Tafel polarization

Figure 71. Tafel polarization measurement at different temperatures performed on MCMB and LiNiCo02 electrodes in 1.0 M LiPFe/EC/DEC/DMC/EMC (1 1 1 3). (Reproduced with permission from ref 515 (Figure 8). Copyright 2003 Elsevier.)...

FiG. 24. Anodic steady-state Tafel polarization relations for the OER at preoxidized Pt in 1 M aqueous HjSO (curve a) and 1 M aqueous NaOH (298 K.) (curve b) 257, 258). 

Fig. 29. Polarization data for the OER on a C03O4 film thermochemically formed on a Ni metal substrate. behavior is shown as a function of potential in relation to the logi versus Tafel polarization curve. (From Ref 302.)...

Fig. 4.8 Tafel polarization curves for anodic and cathodic reactions as related to the nth current channel in Fig. 4.7, illustrating the dependence of the corrosion current, lcorr, on the solution resistance, Rs...

The earlier sections of this chapter discuss the mixed electrode as the interaction of anodic and cathodic reactions at respective anodic and cathodic sites on a metal surface. The mixed electrode is described in terms of the effects of the sizes and distributions of the anodic and cathodic sites on the potential measured as a function of the position of a reference electrode in the adjacent electrolyte and on the distribution of corrosion rates over the surface. For a metal with fine dispersions of anodic and cathodic reactions occurring under Tafel polarization behavior, it is shown (Fig. 4.8) that a single mixed electrode potential, Ecorr, would be measured by a reference electrode at any position in the electrolyte. The counterpart of this mixed electrode potential is the equilibrium potential, E M (or E x), associated with a single half-cell reaction such as Cu in contact with Cu2+ ions under deaerated conditions. The forms of the anodic and cathodic branches of the experimental polarization curves for a single half-cell reaction under charge-transfer control are shown in Fig. 3.11. It is emphasized that the observed experimental curves are curved near i0 and become asymptotic to E M at very low values of the external current. In this section, the experimental polarization of mixed electrodes is interpreted in terms of the polarization parameters of the individual anodic and cathodic reactions establishing the mixed electrode. The interpretation then leads to determination of the corrosion potential, Ecorr, and to determination of the corrosion current density, icorr, from which the corrosion rate can be calculated. 

Fig. 4.19 Schematic representation of polarization curves for the analysis of galvanic coupling when the coupled metals have similar electrochemical parameters. Tafel polarization is represented.

For the Tafel polarization regime (in which most copper plating is carried out), the Wa number can be expressed in terms of ... 

Thus, a number of oxygen reduction half-cell experiments were performed, generating Tafel polarization plots, to investigate whether the perfluoro-compounds results in enhanced rates of reduction. One method of introducing the additive to the electrocatalyst consisted of applying 3-4 mL of the... 

The use of perfluorocarbon compounds, such as perfluorooctane and perfluorodecalin, as additives to enhance the rate of oxygen reduction at R-based electrodes was investigated in oxygen reduction half-cell experiments, generating Tafel polarization plots. The results indicate that the presence of perfluorocarbon fluids have some beneficial effects upon the kinetics of oxygen reduction at Nafion -H-coated Pt-based electrodes. These improvements in... 

Fig. 5. 14 Tafel polarization curves for Ni-Zn-P, Cd, and Zn-Ni coatings in 0.5 M Na2SO4-i-0.5 M H3BO3 solution at pH 7.0 [32]. NACE International 2003.

Fig. 5.15 Comparison of Tafel polarization plots for different coatings. Numbers in the parenthesis correspond to the weight percentage of metals [36].

Fig. 5.18—cont d (a) Tafel polarization curves for chromium corrosion diagram showing the corrosion potential and the corrosion current, (b) The corrosion current and the potential if mass limitations for hydrogen limit the maximum current to 10 A/cm, and (c) to 10 A/cm, respectively. 

J. Tafel, Polarization during cathodic hydrogen development, Z. Phys. Chem. 50 (1904) 641—712. 

Equations 4.129 and 4.132 allow calculating the position and length of the transition region between the Tafel and double Tafel domains of the polarization curve (Figure 4.18). Equating Equations 4.129 and 4.132 gives the point of intersection of the Tafel and double Tafel polarization curves (dashed curves in Figure 4.18) ... 

Figure 31.1 shows a classic electrochemically measured Tafel polarization diagram [33. The Tafel analysis is performed by extrapolating the linear portions of both cathodic and anodic curves on a log (current) versus potential plot to their point of intersection. This intersection point provides both the corrosion potential con and the corrosion current density for the system unperturbed. This is a very simple yet powerful technique for quantitatively characterizing a corrosion process. The Tafel equation can be simplified to provide Eq. (7) by approximation using a power series expansion. 

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