Impact of Membrane Properties and Membrane Degradation on Cathode Catalyst Layer Degradation

Understanding the effect of material properties and the structure of MEA components is critical to understanding MEA performance and degradation. Previous studies have shown that cathode catalyst layer degradation was observed to be influenced by water content within the MEA.  Both relative humidity and membrane type were shown to have a substantial effect on the degradation rates¹.  As the membrane / ionomer plays a key role in the water management within an MEA, affecting water sorption, water crossover and phase changes, an improved understanding of the effects of membrane properties on cathode catalyst degradation is required. This study examines the effect of membrane properties, as well as the effects of membrane degradation on cathode catalyst layer degradation.

In this work, six membranes, including dense membranes Nafion^®211 and Nafion^®212, experimental reinforced PFSA  membranes with low and high equivalent weights (EW), and experimental reinforced partially fluorinated hydrocarbon membranes of high and low equivalent weights, were chosen for investigations of membrane property impacts on beginning of test (BOT) performance and cathode accelerated stress test (AST) durability.  These membranes had EW values ranging from ~ 600 to 1100, while the dry thickness ranged from 13 to 50 microns.  

Performance variations at BOT for the different membranes may be due to a combination of membrane thickness, resistance, and hydrogen and water cross-over effects.  After cathode AST cycling, ECSA loss and performance loss were increased for the thinner, lower EW membranes of each membrane family suggesting that membrane water content was the contributing factor.   The effects of membrane degradation on cathode catalyst layer degradation for three down-selected membranes will also be discussed.

Acknowledgements

Funding was provided by Department of Energy EERE Hydrogen and Fuel Cell Technology Program (Project DE-EE0006375).

References

[1] Silvia Wessel, David Harvey, “Development of Micro-Structural Mitigation Strategies for PEM Fuel Cells: Morphological Simulations and Experimental Approaches”, 2013 Annual Merit Review Proceedings: Fuel Cells, 16 May 2013, Project ID# FC049.