Ideal oxygen transport polarization curve

It is seen that b disappears and Equation 4.80 coineides with Equation 4.129, derived below, for the case of ideal oxygen transport at the small current. Small fo means small fjo or large diffusion coefficient. In both these cases, the oxygen transport does not eontribute to the potential loss. The respective polarization plots cover linear and Tafel regions (Figure 4.15, lower solid curves). 

This is the general polarization curve of the CCL with ideal oxygen transport for the case of large Equation 4.128 describes normal Tafel kinetics at small currents, double Tafel kinetics at large currents and the transition region between these two regimes. Moreover, this equation reduces to a correct limit at jo -> 0. 

FIGURE 4.18 The exact numerical (open circles) and the analytical (sohd hue, Equation 4.128) polarization curves of the CCL with the ideal oxygen transport. Dashed lines the low- and high-current curves. Equations 4.129 and 4.133, respectively. The exact numerical points are calculated with y heing the exact solution to Equation 4.122, while the analytical curve (4.128) is calculated with the approximate y given hy Equation 4.127. The current density is normalized to j = Opb/lci- Parameter ci = 1 and e = 100 (PEEC cathode. Table 5.7). Note the transition from normal to double Tafel slope at the current densities around io = 2. 

Substituting Equations 5.69 and 5.70 into the first term in Equation 5.68, results in the cell polarization curve under ideal oxygen transport in the GDL ... 

Figure 2.4 The general polarization curve of the catalyst layer with ideal transport of the reactant (oxygen). Solid lines analytical solutions, points— the exact numerical curve. Parameter = 0.1 (left panel) and = 10 (right panel). Linear domain is described by fjo = sjo, Tafel region is given by fjo = arcsinh ( jo coth (l/ )) and double-Tafel law is fjo = 21n( jo)-...

Suppose for a moment that the oxygen transport across the GDL is ideal. Then Ch = ct = c and Eq. (4.27) with the polarization curve (4.137) determine the optimal shape of catalyst loading along the channel. 

What is the effect of finite A, at high currents In this section, the case will be considered for poor oxygen diffusivity and ideal proton conductivity of the CCL. In this case, the local polarization curve of the CCL is given by Equation 4.87. Substituting Equation 5.41 into Equation 4.87, one obtains the local polarization curve with the term describing oxygen transport in the GDL ... 

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