Stoichiometry versus Constant Oxygen Flow

Constant Stoichiometry versus Constant Oxygen Flow 

The results of the section Impedance of the Cathode Side of a PEM Fuel Cell, have been obtained assuming constant oxygen stoichiometry X of the flow. However, impedance experiments are usually performed at a constant oxygen flow rate, rather than at a constant X. Indeed, keeping constant X means that the inlet flow rate must be changed in phase with the mean current density perturbation, which is hardly possible. 

Qualitatively, keeping X = const in the equations above means that the regimes with negative slopes of the local static polarization curves, of remote segments, are not considered. These regimes arise under fixed inlet oxygen flow, when this flow is below the critical value (the section Negative Local Resistance ) 

At low inlet fluxes, Equation 5.174 holds and the local polarization curves of remote segments exhibit negative slopes (Kulikovsky et ah, 2004). In this case, the local impedance spectra of remote segments turn into quadrant di(Z) 0, that is, they exhibit negative resistivity. 

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Constant Stoichiometry versus Constant Oxygen Flow... 

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