Impedance Study on Oxygen Diffusion Through Fuel Cell Cathode Catalyst Layer at High Current

Abstract

A mathematical model to simulate the electrochemical impedance spectrum in the frequency domain and the current distribution in the time domain of polymer electrolyte fuel cell cathode catalyst layer (CCL) operated at high currents has been developed. In the model, Fick’s second law in the frequency domain is solved to define oxygen distribution through CCL. The rate of oxygen transportation and proton conductivity are related to the current distribution equation reported in the authors’ previous study for low current operations. The model, compared against the frequency response of an experimental impedance spectrum, is then converted into the time domain using the inverse Laplace transform method. The results show the nonsteady oxygen diffusion in the CCL which allows equilibrium to be established between the bulk concentration supplied at the gas diffusion layer boundary and the surface concentration of the oxygen within the CCL. The developed model can be applied to unveil the effect of kinetic, ohmic, and mass transport mechanisms on current distribution through the thickness of the CCL from the measured impedance results.