Polarization Curves and x Shapes

The system (4.197) through (4.199) with the boundary conditions (4.202), (4.203), (4.204), and (4.209) has been solved numerically using Maple software. The physical and operational parameters are listed in Table 4.1. Note that the boundary conditions (4.202) and (4.204) contain both the cell current density jo and the potential loss rjox,o- However, these values are related by the polarization curve, which a priori is unknown. Thus, iterations are required to find ijox,o, providing the prescribed cell current jo. 

To understand these features, it is advisable to plot the shapes of local parameters through the CCL at several current densities. These shapes for = 0.3 and jo = 50, 

As the cell current increases, the crossover current decreases (Equation 4.205). Unexpectedly, because of a lower rate of methanol conversion in the CCL, the 

FIGURE 4.25 The shapes of local parameters through the CCL thickness for the indicated 

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In all three cases, the cathode is a two-layer structure close to the membrane interface, the MOR rate exceeds the ORR rate, while in the rest part of the CCL, the ORR rate dominates (cf. Figure 4.25, the section Polarization Curves and x Shapes in Chapter 4). As a result, the local proton current first increases with x and then decreases. 

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