Experimental and Numerical Investigation of the Low-Frequency Inductive Features in Differential PEMFCs: Ionomer Humidification and Platinum Oxide Effects

Kurzfassung

The low-frequency inductive features in PEMFC are studied by differential measurements and numerical simulation. Systematic parameter variations are conducted and the discrepancies between the local polarization curve slopes and the capacitive loops of electrochemical impedance spectra (EIS) are evaluated to compute the inductive contributions. These contributions, primarily slow platinum oxide kinetics and ionomer humidification, are disentangled and we show that the latter is more relevant at medium to high currents, leaving mainly kinetics contributions of around 35 mV dec−1 at small currents. We demonstrate that the inductivity reaches over 150 mV dec−1 at high load and that it strongly depends on the current density (j) and on the relative gas humidity (RH), whereas temperature (T) and oxygen partial pressure play a minor role. A new approach for modeling the combination of the oxygen reduction reaction and platinum oxidation leading to inductive loops is presented and integrated into a 1D through-plane model which we parameterize based on our large dataset. We present a comprehensive parameter study with this model. Its current version contains platinum oxide kinetics and electron, proton as well as oxygen transport and yields a good match with both steady-state and EIS data.