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

Abstract

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 Z ccl are derived; for larger currents, we analyze numerical solution for Z ccl . 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 Z N to Z ccl is small up to the current densities 100 mA cm −2 . This makes it difficult reliable determination of Z N from experimental spectra of a standard 10 μm-thick CCL. However, with the decrease in the CCL thickness, the relative contribution of Z N to Z ccl increases. It gives us a chance to determine Z N by 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. Polymer electrolyte membrane fuel cells are ready to take their place in the spectrum of electrochemical sources powering the future society. Still, however, a lot needs to be done to improve stability and reduce the cost of these cells. Development of simple and robust ex situ characterization techniques for the fuel cell research and applications (cars, home appliances etc.) is an urgent task.It is generally accepted that the impedance technique gives much more information on a PEM fuel cell, than the DC methods.

Impedance Spectroscopy Characterization of Oxygen Transport in Low– and High–Pt Loaded PEM Fuel Cells

“…In particular, the model does not separate the oxygen transport in the void pores and in the Nafion film covering Pt/C agglomerates. Attempt to apply the model 23 to separate the oxygen diffusion through the Nafion film has failed. With the expected Nafion film thickness on the order of 10 nm and the oxygen diffusion coefficient in Nafion on the order of 10 −6 cm 2 s −1 (Ref.…”

Resistance Separation of Polymer Electrolyte Membrane Fuel Cell by Polarization Curve and Electrochemical Impedance Spectroscopy

“…To describe this line, differential equations or the finite transmission-line model (TLM) are normally used [13,21,22]. Makharia et al [13] reported the calculation of effective protonic resistance using differential equations and analyzed the results of the H 2 /N 2 experiment.…”

Investigation of Microstructure and Pt Distribution in Catalyst Layer after Accelerated Degradation Test in PEMFC

“…It was thought that the O 2 transport at the interface between the Pt and the ionomer thin layer may play an important role. Kulikovsky (1) show that as the thickness of CL decreased, the contribution of the Nafion film impedance Z N was comparable to the contribution of oxygen transport through the CL depth. Ferreira-Aparicio and Chaparro (2) studied the effect of the thickness of CL on the performance of the MEA.…”

“…The ECSA of MEAs with different Pt loading and degradation in ECSA and Voltage S1 ECSA is the ECSA of the MEA at the beginning of the ADT test. S2 ECSA is the ECSA of the MEA after 30k cycles at the end of the ADT test.…”