. In addition, tile issue of lateral interactions needs to be addressed by detailed dilution studies with alkylthiols. 

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