Electrochemical potential experimental data

Our results indicate that the autoreduction cannot occur by a conventional outer sphere mechanism because of the gross mismatch of the electrochemical potentials. Experimental data available at this time are consistent with homolytic iron-carbon bond cleavage which may or may not involve a simultaneous nucleophilic attack on the coordinated cyanide. The homolytic metal-carbon bond cleavage may serve as a model for similar processes reported for vitamin Bi2 (26). 

The electrochemical potential of single ionic species cannot be determined. In systems with charged components, all energy effects and all thermodynamic properties are associated not with ions of a single type but with combinations of different ions. Hence, the electrochemical potential of an individual ionic species is an experimentally undefined parameter, in contrast to the chemical potential of uncharged species. From the experimental data, only the combined values for electroneutral ensembles of ions can be found. Equally inaccessible to measurements is the electrochemical potential, of free electrons in metals, whereas the chemical potential, p, of the electrons coincides with the Fermi energy and can be calculated very approximately. 

The above effects are more familiar than direct contributions of the metal s components to the properties of the interface. In this chapter, we are primarily interested in the latter these contribute to M(S). The two quantities M(S) and S(M) (or 8% and S m) are easily distinguished theoretically, as the contributions to the potential difference of polarizable components of the metal and solution phases, but apparently cannot be measured individually without adducing the results of calculations or theoretical arguments. A model for the interface which ignores one of these contributions to A V may, suitably parameterized, account for experimental data, but this does not prove that the neglected contribution is not important in reality. Of course, the tradition has been to neglect the metal s contribution to properties of the interface. Recently, however, it has been possible to use modern theories of the structure of metals and metal surfaces to calculate, or, at least, estimate reliably, xM(S) and 5 (as well as discuss 8 m, which enters some theories of the interface). It is this work, and its implications for our understanding of the electrochemical double layer, that we discuss in this chapter. 

Most often, the electrochemical impedance spectroscopy (EIS) measurements are undertaken with a potentiostat, which maintains the electrode at a precisely constant bias potential. A sinusoidal perturbation of 10 mV in a frequency range from 10 to 10 Hz is superimposed on the electrode, and the response is acquired by an impedance analyzer. In the case of semiconductor/electrolyte interfaces, the equivalent circuit fitting the experimental data is modeled as one and sometimes two loops involving a capacitance imaginary term in parallel with a purely ohmic resistance R. 

The experimental data verifying the dependencies of the formal potentials on ion parameters, as shown in Figs 4, 5, and 6 have been accessible only by application of voltammetry of immobilized particles [59], since that method is the only one that allows the study of different compounds that have been chemically synthesized and completely characterized to be measured under the very same conditions. This is not, or only to some extent possible with electrochemically prepared thin films on electrodes. 

The most stable oxidation states for protactinium are Pa(V) and Pa(IV). The chemical behavior of Pa(V) closely mimics that of Nb(V) and Ta(V), and experimental data are consistent with a 5f(l) rather than a 6d(l) electron configuration for the Pa(IV) species [37]. The electrochemical literature for Pa is mainly focused on the characteristics of the Pa(V)/Pa(IV) couple and the electrodeposition of Pa metal films from aqueous and nonaqueous electrolyte solutions. In aqueous solutions, only Pa(V) and Pa(IV) ions are known to exist, and the standard potential for the Pa(V)/Pa(IV) redox couple is in the range of —0.1 to -0.32 V [38]. 

The impedance spectroscopy is most promising for electrochemical in situ characterization. Many papers have been devoted to the AB5 type MH electrode impedance analysis [15-17]. Prepared pellets with different additives were used for electrochemical measurements and comparing. Experimental data are typically represented by one to three semicircles with a tail at low frequencies. These could be described to the complex structure of the MH electrode, both a chemical structure and porosity [18, 19] and it is also related to the contact between a binder and alloy particles [20]. The author thinks that it is independent from the used electrolyte, the mass of the electrode powder and the preparing procedure of electrode. However, in our case the data accuracy at high frequencies is lower in comparison with the medium frequency region. In the case, the dependence on investigated parameters is small. In Figures 3-5, the electrochemical impedance data are shown as a function of applied potential (1 = -0.35V, 2 = -0.50V and 3 = -0.75V). 

Figure 28 A typical Nyquist plot obtained from a nickel electrode polarized to low potentials (0.2 V versus Li/Li+) in PC solutions (1 M LiBF4 in this case). The equivalent circuit analog of 4 R C circuits in series and their separate Nyquist plots (four semicircles) are also shown. The frame in the lower right represents a typical fitting between the experimental data and this equivalent circuit analog [34]. (With copyright from The Electrochemical Society Inc.)...

Since tracks quantitatively the applied potential in electrochemical environments [7], it seems reasonable to conclude that bulk Li electrodeposition can commence when the Ni( 111) surface is covered by only a fraction of a monolayer, as the experimental data presented above appears to indicate. At least two important issues may have to be carefully considered before this suggested model can... 

The work of Larson et al. (62) represented the first detailed study to show agreement between AFM-derived diffuse layer potentials and ((-potentials obtained from traditional electrokinetic techniques. The AFM experimental data was satisfactorily fitted to the theory of McCormack et al. (46). The fitting parameters used, silica and alumina zeta-potentials, were independently determined for the same surfaces used in the AFM study using electrophoretic and streaming-potential measurements, respectively. This same system was later used by another research group (63). Hartley and coworkers 63 also compared dissimilar surface interactions with electrokinetic measurements, namely between a silica probe interacting with a polylysine coated mica flat (see Section III.B.). It is also possible to conduct measurements between a colloid probe and a metal or semiconductor surface whose electrochemical properties are controlled by the experimenter 164-66). In Ref. 64 Raiteri et al. studied the interactions between... 

In the literatme, the work function of a metal, p (in eV), is often used to estimate the degree of charge transfer at semiconductor/metal junctions. The work function of a metal is defined as the minimum potential experienced by an electron as it is removed from the metal into a vacuum. The work function ip is often nsed in lieu of the electrochemical potential of a metal, because the electrochemical potential of a metal is difficult to determine experimentally, whereas tp is readily accessible from vacuum photoemission data. Additionally, the original model of semiconductor/metal contacts, advanced by Schottky, utilized differences in work functions, as opposed to differences in electrochemical potentials, to describe the electrical properties of semiconductor/metal interfaces. A more positive work function for a metal (or more rigorously, a more positive Fermi level for a metal) would therefore be expected to produce a greater amount of charge transfer for an n-type semiconductor/metal contact. Therefore, use of metals with a range of tp (or fip.m) values should, in principle, allow control over the electrical properties of semiconductor/metal contacts. 

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