Polarization curves observed

For the film thicknesses increasing more than 10 nm, the transfer of redox electrons via the conduction band of the film gradually predominates over the 

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Figure 6.8 S-shaped polarization curve observed in the CO oxidation model (for the exact model parameters, see Koperetal. [2001]). The thin line shows the cyclic voltammetry observed at a low scan rate of 2 mV/ s.

Figure 8-7 shows the anodic and cathodic polarization curves observed for a redox couple of hydrated titanium ions Ti /Ti on an electrode of mercury in a sulfuric add solution the Tafel relationship is evident in both anodic and cathodic reactions. FYom the slope of the Tafel plot, we obtain the symmetry factor P nearly equal to 0.5 (p 0.5). 

Fig. 8-7. Cathodic and anodic polarization curves observed for a transfer reaction of redox electrons of hydrated Ti /Ti particles at a mercury electrode in 1 M H28O4 solution containing 0.17 M and 0.03 M Ti 4 at 25°C electrode surface area = 0.15 cm. [From Vetter, 1967.]...

Figure 8-42 illustrates the anodic and cathodic polarization curves observed for an outer-sphere electron transfer reaction with a typical thick film on a metallic niobium electrode. The thick film is anodically formed n-type Nb206 with a band gap of 5.3 eV and the redox particles are hydrated ferric/ferrous cyano-complexes. The Tafel constant obtained from the observed polarization curve is a- 0 for the anodic reaction and a" = 1 for the cathodic reaction these values agree with the Tafel constants for redox electron transfers via the conduction band of n-lype semiconductor electrodes already described in Sec. 8.3.2 and shown in Fig. 8-27. 

Fig. 8-42. Anodic and cathodic polarization curves observed for electron transfer of hydrated redox particles at an electrode of metallic niobium covered with a thick niobium oxide NbsOs film (12 nm thick) in acidic solution reaction is an electron transfer of hydrated redox particles, 0.25MFe(CN)6 /0.25M Fe(CN)g, in 0.1 M acetic add buffer solution of pH 4.6 at 25 C. =...

Figure S-4S shows the polarization curves observed, as a function of the film thickness, for the anodic and cathodic transfer reactions of redox electrons of hydrated ferric/ferrous cyano-complex particles on metallic tin electrodes that are covered with an anodic tin oxide film of various thicknesses. The anodic oxide film of Sn02 is an n-type semiconductor with a band gap of 3.7 eV this film usually contains a donor concentration of 1x10" ° to lxl0 °cm °. For the film thicknesses less than 2.5 nm, the redox electron transfer occurs directly between the redox particles and the electrode metal the Tafel constant, a, is close to 0.5 both in the anodic and in the cathodic curves, indicating that the film-covered tin electrode behaves as a metallic tin electrode with the electron transfer current decreasing with increasing film thickness.

Fig. 8-43. Anodic and cathodic polarization curves observed for a redox electron transfer at metallic tin electrodes covered with an anodic oxide Sn02 film of various thicknesses d in a basic solution reaction is a redox electron transfer of 0.25 M Fe(CN)6 A).25 M Fe(CN)6 in 0.2 M borate buffer solution of pH 9.1 at 25°C. d = film thickness dj = 2 nm ...

Figure 9—4 shows the polarization curves observed for the transfer reaction of cadmium ions (Cd Cd ) at a metallic cadmium electrode in a sulfuric acid solution. It has been proposed in the literature that the transfer of cadmium ions is a single elemental step involving divalent cadmium ions [Conway-Bockris, 1968]. The Tafel constant, a, obtained from the observed polarization curves in Fig. 9-4 agrees well with that derived for a single transfer step of divalent ions the Tafel constant is = (1- P) 1 in the anodic transfer and is a = z p = 1 in the cathodic transfer. 

Fig. 9-5. Anodic and cathodic polarization curves observed for transfer of divalent iron ions (dissolution-deposition) at a metallic iron electrode in a sulfuric add solution at pH 4 (0.5MFesS04-)-0.5MKaS04) = anodic iron dissolution (cathodic iron...

Figure 10-16 shows polarization curves observed for the anodic ox en reaction (anodic hole transfer) and for the cathodic hydrogen reaction (cathodic electron transfer) on an n-type semiconductor electrode of titanium oxide. The data in Fig. 10-16 show that the anodic current due to the transfer of holes (minority... 

Fig. 11-10. Anodic polarization curves observed for metallic iron, nickel, and chromium electrodes in a sulfuric acid solution (0.5 M H 2SO 4) at 25°C solid curve = anodic metal dissolution current dot-dash curve s anodic oxygen evolution current [Sato-Okamoto, 1981.]...

In the potential range catliodic to one frequently observes so-called metastable pitting. A number of pit growtli events are initiated, but tire pits immediately repassivate (an oxide film is fonned in tire pit) because the conditions witliin tire pit are such that no stable pit growtli can be maintained. This results in a polarization curve witli strong current oscillations iU [Pg.2728]

An analysis of Eq. (6.13) show that for n = 1 and P = 0.5 and for current densities less than 4% of t the polarization is very low (less than 1 mV) and can practically be neglected. The linear section of the polarization curve extends up to current densities which are 40% of f. At current densities higher than 4f, the semilogarith-mic polarization relation is observed. 

A break in the polarization curve will not be observed when the kinetic parameters of the two steps and E. 2 t ) are drastically different, and hence,... 

In order to prove the S-shaped character of the polarization curve, the system was studied galvanostatically. The model predicts that the sandwiched branch of the polarization curve should be stable, and therefore measurable under galvanostatic conditions. Figure 6.10 shows the results of the experiment depending on the scan rate, an S-shaped curve can be observed in the back scan, i.e., from high to low current. At low... 

The shapes of the polarization curves shown in Fig. 3, including those generally observed for other reducing agents, are invariably complex, and not representative of simple electrochemical reactions. From the inception of modern electroless deposition practice, a number of mechanisms have been advanced to describe the electroless deposition process, many of which dealt with Ni-P. These classical mechanisms include the following ... 

Fig. 11-6. Polarization curves that can be observed with a corroding metallic electrode (solid curve) compared with anodic and cathodic reaction currents (dashed curve) as Amctions of electrode potential ip (ip ) = anodic (cathodic) polarization current i (i ) = anodic (cathodic) reaction current.

Fig. 11-8. Polarization curves for a corroding metallic electrode of which corrosion rate is controlled by diffusion of oxidants in aqueous solution solid curve = observable polarization curve.

A mixed polarization diagram (where the polarization behavior of the two different electrodes is represented) for the sphalerite-hypersteel combination is given in Fig. 1.10 (Vathsala and Natarajan, 1989), in which the cathodic polarization curves for the sphalerite and the anodic polarization curves for the hypersteel ball material are seen to overlap. The active nature of the ball material is evident. The current values were observed to be lower in the absence of oxygen which indicated a lower anodic dissolution of the hypersteel grinding medium in the absence of oxygen. 

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