Polarization curve model summary

Plotting the activation losses as a function of cathodic exchange current density, we find  

COMMENTS Even a very small crossover results in an extremely significant polarization loss near an open circuit. In the PEFC at low temperatures, 0.1-0.2 V is typically sacrificed to crossover. At high current density, the added effect of the crossover is minimal, though, 

Returning again to our overall model, we now have a complete representation of the polarization curve. If we know several key paramaters relating to the kinetic, ohmic, and mass transfer processes, we can predict the overall polarization curve of the fuel cell. Much more complex models exist in the literature to cover multidimensional, multiphase, and transient aspects as well as approach the problem from various length scales from molecular to full-size stack simulation. However, the approach taken here does include the most important physicochemical phenomena that affect fuel cell performance  

Extension of these relations into multi-dimensional is a matter of additional mathematics, not fundamental understanding. 

The anode and cathode activation polarization losses (r]a,a and ria,c) for most fuel cell reactions can be determined from Eq. (4.35), the BV equation or a simplified form [i.e., Eqs. (4.52)-(4.55)]. 

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