Ph.D. Dissertation Defense: Yubai Li, "Modeling Pt and catalyst layer degradation in polymer electrolyte fuel cells"

Polymer Electrolyte Fuel Cell (PEFC) is one of the most promising clean power sources and is widely applied for material handling equipment, distributed power generation, and most importantly buses and passengers cars for city clean transportation today. However, the full commercialization of PEFCs is limited by two factors: cost and durability. Pt catalyst in catalyst layers is important from both cost and durability point of view. So modeling the Pt catalyst degradation in PEFC cathode catalyst layer (CCL), estimating the non-uniform Pt degradation PEFC and evaluating the effect of non-uniform Pt degradation are urgently needed to design PEFC with longer lifetime and better end-of-life (EOL) performance.

In this dissertation, a physics-based 1D Pt degradation model is first established and validated. This model captures non-uniform Pt degradation in CCL thickness direction, and the effect of temperature and humidity. With this 1D Pt degradation model, one important consequence about thinning the CCL is discussed. Further, this physics-based 1D Pt degradation model is coupled into transient M2 model. Modeling of transient Pt degradation in a low Pt-loading PEFC under current cycling condition is performed, and the non-uniformity of Pt degradation in channel-land direction is estimated. This transient Pt degradation model clearly points limiting the lower current under current cycling condition alleviates Pt degradation. Last, an empirical Pt degradation model is developed and coupled into M2 model to predict the along-channel non-uniform Pt degradation for a single channel PEFC case. For more complex channel arrangements of a medium scale PEFC case, the model is demonstrated to predict in-plane non-uniform Pt degradation and EOL performance, which paves the way for modeling Pt degradation in large scale PEFC case for realistic industrial PEFC design.



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