Analytical physics–based impedance of the cathode catalyst layer in a PEM fuel cell at typical working currents

A transient physical model for the PEM fuel cell cathode catalyst layer (CCL) with fast proton and slow oxygen transport is solved and an analytical expression for the oxygen transport impedance is derived. This expression is combined with the proton transport and faradaic impedances of the PEMFC cathode reported previously. The resulting analytical impedance includes the reaction activation and the proton and oxygen transport losses in the CCL. Validity of this impedance up to the typical working cell currents on the order of several hundred mA cm−2 is demonstrated by fitting the model equation to numerical impedance spectra calculated from the full system of conservation equations