Contribution of heat transport transients to the “inductive” loop in PEM fuel cell impedance: Modeling and experimental study

The origin of the low-frequency “inductive” loop in the impedance spectra of PEM fuel cells is poorly understood. The relaxation of the fuel cell temperature in response to an AC perturbation of the cell current is one of the slowest processes in the cell. Here, we report a simple model for the non-stationary heat transport through the cathode side of a PEM fuel cell. This model establishes a linear relation between the perturbations in the heat flux emitted by the cathode catalyst layer (CCL) and the CCL temperature. Using the Arrhenius temperature dependencies of the CCL proton conductivity and the exchange current density of the oxygen reduction reaction, we derived analytical formulas for the contribution of the CCL temperature oscillations to the cell impedance. This enabled us to accurately fit the cell impedance model to the experimental spectrum measured at 800 mA cm −2 in the frequency range down to 10 mHz. The developed model explains the shape of the “inductive” low-frequency loop in the Nyquist spectrum of our cell.