A systematic analysis, both experimental and model-assisted, has been performed over three main configurations of platinum group metal-free (PGM-free) electrodes in polymer electrolyte fuel cells (PEFCs): Catalyst-coated membrane CCM technology is being compared to the gas-diffusion electrode (GDE) method of electrode fabrication and juxtaposed to a hybrid/combined GDE-CCM method of membrane-electrode assembly (MEA) fabrication. The corresponding electrodes were evaluated for their electrochemical performance, modeled, and studied with in situ and operando X-ray computed tomography (X-ray CT). The study establishes that through-thickness inhomogeneities play the most important role in water withdrawal/water management and affect most significantly PGM-free PEFC performance. The catalyst integration technique results in formation of interfacial regions with increased porosity and surface roughness. These regions form critical interfaces de facto responsible for flooding type behavior of the PEFC as shown for a first time by operando X-ray CT. The computational model shows that the PEFC performance critically depends on liquid water formation and transport at cold and wet conditions.

Pt catalysts in polymer electrolyte fuel cells degrade heterogeneously as the catalyst particles are exposed to local variations throughout the catalyst layer during operation. State-of-the-art analytical techniques for studying degradation of Pt catalysts do not possess fine spatial resolution to elucidate such non-uniform degradation behavior at a large electrode level. A new methodology is developed to spatially resolve and quantify the heterogeneous Pt catalyst degradation over a large area (several cm2) of aged MEAs based on synchrotron X-ray microdiffraction. PEFC single cells are aged using voltage cycling as an accelerated stress test and the degradation heterogeneity at a micrometer length scale is visualized by mapping Pt catalyst particle size after voltage cycling. It is demonstrated in detail that the Pt catalyst particle size growth is non-uniform and follows the flow field geometry. The Pt particle size growth is greater in the area under the flow field land, while it is minimal in the area under the flow field channel. Additional non-uniformity is observed with the Pt particle size increasing more rapidly at the air outlet area than the Pt particle size at the inlet area.

The heterogeneity of polymer electrolyte fuel cell catalyst degradation is studied under varied relative humidity and types of feed gas. Accelerated stress tests (ASTs) are performed on four membrane electrode assemblies (MEAs) under wet and dry conditions in an air or nitrogen environment for 30 000 square voltage cycles. The largest electrochemically active area loss is observed for MEA under wet conditions in a nitrogen gas environment AST due to constant upper potential limit of 0.95 V and significant water content. The mean Pt particle size is larger for the ASTs under wet conditions compared to dry conditions, and the Pt particle size under land is generally larger than under the channel. Observations from ASTs in both conditions and gas environments indicate that water content promotes Pt particle size growth. ASTs under wet conditions and an air environment show the largest difference in Pt particle size growth for inlet versus outlet and channel versus land, which can be attributed to larger water content at outlet and under land compared to inlet and under channel. From X-ray fluorescence experiments Pt particle size increase is a local phenomenon as Pt loading remains relatively uniform across the MEA.