Potential current density curves

Fig. 3.45 Potential-current density curves in 10% sulphuric acid solution at 25°C...

Fig. 3.46 Potential-current density curves in 50% sodium hydroxide solution at 60°C...

FIGURE 2.18 Potential-current density curves for the Ni electrodes in hydrogen fuels containing different concentration of Ff20. (From Nakagawa, N. et al., J. Electrochem. Soc., 142 3474-3479, 1995. Reproduced by permission of ECS-The Electrochemical Society.)... 

To express the preceding in a different, more specific way, we state that codeposition of two or more metals is possible under suitable conditions of potential and polarization. The necessary condition for simultaneous deposition of two or more metals is that the cathode potential-current density curves (polarization curves) be similar and close together. 

The anode potential-current density curves obtained for silicon in electrqpolishing solutions are similar to those observed for metals. A typical anode potential-current density curve for a horizontal p-type silicon electrode facing up in an aqueous solution of 5% HF at 25° C is shown in Fig. 3. This... 

Fig. 3. Typical anode potential-current density curve for a...

Fig. 4. Potential-current density curves for some electrogenerative and fuel cell reactions (O) benzene reduction on Pt (4S) (A) vinyl chloride reduction on Pt (31) (A) ethylene reduction on Pt (25) ( ) ethylene reduction on Pd (48a) (O) oxygen reduction on Pt (49). (Reprinted by permission of the publisher, The Electrochemical Society, Inc.)...

When an electrochemical reaction occurs, the electrode surface can no longer be considered an equipotential boundary and activation overvoltage has to be overcome to cause further reaction. The shift in electrode potential—the slope of the electrode potential/current density curve becomes significant—required to induce increased current flow gives rise to secondary current distribution. 

Measurement of corrosion rate by Tafel. Another method used to determine the corrosion rate as well as polarization resistance is the extrapolation method. This method consists of the exploration of the linear segments of potential-current density curves. In this case, the metal is initially made to act as a cathode. The cathodic potential-current density curve is measured by applying a potential range, defined by the variation between the corr and some potential active to corr, for example c, Figure 19-4. The cathodic current density approaches zero in the corr- Increasing the applied potential in the noble direction, the metal behaves as an anode, and the other part of the curve can be obtained. 

Linear Polarization Resistance. Another widely used polarization method is linear polarization resistance (LPR). The polarization resistance of a material is defined as the AE/Ai slope of a potential-current density curve at the free corrosion potential (Fig. 5.21), yielding the polarization resistance R that can be itself related to the corrosion current (i ) with the help of me Stem-Geary approximation in Eq. (5.22) [8]. 

FIGURE 38.13 Potential-current density curves for some biomaterials [Greener et al., 1972]. 

Figure L.2 Potential-current density curve resulting from concentration overpotential...

Potential-current density (E-i) curves, which have been determined for a number of the austenitic cast irons and also for the nickel-free ferritic irons, indicate that in general the austenitic cast irons show more favourable corrosion characteristics than the ferritic irons in both the active and passive states. 

Figure 4.34 illustrates, by means of potential/anodic current density curves, the influence of pH and Cl ions on the pitting of nickel The tendency to pit is associated with the potential at which a sudden increase in anodic current density is observed within the normally passive range ( b on Curve 1 in Fig. 4.34). It can be seen that in neutral 0-05 M Na2S04 containing 0-02m Cl" (Curve 1) has a value of approximately 0-4 V h- When pitting develops, the solution in the pits becomes acidic owing to hydrolysis of the corrosion product (see Section 1.6) and when this occurs the anodic current density increases by at least two orders of magnitude and tends to follow the curve obtained in 0 05 m H2SO4-t-0-02 m NaCl (Curve 2). Comparison of Curves 2 and 3 illustrates the influence of Cl" ions on the pitting process.

If — during this process — the Cu2+-concentration decreases, the mixed potential will shift along the cathodic partial current density curve (like a polarographic curve in this example) toward the equilibrium potential of the zinc amalgam, in case the amalgam reservior is large enough. 

Figure 5. Typical half-cell potentials vs. current density curves tor an Flj-Oj fuel cell and aDMFC.

Composites are deposited using both electroless62-64 and electrolytic plating processes. In the latter case composite deposition occurs in the presence of an applied electrical field, which is characterized by the cathodic potential or current density. The current density is the most extensively investigated process parameter. Roughly two types of current density dependencies can be distinguished. The particle composite content against current density curve either decreases or increases continuously or exhibits one or two... 

Figure 13 shows ATR-FTIR spectra recorded during the oxidation of a 3-methylthiophene film, Fig. 14 a spectrum of the oxidised state, and Fig. 15 a current density curve of the polymer film on a germanium crystal with an evaporated gold layer showing the potential regions in which spectra were taken. 

M and N drawn in terms of current. The curve for M is offset along the current axis showing the situation for M electrodes with three different areas. As the area of M increases, the couple potential (ignoring effects of ohmic potential drops) approaches the uncoupled corrosion potential for M in the given solution, which is the highest possible couple potential. Similarly, the lowest possible couple potential, found when the N M area ratio is very low, is the uncoupled corrosion potential for N in the environment. The corrosion current is given by the intersection of the two potential-current polarization curves, and the current densities are determined by dividing the current by the electrode areas. 

Anode potential-current density polarization curves. 

Fig. 15.17 Power density versus current density curves with various cathodes (a) and electrode potentials (vs. SCE) as a fimctimi of different cathodes (b) [95]...

Fig. 9 Schematic representation of the establishment of mixed potential, Em, at an electrode. Partial current densities (solid lines) and total current density curve (broken line).

The hysteresis effect in the anode potential vs. current density curves is attributed to the fact that water (or OH") does not easily discharge on occupied sites. With the experimental evidence discussed, Conway and Dzieciuch have concluded for the aqueous formate reaction that the lower slope region corresponds to the rate-determining step... 

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