Creating nano- and microstructure catalyst coated membrane interfaces for improving the performance of proton exchange membrane fuel cells

Proton exchange membrane fuel cells (PEMFCs) are an important low-emission energy generation system that can be utilized for automotive applications. These systems are, however, limited by the use of Pt as the cathode catalyst, where the relatively expensive cost of Pt limits the competition of PEFMCs against petroleum based systems. Due to the unique characteristics of these PEMFC systems, an optimal balance of hydration of the PEM and the catalyst layers must be maintained within the fuel cell. The current densities achievable with the system can be impacted by an inefficient mass transport of the reactants and products that result in over- or under-hydration of the system. Improvements for increasing effective utilization of Pt and optimizing transport characteristics of PEMFCs could further propel this technology into the mainstream. The work presented in this thesis demonstrates an array of approaches to control the interfaces at or within the cathode catalyst layer (CCL). Architectures at the micro- and nanoscale were sought for improving the performance of PEMFCs. These approaches included creating microscale (5 to 50 µm) patterns of the PEM to CCL interface by the direct printing of CCLs and the hot-embossing of the PEMs. Catalyst materials with tuned pore sizes (1 to 0.05 µm) were also prepared with a coating of catalytic nanoparticles (NPs) through the use of polymeric sacrificial templates. Finally, CCLs containing mesoporous (<10 nm) Pt catalysts were prepared by electrodeposition. These CCL architectures were extensively characterized by electron microscopy and electrochemical techniques. Electron microscopy and related spectroscopy techniques were utilized for determining the morphologies and elemental compositions of the structured materials. The performances of these materials were analyzed using ex situ solution-based, three-electrode electrochemical cells. Some of the prepared catalysts were further analyzed with laboratory scale [membrane electrode assemblies (MEAs) with a geometric surface area of 5 cm2] and industrial relevant scale [MEAs with a geometric surface area of 40 cm2] fuel cell test stations. The goal of this thesis is to demonstrate the preparation of these materials with commercially available materials and industrially compatible processes, which can be extended to further catalytic materials in the future for further enhancing the efficiencies of PEMFC systems.

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