Current density profile

Quality control tests are intended to detect produced materials which deviate from manufacturing specifications, and thus may result in questionable performance. The materials are usually subjected to spectrographic analysis which is the primary quality control check. The exposure tests are necessarily of short duration (hours or days), in which the test conditions attempt to reflect the environment of operation, for example using artificial seawater for a marine application. Since a property that is reproducible and indicative of a consistent quality anode is all that is required, there is no attempt to mirror, except in the crudest fashion, current density profiles. 

Figure 1. Local current density profiles along a straight-channel fuel cell as predicted by the same computer model for two cases differing only in two model parameters. ...

Figure 15. Current density profiles as a function of the flow plate electric conductivity (S/m) in a straight-channel fuel cell with an average current density of 0.8 A/cm. ...

Figure 22. Local current density profiles along the channel direction for different humidification levels at Ueii = 0.65 V. Anode and cathode stoichiometries are 1.4 at 1.0...

Figure 24. Local current density profiles along the channel direction of single-channel PEFC for different inlet stoichiometric ratios at Keii = 0.65V at the inlet relative humidity 20% cathode and 100% anode at 80...

Detailed validation for low humidity PEFC, where the current distribution is of more interest and likely leads to discovery of optimal water management strategies, was performed most recently. Figure 35 shows a comparison of simulated and measured current density profiles at cell potentials of 0.85, 0.75, and 0.7 V in a 50 cm cell with anode and cathode RH of 75% and 0%. Both experimental data and simulation results display the characteristics of a low humidity cell the local current density increases initially as the dry reactants gain moisture from product water, and then it decreases toward the cathode outlet as oxygen depletion becomes severe. The location of the peak current density is seen to move toward the cathode inlet at the lower cell potential (i.e., 0.7 V) due to higher water production within the cell, as expected. 

Fig. 10.11 The calculated (a) Nemst potential profile and (b) current density profile at the electro-lyte/anode interface for the standard case ( 1) in Table 10.2.

Figure 4. Two dimensional current density profile in a (3.3 cm x 3.3 cm) structure (see text for conditions).

Figure 2.13 Current density profiles, ifr)/ I o.ads. between two steps of growth according to [2.25]. (a) for different cathodic (upper part of the plot) and anodic Oower part of the plot) overpotentials at /Isd = 0.31 tep- (b) for different surfece diffusion rates O.l tep < -tsd < lO tep at 10 mV cathodic and anodic overpotentials.

The difference between the anodic and the cathodic contributions in the course of copper upd under the influence of iodide specific adsorption can be calculated from a theoretical point of view. In a mixed control system—adsorption/desorption and quasi-reversible charge transfer—the current density profile, jt, can be assayed considering the metallic adsorbate under Langmuirian conditions at a stationary surface excess that is related to the stationary surface coverage, 0 by... 

The current density profile is given as an implicit function of E ... 

This is the explicit form of proton current density profile across the catalyst layer. Figure 6.5 shows the profiles j x) for three values of mean current... 

Local current density profiles in the first and the second case are described by (6.92) vwth = 1 and by (6.95), respectively. In the mixed case close to the... 

The system (6.108), (6.110), (6.111) determines oxygen, water vapour and local current density profiles along the channel in the case of constant A. The parameter E is iterated so that the local current density j gives the prescribed total current density... 

Although the local current density profiles in Figure 9.5 are quite different, the cell voltage does not differ significantly 0.688 V for the base case and 0.6602. 

The total power density dissipation at x(rt, Zi) is determined by integrating over the beam elements dl. To do this, we consider a gaussian beam current density profile written as... 

Convective diffusion equation for the concentration profile. (This requires a knowledge of the current density profile, which is not known presently.)... 

In the development of molten carbonate fuel cells (MCFCs), many issues require mathematical models. Some of them, for example, the design of controllers and the integration of an MCFC stack in a larger plant system, can be solved with spatially lumped models. Other questions such as the analysis of an inhomogeneous current density profile or the optimal design and operation of a fuel cell with respect to temperature Hmitations, need spatially distributed models. Because the latter are usually the more complex models, this chapter is focused on these models. 

Fig. 9 Current density profiles (a) used to obtain porous silicon films and the resulting pore size distributions (b). The solid and dashed lines correspond to filled and open symbols in (b), respectively...

From Fig. 1 and the above equations, one can see that the reaction distribution will depend on the various transport and reaction phenomena. For limiting cases, if one of the reactants is limiting in terms of transport or concentration, then the reaction or transfer current-density profile will be exponential towards the place with the incoming limiting reactant. If both are equally limiting, one obtains a parabolic reaction profile. If the reaction itself is limiting, then one obtains a uniform reaction profile. 

Local current density profiles in the first and the second case are described by (4.76) with = 1 and by (4.79), respectively. In the mixed case, close to the inlet, jiim is given by (4.79) along the rest of the channel it is given by (4.76). The point Zmax, which in the mixed case separates the water- and oxygen-limiting domains, is obtained from the continuity of local currents and oxygen concentrations at this point. Equating (4.78) to (4.76) and (4.79) to (4.76), we get... 

Figure 4.30 (a) Evolution of local current density profile upon variation of the total current J (indicated) in the cell. Solid lines—anal3dical solution (4.243) of reduced system, and dashed lines—numerical solution of the full system of equations (4.197), (4.198) and (4.233). Parameters are = 1, A = 100, = 8, p = 1, and 7 = 2. The other parameters required... 

Current density profile over time of anode exposed to transient CO concentrations - P = 3 atm, T = 80°C, t1j= 0.1 V, 100 ppm CO. (From Zamel, N., X. Li, 2007. International Journal of Hydrogen Energy, 33 1335-1344. With permission.)... 

Assuming that all variables in eq. (4.52) are constant, except time t, one can predict the current density profile as a nonlinear behavior for a particular electrolyte. This is shown in Figure 4.7... 

Figure 4.7 Schematic of nonlinear current density profile of Cottrell equation.

FIGURE 8.5 (a) steady state current density output for MEA13-17 at room temperature, and (b) current density profile over 60min after 24h (—1.8V) and after 48h (—1.75V) for MEA 13 at room temperature. 

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