Current -overpotential curves for

Fig. 22. Current-overpotential curves for hydrogen evolution in concentrated H2S04 on differently prepared WC cathodes. (1) Teflon-bonded powder (2) Teflon-bonded powder pressed onto glided Ti (3, 4) Powder pressed onto graphitic support (in two different conditions). After ref. 432, by permission of IAHE.,...

Fig. 26. Current-overpotential curves for hydrogen evolution in NaOH solution on (1) Ni and (2,3) electrodeposited Ni(79)Mo(20)Cd(l) coatings. Temperature (1, 2) 25 °C (3) 80°C. (---------) Tran-...

Figure 1. Tafel plot for anodic and cathodic branches of the current-overpotential curve for O + e 5 R (n = 1, a = 0.5,...

Figure 3.4.1 Current-overpotential curves for the system O + R with a = 0.5, T = 298 K, //,c = = h and io/ii = 0.2. The dashed lines show the component currents and /a.

Figure 3.4.3 Effect of the transfer coefficient on the symmetry of the current-overpotential curves for O + e R with T = 298 K and jo = 10 A/cm. ...

Fig. 32. Cyclic current-potential curve for Au(l 11), covered with an octadecanethiol SAM, in 0.1 M H2SO4 + 1 mM CUSO4. Scan rate 10 mV s-1. The C18-SAM blocks Cu deposition up to very high overpotentials. Inset Current response of a bare Au(lll) electrode for the same potential cycle [98],...

Therefore, the current density depends on the exchange current density ( o), transfer coefficient ( p), overpotential r ), and temperature (r). Fig. 7 represents typical current-overpotential curves based on Eq. (39). The net current is the result of the combined effects of the forward (anodic) and reverse (cathodic) currents. Although the Butler-Volmer equation for an electrochemical reaction in PEMFC is valid over the full potential range, simpler approximate equations may often be used for limited conditions. Thus, for the common value dp = 1/2, Eq. (39) becomes... 

Figure 2.23 Positions of quasi-Fermi levels at high positive overpotential (A and B) and low negative overpotential (C and D) in the dark and under illumination centre current-potential curve for an w-type semiconductor electrode (Memming, 2000).

Figure 1.1.5 Schematic current-potential curve for the Hg electrode in the cell Hg/H , Br (l M)IAgBvlAg, showing the limiting processes proton reduction with a large negative overpotential and mercury oxidation. The potential axis is defined through the process outlined in the caption to Figure 1.1.4.

The results of such measurements are known as current density-potential curves. They represent cumulative curves given by the superimposition of the current density-potential curves of the individual reactions. For simple electrodes with defined electrode processes, these are the overpotential curves. For metals exposed to electrolytic attack, superimposition of several overpotential curves gives the actual current density-potential curves that are of significance in corrosion testing and research. Figure 20.9 shows the superimposition of the overpotential curves of a hydrogen electrode... 

Figure 1. Experimental current-overpotential curves plotted for various bath temperature values. [AgNO = 0.025 mol/dm [.KAtOj] = 0.5 mol/dm = 0.015 mol/dml... 

Fig. 2.11 Schematic current versus overpotential curve for a cathodic reaction...

Figure 4.24 Tafel plot for ORR current-overpotential curve. Data for a H2-O2 PEFC at 80°C with different cathode catalyst loadings. The slope of the line (Tafel slope) for all conditions is approximately 0.65 mV/decade. (Reproduced with permission from [9].)...

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... 

Steady-State Kinetics, There are two electrochemical methods for determination of the steady-state rate of an electrochemical reaction at the mixed potential. In the first method (the intercept method) the rate is determined as the current coordinate of the intersection of the high overpotential polarization curves for the partial cathodic and anodic processes, measured from the rest potential. In the second method (the low-overpotential method) the rate is determined from the low-overpotential polarization data for partial cathodic and anodic processes, measured from the mixed potential. The first method was illustrated in Figures 8.3 and 8.4. The second method is discussed briefly here. Typical current—potential curves in the vicinity of the mixed potential for the electroless copper deposition (average of six trials) are shown in Figure 8.13. The rate of deposition may be calculated from these curves using the Le Roy equation (29,30) ... 

Fig. 2 Comparison of the experimental dimensionless current-time transients for electrodeposition of mercury onto boron-doped diamond electrode with the theoretical transients for instantaneous (upper curve) and progressive (lower curve) nucleation overpotentials (x) 0.862 V and ( ) 0.903 V (from Ref 33).

Figure 26 exhibits the polarization curves in terms of the cathode overpotential variation with current density for the CL27 obtained from the 3-D, single-phase DNS model prediction,25,27 the experimental observation25,27 and the liquid water transport corrected 1-D macrohomogeneous model.27 The polarization curve refers to the cathode overpotential vs. current density curve in the... 

---