Heterogenous Degradation of Cathode Catalyst Layers: Influence of O2 Partial Pressure and Various Stressors Under Load Cycling Conditions
Authors: Coats Matthew , Braaten Jonathan , Cheng Lei , Stühmeier Björn Marcel , Stewart Sarah , Johnston Christina , Pylypenko Svitlana 
Published: February 2024

Proton exchange membrane fuel cells (PEMFCs) are an important technology to reduce greenhouse gas emissions in the heavy-duty vehicle automotive fleet. Of particular importance is achieving high performance and durability of the cathode catalyst layer (CCL) which uses platinum group metals (PGMs) to catalyze the kinetically sluggish oxygen reduction reaction (ORR).1 Understanding limits of performance under specific stressors and correlating stressors to changes in the microstructure of the membrane electrode assembly (MEA) and properties of the catalyst will enable better understanding of potential pathways to enhance durability of the PEMFCs.

Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) studies have demonstrated through-plane differences in the local Pt content and nanoparticle size with regard to the gas diffusion layer (GDL)-catalyst layer interface, middle of the catalyst layer, and membrane (PEM)-catalyst layer interface.2,3 We have previously shown that there are spatial through-plane differences (e.g., F/Pt profile as a benchmark and nanoparticle size assessment) throughout the CCL depth of MEAs when ran under potential cycling accelerated stress test (AST) conditions under N2 with varied stressors (i.e., temperature, relative humidity, dwell time at upper and lower potential limits, etc.).3 It has also been demonstrated that adjusting these stressors can either mitigate or enhance the rate of degradation under potential cycling conditions.4 Historically, N2-based ASTs have been used, including in our past work, to characterize aging behavior in the CCL. Here, we present an analysis on the effect of oxygen presence in the cathode, more similar to real load/unload PEMFC operation. The elucidation of the through-plane spatial degradation with focus on influence of varied O2 partial pressure and comparison to lower temperature, relative humidity, and upper potential limit at 21% O2 will be discussed. More specifically, the differences in the F/Pt profile, nanoparticle size, depletion layer thickness, Pt band location within the membrane, etc. and its implications on real-world PEMFC testing will be presented.

References

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