Can We Quantify Oxygen Transport in the Nafion Film Covering an Agglomerate of Pt/C Particles?

Abstract

© The Author(s) 2017. Published by ECS. All rights reserved. We report a model of the cathode catalyst layer (CCL) impedance, which includes impedances due to oxygen transport in the Nafion film covering Pt/C agglomerates, and due to oxygen transport through the CCL depth. In the case of small cell current density, analytical solutions for the CCL impedance Zcclare derived; for larger currents, we analyze numerical solution for Zccl. The characteristic frequencies of the oxygen transport through the Nafion film and through the CCL depth are close to each other, and the contribution of the Nafion film impedance ZNto Zcclis small up to the current densities ≃ 100 mA cm-2. This makes it difficult reliable determination of ZNfrom experimental spectra of a standard 10 μm-thick CCL. However, with the decrease in the CCL thickness, the relative contribution of ZNto Zcclincreases. It gives us a chance to determine ZNby fitting the models of this work to measured spectra of a low-loaded MEA with a thin CCL. An example of fitting the model to a synthetic numerical impedance is given.