Variation of PEM Fuel Cell Physical Parameters with Current: Impedance Spectroscopy Study

Experimental impedance spectra of a segmented PEM fuel cell are fitted using a numerical impedance model based on the transient macrohomogeneous equations for the cathode side. Dependence of the cell transport and kinetic parameters on the current density is reported in the range from 50 to 400 mA cm−2. The largest variation (growth by an order of magnitude) exhibit the cathode catalyst layer proton conductivity σp and oxygen diffusivity. Moreover, σp exhibits a stepwise change at the current density ≃ 200 mA cm−2. This jump could lead to formation of current-carrying and current-free zones over the cell surface. Recent experimental data (JES, 156, B301 (2009)) show that this configuration is indeed realized in PEMFCs with the high- and low-current density zones under the channel and rib, respectively