Analytical impedance of oxygen transport in the channel and gas diffusion layer of a PEM fuel cell

Abstract

Analytical model for impedance of oxygen transport in the gas--diffusion layer (GDL) and cathode channel of a PEM fuel cell is developed. The model is based on transient oxygen mass conservation equations coupled to the proton current conservation equation in the catalyst layer. Analytical formula for the "GDL+channel" impedance is derived assuming that the oxygen and proton transport in the cathode catalyst layer (CCL) are fast. In the Nyquist plot, the resulting impedance consists of two arcs describing oxygen transport in the air channel (low-frequency arc) and in the GDL. The characteristic frequency of GDL arc depends on the CCL thickness: large CCL thickness strongly lowers this frequency. At small CCL thickness, the high-frequency feature on the arc shape forms. This effect is important for identification of peaks in distribution of relaxation times spectra of low--Pt PEMFCs.