Current-potential curve

Application of a potential between a semiconductor electrode and a counter electrode in an electrolyte leads to a current flux. For an n-semiconductor in the accumulation region 

The charge transfer on a metal electrode depends on the overlap between occupied and unoccupied energy levels in metal and electrolyte. This can be found around the Fermi level (Chapter 6). The contact of an electrolyte with a redox system and a semiconductor 

If the density of electrons in the conduction band on the surface of the semiconductor is 

Otherwise, the anodic conduction band current is proportional to the density of occupied states in the electrolyte times the density of states in the conduction band 

Similarly, one can formulate for the anodic valence band process with denoting the snr- 

---

In the case of an irreversible electrode reaction, the current-potential curve will display a similar shape, with... 

Maloy, J. T. Factors Affecting the Shape of Current-Potential Curves, ... 

The potential dependence of the velocity of an electrochemical phase boundary reaction is represented by a current-potential curve I(U). It is convenient to relate such curves to the geometric electrode surface area S, i.e., to present them as current-density-potential curves J(U). The determination of such curves is represented schematically in Fig. 2-3. A current is conducted to the counterelectrode Ej in the electrolyte by means of an external circuit (voltage source Uq, ammeter, resistances R and R") and via the electrode E, to be measured, back to the external circuit. In the diagram, the current indicated (0) is positive. The potential of E, is measured with a high-resistance voltmeter as the voltage difference of electrodes El and E2. To accomplish this, the reference electrode, E2, must be equipped with a Haber-Luggin capillary whose probe end must be brought as close as possible to... 

Fig. 2-3 Potential scheme (a) and circuit (b) for measuring a current-potential curve in cathodic polarization (explanation in the text).

In general, according to Eq. (2-10), two electrochemical reactions take place in electrolytic corrosion. In the experimental arrangement in Fig. 2-3, it is therefore not the I(U) curve for one reaction that is being determined, but the total current-potential curve of the mixed electrode, E,. Thus, according to Eq. (2-10), the total potential curve involves the superposition of both partial current-potential curves ... 

The validity of Eq. (3-15) further follows from the results given in Fig. 3-4. It represents the current-potential curve for a buried storage tank. The difference f/ n - I/off is proportional to the current /. The quotient R is equal to the grounding resistance of the tank. The (/) curve corresponds to the true polarization curve. 

Fig. 21-6 The dependence of the passivation process on the shape of the cathodic partial current potential curve (a) Anodic partial current potential curve, (b) cathodic partial current-potential curve without local cathode rest potential (c) cathodic partial current potential curve with local cathode rest potential I7j p.

It must be emphasised that in evaluating the limiting cathode potential to be applied in the separation of two given metals, simple calculation of the equilbrium potentials from the Nernst Equation is insufficient due account must be taken of any overpotential effects. If we carry out, for each metal, the procedure described in Section 12.2 for determination of decomposition potentials, but include a reference electrode (calomel electrode) in the circuit, then we can ascertain the value of the cathode potential for each current setting and plot the current-potential curves. Schematic current-cathode potential... 

FIGURE 1-7 Current-potential curve for the system O + ne - " R, assuming that electron-transfer is rate limiting, C0 = CR, and a = 0.5. Hie dotted lines show the cathodic ((.) and anodic ( ) components. 

FIGURE 1-8 Tafel plots for the cathodic and anodic branches of the current-potential curve. 

Figure 4-12 Current-potential curve for a platinum electrode in 0.5 M H2S04. Regions of oxide formation (QJ and reduction (Qc) as well as formation, of hydrogen (Hc) and its oxidation (H,) are indicated. (Reproduced with permission from reference 33.)...

Figure 7. Current-potential curve of a bipolar membrane of hydrous ironflll) oxide in chloride solution. FeCl3(aq)/Fe(HI)(oxideyNaCl(aq)-Na2Mo04(aq).l The system is kept at room temperature. C, cation A, anion. (Reproduced bom M. Sakashita and N. Sato, Corrosion 35,351,1979, Fig. 4 with permission from NACE International.)...

Figure 11. Dynamic microwave conductivity-potential curves taken with a ZnO single crystal and shown for two potential sweep velocities (a) and (b) and a corresponding dynamic (photo)current-potential curve (bottom). The dark effects and photoeffects are indicated for the two cases. Curves 1 and 2 correspond to (a) and (b) respectively.

Crystal surface specificity of the potential of zero charge, 152 Current-potential curves for bipolar membranes, 228 of iron dissolution in phosphoric acid,... 

Iron dissolution in phosphoric acid, the current-potential curve, 224 Iwasita and Xia, preparation of platinum single crystals, 133... 

Photo current-potential curves, as a function of pulsing frequency, 477 Photo currents... 

Pulsing frequency, photo current-potential curves as a function of, 477... 

Current density versus electrode potential curves (current-potential curves)... 

CP = current-potential curves CV = cyclic voltammetry EXI VA = derivative cyclic voltabsorptometry IP = impedance method. See also list of symbols. 

The co-reduction of copper and selenium is considered as an exception to Kroger s theory. Current-potential curves in the literature show that deposition of copper is rather compulsory to make the deposition of selenium possible. In fact, although the standard potential for Se(IV) reduction is more positive than that of copper (0.741 and 0.340 V vs. SHE, for selenous acid and cupric ion, respectively), it turns out that Se(IV) alone is reduced at more negative potentials than Cu(II). In the presence of copper, the order is reversed. 

The reduction wave of peroxydisulphate at dme starts at the potential of the anodic dissolution of mercury. The current-potential curve exhibits certain anomalous characteristics under various conditions. At potentials more negative than the electrocapillary maximum, a current minimum can be observed this is due to the electrostatic repulsion of the peroxydisulphate ion by the negatively charged electrode surface. The current minimum depends on the concentration and nature of the supporting electrolyte, and can be eliminated by the adsorption of capillary active cations of the type NR4. ... 

Provided the additivity principle holds, the catalytic rate Vcat of reaction (3) at the surface should therefore be the same as the value Vmx predicted from the current-potential curves of the eouples involved. Moreover, the measured potential Eau of the catalyzed mixture should be... 

Each couple present is assumed to act independently so that its current-potential curve is unaffected by the presence of the other couple. 

The main system chosen by Wagner and Traud themselves was the corrosion of zinc amalgam in aqueous HCl. They measured the current-potential curves of... 

Experiments by Freund and Spiro/ with the ferricyanide-iodide system showed that the additivity principle held within experimental error for both the catalytic rate and potential when the platinum disk had been anodically preconditioned, but not when it had been preconditioned cathodically. In the latter case the catalytic rate was ca 25% less than the value predicted from adding the current-potential curves of reactions (15) and (16). This difference in behavior was traced to the fact that iodide ions chemisorb only on reduced platinum surfaces. Small amounts of adsorbed iodide were found to decrease the currents of cathodic Fe(CN)6 voltam-mograms over a wide potential range. The presence of the iodine couple (16) therefore affected the electrochemical behavior of the hexacyanofer-rate (II, III) couple (15). 

Iodide adsorbed on reduced platinum surfaces was found to affect several other systems. The most dramatic effect was shown when the couples U/r and O2/H2O were considered together. Addition of the current-potential curves of these two couples indicated that platinum should significantly catalyze the reaction... 

The current-potential curve of a mixture of couples can be obtained by adding algebraically, at any potential, the currents given by each of the couples present, provided these have been determined in circumstances that correspond to those in the mixture. 

---