Linear current-potential region

Consider the case of low overpotential, often referred to as the micropolarization region or the linear current-potential region. The exponential terms in Eq. 35E can be linearized, using the relationship exp X = 1 -t- X, which is valid for x 1. This yields a linear relationship between the current density and the overpotential, namely ... 

Figure 3.8 Current-potential linear sweep voltammogram and the differential reflectivity change in the hydrogen adsorption region at fixed wavelengths (a) 2.34 pm and (b) 1.93 pm. The sweep rate was 15mVs with a square wave modulation of lOmV at 8.5 Hz. From Bewick et al.

In the case of the CVC curves of Fig. 6.32b, the converted charge increases as the scan rate decreases and they show a clear linear region at potentials above 0.20 V. The slope of these linear zones should be equal to (A cGf)/v (see Eqs. (6.214) and (6.218)). The values of the slopes of the linear regression of these zones for different values of v in the range 0.20-100 V s-1 have been plotted vs. the inverse of the sweep rate and from these data (kcQ ) = (11.3 0.2)nA has been obtained. This value is practically coincident with that obtained from the current-potential curves of Fig. 6.32a. 

A more simple analysis of LSV waves can give essentially the same information as CPSV and NPSV. Analysis of theoretical current-potential data for Nemstian and purely kinetic waves revealed that a nearly linear region... 

With continuing increase in anode potential, the current-potential relationship deviates from the linear relationship. As the potential continues to increase, the increase in the current slows down until it reaches a maximum and then decreases to a minimum point, and finally increases to the limiting current plateau. This is a transition from kinetics of electrochemical reaction domain to mass transport domain. This region may have a very different shape depending on electrolytes, potential scan rate, and other factors. Details of this region are discussed elsewhere [7,8]. 

Consider now the current-potential behavior of a system close to E. Assuming that the two partial currents are in their respective linear Tafel region, we can write... 

Figure 37 presents a current-potential curve for p-type silicon showing two distinct current peaks. The region below the first current peak corresponds to the pore formation regime. The first current peak corresponds to the critical current for electropolishing and exhibits a linear dependence on fluoride concentration, as shown in Fig. 38. Although the potential onset for electropolishing is dependent on the dopant type and concentration, the critical current density is independent of doping level [64], as can be seen in Fig. 9. This is also seen in the current-voltage curves as...

A continuous metal deposit layer may behave as an ohmic contact or a Schottky barrier. For a relatively thick metal film the silicon can still behave like a semiconductor before the onset of current. For example, for n-Si deposited electrochemically with 150nm An, the electrode behavior is similar to that of bare silicon electrode At positive potentials the anodic current is small whereas at cathodic potentials current from hydrogen evolution increases with increasing polarization. " In the potential region before the onset potential for the cathodic current a linear Mott-Schottky plot is obtained giving a flatband potential similar to that of bare silicon sample. In the potential region where hydrogen evolution occurs, it behaves like a metal with potential drops mostly in the Helmholtz layer. 

The electropolishing region does not occur in anhydrous organic solutions due to the lack of water required for the formation of oxide film. Figure 8.6 shows that in anhydrous HF-MeCN solutions the current can increase with potential to a value of about 0.5 A/cm without showing a peak current. The current increases linearly with potential due to the resistance in the solution and silicon substrate except for very small currents near the onset of anodic current where the current increases exponentially with... 

Linear sweep voltammetry delineates several regions in the current/potential relationships for the n-heptyl viologen... 

Figure 22-4 Current-potential curve for electrolysis showing the linear or ohmic region, the onset of polarization, and the limiting cuirent plateau. In the limiting current region, the electrode is said to be completely polarized, since its potential can be changed widely without affecting the current.

The effective electroactive surface may be determined directly by the voltammogram in evaluating the quantity of electricity involved in the adsorption-desorption of hydrogen (region I). The quantity of electricity is obtained by the integration of the current-potential curves, because the potential varies linearly with time. The active surface area (S = 0.56 cm2) is then calculated from the charge under the hydrogen underpotential-deposited (UPD) peaks, which needs 210 pC cm 2, as follows ... 

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