(50c) Elucidating Cation Transport Properties and Effects in Proton Exchange Membrane Fuel Cells

Effective transport of reactants and products is a critical factor that determines the performance and durability of proton exchange membrane fuel cells (PEMFCs). Cation contaminants, introduced through various sources (such as de-alloying of Pt-alloy catalysts,¹ leaching of metal bipolar plates,² and impurities from reactant streams³) can significantly hinder the transport of protons and oxygen to the reaction sites in the electrode. Specifically, cations can bond to the sulfonic acid sites in the membrane and the electrode ionomer, reducing the water uptake of the ionomer and subsequently impeding oxygen and proton transport to the catalyst surface.⁴ However, describing the effect of cation contamination remains severely challenging, due to their mobility in membranes and ionomers being poorly understood.

In this presentation, we discuss our investigations on cation effects in PEMFCs using electrochemical analysis, as well as synchrotron X-ray fluorescence (XRF) imaging methods to characterize the transport properties of cations in membranes and ionomer films. Specifically, we dope decal electrodes with controlled Co²⁺ levels to study the effect on PEMFC performance and to use electrochemical impedance results to estimate the Co²⁺ exchange in the membrane and electrode ionomers. Additionally, we use synchrotron XRF imaging experiment data coupled with a 1-D Nernst-Planck based model to deduce the effective diffusivity and mobility coefficient of Co²⁺ in membranes and ionomer networks. We develop a platform for studying cation mobility in ionomer networks, termed electrode ionomer network (EIN). The EIN aims to replicate the ionomer network in a real electrode without the use of electronically conductive nanocatalysts, enabling us to apply a potential gradient across the material to study the electro migration behavior of cations. The results of our works inform computational models for simulating cation transport in membrane-electrode assemblies and new material designs for mitigating the undesired effects of cation contamination on PEMFC performance.

References:

1. T. E. O’Brien et al., J Electrochem Soc, 168, 054517 (2021).
2. S. K. Babu et al., J Electrochem Soc, 168, 024501 (2021).
3. X. Wang et al., J Electrochem Soc, 161, F1006 (2014).
4. C. Lee et al., ACS Appl Mater Interfaces, 14, 35555–35568 (2022) https://doi.org/10.1021/acsami.2c07085.