Comparison of Two Physical Models for Fitting PEM Fuel Cell Impedance Spectra Measured at a Low Air Flow Stoichiometry

Abstract

Local impedance spectra of a segmented PEM fuel cell operated at an air flow stoichiometry of λ = 2 are measured. The local spectra are fitted with the recent 1D and quasi–2D (q2D) physical models for PEMFC impedance. The q2D model takes into account oxygen transport in the gas channel, while the 1D model ignores this transport assuming infinite stoichiometry of the air flow. Analysis of the q2D expression for the GDL impedance Z∞gdl at λ → ∞ shows that the contribution of Z∞gdl to the total cell impedance rapidly decays with the frequency growth. We derive an equation for the boundary frequency flim, above which this contribution is small. We show that the 1D model can be fitted to the high–frequency part (f > flim) of a spectrum acquired at λ ≃ 2, ignoring the low–frequency arc due to the oxygen transport in the channel. Comparison of fitting parameters resulted from the 1D and q2D models confirms this idea.