Cation Contamination in Polymer Electrolyte Fuel Cells: Impacts, Mechanisms, and Mitigation

Polymer electrolyte fuel cells (PEFCs), a promising source of clean energy in automotive application, still require durability improvement before commercialization. For instance, cationic impurities may get introduced into the PEFCs from the ambient air (e.g. roadside contaminants) and from the corrosion of stack and balance of plant components which are known to have a severe negative effect on the durability and performance of PEFCs such as reduction in proton conductivity and water content in the membrane (1).

In our group, the experimental and theoretical study of the effects of key cathode side cation contaminants on the performance of PEFCs were investigated, and the understanding of contamination mechanism was utilized to develop novel technologies for mitigating the effects of contamination. A list of cation contaminants (Na⁺, K⁺, Mg⁺², Ca⁺², Ni⁺², Ba⁺², Al⁺³, Cr⁺³, and Fe⁺³) were tested for screening studies and one cation was selected for more in-depth studies that was not previously well investigated, prevalent in roadside impurities, and abundant in the nature. The contaminant was tested with a single cell, a segmented cell, and a multilayer membrane cell test configurations.  

In the cation computational model, for the first time, a catalyst agglomerate model was utilized and a decrease in oxygen concentration in the catalyst layer was found due to cation contamination which was a new finding (2). During experimental studies, it was found that water management significantly affects contamination by cations which may result in salt precipitation causing serious mass transport losses, and salt was preferentially deposited at the outlet of the cell at our operating conditions. It was also found that GDL played an important role in the transport of cations in as well as out of the MEA, and hydrophobic nature of the GDL can act as a barrier to the transport of cation solution.

Based on experimental and computational model, mitigation methodologies for cation contamination were designed depending on the presence of contaminants in various parts of the fuel cell. Cation contaminants from the membrane can be completely removed by re-protonating the membrane using acidic solution. For removing salt deposit, an ex-situ acid flush technique was utilized and salt deposit on flow field was completely removed, whereas some white patches of salt deposit still was observed on the GDL (Figure 1). Ex-situ mitigation process using acidic solution worked well, but additional factors need to be identified that hinder the full recovery process.

Acknowledgements

Financial support from the Department of Energy (DOE)-EERE, DE-EE00000467 (University of Hawaii, prime contractor, Jean St-Pierre, PI) is greatly acknowledged.  

References

1. T. Okada, in Handbook of Fuel Cells– Fundamentals, Technology and Applications, W. Vielstich, H. A. Gasteiger, A. Lamm and H. Yokokawa, Editors, John Wiley & Sons, Ltd, New York (2010).
2. M. A. Uddin and U. Pasaogullari, J. Electrochem. Soc., 61, F1081 (2014).