Hydrogen crossover impedance of a PEM fuel cell at open circuit

We report a physics-based model for impedance due to hydrogen crossover in a PEM fuel cell at open circuit. The model takes into account conversion of hydrogen flux to protons in the cathode catalyst layer (CCL). Transient equations for the proton current conservation and for the hydrogen transport in the CCL are formulated and an analytical expression for the impedance due to hydrogen oxidation is derived. This impedance is summed with the impedance due to conversion of the proton current into water derived previously, and the resulting model impedance is fitted to experimental data. Fitting gives an estimate of the hydrogen diffusion coefficient in the CCL Dhy ≃ 10−3 cm2 s−1.