Comprehensive Microscopy Approach toward Proton Exchange Membrane Fuel Cell Degradation

Energy has been the main driving force of human society and with the increasing demand for energy in the recent decades, finding an alternative to fossil fuels is essential. Fuel cells, as efficient and clean power generation devices, have emerged as one alternative solution to conventional energy resources. Low operating temperature, quick start-up, and high efficiency have made the proton exchange membrane fuel cells (PEMFC) one of the most promising solutions for the future transportation industry. However, the electrodes of these devices, particularly the catalyst material are subject to gradual degradation during fuel cell extended performance. While the degradation of the components presents one of the major challenges of PEMFCs, it can be addressed through an understanding of the structure-property-performance relationship in the catalyst layer. Microscopy is often used to study PEMFCs, however, no comprehensive approach has been done so far to establish these correlations in detail. Therefore, a comprehensive microscopy approach is presented here to study the degradation effects in fuel cells. A combination of microscopy methods such as (scanning) transmission electron microscopy-energy dispersive spectroscopy (STEM-EDS), scanning electron microscopy (SEM) and X-ray computed tomography (XCT) in conjunction with innovative quantification analyses and sample preparation was employed to understand the degradation of a membrane electrode assembly (MEA), under different working conditions. The approach revealed how the solid membrane responds to the mechanical stress due to the relative humidity (RH) fluctuations in the system and how the microporous layer (MPL) affects its degradation. In addition, the carbon corrosion and platinum degradation in the MEA were studied in detail using our comprehensive suite of characterization techniques, quantifying several structural and compositional descriptors, uniquely available only in our lab. The correlation of the microscopy data, working conditions, and the performance are presented to provide the community with an understanding of the structure-property-performance relationship in the catalyst layer. Finally, a novel sample preparation technique – epoxy-free ultramicrotomy – was introduced to ease the observation of the ionomer and carbon changes in the fresh and degraded catalyst layer. The approaches and results presented in this thesis contribute new knowledge and understanding of PEMFCs, not been reported before.