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Kinetic resistivity

Even in the absence of Faradaic current, ie, in the case of an ideally polarizable electrode, changing the potential of the electrode causes a transient current to flow, charging the double layer. The metal may have an excess charge near its surface to balance the charge of the specifically adsorbed ions. These two planes of charge separated by a small distance are analogous to a capacitor. Thus the electrode is analogous to a double-layer capacitance in parallel with a kinetic resistance. [Pg.64]

The exchange current density, depends on temperature, the composition of the electrolyte adjacent to the electrode, and the electrode material. The exchange current density is a measure of the kinetic resistance. High values of correspond to fast or reversible kinetics. The three parameters, a, a. ... [Pg.64]

The second bracket contains the aspect ratio. The group in the first bracket is a measure of the approach to the limiting current modified by a total overpotential. The authors describe this group as a ratio of mass-transfer resistance to kinetic resistance. [Pg.187]

Workers have shown theoretically that this effect can be caused both at the microstructural level (due to tunneling of the current near the TPB) as well as on a macroscopic level when the electrode is not perfectly electronically conductive and the current collector makes only intermittent contact. ° Fleig and Maier further showed that current constriction can have a distortional effect on the frequency response (impedance), which is sensitive to the relative importance of the surface vs bulk path. In particular, they showed that unlike the bulk electrolyte resistance, the constriction resistance can appear at frequencies overlapping the interfacial impedance. Thus, the effect can be hard to separate experimentally from interfacial electrochemical-kinetic resistances, particularly when one considers that many of the same microstructural parameters influencing the electrochemical kinetics (TPB area, contact area) also influence the current constriction. [Pg.594]

Ketoglutaifo add, 283,286 Ketones, 275,298 Ketoprofen, 286 Kieselguhr, 117 Kihara potential, 206 Kinetic resistances, 227 Kinetics of adsorption-desorption, 10, 127, 159... [Pg.168]

The first term in the right-hand side of Eq. (1.193) accounts for the pure kinetic resistance of the process (which has been called as activation term), whereas the second combines the influence of the potential and of the mass transport through the limiting current (see Eqs. 1.184 and 1.185). The overall behavior of the current-potential response can be seen in Fig. 1.22. [Pg.57]

F(x) / 0. In other words, the electrode reaction presents a stronger kinetic resistance the smaller is, and, as a consequence, higher // values are required to obtain measurable anodic and cathodic currents. [Pg.145]

Early calculations by Borghi et al (59) determined the contributions of kinetics and external diffusion as a function of bed temperature, particle size, and oxygen concentrations. These show that for particles of 1 mm diameter 1116 K, conditions typical of commercial practice, the diffusion and kinetic resistances are of equal importance. Experimental support for these predictions is provided by Ross and Davidson (60, 61). [Pg.93]

As a rule, the smaller the particles, the more thorough the mixing, then the more readily this process proceeds and the less time it takes to reach its limit. Factors facilitating diffusion would certainly help to alleviate the kinetic resistance. In this special process, ion pairs or molecules move from the surface of the crystalline substance to that of the support with the highly specific surface, either through the vapor phase or directly. However, we have found that direct migration across particles seems to be far more important. In fact, the surface is a much more fluid medium... [Pg.15]

The Wagner parameter, W, is the ratio of the kinetic resistance to the ohmic resistance. The Wagner parameter is the ratio of the true polarization slope given by the partial derivative, dE /di, evaluated at the overpotential of interest at constant pressure, temperature, and concentration, divided by the characteristic length and the solution resistance (2,40). [Pg.147]

Figure 13 Tube-tubesheet arrangement similar to Fig. 12 showing time effects on 90-10 Cu-Ni coupled to Monel 400 tubesheet in flowing seawater. The strong time effect on the potential distribution arises from a changing Ecxt for the Monel 400 and increased kinetic resistance for the 90-10 Cu-Ni as oxide films thicken near the tube entrance. (From Ref. 4.)... Figure 13 Tube-tubesheet arrangement similar to Fig. 12 showing time effects on 90-10 Cu-Ni coupled to Monel 400 tubesheet in flowing seawater. The strong time effect on the potential distribution arises from a changing Ecxt for the Monel 400 and increased kinetic resistance for the 90-10 Cu-Ni as oxide films thicken near the tube entrance. (From Ref. 4.)...
Figure 5.42 shows an example of the effect of humidity on the EIS spectra. It can be seen that the cut-off for anode humidification does not affect the spectra too much compared with the cut-off for cathode humidification. As we know, the fuel cell EIS primarily represents the cathode behaviour. Therefore, cathode humidification can greatly affect the whole impedance spectra. The humidification cut-off at the cathode causes a large difference in both the membrane resistance and the kinetic resistance. Dehydration of the anode also brings about a substantial increase in cathode impedance because a dry anode pulls water away from the cathode and across the membrane, which makes it hard to keep the cathode well hydrated [18],... [Pg.243]

The PBI-based PEM fuel cell can operate from 120°C to 200°C without external humidification. AC impedance shows that kinetics resistance decreases at higher temperatures, as shown in Figure 6.53, which is different from the characteristics of Nafion -based PEM fuel cells at high temperatures, but is consistent with the performance trend of the PBI-based PEM fuel cells, as shown in Figure 6.54. Although there is no humidification of the reactant streams in the operation of PBI PEM fuel cells, mass transfer issues are still observed through AC impedance, as shown in Figure 6.55. [Pg.319]

The results also suggest that through AC impedance measurements, the performance drops caused by individual processes such as electrode kinetic resistance, membrane resistance, and mass transfer resistance can be correlated to either reduction or improvement in cell performance. If individual impedances are known, the contribution to the change in performance can be identified, which is very important in the design and optimization of high-temperature MEA catalyst layer components, structure down-selection, and MEA architecture. [Pg.321]

Reactor capacity per unit volume appears to depend on four resistances in series the gas-phase transfer resistance, two liquid-phase transfer resistances, and the kinetic resistance. The highest resistance limits the capacity of the reactor. The four resistances have the unit of time and each one individually represents the time constant of the particular process under study. For example, 1 lkjigl is the time constant for the transfer of A from the bulk of the gas through the gas film to the gas-liquid interface. The same holds for the three other resistances. For a first-order reaction in a batch reactor, for example, the concentration after a certain time is given by C/C0 = exp(-r/r), in which r = 1/ A is the reaction time constant. For processes in series the individual time constants can be added to find the overall time constant of the total process. [Pg.64]

These equations match the statement of classical chemical kinetics that upon consecutive chemical transformations, one should summarize the kinetic resistances of each consecutive transformation. [Pg.32]

Thus, the overall (global) reaction rate is dependent upon four mass-transfer1 resistances plus a kinetic resistance. [Pg.36]


See other pages where Kinetic resistivity is mentioned: [Pg.105]    [Pg.337]    [Pg.465]    [Pg.557]    [Pg.562]    [Pg.573]    [Pg.590]    [Pg.598]    [Pg.632]    [Pg.8]    [Pg.287]    [Pg.78]    [Pg.15]    [Pg.444]    [Pg.449]    [Pg.454]    [Pg.455]    [Pg.456]    [Pg.219]    [Pg.230]    [Pg.283]    [Pg.314]    [Pg.54]    [Pg.200]    [Pg.330]    [Pg.331]    [Pg.384]   
See also in sourсe #XX -- [ Pg.254 , Pg.255 , Pg.256 , Pg.257 , Pg.258 , Pg.259 ]




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Kinetic resistance

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