Characteristic current density

In their work, Andrieux and Saveant analyse the behaviour in terms of the characteristic current densities for each process. This has the advantage that, in general, the expressions for these characteristic current densities are fairly straightforward and obvious and, therefore, easily derived. In the case where the different processes involved are strictly first-order, the reciprocal of total current density can be obtained by combining the reciprocals of the current densities for the individual steps. For example, the limiting current density, //., for a reaction at the surface of a rotating disc coated by a permeable membrane is given by... 

The above equations were made dimensionless by using the feature width w as the characteristic length, as the characteristic current density, P=°w//c as the characteristic potential, bulk values as characteristic concentrations, and and DaCa/w as characteristic fluxes. The resulting dimensionless equations are... 

Fig. 6. The anodic portion of the potentiodynamic current-potential curve for El 11/A (400 rpm) [186, 187], exhibiting a characteristic current density maximum.

The backing in this model is treated with the Stefan-Maxwell equation to yield the partial pressure of oxygen at the backing/catalyst layer interface from the total pressure Ptot in the gas flow channel, the backing characteristic current density, 7b, and the mole fractions of water vapor and of oxygen, Xws and Xon, respectively ... 

FIGURE 5.7. Plots of the characteristic current densities J, (a), J2 (b), J, (c), and J4 (d) as a function of pH. For various values of Cp (labeled on the curves in units of mol/liter). (Reprinted from Chazalviel et 1991, with permission from Elsevier Science.)... 

The data providing the basis for Figures 7.3 and 7.4 are not generally valid, although they are based on tests and partly on calculations. In addition, they are combined in a way that corresponds to the Pourbaix diagram and at the same time gives a corrosion potential and characteristic current densities in reasonable agreement with observed values. 

From the current-voltage characteristics, current densities were calculated by dividing the current which flows in the filament by the NbTi cross-sectional area. This area was determined from photomicrographs of transverse sections of the filament taken from between the potential leads. Current densities associated with longitudinal magnetization loops were derived by a calculation similar to the one described by Fietz and Webb [ ]. In this case, the mean value of the cross-sectional area of the filaments was deduced from weight measurements made after the matrix had been dissolved. 

Figure 2.13 depicts the effect of porous structure on the relations of 770 vs. Jo, using different fractions of primary and secondary pores that correspond to psds in Figure 2.2. The two characteristic current densities,yNj andare shown for the different graphs. Effects of various parameters onand yg. j have been discussed in Ref. [25]. The model reveals sensitive dependencies of CCL operation on porous structure, thickness, wetting angle, total cathodic...

Volumetric exchange current density of agglomerate or ultrathin CCL Characteristic current density of oxygen diffusion... 

The I-V characteristics (current density vs electric field) were investigated for sol-gel-derived Zr02-Y203 thin films fired at 350 and 700 °C in air, in comparison with those obtained for sol-gel-derived Zr02 thin films [Figure 29(a) and 29(b)]. The reverse bias... 

The function (3.7) is shown in Figure 3.2. The parameters for this plot are listed in Table 3.1. As can be seen, the characteristic current density is small (the last column in Table 3.1) and hence this set of parameters prescribes the high-current regime of cell operation. 

Figure 4.24 Characteristic current density as a function of temperature (Kulikovsky, 2009b).

Superficial exchange current density (A m ) characteristic current density (A m )... 

We note from Table 2.5 that linear Koutecky-Levich plots are expected for the first or the second wave, while in other cases the Koutecky-Levich plot is nonlinear. In some cases a second direct reaction wave is expected, whereas in other cases it is absent. These features can act as diagnostic parameters to help identify the particular kinetic situation. Characteristic current densities can be obtained by determining the Koutecky-Levich intercept when such a plot is linear. 

An expression for the characteristic current density, below which complete liquid-to-vapor conversion is possible, was obtained,... 

In the nonideal case, one has to evaluate the interplay of three effective electrode parameters, viz. volumetric exchange current density P, proton conductivity ap, and oxygen diffusivity D. Instead of considering these parameters, it is more insightful to evaluate and compare three corresponding characteristic current densities. These include the current conversion capability f = PIcl, defined above, the characteristic current density due to proton transport... 

The regime of CCL operation depends on the values of these characteristic current densities relative to each other and relative to Jo- Ideal operation with uniformly distributed reaction rates corresponds to two simultaneously fulfilled conditions... 

---