Current vs. potential curves

Fig. 19.44 Typical current vs. potential curves for alloys of various phase combinations (after...

Figure 3. Current vs. potential curve for iron dissolution in phosphoric acid solution at pH 1,85. Ep, Flade potential Ep, passivation potential Epii- critical pitting potential EiP, transpassivation potential. Solid and broken lines correspond to the cases without and with CF ions, respectively.

Fig. 8-10. Anodic reaction current vs. potential curve for a redox electron transfer of hydrated redox particles at a metal electrode iibi = limiting diffusion current of redox particles 1/3 = potential at which reaction current is half the limiting diffusion current ( = 0.6iiin). [From Bard-Paulkner, 1980.]...

Fig. 6.91. Current vs. potential curves of Rh(111) in 0.12 M HCI04 with increasing amount of H2S04 (50 mv s-1).

Fig. 6.108. Current vs. potential curve for the adsorption of organic molecules on electrodes. The current due to adsorption of organic molecules is a currentless process. When oxidation, reduction, or other electron-transfer reactions take place, high currents may be detected.

Fig. 6.13. Anodic current vs. potential curves for the process of BH4 ions oxidation on the bulk Cu electrode (curve 1 for comparison see curve 2 registered in the same conditions without BH4 ions), on the initial Ti02 electrodes (curve 7 for Ti02 with Nd = 10 19 cm 3 curve 8 for Ti02 with Nd 1018 cm 3) and on the Ti02 electrodes surface modified with different concentration of Cu (curve 3 - 1018 atoms/cm2, curves 4,5 - 1016 atoms/cm2, curve 6 - 1015 atoms/cm2). The values of Nd for Ti02 were 1018 cm 3 (curve 5) and 1019 cm 3 (curves 3,4,6). Curve 9 was obtained with the use of represented electrical circuit modeling the system Ti02 - Cu particles - electrolyte (D - solid-state Schottky diode R - electrical resistor WE, RE and CE - working, reference and counter electrodes, correspondingly). Electrolyte 0.1 M NaBH4 + 0.1 M NaOH. The potential sweep rate is 5 mV/s.

Fig. 29. Current vs. potential curves for the oxidation of borohydride at a gold electrode in various solutions at 75 °C. Potential scanned from negative to positive at 5.56 mV s . ...

Not only is the value of jQ important in electrocatalysis but also the experimental Tafel slope at the operating electrode potential. As expected in an electrocatalytic process, this complex heterogeneous reaction exhibits at least one intermediate (reactant or product) adsorbed species. Therefore, a single or simple Tafel slope for the entire process is not expected, but rather surface coverage and electrolyte composition potential dependent Tafel slopes within the whole potential domain are expected. Instead of calculating the most proper academic Tafel slope, the experimental current vs. potential curve is required for the selected electrocatalysts [4,6]. 

The maximum PI in the current vs. potential curve correlates with the substrate surface transition. The difference in zero charge potentials between the reconstructed (px. 3) and the unreconstructed (1x1) gold surfaces gives rise to an additional current contribution due to double layer charging. Figure ID shows the ideal terminated (1x1) surface with atomic resolution. Around 0.80 V a disorder/order transition takes place within the layer of adsorbed (hydrogen-)sulfate ions [27-30]. The forma-tion/dissolution of the so-called /3 x. 7) overlayer correlates with the... 

The phase behavior of Au(lOO) in aqueous H2SO4 and HCIO4 has been studied before [23,32-34]. Figure 5 shows a typical current vs. potential curve of Au(lOO) in 0.05 M H2SO4. 

Staircase voltammetry is in fact a modified, discrete linear scan (or cyclic) voltammetry. The potential scan can be reversed in SV, similarly as it is done in cyclic voltammetry, and then a cyclic staircase voltammogram can be obtained. Staircase voltammograms are peaked-shaped the same as linear scan voltammo-grams. There are some differences between these voltammetries anyway. A linear scan (or cyclic) voltammogram forms a continuous current vs. potential curve, while each staircase voltammogram consists of a number oii-E points. Also, the peak heights obtained under conditions of identical scan rates in linear scan and staircase voltammetries (v = AE/At) may differ considerably. 

Firstly, if the current vs. potential curve generated in a potential sweep experiment is of the irreversible type, and corresponds only to the electron transfer step, then rate constant information can be extracted from the behavior by standard procedures. Secondly, and of more interest, if a chemical step is coupled before or after it, then the magnitude of currents observed will depend on the ratio of the rate constants for the electrochemical and chemical steps, and the relation between the rate constant of the ratecontrolling step and the time scale of the experimental measurement, i.e., the potential sweep rate. 

Two-dimensional surface processes also give rise to a current vs. potential curve in cyclic voltammetry having a maximum but the curves are distinguished from those for diffusion-controlled processes by a dependence of the currents on the first power of the sweep rate, while the latter processes give currents related to square root of sweep rate. Coupled chemical steps give similar behavior with respect to changing sweep rate and type of mechanism as do the diffusion-controlled processes except that the curves exhibit maxima determined by depletion of the two-dimensional adlayer rather than the three-dimensional diffusion layer. The characteristic behavior found... 

HOR on a Pt/C electrode in alkaline solutions has also been studied by us in a three-electrode arrangement [71]. A semi-empirical equation in agreement with the Tafel-Volmer mechanism was proposed to quantitatively explain the current vs. potential curves obtained in a variety of experimental conditions ... 

No general analytical expression similar to equation (15.14) is available for a steady-state current vs. potential curve at an electrode whose surface is not uniformly accessible. An exception is a microdisk electrode for which an analytical approximation (15.15) provides an accurate description of a quasireversible steady-state voltammogram (13)... 

In this method, applied potential to the system is plotted vs. the logarithm of the current density. The resulting curves would intersect at a point representing the corrosion potential and the corrosion current density. In the vicinity of the corrosion potential, the measured log current vs. potential curves both deviate from linearity. Nevertheless, both often contain linear segments referred to as Tafel regions. 

Figure 3.64 (a) Current vs potential curves for a nanostructured NiO film coated... 

We now turn our attention to the kinetic data. Anodic and cathodic potentiodynamic curves were taken at the faces of the single crystals in the 0.5 M H2SO4 - 0.01 M Fe(CN)e (or Fe(CN)6 ) solution. The current vs. potential curves passed through a maximum whose potential depended on the potential scanning rate V (compare the cathodic curves in Fig. 4.1b). The transfer... 

---